High-level eruption at Shishaldin volcano, Aviation Color Code raised to Red, Alaska

An ash cloud from Alaska’s Shishaldin Volcano soared above 6 km (20 000 feet) above sea level at 13:24 UTC and up to 13.7 km (45 000 feet) by 14:18 UTC on September 25, 2023. The eruption, monitored through an array of sensors and satellite data, led authorities to elevate the Aviation Color Code to Red and the Volcano Alert Level to Warning.

The eruption followed two days of increased volcanic activity. The National Weather Service issued a Special Weather Statement concerning possible trace ash on False Pass and a SIGMET for the ash cloud.

According to the Volcanic Ash Advisory issued by the Anchorage VAAC at 14:18 UTC, the eruption began with multiple lightning strikes. The ash cloud was rising up to 13.7 km (45 000 feet) above sea level at 14:18 UTC.

Hazard analysis suggests that pyroclastic flows and mudflows are likely on the immediate flanks of the volcano, based on previous eruption cycles. Experts anticipate that significant ash emissions will persist for several hours.

Shishaldin Volcano is continuously monitored by a combination of local seismic and infrasound sensors, web cameras, and a telemetered geodetic network. Additional monitoring tools include regional infrasound and lighting data, as well as satellite imagery.

Historically, Shishaldin Volcano has had at least 54 episodes of unrest, including over 26 confirmed eruptions since 1824. Located near the center of Unimak Island in the eastern Aleutian Islands, it has a base diameter of roughly 16 km (10 miles). The volcano typically emits a steam plume and occasional small amounts of ash from a 200 m (660 feet) wide funnel-shaped summit crater. A notable eruption in April – May 1999 generated an ash column that rose to 14 km (45 000 feet) above sea level.

References:

¹ AVO/USGS Volcanic Activity Notice for Shishaldin volcano – 14:02 UTC on September 25, 2023

Featured image credit: USGS/AVO