Last April, a series of earthquakes around and under Mount Edgecumbe brought greater attention to what was considered a dormant volcano. Measurements show that magma is moving deep underneath Edgecumbe. Other signs have also brought new scrutiny: Hikers have discovered vents with bubbling gas near the volcano, and satellite images show a bulging of the ground around Edgecumbe.
None of this means that Edgecumbe will blow anytime soon, but the State of Alaska has reclassified Mount Edgecumbe as a “high risk volcano”. With 73,000 people living in the region, the reclassification was probably wise. Currently, the east side of Edgecumbe is bulging faster than any volcano in Alaska.
The Alaska Volcano Observatory has plans to install seismic sensors and other instruments on Mount Edgecumbe over the coming months. Core samples show that the volcano erupted between 4000 -4300 years ago, and Tlingit oral history tells of an eruption approximately 800 years ago.
Currently, Alaska has one volcano at Code Orange, and four others at Code Yellow.
A couple of weeks ago, I posted about the swarm of earthquakes underneath Mount Edgecumbe. The numbers are in, and radar satellite data reveals a ground deformation around the volcano. Data was analyzed for the past 7.5 years, and since 2018, an uplift around Mt Edgecumbe has been constant. The peak activity, around the crater, has shown an average uplift of 3.4″ per year since 2018, and a total uplift of 10.6″.
With the data of the ground deformation, AVO has come to the conclusion that the swarm of earthquakes is due to the movement of magma below Mount Edgecumbe, and not due to tectonic activity.
Mount Edgecumbe, a 3200 foot high stratovolcano, lies 15 miles to the west of the community of Sitka. There is no volcanic monitoring system on Edgecumbe, but there is at Sitka. AVO plans to install instruments closer to the volcano in the near future.
The rising of magma under a volcano does not necessarily mean that an eruption is imminent. The deformation and earthquakes could cease at any time. If an eruption were to occur, warning signs such as increased rate of deformation, and an increase in the earthquake swarms, would give advance warning of an eruption.
Mount Edgecumbe is a 3200′ stratovolcano located on Kruzof Island. The volcano is approximately 15 miles from the town of Sitka, which was Alaska’s capital prior to its purchase from Russia by the United States.
Mount Edgecumbe has been dormant for at least 800 years. Recently, however, there has been a swarm of over 100 earthquakes from near the volcano. The swarm does not mean that an eruption is near, but the number is somewhat unusual. The previous two years saw only twenty quakes each year. Volcanologists are studying the data to see if these recent earthquakes are volcanic or tectonic in nature.
Tlingit oral history has the volcano having small eruptions roughly 800 years ago. The last eruption in the geological record happened 4500 years ago. Mount Edgecumbe had a massive eruption 13,000 – 15,000 years ago. That eruption dropped dropped 3 feet of volcanic ash on what is now Sitka, and 98 feet of ash fell on Kruzof Island.
Alaska has had 90 volcanos that have erupted in the past 10,000 years. Currently, we have three that are at Level Orange and one that is at Level Yellow.