Geologic Background:
Alamagan is the emergent summit of a large
stratovolcano with a roughly 350-m-deep summit crater
east of the center of the island. The exposed cone is
largely Holocene in age. A 1.6 x 1 km graben cuts the
southwest flank. A voluminous basaltic-andesite lava flow
has extended the northern coast of the island, and a lava
platform also occurs on the south flank. Pyroclastic-flow
deposits erupted about 1000 years ago have been dated.
Historic Activity:
- Most of the recent eruptions have been violently
explosive; thick pyroclastic-flow deposits cover most of
the island. A small eruption was reported in 1864, and
another was thought to have taken place in 1887 or a few
years earlier, but these historical reports are
considered to be invalid..
Recent Activity:
Data Sources:
- Global Volcanism Network (V. 17, No. 6)
|