Yesterday was the 59th anniversary of Alaska’s Good Friday Earthquake. The above photo from the Alaska Digital Archives show the rail line north of Seward after the 9.2 magnitude quake struck South-central Alaska.
Tag Archives: earthquake
Getting Edgy Under Edgecumbe
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.
Reverb in the Nenana Basin
The Nenana Basin lies southwest of Fairbanks. The Parks Highway runs along its eastern boundary, and the Tanana River runs right through the middle of it. The basin is 56 miles long and 7.5 miles wide. Over the course of millions of years, the basin has been filled in with river sediment. Considering that the basin is 4 miles deep (7km), that is a lot of fill.
Several entities have been drilling test holes throughout the basin looking for oil and gas, so the University of Alaska – Fairbanks has been studying the basin’s makeup. One thing they found is that earthquakes last longer and feel a lot stronger in the basin, than just outside the basin.
The shockwaves from an earthquake travel differently through the sediment, which is mostly gravel, than the solid rock along the ridge lines. Reverberation also plays a roll here: The seismic waves are amplified by the basin walls and floor.
Seismic sensors have verified what local residents have been claiming: The shaking is a lot worse down in The Flats than up in the hills.
Source credit: Alaska Public Media, University of Alaska – Fairbanks
Magma Rising
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
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.
Alaskan Swarm
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
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
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
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.
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.
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.
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