West Coast Seismic Alert: 2 Alaskan Volcanoes Erupt
by AMY S.
PrepperFortress.com
MAY 19, 2017
Alaska
The biggest volcanic news of the last month has been the surprising and vigorous eruptions at Bogoslof in the Aleutians of Alaska. After producing a large explosive eruption , the volcano has followed up by adding more explosions every day or so, many of which reached 5 to 10 kilometers (15,000-35,000 feet) over the small island. Just yesterday , the volcano produced another explosion that reached 10 kilometers (33,000 feet). The highly explosive nature of these eruptions is likely rooted in the interaction between the new magma reaching the surface and the abundant seawater it meets when it erupts. That water can quickly flash to steam and help fragment the magma into ash, adding to the explosivity of the eruption.
Alaskan volcanoes have produced one or two eruptions per year since 1900. At least 20 catastrophic caldera-forming eruptions have occurred in the past 10,000 years; the awesome eruption of 1912 at Novarupta in the Katmai National Monument is the most recent. Scientists are particularly concerned about the volcanoes whose eruptions can affect the Cook Inlet region, where 60 percent of Alaska’s population lives.
How many volcanoes are there in Alaska?
The Alaska Peninsula and the Aleutian Islands have about 80 major volcanic centers that consist of one or more volcanoes.
Mount St. Helens is keeping up its unsettled 2017, this time with another small earthquake swarm. The USGS detected over 120 earthquakes over the last few days, all occurring 2-4 kilometers (1-2 miles) beneath the volcano and all very small (less than M1). These earthquakes, like the ones that happened earlier this year, are likely caused by magma moving or faults adjusting as pressure changes within the magmatic system underneath Mount St. Helens. It doesn’t change the status of the volcano: It’s active, taking what will likely be a brief rest before its next eruption. That could still be years from now.
“Mega Quakes” can really happen.
The magnitude of an earthquake is related to the area of the fault on which it occurs – the larger the fault area, the larger the earthquake. The San Andreas Fault is 800 miles long and only about 10-12 miles deep, so that earthquakes larger than magnitude 8.3 are extremely unlikely.
The largest earthquake ever recorded by seismic instruments anywhere on theearth was a magnitude 9.5 earthquake in Chile on May 22, 1960. That earthquake occurred on a fault that is almost 1,000 miles long and 150 miles wide, dipping into the earth at a shallow angle. The magnitude scale is open-ended, meaning that scientists have not put a limit on how large an earthquake could be, but there is a limit just from the size of the earth. A magnitude 12 earthquake would require a fault larger than the earth itself.
Earthquakes only occur on the West Coast in the United States.
Earthquakes can strike any location at any time. But history shows they occur in the same general patterns over time, principally in three large zones of the earth. The world’s greatest earthquake zone, the circum-Pacific seismic belt, is found along the rim of the Pacific Ocean, where about 81 percent of the world’s largest earthquakes occur. That belt extends from Chile, northward along the South American coast through Central America, Mexico, the West Coast of the United States, the southern part of Alaska, through the Aleutian Islands to Japan, the Philippine Islands, New Guinea, the island groups of the Southwest Pacific, and to New Zealand.
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