Report on Great Sitkin (United States) — 6 September-12 September 2023
Smithsonian Institution / US Geological Survey
Weekly Volcanic Activity Report, 6 September-12 September 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, 6 September-12 September 2023. Smithsonian Institution and US Geological Survey.
52.076°N, 176.13°W; summit elev. 1740 m
All times are local (unless otherwise noted)
AVO reported that slow lava effusion likely continued at Great Sitkin during 6-12 September, producing a thick flow in the summit crater that mainly expanded E. Seismicity was low; earthquakes were detected daily and were numerous during 6-7 September. Web camera images showed diffuse gas emissions rising from the summit during 6-7 September and weakly elevated surface temperatures were identified in satellite data during 6-7 and 10-11 September. Weather clouds often prevented satellite and webcam observations. 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 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.