Mount Spurr is grumbling just west of Anchorage. Alaska Volcano Observatory is monitoring earthquakes, visible changes and gas emissions at Spurr. They think that we are headed for a new volcanic eruption. This would be the first one since early 1990. The Yellow Alert has been placed on Spurr due to the recent unrest.
Alaska has more potentially active volcanic sites than any other US state, thanks to the Aleutian chain that stretches from Anchorage to Russia and the Northern Pacific. Also, there are clusters of volcanic peaks in the Wrangell range in eastern Alaska near Juneau. What were Alaska’s biggest eruptions over the last 10,000-year period (also called the Holocene), with all of these volcanoes?
There are some caveats with this list, as there is for any other. This list includes the biggest known eruptions. It is difficult to hide an eruption of this magnitude. Volcanic deposits are easily weathered or eroded so we may underestimate the size of an eruption. This list was compiled based on the best estimates we have at this time, which can sometimes be incorrect. We may be mistaken about the age of an eruption and end up with the Holocene. That’s okay! That’s science!
To rank them, I will use the Volcanic Explosivity Index. The Volcanic Explosivity Index is calculated based on volcanic debris released, which are usually measured in cubic kilometers. One cubic kilometer equals over 264 billion gallon! This information will also come from the Global Volcanism Program Database of the Smithsonian. I will list the oldest ones first, rather than trying to divide them up by volume. This can be difficult in Alaska.
Roundtop VEI 5, 9600 years ago. Many eruptions occur on remote islands, and Roundtop was no exception. Roundtop, located on Unimak Island is covered in glaciers today, but the southwest parts of Alaska Peninsula is still awash with ash and volcanic debris from the VEI 5 eruption. Roundtop has not erupted since that time.
Seguam VEI 5, 9300 years ago. This eruption was from one of many islands that stretch out to the north Pacific from Alaska Peninsula. Seguam was the site of a massive eruption that occurred 9,300 years back. It took place in one of two calderas of this isolated island with the same name. It has since had many smaller eruptions, (VEI 1-3) which have gradually healed the scars left by this explosion. Seguam has literally moved to the middle of nowhere. GVP says that no one is within 100 km of the volcanic crater. This also occurred within the last few hundred of Roundtop. This is odd. This is not unusual in an active volcanic chain like the Aleutians.
Fisher Caldera – VEI 6, 7.420 BCE. The Fisher Caldera is located on Unimak Island, which also includes Roundtop. The volcano, not to be outdone by its rivals, erupted over 9,000-years ago. It created an 18km-long caldera. The Pacific Ocean and Bering sea were flooded with pyroclastic flow from this eruption. The volcano has also had VEI 5 eruptions 5,100 year ago, and erupted between 1826-1830.
Roy Wood of the USGS took this aerial view of Aniakchak, Alaska. Credit: National Park Service
Aniakchak VEI 6, 6,300 to 1645 BCE. I lumped some dates here. Aniakchak is known to have produced several large eruptions. This volcano in Alaska Peninsula has two large explosions. “Aniakchak I”. It’s odd that, despite its size, the volcano didn’t appear to be created. The valleys surrounding the volcano are covered in pyroclastic flows. The more recent eruption, called “Aniakchak II.” The eruption was massive, with 70 cubic kilometres of volcanic tephra. The volcano also released pyroclastic flow 50 km out of the volcano, across Alaska Peninsula to the sea. This generated a tsunami. It has been the most active volcano in the Eastern Aleutians since then.
Black Peak – VEI 6- 1900 BCE: Black Peak may look like a craggy, rocky monster. However, the eruption of 1900 BCE created a large caldera and covered some valleys with volcanic tephra measuring 100 metres. Black Peak, however, has not had any or many eruptions in the past, as opposed to Aniakchak, Veniaminof and other volcanoes.
Veniaminof eruption in 2013: Lava and ash. AVO/USGS.
Veniaminof – VEI 6- 1750 BCE : Another massive eruption from a volcanic cone on Alaska Peninsula… possibly in a 300 year time frame (with Aniakchak, Black Peak). The vents from this caldera-capped volcanic cone extend for many kilometers beyond the Veniaminof caldera. In the 21st Century, it has been extremely active with nine different eruption episodes as recent as 2021. Most of them, as with many other calderas, are caused by cinder cones that form within the caldera and can erupt massive lava flows.
Okmok – VEI 6, 100 BCE : Okmok, located in the Aleutian islands is on Unmak Island. The caldera of Okmok, if drained, would look a lot similar to Oregon’s Crater lake (the site of the biggest eruption in the US for the last 10,000 years). Some deposits in the Okmok Caldera show signs of waves. Okmok’s last eruption was in 2008. One of the cinder cones within the caldera produced lavas as it repaired the scars from previous blasts and that of 2008
Churchill – VEI 6, 847, and 60 CE. I am lumping together Churchill’s two huge blasts, but East and North White River Ash Deposits may have been the most explosive explosions during the Holocene. White River Ash is commonly found in British Isles peatbogs. Volcanologists were unable to agree upon the origin of the deposits until recently. Even today, Mount Churchill is an enigmatic and remote mountain in the Wrangell range that seems to have been the site for these massive eruptions.
Novarupta VEI 6, 1912 C.E.: This is the big Alaskan volcano eruption you may have heard about. It was not only the biggest eruption in the twentieth century but it produced the amazing ” Valley of 10,000 Smokes “. It was an unusual eruption, as it occurred between two known volcanoes. Katmai was not directly affected by the 1912 eruption (though at first thought to be its source). Novarupta, a rhyolite-dome, now caps the source of explosion. Alaska Volcano Observatory released a press release about the impact of this explosion, citing strong winds that blew volcanic ash around earlier in this week.
