Bulletin of the Global Volcanism Network, February 2006

[Kristi Diller <Kristi.Diller@xxxxxxx>]

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Bulletin of the Global Volcanism Network, February 2006
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From: Ed Venzke <venzke@xxxxxxxxxxxxxx>


GVP Website <http://www.volcano.si.edu/>

Bulletin of the Global Volcanism Network
Volume 31, Number 2, February 2006

Manam (Papua New Guinea) Evacuees tempted to return; 27 February eruption
reached stratosphere
Langila (Papua New Guinea) Crater 2 continues activity in November 2005-January 2006
Garbuna (Papua New Guinea) Steam, small earthquakes, and weak tremor since
mid-November 2005
Pago (Papua New Guinea) Quiescent, with minor seismicity, through March 2006
Ulawun (Papua New Guinea) Ash emission on 1 March, more than four months after
last eruption
Rabaul (Papua New Guinea) Intermittent ash eruptions continue
Akan (Japan) Eruption on 21 March 2006 results in small ash fall
Atka (USA) Small steam-and-ash eruption on 23 February 2006 at Korovin
Yellowstone (USA) Low seismicity; ongoing ground-surface deformation
Tenerife (Canary Islands) 2004 seismic crisis; January 2005 escalation in
monitored parameters at Tiede

Editors: Rick Wunderman, Catherine Galley, Edward Venzke, and Gari Mayberry
Volunteer Staff: Robert Andrews, Jerome Hudis, Veronica Bemis, Jackie Gluck, and
Stephen Bentley


Manam
Northeast Papua New Guinea
4.10°S, 145.061°E; summit elev. 1,807 m
All times are local (= UTC + 10 hours)

	Manam currently represents one of Papua New Guinea's most potent volcanic
crises. It erupted several times during October-December 2004 and 
January 2005 (BGVN 29:10, 29:11). According to the Rabaul Volcano Observatory
(RVO), the eruption on the evening of 27 January 2005 (BGVN 30:02) 
was the most severe activity during the current eruption period; 14 people were
injured and one person killed at Warisi village (see villages in 
plan views of island, BGVN 30:02).
	This report discusses the mild outbursts during April-May 2005, and the strong
eruption on 27 February 2006. The latter eruption cloud rose 
into the stratosphere, ascending to a satellite-estimated altitude of 19 km.
After a 9 March eruption, the press reported one elderly person 
missing. An eruption during the reporting interval dropped tephra on a village,
forcing 49 residents to flee.
	Generally mild behavior during April through mid-February 2005. Throughout
April 2005, both summit craters released occasional pale gray to 
brown ash clouds to a few hundred meters above the summit before being blown SW,
W, and NW, resulting in fine ashfall. Occasional low rumbling 
and roaring noises from Southern Crater were heard on 23 April and 29 April. A
weak-to-moderate glow accompanied by projections of incandescent 
lava fragments was visible on 28 and 30 April. There were no audible noises and
no night-time glow from the Main Crater. During the month, 
seismicity was at low-moderate levels, and tremor was occasional and weak. The
daily number of low-frequency earthquakes ranged between 700 and 
1,350.
	A pilot reported a Manam eruption on 13 June 2005 at 0445 UTC. In addition,
Darwin Volcanic Ash Advisory Centre (VAAC) reported ash plumes 
visible on satellite imagery during 16-17 June, 30 June, 1-2, 19, and 20 July.
Imagery indicated that Manam's 19 July ash extended SW. In all 
instances, the heights of the plumes were not reported.
	According to RVO, on 15 August, ash discharged from Southern Crater; otherwise
during 15-21 August, comparatively weak volcanism prevailed and 
the Alert Level was reduced to Level 1. The Darwin VAAC reported a low-level
plume on 22 August imagery. Mild eruptive activity continued during 
22-28 August, with occasional emissions of weak-to-moderate ash plumes on
several days. The ash clouds emitted on 22 and 26 August rose several 
hundred meters above the volcano's crater and drifted NW, depositing ash in
areas between the towns of Jogari and Kuluguma, and beyond to Boisa 
Island.
	During September weak emissions of diffuse white-gray ash clouds continued from
Main Crater. On 17 September, the ash clouds increased slightly 
in volume and were blown to the NW part of the island. No glow was observed at
night and technical problems thwarted seismic recording.
	On 1 October, a pilot observed ash from Manam below ~ 3 km altitude extending
NW. Ash was not visible on satellite imagery. During 3-9 October 
RVO reported that ash emissions continued from Main Crater. Ash clouds rose to
low levels and drifted NW, depositing ash in downwind areas. RVO 
learned that ash was visible on satellite imagery at ~ 3 km altitude.
	During the last 10 days of October, low-level eruptive activity continued at
Manam with plumes visible on satellite imagery extending NW. Manam 
remained at Alert Level 1, indicating low levels of activity from August 2005
through December 2005.
	During January 2006, mild eruptive activity occurred with occasional ash
emissions during 1-4 January, and dull incandescence was visible on 1 
and 2 January. Gas was emitted from Southern Crater during 1-7 January.
Seismicity was at low levels during January 2006.
	Large eruption of 27-28 February 2006. A large eruption began on 27 February
around 1733 from Manam's Southern Crater. According to Andrew 
Tupper of the Darwin VAAC, satellite imagery showed an umbrella cloud above the
volcano and a strong hot spot. The edges of the ash cloud were 
ice-rich and the eruption-plume height appeared to be about 19 km based on a
warm-temperature anomaly in the middle of the cloud indicating 
stratospheric intrusion (figure 1).

Figure 1. An MTSAT image of the eruption cloud over Manam captured at
approximately 2145 (1145 UTC) on 27 February 2006, showing a very strong 
hot spot. The image contains an 11-12 μm enhancement. In past Manam eruptions
where there has been a similar white halo around the thinning 
umbrella cloud, the cloud has later been verified as having a large ice and SO2
content (as well as fine ash and other volcanic aerosols). The 
warm temperature mass persisted for 2-3 hours, suggesting a prolonged,
continuing eruption. Courtesy of Andrew Tupper.

	Fred Prata processed Manam ash cloud data using the Atmospheric Infrared
Sounder (AIRS, which uses a grating spectrometer on the Aqua 
satellite). Prata produced the atmospheric SO2 analyses in the sequential images
in figures 2 and 3, which show areas of greatest concentration 
displaced ~ 70 and ~ 100 km W of Manam, respectively. At the bull's-eye centers,
figure 2 portrays a somewhat higher peak for the product of 
concentration and path length (milli-atmosphere-centimeter values), ~ 60,
compared to figure 3, which indicates ~ 50. Figure 3 also contains a 
much larger low-value area, consistent with post-eruption dispersal. The 27
February eruption clearly emitted considerable SO2, with the two 
analyses on figures 2 and 3 yielding respective assessed masses of 0.027 Tg and
0.054 Tg of SO2.

Figure 2. An AIRS image indicating the Manam ash plume's SO2 content at 1559 UTC
on 27 February 2006. The area of detected SO2 coverage reported 
for this image was 59,173 km2. Further details about the image appear in the
text on the image. Courtesy of Fred Prata.

Figure 3. The Manam ash plume's SO2 content at 0417 UTC on 28 February 2006. The
area of detected SO2 coverage reported for this image was 
155,023 km2. Further details about the image appear in the text on the image.
Courtesy of Fred Prata.

	RVO reported that the strong phase of the eruption declined around 0030 on 28
February. Earlier, during the height of the activity, 
incandescent lava fragments were thrown 700-800 m high above the volcano, but
ejection heights later decreased to 200-300 m. Ash was deposited 
on the E part of the island and lava flowed down the SW valley. Field
inspections on 28 February confirmed that a lava flow traveled down the SW 
valley to about 600 m elevation, a pyroclastic flow traveled down the same
valley to about 500 m elevation, and the maximum ash thickness on the 
E part of the island was about 7-8 cm. Later, on 7 March, it was determined that
pyroclastic flows had also traveled down the SE valley and that 
scoria and ashfall affected the area between Warisi and Bokure 1.
	After mid-February, Manam's seismic station and radio communication with the
observer at Bogia had both ceased operating. RVO noted that the 
island had been inhabited by about 300 former residents who returned to the
island after evacuating following the 27 January 2005 eruption. (A 
March press report, below, indicated over 2,000 people on the island, including
people who had previously refused to leave.) The mid-February 
Alert Level at the volcano was at Level 2. By 1 March, only gas was emitted from
Southern Crater, no noises were heard, and weak incandescence 
was visible around the vent. Occasionally, incandescent lava fragments were
thrown 100-150 m above the vent and fell into the crater. Main 
crater emitted occasional ash clouds, and then gas later in the day.
	Based on information from RVO, the Darwin VAAC reported that a minor explosion
occurred at Manam on 6 March. The height of the resultant plume 
was not reported and ash was not visible on satellite imagery. A report faxed
from RVO said that during 9-11 March, both summit craters at Manam 
released gas, and seismicity then stood at moderate levels.
	According to RVO, a recent (ambiguously disclosed) eruption had endangered
about 49 people (mostly women) pelted by tephra who ran for their 
lives to take shelter at Dangale village to the N. The RVO team called the
evacuation centers on the main island at Mangem and Asaruba where 
people from villages on the E part of the island were located and advised them
not to go to the island unless clearance was given from the 
authorities. RVO warned of possible mudflows during heavy rainfall,
moderate-to-high levels of seismicity, and sporadic explosions.
	Press reports. On 15 March 2005 The National newspaper (online edition)
reported that "[a]uthorities dispatched a vessel, the Motuan Chief, to 
the island [on the afternoon of 14 March] to evacuate over 2,000 islanders who
had refused to move earlier or who had returned recently. A 
sudden explosion last Thursday [9 March] has left an elderly [man] from Wirisi
village missing, believed covered by the pyroclastic [material] 
from the eruption . . .. Authorities . . . reported several houses burnt down
from the hot emissions while others collapsed under the weight of 
ash dust and pyroclastic [material] . . .. [Q]uite a number of resettled people
. . . have moved back to the island after an earlier evacuation 
and now are pleading to be evacuated back to the mainland following the recent
volcanic activities.
	"Some people from Warisi village who were at the [evacuation] centres on the
mainland travelled back to Manam last Thursday to gather food from 
their gardens. They were to return to the [evacuation] centre but unfortunately
their boat . . . was destroyed by rocks from the eruption."
	A January 2006 article in the PNG Post-Courier (and online in the Pacific
Islands Report) noted that the Red Cross and Red Crescent Societies 
had spent about US $377,000 on emergency aid for resettlement camps on the main
island. The article noted that aid societies had helped the 
government, funding 350 houses constructed of bush-materials at the camps since
October 2004. Those camps (also termed care centers) include 
Mangem, Asuramba (Asaruba?), and Potsdam.
	Background. The 10-km-wide island of Manam, lying 13 km off the northern coast
of mainland Papua New Guinea, is one of the country's most 
active volcanoes. Four large radial valleys extend from the unvegetated summit
of the conical 1807-m-high basaltic-andesitic stratovolcano to 
its lower flanks. These "avalanche valleys," regularly spaced 90 degrees apart,
channel lava flows and pyroclastic avalanches that have 
sometimes reached the coast. Five small satellitic centers are located near the
island's shoreline on the northern, southern and western sides. 
Two summit craters are present; both are active, although most historical
eruptions have originated from the southern crater, concentrating 
eruptive products during the past century into the SE avalanche valley. Frequent
historical eruptions have been recorded at Manam since 1616. A 
major eruption in 1919 produced pyroclastic flows that reached the coast, and in
1957-58 pyroclastic flows descended all four radial valleys. 
Lava flows reached the sea in 1946-47 and 1958.
	Information Contacts: Ima Itikarai, Rabaul Volcano Observatory (RVO), P.O. Box
386, Rabaul, Papua New Guinea; Andrew Tupper, Darwin Volcanic 
Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional
Office, PO Box 40050, Casuarina, Northern Territory 0811, 
Australia (URL: http://www.bom.gov.au/info/vaac/); Bonney Bonsella and Thomas
Kilala, The National Online, Lot 13 Section 38, Waigani Drive 
Hohola, PO Box 6817 Boroko, National Capital District, Papua New Guinea (URL:
http://www.thenational.com.pg/); PNG Post-Courier; Pacific Islands 
Report.


Langila
New Britain, SW Pacific
5.525°S, 148.42°E; summit elev. 1,330 m

	Vulcanian eruptions continued at Langila's Crater 2 during 21-27 November 2005,
with a slight increase in the level of activity compared to the 
previous week. The increase in activity was marked by light to dark gray ash
emissions that sometimes rose to heights between 1 and 2 km above 
the summit crater (7,650-10,900 feet altitude). The ash clouds drifted W, SW,
SE, and NW, depositing ash in those areas. Incandescence and 
projections of volcanic material were visible at the volcano during the nights
of 21, 23, and 25-27 November along with weak to loud noises. 
Crater 3 was quiet during the report period. Seismicity was at low-to-moderate
levels, consisting of low-frequency earthquakes associated with 
the Vulcanian activity and periodic volcanic tremor.
	A slight increase in vulcanian activity occurred at Langila's Crater 2 during
1-15 January. The increase was characterized by nearly continuous 
ash emissions that rose to 1-2 km above the summit (7,650-10,900 feet altitude)
and drifted WSW. Occasionally during the report period observers 
noted loud noises, incandescence, and weak emissions of glowing lava fragments.
Crater 3 continued to be quiet during this period.
	Background. Langila, one of the most active volcanoes of New Britain, consists
of a group of four small overlapping composite 
basaltic-andesitic cones on the lower eastern flank of the extinct Talawe
volcano. Talawe is the highest volcano in the Cape Gloucester area of 
NW New Britain. A rectangular, 2.5-km-long crater is breached widely to the SE;
Langila volcano was constructed NE of the breached crater of 
Talawe. An extensive lava field reaches the coast on the north and NE sides of
Langila. Frequent mild-to-moderate explosive eruptions, sometimes 
accompanied by lava flows, have been recorded since the 19th century from three
active craters at the summit of Langila. The youngest and 
smallest crater (number 3 crater) was formed in 1960 and has a diameter of 150 m.
	Information Contacts: RVO and Darwin VAAC (see Manam).


Garbuna Group
New Britain, SW Pacific
5.45°S, 150.03°E; summit elev. 564 m

	Garbuna volcano's first historically witnessed eruption in October 2005 was
reported in BGVN (30:11) and by 14 November the mountain was 
climbed. Since that time two reports from the Rabaul Volcano Observatory (RVO),
one dated 21-27 November 2005 and the other 1-15 January 2006 
both noted weak-to-moderate releases of white vapor from the two vents on the
summit. Both reports also indicated that there were no noises or 
glow accompanying the emissions and that seismic activity was low.
	The November 2005 report stated that on some days plumes rose vertically a few
hundred meters and drifted variably to the NW, W, SW, and 
occasionally SE. It also noted that the distinct moderate tremor recorded in the
previous weeks at the summit ceased by 15 November although 
weak tremor was recorded on some days, as were small high-frequency earthquakes
numbering one to six per day.
	RVO's January report described weak to moderate volumes of white vapor released
from the two summit vents. The accompanying seismicity was low 
and dominated by occasional low-frequency earthquakes, as indicated by the two
stations located 5-6 km E and SW of the summit.
	Background. The basaltic-to-dacitic Garbuna volcano group consists of three
volcanic peaks, Krummel, Garbuna, and Welcker. They are located 
along a 7-km N-S line above a shield-like foundation at the southern end of the
Willaumez Peninsula. The central and lower peaks of the 
centrally located 564-m-high Garbuna volcano contain a large vegetation-free
area that is probably the most extensive thermal field in Papua New 
Guinea. A prominent lava dome and blocky lava flow in the center of thermal area
have resisted destruction by thermal activity, and may be of 
Holocene age. The 854-m-high Krummel volcano at the S end of the group contains
a summit crater, breached to the NW. The highest peak of the 
Garbuna group is 1005-m-high Welcker volcano, which has fed blocky lava flows
that extend to the eastern coast of the peninsula. The last major 
eruption from both it and Garbuna volcanoes took place about 1800 years ago. The
first historical eruption of the complex took place at Garbuna 
in October 2005.
	Information Contacts: RVO and Darwin VAAC (see Manam).


Pago
New Britain, SW Pacific
5.58°S, 150.52°E; summit elev. 742 m

	Since 18 September 2005 (BGVN (30:09) through 31 March 2006, Pago has remained
quiet. Only small volumes of diffuse white vapor released from 
all vents have been observed, with no noises or glow. Between 16 February and 31
March low-frequency earthquakes were recorded at a rate of 1-4 
per day. The daily number of high-frequency events during that period ranged
from 7 to 26.
	Background. Pago is a young post-caldera cone that was constructed within the
5.5 x 7.5 km Witori caldera. Extensive pyroclastic-flow deposits 
are associated with formation of the caldera about 3300 years ago. The gently
sloping outer flanks of Witori volcano consist primarily of 
dacitic pyroclastic-flow and airfall deposits produced during a series of five
major explosive eruptions from about 5600 to 1200 years ago. The 
Buru caldera, which may have formed around the same time, cuts the SW flank of
Witori volcano. The post-caldera cone of Witori, Mount Pago, may 
have formed less than 350 years ago. Pago has grown to a height above that of
the Witori caldera rim. A series of ten dacitic lava flows from 
Pago covers much of the caldera floor. The youngest of these was erupted during
2002-2003 from vents extending from the summit nearly to the NW 
caldera wall.
	Information Contacts: RVO and Darwin VAAC (see Manam).


Ulawun
New Britain, SW Pacific
5.05°S, 151.33°E; summit elev. 2,334 m
All times are local (= UTC + 10 hours)

	Ulawun remained relatively quiet from mid-September 2005, the date of our last
report (BGVN 30:09), until 1-2 March 2006 when strong, 
forcefully expelled "gray-blue emissions" were observed from the main crater.
There may also have been incandescence at the base of the plumes. 
There were no emissions from the NW vent. Small, felt earthquakes occurred and
the sound of roaring was heard by nearby villagers. According to 
the Darwin VAAC, RVO reported that ash reached ~ 3 km (10,000 ft) altitude on 1
March. However, ash was not visible on satellite imagery.
	Background. The symmetrical basaltic-to-andesitic Ulawun stratovolcano is the
highest volcano of the Bismarck arc, and one of Papua New 
Guinea's most frequently active. Ulawun, also known as the North Son, rises
above the N coast of the island of New Britain across a low saddle 
NE of Bamus volcano, the South Son. The upper 1,000 m of 2,334-m-high Ulawun is
unvegetated. A prominent E-W-trending escarpment on the S may be 
the result of large-scale slumping. Satellitic cones occupy the NW and eastern
flanks. A steep-walled valley cuts the NW side of Ulawun, and a 
flank lava-flow complex lies to the S of this valley. Historical eruptions date
back to the beginning of the 18th century. Twentieth-century 
eruptions were mildly explosive until 1967, but after 1970 several larger
eruptions produced lava flows and basaltic pyroclastic flows, greatly 
modifying the summit crater.
	Information Contacts: RVO and Darwin VAAC (see Manam).


Rabaul
New Britain, SW Pacific
4.271°S, 152.203°E; summit elev. 688 m
All times are local (= UTC + 10 hours)

	The previous report on the activity of the Tavurvur cone at Rabaul (BGVN 30:08)
covered the period through 12 September 2005. According to the 
RVO report of 10 October 2005 Tavurvur continued to erupt with discrete
ejections of light to dark gray ash clouds with high ash content. The 
ejections occurred at irregular, but sometimes frequent intervals. Discrete,
convoluted explosion clouds were also observed. Ash plumes from the 
eruptive activity rose between 800 to 1,500 m before being blown variably to the
E, W, and S during the beginning of the 3-9 October 2005 period 
and later in that period towards the NW. Ash fell in the downwind areas.
Occasionally roaring and rumbling noises were heard. Projections of 
glowing lava fragments showering the flanks of Tavurvur were visible at night
during strong explosions.
	Seismic activity was at moderate-to-high levels with most earthquakes
associated with ash emissions and explosions. No high frequency 
explosions were reported and ground deformation measurements showed a general
trend towards a slight deflation.
	The RVO report dated 28 November 2005 stated that as of 20 November ash
emission from the volcano ceased with only very small traces of white 
vapor being released from the now silent vent and other spots on the summit
area. During 21-27 November seismicity was very low and 
ground-deformation measurements showed some small degree of inflation.
	The volcano remained quiet until the middle of January 2006 when activity
resumed. Single ash emissions occurred at 0722 on 10 January, 0854 on 
the 11th, 1638 on the 12th, and 2100 on the 15th of the month (all local dates
and times). The emissions consisted of thick gray ash clouds that 
rose more than 1.5 km above the summit and then drifted E. The ash emissions on
the 12th and 15th lasted three minutes. Seismic activity was at 
a low level with small, low-frequency earthquakes beginning to occur on 7
January 2006. The daily totals fluctuated between zero and seven per day.
	RVO reported that during 30 January to 15 February, Rabaul caldera's Tavurvur
cone continued to be relatively quiet. Variable amounts of gas 
were emitted from an active fumarole at the summit area on the upper part of the
W flank. An average sulfur-dioxide flux of 200 metric tons per 
day was recorded and seismicity was at low levels. According to the Darwin VAAC,
ash from Rabaul was visible on satellite imagery at a height of 
~ 3.7 km (12,100 ft) altitude on 17 February.
	Background. 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 E, where its floor is flooded by 
Blanche Bay; it 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 N. Three small stratovolcanoes lie outside
the N 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: RVO and Darwin VAAC (see Manam).


Akan
Hokkaido, Japan
43.384°N, 144.013°E; summit elev. 1,499 m
All times are local (= UTC + 9 hours)

	Yukio Hayakawa of Gunma University notified the Bulletin staff that a very
small eruption occurred on the morning of 21 March 2006 at Me-Akan. 
Tremor first started at 0628, followed by the eruption 0637. The Japan
Meteorological Agency (JMA) issued a second-level alert at 0643. Ash was 
found on the snow at 10 km SE of the volcano. No towns or villages were
threatened as the volcano is in a remote location, although there are 
some hot-spring hotels in the area. Me-Akan erupted in 1996 and 1998 from within
the summit crater, but the March 2006 eruption was from the NE 
flank.
	According to a news report by Reuters, a JMA official stated that "gray ash was
discovered on the snow around the summit, but no movement of 
lava was detected, and we do not think a large eruption is likely."
	Background. Akan is a 13 x 24 km, elongated caldera that formed more than
31,500 years ago immediately SW of Kutcharo caldera. Growth of four 
post-caldera stratovolcanoes, three at the SW end of the caldera, and the other
at the NE side, have restricted the size of the caldera lake. 
The 1-km-wide Nakamachineshiri crater was formed during a major
pumice-and-scoria eruption about 13,500 years ago. Of the Holocene volcanoes of 
the Akan volcanic complex, only the Me-Akan group, east of Lake Akan, has been
historically active, producing mild phreatic eruptions since the 
beginning of the 19th century. Me-Akan is composed of 9 overlapping cones. The
main cone of Me-Akan proper has a triple crater at its summit. 
Historical eruptions at Me-Akan have consisted of minor phreatic explosions, but
four major magmatic eruptions including pyroclastic flows have 
occurred during the Holocene.
	Information Contacts: Yukio Hayakawa, Gunma University, 4-2 Aramaki-machi,
Maebashi City, Gunma, 371-8510, Japan (Email: hayakawa@xxxxxxxxxxx); 
Japan Meteorological Agency, Kishocho-881, 3-4 Ote-machi, Chiyoda-ku, Tokyo
100-0004, Japan; Reuters Foundation Alert Net (URL: 
http://www.alertnet.org/).


Atka
Aleutian Islands, USA
52.381°N, 174.154°W; summit elev. 1,533 m
All times are local (= UTC - 9 hours)

	The Alaska Volcano Observatory (AVO) received a report that a sudden minor
steam-and-ash eruption occurred at Korovin around 1900 on 23 
February 2006. Korovin is an active volcano of the larger Atka volcanic center
(or complex) in the central Aleutian islands, ~ 184 km E of Adak 
island and ~ 600 km W of Unimak island, and 1,760 km SW of Anchorage. According
to residents of Atka village near Korovin, the initial ash burst 
rose to an altitude of ~ 2.4 km and drifted E. It was followed by several
smaller ash-and-steam bursts.
	No ashfall was reported in Atka village, nor were there reports of accompanying
volcanic odors, earthquakes, or larger volcanic explosions. 
Satellite images of the volcano did not clearly show the presence of ash or any
thermal anomalies. But, on the morning of 24 February 2006 (the 
morning after the eruption) the volcano was still steaming with some vigor.
During the period 25 February-4 March 2006, cloud cover prohibited 
satellite views of the volcano, and no unusual seismicity registered.
	Although Korovin was not monitored by a standard AVO seismic network, Atka
village hosts a seismic station operated by the Alaska Earthquake 
Information Center. That station recorded several increases in seismicity prior
to the 23 February eruption. Distinct seismic signals indicating 
unrest were recorded on 17, 18, 21, and 22 January 2006. The later day brought
an unusually sustained, 11-minute-long signal.
	After 22 February, seismicity decreased and distinct seismic signals like those
recorded earlier were not detected. An 8 March report noted 
that Korovin's rate of occurrence of micro-earthquakes had stabilized and then
declined, and "it has been close to background levels for the 
past week."
	For some days after 22 February, clouds obscured satellite views of the
volcano. However, on the 22nd an aviator reported that, although the 
summit area was obscured by clouds, no signs of ashfall on the flanks or any
steam plume was seen. On 23 February, observers in the village of 
Atka noted the lack of obvious signs of activity. Prior to the ash-and-steam
eruption on the 23rd, AVO received no short-term reports of 
precursory volcanism to indicate an imminent eruption.
	Seismicity at Korovin remained slightly above background levels during 24
February to 3 March 2006. Clouds continued to mask satellite views of 
the volcano, and AVO received no further reports of activity.
	Background. The largest volcanic center in the central Aleutians, Atka consists
of a central shield and Pleistocene caldera ringed by 7 or 8 
satellitic volcanoes. The most prominent of these are the post-caldera cones of
Korovin, Konia, Kliuchev, and Sarichef, some of which have been 
active in historical time. Korovin, the most frequently active volcano of the
Atka volcanic center, contains a 1,533-m-high, double summit with 
two craters located along a NW-SE line. The NW summit has a small crater, but
the 1-km-wide crater of the SE cone has an unusual, open 
cylindrical vent of widely variable depth that sometimes contains a crater lake
or a high magma column (Marsh; in Wood and Kienle, 1990). A 
fresh-looking cinder cone lies on the flank of partially dissected Konia
volcano. Sarichef has a symmetrical profile, and Korovin and Kliuchef 
are relatively uneroded and the source of most if not all historical eruptions.
Hot springs and fumaroles are located on the flanks of Mount 
Kliuchef and in a glacial valley SW of Kliuchef.
	Information Contacts: Alaska Volcano Observatory (AVO), a cooperative program
of the U.S. Geological Survey, 4200 University Drive, Anchorage, 
AK 99508-4667, USA (URL: http://www.avo.alaska.edu), Geophysical Institute,
University of Alaska, P.O. Box 757320, Fairbanks, AK 99775-7320, 
USA, and Alaska Division of Geological & Geophysical Surveys, 794 University
Ave., Suite 200, Fairbanks, AK 99709, USA.


Yellowstone
Wyoming, USA
44.43°N, 110.67°W; summit elev. 2,805 m
All times are local (= UTC - 7 hours)

	According to the Yellowstone Volcano Observatory (YVO), during February 2006
there was relatively low seismicity, with 82 reported earthquakes 
in the region. The largest of these was on 25 February, M 3.1, located near the
N caldera rim (~ 10 km SSW of Canyon Junction). None of these 
earthquakes were reported as felt. Our previous report discussed elevated
temperatures of the ground and increased hydrothermal effects at 
Norris hot springs in 2003 (BGVN 28:07). Norris also represents a frequent
epicentral area for earthquakes inside the caldera. In 2002, for 
example, there were more than 2,350 earthquakes detected at Yellowstone,
including over 500 triggered by the November 2002, M 7.9 Denali 
earthquake. Seismicity during April 2005-April 2006 was comparatively low.
Figure 4 plots quarterly earthquakes (  M 1.5) during 1974-2004 on a 
histogram. Figure 5 depicts earthquake swarms during 1985, 1995, and 2004.

Figure 4. A plot of recorded earthquakes (³ M 1.5) at Yellowstone from 1974
through 2004 (bars, left-hand scale: each bar represents the sum of 
the earthquakes of stated size per quarter (~ 90 days)). The curving solid line
shows the cumulative number of earthquakes for the thirty-year 
period (right-hand scale). Estimates of mean caldera uplift and subsidence are
shown as a dashed-and-dotted line with no scale. Note that this 
figure stopped in 2004 and does not depict some of the stronger deformation seen
in radar and later GPS data (discussed below). Courtesy of YVO 
(after a figure by Waite and Smith, 2002).

Figure 5. A map of Yellowstone caldera and National Park with circles indicating
located earthquakes (³ M 1.5) from the swarm of 1985 (westerly 
cluster), 1995 (easterly cluster with substantial events inside the caldera),
and 2004 (smaller cluster to the N of the other two). Courtesy of YVO.

	Satellite radar created an interferogram of the caldera region (basically, a
depiction of the vertical offset determined by satellite radar 
during 1996-2000). The interferogram portrayed vertical displacement as a large
bull's-eye shape (figure 6), and indicated 12.5 cm of uplift 
centered in the northern portion of the caldera ~ 25 km NW of Yellowstone Lake.

Figure 6. A radar interferogram of the Yellowstone caldera region (after Wicks
and others, 1998; 2006). This image of vertical ground 
deformation was created using data from several satellite passes during 1996
through 2000. The image shows 12.5 cm of uplift centered within the 
northern end of Yellowstone caldera (black dotted line), about 10 km S of Norris
hot springs. Each full spectrum of color (from red to purple) 
represents ~ 28 mm of uplift. The area of uplift is approximately 35 km x 40 km
in size. Courtesy of YVO-USGS.

	In response to increased heat and steam emissions in parts of Norris geyser
basin, a temporary, five-station GPS network was installed in that 
area in 2003. The network was installed by a UNAVCO engineer, University of Utah
students and faculty, and National Park Service scientists as 
part of a monitoring effort by YVO. Permanent station NRWY currently resides
there (figure 7).

Figure 7. GPS stations at Yellowstone caldera, including those both existing
(light triangles) and planned (dark triangles). The irregular loops 
near stations OFW2 and WLWY outline the two active resurgent domes within the
0.64 million-year-old Yellowstone caldera (the Mallard Lake dome 
and the Sour Creek dome, to the W and E, respectively). The figure also includes
Yellowstone caldera topographic margins (T), Yellowstone Lake 
(L), the National Park boundary (PB), and some state boundaries. Courtesy of
YVO-USGS.

	Movement near the N end of Yellowstone Lake was measured by GPS at station LKWY
during 1997 to late 2005 (figure 8). The N-S movement (top 
panel) shown in the past year consisted of displacement of 10-15 mm southward.
This N-S movement was somewhat stronger and more protracted than 
in the earlier parts of the GPS data. The E-W movement (middle panel) was
comparatively steady and unbroken over the past 6 years or more, 
directed westward. Over the past 9 years, the overall E-W motion was ~ 15 mm
westward. The vertical motion (lower panel) was negative 
(subsidence) during 1997 to mid-2004. After that, station LKWY moved sharply
upward, rising ~ 80 mm in the last year and a half. Caldera systems 
frequently undergo ground displacements similar to those observed at Yellowstone
without progressing to eruptive activity.

Figure 8. Relative movement of GPS station LKWY (located in the central part of
the caldera, at the N end of Yellowstone Lake) recorded during 
1997 to late 2005. The top panel shows N-S movement, the middle, E-W movement,
and the bottom, vertical movement. During 2001-2004 station LKSY 
moved downward (subsided) on the order of 20 mm. After mid-2004, LKWY moved
upward ~ 80 mm. Courtesy of YVO-USGS.

	Much of the history of older calderas that preceded Yellowstone are buried in
the subsurface to the W, and a drilling proposal for that region 
is under development. "Hotspot," the Snake River Scientific Drilling Project,
announced an inter-disciplinary workshop with that goal, to be 
held 18-21 May 2006 and focused on issues central to a new intermediate-depth
drilling program in the Snake River Plain of S Idaho, USA. That 
region provides a record of inferred mantle plume volcanism in an
intra-continental setting. Because it is young and tectonically undisturbed, 
the complete record of volcanic activity can be sampled only by drilling. The
preliminary plan was to drill and core 4-6 holes along the axis of 
the E and W Snake River Plain.
	References: Wicks, C., Thatcher, W., and Dzurisin, D., 1998, Migration of
fluids beneath Yellowstone Caldera inferred from satellite radar 
interferometry: Science, v. 282, p. 458-462.
	Wicks, C., Thatcher, W., Dzurisin, D., and Svarc, J., 2006 (in press), Uplift,
thermal unrest, and magma intrusion at Yellowstone Caldera, 
observed with InSAR:  Nature.
	Waite, G.P., and Smith, R.B., 2002, Seismic evidence for fluid migration
accompanying subsidence of the Yellowstone caldera: Journal of 
Geophysical Research, v. 107, p. 2177-2192.
	Background. The Yellowstone Plateau volcanic field developed through three
volcanic cycles spanning two million years that included some of the 
world's largest known eruptions. Eruption of the more than 2,450 cu km
Huckleberry Ridge Tuff about 2.1 million years ago created the more than 
75-km-long Island Park caldera. The second cycle concluded with the eruption of
the Mesa Falls Tuff around 1.3 million years ago, forming the 
16-km-wide Henrys Fork caldera at the western end of the first caldera. Activity
subsequently shifted to the present Yellowstone Plateau and 
culminated 640,000 years ago with the eruption of the more than 1,000 cu km Lava
Creek Tuff and the formation of the present 45 x 85 km caldera. 
Resurgent doming subsequently occurred at both the NE and SW sides of the
caldera and voluminous (1,000 cu km) intracaldera rhyolitic lava flows 
were erupted between 150,000 and 70,000 years ago. No magmatic eruptions have
occurred since the late Pleistocene, but phreatic eruptions took 
place near Yellowstone Lake during the Holocene. Yellowstone is presently the
site of one of the world's largest hydrothermal systems including 
Earth's largest concentration of geysers.
	Information Contacts: Yellowstone Volcano Observatory, a cooperative
arrangement that includes Jacob B. Lowenstern, U.S. Geological Survey, 345 
Middlefield Road, Menlo Park, CA 94025, USA; Robert B. Smith, Department of
Geology and Geophysics, University of Utah, Salt Lake City, UT 
84112, USA; and Henry Heasler, National Park Service, P.O. Box 168, Yellowstone
National Park, WY 82190-0168, USA (URL: 
http://volcanoes.usgs.gov/yvo/).


Tenerife
Canary Islands, Spain
28.271°N, 16.641°W; summit elev. 3,715 m

	Juan Carlos Carracedo notified Bulletin editors that seismic activity in
Tenerife during April and May 2004 was not followed by any volcanic 
activity. More than 200 earthquakes from magnitude 1 to 3 were recorded, but
residents felt only three of them. Most of the epicenters were 
localized around the NW rift zone of Tenerife and in the strait between Gran
Canaria and Tenerife. The crisis was probably related to dike 
emplacement at 3-4 km depth.
	On 12 January 2005, an increase in unrest at Tenerife's Teide volcano over the
previous 2 weeks was reported. Carbon dioxide emissions rose 
from 75 to 354 tons per day, and hydrogen sulfide emissions rose from 35 to 152
tons per day. Seismic activity remained elevated under the 
volcano. Fumaroles increased in pressure, and emitted sounds. No significant
ground deformation was observed.
	In a recent article in Eos, scientists from Spain and The Netherlands (Garcia
et al., 2006), described a monitoring program for the Canary 
Islands. They noted that the Canary Islands started to show signs of
seismo-volcanic activity at the end of 2003. In spring 2004, there was a 
significant increase in the number of seismic events (a mixture of regional,
volcano-tectonic, and volcanic events such as tremor and 
long-period signals) located beneath Tenerife Island. The authors also noted an
increase of fumarolic activity, an increase in carbon dioxide 
emissions in the NW part of the island, and changes in the gravimetric field on
the N flank. After several seismic events had been felt by the 
population, the first alert level was declared by the civil protection division
of the local government.
	The volcano has a history of large eruptions destructive to populated areas.
The authors reported that in 1992, the International Association 
of Volcanology and Chemistry of the Earth's Interior (IAVCEI) identified Teide,
with its high-risk level, as one of the European Laboratory 
Volcanoes, thus receiving special consideration from the European Union
concerning research proposals.
	In the spring of 2005, the Spanish National Research Council (CSIC) initiated
the TEGETEIDE project (Geophysical and Geodetic Techniques for 
the Study of the Teide-Pico Active Volcanic Area). It will monitor the
seismicity of the volcano and include background noise analysis. The 
system's main goal is to detect precursors to a potentially dangerous eruptive
episode at an early stage. The scheme is to use signals in both 
the time and the spectral domains.
	References. Garcia, A., Vila, J., Ortiz, R., Macia, R., Sleeman, R., Marrero,
J.M., Sanchez, N., Tarraga, M., Correig, A.M., 2006, Monitoring 
the reawakening of Canary Islands' Teide Volcano: EOS Transactions, American
Geophysical Union, v. 87, no. 6, p. 61, 65.
	Background. The large triangular island of Tenerife is composed of a complex of
overlapping Miocene-to-Quaternary stratovolcanoes that have 
remained active into historical time. The NE-trending Cordillera Dorsal volcanic
massif joins the Las Cañadas volcano on the SW side of Tenerife 
with older volcanoes, creating the largest volcanic complex of the Canary
Islands. Controversy surrounds the formation of the dramatic 10 x 17 
km Las Cañadas caldera, which is partially filled by 3715-m-high Teide
stratovolcano, the highest peak in the Atlantic Ocean. The origin of the 
caldera has been considered to be due entirely or in part to either a massive
landslide (in a manner similar to the earlier formation of the 
massive La Orotava and Guimar valleys in the Cordillera Dorsal) or due to major
explosive eruptions. The most recent stage of activity beginning 
in the late Pleistocene included the construction of the Pico Viejo and Teide
edifices. Tenerife was perhaps observed in eruption by Christopher 
Columbus, and several flank vents on the Canary Island's most active volcano
have been active during historical time.
	Information Contacts: Juan Carlos Carracedo, Estación Volcanológica de
Canarias, Consejo Superior de Investigaciones Científicas (CSIC, Spanish 
National Research Council), Serrano, 117 28006, Madrid, Spain (Email:
jcarracedo@xxxxxxxxxxxx); Josep Vila, Departament d'Astronomia i 
Meteorologia, Universitat de Barcelona and Laboratori d'Estudis Geofísics
"Eduard Fontserè," Institut d'Estudis Catalans, Barcelona, Spain 
(Email: jvila@xxxxxxxx).

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