Tag Archives: earthquake

Magma Rising

Mount Edgecumbe displacement; Graphic credit: AVO

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″.

Earthquakes in and around Mt Edgecumbe, Map credit: AVO

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

Mount Edgecumbe; Photo credit: AVO

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.

27 March 1964

Anchorage, Alaska after the 9.2 Good Friday Earthquake

Alaskan Swarm

Map credit: AEC

A swarm of earthquakes and aftershocks hit the Aleutian Chain, just past Unalaska, on Tuesday. A couple of foreshocks were detected, then a 6.8 magnitude earthquake – which was the largest of the swarm, followed by a whole series of aftershocks. A dozen of the aftershocks came it at a 4.4 or higher, with one 6.6 magnitude shaker.

According to the Alaska Earthquake Center, the event was a “very unusual, very energetic swarm of earthquakes.”

No major damage was reported, and the earthquakes did not generate any tsunamis.

Varying Frost

Map by AlaskaWx

I found this map fascinating. There is almost a month differential across the Fairbanks Borough on the date of the first freeze this fall. I was in the August 18 Camp, which my zucchini never really recovered from.

Many of the recording areas with “After Sept 14”, will fall today, the 15th, as we are expected to drop into the Blue Zone by morning. My place was at 23F on Tuesday morning.

Officially, the Fairbanks Airport is on a decent streak of 135 days above freezing. Which is the fourth longest since recording began. 144 days is the record, which happened in 1974.

There was a 4.9 magnitude earthquake just east of Fairbanks on Monday night, just before 10pm. The cabin went through a decent shake.

Atka Volcanic Complex

Earthquake activity on Atka Island

The southern portion of Atka Island is older than the north, with some volcanic rock dating back 5 million years. The active northern part of the island once had one large cone, which was lost in a large eruption, and is now peppered with several smaller volcanos.

A volcanic complex can have several vents, and a widely varying composition of lava. Seismic activity within a complex can be difficult to pinpoint the source of the activity. Which vent is rumbling now? Some of those smaller vents have developed into stratovolcanoes.

Korovin Volcano has been very active in recent times, while Mount Kliuchef last erupted in 1812. The Atka Complex recently was elevated to a Level Yellow, due to seismic activity on the island. Interestingly, the swarm of activity is not near the known suspects, but several kilometers the the west and southwest, and approximately 10 miles from the community of Atka.

Source: AVO

Shaking in Chignik

The 8.2 magnitude earthquake and the 140 aftershocks

At around 10:30 on Wednesday night, the alarm bells went off, and people across Alaska’s southern coast made a bee-line for higher ground. An 8.2 magnitude earthquake struck the interface between the subducting Pacific and overriding North American plates. This interface is known as the Aleutian Megathrust,and it is a very active seismic region. In fact, a 7.6 magnitude earthquake hit the area almost a year ago exactly.

Wave action

A tsunami warning was immediately issued for coastal communities, but luckily incoming waves never reached heights over a 1/4 meter, and the warning was lifted a little over two hours later.

This was the first 8.0+ earthquake to hit the United States in 50 years. In the 12 hours after the initial quake, the area received 140 aftershocks, with the largest being a 6.1. In 1938, the same area experienced an 8.3 magnitude shaker.

NWS Priority Warnings Chart

Interestingly, Tsunami Warning is Priority #1 on the National Weather Service priority list. One would hope that Nuclear Power Plant Meltdown is higher on a different agency’s list.

The Good Friday Earthquake

Aerial view of Anchorage’s Park Strip the day after the 9.2 quake; Photo from the University of Alaska Archives

Saturday, March 27 was the 57th Anniversary of the 1964 Good Friday Earthquake that hit south-central Alaska. The 9.2 magnitude earthquake struck at 5:36 pm AST, and the earth shook for the next 4 minutes and 28 seconds. Witnesses say that the earth roared like a freight train for that entire time.

The epicenter was 78 miles from Anchorage in Prince William Sound. It was a relatively shallow quake, with a depth of roughly 15 miles. 131 people were killed due to the earthquake, with 122 of the deaths due to the resulting tsunamis.

Downtown Anchorage after the 1964 earthquake; Photo from the University of Alaska Archives

Seward, Kodiak, Valdez, Chenega, were all hit by tsunamis. Shoup Bay was hit by the largest tsunami with a wave height of 220 feet.

In the first 24 hours after the main shaker, there were 11 aftershocks over 6.0, with another nine over the following three weeks. Thousands of aftershocks hit the area over the next year.

Alaska Jökulhlaup

A large glacial dam gave way in Southeast Alaska this summer. Known by its Icelandic term: jökulhlaup, the power of this sudden release of pent up water can be incredibly destructive.

The terminus of Lituya Glacier; Photo credit: NPS/J. Capra

Desolation Lake, which sits above the Lituya Glacier in Desolation Valley, collects meltwater from both the Desolation and Fairweather Glaciers. That meltwater is normally blocked by the Lituya Glacier, forming the roughly four square mile lake.

The water level suddenly dropped 200 feet.

A commercial fisherman, Jim Moore, along with his two grandsons, tried to enter Lituya Bay to fish for Chinooks in August. They should have been riding the tide into the bay, but the unusually muddy water was moving outward, and it was filled with trees and other debris. The bay was also filled with small icebergs. Moore managed to bring some of the ancient ice onboard for his coolers, then left the bay, instead of fighting the dangerous current.

Lituya Glacier terminus and delta; Satellite image credit: USGS

It is one of the largest jökulhlaups known to have occurred in Alaska. The water found a path under the Lituya Glacier, causing a rush that would have rivaled the hourly discharge of the Amazon River. It would have lasted for several days.*

Lituya Bay has a history. In 1958, an earthquake triggered a landslide that started one of the largest known tsunamis at over 1700 feet.

*NPS Geologist, Michael Loso

Whole Lotta Shakin’

The Alaska Earthquake Center reported 50,289 earthquakes in the state of Alaska for 2019. That did not break the record that was set in 2018, but it’s enough for the year to come in second place.

In the video above, each frame is a day, in a time-lapse of 2019 earthquakes. Pretty amazing to see it in this form. Kudos to AEC.