Tag Archives: AEC

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.


Glacier on the move

Muldrow Glacier in Denali National Park is surging:

Muldrow Glacier, with Traleika Glacier coming in from the top left

In early March, pilot Chris Palm, who took the photo above, noticed something very different about Denali Park’s famed Muldrow Glacier. The normally smooth surface of the glacier was broken up by crevasses stretching across the width of Muldrow.

The long awaited surge had begun.

The 39 mile long, Muldrow Glacier last surged in 1957, so scientists were thrilled to study a natural phenomenon that has not occurred here in 64 years.

Surge-type glaciers are relatively rare, with approximately 1% of the glaciers world-wide being surge glaciers. Denali National Park has several, most of which get their start from the face of North America’s tallest peak.

Newly formed transverse crevasses on Muldrow

As snow and ice builds up at the higher elevations of a glacier, meltwater is also building up underneath the glacier. This meltwater acts as a lubricant when the weight from above passes equilibrium. The glacier then surges downward at a rate of up to 100 times faster than normal. At some point, the meltwater trapped under the glacier will be released in an outburst flood. Once the water is reduced significantly, the glacier’s surge will slow and it will go back to a state of quiescent (non-surge) once again. Over time, the process repeats itself. Muldrow Glacier has a history of surging roughly every 50 years.

An animated time-lapse of Muldrow Glacier on the northeast flank of Denali. The starting time is August 2018.

There are two GPS stations on the glacier to monitor its movement. There are also four time-lapse cameras facing different areas of the glacier, including one at the terminus to monitor the glacier’s “bulldozing action”. Another is looking over the McKinley River in order to capture images of the outburst flood. The Alaska Earthquake Center also has a seismic monitoring station, and a sound station has also been installed in an attempt to capture the grinding sound of the surging glacier.

Mapping Muldrow’s movement

In 1957, most accounts have the surge starting in May, 1956 on Traleika Glacier, which is the main tributary of Muldrow. Muldrow Glacier would advance over 4 miles before the surge ended in September of 1957. Approximately 3.3 cubic kilometers of ice was redistributed from the upper reaches of the glacier to its toe. At the upper levels, the ice thickness had dropped as much as 170 meters, but the toe rose to a 200 foot tall ice wall.

Currently, the Muldrow Glacier is moving between 10 to 20 meters per day, and is only 800 meters short of the 1957 terminus. At the current rate of surge, Muldrow will reach the 1957 distance in June.

All images, photos and maps are courtesy of the NPS; Sources include: NPS – Denali NP&P, Alaska Department of Natural Resources, University of Alaska – Fairbanks


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.


Denali Fault Quake

Photo credit: Daily News-Miner

This week is the 17 year anniversary of the 2002 Denali Earthquake. At a magnitude of 7.9, to date, it is the largest quake I have personally experienced.

On 23 October 2002, the Denali Fault released a magnitude 6.7 quake. That would be a foreshock of what was to come on November 3.

Highway Shift; Richardson Highway, circa 2002

After the 6.7, I remember the Alaska Earthquake Center saying that the Denali Fault was capable of producing an 8.0. Sure enough, the fault came very close.

I was at an intersection in my ’66 Chevy C-20. All of a sudden, the truck was lurching all over the place, and I found it hard to stay on the brake pedal. There were two university students in the next lane, the passenger rolled down his window and asked what the hell was happening. I said, “Earthquake”. He then promptly hit the driver on the arm and said, “I told you it was an earthquake”.

The light changed, I drove on, but had to stop at the next light. The earth was still shaking. An elderly couple had been walking on the sidewalk, and the wife fell to the concrete, the husband was struggling to stay upright by hugging a signpost. Then the shaking was over. I rolled down the other window, to see if the couple was all right. They were, and I headed home to see if there was any damage.

The quake had ruptured 205 miles of earth along three different, yet connected faults in Interior Alaska. It was the largest ever recorded in Alaska’s Interior. It was the largest inland quake North America had seen in almost 150 years.

Both the Parks & Richardson Highways saw major damage. The Trans-Alaska Pipeline moved sideways 18 feet, and rose 5 feet. The engineers had designed for the fault, and the pipeline behaved exactly as it was designed to behave. Although, it did come within two feet of its sideways movement limit.

The Denali Earthquake was felt as far away as Louisiana.

Previously, the largest earthquake Fairbanks had experienced was a magnitude 7.3 in 1937.


How’s it shaking?


Sensor monitor reading at University of Alaska

Interior Alaskans felt the Earth move a bit on Tuesday morning. It wasn’t a big earthquake, at only magnitude 4.6, but it was widely felt at 7:18am. It’s note worthy, mainly because it has been a couple of years since I felt one pass through.

On Sunday morning, Kaktovik, which is located on the Beaufort Sea coast, woke up to a 6.4 magnitude quake. It was the largest earthquake ever recorded on Alaska’s North Slope.

Earthquakes in Alaska are far from unusual. An earthquake is detected once every 15 minutes, on average, within the state. In 2014, Alaska set a record with over 40,000 shakes. Over the past five years, the Alaska Earthquake Center has reported over 150,000 earthquakes. Of those, 31 had a magnitude over 6.0. and four went over 7.0. Seventy-five percent of all earthquakes over 5.0 within the United States happen in Alaska.

The 7.9 magnitude quake, that hit us in 2002 when the Denali Fault ruptured, is the largest I have experience. The 1964 Good Friday Earthquake was a magnitude 9.2, and it is still the second largest earthquake ever recorded anywhere on the globe.

Graph and stats credit: Alaska Earthquake Center