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Report on Great Sitkin (United States) — 2 August-8 August 2023


Great Sitkin

Smithsonian Institution / US Geological Survey
Weekly Volcanic Activity Report, 2 August-8 August 2023
Managing Editor: Sally Sennert.

Please cite this report as:

Global Volcanism Program, 2023. Report on Great Sitkin (United States) (Sennert, S, ed.). Weekly Volcanic Activity Report, 2 August-8 August 2023. Smithsonian Institution and US Geological Survey.

Weekly Report (2 August-8 August 2023)

Great Sitkin

United States

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

All times are local (unless otherwise noted)


AVO reported that slow lava effusion continued at Great Sitkin during 1-8 August, producing a thick flow in the summit crater. The eastern lobe continued to advance into glacial ice surrounding the crater, causing the ice to deform and crack, based on a 1 August satellite image. Seismicity remained slightly elevated throughout the week. Weather clouds often obscured satellite and webcam views, though a clear image showed no unusual activity during 5-6 August and an image showed diffuse steaming from the lava surface during 6-7 August. The Volcano Alert Level remained at Watch (the third level on a four-level scale) and the Aviation Color Code remained at Orange (the third color on a four-color scale).

Geological Summary. The Great Sitkin volcano forms much of the northern side of Great Sitkin Island. A younger 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 older edifice and produced a submarine debris avalanche. Deposits from this and an even 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. Eruptions have been recorded since the late-19th century.

Source: US Geological Survey Alaska Volcano Observatory (AVO)