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This graph shows the number of earthquakes that occurred beneath Mount Spurr every day between October 1 and December 31. During the October and November earthquake swarms, AVO scientists issued updates on October 2 and November 9 warning that "a large eruption is likely within the next 24 to 48 hours". No eruptions occurred, and scientists viewed the seismicity as "failed eruptions" in which magma was rapidly emplaced at shallow depth beneath Crater Peak. During the flurry of earthquakes in December, however, AVO scientists did not change the color code or issue a specific eruption warning.
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.
October 1, 1992
4:00 p.m. ADT
"Two deep (>10 miles) earthquakes were detected beneath Mount Spurr during the past 24 hours. During this period, no shallow earthquakes or tremor were recorded. The level of concern color code remains at YELLOW."
October 2, 1992
4:00 p.m. ADT
"Volcanic tremor continues at Crater Peak. The tremor began yesterday at 7:00 p.m. and remained constant most of the day but increased slightly in the past several hours. The overall seismicity has not changed significantly in the last 24 hours. The continuation of tremor and the recent increases in sulfur dioxide emissions heighten the possibility of an eruption in the next several days. An AVO crew is currently over the volcano measuring sulfur dioxide levels. Another update will be issued if the situation changes."
October 2, 1992
6:30 p.m. ADT
"Volcanic tremor at Crater Peak has increased in amplitude to a point where it is showing up on stations more distant from the vent. The tremor amplitude is comparable to levels which preceded the June 27 and September 17 eruptions. A large eruption is likely within the next 24 to 48 hours. The current color code is RED."
October 3, 1992
4:00 p.m. ADT
"The sustained volcanic tremor, which lasted for 24 hours and resulted in the change to level of concern color code RED late yesterday, ended abruptly at 6:30 p.m. last night. Several short-lived but lower amplitude tremor episodes occurred in the late evening and early morning hours. Following a 12-hour quite interval, tremor began again at 2:38 p.m. today and continues as of this writing. Other earthquake activity has remained unchanged. Sulfur dioxide emissions measured late yesterday afternoon were down somewhat from levels measured on Tuesday."
"The volcano remains restless and the overall high seismicity together with the recent strong tremor episodes indicates an eruption is still possible with little or no warning. For this reason, the level of concern code will remain in RED until 9:00 tomorrow morning, October 4 at which time a new Update will be issued."
October 4, 1992
9:00 a.m. ADT
"The sustained volcanic tremor which has characterized the recent seismicity beneath Crater Peak changed to a more intermittent phase late yesterday afternoon. Periods of tremor one to two hours long alternated with seismically quiet intervals of one or more hours duration through the night. These quiet intervals are increasing in length and as of this writing, no tremor has occurred for the past 6 hours."
"Since the volcano remains restless and periods of strong tremor persist, an eruption with little or no warning is possible and the level of concern code will therefore remain in RED. Evaluation of the state of the volcano will continue throughout the day and another Update will be issued at 5:00 p.m."
October 5, 1992
5:00 p.m. ADT
"Intermittent volcanic tremor, commonly called "banded tremor", has characterized the seismicity beneath Crater Peak for the past 24 hours. Typically periods of tremor one to three hours long have alternated with quiet intervals of one to ten hours duration. The tremor amplitude is down somewhat from that recorded in the two hours preceding the change to level of concern RED on Friday and the average duration of quiet intervals has increased over the past 24 hours."
"Banded tremor of the type now being recorded beneath Crater Peak usually culminates in an eruption as seen in the June eruption and at numerous other volcanoes around the world. Episodes of banded tremor, however, can occur for days and even several months before eruption occurs. For this reason and because the duration of quiet intervals between tremor episodes is increasing, the level of concern code is being downgraded to YELLOW."
"The volcano remains unstable and seismically active and an eruption is likely within the next several days or weeks. Such and eruption could occur with little immediate seismic precursor activity."
November 2, 1992
4:00 p.m. AST
"During the past 24 hours, six earthquakes were located in the vicinity of Crater Peak. Two of these earthquakes were shallow, and the other four were from 9 to 28 kilometers deep. Overall seismicity at Mount Spurr is above normal."
"The volcano remains seismically active, and an eruption is possible within the next several days or weeks. Such an eruption could occur without significant seismic precursor activity."
November 9, 1992
12:00 p.m. AST
"A swarm of shallow seismic events began beneath Crater Peak on Spurr Volcano about 2:00 this morning and is continuing. This increase in seismic activity is being detected only by the station inside the crater, indicating that the possibility of an eruption has increased significantly. Such an eruption could occur without additional warning."
"An additional update will be issued later today."
November 9, 1992
4:00 p.m. AST
"The swarm of shallow seismic events beneath Crater Peak on Spurr Volcano is continuing at an increased rate. This increase in seismic activity continues to be detected only by the station inside the crater. The possibility of an eruption of unknown size, however, is significantly higher than at any point in the last few weeks. Such an eruption could occur without additional warning."
November 9, 1992
10:07 p.m. AST
"Seismic events beneath Crater Peak on Spurr Volcano have increased significantly in the past two hours and this increase is being detected by all stations around the volcano. The level of concern color code is now raised to RED as a large eruption is likely within the next 24 to 48 hours.
"Such an eruption could occur without additional warning."
November 10, 1992
3:00 p.m.
"Seismic events beneath Crater Peak on Spurr Volcano have decreased significantly over the past several hours and the seismic crisis that existed since yesterday noon has ended without eruption. The level of concern color code is therefore lowered to ORANGE. If the seismic activity returns to levels similar to those of yesterday, the level of concern will return to RED. The volcano continues to be unstable and an eruption could occur without additional warning. An overflight at 1:00 - 2:00 p.m. today revealed no changes nor evidence of activity in the crater region."
November 11, 1992
3:00 p.m. AST
"Seismic activity beneath Crater Peak remains low although still above background levels. Because of the size of the recently concluded seismic crisis and uncertainty as to near future activity, the level of concern color code continues to be ORANGE. If the seismic activity returns to levels similar to those of Monday, the level of concern will return to RED. The volcano continues to be unstable and an eruption could occur without additional warning. An overflight this afternoon revealed no changes nor evidence of activity in the crater region."
November 12, 1992
3:00 p.m. AST
"Seismic activity beneath Crater Peak remains low although still above background levels. During the past 24 hours, 13 small earthquakes were located in the vicinity of Crater peak. Because two relatively quiet days have passed since the earthquake swarm of Monday night, the color code today is change to YELLOW. The volcano is still unstable, and an eruption could occur without additional warning."
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URL of this document: http://volcanoes.usgs.gov/About/What/Erupt/NoEruptionSpurr.html
Last modified: December 17, 1998