Increased seismicity, ice-rock avalanche at Iliamna, Alaska

An increase in seismicity has been observed at Iliamna volcano beginning at 20:00 UTC on June 5, 2023. As a result, the Alaska Volcano Observatory (AVO) raised the Aviation Color Code and Volcano Alert level for Iliamna to Yellow and Advisory.

The rate of earthquakes initially occurred in 1-minute intervals and have been becoming more closely spaced. “There is a possibility that the earthquakes may be related to magmatic movement or hydrothermal fluids beneath the volcano,” AVO said.

However, similar activity has been observed before large mass movements or avalanches at Iliamna volcano, and AVO said it cannot rule out either possibility at this time.¹

This earthquake activity culminated in an ice-rock avalanche slightly before 01:14 UTC on June 6.

“Although we lack visual confirmation at this time, the seismic signals recorded match historic observations of avalanches associated with Red Glacier on Iliamna Volcano’s eastern flank.”

Seismicity has since declined to background levels and the Aviation Color Code and Volcano Alert Level were lowered to Green and Normal.

Geological summary

Iliamna is a prominent, 3 053-m-high (10 016 feet) glacier-covered stratovolcano in Lake Clark National Park on the western side of Cook Inlet, about 225 km (140 miles) SW of Anchorage.

Its flat-topped summit is flanked on the south, along a 5-km-long (3.1 miles) ridge, by the prominent North and South Twin Peaks, satellitic lava dome complexes. The Johnson Glacier dome complex lies on the NE flank.

Steep headwalls on the southern and eastern flanks expose an inaccessible cross-section of the volcano. Major glaciers radiate from the summit, and valleys below the summit contain debris-avalanche and lahar deposits.

Only a few major Holocene explosive eruptions have occurred from the deeply dissected volcano, which lacks a distinct crater. Most of the reports of historical eruptions may represent plumes from vigorous fumaroles east and SE of the summit, which are often mistaken for eruption columns (Miller et al., 1998).

Eruptions producing pyroclastic flows have been dated at as recent as about 300 and 140 years ago (into the historical period), and elevated seismicity accompanying dike emplacement beneath the volcano was recorded in 1996.²

References:

¹ AVO/USGS Volcanic Activity Notice for Iliamna volcano – June 5 and 6, 2023

² Iliamna – Geological summary – GVP

Featured image credit: Aerial view of Iliamna’s summit. Credit: Taryn Lopez

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