Report on Great Sitkin (United States) — 22 February-28 February 2023
Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
22 February-28 February 2023
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2023. Report on Great Sitkin (United States). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 22 February-28 February 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 at Great Sitkin was confirmed by recent satellite images. A radar image from 19 February showed advancement of the E lobe of the flow field. Additionally, a smaller lobe to the S was advancing towards the crater rim where lava previously spilled down the SW flank in 2021-2022. Lava effusion in the summit crater was visible in 24 and 26 February satellite images. Seismicity was very low 22-28 February with a few local earthquakes detected during 22-23 and 24-25 February. Weather cloud cover sometimes prevented webcam and satellite views. 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)