Geologic Background:
Gorely consists of five small overlapping
stratovolcanoes with a 9x13.5 km caldera formed
Å40,000-50,000 years ago. The massive Gorely complex
contains 11 summit and 30 flank craters. During the early
Holocene, activity was characterized by frequent mild
eruptions with occasional larger explosions and lava
flows. Quiescent periods became longer between 6,000 and
2,000 years ago, and thereafter the activity was mainly
explosive. About 600-650 years ago intermittent strong
explosions and lava flows accompanied frequent mild
eruptions.
Historic Activity:
- Eruptions in 1828, 1832, 1855, 1929-1931, 1961, and
1980-1981. Historical eruptions consisted of Vulcanian
and phreatic explosions of moderate volume.
Recent Activity:
- Early phreatic explosions followed by later ash
explosions from December 27, 1984 to January 8, 1985. Ash
clouds reached heights of 3 km and extended 100 km to the
east.
- Seismic activity increased on Sept. 19, 1996 when
more than 20 earthquakes (M<1.8) were recorded, but no
sign of eruptive activity was observed.
- Shallow earthquake swarm in October 1999.
- Low seismicity from December 1999 through mid-October
2000.
Data Sources:
- Smithsonian's SEAN Bulletin (V. 5, No. 7 and V. 10,
No. 1)
- Global Volcanism Network (V. 21, No. 9 and V. 25, No.
9).
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