Bulletin of the Global Volcanism Network
Volume 34, Number 9, September 2009
http://www.volcano.si.edu/
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Bulletin of the Global Volcanism Network
Volume 34, Number 9, September 2009
Turrialba (Costa Rica) Non-eruptive in August 2009, but degassing and with widening cracks
Reventador (Ecuador) Lava flows seen and SO2 fluxes recorded during 16-17 September 2009
Kaba (Indonesia) Increased seismicity and whitish vapor emissions
Rinjani (Indonesia) More data relevant to eruptions during 2 May through at least 31 August 2009
Anatahan (Mariana Islands) Quiet except for brief tremor in February 2009 and plume in June 2009
Pagan (Mariana Islands) Emission of a small plume in mid-April 2009
Koryaksky (Russia) Continued ash emissions during May-September 2009
St. Helens (USA) Eruption ceased in late January 2008; quiet continues in late 2009
Editors: Rick Wunderman, Edward Venzke, and Sally Kuhn Sennert
Volunteer Staff: Paul S. Berger, Russell Ross, Hugh Replogle, Catie Carter, Ludmila Eichelberger, Robert Andrews, Margo Morell, Jacquelyn Gluck, and Stephen Bentley
Turrialba
Costa Rica
10.025°N, 83.767°W; summit elev. 3,340 m
All times are local (= UTC - 6 hours)
The Observatorio Vulcanologico y Sismologico de Costa Rica, Universidad Nacional (OVSICORI-UNA) continued monitoring the Turrialba non-eruptive interval of February 2008 through August 2009. As during the previous four months (BGVN 33:01), Turrialba continued to emit sulfurous gas from its central and W craters, and elsewhere, including some new cracks.
Activity during February-December 2008. During February 2008, the area around Turrialba affected by acid rain increased due to degassing. The degassing vents on the N, NW, W, and SW walls were rich in sublimated native sulfur. Gas-emission temperatures ranged from 72 to 132°C. Owing to prevailing winds, the vegetation most affected was on the N, NW, and SW flanks. The effects ranged from discoloration to death of various plant species. Residents in the area reported occasional nausea and irritation of the skin and eyes. On 22 February, local observers reported a gas plume up to ~ 2 km in height.
On the SE and SW walls of the central crater two cracks 2-3 cm wide and 100 m long continued to emit gases at ~ 90°C and produced sulfur deposits (figure 1). In stable atmospheric conditions gas columns often rose ~ 500 m above the crater. Rockslides sometimes covered emitting fumaroles, and new sulfur deposits tended to develop in these areas.
Figure 1. Elongated cracks (red lines on colored version) mapped at Turrialba during in August 2009. From first being noticed in mid-2009 to being measured in August 2009, some cracks opened by as much as 12 cm. Courtesy of OVSICORI-UNA.
During 7-8 March 2008, gas sampling at the summit fumaroles determined the maximum temperature at the largest W wall vent was 278°C. Degassing vents were also noted at spots in the middle of the forest. In some cases emissions had killed all local vegetation.
On 7-8 March 2008, Erick Fernandez and Eliecer Duarte of OVSICORI, and the National University (UNA) took gas samples. The analysis, done by Jorge Andres Diaz and Sergio Achi of the University of Costa Rica, revealed the presence of He at 80,000 ppm (parts per million), whereas the typical He concentration in the neighborhood of a volcano is 25 ppm.
OVSICORI-UNA reported continued degassing during August and September 2008. Multiple fumaroles and areas of sulfur deposition were noted in both the central and W craters. Fumarolic emissions on the S and SE flanks of the W crater continued to damage vegetation in that area.
On 23 September 2008, OVSICORI fieldwork confirmed a severe impact of acid-rain on areas that had been only mildly affected during the preceding 3 years of degassing. At least three sectors showed new impacts on vegetation and infrastructure, from the summit downhill ~ 3 km along the S and SE flanks. The upper sector, which includes the entire caldera and lower sectors to the E, S, and SE near the summit, had been severely burned during August and September. This area goes from the summit down to an elevation of ~ 2,900 m. By 23 September, weeds, dwarf vegetation, and trees had been completely burned; however in these areas some resistant species maintained some green and appeared seemingly viable. Along the external walls to the S of the W crater, plants had been burned down to the soil. Due to the removal of that natural coverage, erosion had cut extended radial gullies.
Between the elevations of 2,900 and 2,600 m, significant forest patches have been partially seared by extreme acidification, particularly the dense birch forests. Below 2,600 m elevation mild burns to the tree canopy and pasture areas were evident. The evidence of chemical burns due to the heavy gases are amplified along canyons and depressions. These conditions caused residents to voluntarily leave their farms in 2007.
Monitored SO2 emissions during the early part of 2008 had been ~ 750 metric tons per day (t/d). At the end of April 2008, an increase to ~ 1,000 t/d was noted, which then increased to ~ 2,000 t/d well into July. During the end of July the emissions declined to ~ 1,100 t/d. The increase in SO2 flux corresponded to increases in vegetation damage.
Activity during January-June 2009. In May 2009 OVSICORI reported ongoing fumarolic degassing during the preceding months from the central crater, from the N, NW, W, SW and S walls, from new vents on the S and SW walls, and other locations. Some locations continued to form sublimated sulfur deposits. The two cracks in the SE and SW walls had temperatures of ~ 87°C. The emissions in the W wall registered ~ 91°C and displayed sulfur deposits. In meteorologically quiet conditions, gas plumes were noted up to 500-600 m above the crater floor. All of these areas had experienced small landslides that occasionally covered some vents.
SO2 flux was variable during early 2009 (figure 2). The flux data were collected with a roughly consistent sun angle, between 0900 and 1100 in the morning on the SW flank. In the graph the SO2 flux varies between ~ 0 and ~ 2,000 t/d, the maximum flux occurred on 23 April.
Figure 2. SO2 fluxes measured at Turrialba during April 2009 (with y-axis showing SO2 flux in metric tons per day and x-axis dates in the format, month/day/year). Courtesy of OVSICORI-UNA.
On 14 June 2009, OVSICORI-UNA reported that fumarolic activity from Turrialba had been observed all around the upper flanks of the active W crater. During the previous two months, the fumarolic activity was also accompanied by widening radial cracks (1.5 cm on average), 1-2 km tall gas-and-vapor plumes, and one sustained seismic swarm. Temperatures of fumarolic vents in the lower parts of the crater were between 120 and 160°C. The temperature of summit cracks was 94°C. By mid-June, dairy pastures and forests had been chemically burned as far away as 3.5 km NW and W. During the last week of August 2009, the W and NW lower flanks, sectors previously reported with moderate effects, showed acute burns, and yellow pastures within 3 to 4 km radius (figures 3, 4, and 5).
Figure 3. Vegetation damage as of late August 2009 at Turrialba plotted on a shaded relief map by F. Robichaud. E. Duarte and others found that damage was generally within several kilometers of the volcano and in broader areas on the W flanks. The large dotted line indicates the boundary of detectible damage. Severe damage covered an irregular area, a strip both directly W of the active crater and a lobe to its SW as well. Courtesy of OVSICORI-UNA.
Figure 4. Newly emerging fumaroles on Turrialba's upper NW flank and burns on vegetation, August 2009. Courtesy of OVSICORI-UNA.
Figure 5. A view from Turrialba's seismic station PICA on the NW flank, showing active degassing from a variety of locations in August 2009. Left mid-ground shows plumes from the lowest fumaroles yet developed on this flank. Green grass is in the foreground, but most of the other foliage is brown to orange. Courtesy of OVSICORI-UNA.
Near the Toro Amarillo river (4 km E of the crater) chemical burning surrounds stands of trees. Such whitening effect had been previously reported at the end of 2007 for areas closer to the active crater, 1.5 km W (figure 6).
Figure 6. An example of a zone with intense burns on grass at the foot of injured trees, damage attributed to acidic gases from Turrialba. The spot is near the Toro Amarillo river in late August 2009. Courtesy of OVSICORI-UNA.
Several elongated cracks were mapped just south of the W crater as well as 1 km downslope NW. One main crack, noticed during mid-2009 due to sulfur depositions on the surface, was opened by August in places as much as 12 cm. In late August 2009 it emitted gasses at 90ºC. The crack trends E-W, in places intersecting a trail used to reach the summit's SW and W sides.
The last two years have caused residents to leave owing to the burned and dead pastures. Some commented on their apprehension related to the emergence of the lower fumaroles. Along the S side of the Irazu summit located 10 km SW of Turrialba's summit, mild burns have been observed on patches of birch, eucalyptus and pine. Lesser impact was reported last year in that same area.
False eruption report. The Washington VAAC received surface observations from an airport near the volcano erroneously indicating an eruption on the morning of 23 September 2009.
The VAAC decided to initially describe the activity as an eruption because it was the first time the airport had reported emissions, the volcano was known to have been degassing for some time, and early morning satellite imagery showed cloud cover, preventing good analysis. In addition, attempts to reach local volcanologists by telephone using contact numbers from the ICAO [International Civil Aviation Organization] handbook and the OVSICORI webpage were not successful. OVSICORI-UNA personnel reported a few hours later that the volcano had not erupted. As a result of the incident, the VAAC has obtained current contact numbers, including personal cell phones, for future use.
Geologic Summary. Turrialba, the easternmost of Costa Rica's Holocene volcanoes, is a large vegetated basaltic-to-dacitic stratovolcano located across a broad saddle NE of Irazu volcano overlooking the city of Cartago. The massive 3,340-m-high Turrialba is exceeded in height only by Irazu, covers an area of 500 sq km, and is one of Costa Rica's most voluminous volcanoes. Three well-defined craters occur at the upper SW end of a broad 800 x 2,200 m wide summit depression that is breached to the NE. Most activity at Turrialba originated from the summit vent complex, but two pyroclastic cones are located on the SW flank. Five major explosive eruptions have occurred at Turrialba during the past 3,500 years. Turrialba has been quiescent since a series of explosive eruptions during the 19th century that were sometimes accompanied by pyroclastic flows. Fumarolic activity continues at the central and SW summit craters.
Information Contacts: Eliecer Duarte, Erick Fernandez, Vilma Barboza, S. Miranda, L. Ortiz, G. Chavez, Jorge Brenes, Thomas Marino, Javier Pacheco, Juan Segura, and Rodolfo van der Laat, Observatorio Vulcanologico y Sismologico de Costa Rica, Universidad Nacional (OVSICORI-UNA), Apdo. 2346-3000, Heredia, Costa Rica (URL: http://www.ovsicori.una.ac.cr/informacion_general/prensa.htm or http://www.ovsicori.una.ac.cr/vulcanologia/Volcan_Turrialba.htm); Francois Robichaud, Universite de Sherbrooke, 2500 boul. de l'Universite, Sherbrooke, Quebec J1K 2R1, Canada; Washington Volcanic Ash Advisory Center, Satellite Analysis Branch (SAB), NOAA/NESDIS E/SP23, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: http://www.ssd.noaa.gov/VAAC/).
Reventador
Ecuador
0.077°S, 77.656°W; summit elev. 3,562 m
Activity at Reventador between August 2008 and late April 2009 was a period of generally low seismicity (BGVN 34:03). During early November 2008 repeated small eruptions occurred with steam-and-ash plumes, Strombolian eruptions, and lava flows. This report continues coverage through October 2009, an interval that included new lava flows advancing ~ 500 m by mid-September 2009.
Based on analysis of satellite imagery, the Washington Volcanic Ash Advisory Center (VAAC) reported that on 1 May a thermal anomaly over Reventador occurred along with a possible low plume drifting W. The Instituto Geofisico-Escuela Politecnica Nacional (IG) reported to the VAAC the presence of lava and gas emissions and possible smoke from burning vegetation, but little to no ash.
On 15 May, the IG observed an ash emission, although neither an ash signature nor a thermal anomaly was detected in satellite imagery. On 26 May, a diffuse ash plume rose to an altitude of 6.4 km and drifted SW. Thermal anomalies were intermittently seen on satellite imagery.
On 21 July-3 August, tremor was sporadic. On 4 August, seismicity increased and periods of tremor frequently saturated the seismic stations. Thermal anomalies, detected in satellite imagery on 1 and 2 August, became more intense on 4, 5, and 10 August. On 6 August, a steam plume rose 1.2 km above the crater and drifted W. Incandescent blocks were ejected from the crater and fell onto the flanks. Thermal images taken from a location 7 km E of Reventador revealed a linear area of higher temperatures, confirming the presence of a new lava flow on the S flank. Incandescence in the crater was seen on 9 August. According to the Washington VAAC, based on information from the IG, an ash plume on 15 August rose to an altitude of 3.6 km and drifted NW.
Field observations on 16-17 September 2009. IG scientists visited Reventador during 16-17 September 2009; among their objectives was to map, sample, and collect thermal images of the new lava flows and to measure the sulfur dioxide (SO2) concentrations with a mobile DOAS.
The team noted that recent lava flows had descended the flanks in a SE to E direction, continuing the same pattern that had begun with the 2005 eruption (figure 7). A dome within the crater showed constant growth (figure 8). Gas was emitted to a height of less than 200 m and drifted mainly W. A small lava flow originating in the dome area had descended ~ 500 m from the cone's S flank.
Figure 7. Panoramic view from the sequential camera of lava flows at Reventador. Courtesy of S. Vallejo.
Figure 8. At Reventador, a photo taken on 16-17 September 2009 of the actively growing dome in the summit crater. Courtesy of J. Bourquin.
Thermal images and SO2 measurements were collected near the caldera, and lavas were sampled. SO2 flux measurements (table 1) were collected both by helicopter and by car (figure 9). A telescope for the SO2 measurements sat below the helicopter blades and those spinning blades may have interfered with the measurements. The values presented may thus underestimate the SO2 fluxes.
Table 1. Reventador SO2 data collected from helicopter on 16 and 17 September 2009. The transects in the first column are indicated on figure 9. Transect 34 measurements clearly indicated that the SO2 gas plume had divided (bifurcated) and the two plumes appear as 34a and 34b. For this transect, the SO2 fluxes were calculated separately for each lava plume segment, than added to get the total emission. Land-based measurements, transects 43 and 46, were collected S and W of the vent. Courtesy of IG.
Transect Wind Wind Data Offset SO2 flux Plume Traverse Intensity
/Route speed direction number (t/d) Width Length Limit
(m/s) (km) (km)
31 5 281 191 -28 811 1.9 52.2 7
34a 5 270 95 -1 1,425 3.6 22.2 7
34b 5 326 124 -8 795 2.5 49.2 7
34 Total -- -- 215 -- 2,220 -- -- --
35 5 337 84 -28 616 1.6 22.8 5
36 5 349 147 -16 557 2.1 30.2 8
43 5 202 471 -14 283 5.2 42.8 5
46 5 236 1222 -14 1,264 16 116 5
Figure 9. Map of Reventador illustrating transects made (in colored version, each transect is in a different color). Transects 31 and 34 were conducted on 16 September; transects 35, 36, 43 and 46 were conducted on 17 September. Courtesy of IG.
Based on a pilot observation, the Washington VAAC reported that on 21 September a plume rose to an altitude of 7.6 km. An ash plume on 4 October drifted W. In both cases, ash was not seen in satellite imagery, although meteorological clouds were present. In the latter case, an occasional thermal anomaly was observed.
Thermal anomalies over the crater area were detected in MODIS satellite imagery on 6, 11, and 13 October. On 13 October, the OMI satellite sensor indicated that the SO2 concentration in the atmosphere near the volcano had increased. On 14 October, seismicity increased and harmonic tremor was detected. A seismic station located at ~ 2,600 m elevation on the NE flank of the cone detected rockfalls. Several people living in the area reported roaring noises and had observed slight incandescence from the crater during the previous few nights.
During an overflight on 16 October, scientists saw the lava dome and a lava flow on the NE flank (figure 10). Bluish gases were being emitted. According to a thermal camera, the incandescent parts in the crater were about 300°C. Other observers heard roaring noises and sounds resembling "cannon shots." Incandescent blocks were ejected from the crater, and steam and gas rose 100 m and drifted SW. Incandescent material was seen on the S flank.
Figure 10. Aerial photo taken on the N side of Reventador on 16 October 2009 showing the lava dome amid weather clouds and some heavy steaming from the NE-flank lava flow. Courtesy of IG.
On 17 October, long period (LP) earthquakes and volcanic explosions lasting up to 10 hours were registered, incandescence on the S flank was noted, and noises similar to the previous day were again heard. A small gray plume was seen the next day. On 19 October, thermal anomalies were again detected on satellite imagery. During an overflight, blue gas plumes containing SO2 were seen (figure 11). The lava flow on the S flank occupied a large area and was divided into two branches.
Figure 11. Photograph of the E side of Revantador's cone taken the morning of 19 October 2009. Note steam rising from dome summit and lava flows on volcano's flanks. Courtesy of IG.
According to the IG, on 21 October, steam-and-gas plumes with little to no ash rose 2-4 km above the crater and drifted in various directions. An explosion that day ejected incandescent material from the crater and blocks rolled down the flanks. On 22 October, a few explosions generated ash-and-steam plumes that rose 4 km. Observations during an overflight revealed a small lava flow on the N flank and a larger flow with four branches on the S flank (figure 12). Part of the lava dome base had disappeared and small spines were present, especially on the S side of the dome. Thermal images revealed that material in the crater was 400°C and the lava-flow fronts were 250°C. Cloudy weather prevented visual observations during 23-26 October. Roaring noises were heard on 25 October.
Figure 12. Aerial photograph displaying the distribution of lava flows on the N side of Reventador's caldera on 22 October 2009. Courtesy of S. Vallejo.
Geologic Summary. Reventador is the most frequently active of a chain of Ecuadorian volcanoes in the Cordillera Real, well E of the principal volcanic axis. The forested, dominantly andesitic Volcan El Reventador stratovolcano rises to 3,562 m above the jungles of the western Amazon basin. A 4-km-wide caldera widely breached to the E was formed by edifice collapse and is partially filled by a young, unvegetated stratovolcano that rises about 1,300 m above the caldera floor to a height comparable to the caldera rim. Reventador has been the source of numerous lava flows as well as explosive eruptions that were visible from Quito in historical time. Frequent lahars in this region of heavy rainfall have constructed a debris plain on the eastern floor of the caldera. The largest historical eruption at Reventador took place in 2002, producing a 17-km-high eruption column, pyroclastic flows that traveled up to 8 km, and lava flows from summit and flank vents.
Information Contacts: Geophysical Institute (IG), Escuela Politecnica Nacional, Apartado 17-01-2759, Quito, Ecuador (URL: http://www.igepn.edu.ec/); Washington Volcanic Ash Advisory Center, Satellite Analysis Branch (SAB), NOAA/NESDIS E/SP23, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: http://www.ssd.noaa.gov/VAAC/); Hawai'i Institute of Geophysics and Planetology (HIGP) Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), University of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://hotspot.higp.hawaii.edu/).
Kaba
Sumatra, Indonesia
3.52°S, 102.62°E; summit elev. 1,952 m
All times are local (= UTC + 7 hours)
Deep volcanic earthquakes, seismic tremor, and five small explosions with corresponding ash emission were reported from Kaba in August 2000 (BGVN 25:11). Since then, Kaba has been quiet, but even in its normal state it almost always emits whitish plumes 25-100 m high.
On 20 October 2009, the Center of Volcanology and Geological Hazard Mitigation (CVGHM) reported that seismic activity from Kaba increased in August and remained elevated into September and October. Inflation was also detected. When weather permitted, diffuse white plumes were seen rising ~ 25-50 m above the summit crater complex and drifting E. Based on the deformation and increased seismicity, CVGHM raised the Alert Level to 2 (on a scale of 1-4).
>From January through August 2009, the frequency of deep volcanic earthquakes averaged 85 events per month, but in August the number of events rose to 257 per month. During August-September, whitish plumes remained similar to September-October. In September seismicity fluctuated but tended to increase. Earthquakes and total tremors recorded at Kaba's monitoring post are shown in table 2.
Table 2. Summary of Kaba seismic data recorded during 12 September-20 October 2009. Courtesy of CVGHM.
Dates (2009) Deep volcanic earthquakes (Count, Characteristics)
Shallow volcanic earthquakes (Count, Characteristics)
Notes
Beginning on 12 September 343
55
1-17 October 253. Max. amplitudes of 1-18 mm; S-wave minus P-wave arrival
times ("S-P") of 0.2-3.5 s with signals lasting 4-35 s.
271. Max. amplitudes 0.5-15 mm, durations of 2.5-11 s.
18 October 68. Max. amplitude of 1-19 mm; S-P times of 0.2-3 s, and a
duration of 3.5-47 s.
67. Max. amplitudes 0.8-16 mm, durations of 2.5-13 s.
19 October 50. Max. amplitudes of 0.5-18 mm; S-P 0.5-2 s, and a duration
of 2-15 s.
127. Max. amplitudes 0.5-15 mm, durations of 2.5-10 s.
Volcanic tremor registered during 0640-0900 local time; max. amplitudes 0.5-2 mm.
20 October 29. Max. amplitudes of 0.5-18 mm; S-P 0.5-2 seconds and a
duration of 2-15 s.
21. Max. amplitudes 0.5-15 mm, durations of 2.5-10 s.
Continuous tremor with amplitudes of 1-7 mm; the most prevalent amplitudes 1-3 mm. During
clear weather, whitish plumes rose ~ 25 m.
Deformation measurements taken using an EDM (electronic distance measurement) method were as follows: Biring station, shorter by 10 cm; Voelsang station, longer by 0.4 cm; and Kaba station, shorter by 2 cm.
Measurements of the crater water temperature on 15 October showed a reading of 72°C, with a pH of 3.24. The sulfurous and associated solfatara areas recorded a temperature of around 106-107°C. There was no other activity in the area of the crater.
Geologic Summary. Kaba, a twin volcano with Mount Hitam, has an elongated summit crater complex dominated by three large historically active craters trending ENE from the summit to the upper NE flank. The SW-most crater of 1,952-m-high Gunung Kaba, Kawah Lama, is the largest. Most historical eruptions have affected only the summit region of the volcano. They mostly originated from the central summit craters, although the upper-NE flank crater Kawah Vogelsang also produced explosions during the 19th and 20th centuries.
Information Contacts: Center of Volcanology and Geological Hazard Mitigation (CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://portal.vsi.esdm.go.id/joomla/).
Rinjani
Lesser Sunda Islands, Indonesia
8.42°S, 116.47°E; summit elev. 3,726 m
A series of eruptions at Rinjani began on 2 May 2009 (BGVN 34:06). The current report, provided by Alain Bernard, presents additional data regarding these eruptions, which continued through 31 August 2009.
Studies of Rinjani volcanic lake are part of a cooperative agreement between Indonesia and Belgium, a collaboration funded by the Commission Universitaire pour le Developpement (CUD, the main Belgian development cooperation agency for universities). Geochemical and physical studies of the Segara Anak lake started in the framework of this collaborative effort during the summer of 2006. During the summer of 2008, investigators installed a monitoring station for continuous measurements of the lake's level and temperature, and for meteorological parameters.
The scientific teams involved in this study were (Indonesia) Akhmad Solikhin, Devy Syabahna and Syegi Kunrat of the Center of Volcanology and Geological Hazards Mitigation (CVGHM); (Belgium) Alain Bernard, Benjamin Barbier, Robin Campion, and Corentin Caudron of the Universite Libre de Bruxelles (ULB), and Vincent Hallet and David Lemadec of the Facultes Universitaires Notre Dame de la Paix (FUNDP).
Segara Anak lake. The majestic Segara Anak lake filling the caldera of Rinjani covers an area of 11 km^2. Prior to the 2009 eruption, the lake's volume was 1.02 km^3. The lake-surface elevation is ~ 2 km (figures 13 and 14).
Figure 13. Bathymetric map of Rinjani's Segara Anak lake made from 65 km of echo-sounder surveys conducted in 2007 and 2008. Maximum depth of the lake is 205 m. Courtesy of the CVGHM, ULB, and FUNDP study team.
Figure 14. Topographic map of Rinjani caldera from Bakosurtanal-Indonesia (National Coordinator for Survey and Mapping Agency, Indonesia). Margins defining squares are 1 km long. "CTD" and "CTD-B" are locations of conductivity-temperature-depth profiles. "Meteo" is the site of the meteorological station monitoring air temperature, humidity, wind velocity, and net solar flux. The labels 51-54 are locations of hot springs discussed below. Courtesy of the CVGHM, ULB, and FUNDP study team.
The lake is neutral (pH: 7-8) and its chemistry dominated by chlorides and sulfates with a relatively high concentration of total-dissolved solids (TDS: 2,640 mg/L). This unusually high TDS value and lake surface temperatures (20-22°C), well above ambient temperatures (14-15°C) for this altitude, reflects a strong input of hydrothermal fluids. Numerous hot springs are located along the shore at the foot of the Barujari cone. Bathymetric profiles showed several areas with columns of gas bubbles escaping from the lake's floor.
Precursory signals of the May 2009 eruption. Changes in Segara Anak lake and the hot springs before the first 2 May 2009 eruption included significant anomalies in the temperature and chemistry of the hot springs.
During field work 10-14 April 2009, the researchers noted an increase in temperature and acidity of hot springs 53 and 54 (figures 15-16) compared to July. This increasing acidity was confirmed in the lab as the consequence of an increase in sulfate levels not observed during studies since 2004.
Figure 15. Geochemistry of Rinjani's Segara Anak lake (from CTD locations, figure 14) and hot springs. NA signifies not analyzed. Courtesy of the CVGHM, ULB, and FUNDP study team.
Figure 16. A plot of 2004 to 2009 sulfate (SO42-) ion concentration versus pH. Note the April 2009 increase in the acidity and sulfate contents of Rinjani's hot springs 53 and 54 (upper left). Courtesy of the CVGHM, ULB, and FUNDP study team.
The Fe-ion concentrations in spring 54, usually below detection limits, peaked at 120 mg/L. This change in chemistry produced a yellowish-brown coloration of the lake waters because of the precipitation of ferric hydroxide, Fe(OH)3 (figures 17-18). An ASTER image from 21 August 2009, processed to enhance the Fe(OH)3 precipitates, revealed a chemical plume close to where hot springs 53 and 54 injected water into the lake.
Figure 17. The Rinjani lake shoreline seen at a point close to the hot spring 54 on 12 April 2009. The water has a brown color and the coating on the rocks is an amorphous ferric hydroxide that precipitated when hydrothermal fluids oxidized by mixing with the lake waters (yellow-brown in color). Rock discoloration reaches the height of the mans lower hand. Changes in lake level were a consequence of the rainy season. Photo by A. Bernard.
Figure 18. A photo of Rinjani and Segara Anak Lake thought to have been taken on 26 April 2009 but certainly before the start of the eruption. A spectacular yellow-brown chemical precipitate floated on the lake's surface (at left). Copyrighted photo by Jim Chow.
A chemical plume of low pH and dissolved oxygen was observed at the lake surface extending up to several hundred meters away from hot spring 54. pH profiles as a function of depth recorded at several locations showed a clear acidification of Segara Anak lake especially at shallow depths (15-20 m) (figure 19). Rainfall in April 2009 caused a shallow zone of higher pH.
Figure 19. Plot showing shifts of pH in Rinjani's caldera lake waters with depth. The 2009 profile was recorded in April 2009, and the 2008 profile, in July 2008. Line 2009b was drawn as an estimate of the curve without the rainfall event. Measurements made with an SBE Seacat 19-Plus profiler. Courtesy of the CVGHM, ULB, and FUNDP study team.
A slight lake surface temperature increase from 20°C in July 2008 to 22°C in early April 2009 was mostly attributed to meteorological effects. Large increases seen in lake level in January and February 2009 were the consequence of heavy rainfalls. Heating of the lake between August 2008 and April 2009 occurred mainly during periods with reduced heat loss to the atmosphere due to less wind.
A report of these field observations was made on 17 April to CVGHM, which prompted them to send another team to the volcano. The new team arrived at the summit of the volcano on 2 May 2009, the day the eruptions started.
Eruptive activity May-August 2009. The 2009 eruptions originated from the same vent of the October 2004 activity (figure 20), and was characterized by mild eruptions that produced a small lava flow and low altitude, ash-poor gas plumes (figure 21). Contrary to that reported in some newspapers, the 2009 eruption did not open a new vent.
Figure 20. This July 2006 photo of Rinjani illustrates the new vent that opened on the NE slope of Gunung Baru in 2004 and then produced a short lava flow. The 2009 eruptive activity at Rinjani started from this same vent, producing a significant lava flow that entered the crater lake and built a delta. Photo by A. Bernard (July 2006).
Figure 21. Eruption of Rinjani seen on 10 June 2009. The plume at this point was relatively small and lava proceeded N to enter the lake. Photo by R. Campion.
Alain Bernard sent a report by Robin Campion (ULB) who was on site June 2009. According to Campion, mild activity was observed from the SE rim during 9-11 June. Pressurized incandescent gas was released at a 1-2 second intervals from a vent located in the 2004 crater, on the S flank of Barujari. At variable intervals (10 seconds to 10 minutes), stronger gas jets ejected lava fragments to heights up to 100 m. Occasional ash ejections occurred from a second vent in the same crater. A third lower vent emitted a viscous lava flow that reached Segara Anak Lake. Contact between the lake and the lava delta resulted in a warm surface current (figure 22).
Figure 22. A 10 June 2009 FLIR thermal camera image of Rinjani's Barujari cone and Segara Anak lake. A thermal plume of hot lake water was drifting from the lava entry points. Temperature scale is for lake waters. Photo by R. Campion.
Figure 23 shows an ASTER satellite image of Rinjani lake-surface temperatures. Increased discharge of the hot springs on the S flank of Barujari produced a distinct plume with an orange-red color. Weak winds carried the steam-and-gas plume (with low ash content) N and W at an altitude of 3-4 km. Activity did not vary during the 3-day observation period.
Figure 23. ASTER satellite image of the N part of Rinjani's Segara Anak lake taken on 29 July 2009 (at 1446 UTC). Thermal infrared bands 13 and 14 processed with a split-window algorithm. Contours are in degrees C. Maximum temperature in the lake water was 57°C. Courtesy of the CVGHM, ULB, and FUNDP study team.
As of 31 August 2009, the eruption was still underway. At that point, the new lava flow covered an area of 0.65 km^2 (figure 24). The shoreline had been significantly modified by the entry of lava into Segara Anak lake, and the lake surface area had been reduced by 0.46 km^2 (figures 24 and 25).
Figure 24. Rinjani seen in ASTER false color on 21 August 2009 (0235 UTC). The new lava covers an area of 650,000 m2 and significantly changed the shoreline. The inset shows the pre-eruption shoreline and the new lava margin (in red on colored versions). Courtesy of the CVGHM, ULB, and FUNDP study team.
Figure 25. Rinjani, in a photo apparently taken on 4 August 2009, showing a new delta built into the lake. Brown waters from hot springs were still visible at the end of the lake and drifted over a large area of the lake. Courtesy of Arjo Vanderjagt.
According to Alain Bernard, updates on Rinjani's activity will be posted on the website of the Commission of Volcanic Lakes (CVL, see information contacts). Bernard sent additional figures describing Rinjani behavior as late as 27 September 2009.
Geologic Summary. Rinjani volcano on the island of Lombok rises to 3,726 m, second in height among Indonesian volcanoes only to Sumatra's Kerinci volcano. Rinjani has a steep-sided conical profile when viewed from the E, but the W side of the compound volcano is truncated by the 6 x 8.5 km, oval-shaped Segara Anak caldera. The western half of the caldera contains a 230 m deep lake whose crescentic form results from growth of the post-caldera cone Barujari at the E end of the caldera. Historical eruptions at Rinjani dating back to 1847 have been restricted to Barujari cone and consist of moderate explosive activity and occasional lava flows that have entered Segara Anak lake.
Information Contacts: Alain Bernard, Benjamin Barbier, Robin Campion, and Corentin Caudron, Universite Libre de Bruxelles (ULB), Belgium (Commission of Volcanic lakes, URL: http://www.ulb.ac.be/sciences/cvl/rinjani/rinjani.html); Akhmad Solikhin, Devy Syabahna, and Syegi Kunrat, Center of Volcanology and Geological Hazards Mitigation (CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://portal.vsi.esdm.go.id/joomla/); Vincent Hallet and David Lemadec, Facultes Universitaires Notre Dame de la Paix (FUNDP, URL: http://www.fundp.ac.be/); Bakosurtanal, Badan Koordinasi Survei dan Pemetaan Nasional (URL: http://www.bakosurtanal.go.id/); Jim Chow (URL: http://www.flickr.com/photos/11668976@N06/3486237730); Arjo Vanderjagt, Oude Boteringestraat 52, 9712 GL Groningen, The Netherlands (URL: http://www.flickr.com/photos/87453322@N00/3794836615).
Anatahan
Mariana Islands, Central Pacific
16.35°N, 145.67°E; summit elev. 790 m
Our most recent report on Anatahan (BGVN 33:12) discussed sulfur dioxide emissions and steam plumes during 2008. This report covers activity between January and October 2009.
A team of research scientists from the University of Tokyo and Kyushu University visited the volcano during the week of 19 January. They worked with the Emergency Management Office of the Commonwealth of the Northern Mariana Islands (CNMI) to perform seismic station maintenance. The team observed no unusual volcanic phenomena. Seismic levels remained low, and no anomalies were observed in satellite imagery.
The U.S. Geological Survey (USGS) reported that seismic activity at Anatahan during the first half of 2009 was generally at background levels. On 11 February a brief episode of tremor occurred. A low level plume was observed in satellite images on 13 June, but there was no evidence that it contained ash. Nothing unusual was observed in satellite images throughout the rest of the week. According to the USGS, Anatahan was quiet as of 6 November.
Geologic Summary. The elongate, 9-km-long island of Anatahan in the central Mariana Islands consists of a large stratovolcano with a 2.3 x 5 km, E-W-trending compound summit caldera. The larger western portion of the caldera is 2.3 x 3 km wide, and its western rim forms the island's 790-m high point. Ponded lava flows overlain by pyroclastic deposits fill the floor of the western caldera, whose SW side is cut by a fresh-looking smaller crater. The 2-km-wide eastern portion of the caldera contained a steep-walled inner crater whose floor prior to the 2003 eruption was only 68 m above sea level. A submarine volcano, named NE Anatahan, rises to within 460 m of the sea surface on the NE flank of the volcano, and numerous other submarine vents are found on the NE-to-SE flanks. Sparseness of vegetation on the most recent lava flows on Anatahan had indicated that they were of Holocene age, but the first historical eruption of Anatahan did not occur until May 2003, when a large explosive eruption took place forming a new crater inside the eastern caldera.
Information Contacts: Dina Venezky, Volcano Hazards Program, U.S. Geological Survey, 345 Middlefield Road, MS 910, Menlo Park, CA 94025, USA (URL: http://volcanoes.usgs.gov/, Email: dvenezky@xxxxxxxx); Emergency Management Office, Commonwealth of the Northern Mariana Islands, PO Box 100007, Saipan, MP 96950, USA (URL: http://www.cnmiemo.gov.mp/).
Pagan
Mariana Islands, Central Pacific
18.13°N, 145.80°E; summit elev. 570 m
Our most recent report on Pagan (BGVN 32:01) covered light ashfall and a small gas plume probably containing some ash during the first week of December 2006. We received no additional information regarding activity at Pagan until April 2009. The U.S. Geological Survey (USGS) does not currently have monitoring instruments on Pagan. Monitoring is by satellite and ground observers.
According to the Washington Volcanic Ash Advisory Center (VAAC), a plume from Pagan on 15 April consisting of intermittent puffs of steam rose to an altitude of 1.8 km and drifted about 37 km W. This observation was confirmed by a ship crew that noted a white plume "with some black" that same day.
On 16 April, the Washington VAAC reported that a narrow plume of unknown composition extended 85 km W from the volcano. According to the CNMI Emergency Management Office, fishermen reported that the plume was "thicker" on 15 April than on 16 April. Weather clouds obscured satellite views. The next day fishermen again reported a plume.
By 17 April, steaming had diminished. A passing pilot reported seeing no activity; however, the Washington VAAC noted a very faint plume extending 85 km NNW in satellite imagery.
Crew on a U.S. National Oceanic and Atmospheric Administration (NOAA) ship observed continuous emissions from the N crater during 21-22 April. Satellite imagery analyzed by the Washington VAAC showed a diffuse plume drifting 15 km W on 23 April. On 28 April, steam emissions had decreased.
Based on analyses of satellite imagery, the Washington VAAC reported that on 14 August a 2-hour-long thermal anomaly detected over Pagan was followed by a small emission. The emission, hotter than its surroundings, drifted NW and quickly dissipated.
No thermal hotspots on Pagan have been detected by MODIS during the last five years.
Geologic Summary. Pagan Island, the largest and one of the most active of the Mariana Islands volcanoes, consists of two stratovolcanoes connected by a narrow isthmus. Both North and South Pagan stratovolcanoes were constructed within calderas, 7 and 4 km in diameter, respectively. The 570-m-high Mount Pagan at the NE end of the island rises above the flat floor of the northern caldera, which probably formed during the early Holocene. South Pagan is a 548-m-high stratovolcano with an elongated summit containing four distinct craters. Almost all of the historical eruptions of Pagan, which date back to the 17th century, have originated from North Pagan volcano. The largest eruption of Pagan during historical time took place in 1981 and prompted the evacuation of the sparsely populated island.
Information Contacts: Dina Venezky, Volcano Hazards Program, U.S. Geological Survey, 345 Middlefield Road, MS 910, Menlo Park, CA 94025, USA (URL: http://volcanoes.usgs.gov/, Email: dvenezky@xxxxxxxx); Emergency Management Office, Commonwealth of the Northern Mariana Islands, PO Box 100007, Saipan, MP 96950, USA (URL: http://www.cnmiemo.gov.mp/); Washington Volcanic Ash Advisory Center, Satellite Analysis Branch (SAB), NOAA/NESDIS E/SP23, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: http://www.ssd.noaa.gov/VAAC/); Hawai'i Institute of Geophysics and Planetology (HIGP) Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), University of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://hotspot.higp.hawaii.edu/).
Koryaksky
Kamchatka Peninsula, Russia
53.320°N, 158.688°E; summit elev. 3,456 m
During March-18 April 2009 (BGVN 34:03) seismicity and volcanism continued at Karymsky, and ash plumes were detected for hundreds of kilometers. This report discusses the interval May-October 2009, with some discussion of earlier seismicity. The key conclusion for this new interval is that seismicity has not stopped and occasional, though smaller ash plumes continued.
In the mid-May 2009 volcanic and seismic activity decreased considerably. The active fumarole on the NW slope produced gas-steam plumes, but no longer contained appreciable ash (figure 26).
Figure 26. Gas-steam emission seen on the NW side Koryaksky on 11 May 2009. The white snow on the volcano confirms the virtual absence of any ash in the plume. Photo by A. Socorenko.
On 2-3 June 2009, observers again saw small areas of snow that were dark gray, indicating some increased ash content. On 15-16 August 2009 instruments began to register a spasmodic volcanic tremor; seismicity increased, and on 17 August ash fell to the SW, forming a deposit 1 mm thick (figure 27).
Figure 27. Ash plume from a vent on NW slope of Koryaksky. Snow on the slope covered fresh ashfall. Dark area around vent is due to local heating and melting of snow cover. Photo taken on 18 August 2009 by S. Chirkov.
Seismic analysis. Seliverstov (2009) analyzed seismicity for May 2008 to 10 June 2009, looking at events larger than Ks 4 (Class 4 earthquakes, roughly those larger than M ~ 1.2) and found a spatial and temporal pattern to this stronger seismicity. During March 2008 a prominent swarm of earthquakes was often centered at about 5-10 km depth. Smaller earthquakes were also seen around that time, several at ~ 12 km depth, and some at 15 km depth. This stronger seismicity then waned for several months until late June. During August 2008 to 10 June 2009, earthquakes were numerous, often centered near 5 km depth.
Figure 28 shows a representative set of hypocenters during 3 January 2009-6 November 2009. The pattern shown was similar to that seen during various months during 2008 through mid-2009. Other patterns during 2008 to mid-2009 included intervals where epicenters dipped, as noted in the analysis presented by Seliverstov (2009). Despite decreased volcanic activity, the elevated seismicity remained until at least 10 June 2009.
Figure 28. Seismicity of Koryaksky (and Avachinsky, to the SE) recorded during May-October 2009. Map shows location and depths of earthquakes (white line is cross-section AB. Cross-section shows hypocenters within 20 km depth. Courtesy of the Kamchatka Branch of the Geophysical Service, Russian Academy of Sciences (KB GS RAS).
The number of earthquakes recorded within 10-15 km of the summit during January through October 2009 by the KB GS RAS peaked in April with 422 events, and again in August with 245 events. Otherwise, the interval commonly had monthly totals of 100-200 with the lowest during January (59 events) and October (37 events).
Geologic Summary. The large symmetrical Koryaksky stratovolcano is the most prominent landmark of the NW-trending Avachinskaya volcano group, which towers above Kamchatka's largest city, Petropavlovsk. Erosion has produced a ribbed surface on the eastern flanks of the 3456-m-high volcano; the youngest lava flows are found on the upper western flank and below SE-flank cinder cones. No strong explosive eruptions have been documented during the Holocene. Extensive Holocene lava fields on the western flank were primarily fed by summit vents; those on the SW flank originated from flank vents. Lahars associated with a period of lava effusion from south- and SW-flank fissure vents about 3900-3500 years ago reached Avacha Bay. Only a few moderate explosive eruptions have occurred during historical time. Koryaksky's first historical eruption, in 1895, also produced a lava flow.
References. Seliverstov, N., 2009, The activity Koryaksky volcano, Kamchatka, Vestnik KRAUNC, Earth Science Series; Petropavlovsk-Kamchatsky, 2009, v. 13, p.7-9 [ISSN 1816-5524]. In Russian.
Information Contacts: Kamchatka Volcanic Eruptions Response Team (KVERT), Far East Division, Russian Academy of Sciences, 9 Piip Blvd., Petropavlovsk-Kamchatsky, 683006, Russia (Email: kvert@xxxxxxxxx, URL: http://www.kscnet.ru/ivs/); Kamchatka Branch of the Geophysical Service of the Russian Academy of Sciences (KB GS RAS), Sergey Senukov, Russia (Email: ssl@xxxxxxxxxxx; URL: http://wwwsat.emsd.ru/alarm.html; http://wwwsat.emsd.ru/~ssl/monitoring/main.htm); Alexander Socorenko and Sergei Chirkov, IV&S FED RAS; Tokyo Volcanic Ash Advisory Center (VAAC), Tokyo, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/).
St. Helens
Washington, USA
46.20°N, 122.18°W; summit elev. 2,549 m
The eruptive episode that began with the volcano reawakening in October 2004 (BGVN 29:09) ended in late January or early February 2008. The activity included explosions containing ash that rose up to ~ 3 km above the crater and lava dome growth. Sherrod and others (2008) provide a comprehensive discussion of the 2004-2006 portion of the eruption. This report spans 28 November 2007 through October 2009.
A GPS receiver on the W part of the active spine recorded continued SW advance at a rate of 3-4 mm per day during September through November 2007. During 28 November-4 December 2007, small inflation-deflation events occurred, which the USGS Cascades Volcano Observatory (CVO) interpreted as dome-growth pulses. On 31 December 2007 aerial observers saw a new small, snow-free spine on top of the active lobe.
On 25 January 2008, a steam plume rose from the dome slightly above the crater rim. Though seismicity had persisted at low levels through mid-February 2008, very few earthquakes were recorded after late January. Locatable earthquakes were fewer than one per day, all under M 2.0. Ground tilt measurements showed an overall subsidence in the area of the new dome. A GPS receiver on the previously active spine settled about 2 cm per day on a southward path. During February, the daily ground-tilt events stopped and gas emissions were barely detectable.
Comparison of photographs taken by remote cameras during late January to mid-February 2008 showed no evidence of extrusion. Cynthia Gardner (CVO), in a personal communication, noted that dome growth stopped in late January or early February (January 27 +/- 10 days).
During March 2008, the most significant developments were a small, M 2.0 earthquake on 4 March and a very small earthquake swarm on 6 March. The latter started with a roughly M 1.2 event, followed by several smaller tremors over a seven-minute period. No tilt changes were associated with the swarm. On 14 March, the Pacific Northwest Seismic Network recorded four very small earthquakes located near the volcano. There were no tilt changes associated with this activity.
Radar imagery analyzed by Jet Propulsion Laboratory staff during late March 2008 showed that the E and W arms of Crater Glacier were touching, or close to touching, just N of the 1980s lava dome. From 30 May 2008 (figure 29) to 8 July 2008, the W arm of the glacier advanced ~ 20 m. By 8 July, the old and new lava domes in the crater were encircled by ice (figure 30). Further down slope glacier ice descended into the gullies that had been carved by erosion into the Pumice Plain. On 10 July, after nearly 5 months without signs of renewed activity, CVO lowered the Alert Level to Normal and the Aviation Color Code to Green.
Figure 29. Aerial view of the St. Helens crater, as seen from the N. The two arms of the Crater Glacier had by 30 May 2008 fully encircled the dome. USGS photograph by Steve Schilling.
Figure 30. Old and new lava domes (center and upper right respectively) in the St. Helens crater encircled by ice, as seen from the NW. USGS photograph taken on 5 August 2009 by Steve Schilling.
As of October 2009, earthquakes, volcanic gas emissions, and ground deformation had all fallen to levels observed prior to the onset of the eruption.
Geologic Summary. Prior to 1980, Mount St. Helens formed a conical, youthful volcano sometimes known as the Fuji-san of America. During the 1980 eruption the upper 400 m of the summit was removed by slope failure, leaving a 2 x 3.5 km horseshoe-shaped crater now partially filled by a lava dome. Mount St. Helens was formed during nine eruptive periods beginning about 40-50,000 years ago and has been the most active volcano in the Cascade Range during the Holocene. Prior to 2,200 years ago, tephra, lava domes, and pyroclastic flows were erupted, forming the older St. Helens edifice, but few lava flows extended beyond the base of the volcano. The modern edifice was constructed during the last 2,200 years, when the volcano produced basaltic as well as andesitic and dacitic products from summit and flank vents. Historical eruptions in the 19th century originated from the Goat Rocks area on the N flank, and were witnessed by early settlers.
References: Lahusen, R.G., 2005, Acoustic flow monitor system-user manual: U.S. Geological Survey Open-File Report 02-429, 22 p.
Sherrod, D.R., Scott, W.E., and Stauffer, P.H., eds., 2008, A volcano rekindled: the renewed eruption of Mount St. Helens, 2004-2006: U.S. Geological Survey, Professional Paper 1750, 856 p.
Information Contacts: Cascades Volcano Observatory (CVO), U.S. Geological Survey, 1300 SE Cardinal Court, Building 10, Suite 100, Vancouver, WA 98683-9589, USA (URL: http://vulcan.wr.usgs.gov/); Pacific Northwest Seismic Network, University of Washington, Dept. of Earth and Space Sciences, Box 351310, Seattle, WA 98195-1310, USA (URL: http://www.pnsn.org/); Hawai'i Institute of Geophysics and Planetology (HIGP) Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://hotspot.higp.hawaii.edu/).
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Volume 34, Number 9, September 2009
http://www.volcano.si.edu/
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Bulletin of the Global Volcanism Network
Volume 34, Number 9, September 2009
Turrialba (Costa Rica) Non-eruptive in August 2009, but degassing and with widening cracks
Reventador (Ecuador) Lava flows seen and SO2 fluxes recorded during 16-17 September 2009
Kaba (Indonesia) Increased seismicity and whitish vapor emissions
Rinjani (Indonesia) More data relevant to eruptions during 2 May through at least 31 August 2009
Anatahan (Mariana Islands) Quiet except for brief tremor in February 2009 and plume in June 2009
Pagan (Mariana Islands) Emission of a small plume in mid-April 2009
Koryaksky (Russia) Continued ash emissions during May-September 2009
St. Helens (USA) Eruption ceased in late January 2008; quiet continues in late 2009
Editors: Rick Wunderman, Edward Venzke, and Sally Kuhn Sennert
Volunteer Staff: Paul S. Berger, Russell Ross, Hugh Replogle, Catie Carter, Ludmila Eichelberger, Robert Andrews, Margo Morell, Jacquelyn Gluck, and Stephen Bentley
Turrialba
Costa Rica
10.025°N, 83.767°W; summit elev. 3,340 m
All times are local (= UTC - 6 hours)
The Observatorio Vulcanologico y Sismologico de Costa Rica, Universidad Nacional (OVSICORI-UNA) continued monitoring the Turrialba non-eruptive interval of February 2008 through August 2009. As during the previous four months (BGVN 33:01), Turrialba continued to emit sulfurous gas from its central and W craters, and elsewhere, including some new cracks.
Activity during February-December 2008. During February 2008, the area around Turrialba affected by acid rain increased due to degassing. The degassing vents on the N, NW, W, and SW walls were rich in sublimated native sulfur. Gas-emission temperatures ranged from 72 to 132°C. Owing to prevailing winds, the vegetation most affected was on the N, NW, and SW flanks. The effects ranged from discoloration to death of various plant species. Residents in the area reported occasional nausea and irritation of the skin and eyes. On 22 February, local observers reported a gas plume up to ~ 2 km in height.
On the SE and SW walls of the central crater two cracks 2-3 cm wide and 100 m long continued to emit gases at ~ 90°C and produced sulfur deposits (figure 1). In stable atmospheric conditions gas columns often rose ~ 500 m above the crater. Rockslides sometimes covered emitting fumaroles, and new sulfur deposits tended to develop in these areas.
Figure 1. Elongated cracks (red lines on colored version) mapped at Turrialba during in August 2009. From first being noticed in mid-2009 to being measured in August 2009, some cracks opened by as much as 12 cm. Courtesy of OVSICORI-UNA.
During 7-8 March 2008, gas sampling at the summit fumaroles determined the maximum temperature at the largest W wall vent was 278°C. Degassing vents were also noted at spots in the middle of the forest. In some cases emissions had killed all local vegetation.
On 7-8 March 2008, Erick Fernandez and Eliecer Duarte of OVSICORI, and the National University (UNA) took gas samples. The analysis, done by Jorge Andres Diaz and Sergio Achi of the University of Costa Rica, revealed the presence of He at 80,000 ppm (parts per million), whereas the typical He concentration in the neighborhood of a volcano is 25 ppm.
OVSICORI-UNA reported continued degassing during August and September 2008. Multiple fumaroles and areas of sulfur deposition were noted in both the central and W craters. Fumarolic emissions on the S and SE flanks of the W crater continued to damage vegetation in that area.
On 23 September 2008, OVSICORI fieldwork confirmed a severe impact of acid-rain on areas that had been only mildly affected during the preceding 3 years of degassing. At least three sectors showed new impacts on vegetation and infrastructure, from the summit downhill ~ 3 km along the S and SE flanks. The upper sector, which includes the entire caldera and lower sectors to the E, S, and SE near the summit, had been severely burned during August and September. This area goes from the summit down to an elevation of ~ 2,900 m. By 23 September, weeds, dwarf vegetation, and trees had been completely burned; however in these areas some resistant species maintained some green and appeared seemingly viable. Along the external walls to the S of the W crater, plants had been burned down to the soil. Due to the removal of that natural coverage, erosion had cut extended radial gullies.
Between the elevations of 2,900 and 2,600 m, significant forest patches have been partially seared by extreme acidification, particularly the dense birch forests. Below 2,600 m elevation mild burns to the tree canopy and pasture areas were evident. The evidence of chemical burns due to the heavy gases are amplified along canyons and depressions. These conditions caused residents to voluntarily leave their farms in 2007.
Monitored SO2 emissions during the early part of 2008 had been ~ 750 metric tons per day (t/d). At the end of April 2008, an increase to ~ 1,000 t/d was noted, which then increased to ~ 2,000 t/d well into July. During the end of July the emissions declined to ~ 1,100 t/d. The increase in SO2 flux corresponded to increases in vegetation damage.
Activity during January-June 2009. In May 2009 OVSICORI reported ongoing fumarolic degassing during the preceding months from the central crater, from the N, NW, W, SW and S walls, from new vents on the S and SW walls, and other locations. Some locations continued to form sublimated sulfur deposits. The two cracks in the SE and SW walls had temperatures of ~ 87°C. The emissions in the W wall registered ~ 91°C and displayed sulfur deposits. In meteorologically quiet conditions, gas plumes were noted up to 500-600 m above the crater floor. All of these areas had experienced small landslides that occasionally covered some vents.
SO2 flux was variable during early 2009 (figure 2). The flux data were collected with a roughly consistent sun angle, between 0900 and 1100 in the morning on the SW flank. In the graph the SO2 flux varies between ~ 0 and ~ 2,000 t/d, the maximum flux occurred on 23 April.
Figure 2. SO2 fluxes measured at Turrialba during April 2009 (with y-axis showing SO2 flux in metric tons per day and x-axis dates in the format, month/day/year). Courtesy of OVSICORI-UNA.
On 14 June 2009, OVSICORI-UNA reported that fumarolic activity from Turrialba had been observed all around the upper flanks of the active W crater. During the previous two months, the fumarolic activity was also accompanied by widening radial cracks (1.5 cm on average), 1-2 km tall gas-and-vapor plumes, and one sustained seismic swarm. Temperatures of fumarolic vents in the lower parts of the crater were between 120 and 160°C. The temperature of summit cracks was 94°C. By mid-June, dairy pastures and forests had been chemically burned as far away as 3.5 km NW and W. During the last week of August 2009, the W and NW lower flanks, sectors previously reported with moderate effects, showed acute burns, and yellow pastures within 3 to 4 km radius (figures 3, 4, and 5).
Figure 3. Vegetation damage as of late August 2009 at Turrialba plotted on a shaded relief map by F. Robichaud. E. Duarte and others found that damage was generally within several kilometers of the volcano and in broader areas on the W flanks. The large dotted line indicates the boundary of detectible damage. Severe damage covered an irregular area, a strip both directly W of the active crater and a lobe to its SW as well. Courtesy of OVSICORI-UNA.
Figure 4. Newly emerging fumaroles on Turrialba's upper NW flank and burns on vegetation, August 2009. Courtesy of OVSICORI-UNA.
Figure 5. A view from Turrialba's seismic station PICA on the NW flank, showing active degassing from a variety of locations in August 2009. Left mid-ground shows plumes from the lowest fumaroles yet developed on this flank. Green grass is in the foreground, but most of the other foliage is brown to orange. Courtesy of OVSICORI-UNA.
Near the Toro Amarillo river (4 km E of the crater) chemical burning surrounds stands of trees. Such whitening effect had been previously reported at the end of 2007 for areas closer to the active crater, 1.5 km W (figure 6).
Figure 6. An example of a zone with intense burns on grass at the foot of injured trees, damage attributed to acidic gases from Turrialba. The spot is near the Toro Amarillo river in late August 2009. Courtesy of OVSICORI-UNA.
Several elongated cracks were mapped just south of the W crater as well as 1 km downslope NW. One main crack, noticed during mid-2009 due to sulfur depositions on the surface, was opened by August in places as much as 12 cm. In late August 2009 it emitted gasses at 90ºC. The crack trends E-W, in places intersecting a trail used to reach the summit's SW and W sides.
The last two years have caused residents to leave owing to the burned and dead pastures. Some commented on their apprehension related to the emergence of the lower fumaroles. Along the S side of the Irazu summit located 10 km SW of Turrialba's summit, mild burns have been observed on patches of birch, eucalyptus and pine. Lesser impact was reported last year in that same area.
False eruption report. The Washington VAAC received surface observations from an airport near the volcano erroneously indicating an eruption on the morning of 23 September 2009.
The VAAC decided to initially describe the activity as an eruption because it was the first time the airport had reported emissions, the volcano was known to have been degassing for some time, and early morning satellite imagery showed cloud cover, preventing good analysis. In addition, attempts to reach local volcanologists by telephone using contact numbers from the ICAO [International Civil Aviation Organization] handbook and the OVSICORI webpage were not successful. OVSICORI-UNA personnel reported a few hours later that the volcano had not erupted. As a result of the incident, the VAAC has obtained current contact numbers, including personal cell phones, for future use.
Geologic Summary. Turrialba, the easternmost of Costa Rica's Holocene volcanoes, is a large vegetated basaltic-to-dacitic stratovolcano located across a broad saddle NE of Irazu volcano overlooking the city of Cartago. The massive 3,340-m-high Turrialba is exceeded in height only by Irazu, covers an area of 500 sq km, and is one of Costa Rica's most voluminous volcanoes. Three well-defined craters occur at the upper SW end of a broad 800 x 2,200 m wide summit depression that is breached to the NE. Most activity at Turrialba originated from the summit vent complex, but two pyroclastic cones are located on the SW flank. Five major explosive eruptions have occurred at Turrialba during the past 3,500 years. Turrialba has been quiescent since a series of explosive eruptions during the 19th century that were sometimes accompanied by pyroclastic flows. Fumarolic activity continues at the central and SW summit craters.
Information Contacts: Eliecer Duarte, Erick Fernandez, Vilma Barboza, S. Miranda, L. Ortiz, G. Chavez, Jorge Brenes, Thomas Marino, Javier Pacheco, Juan Segura, and Rodolfo van der Laat, Observatorio Vulcanologico y Sismologico de Costa Rica, Universidad Nacional (OVSICORI-UNA), Apdo. 2346-3000, Heredia, Costa Rica (URL: http://www.ovsicori.una.ac.cr/informacion_general/prensa.htm or http://www.ovsicori.una.ac.cr/vulcanologia/Volcan_Turrialba.htm); Francois Robichaud, Universite de Sherbrooke, 2500 boul. de l'Universite, Sherbrooke, Quebec J1K 2R1, Canada; Washington Volcanic Ash Advisory Center, Satellite Analysis Branch (SAB), NOAA/NESDIS E/SP23, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: http://www.ssd.noaa.gov/VAAC/).
Reventador
Ecuador
0.077°S, 77.656°W; summit elev. 3,562 m
Activity at Reventador between August 2008 and late April 2009 was a period of generally low seismicity (BGVN 34:03). During early November 2008 repeated small eruptions occurred with steam-and-ash plumes, Strombolian eruptions, and lava flows. This report continues coverage through October 2009, an interval that included new lava flows advancing ~ 500 m by mid-September 2009.
Based on analysis of satellite imagery, the Washington Volcanic Ash Advisory Center (VAAC) reported that on 1 May a thermal anomaly over Reventador occurred along with a possible low plume drifting W. The Instituto Geofisico-Escuela Politecnica Nacional (IG) reported to the VAAC the presence of lava and gas emissions and possible smoke from burning vegetation, but little to no ash.
On 15 May, the IG observed an ash emission, although neither an ash signature nor a thermal anomaly was detected in satellite imagery. On 26 May, a diffuse ash plume rose to an altitude of 6.4 km and drifted SW. Thermal anomalies were intermittently seen on satellite imagery.
On 21 July-3 August, tremor was sporadic. On 4 August, seismicity increased and periods of tremor frequently saturated the seismic stations. Thermal anomalies, detected in satellite imagery on 1 and 2 August, became more intense on 4, 5, and 10 August. On 6 August, a steam plume rose 1.2 km above the crater and drifted W. Incandescent blocks were ejected from the crater and fell onto the flanks. Thermal images taken from a location 7 km E of Reventador revealed a linear area of higher temperatures, confirming the presence of a new lava flow on the S flank. Incandescence in the crater was seen on 9 August. According to the Washington VAAC, based on information from the IG, an ash plume on 15 August rose to an altitude of 3.6 km and drifted NW.
Field observations on 16-17 September 2009. IG scientists visited Reventador during 16-17 September 2009; among their objectives was to map, sample, and collect thermal images of the new lava flows and to measure the sulfur dioxide (SO2) concentrations with a mobile DOAS.
The team noted that recent lava flows had descended the flanks in a SE to E direction, continuing the same pattern that had begun with the 2005 eruption (figure 7). A dome within the crater showed constant growth (figure 8). Gas was emitted to a height of less than 200 m and drifted mainly W. A small lava flow originating in the dome area had descended ~ 500 m from the cone's S flank.
Figure 7. Panoramic view from the sequential camera of lava flows at Reventador. Courtesy of S. Vallejo.
Figure 8. At Reventador, a photo taken on 16-17 September 2009 of the actively growing dome in the summit crater. Courtesy of J. Bourquin.
Thermal images and SO2 measurements were collected near the caldera, and lavas were sampled. SO2 flux measurements (table 1) were collected both by helicopter and by car (figure 9). A telescope for the SO2 measurements sat below the helicopter blades and those spinning blades may have interfered with the measurements. The values presented may thus underestimate the SO2 fluxes.
Table 1. Reventador SO2 data collected from helicopter on 16 and 17 September 2009. The transects in the first column are indicated on figure 9. Transect 34 measurements clearly indicated that the SO2 gas plume had divided (bifurcated) and the two plumes appear as 34a and 34b. For this transect, the SO2 fluxes were calculated separately for each lava plume segment, than added to get the total emission. Land-based measurements, transects 43 and 46, were collected S and W of the vent. Courtesy of IG.
Transect Wind Wind Data Offset SO2 flux Plume Traverse Intensity
/Route speed direction number (t/d) Width Length Limit
(m/s) (km) (km)
31 5 281 191 -28 811 1.9 52.2 7
34a 5 270 95 -1 1,425 3.6 22.2 7
34b 5 326 124 -8 795 2.5 49.2 7
34 Total -- -- 215 -- 2,220 -- -- --
35 5 337 84 -28 616 1.6 22.8 5
36 5 349 147 -16 557 2.1 30.2 8
43 5 202 471 -14 283 5.2 42.8 5
46 5 236 1222 -14 1,264 16 116 5
Figure 9. Map of Reventador illustrating transects made (in colored version, each transect is in a different color). Transects 31 and 34 were conducted on 16 September; transects 35, 36, 43 and 46 were conducted on 17 September. Courtesy of IG.
Based on a pilot observation, the Washington VAAC reported that on 21 September a plume rose to an altitude of 7.6 km. An ash plume on 4 October drifted W. In both cases, ash was not seen in satellite imagery, although meteorological clouds were present. In the latter case, an occasional thermal anomaly was observed.
Thermal anomalies over the crater area were detected in MODIS satellite imagery on 6, 11, and 13 October. On 13 October, the OMI satellite sensor indicated that the SO2 concentration in the atmosphere near the volcano had increased. On 14 October, seismicity increased and harmonic tremor was detected. A seismic station located at ~ 2,600 m elevation on the NE flank of the cone detected rockfalls. Several people living in the area reported roaring noises and had observed slight incandescence from the crater during the previous few nights.
During an overflight on 16 October, scientists saw the lava dome and a lava flow on the NE flank (figure 10). Bluish gases were being emitted. According to a thermal camera, the incandescent parts in the crater were about 300°C. Other observers heard roaring noises and sounds resembling "cannon shots." Incandescent blocks were ejected from the crater, and steam and gas rose 100 m and drifted SW. Incandescent material was seen on the S flank.
Figure 10. Aerial photo taken on the N side of Reventador on 16 October 2009 showing the lava dome amid weather clouds and some heavy steaming from the NE-flank lava flow. Courtesy of IG.
On 17 October, long period (LP) earthquakes and volcanic explosions lasting up to 10 hours were registered, incandescence on the S flank was noted, and noises similar to the previous day were again heard. A small gray plume was seen the next day. On 19 October, thermal anomalies were again detected on satellite imagery. During an overflight, blue gas plumes containing SO2 were seen (figure 11). The lava flow on the S flank occupied a large area and was divided into two branches.
Figure 11. Photograph of the E side of Revantador's cone taken the morning of 19 October 2009. Note steam rising from dome summit and lava flows on volcano's flanks. Courtesy of IG.
According to the IG, on 21 October, steam-and-gas plumes with little to no ash rose 2-4 km above the crater and drifted in various directions. An explosion that day ejected incandescent material from the crater and blocks rolled down the flanks. On 22 October, a few explosions generated ash-and-steam plumes that rose 4 km. Observations during an overflight revealed a small lava flow on the N flank and a larger flow with four branches on the S flank (figure 12). Part of the lava dome base had disappeared and small spines were present, especially on the S side of the dome. Thermal images revealed that material in the crater was 400°C and the lava-flow fronts were 250°C. Cloudy weather prevented visual observations during 23-26 October. Roaring noises were heard on 25 October.
Figure 12. Aerial photograph displaying the distribution of lava flows on the N side of Reventador's caldera on 22 October 2009. Courtesy of S. Vallejo.
Geologic Summary. Reventador is the most frequently active of a chain of Ecuadorian volcanoes in the Cordillera Real, well E of the principal volcanic axis. The forested, dominantly andesitic Volcan El Reventador stratovolcano rises to 3,562 m above the jungles of the western Amazon basin. A 4-km-wide caldera widely breached to the E was formed by edifice collapse and is partially filled by a young, unvegetated stratovolcano that rises about 1,300 m above the caldera floor to a height comparable to the caldera rim. Reventador has been the source of numerous lava flows as well as explosive eruptions that were visible from Quito in historical time. Frequent lahars in this region of heavy rainfall have constructed a debris plain on the eastern floor of the caldera. The largest historical eruption at Reventador took place in 2002, producing a 17-km-high eruption column, pyroclastic flows that traveled up to 8 km, and lava flows from summit and flank vents.
Information Contacts: Geophysical Institute (IG), Escuela Politecnica Nacional, Apartado 17-01-2759, Quito, Ecuador (URL: http://www.igepn.edu.ec/); Washington Volcanic Ash Advisory Center, Satellite Analysis Branch (SAB), NOAA/NESDIS E/SP23, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: http://www.ssd.noaa.gov/VAAC/); Hawai'i Institute of Geophysics and Planetology (HIGP) Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), University of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://hotspot.higp.hawaii.edu/).
Kaba
Sumatra, Indonesia
3.52°S, 102.62°E; summit elev. 1,952 m
All times are local (= UTC + 7 hours)
Deep volcanic earthquakes, seismic tremor, and five small explosions with corresponding ash emission were reported from Kaba in August 2000 (BGVN 25:11). Since then, Kaba has been quiet, but even in its normal state it almost always emits whitish plumes 25-100 m high.
On 20 October 2009, the Center of Volcanology and Geological Hazard Mitigation (CVGHM) reported that seismic activity from Kaba increased in August and remained elevated into September and October. Inflation was also detected. When weather permitted, diffuse white plumes were seen rising ~ 25-50 m above the summit crater complex and drifting E. Based on the deformation and increased seismicity, CVGHM raised the Alert Level to 2 (on a scale of 1-4).
>From January through August 2009, the frequency of deep volcanic earthquakes averaged 85 events per month, but in August the number of events rose to 257 per month. During August-September, whitish plumes remained similar to September-October. In September seismicity fluctuated but tended to increase. Earthquakes and total tremors recorded at Kaba's monitoring post are shown in table 2.
Table 2. Summary of Kaba seismic data recorded during 12 September-20 October 2009. Courtesy of CVGHM.
Dates (2009) Deep volcanic earthquakes (Count, Characteristics)
Shallow volcanic earthquakes (Count, Characteristics)
Notes
Beginning on 12 September 343
55
1-17 October 253. Max. amplitudes of 1-18 mm; S-wave minus P-wave arrival
times ("S-P") of 0.2-3.5 s with signals lasting 4-35 s.
271. Max. amplitudes 0.5-15 mm, durations of 2.5-11 s.
18 October 68. Max. amplitude of 1-19 mm; S-P times of 0.2-3 s, and a
duration of 3.5-47 s.
67. Max. amplitudes 0.8-16 mm, durations of 2.5-13 s.
19 October 50. Max. amplitudes of 0.5-18 mm; S-P 0.5-2 s, and a duration
of 2-15 s.
127. Max. amplitudes 0.5-15 mm, durations of 2.5-10 s.
Volcanic tremor registered during 0640-0900 local time; max. amplitudes 0.5-2 mm.
20 October 29. Max. amplitudes of 0.5-18 mm; S-P 0.5-2 seconds and a
duration of 2-15 s.
21. Max. amplitudes 0.5-15 mm, durations of 2.5-10 s.
Continuous tremor with amplitudes of 1-7 mm; the most prevalent amplitudes 1-3 mm. During
clear weather, whitish plumes rose ~ 25 m.
Deformation measurements taken using an EDM (electronic distance measurement) method were as follows: Biring station, shorter by 10 cm; Voelsang station, longer by 0.4 cm; and Kaba station, shorter by 2 cm.
Measurements of the crater water temperature on 15 October showed a reading of 72°C, with a pH of 3.24. The sulfurous and associated solfatara areas recorded a temperature of around 106-107°C. There was no other activity in the area of the crater.
Geologic Summary. Kaba, a twin volcano with Mount Hitam, has an elongated summit crater complex dominated by three large historically active craters trending ENE from the summit to the upper NE flank. The SW-most crater of 1,952-m-high Gunung Kaba, Kawah Lama, is the largest. Most historical eruptions have affected only the summit region of the volcano. They mostly originated from the central summit craters, although the upper-NE flank crater Kawah Vogelsang also produced explosions during the 19th and 20th centuries.
Information Contacts: Center of Volcanology and Geological Hazard Mitigation (CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://portal.vsi.esdm.go.id/joomla/).
Rinjani
Lesser Sunda Islands, Indonesia
8.42°S, 116.47°E; summit elev. 3,726 m
A series of eruptions at Rinjani began on 2 May 2009 (BGVN 34:06). The current report, provided by Alain Bernard, presents additional data regarding these eruptions, which continued through 31 August 2009.
Studies of Rinjani volcanic lake are part of a cooperative agreement between Indonesia and Belgium, a collaboration funded by the Commission Universitaire pour le Developpement (CUD, the main Belgian development cooperation agency for universities). Geochemical and physical studies of the Segara Anak lake started in the framework of this collaborative effort during the summer of 2006. During the summer of 2008, investigators installed a monitoring station for continuous measurements of the lake's level and temperature, and for meteorological parameters.
The scientific teams involved in this study were (Indonesia) Akhmad Solikhin, Devy Syabahna and Syegi Kunrat of the Center of Volcanology and Geological Hazards Mitigation (CVGHM); (Belgium) Alain Bernard, Benjamin Barbier, Robin Campion, and Corentin Caudron of the Universite Libre de Bruxelles (ULB), and Vincent Hallet and David Lemadec of the Facultes Universitaires Notre Dame de la Paix (FUNDP).
Segara Anak lake. The majestic Segara Anak lake filling the caldera of Rinjani covers an area of 11 km^2. Prior to the 2009 eruption, the lake's volume was 1.02 km^3. The lake-surface elevation is ~ 2 km (figures 13 and 14).
Figure 13. Bathymetric map of Rinjani's Segara Anak lake made from 65 km of echo-sounder surveys conducted in 2007 and 2008. Maximum depth of the lake is 205 m. Courtesy of the CVGHM, ULB, and FUNDP study team.
Figure 14. Topographic map of Rinjani caldera from Bakosurtanal-Indonesia (National Coordinator for Survey and Mapping Agency, Indonesia). Margins defining squares are 1 km long. "CTD" and "CTD-B" are locations of conductivity-temperature-depth profiles. "Meteo" is the site of the meteorological station monitoring air temperature, humidity, wind velocity, and net solar flux. The labels 51-54 are locations of hot springs discussed below. Courtesy of the CVGHM, ULB, and FUNDP study team.
The lake is neutral (pH: 7-8) and its chemistry dominated by chlorides and sulfates with a relatively high concentration of total-dissolved solids (TDS: 2,640 mg/L). This unusually high TDS value and lake surface temperatures (20-22°C), well above ambient temperatures (14-15°C) for this altitude, reflects a strong input of hydrothermal fluids. Numerous hot springs are located along the shore at the foot of the Barujari cone. Bathymetric profiles showed several areas with columns of gas bubbles escaping from the lake's floor.
Precursory signals of the May 2009 eruption. Changes in Segara Anak lake and the hot springs before the first 2 May 2009 eruption included significant anomalies in the temperature and chemistry of the hot springs.
During field work 10-14 April 2009, the researchers noted an increase in temperature and acidity of hot springs 53 and 54 (figures 15-16) compared to July. This increasing acidity was confirmed in the lab as the consequence of an increase in sulfate levels not observed during studies since 2004.
Figure 15. Geochemistry of Rinjani's Segara Anak lake (from CTD locations, figure 14) and hot springs. NA signifies not analyzed. Courtesy of the CVGHM, ULB, and FUNDP study team.
Figure 16. A plot of 2004 to 2009 sulfate (SO42-) ion concentration versus pH. Note the April 2009 increase in the acidity and sulfate contents of Rinjani's hot springs 53 and 54 (upper left). Courtesy of the CVGHM, ULB, and FUNDP study team.
The Fe-ion concentrations in spring 54, usually below detection limits, peaked at 120 mg/L. This change in chemistry produced a yellowish-brown coloration of the lake waters because of the precipitation of ferric hydroxide, Fe(OH)3 (figures 17-18). An ASTER image from 21 August 2009, processed to enhance the Fe(OH)3 precipitates, revealed a chemical plume close to where hot springs 53 and 54 injected water into the lake.
Figure 17. The Rinjani lake shoreline seen at a point close to the hot spring 54 on 12 April 2009. The water has a brown color and the coating on the rocks is an amorphous ferric hydroxide that precipitated when hydrothermal fluids oxidized by mixing with the lake waters (yellow-brown in color). Rock discoloration reaches the height of the mans lower hand. Changes in lake level were a consequence of the rainy season. Photo by A. Bernard.
Figure 18. A photo of Rinjani and Segara Anak Lake thought to have been taken on 26 April 2009 but certainly before the start of the eruption. A spectacular yellow-brown chemical precipitate floated on the lake's surface (at left). Copyrighted photo by Jim Chow.
A chemical plume of low pH and dissolved oxygen was observed at the lake surface extending up to several hundred meters away from hot spring 54. pH profiles as a function of depth recorded at several locations showed a clear acidification of Segara Anak lake especially at shallow depths (15-20 m) (figure 19). Rainfall in April 2009 caused a shallow zone of higher pH.
Figure 19. Plot showing shifts of pH in Rinjani's caldera lake waters with depth. The 2009 profile was recorded in April 2009, and the 2008 profile, in July 2008. Line 2009b was drawn as an estimate of the curve without the rainfall event. Measurements made with an SBE Seacat 19-Plus profiler. Courtesy of the CVGHM, ULB, and FUNDP study team.
A slight lake surface temperature increase from 20°C in July 2008 to 22°C in early April 2009 was mostly attributed to meteorological effects. Large increases seen in lake level in January and February 2009 were the consequence of heavy rainfalls. Heating of the lake between August 2008 and April 2009 occurred mainly during periods with reduced heat loss to the atmosphere due to less wind.
A report of these field observations was made on 17 April to CVGHM, which prompted them to send another team to the volcano. The new team arrived at the summit of the volcano on 2 May 2009, the day the eruptions started.
Eruptive activity May-August 2009. The 2009 eruptions originated from the same vent of the October 2004 activity (figure 20), and was characterized by mild eruptions that produced a small lava flow and low altitude, ash-poor gas plumes (figure 21). Contrary to that reported in some newspapers, the 2009 eruption did not open a new vent.
Figure 20. This July 2006 photo of Rinjani illustrates the new vent that opened on the NE slope of Gunung Baru in 2004 and then produced a short lava flow. The 2009 eruptive activity at Rinjani started from this same vent, producing a significant lava flow that entered the crater lake and built a delta. Photo by A. Bernard (July 2006).
Figure 21. Eruption of Rinjani seen on 10 June 2009. The plume at this point was relatively small and lava proceeded N to enter the lake. Photo by R. Campion.
Alain Bernard sent a report by Robin Campion (ULB) who was on site June 2009. According to Campion, mild activity was observed from the SE rim during 9-11 June. Pressurized incandescent gas was released at a 1-2 second intervals from a vent located in the 2004 crater, on the S flank of Barujari. At variable intervals (10 seconds to 10 minutes), stronger gas jets ejected lava fragments to heights up to 100 m. Occasional ash ejections occurred from a second vent in the same crater. A third lower vent emitted a viscous lava flow that reached Segara Anak Lake. Contact between the lake and the lava delta resulted in a warm surface current (figure 22).
Figure 22. A 10 June 2009 FLIR thermal camera image of Rinjani's Barujari cone and Segara Anak lake. A thermal plume of hot lake water was drifting from the lava entry points. Temperature scale is for lake waters. Photo by R. Campion.
Figure 23 shows an ASTER satellite image of Rinjani lake-surface temperatures. Increased discharge of the hot springs on the S flank of Barujari produced a distinct plume with an orange-red color. Weak winds carried the steam-and-gas plume (with low ash content) N and W at an altitude of 3-4 km. Activity did not vary during the 3-day observation period.
Figure 23. ASTER satellite image of the N part of Rinjani's Segara Anak lake taken on 29 July 2009 (at 1446 UTC). Thermal infrared bands 13 and 14 processed with a split-window algorithm. Contours are in degrees C. Maximum temperature in the lake water was 57°C. Courtesy of the CVGHM, ULB, and FUNDP study team.
As of 31 August 2009, the eruption was still underway. At that point, the new lava flow covered an area of 0.65 km^2 (figure 24). The shoreline had been significantly modified by the entry of lava into Segara Anak lake, and the lake surface area had been reduced by 0.46 km^2 (figures 24 and 25).
Figure 24. Rinjani seen in ASTER false color on 21 August 2009 (0235 UTC). The new lava covers an area of 650,000 m2 and significantly changed the shoreline. The inset shows the pre-eruption shoreline and the new lava margin (in red on colored versions). Courtesy of the CVGHM, ULB, and FUNDP study team.
Figure 25. Rinjani, in a photo apparently taken on 4 August 2009, showing a new delta built into the lake. Brown waters from hot springs were still visible at the end of the lake and drifted over a large area of the lake. Courtesy of Arjo Vanderjagt.
According to Alain Bernard, updates on Rinjani's activity will be posted on the website of the Commission of Volcanic Lakes (CVL, see information contacts). Bernard sent additional figures describing Rinjani behavior as late as 27 September 2009.
Geologic Summary. Rinjani volcano on the island of Lombok rises to 3,726 m, second in height among Indonesian volcanoes only to Sumatra's Kerinci volcano. Rinjani has a steep-sided conical profile when viewed from the E, but the W side of the compound volcano is truncated by the 6 x 8.5 km, oval-shaped Segara Anak caldera. The western half of the caldera contains a 230 m deep lake whose crescentic form results from growth of the post-caldera cone Barujari at the E end of the caldera. Historical eruptions at Rinjani dating back to 1847 have been restricted to Barujari cone and consist of moderate explosive activity and occasional lava flows that have entered Segara Anak lake.
Information Contacts: Alain Bernard, Benjamin Barbier, Robin Campion, and Corentin Caudron, Universite Libre de Bruxelles (ULB), Belgium (Commission of Volcanic lakes, URL: http://www.ulb.ac.be/sciences/cvl/rinjani/rinjani.html); Akhmad Solikhin, Devy Syabahna, and Syegi Kunrat, Center of Volcanology and Geological Hazards Mitigation (CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://portal.vsi.esdm.go.id/joomla/); Vincent Hallet and David Lemadec, Facultes Universitaires Notre Dame de la Paix (FUNDP, URL: http://www.fundp.ac.be/); Bakosurtanal, Badan Koordinasi Survei dan Pemetaan Nasional (URL: http://www.bakosurtanal.go.id/); Jim Chow (URL: http://www.flickr.com/photos/11668976@N06/3486237730); Arjo Vanderjagt, Oude Boteringestraat 52, 9712 GL Groningen, The Netherlands (URL: http://www.flickr.com/photos/87453322@N00/3794836615).
Anatahan
Mariana Islands, Central Pacific
16.35°N, 145.67°E; summit elev. 790 m
Our most recent report on Anatahan (BGVN 33:12) discussed sulfur dioxide emissions and steam plumes during 2008. This report covers activity between January and October 2009.
A team of research scientists from the University of Tokyo and Kyushu University visited the volcano during the week of 19 January. They worked with the Emergency Management Office of the Commonwealth of the Northern Mariana Islands (CNMI) to perform seismic station maintenance. The team observed no unusual volcanic phenomena. Seismic levels remained low, and no anomalies were observed in satellite imagery.
The U.S. Geological Survey (USGS) reported that seismic activity at Anatahan during the first half of 2009 was generally at background levels. On 11 February a brief episode of tremor occurred. A low level plume was observed in satellite images on 13 June, but there was no evidence that it contained ash. Nothing unusual was observed in satellite images throughout the rest of the week. According to the USGS, Anatahan was quiet as of 6 November.
Geologic Summary. The elongate, 9-km-long island of Anatahan in the central Mariana Islands consists of a large stratovolcano with a 2.3 x 5 km, E-W-trending compound summit caldera. The larger western portion of the caldera is 2.3 x 3 km wide, and its western rim forms the island's 790-m high point. Ponded lava flows overlain by pyroclastic deposits fill the floor of the western caldera, whose SW side is cut by a fresh-looking smaller crater. The 2-km-wide eastern portion of the caldera contained a steep-walled inner crater whose floor prior to the 2003 eruption was only 68 m above sea level. A submarine volcano, named NE Anatahan, rises to within 460 m of the sea surface on the NE flank of the volcano, and numerous other submarine vents are found on the NE-to-SE flanks. Sparseness of vegetation on the most recent lava flows on Anatahan had indicated that they were of Holocene age, but the first historical eruption of Anatahan did not occur until May 2003, when a large explosive eruption took place forming a new crater inside the eastern caldera.
Information Contacts: Dina Venezky, Volcano Hazards Program, U.S. Geological Survey, 345 Middlefield Road, MS 910, Menlo Park, CA 94025, USA (URL: http://volcanoes.usgs.gov/, Email: dvenezky@xxxxxxxx); Emergency Management Office, Commonwealth of the Northern Mariana Islands, PO Box 100007, Saipan, MP 96950, USA (URL: http://www.cnmiemo.gov.mp/).
Pagan
Mariana Islands, Central Pacific
18.13°N, 145.80°E; summit elev. 570 m
Our most recent report on Pagan (BGVN 32:01) covered light ashfall and a small gas plume probably containing some ash during the first week of December 2006. We received no additional information regarding activity at Pagan until April 2009. The U.S. Geological Survey (USGS) does not currently have monitoring instruments on Pagan. Monitoring is by satellite and ground observers.
According to the Washington Volcanic Ash Advisory Center (VAAC), a plume from Pagan on 15 April consisting of intermittent puffs of steam rose to an altitude of 1.8 km and drifted about 37 km W. This observation was confirmed by a ship crew that noted a white plume "with some black" that same day.
On 16 April, the Washington VAAC reported that a narrow plume of unknown composition extended 85 km W from the volcano. According to the CNMI Emergency Management Office, fishermen reported that the plume was "thicker" on 15 April than on 16 April. Weather clouds obscured satellite views. The next day fishermen again reported a plume.
By 17 April, steaming had diminished. A passing pilot reported seeing no activity; however, the Washington VAAC noted a very faint plume extending 85 km NNW in satellite imagery.
Crew on a U.S. National Oceanic and Atmospheric Administration (NOAA) ship observed continuous emissions from the N crater during 21-22 April. Satellite imagery analyzed by the Washington VAAC showed a diffuse plume drifting 15 km W on 23 April. On 28 April, steam emissions had decreased.
Based on analyses of satellite imagery, the Washington VAAC reported that on 14 August a 2-hour-long thermal anomaly detected over Pagan was followed by a small emission. The emission, hotter than its surroundings, drifted NW and quickly dissipated.
No thermal hotspots on Pagan have been detected by MODIS during the last five years.
Geologic Summary. Pagan Island, the largest and one of the most active of the Mariana Islands volcanoes, consists of two stratovolcanoes connected by a narrow isthmus. Both North and South Pagan stratovolcanoes were constructed within calderas, 7 and 4 km in diameter, respectively. The 570-m-high Mount Pagan at the NE end of the island rises above the flat floor of the northern caldera, which probably formed during the early Holocene. South Pagan is a 548-m-high stratovolcano with an elongated summit containing four distinct craters. Almost all of the historical eruptions of Pagan, which date back to the 17th century, have originated from North Pagan volcano. The largest eruption of Pagan during historical time took place in 1981 and prompted the evacuation of the sparsely populated island.
Information Contacts: Dina Venezky, Volcano Hazards Program, U.S. Geological Survey, 345 Middlefield Road, MS 910, Menlo Park, CA 94025, USA (URL: http://volcanoes.usgs.gov/, Email: dvenezky@xxxxxxxx); Emergency Management Office, Commonwealth of the Northern Mariana Islands, PO Box 100007, Saipan, MP 96950, USA (URL: http://www.cnmiemo.gov.mp/); Washington Volcanic Ash Advisory Center, Satellite Analysis Branch (SAB), NOAA/NESDIS E/SP23, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: http://www.ssd.noaa.gov/VAAC/); Hawai'i Institute of Geophysics and Planetology (HIGP) Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), University of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://hotspot.higp.hawaii.edu/).
Koryaksky
Kamchatka Peninsula, Russia
53.320°N, 158.688°E; summit elev. 3,456 m
During March-18 April 2009 (BGVN 34:03) seismicity and volcanism continued at Karymsky, and ash plumes were detected for hundreds of kilometers. This report discusses the interval May-October 2009, with some discussion of earlier seismicity. The key conclusion for this new interval is that seismicity has not stopped and occasional, though smaller ash plumes continued.
In the mid-May 2009 volcanic and seismic activity decreased considerably. The active fumarole on the NW slope produced gas-steam plumes, but no longer contained appreciable ash (figure 26).
Figure 26. Gas-steam emission seen on the NW side Koryaksky on 11 May 2009. The white snow on the volcano confirms the virtual absence of any ash in the plume. Photo by A. Socorenko.
On 2-3 June 2009, observers again saw small areas of snow that were dark gray, indicating some increased ash content. On 15-16 August 2009 instruments began to register a spasmodic volcanic tremor; seismicity increased, and on 17 August ash fell to the SW, forming a deposit 1 mm thick (figure 27).
Figure 27. Ash plume from a vent on NW slope of Koryaksky. Snow on the slope covered fresh ashfall. Dark area around vent is due to local heating and melting of snow cover. Photo taken on 18 August 2009 by S. Chirkov.
Seismic analysis. Seliverstov (2009) analyzed seismicity for May 2008 to 10 June 2009, looking at events larger than Ks 4 (Class 4 earthquakes, roughly those larger than M ~ 1.2) and found a spatial and temporal pattern to this stronger seismicity. During March 2008 a prominent swarm of earthquakes was often centered at about 5-10 km depth. Smaller earthquakes were also seen around that time, several at ~ 12 km depth, and some at 15 km depth. This stronger seismicity then waned for several months until late June. During August 2008 to 10 June 2009, earthquakes were numerous, often centered near 5 km depth.
Figure 28 shows a representative set of hypocenters during 3 January 2009-6 November 2009. The pattern shown was similar to that seen during various months during 2008 through mid-2009. Other patterns during 2008 to mid-2009 included intervals where epicenters dipped, as noted in the analysis presented by Seliverstov (2009). Despite decreased volcanic activity, the elevated seismicity remained until at least 10 June 2009.
Figure 28. Seismicity of Koryaksky (and Avachinsky, to the SE) recorded during May-October 2009. Map shows location and depths of earthquakes (white line is cross-section AB. Cross-section shows hypocenters within 20 km depth. Courtesy of the Kamchatka Branch of the Geophysical Service, Russian Academy of Sciences (KB GS RAS).
The number of earthquakes recorded within 10-15 km of the summit during January through October 2009 by the KB GS RAS peaked in April with 422 events, and again in August with 245 events. Otherwise, the interval commonly had monthly totals of 100-200 with the lowest during January (59 events) and October (37 events).
Geologic Summary. The large symmetrical Koryaksky stratovolcano is the most prominent landmark of the NW-trending Avachinskaya volcano group, which towers above Kamchatka's largest city, Petropavlovsk. Erosion has produced a ribbed surface on the eastern flanks of the 3456-m-high volcano; the youngest lava flows are found on the upper western flank and below SE-flank cinder cones. No strong explosive eruptions have been documented during the Holocene. Extensive Holocene lava fields on the western flank were primarily fed by summit vents; those on the SW flank originated from flank vents. Lahars associated with a period of lava effusion from south- and SW-flank fissure vents about 3900-3500 years ago reached Avacha Bay. Only a few moderate explosive eruptions have occurred during historical time. Koryaksky's first historical eruption, in 1895, also produced a lava flow.
References. Seliverstov, N., 2009, The activity Koryaksky volcano, Kamchatka, Vestnik KRAUNC, Earth Science Series; Petropavlovsk-Kamchatsky, 2009, v. 13, p.7-9 [ISSN 1816-5524]. In Russian.
Information Contacts: Kamchatka Volcanic Eruptions Response Team (KVERT), Far East Division, Russian Academy of Sciences, 9 Piip Blvd., Petropavlovsk-Kamchatsky, 683006, Russia (Email: kvert@xxxxxxxxx, URL: http://www.kscnet.ru/ivs/); Kamchatka Branch of the Geophysical Service of the Russian Academy of Sciences (KB GS RAS), Sergey Senukov, Russia (Email: ssl@xxxxxxxxxxx; URL: http://wwwsat.emsd.ru/alarm.html; http://wwwsat.emsd.ru/~ssl/monitoring/main.htm); Alexander Socorenko and Sergei Chirkov, IV&S FED RAS; Tokyo Volcanic Ash Advisory Center (VAAC), Tokyo, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/).
St. Helens
Washington, USA
46.20°N, 122.18°W; summit elev. 2,549 m
The eruptive episode that began with the volcano reawakening in October 2004 (BGVN 29:09) ended in late January or early February 2008. The activity included explosions containing ash that rose up to ~ 3 km above the crater and lava dome growth. Sherrod and others (2008) provide a comprehensive discussion of the 2004-2006 portion of the eruption. This report spans 28 November 2007 through October 2009.
A GPS receiver on the W part of the active spine recorded continued SW advance at a rate of 3-4 mm per day during September through November 2007. During 28 November-4 December 2007, small inflation-deflation events occurred, which the USGS Cascades Volcano Observatory (CVO) interpreted as dome-growth pulses. On 31 December 2007 aerial observers saw a new small, snow-free spine on top of the active lobe.
On 25 January 2008, a steam plume rose from the dome slightly above the crater rim. Though seismicity had persisted at low levels through mid-February 2008, very few earthquakes were recorded after late January. Locatable earthquakes were fewer than one per day, all under M 2.0. Ground tilt measurements showed an overall subsidence in the area of the new dome. A GPS receiver on the previously active spine settled about 2 cm per day on a southward path. During February, the daily ground-tilt events stopped and gas emissions were barely detectable.
Comparison of photographs taken by remote cameras during late January to mid-February 2008 showed no evidence of extrusion. Cynthia Gardner (CVO), in a personal communication, noted that dome growth stopped in late January or early February (January 27 +/- 10 days).
During March 2008, the most significant developments were a small, M 2.0 earthquake on 4 March and a very small earthquake swarm on 6 March. The latter started with a roughly M 1.2 event, followed by several smaller tremors over a seven-minute period. No tilt changes were associated with the swarm. On 14 March, the Pacific Northwest Seismic Network recorded four very small earthquakes located near the volcano. There were no tilt changes associated with this activity.
Radar imagery analyzed by Jet Propulsion Laboratory staff during late March 2008 showed that the E and W arms of Crater Glacier were touching, or close to touching, just N of the 1980s lava dome. From 30 May 2008 (figure 29) to 8 July 2008, the W arm of the glacier advanced ~ 20 m. By 8 July, the old and new lava domes in the crater were encircled by ice (figure 30). Further down slope glacier ice descended into the gullies that had been carved by erosion into the Pumice Plain. On 10 July, after nearly 5 months without signs of renewed activity, CVO lowered the Alert Level to Normal and the Aviation Color Code to Green.
Figure 29. Aerial view of the St. Helens crater, as seen from the N. The two arms of the Crater Glacier had by 30 May 2008 fully encircled the dome. USGS photograph by Steve Schilling.
Figure 30. Old and new lava domes (center and upper right respectively) in the St. Helens crater encircled by ice, as seen from the NW. USGS photograph taken on 5 August 2009 by Steve Schilling.
As of October 2009, earthquakes, volcanic gas emissions, and ground deformation had all fallen to levels observed prior to the onset of the eruption.
Geologic Summary. Prior to 1980, Mount St. Helens formed a conical, youthful volcano sometimes known as the Fuji-san of America. During the 1980 eruption the upper 400 m of the summit was removed by slope failure, leaving a 2 x 3.5 km horseshoe-shaped crater now partially filled by a lava dome. Mount St. Helens was formed during nine eruptive periods beginning about 40-50,000 years ago and has been the most active volcano in the Cascade Range during the Holocene. Prior to 2,200 years ago, tephra, lava domes, and pyroclastic flows were erupted, forming the older St. Helens edifice, but few lava flows extended beyond the base of the volcano. The modern edifice was constructed during the last 2,200 years, when the volcano produced basaltic as well as andesitic and dacitic products from summit and flank vents. Historical eruptions in the 19th century originated from the Goat Rocks area on the N flank, and were witnessed by early settlers.
References: Lahusen, R.G., 2005, Acoustic flow monitor system-user manual: U.S. Geological Survey Open-File Report 02-429, 22 p.
Sherrod, D.R., Scott, W.E., and Stauffer, P.H., eds., 2008, A volcano rekindled: the renewed eruption of Mount St. Helens, 2004-2006: U.S. Geological Survey, Professional Paper 1750, 856 p.
Information Contacts: Cascades Volcano Observatory (CVO), U.S. Geological Survey, 1300 SE Cardinal Court, Building 10, Suite 100, Vancouver, WA 98683-9589, USA (URL: http://vulcan.wr.usgs.gov/); Pacific Northwest Seismic Network, University of Washington, Dept. of Earth and Space Sciences, Box 351310, Seattle, WA 98195-1310, USA (URL: http://www.pnsn.org/); Hawai'i Institute of Geophysics and Planetology (HIGP) Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://hotspot.higp.hawaii.edu/).
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