When earthquakes start to show up in clusters, volcanic activity often follows close behind. That's exactly what's happening in Alaska, where a long-dormant volcano, Mount Edgecumbe, appears to be waking up.
What's Happening With Mount Edgecumbe?
In April 2022, scientists noticed a cluster of earthquake activity at Mount Edgecumbe, a dormant volcano about 15 miles outside Sitka, Alaska. While Mount Edgecumbe has been inactive for more than 800 years, it appears that volcanic activity is the source of the earthquakes.
Scientists at the Alaska Volcano Observatory and Alaska Satellite Facility determined that the increased seismic activity was the result of magma movement under the volcano. The magma, which is the semi-molten, subterranean material that becomes lava when a volcano erupts, had held steady at 12 miles under the Earth's surface. However, satellite radar and computer data revealed that the magma had risen to only 6 miles under the surface.
This movement of magma caused the earthquakes and some deformation of the ground around the volcano. The surface elevation of the volcano changed by about 10.6 inches. This movement started in about 2018, with the Earth's surface moving 3.4 inches per year since then.
Mount Edgecumbe has been dormant for 800 to 900 years, according to indigenous oral histories. Its last major eruption appears to have occurred 4,500 years ago. Its recent magma movement is the quickest rate of volcanic deformation noticed in Alaska. What's happening is fairly unusual since dormant volcanoes rarely reactivate in such a fashion.
Scientists are also interested in what's happening at Mount Edgecumbe because the volcano sits on a transform fault, where two tectonic plates slide past each other. Volcanoes on transform faults are not typically active and don't tend to erupt. The unusual activity occurring at Mount Edgecumbe is, therefore, especially intriguing.
How Can Scientists Tell a Volcano Is Becoming Active?
Volcanologists use seismometers to detect the movement of the earth, placing them around the perimeter of a volcano to figure out just where earthquakes are happening. These sensitive instruments can detect even the smallest tremors, far smaller than a human would notice.
When magma moves under a volcano, it can cause tiny earthquakes in a couple of ways. Sometimes the magma forces itself into existing cracks, moving the earth slightly. It can also form pools that expand, pushing the earth out of its way. As magma moves upward, the earth bulges, triggering small seismic movements that seismometers can pick up.
Seismologists and volcanologists also use satellite-based instruments to monitor volcano activity. Sensitive radar tools can measure tiny changes in the shape of the Earth. When magma approaches within a few miles of the Earth's surface, these satellite instruments can measure the resulting bulge. Scientists combine that data with their seismometer information to determine the exact location of the magma and its shape.
The Chances of an Eruption
The life cycle of a volcano can stretch across hundreds of thousands of years. When magma from a volcano reaches the surface, it's considered active. When that magma cools and stays put beneath the surface, the volcano is considered dormant. Over the years and centuries, a dormant volcano can become active again when magma becomes restless and starts to move about.
However, that doesn't mean the volcano is going to erupt. Typically, magma and seismic activity surrounding a volcano quiets down after several months.
And there are no signs that Mount Edgecumbe is going to erupt in the foreseeable future. While the volcano has been recategorized as "historically active" (rather than "dormant"), it's not showing the changes in deformation of the Earth's surface and levels of seismic activity that accompany volcanoes in their pre-eruption mode.
Scientists have placed extra monitoring equipment around the volcano and are keeping an eye on other local volcanoes. However, there's no need for anyone in the Sitka area to be concerned unless they see smoke coming from the top of the volcano — an event that's extremely unlikely.
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