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Report on Great Sitkin (United States) — 13 October-19 October 2021


Great Sitkin

Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
13 October-19 October 2021
Managing Editor: Sally Kuhn Sennert

Please cite this report as:

Global Volcanism Program, 2021. Report on Great Sitkin (United States). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 13 October-19 October 2021. Smithsonian Institution and US Geological Survey.

Weekly Report (13 October-19 October 2021)

Great Sitkin

United States

52.076°N, 176.13°W; summit elev. 1740 m

All times are local (unless otherwise noted)


AVO reported that lava effusion continued at Great Sitkin during 13-19 October. Seismicity remained elevated and was characterized by small earthquakes consistent with lava effusion, though an outage affected geophysical data streams during 16-18 October. Satellite images acquired on 11 October showed that lava filled more than half of the summit crater, flowing onto the S and W flanks, and had recently reached the N crater rim. Lava traveled 330 m down the S flank, 350 m down the W flank, descended small valleys, and in some areas, advanced over snow and ice. Blocks that had detached from the end of the W flow descended 450 m. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Geological Summary. The Great Sitkin volcano forms much of the northern side of Great Sitkin Island. A younger parasitic volcano capped by a small, 0.8 x 1.2 km ice-filled summit caldera was constructed within a large late-Pleistocene or early Holocene scarp formed by massive edifice failure that truncated an ancestral volcano and produced a submarine debris avalanche. Deposits from this and an older debris avalanche from a source to the south cover a broad area of the ocean floor north of the volcano. The summit lies along the eastern rim of the younger collapse scarp. Deposits from an earlier caldera-forming eruption of unknown age cover the flanks of the island to a depth up to 6 m. The small younger caldera was partially filled by lava domes emplaced in 1945 and 1974, and five small older flank lava domes, two of which lie on the coastline, were constructed along northwest- and NNW-trending lines. Hot springs, mud pots, and fumaroles occur near the head of Big Fox Creek, south of the volcano. Historical eruptions have been recorded since the late-19th century.

Source: US Geological Survey Alaska Volcano Observatory (AVO)