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Global Volcanism Program <http://www.volcano.si.edu/>
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Bulletin of the Global Volcanism Network
Volume 31, Number 7, July 2006
Tungurahua (Ecuador) 14-15 July 2006 eruption, the strongest since onset
of eruption in 1999
Galeras (Colombia) Ongoing dome growth and elevated seismicity,
thousands evacuated in July 2006
Karthala (Comoros) Seismic crisis on 28 May 2006 precedes lava lake
eruption in Chahale crater
Etna (Italy) An upper E-flank fissure eruption lasting from 14 to 24
July 2006
St. Helens (Washington) Eruption still extrudes dacitic dome lavas
without energetic explosions
Cleveland (Aleutian Islands) Astronauts capture photo of 23 May eruption
Karymsky (Kamchatka) Ash plumes reaching 5 km; ongoing eruptions through
at least mid-2006
Mayon (Philippines) New eruptive pulse starting 13 July; lava flows;
thousands evacuated
Sulu Range (Papua New Guinea) North-central New Britain volcano has
first historical eruption
Editors: Rick Wunderman, Edward Venzke, Sally Kuhn, and Catherine Galley
Volunteer Staff: Veronica Bemis, Zahra Hirji, Jerome Hudis, Robert
Andrews, Jackie Gluck, William Henoch, and Stephen Bentley
Tungurahua
Ecuador
1.467ES, 78.442EW; summit elev. 5,023 m
All times are local (= UTC - 5 hours)
This report discusses Tungurahua's behavior during August 2005 through
the end of July 2006. Material presented here was chiefly gleaned from a
series of special reports issued in Spanish by the Instituto Geofisico
of the Escuela Politecnica Nacional (IGEPN, hereafter IG). Daily reports
for mid-2005 through early 2006 were dominated by descriptions of small
plumes and minor ashfall; the reports also noted occasional small
rain-generated lahars. For the most part 2005 was the quietest year
since eruptions began in 1999, leading residents and volcanologists to
ponder if emissions were terminating. This report omits much discussion
of evacuations and hazard-status postings. Large eruptions with a
Volcanic Explosivity Index (VEI) of 3 that continued into at least late
August 2006 will be the subject of the next Bulletin report.
During late December 2005 seismometers detected sudden clusters of
tremor and earthquakes. Intervals of quiet were broken by the arrival of
signals with energy over a broad frequency range (figures 1 and 2).
These signals and later manifestations at the surface in late
March-early April were thought to be related to a new injection of
magma. As a consequence, IG began to produce a series of special reports
(table 1). Beginning in February 2006 and particularly during May-June
2006, the volcano was the scene of particularly significant events,
including the largest detonations heard and seen since eruptions renewed
in 1999. Other observations included a shift in eruptive style, and
generation of some pyroclastic flows during the 14 July (VEI 2)
eruption. Notable also were constant "roars" and vibrations of such
strength and duration that they keep residents awake at night and caused
some to voluntarily evacuate.
Table 1. A summary of special reports on Tungurahua issued by the IG
during 2006 (reports numbered 1-8; See IG web page-Informes
Especiales-Volcanicos).
Number Date Key observation(s)
1 18 Feb 2006 Moderate explosions and tephra falls in Puela (SW), Paillate (W), Ambato (NW) and Banos (N).
2 07 Apr 2006 Episodes of strong volcanic tremor and increase in number of
long-period seismic events, indicating new magma injection.
3 25 Apr 2006 Notable banded tremor, the inferred product of new injected magma interacting with the hydrothermal system.
4 12 May 2006 10 May-start of major increase in number of explosions, long-period seismic events and tremor episodes. Very strong detonations (12 per hour). Peak of energy release on 14 May, then decline. Aborted eruption.
5 30 May 2006 Starting 16 May, significant decrease in activity and superficial manifestations. Explosions occur 2-3 times per day; columns of gases (water vapor mainly) with light ash content predominate.
6 14 Jul 2006 Advisory of intensified eruptive activity; notable increase in emissions and strong detonations (at 2210 & 2250 UTC). Incandescent lava flung from crater.Strong ground movements reported on W flank.
7 14 Jul 2006 Very strong detonations, period of calm, then ascent of 15-km-high, dark, ash-laden column. First pyroclastic flow (at 2250 UTC) and others to descend six valleys (quebradas) on the W-NW-N flanks. Intense lava fountaining; moderate ash and scoria fall to the W.
8 15 Jul 2006 Unusually large discharges with a detonation (at 0559 UTC), leading to the largest registered since 1999. Plume rose to ~ 15 km altitude. The eruptive style later shifted to periodic detonations with intervals of calm.
A map and table of commonly referred-to locations appeared in a previous
issue (BGVN 29:01). Our last report on Tungurahua covered February 2004
to July 2005 (BGVN 30:06), during which time volcanic and seismic
activity varied, but included some intervals with comparatively low
activity and seismicity such as February to mid-July 2005.
Activity during June to mid-December 2005. From June 2005 through
mid-December 2005, volcanic and seismic activity at Tungurahua was at
relatively low levels. Low-energy plumes composed of gas, steam, and
occasionally small amounts of ash were emitted frequently. Some
noteworthy events during this interval follow.
On 7 June 2005, fine ash fell in the Puela sector, ~ 8 km SW. On 24
June, about an hour after an ash eruption, a narrow plume was identified
in multispectral satellite imagery. The ash plume was at an altitude of
~ 5.5 km and extended 35-45 km W from the summit.
Ash plumes rose to an altitude of 5.8 km on 4 July. On 21 and 22 August,
ash fell in the town of Bilbao, 8 km W of the volcano. On 25 August, ash
fell NW of the volcano in the towns of Bilbao and Cusua. On 1 September,
ash fell ~ 8 km SW of the summit in the Puela sector.
On 10 September, a lahar affected an area near the new Banos-Penipe
highway. On 14 September, a steam column with little ash reached ~ 300
m above the crater and drifted W; small amounts of ash fell in Puela. A
small amount of ash fell in the towns of Cusua and Bilbao during the
morning of 21 September. Fumaroles on the outer edge of the crater were
visible from Runtun (6 km NNE of the summit) after not being seen for 6
months. Steam-and-gas plumes rose ~ 1 km and drifted W. A pilot reported
an ash plume on 29 September at an altitude of ~ 6.1 km.
During October, and November heavy rain caused lahars to travel down
some of the gorges on the volcano's flanks. On 3 and 13 November lahars
caused the temporary closure of the Banos-Riobamba highway, and a
highway in Pampas. On 15 November ash plumes rose to ~ 9.1 km; on 23
November plumes rose to ~ 6.7 km.
On 13 December, lahars were generated at Tungurahua that traveled down
the Juive (NNW) and Achupashal (W) gorges. On 14 December a
steam-and-ash cloud rose ~ 1 km above the volcano. On 17 December,
lahars were generated in the NW and W zone of the volcano. There were
reports of lahars to the W in the Chontapamba sector that blocked the
Banos-Penipe highway, in the Salado sector where the volume of water in
the Vazcun increased by 70 percent, and in the NW (La Pampa) sector.
Return, incidence, and significance of broadband seismicity. An
important variation in behavior was noted during late December 2005,
with the appearance of long-period-earthquake swarms. The swarms
preceded emissions and explosions. Such swarms were associated with
mid-February 2006 ash-bearing explosions discussed below. After 21 March
2006, the swarms became yet more common and stronger. They were joined
by low-frequency harmonic tremor.
Interpreted as related to the motion of magma, the tremor and swarms
also seemed closely associated with lava fountains seen in the crater on
25 March 2006. Along with long-period earthquakes there were two
episodes of high-amplitude tremor during 4-5 April 2006. Such seismicity
had been absent for about a year. Small lava fountains witnessed on the
night of 17 April 2006 were again preceded by long-period earthquakes
and banded tremor.
As a result, IG distributed two special reports (#2 & 3). The latter
contained a spectrogram for late April 2006, illustrating intervals of
relative quiet (up to ~ 5 hours long) punctuated by broad-band signals
(i.e. coincident earthquakes and tremor) sometimes in tight clusters
lasting ~ 90 minutes.
January-May 2006. At the beginning of January 2006, explosions generated
moderate amounts of ash, but seismicity remained low. Though clouds
obscured the volcano during much of 18-24 January 2006, steam clouds
with minor ash content were seen on 20 and 22 January. A discharge of
muddy, sediment-laden water along W-flank valleys on 23-24 January
blocked the highway. On 25 January light rain caused lahars to flow in
the NW sector. The lahars descended a NNW-flank gorge from the village
of Juive, causing the closure of the Banos-Penipe highway. Around 28
January, ash fell in the village of Puela. On 31 January, a
steam-and-ash plume rose ~ 1 km above the volcano and drifted W. A small
lahar closed a road in Pampas for 2 hours.
On 5 February at 0600, a moderate explosion sent a steam plume, with a
small amount of ash, to ~ 1 km above the volcano; the plume drifted SW.
Light rainfall on 7 February generated a lahar in the La Pampa area NW
of the volcano.
During 6-14 February, several moderate-sized emissions of gas and ash
occurred at Tungurahua, with plumes rising to ~ 500 m above the volcano.
Long-period earthquakes increased in number on the 6th. An explosion
around midnight on 12 February expelled incandescent volcanic material
that traveled down the N flank of the volcano. A small amount of ash
fell in the town of Puela, SW of the volcano.
IG issued a report (#1; Boletin Especial Volcan Tungurahua) on 18
February 2006 noting slight increases in activity that week. Explosions
were moderate; however, ashfall occurred in some settlements bordering
the volcano. IG summarized the week with a table similar to one below,
with multiple cases of ash fall on local towns (table 2).
Table 2. A summary of Tungurahua's ash falls during an active interval,
13-18 February 2006, and the settlements affected. OVT stands for the
Observatorio Volcan Tungurahua, a facility 13 km NW of the summit, down
valley from the town of Patate. The report was issued at 1330 on the
18th, explaining why the entries only applied to the first half of that
day. Courtesy of IG (special report #1).
Date Number Location and comment
of explosions
13 Feb 2006 1 Puela (~ 8 km SW of the summit),
ashfall during the day.
14 Feb 2006 4 Puela, ashfall during the afternoon.
15 Feb 2006 4 No ashfall reported.
16 Feb 2006 9 Runtun, ashfall at dawn; Observatory
(OVT), Pelileo, Banos, and Garcia Moreno subjected to light ashfall in the morning; Bilbao, Cusua, Puela, Humbalo, Bolivar, and Pillate subjected to strong ashfall in the
morning.
17 Feb 2006 3 In Chacauco, Cusua, and Juive ash fell at dawn and part of the morning. In Pillate, Cotalo, Cusua, and Huambalo, ash in the morning. In Bilbao, ashfall all day; and Chogluntus, small ashfall during the afternoon.
18 Feb 2006 1 In Banos, OVT, Salasaca, Pondoa,
Bilbao, San Juan, and (until about Pelileo, ashfall at dawn. In Banos and Ambato, ashfall in 1200) both the morning and afternoon.
Activity at Tungurahua during 28 February to 6 March consisted of
low-level seismicity and emissions of steam and gas, with low ash
content. An explosion on the 28th produced a plume composed of steam,
gas, and some ash that reached ~ 3 km high.
In addition to the moderate explosions during 8-10 March, light drizzle
produced muddy water in the gorges on the volcano's W flank. As a result
the Banos-Penipe highway was closed for several hours. On 9 March, ash
fell in the zone of Juive on the volcano's NW flank. On 10 March, ash
fell in the towns of Pillate, Pondoa, Runtun, and Cusua (on the W to NW
to NNE flanks).
During 16-20 March, small-to-moderate explosions occurred at Tungurahua
that consisted of gas, steam, and small amounts of ash. Plumes rose to ~
3 km above the volcano. During 22-27 March, similar explosions consisted
of gas, steam, and small amounts of ash. Plumes rose as high as ~ 1 km
above the volcano on several days. An explosion on 26 March was
accompanied by incandescent blocks that rolled down the volcano's NW
flank.
On 18 February, small amounts of ashfall were reported at the
observatory, Cotalo, Cusua, and other settlements (table 2). On 19
February, rainfall generated a small mudflow SW of the volcano in the
Quebrada Rea sector of Puela.
Table 3 summarizes observations associated with plumes and seismicity
during 15 February to 8 May 2006. Many observations in that interval
noted small-to-moderate explosions or other emissions. Ash plumes to 1-3
km above the volcano (6-8 km altitude) were typical.
Table 3. A compilation of some daily and weekly observations from
Tungurahua during 15 February to 8 May 2006. Courtesy of IG.
Date range Description of activity (plume heights in kilometers above the summit).
(2006)
15 Feb-19 Feb Ash plume as high as 3 km.
26 Feb-27 Feb Steam and gas with low ash content; on the 26th, 1
plume to ~ 3 km; on the 27th, to 1 km. Both plumes drifted NW.
28 Feb-06 Mar Steam and gas with low ash content; on the 28th, 1
plume to ~ 3 km. Low seismicity.
08 Mar-10 Mar Several explosions with low ash content resulting
in plumes under 2 km.
16 Mar-20 Mar Small-to-moderate explosions consisting of gas,
steam, and small amounts of ash. Plumes rose to ~ 3 km.
22 Mar-27 Mar Small-to-moderate explosions consisting of gas,
steam, and small amounts of ash. Plumes rose as high as ~ 1 km above the
volcano on several days.
29 Mar-02 Apr Small-to-moderate explosions consisting of gas,
steam, and small amounts of ash.
04 Apr-10 Apr Small-to-moderate explosions at Tungurahua
consisting of gas, steam, and small amounts of ash. On the 9th, plumes rose to
~ 3 km.
11 Apr-17 Apr Small-to-moderate explosions produced gas, steam,
and small amounts of ash. On the 13th, plumes rose to ~ 2 km. High seismicity.
19 Apr-23 Apr Small-to-moderate explosions produced gas, steam,
and small amounts of ash. On the 19th, plumes rose to ~ 3 km. High seismicity.
28 Apr-01 May Small-to-moderate explosions; gas, steam, and small
amounts of ash. On the 28th, a plume rose to a maximum height of ~ 2 km.
High seismicity.
04 May-08 May Small-to-moderate explosions; gas, steam, and small
amounts of ash. High seismicity, dominated by explosions and
long-period earthquakes.
During this 15 February to 8 May time interval ash affected localities
as follows. During 29 March to 2 April, ash fell in the Bilbao,
Choglontus, Puela, and Manzano sectors, and incandescent blocks rolled
down the volcano's NW flank. Around 9 March, ash fell in the Banos,
Guadalupe, Chogluntus, Bilbao, and Manzano sectors. Around 1500 on 9
March, several lahars traveled down W-flank gorges, disrupting traffic
along the Banos-Penipe highway. An explosion on 26 March was accompanied
by incandescent blocks that rolled down the NW flank. During 11-17
April, a small amount of ash fell in the Pondoa sector N of the volcano.
Increased activity starting 10 May 2006. Seismicity for mid-April 2006
to mid-August 2006 appears in figure 3. The figure shows the time
sequence of hypocenters with various signal types given separate
symbols. Between April and May there was a shallowing of event locations
(indicated by the arrow on the left) from -4 km to +2 km. At that point,
explosion signals suddenly began to dominate. Those explosion signals
came from depths in the range from 0 to over +4 km depth. The 14 May
seismic crisis seemingly ended without a large eruption. Explosion
signals continued; however, they ceased dominating until around the time
of the 14 July eruption when they again became the chief signal (circled
area) just prior to the eruption breaking out at the surface.
IG put out special report #4 with a cautionary tone. In the 48 hours
starting around 10 May, there was a very important increase in activity.
IG judged the anomalous, high-activity conditions as severe as previous
ones during this crisis (specifically, equivalent to those of
October-December 1999, August 2001, September 2002, and October 2003).
The summary that follows largely omits the discussion of plausible
scenarios aimed at public safety; however, the IG noted that if rapid
escalation were to occur during the current unstable situation, they
might not have time to issue alerts. They also noted that the eruption
might calm.
During the roughly two-day interval, seismometers registered over 130
explosion signals, averaging about three explosions per hour, but with a
maximum of 12 per hour. The general tendency was towards yet more
increases in the number of explosion signals. The activity was
accompanied by continuous signals described as harmonic tremor and
emission-related tremor, and after 10 May these tremor signals were also
more intense and frequent. In spite of the increase in explosion and
tremor signals, emissions of magmatic gases (SO2) and ash stayed at
relatively low levels.
First-hand observations during 10-12 May described extraordinarily loud
explosions heard from 30-40 km away in Pillaro and from~ 31 km NW in
Ambato, but absent 30 km SW in Riobamba. In settlements near the
volcano, including Cusua on the volcano's W foot, glass windows
shattered. In some areas, roars were sufficiently intense that
vibrations in windows and houses kept inhabitants awake at night. The
intensities of eruptions from 10 May were reminiscent of the eruption's
onset in 1999.
From the observatory in the Guadelupe sector (13 km NW of the cone)
night observers saw the ejection and rolling descent of large glowing
blocks of lava, and the crater gave off a permanent glow. However, ash
emissions were considerably reduced; the chief component venting was
steam with few other gases. The resulting outbursts were not continuous
and they were too weak to form mushroom clouds. This was in contrast to
other periods of high activity (e.g. August 2001, September 2002, and
October 2003), when sustained ash-bearing eruption columns and ash falls
were common.
IG special report #4 noted that the tremor signals during a 48-hour
interval after 10 May were the strongest recorded since the eruptions
renewed in 1999. The number of explosions and their seismic energy were
the highest recorded since the end of 2003, but was less than registered
during November 1999 and mid-2000.
On 30 May IG issued its next special report (#5), which noted elevated
eruptive activity during 8-14 May, but a clear decrease thereafter.
During 10-21 May, the following instruments detected the stated numbers
of explosions: seismometers, 801; and infrasonic recorders, 682. The
peak in these explosions occurred on 14 May, a day when the instrument
counts were as follows: seismometers, 221; infrasonic, 204. As in the
previous report, inhabitants close to the volcano heard loud roars, and
in some cases were sleepless due to vibrations heard or felt in their
homes at night. These conditions convinced residents in Cusua to move
during the night. But starting the 16th, the number and intensity of
explosions per day decreased drastically, with only 17 explosions
recorded on the 16th, dropping in later days to 2 or 3 daily explosions.
According to a local mayor, given the lack of noises and relative calm,
evacuees from Cusua returned home.
The lull in explosions coincided with ongoing fluctuations in
seismicity. The IG interpreted this as a sign of continued instability
linked to the motion of fluids at depth. The lull in explosion signals
accompanied increased gas emissions, which gradually came to contain
more and more ash. Small, local ash fall again began to occur. Starting
17 May it became common to see ash columns extending to 4 km above the
summit, frequently blown NW.
Reports for the week following 17 May by the Washington VAAC also
discussed the increasing ash plumes. On 18 May, an ash plume reached an
altitude of 5.2 km above the crater and extended NW. The Washington VAAC
also noted that on 19 May, the Instituto Geofisico observed an ash plume
that reached an altitude of 12 km. On satellite imagery, ash plumes were
visible on 20 and 23 May and extended SW. Hotspots were visible on
satellite imagery 19, 20 and 23 May. The ash plume and incandescence on
23 May were also observed on the scene by Instituto Geofisico staff. On
25 May a significant meteorological advisory (SIGMET) indicated an ash
plume to an altitude of 5 km. On 27 and 30 May, the VAAC reported that
the Instituto Geofisico observed ash plumes at altitudes of 7.9 km and 5
km respectively. IG noted that behavior during the last few weeks of May
seemed consistent with a gradual decrease from the state of elevated
activity seen in mid-May.
Although satellite thermal data produced alerts during 8-14 May, these
ceased later in the month. The reduced thermal flux was taken to suggest
reduced manifestations in the crater during mid to late May. Coincident
with that, deformation data suggested relative stability, particularly
compared to the significant variations seen earlier in May.
During 28 June-4 July, small-to-moderate explosions at Tungurahua
produced plumes composed of gas, steam, and small amounts of ash that
reached 1.5 km above the summit. Light ashfall was reported in nearby
localities during 29 June-2 July. On 29 June, reports of ground movement
coincided with an explosive eruption that sent blocks of incandescent
material as far as 1 km down the W flank.
During 5-11 July, seismic activity indicating explosions increased at
Tungurahua. Incandescent blocks were ejected from the crater during 5 to
8 July, when blocks rolled approximately 1 km down the NW flank.
Ash-and-steam plumes with moderate to no ash content were observed to
reach maximum heights of 2.5 km above the summit and drifted to the W
and NW.
Eruptive style changes after powerful discharges of mid-July 2006. On 14
and 15 July, IG issued its next special reports (#6, 7, and 8)
documenting events surrounding the strongest eruption yet seen during
the entire 1999-2006 eruptive process. The basis for the size assesment
was made from the seismic record based on reduced displacement,
sometimes called normalized or root-mean-square amplitude (a means to
correct seismic data to a common reference point; McNutt, 2000) The
largest discharge occurred at 0559 on 15 July.
On 14 July, seismicity was elevated above that seen in the previous
several days. IG noted that at 1710 several large explosions were
recorded on instruments, as well as heard by people. An eruption column
formed, bearing moderate ash. It initially rose several kilometers but
later was estimated to have attained ~ 15 km altitude. This was followed
by 20 minutes of quiet. At 1733 a huge explosion presumably opened the
conduit. Immediately local authorities were contacted and they evacuated
people living on the lower NW-W flanks of the cone. Pyroclastic flows
and explosion signals are notable in the seismic record (figure 4).
At 0050 on 14 July a pyroclastic flow poured down the NW flank (the
Juive Grande drainage). An associated fine ashfall was noted 8 km SW in
the town of Puela. Intense Strombolian activity ensued, including
glowing blocks tossed 500 m above the crater that bounced downslope for
considerable distances. Associated noises were particularly loud and
heard widely, including in Ambato (30 km NW). Lookouts described these
sounds as distinctive ("bramidos doble golpe;" roughly translated as
'double roars'), a new sound in the suite of those heard since 1999. In
the Cusua area, and up to 13 km NW in the sector of the Observatory of
Guadelupe, residents felt intense ground movements.
At 1930 that day pumice fell on the W flank (the sector of Pillate)
reaching a thickness of ~ 1 cm. About 10 minutes after the pumice fall,
the IG issued the second special report (#7) on the 14 July events. It
cautioned residents to remain away from the volcano's W side. The next
special report (#8) noted that variations in activity prevailed through
the end of 14 July, and that much of the first hour of 15 July brought
decreased activity. Tremor continued on 15 July, often in episodes with
durations of 4 to 5 minutes, separated by intervening calm intervals of
similar duration.
After 0500 on 15 July the eruptive process changed, with the new regime
characterized by sequences of abundant large explosions followed by
intervals of calm lasting 30-40 minutes. A critical detonation occurred
at 0559 on 15 July. On the basis of reduced displacement, it ranked as
the largest since the eruption began in 1999. Other detonations with
similar character followed the initial one. During 0500-0555 there were
20 large detonations. In assessing the 14-15 July eruptions, satellite
analysis by both the Washington Volcanic Ash Advisory Center and the
U.S. Air Force Weather Agency confirmed the highest ash-plume tops to
altitudes of 15-16 km.
At sunup on 15 July observers found signs that a pyroclastic flow had
descended a W-flank drainage (Achupashal valley, between Cusua and
Bilbao). The deposits filled the valley (to 5- to 10-m thickness). Small
fires had ignited in the vegetation. A rockfall was also seen in the
Bilbao area. Ash falls were reported, containing both ash and scoria
fragments, affecting the cities of Penipe, Quero, Cevallo, Mocha,
Riobamba, and Guaranda.
Additional fieldwork revealed that pyroclastic flows had traveled down
at least six quebradas around the volcano, including Achupasal, Cusua,
Mandur, Hacienda, Juive Grande, and Vascun valleys (the latter, upslope
from the western part of the touristic city of Banos).
Geologic Summary. Tungurahua, a steep-sided andesitic-dacitic
stratovolcano that towers more than 3 km above its northern base, is one
of Ecuador's most active volcanoes. Three major volcanic edifices have
been sequentially constructed since the mid-Pleistocene over a basement
of metamorphic rocks. Tungurahua II was built within the past 14,000
years following the collapse of the initial edifice. Tungurahua II
itself collapsed about 3000 years ago and produced a large
debris-avalanche deposit and a horseshoe-shaped caldera open to the W,
inside which the modern glacier-capped stratovolcano (Tungurahua III)
was constructed. Historical eruptions have all originated from the
summit crater. They have been accompanied by strong explosions and
sometimes by pyroclastic flows and lava flows that reached populated
areas at the volcano's base. Prior to a long-term eruption beginning in
1995 that caused the temporary evacuation of the city of Banos at the
foot of the volcano, the last major eruption had occurred from 1916 to
1918, although minor activity continued until 1925.
Information Contacts: Geophysical Institute (IG), Escuela Politecnica
Nacional, Apartado 17-01-2759, Quito, Ecuador (URL:
http://www.igepn.edu.ec/).
Galeras
Colombia
1.22EN, 77.37EW; summit elev. 4,276 m
All times are local (= UTC -5 hours)
On 24 November 2005 an eruption began at Galeras that resulted in local
ash fall (BGVN 31:01and 31:03). This report discusses behavior through
mid-August 2006.
Through December 2005 to the end of March 2006, the lava dome in the
main crater continued to grow and seismicity remained elevated. Because
of an increase in tremor at Galeras on 28 March 2006, Instituto
Colombiano de Geologia y Mineria (INGEOMINAS) raised the Alert Level
from 3 (changes in the behavior of volcanic activity have been noted) to
2 (likely eruption in days or weeks). Although the seismic activity
apparently decreased on 29 March, Galeras remained at Alert Level 2.
INGEOMINAS reported that Galeras remained at a critical state during
April and May 2006, with a partially solidified lava dome in the main
crater. Seismicity, deformation, gas emissions, and temperatures all
decreased. During 10-17 April, there were small gas emissions from the
volcano. During 9-15 May, there were small gas and sporadic ash
emissions. During 12-19 June, ash columns reached heights of 0.6-1.4 km
above the summit.
According to Reuters and BBC reports, an increase in volcanic activity
12 July prompted the Colombian government to order the evacuation of ~
10,000 people living near Galeras. INGEOMINAS reported an increase in
seismic activity and at least two explosive eruptions. Ash accumulated
in the towns of La Florida and Narino, about 10 km N, and in the town of
Genoy, 5 km NE. The Alert Level was increased from 2 (likely eruption in
days to weeks) to 1 (eruption imminent or occurring). On 13 July,
because of decreased activity, the Alert Level was lowered from 1 to 3.
Approximately 2,000 people had been taken to shelters.
On 17 July, INGEOMINAS reported that after the 12 July eruption of
Galeras, seismic activity decreased considerably. Observations of the
dome and secondary craters in the W sector after 12 July showed minor
physical changes. Weak gas plumes were observed without associated
seismic activity. Through the first two weeks of August 2006, seismic
activity remained at low levels. Gas and steam emissions from the main
crater continued. Galeras remained at Alert Level 3 (changes in the
behavior of volcanic activity have been noted).
Geologic Summary. Galeras, a stratovolcano with a large breached caldera
located immediately W of the city of Pasto, is one of Colombia's most
frequently active volcanoes. The dominantly andesitic Galeras volcanic
complex has been active for more than 1 million years, and two major
caldera collapse eruptions took place during the late Pleistocene.
Long-term extensive hydrothermal alteration has affected the volcano.
This has contributed to large-scale edifice collapse that has occurred
on at least three occasions, producing debris avalanches that swept to
the W and left a large horseshoe-shaped caldera inside which the modern
cone has been constructed. Major explosive eruptions since the mid
Holocene have produced widespread tephra deposits and pyroclastic flows
that swept all but the southern flanks. A central cone slightly lower
than the caldera rim has been the site of numerous small-to-moderate
historical eruptions since the time of the Spanish conquistadors.
Information Contacts: Diego Gomez Martinez, Observatorio Vulcanologico y
Sismologico de Pasto (OVSP), INGEOMINAS, Carrera 31, 1807 Parque
Infantil, PO Box 1795, Pasto, Colombia (Email: dgomez@ ingeomin.gov.co;
URL: http://www.ingeomin.gov.co/pasto/; Email: ovp@xxxxxxxxxxxxxxx);
Washington Volcanic Ash Advisory Center (VAAC), 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/); El
Pais (URL: http://elpais-cali.terra.com.co/paisonline/); Reuters;
British Broadcasting Company (BBC) (URL: http://www.bbc.co.uk/).
Karthala
Comoros
11.75ES, 43.38EE; summit elev. 2,361 m
All times are local (= UTC + 3 hours)
On 28 May 2006, a magmatic eruption occurred inside the Chahale caldera
of Karthala volcano. Information in the previous report (BGVN 31:06) was
based on newspaper accounts. This report comes from Hamidou Nassor,
Julie Morin, Christopher Gomez, Magali Smietana, Francois Sauvestre, and
Christopher Gomez. They noted some key references relating to Karthala,
including a 2001 dissertation (Bachelery and others, 1995; Krafft, 1982;
and Nassor, 2001).
The 28 May 2006 crisis began with a few hours of elevated seismic
activity, beginning around 1230 (local time). Three hours later, seismic
stations recorded a small crisis that lasted for 6 hours and produced
both SP and LP signals. Around 2107 the magmatic eruption began.
Seismographs recorded a tremor only a few seconds later.
From the coast of the island a red cloud was visible above the volcano.
Scientists at the Karthala observatory met with government
representatives and confirmed a magmatic eruption. It was not yet known
if the eruption had occurred on the caldera floor or inside the main
crater. A trip to the volcano was necessary in order to assess the
volcanic activity and determine the exact location of the eruption. Two
hypotheses were proposed: (1) If the eruption was located in the N part
of the caldera, the lava could flow outside the caldera, towards
populated areas; (2) If the eruption was located inside the main crater,
to the S, lava would remain inside the crater. The Comorian authorities
helped the scientific team to get assistance from the South African Army
(AMISEC) to fly over the volcano.
On the morning of 29 May 2006, the scientific team and AMISEC personnel
flew over the volcano. They saw that the eruption was contained inside
the main (Chahale) crater, where the past three eruptions had occurred.
A lava fountain was observed in the middle of the lava lake (figure 11).
No lava flow was observed outside the caldera. Seismic records showed a
tremor caused by the lava fountain; the fountain was apparently spurting
since the beginning of the eruption.
On the morning of 31 May, the scientific team returned to Karthala with
AMISEC forces. Part of the lake was still mobile and bubbling, but part
had solidified on the surface in the SE and a few blocks were floating
on the side of the lake (figure 12). No projectiles overshot the caldera
rim.
On 1 June 2006 seismic monitoring indicated the end of the tremor phase.
On 2 June scientists returned to the summit with AMISEC forces. They
observed that the surface of the lava lake was solidified, but the
deeper portions of the lake remained hot (figure 13).
References: Bachelery, P., Damir, B.A., Desgrolard, F., Toutain, J.P,
Coudray, J.P., Cheminee, J-L., Delmond, J.C., and Klein, J.L. 1995,
L'eruption phreatique du Karthala (Grande Comore) en juillet 1991: C.R
Acad. Sci. Paris, 320, serie Iia, p. 691-698.
Krafft, M., 1982, L'eruption volcanique du Karthala en avril 1977
(Grande Comore, Ocean Indien): C.R. Acad. Sci. Paris, t 294, serie II,
p. 753-758.
Nassor, H., 2001, Contribution a l'etude du risque volcanique sur les
grands volcans boucliers basaltiques: le Karthala et le Piton de la
Fournaise: Ph.D. thesis, Univ. Reunion.
Geologic Summary. The southernmost and larger of the two shield
volcanoes forming Grand Comore Island (also known as Ngazidja Island),
Karthala contains a 3 x 4 km summit caldera generated by repeated
collapse. Elongated rift zones extend to the NNW and SE from the summit
of the Hawaiian-style basaltic shield, which has an asymmetrical profile
that is steeper to the south. The lower SE rift zone forms the Massif du
Badjini, a peninsula at the SE tip of the island. Historical eruptions
have modified the morphology of the compound, irregular summit caldera.
More than twenty eruptions have been recorded since the 19th century
from both summit and flank vents. Many lava flows have reached the sea
on both sides of the island, including during many 19th-century
eruptions from the summit caldera and vents on the northern and southern
flanks. An 1860 lava flow from the summit caldera traveled ~ 13 km to
the NW, reaching the western coast north of the capital city of Moroni.
Information Contacts: Hamidou Nassor (LSTUR) Universite de la Reunion BP
7151, 15 Avenue, Rene Cassin, 97715 Saint-Denis (Email:
hamidou.nassor@xxxxxxxxxxxxxxx; hamidounassor@xxxxxxxxxxx; Julie Morin,
Email: julieapi@xxxxxxxx; Christopher Gomez, Laboratoire de geographie
physique CNRS LGP, Email: kurisusing@xxxxxxxxxxx; Magali Smietana ,
Email: magali.smietana@xxxxxxxxxxxxxxxxxxxxxxxx; Francois Sauvestre
(CNDRS), BP 169, Moroni (URL:
http//volcano.ipgp.jussieu.fr:8080/Karthala/stationkar.html).
Etna
Italy
37.734EN, 15.004EE; summit elev. 3,350 m
All times are local (= UTC + 1 hours)
This report covers the new eruption from an E-flank fissure during mid
July 2006. Previously, on 7 September 2004, an eruptive period began
that lasted until March 2005 (BGVN 29:09, 30:01). From March 2005 until
November quiet degassing took place at the summit craters; on 16
December 2005 an explosive sequence at the summit was accompanied by an
ash emission from the Bocca Nuova crater (BGVN 30:12). This report is
from Sonia Calvari of the Istituto Nazionale di Geofisica e Vulcanologia
(INGV) and covers the interval through 26 July. Brief mention is made
at the end of the report about another episode starting on 31 August and
going into at least mid-September.
On 14 July 2006 at 2330 a fissure opened on the E flank of the
South-East Crater (SEC) summit cone. Two vents along the fissure
produced a lava flow spreading E to the Valle del Bove (figure 14). A
helicopter survey carried out on 16 July at 0730 showed a braided lava
flow field up to 1.7 km long. Based on the surface area and approximate
volume of this lava flow field, workers estimated a mean output rate of
~ 2.6 m3/s during the first 32 hours of eruption. During the opening
phase of the eruptive fissure, moderate strombolian emissions occurred
at a third upper vent, located at about 3,100 m on the E flank of the
SEC, just below the wide depression that cuts its eastern flank. It
produced minor ash fallout on Catania. The composition of the ash was
80% juvenile, with small amount of lithics probably due to the opening
phase of the vents.
On 17 July, the lava flow field was situated on the W wall of the Valle
del Bove, and the two main flow fronts reached about 2,100 m elevation,
spreading N of the Serra Giannicola Piccola ridge. The lava discharge
peaked on 20 July (figure 15), when an effusion rate of ~ 10 m3/s drove
the lava flow advance to a maximum distance of ~ 3 km within the Valle
del Bove. The lava flow front widened at the base of Monte Centenari, at
1,800 m elevation, located at least 15 km from the closest villages. The
effusion rate on 23 July decreased to ~ 3 m3/s. At that time the lava
channels had narrowed and levees had partially collapsed. The eruption
appeared to end on 24 July.
On 26 July, observers on the rim of the NE Crater heard strong
explosions, and saw lapilli fall. This crater, together with the south
pit within Bocca Nuova, showed significant thermal anomalies during a
helicopter survey carried out on 24 July.
In the early morning of 31 August, Strombolian activity resumed at SEC's
summit. In the next two weeks SEC was the scene of a series of dramatic
events. By 11 September, lava from the SE flank of the SEC had advanced
to reach ~ 3 km ESE. The resulting ribbon of lava was in places over
200 m wide. More details will follow in a subsequent report.
Geologic Summary. Mount Etna, towering above Catania, Sicily's second
largest city, has one of the world'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 E. 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/); Reuters (URL:
http://today.reuters.com/).
St. Helens
Washington, USA
46.20EN, 122.18EW; summit elev. 2,549 m
All times are local (= UTC - 8 hours)
The current and ongoing eruption of the St. Helens started on 11 October
2004. Extrusion of the growing lava dome has continued in the same
quiescent mode exhibited over the past year, and levels of seismicity
remained generally low, with low emissions of steam and volcanic gases
and minor production of ash. From 1830 hours on 26 October 2004 to 15
August 2006, a total of 13,841 seismic triggers have occurred. Figures
16 and 17 summarize seismicity over the past year. A decade-long
time-depth plot clearly shows the start of the current eruption (figure
18).
Pictures and movies taken in August 2006 with the Brutus camera (located
on the E rim of the 1980 Mount St. Helens crater) showed continued
extrusion of spine 7 on the growing lava dome (figure 19) (photos and
movies are also available on the CVO website). Between 4-5 and 7-8
August a segment of the middle part of spine 7 temporarily stopped
moving. At 1310 on 5 August a magnitude 3.6 earthquake occurred, and
subsequent photographs showed that the "stuck" segment became unstuck.
Motion again stopped sometime after 1310 on 7 August and much of 8
August, when a M 3.3 earthquake occurred at 2001 on 8 August. Clouds
obscured the volcano from view on 9 August, but parted enough on 10
August to show that once again the segment became unstuck. One
explanation by CVO scientists for these observations is that the large
earthquakes were caused by parts of the spine sticking and then
slipping.
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 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: U.S. Geological Survey Cascades Volcano
Observatory, Vancouver, WA (URL: http://vulcan.wr.usgs.gov/); The
Pacific Northwest Seismograph Network, University of Washington Dept. of
Earth and Space Sciences, Box 351310, Seattle, WA (URL:
http://www.geophys.washington.edu/SEIS/PNSN/).
Cleveland
Aleutian Islands, USA
52.825EN, 169.944EW; summit elev. 1,790 m
On 23 May 2006, the Alaska Volcano Observatory (AVO) received a report
from the International Space Station indicating that a plume was
observed moving W from Cleveland volcano at 2300 UTC (BGVN 31:06). A
photograph of the plume taken from the International Space Station was
released by the National Aeronautics and Space Administration (NASA).
Starting at about 2300 UTC, just before this image was taken, Cleveland
underwent a short eruption. The volcanic plume was seen in Advanced Very
High Resolution Radiometer (AVHRR) polar-orbiting satellite data
beginning from 2307 UTC. By 0100 UTC on 24 May the ash plume had
detached from the vent and was approximately 130 kilometers SW of the
volcano. Satellite data showed a cloud height of about 6.1 km asl (table
4). The plume was no longer detectable in satellite imagery by 0057 UTC
on 25 May. In response to the event, AVO raised the Level of Concern
Color Code to 'Yellow.'
Table 4. Satellite observations of ash plume from Cleveland volcano.
Courtesy of the Washington Volcanic Ash Advisory Center (VAAC).
Date and Time (UTC) Plume altitude Direction and speed
24 May 2006 (0200) 8.2 km SW at 55 km/hour
24 May 2006 (0800) 6.7 km SW at 37-46 km/hour
24 May 2006 (1400) 6.1 km W at 37-46 km/hour
The last eruption of Cleveland was 6 February 2006 (BGVN 31:01). Since
24 May 2006, no new information about ash emissions had been received,
nor have indications of continuing activity been detected from satellite
data for the volcano. This short-lived event was typical of recent
Cleveland activity. On 7 August 2006, AVO downgraded the Level of
Concern Color Code for Cleveland from 'Yellow' to 'Not Assigned."
Because Cleveland is not monitored with real-time seismic
instrumentation, during intervals of repose it does not receive an
assignment of Color Code 'Green,' but instead is left 'Not Assigned.'
Geologic Summary. Beautifully symmetrical Mount Cleveland stratovolcano
is situated at the western end of the uninhabited, dumbbell-shaped
Chuginadak Island. It lies SE across Carlisle Pass strait from Carlisle
volcano and NE across Chuginadak Pass strait from Herbert volcano.
Cleveland is joined to the rest of Chuginadak Island by a low isthmus.
The 1,730-m-high volcano is the highest of the Islands of the Four
Mountains group and is one of the most active of the Aleutian Islands.
The native name for Mount Cleveland, Chuginadak, refers to the Aleut
goddess of fire, who was thought to reside on the volcano. Numerous
large lava flows descend the steep-sided flanks of the volcano. It is
possible that some 18th to 19th century eruptions attributed to Carlisle
should be ascribed to Cleveland (Miller and others, 1998). In 1944
Cleveland produced the only known fatality from an Aleutian eruption.
Recent eruptions from Mount Cleveland have been characterized by
short-lived explosive ash emissions, at times accompanied by lava
fountaining and lava flows down the flanks.
Information Contacts: National Aeronautics and Space Administration
(NASA) Earth Observatory (URL: http://earthobservatory.nasa.gov/);
Washington Volcanic Ash Advisory Center (VAAC) (URL:
http://www.ssd.noaa.gov/VAAC/washington.html); Jeffery Williams, NASA,
ISS Crew Earth Observations and the Image Science & Analysis Group,
Johnson Space Center 2101 NASA Parkway, Houston, TX 77058, USA.
Karymsky
Kamchatka Peninsula, Russia
54.05EN, 159.45EE; summit elev. 1,536 m
During April, May and June 2006, intermittent eruptive activity at
Karymsky continued. Pilots had previously reported ash emissions from
Karymsky rising to 3-5 km altitude during January to April 2006, during
which time Karymsky remained at Concern Color Code Orange (BGVN 31:04).
The same color code stayed in effect through August 2006.
Based on interpretations of April-June 2006 seismic data, ash plumes
rose to altitudes of between 3 and 8 km. Satellite imagery showed a
large thermal anomaly at the volcano's crater from January to August
2006, and numerous ash plumes and deposits extended 10-200 km SE and E
of the volcano.
During 10-16 June 2006, 400-600 shallow earthquakes occurred daily. Ash
plumes up to 5 km altitude traveling SE were observed by pilots. On 19
June, the Advanced Spaceborne Thermal Emission and Reflection Radiometer
(ASTER) on NASA's Terra satellite captured a false-color image of an ash
plume from Karymsky (figure 21). During 21-27 June 200-700 shallow
earthquakes occurred daily; during 23-30 June, 100-350 shallow
earthquakes occurred daily.
According to the Tokyo VAAC, the Kamchatkan Experimental and Methodical
Seismological Department (KEMSD) reported that during July 2006 ash
plumes reached altitudes between 3 and 7 km. Approximately 100-350
shallow earthquakes occurred daily during 29 June to 3 July, and
increased to 1,000 per day during 4-5 July.
Activity at Karymsky continued during 8-14 July, with 250-1000 shallow
earthquakes occurring daily. Based on interpretations of seismic data,
ash plumes reached altitudes of 5 km.
During August 2006, 100-300 shallow earthquakes occurred daily. Based on
interpretations of seismic data, ash plumes reached altitudes of 3-3.7
km.
Geologic Summary. Karymsky, the most active volcano of Kamchatka's
eastern volcanic zone, is a symmetrical stratovolcano constructed within
a 5-km-wide caldera that formed during the early Holocene. The caldera
cuts the S side of the Pleistocene Dvor volcano and is located outside
the N margin of the large mid-Pleistocene Polovinka caldera, which
contains the smaller Akademia Nauk and Odnoboky calderas. Most
seismicity preceding Karymsky eruptions originated beneath Akademia Nauk
caldera, which is located immediately S of Karymsky volcano. The caldera
enclosing Karymsky volcano formed about 7,600-7,700 radiocarbon years
ago; construction of the Karymsky stratovolcano began about 2,000 years
later. The latest eruptive period began about 500 years ago, following a
2,300-year quiescence. Much of the cone is mantled by lava flows less
than 200 years old. Historical eruptions have been vulcanian or
vulcanian-strombolian with moderate explosive activity and occasional
lava flows from the summit crater.
Information Contacts: Olga Girina, Kamchatka Volcanic Eruptions Response
Team (KVERT), a cooperative program of the Institute of Volcanic Geology
and Geochemistry, Far East Division, Russian Academy of Sciences, Piip
Ave. 9, Petropavlovsk-Kamchatskii 683006, Russia (Email:
girina@xxxxxxxxxx), the Kamchatka Experimental and Methodical
Seismological Department (KEMSD), GS RAS (Russia), and the Alaska
Volcano Observatory (USA); 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/;
Email: tlmurray@ usgs.gov), the Geophysical Institute, University of
Alaska, P.O. Box 757320, Fairbanks, AK 99775-7320, USA (Email:
eisch@xxxxxxxxxxxxxxxxxx), and the Alaska Division of Geological and
Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK
99709, USA (Email: cnye@xxxxxxxxxxxxxxxxx); Tokyo Volcanic Ash Advisory
Center (VAAC) (URL:
http://www.jma.go.jp/JMA_HP/jma/jma-eng/jma-center/vaac/; Email:
vaac@xxxxxxxxxxxxxxxxxx).
Mayon
Luzon, Philippines
13.257EN, 123.685EE; summit elev. 2,462 m
All times are local (= UTC + 8 hours)
Mayon was last reported on in March 2006 (BGVN 31:03), discussing an
eruption in February 2006. Low-level activity and seismicity prevailed
through early July. This report covers an eruptive pulse that began on
13 July 2006 and continued through August 2006. On 13 July there were
phreatic eruptions that produced light ashfall in the areas of Calbayog
and Malilipot. At 2200 on 14 July, authorities raised the Alert Level
from 1 to 3 due to moderate white steam drifting NE and lava flows
extending 0.7-1.0 km from the summit onto the SE slopes. On 15 July, the
lava flow continued its SE progression towards Bonga gully.
On 16 July, the 6 km radius hazard zone known as the Permanent Danger
Zone (PDZ) established around the SE area, was extended to 7 km and
during the period covered by this report the radius of the danger zone
around the southern sector was extended to 8 km. On 18 July, the
Philippine Institute of Volcanology and Seismology (PHIVOLCS) reported
that the lava flow had reached 1 km in length and incandescent boulders
had rolled 3 km towards the Bonga gully. Seismicity, reported SO2
fluxes, and posted alert levels appear in table 5.
Table 5. Mayon's reported seismicity, SO2 fluxes, and alert levels
during 15 July 2006 to 24 August 2006. "--" indicates information not
available. Courtesy of PHIVOLCS.
Date Volcanic Tremor SO2 flux Alert
earthquakes episodes (t/d) Level
15 Jul 2006 -- 111 2,211 3
17 Jul 2006 -- 314 1,513 3
18 Jul 2006 -- -- -- 3
19 Jul 2006 -- 250 2,157 3
20 Jul 2006 -- -- -- --
21 Jul 2006 -- -- -- --
22 Jul 2006 -- -- -- --
23 Jul 2006 -- -- -- --
24 Jul 2006 11 324 7,020 3
25 Jul 2006 12 564 5,886 3
26 Jul 2006 7 316 9,275 3
27 Jul 2006 6 421 4,550 3
28 Jul 2006 8 423 8,724 3
29 Jul 2006 4 394 6,099 3
31 Jul 2006 -- 388 12,548 3
01 Aug 2006 -- 354 7,418 3
02 Aug 2006 16 450 7,050 3
03 Aug 2006 51 343 4,760 3
04 Aug 2006 18 354 2,965 3
05 Aug 2006 18 354 2,965 3
06 Aug 2006 12 371 1,919 3
07 Aug 2006 -- -- -- --
08 Aug 2006 109 344 12,745 4
09 Aug 2006 21 294 7,829 4
10 Aug 2006 3 501 6,573 4
11 Aug 2006 6 213 6,876 4
12 Aug 2006 6 191 3,423 4
13 Aug 2006 13 158 5,427 4
14 Aug 2006 16 152 3,493 4
16 Aug 2006 15 154 8,086 4
17 Aug 2006 5 130 2,937 4
18 Aug 2006 32 307 2,937 4
19 Aug 2006 22 240 2,712 4
20 Aug 2006 15 253 6,634 4
21 Aug 2006 15 274 5,390 4
22 Aug 2006 24 431 2,445 4
23 Aug 2006 10 316 5,215 4
24 Aug 2006 18 451 6,328 4
Pyroclastic flows on the SE slopes prompted approximately 100 families
to evacuate on 20 July. On 22 July, lava flows advanced NE towards the
Mabinit channel. By 24 July, lava flows had traveled SSE, ~ 4 km from
the summit toward Bonga gully, and branched off to the W and E.
Incandescent blocks shed from the toe and margins of the flows traveled
SE and were visible at night. Additionally, on 24 July seismographs
recorded more than 324 tremor episodes and 11 volcanic earthquakes. SO2
emissions from the summit crater reached 7,000 metric tons per day,
several times larger than fluxes reported earlier.
PHIVOLCS reported lava flow advance in terms of straight-line distances,
which progressed as follows: 26 July, 4.45 km; 27 July, 4.7 km; and 29
July, 5.4 km. During this time, SO2 rates remained high (table 5),
suggesting fresh magma at shallow levels in the volcano. The number of
tremor episodes and earthquakes also remained high. Tremor was thought
to indicate near-continuous lava blocks detaching from the lava flows.
Volcanic earthquakes were thought to reflect ascending magma. Figure 22
shows the lava flow front on 29 July.
On 29 July, light ash accumulation was reported about 12 km S and SE, in
Daraga municipality and Legazpi City and vicinity, respectively.
Emissions of sulfur-dioxide reached ~ 12,500 tons per day on 31 July, a
record high for this reporting interval. By 1 August, in the SE sector
of the Bonga gully, lava flows had advanced ~ 1.35 km, and in the SSE
sector they had advanced a maximum distance of 5.8 km from the summit.
According to a Philippine Information Agency (PIA) press report,
military and police checkpoints were set up on 2 August around the
6-km-radius PDZ to prohibit entry. A large lava deposit had grown on the
SE flanks. The lava which faced Legazpi and Daraga, had piled up during
the initial two weeks of the eruption and threatened to cross the PDZ.
PHIVOLCS had reported that the advancing incandescent front of the lava
flow was ~ 20 m high and 50 m wide (figure 23). PHIVOLCS estimated that
the lava front could breach the 6-km-radius PDZ within two to three
days.
An overflight of Mayon on 6 August revealed that lavas discharging from
the summit crater extended along the Mabinit channel and spilled into
the Bonga gully, E of the Mabinit channel. Due to the decreased supply
of lava to the Mabinit channel, the flow there was expected to cease a
short distance beyond the 6-km-radius PDZ. Six ash explosions sent ash
columns up to 800 m above the summit, prompting PHIVOLCS to raise the
alert level from 3 to 4, indicating an eruption is imminent. According
to the Manila Bulletin Online, as many as 50,00 people in the Albay
province were evacuated.
On 7 August, an advancing lava flow crossed 100 m beyond the 6-km-radius
PDZ. According to the Manila Standard Today, authorities warned
residents of more lava and fires as the lava flows crept along the
Mabinit and Bonga gullies.
During 9-15 August, explosive activity continued at Mayon after a brief
respite on 8 August. Based on interpretations of seismic data, minor
explosions during 9-11 and 13-15 August were accompanied by lava
extrusion and collapsing lava flow fronts that released blocks and small
fragments. A drop in SO2 emissions on 9 August worried volcanologists
that something had blocked the flow of magma in Mayon's conduit and
could therefore cause a build up in pressure resulting in a larger
eruption. Visual observations were commonly obscured by clouds. On 11
August an ash plume was seen drifting ESE. On 12 August, four explosions
occurred; one produced a pyroclastic flow that traveled over the SE and
E slopes and generated a plume that rose to an altitude of 500 m and
then drifted NE. On 15 August, a brief break in the clouds allowed for a
view and confirmed the presence of fresh pyroclastic deposits from
activity in the previous days. Approximately 40,000 people remained in
evacuation centers and authorities maintained an Extended Danger Zone at
8 km from the summit in the SE sector.
PHIVOLCS reported that explosions from Mayon continued during 16-19
August. On 17 August, ash-and-steam plumes drifted at least 5.3 km NE
and reached the town Calbayog, where light ashfall was reported. Lava
extrusion continued and on the SE slopes lava-flow fronts shed blocks
and small fragments. On 18 August, the Mibinit and Bonga gully lava
flows reached ~ 6.8 km SE from the summit. PHIVOLCS estimated the volume
of erupted materials at between 36 and 41 million cubic meters.
Geologic Summary. Beautifully symmetrical Mayon volcano, which rises to
2,462 m above the Albay Gulf, is the Philippines' most active volcano.
The structurally simple volcano has steep upper slopes averaging 35-40
degrees that are capped by a small summit crater. The historical
eruptions of this basaltic-andesitic volcano date back to 1616 and range
from strombolian to basaltic plinian, with cyclical activity beginning
with basaltic eruptions, followed by longer term andesitic lava flows.
Eruptions occur predominately from the central conduit and have also
produced lava flows that travel far down the flanks. Pyroclastic flows
and mudflows have commonly swept down many of the approximately 40
ravines that radiate from the summit and have often devastated populated
lowland areas. Mayon's most violent eruption, in 1814, killed more than
1,200 people and devastated several towns.
Information Contacts: Philippine Institute of Volcanology and Seismology
(PHIVOLCS), PHIVOLCS Building, C.P. Garcia Avenue, U.P. Campus, Diliman,
Quezon City, Philippines, Reuters Alert Network (URL:
http://www.alertnet.org/thenews/newsdesk/MAN212904.htm); The Associated
Press (URL: http://www.ap.org/); Manila Standard Today (URL:
http://www.manilastandardtoday.com); Manila Bulletin Online (URL:
http://www.mb.com.ph/).
Sulu Range
New Britain, SW Pacific
5.50ES, 150.942EE; summit elev. 610 m
All times are local (= UTC + 10 hours)
On 7 July 2006, observers reported the first historical indication of
volcanic activity in the Sulu Range of New Britain (in the nation of
Papua New Guinea (PNG)). The Sulu Range lies near
the N coast of New Britain Island. This spot sits in the Province of
West New Britain but in terms of geometry, lies closer to the middle of
the island ~100 km E of the prominent, N-trending Willaumez Peninsula
and ~200 km SW of Rabaul at the island's E end.
Rabaul Volcano Observatory (RVO) noted that ground observations at the
Sulu Range, confirmed by aerial inspection, indicated that the emissions
were coming from an area initially incorrectly disclosed as Mount Karai.
(Karai is reportedly equivalent to Mount Ruckenberg, mentioned below.)
Later reports correcting the initial vent location, stated that the
eruption took place 2 km SW of Mount Karai between Ubia and Ululu
volcanoes.
Considerable light on the Sulu Range and other volcanoes in the vicinity
is shed by an Australian Bureau of Mineral Resources report by Johnson
(1971). The coordinates and summit elevation given in the header above
apply to the highest point in the Sulu Range, Mount Malopu (synonyms
include "Malutu" and "Malobu").
Changes in our nomenclature. We indicate Walo hot springs on the lower
map of figure 24, the only feature in this vicinity previously
identified in our database on active volcanoes. Walo was listed as a
thermal feature in the Melanesian portion of the Catalog of Active
Volcanoes of the World (Fisher, 1957) and in Simkin and Siebert (1994).
Walo rests in a low swampy area ~ 3 km W of the edge of the Sulu Range,
which we apply broadly to a ~ 10 km diameter mountainous area with
multiple peaks of ~ 500-600 m elevation. The highland areas associated
with the Sulu Range's NE end contains a cone near the coast, which is
labeled "Mount Ruckenberg (extinct volcano)" on the Bangula Sheet (Papua
New Guinea 1:100,000 Topographic Survey, 1975).
The Sulu Range eruption has spurred restructuring of our naming
conventions. Walo is now listed as a thermal feature associated with the
larger volcanic field called the Sulu Range (and it preserves the
Volcano Number that used to apply only to Walo, 0502-09=).
2006 eruption and earthquakes. RVO reported that there were indications
as early as February 2006 that something was changing at Sulu Range
because vegetation there was dying off. RVO noted that earthquakes
began on 6 July and most river systems near Mount Karai had turned muddy
due to the continuous shaking. Seismic activity was followed by the
emission of puffs of white vapor from the area and loud booming and
rumbling noises accompanied strong tremors.
Eruptions started with forceful dark emissions late on 7 and 8 July and
decreased to moderate emissions by 10 July. At the settlement Bialla,
~20 km NE of the Sulu Range, tremors were felt. These were also picked
up by the seismic stations at Garbuna and Ulawun (~100 km W and ENE,
respectively).
In a report discussing 10-11 July, RVO reported that three villages N of
Mount Karai had been evacuated. For the 10th, RVO described the activity
as weak-to-moderate emission of white vapor with no evidence of ashfall
and with occasional weak-to-moderate roaring noises accompanying the
emissions. On the 11th, associated with earthquakes, white puffs
discharged. Similar observations of white emissions prevailed through
the 12th.
Earthquakes increased both in size and frequency of occurrence, and on
11 July at Bialla they took place every 10-20 minutes. Near Ubia
volcano, seismicity was very elevated, with earthquakes every few
minutes. At 0820 on 12 July a large earthquake of Modified Mercalli (MM)
intensity VII or more occurred in the region. It disturbed the
shoreline, which discolored the seawater; shaking also caused the sea
surface to become choppy.
The USGS epicenter for the above-cited 12 July (local time) earthquake
was listed at very nearly the same time (in UTC, on 11 July at 2222)
with epicenter at 5.48ES, 150.83EE, a depth of 37 km and a body
magnitude (mb) of 4.90. That spot lies 12 km NE of Sulu Range (using
the coordinates listed in the header above). On a table of earthquakes
the same day (11 July, UTC), seven others, mb 3.9-4.7 occurred within
several hundred kilometers of Sulu Range. All took place earlier, but a
pattern of substantial ongoing earthquakes also prevailed later as well.
RVO noted that from 1600 on 12 July to 0900 on 13 July high-frequency
earthquakes occurring at the rate of one every minute were recorded on
the seismograph deployed at Bialla. The earthquakes recorded were of
varying (though unstated) magnitudes and towards 0900 decreased slightly
to one every 30 minutes. Shortly afterwards, from 1000 to 1400 on 13
July, the seismograph was deployed in Kaiamu village on the small point
immediately NW of the uplands portions of the Sulu Range, where it
recorded continuous strings of high frequency earthquakes. Although
the instrument was out of service after 1400 on the 13th, recording
resumed that afternoon and seismic activity continued at a high level
through 0900 on 15 July. During this time, the occurrence of felt
earthquakes with maximum MM intensity V increased from one every 40-60
minutes to one every 2-3 minutes. Details of a subsequent decline in
seismicity are sketchy.
The last reported visible emissions from the Sulu Range were on 12 July.
By early August 2006 seismic activity had decreased to earthquakes of MM
intensity I to II occurring at increasing intervals.
Again referring to USGS seismicity tables, the previously mentioned
pattern of ongoing earthquakes on 11 July, generally mb 3.9-4.9,
continued. An exception, the largest magnitude event during 9-18 July
struck 31 km from Sulu Range, listed in UTC on 13 July at 2248; mb 5.1.
It was at 39 km depth with epicenter ~12 km away. About 5 hours later
a mb 4.7 event was recorded directly at volcano. On the 19th two larger
earthquakes struck. One an Ms 6.4 centered 28 km away; the second, an
Mw 5.90, 33 km away. These were the largest earthquakes within 50 km
during 1 July to 11 September 2006.
References: Fisher N H, 1957, Melanesia: Catalog of Active Volcanoes of
the World and Solfatara Fields, Rome, IAVCEI, v. 5, p. 1-105.
Johnson, R.W., 1971, Bamus volcano, Lake Hargy area, and Sulu Range, New
Britain: Volcanic geology and petrology, Aust. Bur. Min. Res. Geol.
Geophys. Rec, 1971/55, p. 1-36.
Papua New Guinea 1:100,000 Topographic Survey, 1975, Bangula Sheet,
Sheet 9187, Series T601: Royal Australian Survey Corps (Reprinted by the
National Mapping Bureau, 1985).
Simkin, T., and Siebert, L., 1994, Volcanoes of the World: Geoscience
Press, Tucson, Arizona, 349 p. (ISBN 0-945005-12-1).
Geologic Summary. The Sulu Range consists of a group of partially
overlapping small stratovolcanoes in north-central New Britain off
Bangula Bay. The 610-m Mount Malopu forms the high point of the
basaltic-to-rhyolitic complex at its SW end. Lava Point (also known as
Lara Point) forms a peninsula of volcaniclastic-covered lava flows with
a small lake extending about 1 km into Bangula Bay at the NW side of the
Sulu Range. The Walo hydrothermal area, consisting of solfataras and mud
pots, lies on the coastal plain about 3 km W of the SW base of the Sulu
Range. Prior to 2006, no historical eruptions had occurred from the Sulu
Range, although some of the cones display a relatively undissected
morphology.
Information Contacts: Herman Patia and Steve Saunders, Rabaul Volcano
Observatory (RVO), P.O. Box 386, Rabaul, Papua New Guinea.
Global Volcanism Program http://www.volcano.si.edu/
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