·

Ash emissions at Semisopochnoi increase, Aviation Color Code raised to Red, Alaska

ash-emissions-at-semisopochnoi-increase-aviation-color-code-raised-to-red-alaska

Ash emissions from the ongoing eruption at Semisopochnoi volcano, Alaska have increased in frequency and intensity, prompting the Alaska Volcano Observatory (AVO) to raise the Aviation Color Code to Red at 05:58 UTC on September 20, 2021.

Satellite images show an ash cloud at an estimated altitude of 4.6 km (15 000 feet) above sea level extending approximately 100 km (60 miles) to the southeast through 05:00 UTC.

Explosions have been observed throughout the day and increased sulfur dioxide gas emissions have been observed in satellite data.

"These observations represent an increase in eruptive activity and Aviation Color Code and Volcano Alert Level are being increased to RED/WARNING," AVO said.1

Increasing high clouds over Semisopochnoi will likely obscure satellite views of ash emissions.

Seismic and infrasound monitoring will continue to provide notice of ongoing explosive activity, however, it cannot determine the height or extent of ash emissions. 

Geological summary

Semisopochnoi, the largest subaerial volcano of the western Aleutians, is 20 km (12.4 miles) wide at sea level and contains an 8 km (5 miles) wide caldera. It formed as a result of the collapse of a low-angle, dominantly basaltic volcano following the eruption of a large volume of dacitic pumice.

The high point of the island is 1 221 m (4 005 feet) high Anvil Peak, a double-peaked late-Pleistocene cone that forms much of the island's northern part.

The three-peaked 774 m (2 539 feet) high Mount Cerberus volcano was constructed during the Holocene within the caldera. Each of the peaks contains a summit crater; lava flows on the northern flank of Cerberus appear younger than those on the southern side. 

Other post-caldera volcanoes include the symmetrical 855 m (2 903 feet) high Sugarloaf Peak SSE of the caldera and Lakeshore Cone, a small cinder cone at the edge of Fenner Lake in the NE part of the caldera.

Most documented historical eruptions have originated from Cerberus, although Coats (1950) considered that both Sugarloaf and Lakeshore Cone within the caldera could have been active during historical time.

This volcano is located within the Aleutian Islands, a UNESCO Biosphere Reserve property.2

References:

1 VOLCANO OBSERVATORY NOTICE FOR AVIATION (VONA) – Issued: 20210920/0558Z

2 Semisopochnoi – Geological summary – GVP

Featured image credit: AVO/USGS. Acquired on August 3, 2021

If you value what we do here, open your ad-free account and support our journalism.

Share:

Related articles

Producing content you read on this website takes a lot of time, effort, and hard work. If you value what we do here, select the level of your support and register your account.

Your support makes this project fully self-sustainable and keeps us independent and focused on the content we love to create and share.

All our supporters can browse the website without ads, allowing much faster speeds and a clean interface. Your comments will be instantly approved and you’ll have a direct line of communication with us from within your account dashboard. You can suggest new features and apps and you’ll be able to use them before they go live.

You can choose the level of your support.

Stay kind, vigilant and ready!

$5 /month

  • Ad-free account
  • Instant comments
  • Direct communication
  • New features and apps suggestions
  • Early access to new apps and features

$50 /year

$10 /month

  • Ad-free account
  • Instant comments
  • Direct communication
  • New features and apps suggestions
  • Early access to new apps and features

$100 /year

$25 /month

  • Ad-free account
  • Instant comments
  • Direct communication
  • New features and apps suggestions
  • Early access to new apps and features

$200 /year

You can also support us by sending us a one-off payment using PayPal:

Leave a reply

Your email address will not be published.