Alerts raised after significant earthquakes under Makushin volcano in Alaska, U.S.

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Two earthquakes with magnitudes larger than 4.0 were registered in the vicinity of Makushin volcano, Alaska over the past 12 hours, representing a significant departure from background earthquake activity. The last eruption of this volcano took place in 2005 (VEI 1). A powerful VEI 5 eruption took place in 6100 BCE ± 50 years. Although no large eruptions have occurred in this century, small-to-moderate explosive eruptions have been recorded at Makushin since 1786.

The events — measuring M4.5 at 21:16 UTC on June 15, M4.1 at 00:34 UTC on June 16, and M3.9 at 02:38 UTC on June 16 — could be associated with volcanic unrest, the Alaska Volcano Observatory said.

As a result, the Aviation Color Code was raised to Yellow and Volcano Alert Level to Advisory.

Image credit: TW/SAM, Google

Makushin volcano as seen by Copernicus EU/Sentinel-2 satellite on June 3, 2020. Annotation: TW

"The unrest could result in a future eruption, however, that is not a certainty," AVO said. "Aftershocks continue, as would be expected with earthquakes of this size."

The volcano is monitored with a network of seismic instruments, web camera, GPS, satellite data, and regional infrasound and lightning detection instruments.

Geological summary

The ice-covered, 1800 m (5 905 feet) high Makushin volcano on northern Unalaska Island west of the town of Dutch Harbor is capped by a 2.5 km (1.5 miles) wide caldera. The broad, domical structure of Makushin contrasts with the steep-sided profiles of most other Aleutian stratovolcanoes.

Much of the volcano was formed during the Pleistocene, but the caldera (which formed about 8 000 years ago), Sugarloaf cone on the ENE flank, and a cluster of about a dozen explosion pits and cinder cones at Point Kadin on the WNW flank, are of Holocene age.

A broad band of NE-SW-trending satellitic vents cuts across the volcano. The composite Pakushin cone, with multiple summit craters, lies 8 km (5 miles) to the SW of Makushin.

 

Frequent explosive eruptions have occurred during the past 4 000 years, sometimes accompanied by pyroclastic flows and surges. Geothermal areas are found in the summit caldera of Makushin and on the SE and eastern flanks of the volcano. They represent the largest and most investigated high-temperature geothermal resources in Alaska. Small-to-moderate explosive eruptions have been recorded at Makushin since 1786.

This volcano is located within the Aleutian Islands, a UNESCO Biosphere Reserve property.

Featured image: Winter day at Makushin hot springs. Credit Travis Swangel

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