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Global Volcanism Program <http://www.volcano.si.edu/>
Bulletin of the Global Volcanism Network
Volume 31, Number 9, September 2006
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Home Reef (Tonga) Extensive pumice rafts between Tonga and Fiji during
August-October
Rabaul (Papua New Guinea) Strong eruption at Tavurvur ejected ash and
large plumes to the troposphere
Bamus (Papua New Guinea) Forceful vapor emission seen on 12 July 2006
Sulu Range (Papua New Guinea) Volcano seismicity declines in September
and October 2006
Barren Island (India) Ongoing emissions, including lava, but
late-September news reports of slowing pace
Bulusan (Philippines) Ten explosions recorded seismically between 21
March and 28 June 2006
Cleveland (Alaska) Short duration explosions during August-October 2006
Fourpeaked (Alaska) Eruption on 17 September, followed by emissions
until at least early November
Soufriere Hills (Montserrat) Extrusive dome dynamics during
May-September 2006
San Cristobal (Nicaragua) Multi-year update: 13 June 2004, local ash
fall; early 2006, small eruptions
Montagu Island (S Sandwich Islands) Five years of nearly persistent
eruptive activity
Editors: Rick Wunderman, Edward Venzke, Sally Kuhn Sennert, and
Catherine Galley
Volunteer Staff: Robert Andrews, Jerome Hudis, Veronica Bemis, Jackie
Gluck, William Henoch,
Hugh Replogle, Zahra Hirji, Stephen Bentley, Paul Berger, Jeremy
Bookbinder, and Antonia Bookbinder
Home Reef
Tonga Islands, SW Pacific
18.992ES, 174.775EW; summit elev. -2 m
All times are local (= UTC + 13 hours)
Pumice rafts drifting from Tonga to Fiji occurred during August-October
2006. The source of these pumice rafts was Home Reef, which was first
observed to be in eruption on 9 August and was clearly building an
island by 12 August (figure 1). A compilation of report sightings
through mid-October 2006, plotted using Google Earth, shows the timing
and distribution of the pumice rafts that are discussed in this report
(figure 2). As is our convention, and as available, a list of
contributors (and their vessels) is noted in last section of this report.
Pumice traveled both N and S around Fiji's Lau Group. To the N, pumice
reached Taveuni through the Nanuku passage and entered the Koro sea,
washing onto southern Vanua Levu, before moving into the Bligh Waters N
of Viti Levu by 20 September. To the S, extensive pumice was seen N of
Vatoa Island on 16 September, and on Kadavu Island by the end of the
month. Pumice was also encountered by the Encore II W of Viti Levu on 30
September while enroute to New Caledonia.
Figure 1. Photograph of the new island being built by the eruption at
Home Reef as seen on 12 August 2006. The island was ~1.5 km in diameter.
View is towards the W from about 2.8 km away. Courtesy of Fredrik
Fransson of the Maiken.
Figure 2. Map of Tonga (right) and Fiji (upper left) showing dates and
locations where observers saw pumice rafts (placemarks with dots) or
where mariners crossing between Tonga and Fiji failed to see rafts
(placemarks with crosses). Some locations are approximate; see text for
additional details and sources of each observation. The base map is from
Google Earth with points plotted by Bulletin editors.
Early observations of the eruption. The news service Matangi Tonga
Online quoted Allan Bowe, the owner of the Mounu Island Resort in
southern Vava’u, regarding volcanic activity in the direction of Home
Reef during 9-11 August. Bowe heard “. . . what sounded like continuous
thunder rumbling to the S and there was a huge plume of smoke and cloud
rising up into the sky.” In another Matangi news article, Siaosi
Fenukitau, a captain of one of the fishing boats of the Maritime
Projects Co. (Tonga) Ltd., reported that around mid-September they
sighted a new volcanic island near Home Reef that was larger than
Fotuha’a, a small island in Ha’apai with a population of about 134 people.
The yacht Maiken left Neiafu on 11 August, passing the N side of Late
Island. After about 9 km the crew noticed brown, somewhat grainy streaks
in the water. The streaks became larger and more frequent as they
continued SW “until the whole horizon was a solid line to what looked
like a desert.” The brownish pumice fragments the size of a fist were
floating in water that was strangely green. They motored into the vast
(many miles wide) belt of densely packed pumice, and within seconds
Maiken slowed down from seven to one knot. Initially the thin layer on
the surface was pushed away by the bow wave, but when they entered the
solid field it started to pile up and “behaved like wet concrete” and
“looked like rolling sand dunes as far as the eye could see.” After
retreating from the pumice with only minor paint abrasion along the
waterline, and then cleaning their intake filters, they decided to
anchor in Vaiutukakau bay outside Vava’u for the night. The next
morning, 12 August, they received radio confirmation of an eruption, but
the vent and extent were uncertain. They decided to go S to avoid the
pumice rafts floating NW, heading SSW until they encountered the pumice,
then sailing alongside until the rafts were broken up enough to safely
travel through.
As they approached Home Reef it became clear that one of the clouds on
the horizon was a volcanic plume. Observations from a closer vantage
point revealed that an intermittent “massive black pillar shot upwards
toward the sky” and particles were raining down. Since the wind was
pushing the plume NW, the Maiken motored up to within 2.8 km of the
island (to 18E59.5’S, 174E46.3’W) while the sun was going down. Multiple
peaks forming a crater open to the sea on one side were visible, and it
looked like it was “made of black coal.” Not wanting to encounter more
pumice rafts after dark, they continued SSW towards the southern part of
the Lau Group.
Pumice sightings between Tonga and Fiji. Boats that later noted seeing
pumice in Fiji did not report any activity or rafts near Tonga during
27-29 August. The Soren Larsen sailed through “a sea of floating pumice”
one evening that “sounded like we were sailing through ice” just before
reaching Fiji. This encounter was probably on 30 August when their
online tracker located the ship just W of the central Lau islands after
departing Neiafu on the 28th. No eruptive activity or pumice was noted
in the online log of the Soren Larsen for 14-15 and 23-24 August when
they transited to northern Tonga to the E of Home Reef.
While the Encore II crew was visiting the Mounu Island Resort on 2
September there were “grapefruit-sized” pumice pieces on the beach. A
few days later, while listening to the “Rag of the Air” net broadcast
out of Fiji, the Encore II crew learned of pumice rafts along their
expected route. The operator of this broadcast, Jim Bandy, provides
weather reports for boats going between Tonga and Fiji. One report was
of a mass of pumice about 11 km long and at least a meter (“many feet”)
deep. The Encore II departed from Neiafu on 8 September on a course
around a set of Fijian islands and reefs called the Lau Group. The crew
believed that this route, going NW around the Lau Group, helped them
avoid most of the pumice.
As the Encore II approached their turning point about two thirds of the
way to Fiji, on 10 September, they encountered “rivers of pumice”
floating roughly parallel to their NW course due to the SE winds (figure
3). Some pumice fragments that they collected were about 5-10 cm in
diameter, although most were about the size of pea gravel. The parallel
streams of pumice, only a single layer in depth, were sometimes up to 90
m wide and 400 m long. The crew later heard reports from several boats
that had taken a more westerly route through the Lau Group to Fiji and
encountered much larger areas of pumice. The crew on the Norwegian
sailboat Stormsvalen went through larger and thicker areas of pumice,
leaving a track in the pumice as they went through (figures 4 and 5).
They noted that boats traveling through the pumice during higher winds
and seas encountered a problem of airborne pumice pelting the crews and
their boats. One crew reported pumice covering their deck.
Figure 3. Photograph showing small areas of floating pumice just NE of
the Lau Group of islands, Fiji, around 10 September 2006. Courtesy of
the Encore II crew.
Figure 4. Photograph showing a large pumice raft near the Lau Group of
islands, Fiji, on an unknown date in early to mid-September 2006.
Courtesy of the Stormsvalen crew via the Encore II.
Figure 5. View of a large pumice raft after the passage of a sailing
vessel near the Lau Group of islands, Fiji, on an unknown date in early
to mid-September 2006. Courtesy of the Stormsvalen crew via the Encore II.
A sailboat blog entry by Sara Berman and Jean Philippe Chabot noted a
“strong sulfur odor” in the direction of the volcano upon leaving Tongan
waters around 20 September. As they progressed SW towards Fiji they
passed through streams of pumice containing pieces ranging from very
small pebbles to larger pieces the size of a baseball. Every time a wave
crashed on deck they heard the pumice making its way onto the boat and
into the cockpit.
On 30 September the Windbird log noted that “. . . cruisers are still
having to avoid the huge pumice field that is floating about between
Tonga and Fiji.”
Bob McDavitt’s “Weathergram” for 15 October noted that reports from
yachts sailing between Tonga and Fiji indicated an absence of pumice.
These observations suggest that the bulk of material produced by the
eruption, or series of eruptions, had crossed to Fiji by mid-October.
Pumice rafts in northern Fiji. The earliest known direct observations of
the floating pumice in Fiji come from a boat with callsign KB1LSY, the
crew of which noted that “thick pumice” slowed them to 2 knots for 30
minutes during the early morning hours of 28 August. This occurred as
they approached the northern islands of the Lau Group in Fiji, about 500
km NW of Home Reef.
According to Roberta Davis, the pumice arrived at Taveuni, Fiji, on 14
September. There were several rafts ~300 m from shore with other rafts
scattered farther out. Local mariners noted that pieces in the top layer
were approximately the size of pea gravel. Suspended below the surface
were pieces almost as large as footballs. The beaches on the northern
shores of Taveuni were covered in what appeared to be black popcorn. The
pumice was present at Taveuni for up to 6 days.
On 19 September David Forsythe reported that large rafts of pumice were
passing through the northern Lau group in Fiji (figure 6). He noted
gooseneck barnacles up to 10 mm long on the largest pieces. Bulletin
editors found compiled growth rates for various stalked barnacles (
Thiel and Gutow, 2005), which indicated 17-29 days of growth.
Figure 6. Panoramic view of Indigo Swan Beach filled with pumice,
Naitauba Island, Fiji, as seen in September 2006. Courtesy of David
Forsythe.
The Encore II crew observed pumice along the S side of Vanua Levu, W of
the Lau Group, around 16 September. They noted pumice at Fawn Harbour
that obscured the channel into the harbor and it made a boat at anchor
appear to be aground on an island. They also observed streams of pumice
near the Makogai Channel on 20 September. The Fiji Times Online reported
on 20 September that villagers living along the coastal areas of Saqani
in Cakaudrove (Vanua Levu) were battling to clear their pumice-covered
seashores and rivers. Villagers saw the pumice floating in the sea near
their homes on 18 September, and by the next day the pumice covered the
river and villagers could not fish or travel by boats and bamboo rafts
to their plantations.
While diving at the “Bligh Triangle” of Fiji at sites NW of Viti Levu,
the crew aboard the Nai’a encountered floating pumice during 20
September-7 October. The pumice was “surrounding the Nai’a and the
skiffs with occasional big carpets of floating rock.” Roman Leslie, an
Australian volcanologist who was fishing in Koro (Lomaiviti Group), also
observed the pumice in late September.
Scientists aboard the research vessel Yokosuka observed pumice settling
to the shore of Viti Levu on 6 October. The rafts were in bands up to
70-80 m wide and several hundred meters long. The pumice fragments were
fully abraded, and dominantly less than 1 cm in diameter with occasional
large blocks up to 15-20 cm in diameter. The pumice seemed to be quite
phenocryst-rich. The sound of the moving, abrading rafts was described
as “sizzling.”
Pumice rafts in southern Fiji. A biologist aboard the National
Geographic motor vessel Endeavour reported that on the morning of 16
September they observed an extensive region of floating pumice “... in
long, wind-driven rows, approximately 1-5 m wide and up to several
hundred meters long.” Pieces of pumice averaged 0.5-8 cm in longest
dimension. The largest piece observed was approximately 15 cm in longest
dimension. The observations continued over the next 90 km, for 3.5
hours, with little interruption, until they made landfall at Vatoa
Island in the Lau Group. Moderate windrows of pumice, up to several
inches deep, were observed on the beaches of Vatoa.
Roger Matthews arrived in Kadavu, Fiji, on 30 September and reported
that pumice had been coming ashore for about a week. On the southern
coast of the island near the airport, the layer of pumice on 30
September was 10-15 cm thick floating on top of ~1 m of water (figure
7). Farther NE, pumice that began coming ashore at the Matava Resort on
3 October carried goose barnacle shells that measured about 2-3 mm on
the bigger clasts. By 7 October barnacle size on arriving pumice had
increased to around 4-6 mm. While scuba diving, Matthews noted neutrally
buoyant bits of pumice, generally in the 3-10 mm size range, down to at
least 40 m water depth. The pumice did not appear to have an even size
distribution (figure 8). There were a number of big clasts, 2-3 cm, with
a large amount of material in the 8-15 mm range. In the shore deposits
there appeared to be a large volume of fines in the sub-2 mm size. The
material was clean with no algae, just the occasional barnacles. The
clasts contained phenocrysts up to 2 mm long. The raft drifted in and
out depending on wind conditions, at times extending 75-100 m from
shore, and invaded streams at high tide. On shore there were 20-cm-thick
deposits, some of which was used as fill behind the sea walls (figure 9).
Figure 7. Pumice found floating in North Bay along the southern coast of
Kadavu, Fiji, on 30 September 2006. Courtesy of Roger Matthews.
Figure 8. A close up view of pumice seen near Matava Resort on the S
shore of Kadavu, Fiji, 3 October 2006. Courtesy of Roger Matthews.
Figure 9. Pumice deposits seen at ebb tide near Matava Resort on the S
shore of Kadavu, Fiji, 8 October 2006. Some of the pumice has been used
as fill behind the sea wall. Deposits can be seen on the steps into the
water, and waves propagating through the pumice could still break.
Courtesy of Roger Matthews.
A 31 October story in the Fiji Times described transportation
difficulties between Daviqele Village, on the W end of Kadavu, and other
parts of the island due to pumice that a resident said had “covered
[Naluvea Bay] for over two months now.” Similar problems were reported
by Adrian Watt at Matava Resort on the S shore of Kadavu. In an email
relayed by Roberta Davis, Watt noted that by 2 November the pumice had
mostly stopped coming in, with “... just a few strands of small pieces
being blown along wind lines here and there.” The pieces were generally
5-10 mm in diameter, but several were bigger, and one was larger than 30
cm across. Large bays on Kadavu's SE side were pumice choked, hampering
boat travel, and clogged cooling systems damaged or destroyed many
outboard engines.
Geologic Summary. Home Reef, a submarine volcano midway between Metis
Shoal and Late Island in the central Tonga islands, was first reported
active in the mid-19th century, when an ephemeral island formed. An
eruption in 1984 produced a 12-km-high eruption plume, copious amounts
of floating pumice, and an ephemeral island 500 x 1,500 m wide, with
cliffs 30-50 m high that enclosed a water-filled crater.
Reference: Thiel, M., and Gutow, L., 2005, The ecology of rafting in the
marine environment. II. The rafting organisms and community:
Oceanography and Marine Biology: An Annual Review, 2005, v. 43, p. 279-418.
Information Contacts: Fredrik Fransson and HDkan Larsson, Yacht Maiken,
32 Macrossan St., Unit 70, Brisbane 4000, Australia (URL:
http://yacht-maiken.blogspot.com/, Email: fredrikfransson@xxxxxxxxx);
Paul and Nancy Horst, Encore II (URL: http://www.encorevoyages.com/;
Email: encore.crew@xxxxxxxxxxxxx); KB1LSY Crew (URL:
http://www.pangolin.co.nz/yotreps/tracker.php?ident=KB1LSY); Matangi
Tonga Online, Vava’u Press Ltd., PO Box 958, Nuku’alofa, Tonga (URL:
http://www.matangitonga.to/, Email: mfonua@xxxxxxxxxxxxxxx); Roger
Matthews, Private Bag 93500, Takapuna, North Shore City 1332, New
Zealand (Email: roger.matthews@xxxxxxxxxxxxxxxxxxxxxx); Ken Tani, R/V
Yokosuka (Email: kentani@xxxxxxxxxxxxx); David Forsythe, Naitauba
Island, Fiji (Email: Da-vid_Forsythe@xxxxxxxxxx); David Cothran, 1211
Colestin Rd., Ashland, OR 97520, USA (Email: david@xxxxxxxxx); Bob
McDavitt’s Weathergram (URL:
http://www.pangolin.co.nz/yotreps/list_manager.php#Bob McDavitt’s
Pacific Weathergrams); Nick Sambrook, Tall Ship Soren Larsen, P.O.Box
60-660 Titirangi Auckland 0642, New Zealand (URL:
http://www.sorenlarsen.co.nz/2006/V237_Tonga-Fiji/V237_Tonga-Fiji_Nick.htm,
http://www.sorenlarsen.co.nz/Voylog_Track.htm, Email:
escape@xxxxxxxxxxxxxxxxx); Windbird Crew (URL:
http://handleysail.com/logs/?cat=1&paged=2); NAI’A Liveaboard Scuba
Diving, Lautoka, Fiji (URL: http://www.naia.com.fj/, Email:
explore@xxxxxxxxxxx); Roberta Davis, Makaira by the Sea, Taveuni, Fiji
(URL: http://www.fijibeachfrontatmakaira.com, Email:
makaira@xxxxxxxxxxxxxx); Adrian Watt, Matava Resort, Kadavu, Fiji (URL:
http://www.matava.com/, Email: matava@xxxxxxxxxxxxxx); Sara Berman and
Jean Philippe Chabot (URL: http://zayasail.blogspot.com/2006/09/east.html).
Rabaul
New Britain, SW Pacific
4.271ES, 152.203EE; summit elev. 688 m
All times are local (= UTC + 10 hours)
A 7 October Rabaul eruption obscured visibility in and around the
caldera, which sits at the NE end of New Britain Island (figure 10). The
eruption took place at the intra-caldera cone Tavurvur, and emissions
included lava flows. Intermittent eruptions had occurred at Tavurvur
since 1994, the last of which took place on 15 January 2006 (BGVN
31:02). Photos by pilots shortly after the eruption documented a
dramatic umbrella-shaped plume, which rose to the tropopause and created
an SO2 cloud that later divided into two parts, one moving NW, the other SE.
Figure 10. (Top) Index maps indicating the location and geography around
Rabaul caldera. (Bottom) A map of Rabaul derived from work by Almond and
McKee and prepared by Lyn Topinka (US Geological Survey). For other maps
see previous Bulletin reports on Rabaul (most recently, BGVN 28:01).
Rabaul Volcano Observatory (RVO) observations. The RVO announced that a
sustained eruption from Tavurvur did not appear to have been any
immediate precursors apart from a small deflation. The sub-Plinian
eruption began at about 0845 on 7 October 2006 and continued into the
early afternoon. Semi-continuous to rhythmic air blasts were obvious in
Rabaul town, with doors slamming and windows rattling. Rabaul received
moderately heavy ashfall; heavy lapilli of ~ 1 mm diameter fell, and a
few lithics up to 3 cm across fell around the S and SW parts of the
caldera. According to Herman Patia at RVO, a small pumice raft
accumulated in Greet Harbor and pumice was still drifting about several
weeks later.
Ashfall affected the whole of the Gazelle peninsula (the name given to
the bulbous, 50-km-diameter NE end of New Britain island). About 1 cm of
ash was deposited on the SW side of the caldera in the Blue
Lagoon-Vulcan sector. Ashfall occurred ~ 7 km SE of Rabaul caldera’s
center point in Kokopo and -20 km S of the center point in Warangoi. The
density of ashfall was such that Tavurvur was obscured from all
directions. In the town of Rabaul the experience was very similar to the
October 1996 and January 1997 Strombolian eruptions.
At 1200 on 7 October 2006 the RSAM was about 1900 units and its rate
appeared to be decreasing. (The Real-time Seismic Amplitude is an
often-used tool to summarize seismic activity during volcanic crises by
presenting a measure of the average amplitude of ground shaking over
successive 10-min intervals.)
Thick ash clouds rose to a height of about 18 km. The cloud subsequently
dispersed over a broad western swath (N to W to S).
The nature of the eruption changed to Strombolian at 1415 hours, with
activity characterized by frequent explosions accompanied by shock
waves. At 1730 hours, the Strombolian activity began to subside. A
moderate to bright glow was visible during the evening of 7 October on
Tavurvur’s N rim, accompanied by occasional explosions and loud roaring
noises throughout the night.
In the morning of 8 October, thick white and blue vapor accompanied
occasional ash explosions drifted N and NW of Tavurvur. Inspection from
Rapindik (2 km NNW from Tavurvur) revealed lava flows emplaced down the
cone’s W and N flanks. The W flank flow went into the harbor and caused
small secondary explosions; visibility of the N flank was poor due to
the white vapor emission. The RSAM level decreased to the background
value of ~ 70 units.
Herman Patia reported that by 28 October 2006 the eruption had quieted
down with only occasional ash emission accompanied by rare explosions.
Seismic activity was at a low level and ground deformation was at a low
rate. On 30 October mild eruptive activity continued at Tavurvur. The
activity consisted of continuous emission of thick pale to dark gray ash
clouds that drifted N to NW of the volcano. Fine ash fall occurred in
the NE caldera at Namanula, and also in surrounding areas downwind and
on the E side of Rabaul Town. There were no audible noises and no glow
visible. The low-level eruptive activity consisted of occasional ash
emissions similar to those that have occurred regularly since 1994.
Pilot observations. Figures 11 and 12 are pilot’s photographs provided
by Tony Gridley, Air Niugini, indicating the well-developed ash clouds
visible 1-2 hours after the eruption. The photos are reminiscent of the
20 September 1994 photo of the eruption cloud taken from the orbiting
Space Shuttle, an oblique, downward-looking perspective from the NE
about 24 hours after the start of that eruption (BGVN 19:08).
Figure 11. Aerial photo taken 1 or 2 hours after the eruption of 7
October 2006 at ~ 3.7 km (~ 12,000 ft) and ~ 90 km (~ 50 nautical miles)
from Tokua airport (Rabaul’s new airport, on the S side of the caldera)
while flying at a heading of about 060E (i.e. looking ENE). The flight
was “on the Hoskins-Tokua track.” Courtesy of Tony Gridley, Air Niugini.
Figure 12. Aerial photo taken 1 or 2 hours after the eruption of 7
October 2006 at ~ 3.7 km (~ 12,000 ft) and ~ 90 km from Tokua airport,
heading about 060E. Courtesy of Tony Gridley, Air Niugini.
Satellite observations. According to Andrew Tupper, the 7 October
eruption was clearly visible on infrared and visible imagery (to around
tropopause altitudes). Figure 13 shows the ash cloud imaged from the
MODIS satellite on 7 October 2006. Figure 14 depicts the sulfur dioxide
(SO2) in Dobson Units (DU) from the Ozone Monitoring Instrument (OMI)
for 7-9 October 2006. Further details appear in the figure caption. The
SO2 concentration-pathlengths on the figure are shown using the
logarithmic scale of Dobson Units. (As one explanation of this unit, if
all SO2 in the air column the satellite observed was flattened into a
thin layer at the surface of the Earth at a temperature of 0E C, then 1
Dobson Unit would make a layer of pure SO2 0.01 mm thick.)
Figure 13. True-color (above) and false-color (below) images of a Rabaul
eruption cloud created by the Moderate Resolution Imaging
Spectroradiometer (MODIS) on NASA’s Aqua satellite, 7 October 2006.
Volcanic emissions block the view of most of the island but Rabaul’s
approximate location is at the solid triangle. The brown or tan plume in
the E clearly bears volcanic ash. The bright “cloud” to the immediate
left of the brown ash represents a portion of the volcanic ash plume
that reached a high enough altitude for the water content of that plume
to turn to ice crystals that “white out” the ash content that would
otherwise appear tan or brown. Courtesy of the NASA Earth Observatory
web site.
Figure 14. The Rabaul eruption injected SO2 into the atmosphere and
measurements from satellite spectrometers led to creation of this series
of images mapping the SO2 concentrations over the region during 7-9
October 2006. Data are from the Ozone Monitoring Instrument on NASA’s
Aura satellite. On 7 October, high SO2 concentrations lingered over New
Britain. By 8 October, the original plume had split into two clouds, one
spreading NW, the other, SE. On 9 October, the SO2 had diffused more,
but a core of elevated concentration-pathlength values remained in the
northern plume. Courtesy of NASA Earth Observatory and Simon Carn,
University of Maryland Baltimore County.
Based on information from the RVO, the Darwin VAAC reported that a brief
eruption of Rabaul on 11 October produced a plume that reached an
altitude of 7.6 km altitude and dissipated NW. Continuous low-level
emissions and vulcanian eruptions produced plumes to 1 km altitude
during 12-17 October.
Moderate Resolution Infrared Spectroradiometry (MODIS) thermal
anomalies. Table 1 shows the thermal anomalies as measured from the
MODIS satellite during the eruption period. Note that there were no
anomalies for several months before this period. The anomalies are in
harmony with the observed lava flows.
Table 1. MODIS thermal anomalies for Rabaul volcano for 7-17 October
2006. Courtesy of Hawai’i Institute of Geophysics and Planetology.
Date Time Number Satellite
(UTC) of Pixels (A=aqua, T=Terra)
07 Oct 2006 1140 4 T
08 Oct 2006 0000 2 T
08 Oct 2006 1220 6 T
08 Oct 2006 1520 4 A
10 Oct 2006 1210 2 T
11 Oct 2006 0035 1 T
11 Oct 2006 1250 1 T
15 Oct 2006 1230 1 T
15 Oct 2006 1525 3 A
17 Oct 2006 1215 1 T
22 Oct 2006 0015 2 T
22 Oct 2006 1535 1 A
24 Oct 2006 1220 2 T
News releases. According to Reuters news service the 7 October blast
shattered windows up to 12 km from the caldera. In 1994, a large
eruption at Tavurvur and the nearby Vulcan peak destroyed much of
Rabaul, covering the airport and much of the town with ash, and forcing
the construction of a new capital, Kokopo, 20 km away. Ash was falling
on Kokopo, causing power and phone cuts. There were no reports of death
or injuries. In addition Reuters noted that “Rabaul Chamber of Commerce
President and hotelier Bruce Alexander told Australian Associated Press
that around 2,000 people--or 90 percent of the local population--had
fled the town as Mt. Tavurvur erupted. All flights into Tokua airport
across the harbor from Rabaul had been canceled due to ash falls.”
According to The Sydney Morning Herald, with 90% of the residents absent
and only essential personnel in Rabaul, local officials feared looters.
Accordingly, extra police were called in, and armed police patrols were
stepped up.
Geologic Summary. The low-lying Rabaul caldera on the tip of the Gazelle
Peninsula at the NE end of New Britain forms a broad sheltered harbor
utilized by what was the island’s largest city prior to a major eruption
in 1994. The outer flanks of the 688-m-high asymmetrical pyroclastic
shield volcano are formed by thick pyroclastic-flow deposits. The 8 x 14
km caldera is widely breached on the east, where its floor is flooded by
Blanche Bay and was formed about 1,400 years ago. An earlier
caldera-forming eruption about 7,100 years ago is now considered to have
originated from Tavui caldera, offshore to the north. Three small
stratovolcanoes lie outside the northern and NE caldera rims of Rabaul.
Post-caldera eruptions built basaltic-to-dacitic pyroclastic cones on
the caldera floor near the NE and western caldera walls. Several of
these, including Vulcan cone, which was formed during a large eruption
in 1878, have produced major explosive activity during historical time.
A powerful explosive eruption in 1994 occurred simultaneously from
Vulcan and Tavurvur volcanoes and forced the temporary abandonment of
Rabaul city.
Information Contacts: Steve Saunders and Herman Patia, Rabaul
Volcanological Observatory (RVO), Department of Mining, Private Mail
Bag, Port Moresby Post Office, National Capitol District, Papua, New
Guinea (Email: hguria@xxxxxxxxxxxxx); Andrews Tupper, Darwin Volcanic
Ash Advisory Centre (VAAC), Bureau of Meteorology, Darwin, Australia
(Email: A.Tupper@xxxxxxxxxx); Peter Webley, ARSC/UAF, 909 Koyukuk Drive,
Fairbanks, Alaska (Email: pwebley@xxxxxxxxxxxxx); Simon Carn, Joint
Center for Earth Systems Technology (JCET), University of Maryland
Baltimore County (UMBC), 1000 Hilltop Circle, Baltimore, MD 21250, USA
(Email: scarn@xxxxxxxx); National Aeronautics and Space Administration
Earth Observatory (URL:
http://earthobservatory.nasa.gov/NaturalHazards); RSAM definition (URL:
http://vulcan.wr.usgs.gov/Monitoring/Descriptions/description
_RSAM_SSAM.html); HIGP MODIS Thermal Alert System, Hawai'i Institute of
Geophysics and Planetology (HIGP), University of Hawaii at Manoa, 168
East-West Road, Post 602, Honolulu, HI 96822, USA (URL:
http://modis.higp.hawaii.edu/).
Bamus
New Britain, SW Pacific
5.20ES, 151.23EE; summit elev. 2,248 m
All times are local (= UTC +10 hours)
According to the Papua New Guinea Department of Mining (DOM), reports
coming from Bialla Local Level Government (LLG) indicated that Bamus
showed signs of unusual activity. At 1010 on 12 July 2006 observers saw
white vapor coming out at the summit. The emission was forceful at about
1110 that day, with a tint of gray color in the emission. The vapor-rich
plume blew inland to the SSE. No ashfall was reported.
Officials from Bialla LLG together with a DOM observer witnessed the
activity, as did Max Benjamin from Walindi Resort (~ 40-50 km away).
Benjamin called the Rabaul Volcano Observatory to report the activity.
No satellite-detected thermal anomalies at the volcano were reported by
the MODIS website for this time frame.
Geologic Summary. Symmetrical 2,248-m-high Bamus volcano, also referred
to locally as South Son, is located SW of Ulawun volcano, known as the
North Son. These two volcanoes are the highest in the 1,000-km-long
Bismarck volcanic arc. The andesitic Bamus stratovolcano is draped by
rainforest and contains a breached summit crater filled with a lava
dome. A satellitic cone is located on the southern flank, and a
prominent 1.5-km-wide crater with two small adjacent cones is situated
halfway up the SE flank. Young pyroclastic-flow deposits are found on
the volcano’s flanks, and villagers describe an eruption that took place
during the late-19th century.
Information Contacts: Steve Saunders and Herman Patia, Rabaul
Volcanological Observatory (RVO), Department of Mining, Private Mail
Bag, Port Moresby Post Office, National Capitol District, Papua, New
Guinea (Email: hguria@xxxxxxxxxxxxx).
Sulu Range
New Britain, SW Pacific
5.50ES, 150.942EE; summit elev. 610 m
On 31 October 2006 the Rabaul Volcanological Observatory (RVO) issued a
followup report to the eruptive activity in the Sulu Range through much
of October. Sulu Range was previously discussed in BGVN 31:07, but that
report was ambiguous on the nature of the activity that had taken place
during July 2006. This report and personal communications establishes
that RVO staff are doubtful that the most energetic events were magmatic
in character. Furthermore, RVO reported that in the weeks that followed,
seismicity continued to decline.
The seismic unrest that began on 6 July declined from over 2,000 daily
volcano-tectonic (VT) events to below 50 daily VT events during October
(figure 15). The number fluctuated between 35 and 50 from late September
to early October and between 5 and 25 during the third week of October.
Figure 15. Sulu Range seismicity plot of daily VT earthquakes from 22
July 2006 to 24 October 2006 at the Kaiamu Seismic Station. The station
did not operate on the days that lack earthquakes. Courtesy of RVO.
RVO noted that about two to three felt earthquakes with intensity 2
continued to be felt daily at irregular intervals within the Bialla area
and that white steam emissions from the Silanga Hot Springs were still
visible from Bialla. In addition, a moderately strong sulfur smell from
the Silanga and Talopu hot springs continued to be reported.
An analysis by RVO scientists concluded that at no point did magma reach
the surface. The declining trend in seismic activity from early to late
October may indicate that the new magma that apparently intruded to
shallow levels in July is beginning to stall.
A permanent seismic station will be installed at Kaiamu in December 2006
to provide continuous monitoring of activity from the Sulu Range and
surrounding areas.
In an extension of elevated regional tectonic seismicity, a strong
earthquake, M ~ 6.5, struck the S side of central New Britain on 17
October. The USGS computed the focal depth as ~ 60 km, with epicenter ~
50 km S of the Sulu Range. According to a USGS machine-generated shaking
and intensity map, the Sulu Range lies within the zone of highest
computed intensity (VI).
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 west 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: Steve Saunders and Herman Patia, Rabaul
Volcanological Observatory (RVO), Department of Mining, Private Mail
Bag, Port Moresby Post Office, National Capitol District, Papua, New
Guinea (Email: hguria@xxxxxxxxxxxxx); USGS Earthquakes Hazard Program
(URL: http://earthquakes.usgs.gov/)
Barren Island
Andaman Islands, Indian Ocean
12.278EN, 93.858EE; summit elev. 354 m
Our last report on Barren Island discussed events through much of
January 2006 (BGVN 31:01); since that time we have only found sporadic
reports of activity.
According to a news article by The Indo-Asian News Service, a team of
scientists that visited Barren Island around 12 March 2006 found that
the volcano was still very active. The height of the volcanic cone had
increased by 50 m since eruptive activity began in May 2005. In
addition, lava flows covered the NW side of the island.
Since March 2006 there have been only a few satellite images and pilot
reports of continued activity. Based on a pilot report and satellite
imagery, the Darwin VAAC reported that an ash plume was emitted during
5-6 April that did not rise higher than 4.6 km altitude. On 19 April a
low-level plume extending W was visible on satellite imagery.
On 2 May satellite imagery detected a plume from Barren Island near 3.7
km altitude. The following day low-level ash plumes extended N. Based on
a pilot report, the Darwin VAAC reported an ash plume at 1230 on 26 May
that remained below 3 km altitude and drifted N.
On 23 September a news report in The Hindu stated that Indian Coast
Guard officials indicated that the continuing eruption at Barren Island
was decreasing in intensity. The news piece cited a surveillance report
statement that there was less lava but more “smoke” from the volcano.
Geologic Summary. Barren Island, a possession of India in the Andaman
Sea about 135 km NE of Port Blair in the Andaman Islands, is the only
historically active volcano along the N-S-trending volcanic arc
extending between Sumatra and Burma (Myanmar). The 354-m-high island is
the emergent summit of a volcano that rises from a depth of about 2,250
m. The small, uninhabited 3-km-wide island contains a roughly 2-km-wide
caldera with walls 250-350 m high. The caldera, which is open to the sea
on the W, was created during a major explosive eruption in the late
Pleistocene that produced pyroclastic-flow and -surge deposits. The
morphology of a fresh pyroclastic cone that was constructed in the
center of the caldera has varied during the course of historical
eruptions. Lava flows fill much of the caldera floor and have reached
the sea along the western coast during historical eruptions.
Information Contacts: The Hindu (URL: http://www.hinduonline.com);
Indo-Asian News Service (IANS) (URL: http://www.eians.com/); Geological
Survey of India, 27 Jawaharlal Nehru road, Kolkata 700 016, India (URL:
http://www.gsi.gov.in/barren.htm); Indian Coast Guard, National Stadium
Complex, New Delhi 110 001, India (URL:
http://indiancoastguard.nic.in/indiancoastguard/); Darwin Volcanic Ash
Advisory Center, Bureau of Meteorology, Northern Territory Regional
Office, PO Box 40050, Casuarina, Northern Territory 0811, Australia
(URL: http://www.bom.gov.au/info/vaac/).
Bulusan
Luzon, Philippines
12.770EN, 124.05EE; summit elev. 1,565 m
All times are local (= UTC + 8 hours)
On 19 March 2006, the Philippine Institute of Volcanology and Seismology
(PHIVOLCS) raised the status of Bulusan from Zero Alert (no alert) to
Alert Level 1 to reflect elevated seismic, fumarolic, and other unrest
(BGVN 31:05). From that date until an ash explosion on 28 June 2006, 10
explosions were recorded (see table 2).
Table 2. Summary of significant events through late July 2006 at Bulusan
. Numbering of explosion-type (E-type) quakes began 21 March 2006.
Courtesy of Philippine Institute of Volcanology and Seismology (PHIVOLCS).
Date Local Plume Drift Comments
(2006) time Altitude Direction
19 Mar -- -- -- Seismic swarm which lasted until 21 Mar; Alert
Level raised to 1
21 Mar 2258 1.5 km N, W, SW 1st explosion-type (E-type) earthquake lasted 20
min; total of 4 E-type earthquakes recorded
08 Apr 2000 -- -- Lahar at Cogon spillway
09 Apr 1036-1058 -- -- Lahar at Cogon spillway
29 Apr 1044 1.5 km WSW, NW 2nd E-type earthquake; total of 3 E-type
earthquakes recorded
25 May 2117-2130 cloud-covered summit 3rd E-type earthquake; ash
deposits, trace to
2 mm thick in Juban, Irosin
31 May 1617 1.5 W, WNW 4th E-type earthquake
07 Jun 2017-2030 2.0 N, W, SW 5th E-type earthquake; smaller E-type
earthquake
at 0225 on 8 Jun; Alert Level raised to 2
10 Jun 1218 1.0 NE, E 6th E-type earthquake, lasting 25 min
13 Jun 1904 1.5 NW 7th E-type earthquake, lasting 13 min
18 Jun 1556 1.5 W 8th E-type earthquake
20 Jun 2013 cloud-covered summit 9th E-type earthquake – mild; event not
observed; seismic signal recorded for 17 min;
rains generated some lahars
24 Jun 2300 -- -- Lahar at Cogon spillway
28 Jun 0206 cloud-covered summit 10th E-type earthquake; the associated
volcanic
event was not observed but seismic signal
recorded as E-type earthquake lasted 4 min
29 Jun 0800 -- -- Continuous decline in Bulusan activity; Alert
Level lowered to 1
After the ash explosion of 28 June 2006, Bulusan’s monitored parameters
gradually decreased to near baseline levels. The daily count of volcanic
earthquakes was very low, and SO2 emission rates and ground-deformation
data revealed the volcano’s deflated condition, indicating the absence
of active magma ascent. Ash emission stopped and steaming from the
active vents and fissures gradually returned to normal levels. Due to
the decline in activity, on 29 July PHIVOLCS lowered the status of
Bulusan from Alert Level 2 to 1.
On 10 October 2006 at 1256 UTC, the Tokyo Volcanic Ash Advisory Center
announced that an eruption plume from Bulusan was visible on satellite
imagery reaching altitudes of 3 km and drifting SW and SSE.
Unlike nearby Mayon volcano (~ 70 km NW) (see BGVN 31:08), no thermal
anomalies were detected at Bulusan by satellite or recorded by the
Hawai’i Institute of Geophysics and Planetology (HIGP) MODIS/ MODVOLC
web site from the beginning of 2006 to 10 October 2006.
Geologic Summary. Luzon’s southernmost volcano, Bulusan, was constructed
along the rim of the 11-km-diameter dacitic-to-rhyolitic Irosin caldera,
which was formed about 35,000-40,000 years ago. Bulusan lies at the SE
end of the Bicol volcanic arc occupying the peninsula of the same name
that forms the elongated SE tip of Luzon. A broad, flat moat is located
below the topographically prominent SW rim of Irosin caldera; the NE rim
is buried by the andesitic Bulusan complex. Bulusan is flanked by
several other large intracaldera lava domes and cones, including the
prominent Mount Jormajan lava dome on the SW flank and Sharp Peak to the
NE. The summit of 1,565-m-high Bulusan volcano is unvegetated and
contains a 300-m-wide, 50-m-deep crater. Three small craters are located
on the SE flank. Many moderate explosive eruptions have been recorded at
Bulusan since the mid-19th century.
Information Contacts: Philippine Institute of Volcanology and Seismology
(PHIVOLCS), University of the Philippines Campus, Diliman, Quezon City,
Philippines (URL: http://www.phivolcs.dost.gov.ph); Tokyo Volcanic Ash
Advisory Center (VAAC) (URL:
http://www.jma.go.jp/jma/jma-eng/jma-center/vaac/index/html); HIGP MODIS
Thermal Alert System, Hawai'i Institute of Geophysics and Planetology
(HIGP), University of Hawaii at Manoa, 168 East-West Road, Post 602,
Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/).
Cleveland
Aleutian Islands, USA
52.825EN, 169.944EW; summit elev. 1,730 m
All times are local (= UTC - 10 hours)
Cleveland’s commonly observed activity consisting of short duration
explosions, such as those seen earlier in the year on 6 February 2006
(BGVN 31:01) and on 23 May 2006 (BGVN 31:07), continued during August
and October 2006. This report will cover the 24 August and 28 October
eruptions.
At 1955 on 24 August a brief eruption was seen by mariners on a passing
ship. The eruption was unconfirmed by satellite data. Video footage sent
to the Alaska Volcano Observatory (AVO) on 28 August showed that an ash
cloud rose to an approximate altitude of 3 km and produced minor
ashfall. Shortly after the eruption, minor steaming was observed from
the vent on additional footage. In response to the eruption, the AVO
raised the level of Concern Color Code from ‘unassigned’ to ‘Yellow’ on
7 September. A weak thermal anomaly in the summit crater was present in
subsequent satellite images.
Clouds obstructed visibility through most of September and October.
A pilot reported that a minor eruption started at 1345 on 28 October.
Satellite data confirmed the presence of an ash cloud drifting ENE of
the volcano. The height of the cloud was estimated at an altitude of 6
km using the satellite imagery. One pilot reported the plume top at an
altitude of 9 km. The AVO raised the alert level to ‘Orange’ during
28-29 October. On 30 October the AVO lowered the level to ‘Yellow’
because of no further evidence of activity.
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 1730-m-high Mount Cleveland 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 et al., 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: Alaska Volcano Observatory (AVO), a cooperative
program of the U.S. Geological Survey, 4200 University Drive, Anchorage,
AK 99508-4667, USA; 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 (URL: http://www.avo.alaska.edu/).
Fourpeaked
Alaska Peninsula, USA
58.770EN, 153.672EW; summit elev. 2,105 m
All times are local (= UTC - 9 hours [or 8 hours early April-late October])
Until the eruption of Fourpeaked on 17 September, evidence for eruptive
activity in the past 10,000 years was uncertain. The volcano is largely
glacier covered with only isolated outcrops (figure 16). This report
discusses the initial observation of plumes and subsequent activity
until the end of October 2006. Fourpeaked is in S Alaska ~ 320 km SW of
Anchorage. It is SW of the mouth of Cook Inlet and within NE Katmai
National Park (figure 17).
Figure 16. Fourpeaked volcano, the glacier-covered peak at the upper
left is one of a group of poorly known volcanoes NE of Katmai National
Park. In the foreground of this photo is Kaguyak caldera, which hosts a
2.5-km- wide lake. Pre-eruption photo at uncertain date taken by Chris
Nye (Alaska Division of Geological and Geophysical Surveys, Alaska
Volcano Observatory.
Figure 17. A map showing the location of Fourpeaked and Douglas
volcanoes, Cook Inlet, and adjacent settlements including the city of
Homer on the SW Kenai Peninsula. Created by Seth Snedigar and Janet
Schaafer, AVO-ADGGS.
On the evening of 17 September, AVO received several reports of two
discrete plumes rising from the Cape Douglas area. The plumes were
photographed at an unstated time on 17 September from the town of Homer
(figure 18). At this stage, neither Douglas nor Fourpeaked had devoted
seismic instruments.
Figure 18. A photograph of the eruption of Fourpeaked on 17 September
2006. The photo was taken from Main Street in Homer at an unstated time.
Copyrighted photograph by Lanny Simpson, Alaska High Mountain Images
(shown on AVO’s website).
Retrospective analysis of data from the NEXRAD Doppler radar in King
Salmon showed an unusual cloud starting at 1200 on 17 September. The
maximum cloud height determined by radar during the first hour of the
event was 6 km altitude. The radar return from the cloud continued until
at least 2145 (figure 19).
Figure 19. Image from the King Salmon NEXRAD weather radar showing the
volcanic cloud at Fourpeaked on 17 September 2006 at 1240 (2040 UTC). In
color the radar reflectivity ranges from light blue (low) to dark green
(moderate), which corresponds to greater numbers and/or sizes of
particles. It cannot be determined whether the signal is due to large
water droplets, ice particles, coarse-grained ash, or a mixture. Image
created by Dave Schneider, AVO/USGS, using data and software from the
NOAA National Climatic Data Center.
A cloud of sulfur dioxide gas was observed by colleagues at the Volcanic
Emissions Group at the University of Maryland Baltimore. They used data
collected at 1500 by the Ozone Monitoring Instrument (OMI) on NASA’s
Aura satellite (figure 20).
Figure 20. Image showing the total amount of sulfur dioxide over
Fourpeaked on 17 September 2006 as measured by the Ozone Monitoring
Instrument on NASA’s Aura satellite. Sulfur dioxide is displayed in
Dobson Units (DU, a measure of the number of molecules in a unit area of
the atmospheric column). Image created by the Volcanic Emissions Group
at the University of Maryland Baltimore County.
On the basis of the suite of visual, radar, and satellite observations,
all the 17 September clouds were inferred volcanic in origin. Although
satellite data did not detect ash during this event, AVO received
reports of a trace of ashfall at Nonvianuk Lake outlet (110 km WNW) and
near Homer (150 km NE). Field observers saw deep scouring of a glacier
flowing W from the summit, indicating flooding, probably from the 17
September event.
In the caption to a 20 September AVO photo by K.L. Wallace there was
noted a "continuous layer of discolored snow and ice above [~1 km
elevation,]~3,000 feet asl on the NE flank of Fourpeaked volcano (S of
Douglas volcano). Could possibly be ash from the 9/17/06 event."
Both fixed-wing and helicopter overflights in the Cape Douglas area on
20 September confirmed the source of volcanic activity to be Fourpeaked
volcano. AVO raised the Level of Concern Color Code from “Not Assigned”
to YELLOW on 20 September.
A 23 September observation flight conducted in relatively good weather
permitted the first look at the summit since the event of 17 September.
Observers saw a linear series of vents running N from the summit for
about 1 km. Most of these vents vigorously emitted steam and other
volcanic gases. Gas measurements indicated abundant quantities of sulfur
dioxide, hydrogen sulfide, and carbon dioxide. Thermal measurements of
up to 75EC were recorded at the vents, although steam was likely
obscuring hotter areas. Adjacent glacial ice had been disrupted and
showed signs of subsidence. Airborne gas measurements taken on 23, 24,
and 30 September again documented high emission rates of sulfur dioxide,
hydrogen sulfide, and carbon dioxide, and a distinct sulfur smell was
evident up to 50 km from the summit. An AVO status report on 3 October
noted that cloudy conditions had prevented visual or satellite
observations, but limited seismic data being received did not indicate
significant volcanic activity.
The AVO reported that volcanic unrest continued at Fourpeaked during 30
September-24 October. A seismometer installed on 25 September indicated
ongoing low-level seismicity. Due to the limited number of seismometers,
earthquake epicenters were not located. Emission rates of sulfur dioxide
were high during 4-10 October and on 27 October. Observations were
hindered due to cloud cover, but on 12 October AVO staff reported that
two prominent vents were emitting steam and gas. Figure 21 shows several
shots illustrating the enlarged opening in the ice on 15 October.
Figure 21. Photographs of the steaming vent area at Fourpeaked volcano
on 15 October 2006. Courtesy of Kate Bull (AVO-ADGGS).
On 20 October, field crews installed a web camera located 16 km (10
miles) N of Fourpeaked. Steam plumes originating from vents along the
summit were visible via the web camera on 27 and 30 October. Steaming
continued through at least 4 November (figure 22).
Figure 22. A 4 November 2006 photograph documenting steaming on the
uppermost section of the northern flank of Fourpeaked volcano. Courtesy
of Jennifer Adleman (AVO/USGS).
Geologic Summary. Poorly known Fourpeaked volcano in NE Katmai National
Park consists of isolated outcrops surrounded by the Fourpeaked glacier,
which descends eastward almost to the Shelikof strait. The orientation
of lava flows and extensive hydrothermal alteration of rocks near the
present summit suggest that it probably marks the vent of Fourpeaked
volcano (Swanson, in Wood and Kienle 1990).
Information Contacts: Alaska Volcano Observatory (AVO), a cooperative
program of the U.S. Geological Survey, 4200 University Drive, Anchorage,
AK 99508-4667, USA; 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 (URL: http://www.avo.alaska.edu/); S.A. Carn,
N.A. Krotkov, A.J. Krueger, and K. Yang, Joint Center for Earth Systems
Technology (JCET), University of Maryland Baltimore County (UMBC), 1000
Hilltop Circle, Baltimore, MD 21250, USA (Email: scarn@xxxxxxxx).
Soufriere Hills
West Indies
16.72EN, 62.18EW; summit elev. 915 m
All times are local (= UTC - 4 hours)
Since the 20 May 2006 dome collapse, the lava dome at Soufriere Hills
has continued to grow. Only weeks after the collapse, the alert level
was raised to 4 as a result of increased seismic activity. At
approximately 1300 on 30 June, the lava dome partially collapsed again,
producing pyroclastic flows that traveled E. According to the Washington
VAAC, a pilot reported an ash plume that reached ~ 3 km altitude and
drifted NW. At 1830 on 30 June, Montserrat Volcano Observatory (MVO)
indicated a second dome collapse that also generated ash plumes to an
altitude of 3.0-3.5 km (figure 23). According to MVO, on 27 June (prior
to the collapse on 30 June) the lava dome had an estimated volume of 27
million cubic meters.
Figure 23. A photo taken on 30 June 2006 of Soufriere Hills as viewed
from the Montserrat Volcano Observatory showing the first partial dome
collapse of the day. The partial collapse began just before 1300 local
time and lasted ~ 20 minutes, generating ash clouds to an altitude of ~
3.5 km that drifted WNW. Pyroclastic flows (left side of picture) were
confined to the Tar River valley and ultimately reached the sea. Most of
the lava dome remained intact. Photo courtesy of MVO.
On 7 July, the alert level was lowered from 4 to 3. Increased rockfall
activity and dome growth to the NE were observed on 21 July, and the
post-collapse dome developed an asymmetric profile owing to a blocky
spine on the NE. On 18 July the spine’s summit stood at ~ 895 m
elevation. As the dome continued to grow during July (figure 24), visual
observations revealed that the still intact blocky spine began leaning E.
Figure 24. A photo of Soufriere Hills taken on 25 July showing spines at
the summit of the lava dome as viewed from the NE. Photo courtesy Greg
Scott of Caribbean Helicopters.
During August the dome lost spines from its crest, giving it a more
symmetrical profile as it continued to grow E. Heightened activity
during the last week of August included an increase in seismicity and
pyroclastic flows. On 29 August, pyroclastic flows reached the Tar River
valley and generated a steam-and-ash cloud that reached an altitude of ~
9 km. Heavy rainfall produced mudflows around the base of the volcano.
At 0300 on 31 August, two vigorous ash-and-steam vents opened on the W
and N flanks of the dome (figure 25). The venting episode was audible at
times from the town of Salem and the surrounding areas. MVO noted the
continued dome growth and the opening of these vents when on 31 August
they raised the alert level to 4.
Figure 25. Photos showing activity at Soufriere Hills on 31 August 2006.
(top) Emissions from the vigorous new vent inside Gages wall (Gages
Mountain to the left of the vent and Chances Peak to the right).
(bottom) N-looking photo showing the N crater wall, lava dome, and the
new vigorous ash vent on the N side of the lava dome. Courtesy of MVO.
Heightened activity continued in September. The dome continued to
develop substantially with a majority of growth on the W side. The vents
that opened on 31 August remained active, with the vent above Gage’s
wall emitting a plume of hot gases and the N vent on the dome producing
mainly ash-and-steam (figure 26). The opening of these vents coincided
with high lava extrusion rates and consequent dome growth.
Figure 26. A photo showing lava-dome glow viewed from the S at MVO at
2200 on 7 September 2006. Incandescent rocks can be seen tumbling down
all flanks of the lava dome on this clear night. A faint glow is visible
from the very hot and active gas vent just inside the Gages wall (just
right of the dome in the picture). Photo courtesy of MVO.
At 0100 on 10 September, the vent above Gage’s wall became more vigorous
throughout the day, broadening the vent and generating a wide vertical
ash column. By 1300 the venting there became violent and explosive with
black jets of ash rising ~ 100 m. Pyroclastic flows traveled down the
Gages valley for ~ 1 km (figure 27). The vent formed a crater in the
Gages wall, reducing its height compared to that of Chances Peak by
30-50 m. By 11 September, pyroclastic flows from vent emissions had
ceased, but vigorous ash venting continued. At 0830 an overhanging lava
lobe that developed on the NE collapsed sending a pyroclastic flow
almost to the sea at the end of the Tar River valley.
Figure 27. A photo showing explosive ash venting from a spot above Gages
valley at 1530 on 10 September. Pyroclastic flows can be seen advancing
into Gages valley in the foreground. Photo courtesy of MVO.
Although volcanic tremor ended early on 16 September, an intense episode
of volcanic tremor lasting just half an hour started at 1400 on 19
September. It was accompanied by intense rockfall activity giving rise
to minor pyroclastic flows down the N and NE flanks of the lava dome. On
21 September the alert level was reduced to 3.
Geologic Summary. 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. English’s Crater, a 1-km-wide crater breached
widely to the E, 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/).
San Cristobal
Nicaragua
12.702EN, 87.004EW; summit elev. 1,745 m
All times are local (= UTC - 6 hours)
San Cristobal was last reported on in BGVN 28:10, covering intermittent
gas and ash emissions between August 2002 and September 2003. The
Instituto Nicaraguense de Estudios Territoriales (INETER) noted that low
seismicity and minor gas and ash emissions characterized the period from
October 2003 to June 2004.
On 7 June 2004 a lahar flowed more than 600 m. On 13 June 2004, an
eruption caused ash to fall in the communities of Las Rojas, El Chonco,
and El Viejo.
On 20 July 2004 at 1430, an M 4.3 earthquake occurred to the N of the
volcano at a depth of less than four km. The earthquake was felt in the
regions of Carlos Fonseca, Villa 15 de Julio, La Suiza, Las Rojas,
Mocoron, San Jose del Obraje, Santa Carlota, San Antonio, Rancheria, and
bordering regions. Some houses were damaged and the population was
alarmed. The earthquake was felt in Matagalpa and Ocotal, and San
Cristobal emitted abundant gases for the following two days. During the
rest of July, 95 aftershocks were registered; residents felt two more
earthquakes, which occurred on 23 and 30 July.
During August to early December 2004, minor seismicity and ash and gas
emissions were the norm. Ash explosions occurred on 3, 4, and 7
December. According to local people, ash fell in Chinandega and El Viejo.
The next available report discussed 16-22 November 2005. INETER detected
an increase in seismicity beginning on 19 November. Increased tremor was
interpreted as being related to gas and ash emissions. Ash fell W of the
volcano and near the town of Chinandega, ~ 15 km SW of the volcano. The
amount of tremor decreased later.
According to an Associated Press news report, explosions on 6 March 2006
produced columns of ash and gas that rose above the volcano. The
activity ceased by 8 March and there were no evacuations.
INETER noted that phreatomagmatic eruptions began at San Cristobal on 21
April 2006. Seismic tremor increased the same day around 1300. Small
explosions produced gas-and-ash plumes during 21-23 April that deposited
small amounts of ash in nearby towns.
Geologic Summary. The San Cristobal volcanic complex, consisting of five
principal volcanic edifices, forms the NW end of the Marrabios Range.
The symmetrical 1,745-m-high youngest cone, named San Cristobal (also
known as El Viejo), is Nicaragua’s highest volcano and is capped by a
500 x 600 m wide crater. El Chonco, with several flank lava domes, is
located 4 km to the west of San Cristobal; it and the eroded Moyotepe
volcano, 4 km to the NE of San Cristobal, are of Pleistocene age. Volcan
Casita, containing an elongated summit crater, lies immediately east of
San Cristobal and was the site of a catastrophic landslide and lahar in
1998. The Plio-Pleistocene La Pelona caldera is located at the eastern
end of the San Cristobal complex. Historical eruptions from San
Cristobal, consisting of small-to-moderate explosive activity, have been
reported since the 16th century. Some other 16th-century eruptions
attributed to Casita volcano are uncertain and may pertain to other
Marrabios Range volcanoes.
Information Contact: Virginia Tenorio, Emilio Talavera, and Martha
Navarro, Instituto Nicaraguense de Estudios Territoriales (INETER),
Apartado Postal 2110, Managua, Nicaragua (Email: ineter@xxxxxxxxxx; URL:
http://www.ineter.gob.ni/geofisica/); Associated Press, (URL:
http://www.ap.org/).
Montagu Island
South Sandwich Islands
58.42ES, 26.33EW; summit elev. 1,370 m
All times are local (= UTC - 2 hours)
Matthew Patrick reported that the month of October represents the 5-year
anniversary of the start of the still-ongoing eruption at Mount Belinda
on Montagu Island. The first satellite thermal alert for the volcano
occurred on 20 October 2001, and was the first definitive record of
historical volcanic activity on the island (BGVN 28:02) (Patrick and
others, 2005). The MODVOLC monitoring system uses MODIS (Moderate
Resolution Imaging Spectroradiometer) satellite data processed at the
University of Hawai’i-Manoa. Current MODVOLC results, shown in figure
28A, indicate more-or-less persistent activity throughout the 5-year
period, with radiant heat flux apparently peaking in late 2005 and early
2006.
Figure 28. Plots of MODVOLC data at Belinda volcano on Montagu Island
from 2001 to October 2006. (A) Chronological graph of radiant heat
output from Mount Belinda measured from satellite sensors. (B)
Chronological plot showing the distance of satellite-measured thermal
anomaly pixels from the Mount Belinda vent. Courtesy of HIGP Thermal
Alerts Team.
Landsat and ASTER (Advanced Spaceborne Thermal Emission and Reflection
Radiometer) imagery has shown that the eruption consisted of central
vent activity producing lava flows. Small-scale explosive activity has
also commonly blanketed the E side of the island. Three effusive events
have been observed in ASTER/Landsat imagery, with the most recent
(September-October 2005) producing a lava flow that traveled 3.5 km and
reached the sea to build a 500-m-wide delta of lava (BGVN 30:09 and 30:11).
Figure 28B shows relative location (distance from the vent) comparing
Mount Belinda’s vent with the locations of MODVOLC alert pixels. This
plot clearly shows longer flows during the September 2005 effusive
event. Following this period, there were several other long-distance
events. It is unclear if these reflect additional effusive events.
In addition, the first two effusive events observed in the ASTER/Landsat
images do not appear on the MODVOLC plot (figure 28B), due either to
cloud cover or their short flow lengths. Since the beginning of 2006, no
cloud-free ASTER images have been available.
Geographic terminology. The nomenclature of volcanic features on Montagu
Island, particularly in regard to Mount Belinda, has been quite
variable. Although the name Montagu has been applied to the major
volcanic edifice forming the island (LeMasurier and Thomson, 1990), the
name Mount Belinda has been variously applied to the entire volcano, the
currently active young cone on the northern side of the island, the
6-km-wide summit caldera, and a peak on the southern caldera rim that is
the island’s high point. In consultation with John Smellie of the
British Antarctic Survey, we have used Montagu to refer to the volcano
forming the island and Mount Belinda for the currently active cone.
References. LeMasurier, W.E., and Thomson, J.W. (eds.), 1990, Volcanoes
of the Antarctic Plate and Southern Oceans: Washington, D C: American
Geophysical Union, 487 p.
Patrick, M.R., Smellie, J.L., Harris, A.J.L., Wright, R., Dean, K.,
Izbekov, P., Garbeil, H., and Pilger, E., 2005, First recorded eruption
of Mount Belinda volcano (Montagu Island), South Sandwich Islands,
Bulletin of Volcanology, v. 67, no. 5, p. 415-422.
Geologic Summary. The largest of the South Sandwich Islands, Montagu
consists of a massive shield volcano cut by a 6-km-wide ice-filled
summit caldera. The summit of the 10 x 12 km wide island rises about
3000 m from the sea floor between Bristol and Saunders Islands. Around
90% of the island is ice-covered; glaciers extending to the sea
typically form vertical ice cliffs. The name Mount Belinda has been
applied both to the high point at the southern end of the summit caldera
and to the young central cone. Mount Oceanite, an isolated 900-m-high
peak with a 270-m-wide summit crater, lies at the SE tip of the island
and was the source of lava flows exposed at Mathias Point and Allen
Point. There was no record of Holocene or historical eruptive activity
at Montagu until MODIS satellite data, beginning in late 2001, revealed
thermal anomalies consistent with lava lake activity that has been
persistent since then. Apparent plumes and single anomalous pixels were
observed intermittently on AVHRR images during the period March 1995 to
February 1998, possibly indicating earlier unconfirmed and more sporadic
volcanic activity.
Information Contact: Matthew Patrick, Dept. of Geological and Mining
Engineering and Sciences, Michigan Technological University, 1400
Townsend Drive, Houghton, MI 49931, USA (Email: mpatrick@xxxxxxx; URL:
http://www.geo.mtu.edu/~mpatrick); HIGP MODIS Thermal Alert System,
Hawai'i Institute of Geophysics and Planetology (HIGP), University of
Hawaii at Manoa, 168 East-West Road, Post 602, Honolulu, HI 96822, USA
(URL: http://modis.higp.hawaii.edu/); John Smellie, British Antarctic
Survey, Natural Environment Research Council, High Cross, Madingly Road,
Cambridge CB3 0ET, United Kingdom (URL: http://www.anarctica.ac.uk/,
Email: jtsm@xxxxxxxxx).
Global Volcanism Program <http://www.volcano.si.edu/>
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