| UNREST AT SHISHALDIN VOLCANO |
February/March, 1999 |  |
WEEKLY UPDATE
Friday, April 30, 1999 1 pm ADT (2100 UT) SHISHALDIN VOLCANO
54°45.33' 163°58.00'
Summit Elevation 9,373 ft (2,857 m) Level of Concern Color Code: YELLOW The Level of Concern Color Code at Shishaldin was downgraded to YELLOW on Wednesday, April 28. Since then, no plumes have been observed or reported. Seismicity remains low but eruptive activity could resume with little or no warning. AVO staff continues to monitor the situation 24 hours a day with real-time seismic and satellite data.
ALASKA VOLCANO OBSERVATORY
INFORMATION RELEASE
Wednesday, April 28, 1999 1:30 PM ADT (2130 UT) SHISHALDIN VOLCANO
54°45.33' 163°58.00'
Summit Elevation 9,373 ft (2,857 m) Level of Concern Color Code: YELLOW
Previous Level of Concern Color Code: ORANGE Seismicity has now declined to the point where it is unlikely that any significant eruptive activity is occurring at the volcano. The thermal anomaly that has been a persistent feature on satellite images at Shishaldin for many weeks has not been observed for at least 5 days and no significant plumes have been observed for 2 days. For these reasons, the Level of Concern Color Code has been downgraded to YELLOW. Plumes are likely to be issuing from the summit vent; these will consist mostly of gas and vapor but can occasionally contain small amounts of ash. Since more vigorous eruptions could occur with little or no warning , AVO staff will continue to monitor the situation 24 hours a day with real-time seismic and satellite data. Additional information releases will be issued as the situation warrants. After more than 2 1/2 months of unrest, AVO observed low-level strombolian eruptive activity in the summit crater on Saturday, April 17. A major explosive eruption at Shishaldin volcano began at 11:33 am ADT (1933 UT) on Monday, April 19, sending an ash plume to at least 45,000 ft ASL. The main eruptive pulse lasted for about 7 hours and the volcano was placed in a Level of Concern Color Code RED for a 21 hour period. After seismicity at the volcano declined dramatically, the Level of Concern Color Code was downgraded to ORANGE. The volcano was again placed in Color Code RED on Thursday night, April 22, when an explosive eruption began about 9:00 PM ADT (0500 UT). This eruptive activity ended about 2:10 AM ADT (1010 UT) Friday morning, April 23, and the Level of Concern Code was again lowered to ORANGE 0750 AM ADT (1550 UT) Friday morning.
ALASKA VOLCANO OBSERVATORY
INFORMATION RELEASE
Tuesday, April 27, 1999 12:00 PM ADT (2000 UT) SHISHALDIN VOLCANO
54°45.33' 163°58.00'
Summit Elevation 9,373 ft (2,857 m) Level of Concern Color Code: ORANGE Seismicity continues to be somewhat elevated and occasional low-level Strombolian eruptions similar to those of yesterday may still be occurring at the volcano. These mildly explosive events can send short-lived ash clouds to 15,000 feet ASL. The volcano is obscuRED by clouds today and no visible or satellite observations are available. Satellite imagery throughout yesterday indicated a narrow arcuate-shaped plume extending northeast from the volcano for over 100 miles. This plume, which was estimated by satellite imagery, ground observers, and pilots to between 10,000-15,000 feet ASL, was probably mostly gas and vapor but did appear to contain small amounts of ash. The flanks of the volcano are marked by ash, mudflows, and probable spatter-fed lava flows from earlier eruptive activity. A more vigorous eruption could occur with little or no warning and AVO staff are monitoring the situation 24 hours a day with real-time seismic and satellite data. Additional information releases will be issued as the situation warrants. After more than 2 1/2 months of unrest, AVO observed low-level strombolian eruptive activity in the summit crater on Saturday, April 17. A major explosive eruption at Shishaldin volcano began at 11:33 am ADT (1933 UT) on Monday, April 19, sending an ash plume to at least 45,000 ft ASL. The main eruptive pulse lasted for about 7 hours and the volcano was placed in a Level of Concern Color Code RED for a 21 hour period. After seismicity at the volcano declined dramatically, the Level of Concern Color Code was downgraded to ORANGE. The volcano was again placed in Color Code RED on Thursday night, April 22, when an explosive eruption began about 9:00 PM ADT (0500 UT). This eruptive activity ended about 2:10 AM ADT (1010 UT) Friday morning, April 23, and the Level of Concern Code was again lowered to ORANGE 0750 AM ADT (1550 UT) Friday morning.
ALASKA VOLCANO OBSERVATORY
INFORMATION RELEASE
Monday, April 26, 1999 11:30 AM ADT (1930 UT) SHISHALDIN VOLCANO
54°45.33' 163°58.00'
Summit Elevation 9,373 ft (2,857 m) Level of Concern Color Code: ORANGE Seismicity continues to be relatively low but indicates that occasional low-level Strombolian eruptions are still occurring at the volcano. These mildly explosive events can send short-lived ash clouds to 15,000 feet ASL. Early this morning, a very light ash fall was reported by a fishing boat 40 miles east of the volcano near the southeast corner of Unimak Island off Cape Pankof. Satellite imagery currently indicates a narrow plume extending from the volcano to the northeast for over 100 miles. This plume, which is estimated by ground observers and pilots to be 15,000 feet ASL, is probably mostly gas and vapor but contains small amounts of ash. The flanks of the volcano are marked by ash, mudflows, and probable spatter-fed lava flows from earlier eruptive activity. A more vigorous eruption could occur with little or no warning and AVO staff are monitoring the situation 24 hours a day with real-time seismic and satellite data. Additional information releases will be issued as the situation warrants. After more than 2 1/2 months of unrest, AVO observed low-level strombolian eruptive activity in the summit crater on Saturday, April 17. A major explosive eruption at Shishaldin volcano began at 11:33 am ADT (1933 UT) on Monday, April 19, sending an ash plume to at least 45,000 ft ASL. The main eruptive pulse lasted for about 7 hours and the volcano was placed in a Level of Concern Color Code RED for a 21 hour period. After seismicity at the volcano declined dramatically, the Level of Concern Color Code was downgraded to ORANGE. The volcano was again placed in Color Code RED on Thursday night, April 22, when an explosive eruption began about 9:00 PM ADT (0500 UT). This eruptive activity ended about 2:10 AM ADT (1010 UT) Friday morning, April 23, and the Level of Concern Code was again lowered to ORANGE 0750 AM ADT (1550 UT) Friday morning.
ALASKA VOLCANO OBSERVATORY
INFORMATION RELEASE
Sunday, April 25, 1999 12:00 PM ADT (2000 UT) SHISHALDIN VOLCANO
54°45.33' 163°58.00'
Summit Elevation 9,373 ft (2,857 m) Level of Concern Color Code: ORANGE Seismicity continues to be relatively low but, along with satellite data showing a thermal anomaly at the vent, indicates that occasional low-level Strombolian eruptions are still occurring at the volcano. These mildly explosive events can send short-lived ash clouds to 15,000 feet ASL. The flanks of the volcano are marked by ash, mudflows, and probable spatter-fed lava flows from earlier eruptive activity. A more vigorous eruption could occur with little or no warning and AVO staff are monitoring the situation 24 hours a day with real-time seismic and satellite data. Additional information releases will be issued as the situation warrants. After more than 2 1/2 months of unrest, AVO observed low-level strombolian eruptive activity in the summit crater on Saturday, April 17. A major explosive eruption at Shishaldin volcano began at 11:33 am ADT (1933 UT) on Monday, April 19, sending an ash plume to at least 45,000 ft ASL. The main eruptive pulse lasted for about 7 hours and the volcano was placed in a Level of Concern Color Code RED for a 21 hour period. After seismicity at the volcano declined dramatically, the Level of Concern Color Code was downgraded to ORANGE. The volcano was again placed in Color Code RED on Thursday night, April 22, when an explosive eruption began about 9:00 PM ADT (0500 UT). This eruptive activity ended about 2:10 AM ADT (1010 UT) Friday morning, April 23, and the Level of Concern Code was again lowered to ORANGE 0750 AM ADT (1550 UT) Friday morning.
ALASKA VOLCANO OBSERVATORY
INFORMATION RELEASE
Saturday, April 24, 1999 12:30 PM ADT (2030 UT) SHISHALDIN VOLCANO
54°45.33' 163°58.00'
Summit Elevation 9,373 ft (2,857 m) Level of Concern Color Code: ORANGE Seismicity continues to be relatively low but indicates that occasional low-level Strombolian eruptions are occurring at the vent. These mildly explosive events can send short-lived ash clouds to 15,000 feet ASL as confirmed yesterday by an airborne AVO observer. The flanks of the volcano are marked by ash, mudflows, and probable spatter-fed lava flows from earlier activity. Satellite data continue to show a thermal anomaly at the vent and incandescent material was observed in the summit vent yesterday. A more vigorous eruption could occur with little or no warning and AVO staff are monitoring the situation 24 hours a day with real-time seismic and satellite data. Additional information releases will be issued as the situation warrants. After more than 2 1/2 months of unrest, AVO observed low-level strombolian eruptive activity in the summit crater on Saturday, April 17. A major explosive eruption at Shishaldin volcano began at 11:33 am ADT (1933 UT) on Monday, April 19, sending an ash plume to at least 45,000 ft ASL. The main eruptive pulse lasted for about 7 hours and the volcano was placed in a Level of Concern Color Code RED for a 21 hour period. After seismicity at the volcano declined dramatically, the Level of Concern Color Code was downgraded to ORANGE. The volcano was again placed in Color Code RED on Thursday night, April 22, when an explosive eruption began about 9:00 PM ADT (0500 UT). This eruptive activity ended about 2:10 AM ADT (1010 UT) Friday morning, April 23, and the Level of Concern Code was again lowered to ORANGE 0750 AM ADT (1550 UT) Friday morning.
ALASKA VOLCANO OBSERVATORY
INFORMATION RELEASE
Friday, April 23, 1999 04:30 PM ADT (0030 UT) SHISHALDIN VOLCANO
54°45.33' 163°58.00'
Summit Elevation 9,373 ft (2,857 m) Level of Concern Color Code: ORANGE Seismicity continues to be relatively low but indicates occasional low-level Strombolian eruptions are occurring at the vent. Ash clouds, if present, are likely rising only hundreds of feet above the summit. Satellite data continues to show a thermal anomaly at the vent and an eruption could occur with little or no warning. AVO staff are monitoring the situation 24 hours a day with real-time seismic and satellite data. Additional information releases will be issued as the situation warrants. After more than 2 1/2 months of unrest, AVO observed low-level strombolian eruptive activity in the summit crater on Saturday, April 17. A major explosive eruption at Shishaldin volcano began at 11:33 am ADT (1933 UT) on Monday, April 19, sending an ash plume to at least 45,000 ft ASL. The main eruptive pulse lasted for about 7 hours and the volcano was placed in a Level of Concern Color Code RED for a 21 hour period. After seismicity at the volcano declined dramatically, the Level of Concern Color Code was downgraded to ORANGE. The volcano was again placed in Color Code RED on Thursday night, April 22, when an explosive eruption began about 9:00 PM ADT (0500 UT). This eruptive activity ended about 2:10 AM ADT (1010 UT) Friday morning, April 23, and the Level of Concern Code was again lowered to ORANGE 0750 AM ADT (1550 UT) Friday morning.
ALASKA VOLCANO OBSERVATORY
INFORMATION RELEASE
Friday, April 23, 1999 0750 AM ADT (1550 UT)
SHISHALDIN VOLCANO
54°45.33' 163°58.00'
Summit Elevation 9,373 ft (2,857 m) Level of Concern Color Code: ORANGE
Previous Level of Concern Color Code: RED The explosive eruption that occurred at Shishaldin volcano begining at 9:00 PM ADT (0500 UT) last evening has ended and the Color Code has been downgraded to ORANGE. Eruptive activity diminshied rapidly at about 2:00 AM ADT (1000UT) based on a rapid decline in tremor levels. Satellite data from 6:16 AM (1416UT) shows a thermal anomaly that indicates low-level Strombolian activity at the vent. Ash clouds are not evident on the most recent satellite imagery. AVO staff are monitoring the situation 24 hours a day with real-time seismic and satellite data. Additional information releases will be issued as the situation warrants. After more than 2 1/2 months of unrest, AVO observed low-level strombolian eruptive activity in the summit crater on Saturday, April 17. A major explosive eruption at Shishaldin volcano began at 11:33 am ADT (1933 UT) on Monday, April 19, sending an ash plume to at least 45,000 ft ASL. The main eruptive pulse lasted for about 7 hours and the volcano was placed in a Level of Concern Color Code RED for a 21 hour period. After seismicity at the volcano declined dramatically, the Level of Concern Color Code was downgraded to ORANGE. The volcano was again placed in Color Code RED on Thursday night, April 22, when an explosive eruption began about 9:00 PM ADT (0500 UT). This eruptive activity ended about 2:10 AM ADT (1010 UT) Friday morning, April 23, and the Level of Concern Code was again lowered to ORANGE 0750 AM ADT (1550 UT) Friday morning.
ALASKA VOLCANO OBSERVATORY
INFORMATION RELEASE
Thursday, April 22, 1999 2150 PM ADT (0550 UT) SHISHALDIN VOLCANO
54°45.33' 163°58.00'
Summit Elevation 9,373 ft (2,857 m) Level of Concern Color Code: RED An explosive eruption is occurring at Shishaldin volcano and the Color Code is increased to RED. AVO personnel flying over the volcano at 6:00pm (0200UT) this evening observed low-level strombolian activity reaching as high as 500 ft above the vent. Since that time, seismicity has increased substantially on all stations. The eruption is estimated to have started around 9:00 PM ADT (0500UT) based on a rapid increase in tremor levels starting at that time. Satellite data from 8:20 PM shows a narrow plume extending 45 km south of the volcano. AVO staff are monitoring the situation 24 hours a day with real-time seismic and satellite data. Additional information releases will be issued as the situation warrants. After more than 2 1/2 months of unrest, AVO observed low-level strombolian eruptive activity in the summit crater on Saturday, April 17. A major explosive eruption at Shishaldin volcano began at 11:33 am ADT (1933 UT) on Monday, April 19, sending an ash plume to at least 45,000 ft ASL. The main eruptive pulse lasted for about 7 hours and the volcano was placed in a Level of Concern Color Code RED for a 21 hour period. After seismicity at the volcano declined dramatically, the Level of Concern Color Code was downgraded to ORANGE. The volcano was again placed in Color Code RED on Thursday night, April 22, when an explosive eruption began about 9:00 PM ADT (0500 UT). This eruptive activity ended about 2:10 AM ADT (1010 UT) Friday morning, April 23, and the Level of Concern Code was again lowered to ORANGE 0750 AM ADT (1550 UT) Friday morning.
ALASKA VOLCANO OBSERVATORY
INFORMATION RELEASE
Thursday, April 22, 1999 4:20 PM ADT (0020 UT) SHISHALDIN VOLCANO
54°45.33' 163°58.00'
Summit Elevation 9,373 ft (2,857 m) Level of Concern Color Code: ORANGE A moderate strombolian eruption continued throughout the day at Shishaldin along with very elevated seismic activity and a large thermal anomaly visible on satellite imagery. Lava is probably fountaining to heights of a few hundred feet above the 9,373 foot-high summit. Although plumes have not been detected in satellite imagery, diffuse steam and ash clouds may be present near the vent; these clouds probably extend for no more than a few tens of miles and at altitudes below 15,000 feet ASL. The possibility of a more explosive eruption at any time remains high. AVO staff are monitoring the situation 24 hours a day with real-time seismic and satellite data. Additional information releases will be issued as the situation warrants. After more than 2 1/2 months of unrest, AVO observed low-level strombolian eruptive activity in the summit crater on Saturday, April 17. A major explosive eruption at Shishaldin volcano began at 11:33 am ADT (1933 UT) on Monday, April 19, sending an ash plume to at least 45,000 ft ASL. The main eruptive pulse lasted for about 7 hours and the volcano was placed in a Level of Concern Color Code RED for a 21 hour period. After seismicity at the volcano declined dramatically, the Level of Concern Color Code was downgraded to ORANGE. The volcano was again placed in Color Code RED on Thursday night, April 22, when an explosive eruption began about 9:00 PM ADT (0500 UT). This eruptive activity ended about 2:10 AM ADT (1010 UT) Friday morning, April 23, and the Level of Concern Code was again lowered to ORANGE 0750 AM ADT (1550 UT) Friday morning.
ALASKA VOLCANO OBSERVATORY
INFORMATION RELEASE
Thursday, April 22, 1999 10:00 AM ADT (1800 UT) SHISHALDIN VOLCANO
54°45.33' 163°58.00'
Summit Elevation 9,373 ft (2,857 m) Level of Concern Color Code: ORANGE Previous Level of Concern Color Code: RED A moderate strombolian eruption continued through the night at Shishaldin along with elevated seismic activity and a very large thermal anomaly visible on satellite imagery. Lava fountaining was observed to a few hunred feet above the 9,373 foot-high summit and satellite imagery indicates occasional steam and sparse ash clouds extending for less than 30 miles at altitudes of less than 15,000 feet ASL. Since a major explosive eruption has not occurred in the last 24 hours, the Level of Concern Color Code has been lowered to ORANGE, although the possibility of a more explosive eruption at any time remains high. AVO staff are monitoring the situation 24 hours a day with real-time seismic and satellite data. Additional information releases will be issued as the situation warrants. After more than 2 1/2 months of unrest, AVO observed low-level strombolian eruptive activity in the summit crater on Saturday, April 17. A major explosive eruption at Shishaldin volcano began at 11:33 am ADT (1933 UT) on Monday, April 19, sending an ash plume to at least 45,000 ft ASL. The main eruptive pulse lasted for about 7 hours and the volcano was placed in a Level of Concern Color Code RED for a 21 hour period. After seismicity at the volcano declined dramatically, the Level of Concern Color Code was downgraded to ORANGE. The volcano was again placed in Color Code RED on Thursday night, April 22, when an explosive eruption began about 9:00 PM ADT (0500 UT). This eruptive activity ended about 2:10 AM ADT (1010 UT) Friday morning, April 23, and the Level of Concern Code was again lowered to ORANGE 0750 AM ADT (1550 UT) Friday morning.
ALASKA VOLCANO OBSERVATORY
INFORMATION RELEASE
Wednesday, April 21, 1999 6:00 PM ADT (0200 UT) SHISHALDIN VOLCANO
54°45.33' 163°58.00'
Summit Elevation 9,373 ft (2,857 m) Level of Concern Color Code: RED Seismic activity is flucuating at elevated levels but somewhat REDuced from this morning. The possibility for an explosive eruption is still high and the Level of Concern Color Code is being kept at RED. We believe that while moderate strombolian eruptive activity is occurring at present, satellite imagery has not shown a major ash cloud today. AVO staff are monitoring the situation 24 hours a day with real-time seismic and satellite data. Additional information releases will be issued as the situation warrants. After more than 2 1/2 months of unrest, AVO observed low-level strombolian eruptive activity in the summit crater on Saturday, April 17. A major explosive eruption at Shishaldin volcano began at 11:33 am ADT (1933 UT) on Monday, April 19, sending an ash plume to at least 45,000 ft ASL. The main eruptive pulse lasted for about 7 hours and the volcano was placed in a Level of Concern Color Code RED for a 21 hour period. After seismicity at the volcano declined dramatically, the Level of Concern Color Code was downgraded to ORANGE. The volcano was again placed in Color Code RED on Thursday night, April 22, when an explosive eruption began about 9:00 PM ADT (0500 UT). This eruptive activity ended about 2:10 AM ADT (1010 UT) Friday morning, April 23, and the Level of Concern Code was again lowered to ORANGE 0750 AM ADT (1550 UT) Friday morning.
ALASKA VOLCANO OBSERVATORY
INFORMATION RELEASE
Wednesday, April 21, 1999 11:15AM ADT (1915 UT) SHISHALDIN VOLCANO
54°45.33' 163°58.00'
Summit Elevation 9,373 ft (2,857 m) Level of Concern Color Code: RED Seismic tremor levels are now at those seen at the start of the previous explosive eruption on April 19, and are being recorded on more distant stations. A significant explosive eruption may occur within the next several hours, and we are therefore raising our Level of Concern Color Code for Shishaldin to RED. A moderately strong strombolian eruption is likely occurring now and is probably sending ejecta to several hundred feet above the summit. Satellite imagery continues to show a large thermal anomaly in the summit crater, but an ash cloud has not been detected at this time. AVO staff are monitoring the situation 24 hours a day with real-time seismic and satellite data. Another information release will be issued by close of business today or sooner as the situation warrants. After more than 2 1/2 months of unrest, AVO observed low-level strombolian eruptive activity in the summit crater on Saturday, April 17. A major explosive eruption at Shishaldin volcano began at 11:33 am ADT (1933 UT) on Monday, April 19, sending an ash plume to at least 45,000 ft ASL. The main eruptive pulse lasted for about 7 hours and the volcano was placed in a Level of Concern Color Code RED for a 21 hour period. After seismicity at the volcano declined dramatically, the Level of Concern Color Code was downgraded to ORANGE. The volcano was again placed in Color Code RED on Thursday night, April 22, when an explosive eruption began about 9:00 PM ADT (0500 UT). This eruptive activity ended about 2:10 AM ADT (1010 UT) Friday morning, April 23, and the Level of Concern Code was again lowered to ORANGE 0750 AM ADT (1550 UT) Friday morning.
ALASKA VOLCANO OBSERVATORY
INFORMATION RELEASE
Wednesday, April 21, 1999 10:15 AM ADT (1815 UT) SHISHALDIN VOLCANO
54°45.33' N 163°58.00' W
Summit Elevation 9373 ft (2,857 m) Current Level of Concern Color Code: ORANGE The increase in seismic activity at Shishaldin volcano that began yesterday afternoon at 4:00 PM (0000 UT) strengthened about 11:00 PM (0700 UT) last night and is now at levels similar to those recorded in the hours before the explosive eruption on April 19. Satellite imagery continues to show a thermal anomaly in the summit crater. We are therefore maintaining the Level of Concern Color Code at ORANGE. The volcano remains restless and low level strombolian activity may be occurring now; more explosive eruptive activity could resume with little or no warning. AVO staff are monitoring the situation 24 hours a day with real-time seismic and satellite data. Another information release will be issued by close of business today or sooner as the situation warrants. After more than 2 1/2 months of unrest, AVO observed low-level strombolian eruptive activity in the summit crater on Saturday, April 17. A major explosive eruption at Shishaldin volcano began at 11:33 am ADT (1933 UT) on Monday, April 19, sending an ash plume to at least 45,000 ft ASL. The main eruptive pulse lasted for about 7 hours and the volcano was placed in a Level of Concern Color Code RED for a 21 hour period. After seismicity at the volcano declined dramatically, the Level of Concern Color Code was downgraded to ORANGE. The volcano was again placed in Color Code RED on Thursday night, April 22, when an explosive eruption began about 9:00 PM ADT (0500 UT). This eruptive activity ended about 2:10 AM ADT (1010 UT) Friday morning, April 23, and the Level of Concern Code was again lowered to ORANGE 0750 AM ADT (1550 UT) Friday morning.
ALASKA VOLCANO OBSERVATORY
INFORMATION RELEASE
Tuesday, April 20, 1999 05:45 PM ADT (0145 UTC) SHISHALDIN VOLCANO
54°45.33' N 163°58.00' W
Summit Elevation 9373 ft (2,857 m) Current Level of Concern Color Code: ORANGE Seismic activity at Shishaldin volcano, which had significantly declined this morning beginning at 3:45 am ADT (1145 UT), began to increase again about 4:00 PM ADT (0000 UT). Satellite imagery continues to show a thermal anomaly in the summit crater. We are therefore maintaining the Level of Concern Color Code at ORANGE through the evening. The volcano remains restless and explosive activity could resume with little or no warning. AVO staff are monitoring the situation 24 hours a day with real-time seismic and satellite data. After more than 2 1/2 months of unrest, AVO observed low-level strombolian eruptive activity in the summit crater on Saturday, April 17. A major explosive eruption at Shishaldin volcano began at 11:33 am ADT (1933 UT) on Monday, April 19, sending an ash plume to at least 45,000 ft ASL. The main eruptive pulse lasted for about 7 hours and the volcano was placed in a Level of Concern Color Code RED for a 21 hour period. After seismicity at the volcano declined dramatically, the Level of Concern Color Code was downgraded to ORANGE. The volcano was again placed in Color Code RED on Thursday night, April 22, when an explosive eruption began about 9:00 PM ADT (0500 UT). This eruptive activity ended about 2:10 AM ADT (1010 UT) Friday morning, April 23, and the Level of Concern Code was again lowered to ORANGE 0750 AM ADT (1550 UT) Friday morning.
ALASKA VOLCANO OBSERVATORY
INFORMATION RELEASE
Tuesday, April 20, 1999 09:45 AM ADT (1745 UTC) SHISHALDIN VOLCANO
54°45.33' N 163°58.00' W
Summit Elevation 9373 ft (2,857 m) Current Level of Concern Color Code: ORANGE Previous Level of Concern Color Code: RED Seismic activity at Shishaldin volcano abruptly and significantly declined this morning at about 3:45 am ADT (1145 UT), indicating that explosive eruptive activity has subsided, although satellite imagery from 6:50 am ADT (1450 UT) shows a thermal anomaly persisting in the summit crater. We are therefore reducing the Level of Concern Color Code to ORANGE. The volcano remains restless and explosive activity could resume with little or no warning. AVO staff are monitoring the situation 24 hours a day with real-time seismic and satellite data. Another information release will be issued by close of business this day. After more than 2 1/2 months of unrest, an explosive eruption at Shishaldin volcano began at 11:33 am ADT (1933 UT) on Monday, April 19, sending an ash plume to at least 45,000 ft ASL. The main eruptive pulse lasted for about 7 hours and was preceeded by at least several days of low-level strombolian eruptive activity that was largely confined to within the summit crater.
ALASKA VOLCANO OBSERVATORY
INFORMATION RELEASE
Monday, April 19, 1999 11:00 PM ADT (0700 UTC) SHISHALDIN VOLCANO
54°45.33' N 163°58.00' W
Summit Elevation 9373 ft (2,857 m)
Current Level of Concern Color Code: RED A major eruption at Shishaldin volcano began at 11:33 am ADT (1933UT) today and reached an altitude of at least 45,000 ft asl by early afternoon. The eruption lasted about 7 hrs with the ash plume at higher elevations moving north and that at lower elevations drifting south. Currently, seismic tremor has decreased substantially but the strombolian eruption continues at moderate levels. Because additional explosive eruptions could occur with little or no warning, AVO will stay in Color Code RED. A low-level strombolian eruption was first observed Saturday at Shishaldin volcano at 5:00pm ADT by AVO staff flying in the area with the Alaska State Troopers. Incandescent blocks and spatter were erupting as high as 200m above the vent but at that time no lava had come over the crater rim. National Weather Service (NWS) observers in Cold Bay and a NWS ship in the area Sunday morning reported seeing incandescent lava at the summit of the volcano and snowmelt running partway down the NW flank. Ash clouds present significant hazards to aircraft flying over this part of the Aleutians, and may also cause minor ash falls in nearby communities. Mudflows down the volcano flanks are dangerous to hikers in the area and could be generated at any time. AVO staff is monitoring the eruption 24 hrs a day with real-time seismic and satellite data and further updates will be issued as new information becomes available.
URGENT ALASKA VOLCANO OBSERVATORY
INFORMATION RELEASE
Monday, April 19, 1999 12:15 PM ADT (2015 UTC) SHISHALDIN VOLCANO
54°45.33' N 163°58.00' W
Summit Elevation 9373 ft (2,857 m)
Current Level of Concern Color Code: RED
Previous Level of Concern Color Code: ORANGE A pilot report at 11:45 am indicates that a steam-and-ash plume from Shishaldin Volcano has reached 30,000 ft. Tremor amplitudes have also dramatically increased since 11:33 and have started showing up at more distant stations, after a steady increase in tremor levels over the last two days. A significant eruption is occurring, and we are raising our Level of Concern Color Code for a Shishaldin to RED. A low-level strombolian eruption was first observed Saturday at Shishaldin volcano at 5:00pm ADT by AVO staff flying in the area with the Alaska State Troopers. Incandescent blocks and spatter were erupting as high as 200m above the vent but at that time no lava had come over the crater rim. National Weather Service (NWS) observers in Cold Bay and a NWS ship in the area this morning reported seeing incandescent lava at the summit of the volcano and snowmelt running partway down the NW flank. Ash clouds present significant hazards to aircraft flying over this part of the Aleutians, and may also cause minor ash falls in nearby communities. Mudflows down the volcano flanks would be dangerous to hikers in the area and could be generated at any time. AVO staff is monitoring the eruption 24 hrs a day with real-time seismic and satellite data and further updates will be issued as new information becomes available.
ALASKA VOLCANO OBSERVATORY
INFORMATION RELEASE
Sunday, April 18, 1999 10:00 AM ADT (1800 UTC) SHISHALDIN VOLCANO
54°45.33' N 163°58.00' W
Summit Elevation 9373 ft (2,857 m) Current Level of Concern Color Code: ORANGE A low-level strombolian eruption was first observed yesterday at Shishaldin volcano and 5:00pm ADT by AVO staff flying in the area with the Alaska State Troopers. Incandescent blocks and spatter were erupting as high as 200m above the vent but at that time no lava had come over the crater rim. National Weather Service (NWS) observers in Cold Bay and a NWS ship in the area this morning reported seeing incandescent lava at the summit of the volcano and snowmelt running partway down the NW flank. Mudflows down the volcano flanks would be dangerous to hikers in the area and could be generated at any time. A small steam plume with little or no ash is being generated as hot lava contacts snow at the summit of the volcano. The eruption could reach a phase in which small explosions could produce a small low level ash plume. This type of eruption could continue for weeks to months. Tremor seismicity continues at an elevated level and the thermal anomaly observed by satellite imagery persists. AVO staff is monitoring the eruption 24 hrs a day with real-time seismic and satellite data and further updates will be issued as new information becomes available.
ALASKA VOLCANO OBSERVATORY
ALASKA VOLCANOES WEEKLY UPDATE
Friday, April 16, 1999 1:00 PM ADT (2100 UTC) SHISHALDIN VOLCANO
54°45.33' N 163°58.00' W
Summit Elevation 9373 ft (2,857 m) Current Level of Concern Color Code: ORANGE The tremor seismicity at Shishaldin volcano decreased following Tuesday's tremor episode which lasted for over a day. Fluctuating levels of tremor indicate that the volcano continues to be restless. Aftershocks of the M5.2 earthquake of March 4 are continuing west of the volcano. Satellite imagery through today shows a persistent thermal anomaly at the vent. The Level of Concern Color Code will remain at ORANGE as AVO continues 24-hr watch and evaluates the status of volcanic unrest.
ALASKA VOLCANO OBSERVATORY
INFORMATION RELEASE
Wednesday, April 14, 1999 1:15 PM ADT (2115 UTC) SHISHALDIN VOLCANO
54°45.33' N 163°58.00' W
Summit Elevation 9373 ft (2857 m)
Level of Concern Color Code: ORANGE
Previous Level of Concern Color Code: YELLOW The tremor seismicity at Shishaldin volcano increased markedly late Monday [sic, Tuesday] night following a M 4.5 earthquake and associated aftershocks [which occurred Monday] west of the volcano. Since then tremor levels have fluctuated, but continue to remain elevated. Satellite imagery from yesterday afternoon through today shows the persistent thermal anomaly at the vent. The Level of Concern Color Code is therefore being increased to ORANGE as data indicate the possibility of an eruption has again increased.
ALASKA VOLCANO OBSERVATORY
INFORMATION RELEASE
Monday, April 12, 1999 9:30 PM ADT (1730 UTC) SHISHALDIN VOLCANO
54°45.33' N 163°58.00' W
Summit Elevation 9373 ft (2857 m) Level of Concern Color Code: YELLOW
Previous Level of Concern Color Code: ORANGE The seismicity at Shishaldin volcano remains above background levels; however, the seismic tremor has been steady since 8 April without any significant changes. The Level of Concern Color Code is therefore being decreased to YELLOW. The thermal anomaly observed in satellite imagery persists. A small eruption is possible with little or no warning.
ALASKA VOLCANO OBSERVATORY
INFORMATION RELEASE
Friday, April 9, 1999 3:00 PM ADT (2300 UTC) SHISHALDIN VOLCANO
54°45.33' N 163°58.00' W
Summit Elevation 9373 ft (2857 m) Level of Concern Color Code: ORANGE Following weeks of elevated seismicity and persistence of a thermal anomaly in the summit crater, a several-hour-long episode of strong tremor began at Shishaldin on Wednesday morning prompting an increase in the Level of Concern Color Code to ORANGE. The strong tremor declined Wednesday afternoon and returned to previous levels, however, seismicity remains above normal. The Level of Concern Color Code will remain ORANGE as we further evaluate the situation. Poor weather has prevented pilot and ground observations at the volcano and no evidence of eruptive activity has been apparent on satellite imagery. We will continue to closely monitor the volcano 24 hours a day and issue further updates as new information becomes available.
ALASKA VOLCANO OBSERVATORY
INFORMATION RELEASE
Wednesday, April 7, 1999 10:30 AM ADT (1830 UTC) SHISHALDIN VOLCANO
54°45.33' N 163°58.00' W
Summit Elevation 9373 ft (2857 m) Level of Concern Color Code: ORANGE
Previous Level of Concern Color Code: YELLOW Seismic activity consisting chiefly of strong tremor substantially increased above previous levels this morning at about 1600 UTC (8:00 AM ADT) and we are raising the level of concern color code to ORANGE. We have no confirmation that an eruption is currently in progress; however, a lava plug or flow may be forming in the summit crater. An explosive ash burst or lava eruption could occur over the next several hours or days. Weather in the area is overcast with haze, and a large storm system is approaching. A new seismic net monitoring Shishaldin volcano recorded slightly elevated seismicity beginning the end of January. Satellite imagery of February 9 showed a steam plume and a thermal anomaly at the vent. The thermal anomaly has persisted since that time. Heating of the summit area has melted snow at the top of the cone. A shallow magnitude 5.2 earthquake located about 9 mi (14 km) southwest of Shishaldin occurred early on the morning of March 4, 1999, followed by hundreds of small aftershocks. Shishaldin volcano, located near the center of Unimak Island in the eastern Aleutian Islands, is a spectacular symmetric cone with base diameter of approximately 10 miles (16 km). A small summit crater typically emits a noticeable steam plume with occasional small amounts of ash. Shishaldin is one of the most active volcanoes in the Aleutian volcanic arc, erupting at least 27 times since 1775. The most recent eruptive period occurred in late 1995 and early 1996 and consisted of minor explosions that produced low level steam and ash emissions.
ALASKA VOLCANO OBSERVATORY
ALASKA VOLCANOES WEEKLY UPDATE
Friday, April 2, 1999 11:00 AM AST (2000 UTC) SHISHALDIN VOLCANO
54°45.33' N 163°58.00' W
Summit Elevation 9373 ft (2,857 m)
Level of Concern Color Code: YELLOW
Low-level seismicity at Shishaldin volcano continued during the past week and the thermal anomaly visible in satellite imagery persists. A pilot report from this past week confirmed snowmelt at the summit. Small aftershocks continue from the shallow magnitude 5.0 earthquake that occurred on March 4 and was located about 9 mi (14 km) southwest of Shishaldin. A new seismic net at Shishaldin recorded slightly elevated seismicity beginning near the end of January. On February 9, a thermal anomaly appeared on satellite imagery and vigorous steam plumes were reported then and during the next week. No ash has been detected on satellite imagery. Low-level tremor was identified about a month ago prompting us to raise the level of concern color code to YELLOW on February 18. The tremor has subsequently diminished; however, seismicity remains above normal. With persistence of the thermal anomaly at the summit vent and above normal seismicity, an ash burst could occur with little or no warning.
Due to the high number of updates concerning Shishaldin Volcano, we have archived information releases prior to the month of June. May updates
April updates
March updates
February updates ABBREVIATED COLOR CODE KEY (contact AVO for complete description)
GREEN -- volcano is dormant; normal seismicity and fumarolic activity occurring
YELLOW -- volcano is restless; eruption may occur
ORANGE -- volcano is in eruption or eruption may occur at any time
RED -- significant eruption is occurring or explosive eruption expected at any time RECORDING OF THE STATUS OF ALASKA'S VOLCANOES (907) 786-7478 CONTACT INFORMATION:
Terry Keith, Scientist-in-Charge, USGS tkeith@tundra.wr.usgs.gov (907) 786-7443
John Eichelberger, Coordinating Scientist, UAF-GI eich@gi.alaska.edu (907) 474-5530 The Alaska Volcano Observatory is a cooperative program of the U.S. Geological Survey, the University of Alaska Fairbanks Geophysical Institute, and the Alaska Division of Geological and Geophysical Surveys.
