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Bulletin of the Global Volcanism Network, December 2005
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From: Ed Venzke <venzke@xxxxxxxxxxxxxx>
Global Volcanism Program (www.volcano.si.edu)
Bulletin of the Global Volcanism Network
Volume 30, Number 12, December 2005
Augustine (Alaska, USA) Eruptions begin 11 January 2005 and eight
outbursts occur by late January
St. Helens (Washington, USA) 2005 dome building amid comparative
seismic, deformational quiet
South Sister (Oregon, USA) Uplift continues during 2005, but at perhaps
half the previous rate
Soufrière Hills (Montserrat) Slow lava dome growth continued
Popocatépetl (México) Modest eruptions continue throughout 2005
Lopevi (Vanuatu) Minor discharges on 24-25 January 2006
Aoba (Vanuatu) Landscape changes resulting from November 2005 eruption
Tangukubanparahu (Indonesia) Seismic unrest during 12-19 April 2005
Elgon (East African rift) False report of activity; confusion caused by
burning dung in a lava tube
Etna (Italy) Late degassing, summit explosion and ash release in
December 2005
Editors: Rick Wunderman, Catherine Galley, Edward Venzke, and Gari Mayberry
Volunteer Staff: Robert Andrews, Jerome Hudis, Jackie Gluck, William
Henoch, Veronica Bemis, and Stephen Bentley
Bulletin of the Global Volcanism Network
Volume 30, Number 12, December 2005
Augustine (Alaska, USA) Eruptions begin 11 January 2005 and eight
outbursts occur by late January
St. Helens (Washington, USA) 2005 dome building amid comparative
seismic, deformational quiet
South Sister (Oregon, USA) Uplift continues during 2005, but at perhaps
half the previous rate
Soufriere Hills (Montserrat) Slow lava dome growth continued
Popocatepetl (Mexico) Modest eruptions continue throughout 2005
Lopevi (Vanuatu) Minor discharges on 24-25 January 2006
Aoba (Vanuatu) Landscape changes resulting from November 2005 eruption
Tangukubanparahu (Indonesia) Seismic unrest during 12-19 April 2005
Elgon (East African rift) False report of activity; confusion caused by
burning dung in a lava tube
Etna (Italy) Late degassing, summit explosion and ash release in
December 2005
Editors: Rick Wunderman, Catherine Galley, Edward Venzke, and Gari Mayberry
Volunteer Staff: Robert Andrews, Jerome Hudis, Jackie Gluck, William
Henoch, Veronica Bemis, and Stephen Bentley
Augustine
southwestern Alaska
59.363 N, 153.43 W; summit elev. 1,252 m
All times are local (= UTC - 9 hours)
This report covers events from May 2005 through 26 January 2006. The
first substantial ash-bearing eruption took place on 11 January; another
one, on 17 January, rose to ~ 13.7 km. By late January there had been
eight eruptions.
A National Oceanic and Atmospheric Administration (NOAA) message pointed
out that life-threatening costly damages can occur to aircraft that fly
through an eruption cloud. It added that the Federal Aviation
Administration put NOAAâ??s information to work, giving air traffic
managers and controllers a heads-up to ensure airspace safety around the
volcano as well as along the forecast trajectory of the ash plumes.
Augustine eruptions had also automatically alerted the West Coast and
Alaska Tsunami Warning Center. The geography of the Cook Inlet, where
Augustine is located, is shown on figure 1.
Figure 1. Map showing Augustine in its relation to nearby volcanoes,
Cook Inlet, and surrounding communities. Courtesy of Janet Schaefer and
AVO / Alaska Division of Geological & Geophysical Surveys.
1985-89 crisis and eruption. The last major eruption of Augustine was in
March 1986. Between mid-July and early August 1985, seismicity at
Augustine began to increase. From then until late February 1986,
recorded earthquakes averaged 12/day, with occasional short bursts of
seismicity. On 17 February 1986 an explosion plume was observed over the
volcano. Seismicity intensified after the end of February. On 27 March
1986 explosions sent eruption clouds into the stratosphere and generated
pyroclastic flows that reached the sea. Ash was deposited over a wide
area and international air traffic was disrupted. Explosive activity,
ash plumes, and pyroclastic flows continued through August and September
1986, and Augustine steamed continuously through at least July 1989
(BGVN 11:02-11:08, 13:07, 14:09).
Current eruption. This report is chiefly based on the continuing
coverage of the Augustine eruption by the Alaska Volcano Observatory
(AVO). The AVO website presents observations and remarkable photos
documenting eruptive stages seen thus far.
Beginning in May 2005, there was a slow increase in the number of
earthquakes under Augustine. The earthquakes were generally small (less
than M 1) and concentrated roughly 1 km below the volcanoâ??s summit.
These earthquakes slowly increased from 4-8 per day to 20-35 per day.
Data from a Global Positioning System (GPS) network on Augustine
indicated that a slow, steady inflation of the volcano started in
mid-summer 2005, continuing until the present. The GPS benchmark located
nearest the summit moved a total of 2.5 cm. This motion is consistent
with a source of inflation or pressure change centered under the
volcano. This was the first such deformation detected at Augustine since
measurements began just prior to the 1986 eruption.
On 29 November 2005 AVO raised the Concern Color Code from Green to
Yellow after recording important long-term changes in seismicity and
ground deformation consistent with renewed volcanic unrest. There were
no indications that an eruption was imminent or certain. Seismicity
remained at elevated levels during 30 November to 12 December 2005.
During 9-12 December, changes in the style of earthquake activity at the
volcano were recorded, and there were reports of gas emissions and
steaming. Seismic events on 9 and 11 December may have perturbed the
hydrothermal system, initiating steam explosions. These seismic events
were consistent with reports of steaming at the summit observed on 10
December, and reports of a distinct sulfur smell ("like from a sewer")
in the air on the evening of 11 December at Nanwalek and Port Graham, ~
80 km E of the volcano. Augustine remained at Concern Color Code Yellow.
On 12 December a steam plume visible on video and satellite images
extended 75 km SE (figure 2).
Figure 2. On 12 December 2005, a plume of volcanic gas and steam
billowed from Augustine and spread ~ 80 km SE. This image was captured
the same day by the Moderate Resolution Imaging Spectroradiometer
(MODIS) onboard the Aqua satellite. In this image, the volcanic plume
streams from the tiny, snow-capped volcanic island where Augustine is
located and dissipates over the ocean. NASA image created by Jesse
Allen, Earth Observatory, using data obtained courtesy of the MODIS
Rapid Response team.
During a 12 December flyover, AVO scientists saw profuse steaming from
numerous summit fumaroles, emanating mainly from behind the 1986 lava
dome. Several energetic fumaroles were also located 200 m down the SE
flank. A gas-and-steam plume extended 75 km SE. Augustine remained at
Concern Color Code Yellow. Reports during 14-23 December mentioned that
residents E of the volcano smelled sulfur; and the reports noted
intervals of elevated seismicity, and several small steam explosions.
A gas-measurement flight on 20 December detected SO2 for the first time
at Augustine since routine airborne measurements began in the early
1990s. Aerial observations and analysis of photography and video of the
summit area indicated some deformation within the summit crater area. A
crack or fissure was noted cutting the 1986 lava dome and extending to
the SE (figure 3). Heavy steam from this feature, along with patches of
bare ground, indicated an increase in the summitâ??s heat output.
Figure 3. On 20 December 2005, Augustine emitted a steam jet from a
SE-flank fissure and gave off steam from its summit area. Courtesy of
C.F.Waythomas and AVO / USGS.
Thermal imaging of the summit area took place on 22 December, using a
helicopter-mounted FLIR (Forward Looking Infrared Radiometer). The
imaging confirmed the presence of a new, high-temperature fumarole or
gas vent located high on Augustineâ??s S flank.
Seismicity decreased during the last week of December compared to the
previous week; but steam and gas emissions continued. AVO scientists
visited the volcano to install additional GPS receivers and deploy
additional ash-collection devices. Observations continued to suggest
that new magma was present. The level of seismicity was still well below
that observed just prior to the 1986 eruption. Augustine remained at
Concern Color Code Yellow.
During the first week of January 2006, seismicity increased slightly
compared to the previous week. The volcano continued to steam vigorously
from several summit fumaroles. AVO scientists visited the volcano to
install additional seismic monitoring equipment, to deploy additional
ash-collection devices, and to undertake helicopter-aided thermal
surveys of the summit area. The high-temperature fumarole or gas vent on
Augustineâ??s upper S flank, previously reported on for 22 December, had
cooled significantly, but elevated temperatures were detected at one
summit fumarole imaged through the steam and gas. Although fumarole
temperatures varied, there were no significant changes in the
distribution of thermal features compared to the previous survey . A
gas-measurement flight detected a significant increase in SO2 compared
to 20 December.
On 10 January 2006, AVO raised the Concern Color Code from Yellow to
Orange. Earthquake activity beneath Augustine had increased markedly,
indicating the heightened possibility of an explosive eruption within
hours to days.
On 11 January 2006, AVO raised the Concern Color Code from Orange to Red
after recording two discrete explosions at the summit at 0440 and 0513.
Satellite data confirmed that an ash cloud was produced and, in
collaboration with the National Weather Service (NWS), the top of the
cloud was estimated at 9 km altitude. NWS and AVO tracked the ash plume,
which detached from the vent and drifted to the N and E. By 0740, the
ash cloud had traveled 40 km E and 50 km N. An ash-fall advisory was
issued by the NWS at 0644. Seismicity decreased significantly after the
explosions. During an 11 January afternoon overflight, AVO scientists
observed a pure white steam cloud rising to about 3.5 km altitude and
drifting NE. Little volcanic ash was observed on the island itself, but
volcanic mudflows were evident on the E, S, and W sides of the volcano
(figure 4). A brown haze in the air was observed over the central part
of Cook Inlet.
Figure 4. A W-looking view of Augustine from an observation flight made
after the early morning steam emission on 11 January 2006. The image
shows a snow-and-rock avalanche on the SW flank (to the left) and lahars
visible as gray lobes on E and N flanks (to the right). Courtesy of
Stephanie Prejean and AVO / USGS.
After the eruption on 11 January, seismic activity declined. On 12
January 2006 the Level of Concern Color Code was lowered from Red to
Orange.
Explosive eruptions on 13 and 14 January 2006 produced clouds of
volcanic ash and flows of mud and rock fragments. A marked increase in
seismicity early on 13 January preceded an eruption interval that began
at around 0355 and ended around 0439. NWS subsequently reported ash
heights of 10 km altitude. Other explosive events followed on 13
January, occurring at 0847, 1122, 1640 (figure 5) and 1858; and on 14
January at 0014 (figure 6). Each of these events produced ash plumes,
mudflows, and pyroclastic flows on the island.
Figure 5. This photo of a large Augustineâ??s eruption cloud was taken
between about 1645 and 1700 on 13 January 2006 from Kokhanok on the SE
side of Lake Iliamna, a spot ~ 80 km W of the volcano. Image courtesy of
Gerald Andrew.
Figure 6. The Moderate Resolution Imaging Spectroradiometer (MODIS)
flying onboard the Aqua satellite captured this image of an Augustine
plume on 13 January 2006. Within a few tenâ??s of kilometers of Augustine,
a narrow steam and ash plume streams out and heads E over the ocean.
Much broader zones of ash cloud dominate the middle of the image for
over 100 km, both as an elongate zone to the ESE and more widely in a
dispersed zone covering areas to the E and NE. In the colored image the
ash clouds in the middle part of the image appear brown and white, and
may well represent Augustine products in the atmosphere. NASA image
created by Jesse Allen, Earth Observatory, using data obtained from the
Goddard Earth Sciences DAAC (Distributed Active Archive Center).
Ash clouds surpassed 9 km altitude, as reported by pilots and determined
by radar data provided by the National Weather Service (NWS). Ash was
carried to the E-SE and light ash falls were reported in communities of
the southwestern Kenai Peninsula. According to preliminary assessment by
Pavel Izbekov (Geophysical Institute, University of Alaska Fairbanks and
AVO), the majority of ash particles in the 13 January seemed to be
juvenile, though there are large variations in the morphology of ash
particles as well as the composition of matrix glass. Enlargements of
two ash grains appear in figures 7 and 8.
Figure 7. SEM image of an ash particle erupted by Augustine on 13
January 2006. This is an individual plagioclase crystal. The ash sample
was collected in Homer by John Paskievitch of AVO. Image courtesy of
Pavel Izbekov, the University of Alaska Fairbanks, Geophysical Institute
and the AVO.
Figure 8. SEM image of an irregularly shaped ash particle erupted by
Augustine on 13 January 2006. The ash sample was collected during the
ashfall in Homer, Alaska by John Paskievitch, AVO. Image courtesy of
Pavel Izbekov, the University of Alaska Fairbanks, Geophysical Institute
and the AVO.
On 14 January, AVO received reports from pilots of sulfurous odors and
diffuse brown haze at flight altitudes when flying 400-500 km E of
Augustine in SE Alaska (near Yakatat and Sitka). These diffuse
ash-and-gas clouds were presumably from Augustineâ??s explosive events on
13 January.
Seismicity declined in the 30 hours after the event early on 14 January,
and AVO downgraded the color code from Red to Orange. The level of
seismic activity at the volcano remained above background.
On 17 January 2006 an explosive eruption began at 0758 and ended at
0803. Seismic and pressure-sensor data indicated numerous small
explosions, which could produce small amounts of low-level ash and could
initiate small rock avalanches on the flanks. AVO raised the concern
color from Orange to Red. A flight later on 17 January disclosed a brown
ashy haze lingering over the island. Occasional views through the haze
showed that most of the lava dome that formed following the 14 January
eruption was destroyed in the explosion of 17 January. Observations made
during a flight on the afternoon of 18 January 2006 indicated that the
summit was steaming vigorously, consistent with the formation of a new
lava dome. Evidence of explosive ejection of volcanic bombs included
circular craters the size of large trucks seen on the NW flank.
Block-and-ash-flow deposits with car-sized blocks produced by dome
collapse covered parts of the SE flank. Surge deposits were observed on
the NW flank. A white steam plume was observed rising to about 2,600 m
altitude before it trailed off as a bluish haze to the E. Little to no
ash appeared to be present in the plume.
After the eruption at 0758 on 17 January, seismicity diminished
significantly and AVO lowered the color code from Red to Orange late on
18 January. By the morning of 19 January seismicity remained fixed at
lower levels; it decreased further on 20 January but still stood above
background. Periods of quiescence and low seismicity in the intervals
between eruptive events are not unusual at Augustine, having occurred
during the 1976 and 1986 eruptive episodes. By 25 January seismic
activity at Augustine remained low but above background levels. During
23-26 January, satellite observations indicated the persistence of faint
thermal anomalies. On 26 January steaming continued at the summit
(figure 9).
Figure 9. Augustine as seen from the NE on 24 January 2006 when a
steam-and-gas plume drifted SSE. Image courtesy of M.L. Coombs and AVO/
USGS.
Background. Augustine volcano, rising above Kamishak Bay in the southern
Cook Inlet about 290 km SW of Anchorage, is the most active volcano of
the eastern Aleutian arc. It consists of a complex of overlapping summit
lava domes surrounded by an apron of volcaniclastic debris that descends
to the sea on all sides. Few lava flows are exposed; the flanks consist
mainly of debris-avalanche and pyroclastic-flow deposits formed by
repeated collapse and regrowth of the volcanoâ??s summit. The latest
episode of edifice collapse occurred during Augustineâ??s largest
historical eruption in 1883; subsequent dome growth has restored the
volcano to a height comparable to that prior to 1883. The oldest dated
volcanic rocks on Augustine are more than 40,000 years old. At least 11
large debris avalanches have reached the sea during the past 1,800-2,000
years, and five major pumiceous tephras have been erupted during this
interval. Historical eruptions have typically consisted of explosive
activity with emplacement of pumiceous pyroclastic-flow deposits
followed by lava dome extrusion with associated block-and-ash flows.
Information Contacts: Alaska Volcano Observatory (AVO), a cooperative
program of the U.S. Geological Survey, 4200 University Drive, Anchorage,
AK 99508-4667, USA (URL: http://www.avo.alaska.edu/), Geophysical
Institute, University of Alaska, P.O. Box 757320, Fairbanks, AK
99775-7320, USA, and Alaska Division of Geological & Geophysical
Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA; Jesse
Allen, NASA Earth Observatory, Pavel E. Izbekov, Geophysical Institute,
University of Alaska Fairbanks, 903 Koyukuk Drive, P.O. Box 757320
Fairbanks, AK 99775-7320 USA (Email: pavel@xxxxxxxxxxxxx); Anchorage
VAAC, Alaska Aviation Weather Unit, 6930 Sand Lake Road, Anchorage, AK
99502-1845,USA, (URL: http://pafc.arh.noaa.gov/).
St. Helens
Washington, USA
46.20 N, 122.18 W; summit elev. 2,549 m
All times are local (= UTC - 8 hours)
Throughout the period covered by this report, August 2005 to December
2005, growth of the lava dome inside the crater of Mount St. Helens
continued, accompanied by low rates of seismicity, low emissions of
steam and volcanic gases, and minor production of ash. This report came
from those posted on the website of the Cascade Volcano Observatory
(CVO, part of the U.S. Geological Survey). The hazard status remained at
Volcano Advisory (Alert Level 2); aviation color code Orange. During the
month of August 2005, growth of the lava dome produced rockfalls,
resulting in ash plumes that occasionally rose above the rim (figure
10). A rockfall on 21 August at 2056 generated a bright glow of hot rock
and a thick ash plume. The induced atmospheric conditions temporarily
affected radio transmissions from instruments in the crater.
Figure 10. Before and after views of a rockfall that removed the upper
portions of a spiny ridge on the growing St. Helens dome. View as seen
from remote camera on the SW crater rim. Both photos were taken on 21
August 2005. Courtesy of USGS Cascades Volcano Observatory.
A digital elevation model of the active lava dome, which was created
from aerial photographs taken on 10 August, showed that the volume had
grown to 62 million cubic meters with the average growth during late
July and early August at about 2 million cubic meters per second.
During 31 August-6 September 2005, the new lava dome inside the crater
of St. Helens continued to grow, accompanied by low rates of seismicity,
low emissions of steam and volcanic gases, and minor production of ash.
Images of the crater showed continued westward motion of the new lava dome.
On 6 September 2005, dry conditions and rockfalls from the lava dome
generated occasional ash plumes that rose above the volcano and rapidly
dissipated. During the week of 7-13 September 2005, growth of the lava
dome continued and photos showed continued slumping of the central part
of the dome and W motion of the presently active area. This movement
continued throughout September 2005 and is illustrated in a time-series
of images showing the active NW portion of the new lava dome as it
continued to move W, butting into the W arm of a glacier, spawning
rockfalls. This time-series of images is available on the CVO website.
During 28 September-4 October 2005, growth of the new lava dome inside
the crater continued to grow, accompanied by low rates of seismicity,
low emissions of steam and volcanic gases, and minor production of ash.
Reanalysis of late September time-series photographs of the active part
of the new lava dome indicated that points on the dome then moved NW and
upward at about 5.5 m per day as extrusion continued.
Images taken on 10 of October showed that the pattern of dome growth
established during the previous few months continued. The actively
growing portion of the dome moved NW; pushing the W arm of the glacier
against the W crater wall, causing the glacier to narrow, thicken, and
become increasingly fractured. From the end of October to 21 November
there were no significant changes in seismicity or edifice deformation.
During the previous few weeks, a prominent linear feature developed on
the disintegrating "whaleback" that grew during the previous spring and
summer and was currently located E of the actively growing part of the
new lava dome (figure 11).
Figure 11. Linear feature developed at St. Helens on the Spring/Summer
2005 spine. Photo taken on 18 October 2005. Courtesy of USGS CVO.
On 22 of November two notable rockfalls occurred at 1200 and shortly
after 1500. Both produced dilute ash clouds that rose a few hundred
meters above the crater rim, which are common during lava-dome growth
(figure 12).
Figure 12. Two photos of dense local plumes created as a result
rockfalls from St. Helensâ?? dome on 22 November 2005. The photo on the
top was taken from the NE; the photo on the bottom was taken from the
NW. Courtesy of USGS CVO.
The well-established pattern of tiny "drumbeat" earthquakes continued at
a rate of one every 1-2 minutes; other monitoring data remained in
typical ranges. Despite the continuing procession of earthquakes, the
overall seismic energy release was very low compared to that during
early phases of the eruption. Small rockfalls continued from the growing
lava dome, with larger ones producing ash plumes that were visible above
the crater rim.
The volume of the lava dome measured on 24 October was 70 million cubic
metersâ??about 90% of the volume of the 1980-1986 dome. Repeat images
taken on 15 December from fixed cameras within the crater and at the
crater rim showed the seventh lava spine to emerge during the current
activity. It continued to push upward and SW from a source just S of the
1980-186 dome (figure 13).
Figure 13. St. Helensâ?? recent dome complex as seen from the NW. Four
different stages of growth are visible in this image. They were given
these sequence numbers: 4, 5, 6, and 7 (the latter for the one currently
extruding). All occurred as whalebacks or spines in 2005. Photo was
taken 8 December 2005 by Willie Scott. Courtesy of USGS CVO.
During 21-27 December 2005, seismicity was marked by the repetitive
small earthquakes, occurring every 2-3 minutes, that have come to
characterize the past 15 months. Tiltmeters within 500 m of the new lava
dome showed minute ground deformation; whereas the volcanoâ??s flanks were
quiet. At the end of December 2005, St. Helens remained at Volcano
Advisory (Alert Level 2); aviation color code Orange.
Table 1 gives a summary of the growth of the dome since October 2004. It
was reported on 26 January 2006 that initial analysis of recent
photographs from fixed cameras in the crater showed that the top of the
currently active part of the new lava dome is at ~ 2,240 m elevation,
which is about 90 m higher than it was in early November 2005. On
several occasions during the eruption, parts of the dome have been
considerably higher, for instance 2,365 m in July 2005. Those high
points have since been lowered by disintegration, but still are higher
than the top of the currently active part.
Table 1. St. Helens dome summit elevations and volumes compiled at a
series of times during October 2004-January 2006. The dome summit
elevations have decreased due to repeated failure of the unstable
blocks, spires, and protrusions along the dome summits. Also, the method
of assessing dome volumes changed in April 2005 (indicated by the
asterisk). Courtesy USGS Cascades Volcano Observatory.
Date Volume Elevation of
(10^6 m^3) dome top (m)
04 Oct 2004 5 --
13 Oct 2004 12 --
04 Nov 2004 20 --
01 Feb 2005 -- 2,332
21 Feb 2005 -- 2,341
10 Mar 2005 58 2,339
12 Apr 2005 47.5* --
15 Jun 2005 54 --
Jul 2005 58 2,365
10 Aug 2005 62 --
24 Oct 2005 70 --
Early Nov 2005 -- 2,150
26 Jan 2006 -- 2,240
Background. 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 2200 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 2200
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 north flank,
and were witnessed by early settlers.
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/, Email:
GSCVOWEB@ usgs.gov).
South Sister
Oregon, USA
44.10 N, 121.77 W; summit elev. 3,157 m
All times are local (= UTC - 8 hours)
According to the U.S. Geological Survey, field surveys indicated that
the uplift of the broad area in the Three Sisters region of central
Oregon, gradually swelling since late 1997 (BGVN 26:05), continued as of
14 December 2005. However, the swelling may have slowed somewhat during
the past year.
The area of uplift is 20 km in diameter and is centered 5 km W of
South Sister volcano. The middle of the uplift rose at an average rate
of 2.5 cm per year as a result of intrusion of a modest volume of magma
7 km below the ground surface. Seismic activity related to the uplift
has been scant, except for a swarm of more than 300 small earthquakes in
late March 2004 (BGVN 29:06). Volcanic gases released from the intruding
magma dissolve in ground water so water in local springs and streams is
slightly enriched in chemical components derived from volcanic gases.
Scientists believe that periods of intrusion similar to the present one
have occurred in the area before. The duration and outcome of the
current episode are considered to be impossible to forecast, and only
continued monitoring will show whether or not this episode of intrusion
is slowly ending.
Investigations during 2005 showed the following. (1) Earthquakes
continued at a low rate--only five were located in the uplift area in
2005; these were small, up to M1.5. (2) The chemical composition of
local spring and stream water remained unchanged from that of the past 5
years. (3) Uplift of the ground surface continued, but seems to have
slowed from the rate observed in past years. The three techniques used
to measure ground deformation, all having a degree of uncertainty,
together suggest that the rate decreased in 2004-2005, perhaps by as
much as one half. If so, the rate of intrusion of magma has declined as
well.
Background. South Sister is the highest and youngest of the Three
Sisters volcanoes that dominate the landscape of the central Oregon
Cascades. The main edifice of South Sister is constructed of andesitic
and dacitic lava flows capped by a symmetrical summit cinder cone of
probable latest-Pleistocene age. The late Pleistocene or early Holocene
Cayuse Crater on the SW flank of Broken Top volcano and other flank
vents such as Le Conte Crater on the SW flank of South Sister mark mafic
vents that have erupted at considerable distances from South Sister
itself. Late-Holocene eruptions formed a chain of dike-fed rhyodacitic
lava domes and flows on the volcanoâ??s SE-to-SW flanks about 2000 years
ago. Satellite radar interferometry (InSAR) data obtained by U S
Geological Survey scientists detected continuing long-term slight uplift
of the ground surface over a broad region centered 5 km west of South
Sister volcano that began in 1997.
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/, Email:
GSCVOWEB@ usgs.gov).
Soufriere Hills
Montserrat, West Indies
16.72 N, 62.18 W; summit elev. 915 m
All times are local (= UTC - 4 hours)
Activity at Soufriere Hills continues to remain elevated during the
latter half of 2005 (table 2). Since 5 September slow lava dome growth
continued. During the week of 30 September through 7 October dome growth
increased on the western side. On 26 October a pyroclastic flow with a
runout of 2 km was reported around 2400. The pyroclastic flow was
confined to the Tar River Valley.
Table 2. Soufriere Hills seismicity during 26 August to 30 December
2005. Courtesy of MVO.
Report Date Number of earthquakes
(2005) Hybrid Volcano-tectonic Long-period
26 Aug-02 Sep 10 3 9
02 Sep-09 Sep 5 6 --
09 Sep-16 Sep 13 70 5
16 Sep-23 Sep 3 6 5
23 Sep-30 Sep -- 42 3
30 Sep-07 Oct -- 50 2
07 Oct-14 Oct -- 183 --
14 Oct-21 Oct 1 359 15
21 Oct-28 Oct -- 53 2
28 Oct-04 Nov -- 19 2
04 Nov-11 Nov 2 14 6
11 Nov-18 Nov -- 3 8
18 Nov-25 Nov 7 21 176
25 Nov-02 Dec 2 1 93
09 Dec-16 Dec -- -- 31
16 Dec-23 Dec 2 1 40
23 Dec-30 Dec 19 9 63
On 4 November dome growth on the southern flank was observed. The
following week, reports yielded growth on the E, S, and SE flanks. Radar
imaging of the dome indicated a dome volume of about 6.5 million cubic
meters, suggesting a growth rate over the past two weeks of between 1.3
and 1.8 cubic meters per second with incandescence visible at night.
Observations on the morning of 18 November indicated the dome continued
to grow and spilled rockfalls to the E, S, W, and N. A pyroclastic flow
was observed in the Tar River valley on 15 November and reached to
within 1km of the sea. The ash cloud associated with this event rose to
~ 2.1 km.
A pyroclastic flow was observed in the upper reaches of the Tar River
valley on 22 November (figure 14). Minor venting of ash occurred, with
one event taking place on the afternoon of 24 November, which produced
an ash cloud that rose ~ 1 km above the summit (figure 15).
Figure 14. A photo showing a Soufriere Hills pyroclastic flow as seen
from the NE on 22 November 2005. Photo courtesy of MVO.
Figure 15. A photo showing a Soufriere Hills ash cloud as seen from the
SE on 24 November 2005. Photo courtesy of MVO.
During the month of December, dome growth continued on all flanks
although more intense on the S and E flanks. More rockfalls and smaller
pyroclastic flows have been reported with incandescence observed at
night along the SE and E flanks.
Background. The complex dominantly andesitic Soufriere Hills volcano
occupies the southern half of the island of Montserrat. The summit area
consists primarily of a series of lava domes emplaced along an
ESE-trending zone. Englishâ??s Crater, a 1-km-wide crater breached widely
to the east, was formed during an eruption about 4,000 years ago in
which the summit collapsed, producing a large submarine debris
avalanche. Block-and-ash flow and surge deposits associated with dome
growth predominate in flank deposits at Soufriere Hills. Non-eruptive
seismic swarms occurred at 30-year intervals in the 20th century, but
with the exception of a 17th-century eruption that produced the Castle
Peak lava dome, no historical eruptions were recorded on Montserrat
until 1995. Long-term small-to-moderate ash eruptions beginning in that
year were later accompanied by lava-dome growth and pyroclastic flows
that forced evacuation of the southern half of the island and ultimately
destroyed the capital city of Plymouth, causing major social and
economic disruption.
Information Contacts: Montserrat Volcano Observatory (MVO), Fleming,
Montserrat, West Indies (URL: http://www.mvo.ms/).
Popocatepetl
Mexico
19.023 N, 98.622 W; summit elev. 5,426 m
All times are local (= UTC - 6 hours)
The last report on Popocatepetl covered the period December 2004-January
2005 (BGVN 30:01). This report covers the rest of 2005
(February-December) and comes from the Mexican group Centro Nacional de
Prevencion de Desastres (CENAPRED).
The volcano has been relatively quiet with daily, low-intensity
exhalations of steam and gas sometimes containing minor ash. Some
highlights of the reporting interval follow (both in text and in
tables), essentially a list of ash-bearing eruptions that usually rose
1-3 km above the crater rim. On 1 December an ash plume rose 5 km.
At 0723 on 13 July an exhalation of moderate intensity produced an ash
emission that reached 2 km above the level of the crater. Reports were
received of ash fall in Yecapixtla and Ocuituco in the state of Morelos,
respectively ~ 30 and ~ 23 km SW of the volcano.
At 0906 on 21 July an exhalation of moderate intensity followed a tremor
of high frequency and produced an ash emission that reached 2 km.
At 0313 on 29 July, a moderate exhalation with an explosive component
occurred, throwing incandescent fragments onto the E side of the cone,
out to a distance of about 1 km. The duration of the intense phase was ~
1 minute; it was preceded by high-frequency tremor, the same signal was
observed for 15 minutes after the explosion. The height of the steam,
gas, and ash plume was estimated at 2 km. There were no reports
mentioning ash fall.
At 0614 on 29 July a new exhalation with explosive component occurred
producing an ash column ~ 2.5 km above the crater. The winds directed
the plume NW. The duration of the intense phase was 30 seconds followed
by high-frequency tremor (4 minutes). Reports of ashfall in the Milpa
Alta area (SE of Mexico City) were received.
At 0819 on 30 July high-frequency tremor started, associated with an ash
column. The plume reached 2 km and was directed NW. The emission
continued in its most intense phase until 0845. On 2 August at 1247 an
exhalation of moderate intensity produced an ash emission that reached 2 km.
At 0305 on 24 October an exhalation of moderate intensity occurred. It
was followed by a tremor of high-frequency. The resulting ash plume
reached 1.2 km and traveled NE.
At 0653 on 1 December a moderate exhalation sent an ash column to a
height of 5 km above the summit, the highest reported ash column in
2005. It was dispersed towards the ENE. The intense episode lasted 2
minutes and was followed by high-frequency tremor lasting 30 minutes. A
small ash fall was reported in Amecameca and a warning was issued noting
that minor ash fall could occur within the next few hours in Tlaxcala
and Puebla states. At 0920 another, smaller eruption produced an ash
column 2.5 km above the crater, which also blew ENE.
An eruption that occurred at 1653 on 4 December resulted in reports of
ash fall in the states of Tlaxcala and Puebla.
At 2225 on 13 December an explosion at Popocatepetl ejected incandescent
fragments over its SE flanks. The explosion lasted ~ 1 minute and was
followed by 30 minutes of tremor. The explosion produced a 2.5 km ash
column carried by winds to the SE. After the explosion, the volcano
returned to its previous low level of activity.
At 0457 on 18 December a small explosion was detected at the
Popocatepetl. This event produced an ash column that reached 2.5 km over
the summit. The plume traveled towards the NE. The explosion lasted ~ 1
minute and was followed by 8 minutes of high-frequency tremor.
At 0447 on 25 December a moderate exhalation with a minor explosive
component occurred. Some incandescent fragments fell on the E side of
the cone extending 700 m from the crater edge. The accompanying ash
column reached a height of about 3 km moving ENE. The total duration of
seismicity associated with this event was nearly 3 minutes, of which 50
seconds corresponded to the intense phase. There were no reports of
resulting ash fall.
All of the reported ash-producing events for the February-December 2005
reporting interval are listed in table 3. Table 4 contains the reported
earthquakes.
Table 3. Discharges at Popocatepetl during February-December 2005.
Courtesy of CENAPRED.
Date Local Height of ash Ash plume Comments
(2005) Time column (km) blown
30 Mar 0521 1.5 NE --
12 May 1048 1.8 -- --
13 Jul 0723 2 -- Ash falls reported
in Yecapixtla and
Ocuituco in the
State of Morales.
14 Jul 1005 2 -- Followed a
high-frequency tremor
29 Jul 0313 2 -- See text.
29 Jul 0614 2.5 NW See text.
30 Jul 0819 2 NW The emission
continued in its most intense
phase until 0845.
02 Aug 1247 2 -- --
24 Oct 0305 1.2 -- Followed a
high-frequency tremor.
01 Dec 0653 5 ENE See text.
04 Dec 1653 -- -- Ash falls reported
in the States of Tlaxcala
and Puebla.
13 Dec 2225 2.5 SE See text.
18 Dec 0457 2.5 NE The 1-minute
explosion was followed by 8
minutes of
high-frequency tremor.
25 Dec 0447 3 ENE See text.
Table 4. Earthquakes at Popocatepetl during February-December 2005.
"Below" refers to earthquakes below or in the edifice. Courtesy of CENAPRED.
Date Time Magnitude Depth (km) Distance (km)
Direction
(Local)
09 Feb 0715 2.2 3.7 -- SE
18 Feb 0624 2.2 3.0 8 SE
18 Feb 1248 2.7 9.0 8.5 SE
18 Feb 1607 2.5 9.0 8.5 SE
19 Feb 0056 2.4 4.0 2 E
24 Feb 2003 2.1 3.8 7.5 SE
14 Mar 1103 2.7 4.0 8 SE
22 Mar -- 2.5 6.8 8 SE
24 Mar -- 2.7 -- -- --
24 Mar -- 2.7 -- -- --
02 Apr 0112 2.6 6.5 4 SW
03 Apr 0721 2.2 4.4 1 E
05 May -- 2.4 -- -- --
14 May 2146 2.1 -- 8 SE
15-16 May 2144-0648 4 events 5-10 -- SE
2.0-2.6
16 May 1433 2.5 5.8 1 N
16 May 2318 2.4 5.0 8 SE
17 May 0511 2.3 4.9 8 SE
20 May 0231 2.6 4.8 8 SE
29 May 1039 2.2 2.5 8 SE
01 Jun 1446 2.0 5.4 -- --
13 Jun -- 2.1 4.7 -- --
13 Jun -- 2.2 3.7 -- --
16 Jun -- 2.1 5.5 8 SE
20 Jun 1023 2.0 4.6 0.5 NW
20 Jun 1251 2.0 5.0 Below --
25 Jun 0640 2.7 5.0 Below --
29 Jun 0133 2.9 8.7 2.5 SW
29 Jun 0142 2.2 6.0 8 SE
07 Jul 0009 2.6 5.9 Below --
12 Jul 1645 2.0 -- 8 SE
19 Jul 1921 2.4 4.6 Below --
02 Aug 2319 2.5 5.4 3 NW
05 Aug 2153 2.2 5.3 7 SE
14 Aug 1516 2.6 6.5 8 SE
17 Aug 1118 2.5 -- 8 SE
29 Aug 0055 2.3 -- 2 NW
29 Aug 0238 2.7 -- Below --
15 Sep 0325 2.3 8.0 8 SE
17 Sep 0430 2.1 5.5 Below --
18 Sep 1757 2.1 5.2 Below --
19 Sep 0443 1.9 3.5 8 SE
19 Sep 2333 2.1 5.2 2 SE
21 Sep 1738 2.0 4.0 Below --
11 Oct 1004 2.2 4.4 1 E
12 Oct 1946 2.3 5.3 2 N
14 Oct 1416 2.2 6.0 2 N
24 Oct 2152 2.7 3.0 2 E
26 Oct 1537 2.3 4.2 Below --
29 Oct 0336 2.0 -- 8 SE
09 Nov 0052 2.7 6 1.5 W
09 Nov 0235 2.4 6 1.5 W
09 Nov 0612 2.1 5 Below --
11 Nov -- 2.5 6 1.5 W
12 Nov -- 2.7 -- -- --
23 Nov 1713 1.6 5.7 2 NE
24 Nov 0242 2.0 5.4 2 NE
25 Nov -- 2.0 3.8 8 SE
01 Dec -- 2.3 4.8 Below --
01 Dec -- 2.1 4.5 Below --
05 Dec 1838 2.4 3.8 1 SE
06 Dec 1800 2.0 3.6 Below --
08 Dec 0824 1.9 4.3 5.5 S
08 Dec 0907 1.9 5.0 5.5 S
Background. Volcan Popocatepetl, whose name is the Aztec word for
smoking mountain, towers to 5426 m 70 km SE of Mexico City to form North
Americaâ??s 2nd-highest volcano. The glacier-clad stratovolcano contains a
steep-walled, 250-450 m deep crater. The generally symmetrical volcano
is modified by the sharp-peaked Ventorrillo on the NW, a remnant of an
earlier volcano. At least three previous major cones were destroyed by
gravitational failure during the Pleistocene, producing massive
debris-avalanche deposits covering broad areas south of the volcano. The
modern volcano was constructed to the south of the late-Pleistocene to
Holocene El Fraile cone. Three major plinian eruptions, the most recent
of which took place about 800 AD, have occurred from Popocatepetl since
the mid Holocene, accompanied by pyroclastic flows and voluminous lahars
that swept basins below the volcano. Frequent historical eruptions,
first recorded in Aztec codices, have occurred since pre-Columbian time.
Information Contacts: Centro Nacional de Prevencion de Desastres
(CENAPRED), Av. Delfin Madrigal No.665. Coyoacan, Mexico D.F. 04360,
Mexico. Email: amb@xxxxxxxxxxxxxxxx gvazquez@xxxxxxxxxxxxxxxx; URL:
http://www.cenapred.unam.mx/).
Lopevi
Vanuatu
16.507 S, 168.346 E; summit elev. 1,413 m
All times are local (= UTC + 11 hours)
As noted by the Wellington Volcanic Ash Advisory Center (24 and 25
January 2006), pilots reported a vertical plume rising from Lopevi at
0845 hours on 24 January 2006 to an altitude of 2.1-2.4 km and drifting
to the S. At 0845 the next day, 25 January, the plume extended SE and
was reportedly at 2.7 km.
MODIS satellite data also detected thermal anomalies around this time
(0055 and 1020 hours on 24 January), preceded by an absence of measured
anomalies for ~ 9 days (since 2240 hours on 15 January). Satellite
thermal anomalies are often detected over this volcano.
Background. The small 7-km-wide conical island of Lopevi is one of
Vanuatuâ??s most active volcanoes. A small summit crater containing a
cinder cone is breached to the NW and tops an older cone that is rimmed
by the remnant of a larger crater. The basaltic-to-andesitic volcano has
been active during historical time at both summit and flank vents,
primarily along a NW-SE-trending fissure that cuts across the island,
producing moderate explosive eruptions and lava flows that reached the
coast. Historical eruptions at the 1,413-m-high volcano date back to the
mid-19th century. The island was evacuated following eruptions in 1939
and 1960. The latter eruption, from a NW-flank fissure vent, produced a
pyroclastic flow that swept to the sea and a lava flow that formed a new
peninsula on the western coast.
Information Contacts: Rob Wright, Luke Flynn, and Eric Pilger, Hawaiâ??i
Institute of Geophysics and Planetology, University of Hawaii and Manoa,
168 East-West Road, Post 602, Honolulu, HI 96822
(wright@xxxxxxxxxxxxxxx, flynn@xxxxxxxxxxxxxxx, pilger@xxxxxxxxxxxxxxx;
URL: http://modis.higp.hawaii.edu/); Wellington Volcanic Ash Advisory
Center (VAAC), MetService, PO Box 722, Wellington, New Zealand (URL:
http://www.metservice.co.nz/).
Aoba
Ambae Island, Vanuatu
167.83 E, 15.40 S; summit elev. 1,496 m
All times are local (= UTC + 11 hours)
As previously reported (BGVN 30:11), a new eruption of Aoba began on 27
November 2005 when vapor plumes and ash columns were observed
originating from Lake Voui, a crater lake at the summit. Activity
continued into early January, building a large cinder cone in the
west-central part of Lake Voui (figure 16). The new cone also contained
its own crater lake.
Figure 16. A N-looking view of Aobaâ??s Lake Voui taken 9 January 2006.
The new island is composed of a cinder cone and the coneâ??s crater
appears to host a new, steaming internal lake. This photograph was taken
from a fixed-wing aircraft by Job Eassau during his trip to Pentecote
Island. Courtesy of Esline Garaebiti, Department of Geology, Mines and
Water Resources, Port Vila, Vanuatu.
An image taken by ASTERâ??s visible, near infra-red (VNIR) telescope on 24
December 2005 (UTC) showed the two larger caldera lakes, and steam
escaping from an island in the center of Lake Voui (figure 17). The VNIR
telescope has a resolution of ~ 15 m and operates in the spectral range
0.52-0.86 um.
Figure 17. ASTER VNIR image of Aoba taken at the stated UTC time and
date (N is upwards), as it continued to emit a vapor plume from Lake
Voui. The 27 November 2005 eruption built a substantial new island (dark
area venting steam in the center of lake Voui). This island is almost
circular in shape with a mean diameter of 525 m. Lake Manaro Lakua sits
in the E caldera and is partly obscured by cloud or shadow. Courtesy of
NASA and Alain Bernard (IAVCEI Commission on Volcanic Lakes and
Universite Libre de Bruxelles).
During September through December 2005, infrared satellite data provided
by Moderate Resolution Imaging Spectroradiometer (MODIS) and processed
by the MODVOLC Hot-Spot algorithm at the Hawaii Institute of Geophysics
and Planetology (HIGP) only observed a single-pixel thermal anomaly. It
occurred at 0110 local time on 26 November 2005 ( the image was acquired
at 1410 UTC on 25 November 2005). That was 1 day prior to reports of the
eruption from ground-based observers, although the ground-based reports
could easily have been delayed so it is not clear that the MODVOLC
thermal anomaly was actually prior to ground based observations.
Matt Patrick noted that the anomaly is nicely centered in the caldera
and is almost certainly volcanic â?? no other anomalies occurred on the
island in the previous 5 years.
Background. Aoba is a massive 2,500 km^3 basaltic shield volcano that is
the most voluminous volcano of the New Hebrides archipelago. A
pronounced NE-SW-trending rift zone dotted with scoria cones gives the
16 x 38 km island an elongated form. A broad pyroclastic cone containing
three crater lakes is located at the summit of the Hawaiian-style shield
volcano within the youngest of at least two nested calderas, the largest
of which is 6 km in diameter. Post-caldera explosive eruptions formed
the summit craters of Lake Voui (also spelled Vui) and Lake Manaro Ngoru
about 360 years ago. A tuff cone was constructed within Lake Voui about
60 years later. The latest known flank eruption, about 300 years ago,
destroyed the population of the Nduindui area near the western coast.
Information Contact: Alain Bernard, IAVCEI Commission on Volcanic Lakes,
Universite Libre de Bruxelles, Brussels, Belgium (URL:
http://www.ulb.ac.be/sciences/cvl/aoba/Ambae1.html); NASA Earth
Observatory (URL: http://earthobservatory.nasa.gov/); Esline Garaebiti,
Department of Geology, Mines and Water Resources, Port Vila, Vanuatu;
Matt Patrick, University of Hawaii, Hawaii Institute of Geophysics and
Planetology (HIGP) Thermal Alerts Team, 2525 Correa Road, Honolulu, HI
96822 (URL: http://www.modis.higp.hawaii.edu, Email:
patrick@xxxxxxxxxxxxxxx).
Tangkubanparahu
western Java, Indonesia
6.77 S, 107.60 E; summit elev. 2,084 m
Typically quiet, Tangkubanparahu went into a period of unrest from 12 to
19 April 2005. After that, it became relatively quiet again. The reports
during this period did not in general cover an entire day, but rather
only 6 or 12 hours. The reports chiefly discussed a seismic crisis and
elevated SO2 fluxes. A brief review for this period follows.
Seismic activity increased dramatically beginning on 12 April 2005.
Normally about two volcanic eruptions occurred daily. Volcanic
earthquakes recorded on 12 April consisted of five deep (type-A events
with peak-to-peak amplitudes of 7-24 mm) and 56 shallow (type-B events
with peak-to-peak amplitudes of 3-10 mm), with numbers increasing
throughout the day. About 8 hours of tremor on 13 April, a swarm of
earthquakes took place, of which 111 were deep type-A events and 181
were shallow type-B events. The peak of the activity occurred on 14
April, when the deep events numbered 108 and the shallow events numbered
327. A located hypocenter was 1.6-1.9 km beneath the Domas crater.
Based on the above seismic data, the hazard status for the volcano was
raised on 13 April 2005 at 0825 to Level 2, and then at 1300 to Level 3.
The SO2 measurement around Domas crater yielded about 10 metric tons/day
(t/d) on 14 April. It was less than 2 t/d on 18 April.
The hazard status of the volcano was downgraded to Level 2 on 19 April
2005 at 1200, and the area was re-opened to the public. The other
craters (Upas, Domas, Baru, Jarian) remained closed to the public.
Background. Tangkubanparahu (also known as Tangkuban Perahu) is a broad
shield-like stratovolcano overlooking Indonesiaâ??s former capital city of
Bandung that was constructed within the 6 x 8 km Pleistocene Sunda
caldera. The volcanoâ??s low profile is the subject of legends referring
to the mountain of the "upturned boat." The age the caldera-forming
eruption exceeds the >40,000 year range of radiocarbon dating (Newhall
and Dzurisin, 1988). The rim of Sunda caldera forms a prominent ridge on
the western side; elsewhere the caldera rim is largely buried by
deposits of Tangkubanparahu volcano. The dominantly small phreatic
historical eruptions recorded since the 19th century have originated
from several nested craters within an elliptical 1 x 1.5 km summit
depression.
Information Contact: Directorate of Volcanology and Geological Hazard
Mitigation (DVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia
(Email: dali@xxxxxxxxxxxxxx; URL: http://www.vsi.esdm.go.id/).
Elgon
Kenya and Uganda (East African rift)
1.133 N, 34.550 E; summit elev. 4,321 m
An eruption at Mount Elgon was mistakenly inferred when fumes escaped
from this otherwise quiet volcano. The fumes were eventually traced to
dung burning in a lava-tube cave. The cave is home to, or visited by,
wildlife ranging from bats to elephants. Mt. Elgon (Ol Doinyo Ilgoon) is
a stratovolcano on the SW margin of a 13 x 16 km caldera that straddles
the Uganda-Kenya border 140 km NE of the N shore of Lake Victoria. No
eruptions are known in the historical record or in the Holocene.
On 7 September 2004 the web site of the Kenyan newspaper The Daily
Nation reported that villagers sighted and smelled noxious fumes from a
cave on the flank of Mt. Elgon during August 2005. The villagersâ??
concerns were taken quite seriously by both nations, to the extent that
evacuation of nearby villages was considered.
The Daily Nation article added that shortly after the villagersâ??
reports, Moses Masibo, Kenyaâ??s Western Province geology officer visited
the cave, confirmed the villagers observations, and added that the
temperature in the cave was 170 deg C. He recommended that nearby
villagers move to safer locations. Masibo and Silas Simiyu of KenGens
geothermal department collected ashes from the cave for testing.
Gerald Ernst reported on 19 September 2004 that he spoke with two local
geologists involved with the Elgon crisis from the Geology Department of
the University of Nairobi (Jiromo campus): Professor Nyambok and
Zacharia Kuria (the former is a senior scientist who was unable to go in
the field; the latter is a junior scientist who visited the site).
According to Ernst their interpretation is that somebody set fire to bat
guano in one of the caves. The fire was intense and probably explains
the vigorous fuming, high temperatures, and suffocated animals. The
event was also accompanied by emissions of gases with an ammonia odor.
Ernst noted that this was not surprising considering the high nitrogen
content of guano--ammonia is highly toxic and can also explain the
animal deaths. The intense fumes initially caused substantial panic in
the area.
It was Ernstâ??s understanding that the authorities ordered evacuations
while awaiting a report from local scientists, but that people returned
before the report reached the authorities. The fire presumably prompted
the response of local authorities who then urged the University
geologists to analyze the situation. By the time geologists arrived, the
fuming had ceased, or nearly so. The residue left by the fire and other
observations led them to conclude that nothing remotely related to a
volcanic eruption had occurred.
However, the incident emphasized the problem due to lack of a seismic
station to monitor tectonic activity related to a local triple junction
associated with the rift valley or volcanic seismicity. In response, one
seismic station was moved from S Kenya to the area of Mt. Elgon so that
local seismicity can be monitored in the future.
Information Contacts: Gerald Ernst, Univ. of Ghent, Krijgslaan 281/S8,
B-9000, Belgium (Email: plumeman2000@xxxxxxxxxxx); Chris Newhall, USGS,
Univ. of Washington, Dept. of Earth & Space Sciences, Box 351310,
Seattle, WA 98195-1310, USA (Email: cnewhall@xxxxxxxxxxxxxxxxxx; URL:
http://www.ess.washington.edu/); The Daily Nation
(http://www.nationmedia.com/dailynation/); Uganda Tourist Board (URL:
http://www.visituganda.com/).
Etna
Italy
37.734 N, 15.004 E; summit elev. 3,350 m
The previous report on Mount Etna (BGVN 30:01) described what turned out
to be the final activity of the 2004-05 eruption, which ended by March
(Burton and others, 2005). From March 2005 until November there was only
a low and quiet degassing at the summit craters. Between the end of
November and early December 2005 a significant increase in the SO2
output was accompanied by an increase of volcanic tremor and a minor
deformation of the summit part of the volcanic cone.
On 16 December 2005 an explosive sequence was recorded by the INGV-CT
seismic network, localized at the summit. This was accompanied by an
increase in SO2 emission, which reached peaks 10 times the background
flux levels. On 22 December the increase in gas pressure was accompanied
by a dilute emission of juvenile ash from the Bocca Nuova crater. This
vent had been blocked since the end of the previous summit eruption.
However, the very fine-grained nature of the ash suggested a deep level
of the magma column within the conduit.
Reference: Burton, M., Neri, M., Andronico, D., Branca, S., Caltabiano,
T., Calvari, S., Corsaro, R.A., Del Carlo, P., Lanzafame, G., Lodato,
L., Miraglia, L., Mure, F., Salerno, G., and Spampinato, L., 2005, Etna
2004-05: an archetype for geodynamically-controlled effusive eruptions:
Geophysical Research Letters, v. 32, L09303, doi:10.1029/2005GL022527.
Background. Mount Etna, towering above Catania, Sicilyâ??s second largest
city, has one of the worldâ??s longest documented records of historical
volcanism, dating back to 1500 BC. Historical lava flows of basaltic
composition cover much of the surface of this massive volcano, whose
edifice is the highest and most voluminous in Italy. The Mongibello
stratovolcano, truncated by several small calderas, was constructed
during the late Pleistocene and Holocene over an older shield volcano.
The most prominent morphological feature of Etna is the Valle del Bove,
a 5 x 10 km horseshoe-shaped caldera open to the east. Two styles of
eruptive activity typically occur at Etna. Persistent explosive
eruptions, sometimes with minor lava emissions, take place from one or
more of the three prominent summit craters, the Central Crater, NE
Crater, and SE Crater (the latter formed in 1978). Flank vents,
typically with higher effusion rates, are less frequently active and
originate from fissures that open progressively downward from near the
summit (usually accompanied by strombolian eruptions at the upper end).
Cinder cones are commonly constructed over the vents of lower-flank lava
flows. Lava flows extend to the foot of the volcano on all sides and
have reached the sea over a broad area on the SE flank.
Information Contact: Sonia Calvari, Istituto Nazionale di Geofisica e
Vulcanologia Sezione di Catania, Piazza Roma 2, 95123 Catania, Italy
(Email: calvari@xxxxxxxxxx, URL: http://www.ct.ingv.it/).
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