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This graph shows the number of earthquakes that occurred beneath Mount Spurr every day between July 1 and August 31, 1992. The red line indicates the time of the August 18 eruption. The earthquake activity did not change in the days or hours before the eruption and scientists did not issue a specific warning before the eruption occurred.
The Alaska Volcano Observatory provides information about Alaskan volcanoes through written updates (weekly and as needed), a level of concern color code, emergency notification by telephone, and direct personal communication with the public and individuals working in private industry, Federal, State, and local government agencies, and the news media. The written updates that provided key information about Mount Spurr during this activity.
July 2, 1992
4:00 p.m. ADT
"Seismic activity at Mt. Spurr declined steadily the first three days following the end of the eruption on Saturday, June 27 (about 11:00 a.m. ADT) and has remained about level the past three days. Most of the events are of shallow volcanic character and do not appear to reflect magma intrusion. As long as these volcanic events continue, the volcano must be considered restless and additional eruptive events are possible over the next few days or weeks. These events may occur with little or no advance warning. Thus the level of concern will remain at color code YELLOW."
"Fumaroles within the crater of the volcano continue to emit steam which condenses into a white plume that has been observed at times rising several thousand feet above the crater."
"Winds are light and variable, moving generally north, in the vicinity of the volcano."
"Spurr volcano remains active. The Alaska Volcano Observatory continues to monitor the volcano 24 hours a day, and will update the level of concern color code as appropriate."
July 6, 1992
4:00 p.m. ADT
"The level of micro-earthquake activity remains sufficiently high to remain at color code YELLOW for at least the next few days. AVO will be going off manned 24-hour duty at 5:00 p.m. tonight. The electronic alarm system on the seismic helicorders will remain on."
"Fumaroles within the crater of the volcano continue to emit steam which condenses into a white plume that has been observed at times rising several thousand feet above the crater."
"A helicopter-supported AVO field crew worked inside the crater of Crater Peak on Friday and also sampled the ash fall-out for about 40 miles north of the volcano. An abundance of basaltic- andesite bombs and scattered pumice lapilli in and around the crater indicates that the June 27 eruption had a strong juvenile, or magmatic component. The actual vent area appeared to have been enlarged somewhat to the north and west and contains numerous new fumaroles. New surge and tephra deposits are common inside the crater and, in some cases, mantle pre-eruption snow and ice. Temperatures of about 325o C were recorded at depths of eight inches in ash and cinder overlying fumaroles."
July 8, 1992
3:00 p.m. ADT
"The level of micro-earthquake activity has declined to the lowest levels in the past few months and the level of concern color code has therefore been reduced to GREEN. AVO is no longer on manned 24-hour duty in Fairbanks and Anchorage. The volcano, however, is monitored seismically 24 hours a day and the seismic electronic alarm system will be operating during non- duty hours."
"Fumaroles within the crater of the volcano continue to emit steam which condenses into a white plume that has been observed at times rising several thousand feet above the volcano. Such activity can be expected to continue for the next several months."
"This will be the last Update specifically dedicated to Mt. Spurr until further notice. Activity at Spurr will be included on the regular weekly AVO update issued on Fridays."
July 24, 1992
12:00 p.m. ADT
"The level of micro-earthquake activity at Mt. Spurr remains low. Two deep earthquakes, at about 20 miles depth, are the only noteworthy events this week. The level of concern color code continues to be GREEN. Fumaroles within the crater continue to emit steam that has been observed at times rising several thousand feet above the volcano. The volcano is monitored seismically 24 hours a day and the seismic electronic alarm system operates during non-duty hours."
August 14, 1992
3:00 p.m. ADT
"The level of micro-earthquake activity at Mt. Spurr remains low and the level of concern color code continues to be GREEN. Fumaroles within Crater Peak may at times produce steam plumes that rise several thousand feet above the volcano. Mt. Spurr is monitored seismically 24 hours a day and the seismic electronic alarm system operates during non-duty hours."
On August 18, 1992, at 4:25 p.m. ADT, AVO initiates notification by phone that the color code is now YELLOW; pilot reports confirm presence of an ash plume 300 - 600 meters above Crater Peak.
August 18, 1992
4:48 p.m. ADT
"A moderate explosive eruption began at Mt. Spurr at 4:41 p.m. today. Pilots reported an ash plume reached an altitude of at least 35,000 feet. The eruption was apparently preceded by a minor eruptive event at 3:35 p.m. Accordingly AVO has raised the level of concern color code to RED. Calculated wind directions indicate ash trajectories to the east of Mt. Spurr, in the direction of Anchorage. Based on wind velocities ash could begin falling in the Anchorage area within several hours of the start of the eruption."
"Seismic data from the volcano suggests the eruption is continuing at this time [and is] likely producing additional amounts of ash."
"The Alaska Volcano Observatory has instituted 24 hour a day monitoring from both the Anchorage and Fairbanks offices, and will update the level of concern color code as appropriate. Further updates will follow as information becomes available."
August 18
9:30 p.m. ADT
"Based on seismic information, the strong phase of the eruption from Crater Peak, a flank vent of Mt. Spurr, began at 4:41 p.m. and lasted approximately 3 hours and 20 minutes. Seismicity began to decline significantly at about 8:00 p.m. A pilot report at 8:30 p.m. indicated that only a steam plume rising to 16,000 feet could be seen a the volcano. Accordingly, as of 9:30 p.m., we are decreasing our level of concern color code to ORANGE."
"Ashfall began in Anchorage about 8:20 in the evening and continues at this time with accumulations of at least a few millimeters. Ashfall has been reported in Hope, on the norther Kenai Peninsula and in Whittier. In conjunction with diminishing seismicity, ashfall appears to be decreasing on the west side of Cook Inlet."
"Forecast and observed wind directions indicate that ash should continue to move east-southeast from Spurr, over Anchorage and the Turnagain Arm and further east out over the Prince William Sound. It appears that the main axis of the ash plume will pass south of Anchorage."
"At this time the eruption appears to be following the pattern of the June 27 eruption in size and duration. That eruption lasted four hours and produced about 50 million cubic meters of airfall."
August 19, 1992
8:30 a.m. ADT
"There is no indication that additional ash production is occurring from Crater Peak at this time. This eruption is generally similar in character to that of June 27 and we consider the likelihood of additional ash eruptions in the next few days to be small. However, we believe that the volcano is in an open-vent situation and if additional eruptions do occur, there may be little or no precursory seismicity. Since ash emission has ceased and the level of seismicity has remained low compared to the first few hours of the eruption, we are downgrading our level of concern color code to YELLOW."
September 16-17, 1992 Another example of an eruption preceded by little or no precursory earthquake activity.
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URL of this document: http://volcanoes.usgs.gov/About/What/Erupt/SpurrNoChange.html
Last modified: December 17, 1998