Alaska earthquake shakes up Beaver Creek Reservoir
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The magnitude 7.9 earthquake in Alaska on Sunday left local Earth science teacher and avid fisherman Keith Evenson scrambling for his gear on the banks of Beaver Creek Reservoir.
Evenson said he had just finished a weekend of fishing about 3:20 p.m. Upon pulling his kickboat out of the water, he put his life jacket and swim fins near the boat on shore and began to clean his catch.
Evenson described the lake that day as being "like glass" until the water level rose a foot, sweeping his boat, his gear and half of his fish back out into the water.
As he struggled to bring his boat back in and collect his gear, the rise and fall continued. Evenson said the rise and fall began about 3:30 p.m. and lasted about a minute. The water level continued to fluctuate by about 2 to 3 inches for another five minutes.
Evenson said he was confused by the sudden fluctuation, but thought that it could be one of two things.
First, he thought the water may have been "turning over," an event that Evenson said occurs in lakes in the fall when the warm water at the bottom of the lake replaces the colder water at the top.
Second, Evenson speculated the changes in water level could have been caused by an earthquake.
Evenson listened to the radio on his way home, but didn't hear anything about a quake, so he consulted with a local geologist, who told him that the water would have turned over about a month ago.
When Evenson saw coverage of the Alaska earthquake, he realized that the water level fluctuations were indeed caused by an earthquake that occurred nearly 1,700 miles away at 3:13 p.m. MST.
John Minsch of the U.S. Geological Survey Earthquake Center in Golden, Colo., Tuesday confirmed that Evenson witnessed effects from the surface waves of the earthquake, along the Denali fault line 90 miles south of Fairbanks, Alaska.
"It's called seiche,'" Minsch said. "When an enclosed body of water rises and falls immediately following an earthquake, it is caused by the surface waves from the quake."
The waves are too low frequency to actually be felt in the ground, but they do cause water level fluctuations similar to those Evenson described, Minsch said.
The surface waves are slower traveling than the initial shock waves, so, Minsch said, the time lapse would have been about right.
The earthquake caused similar effects as far away as Louisiana.