Pondering the Mysteries of the Aleutian Arc
If a space alien pondering Earth wanted to figure out what's going on within this blue and brown sphere, it would do well to touch down near the Aleutian Arc, where fresh craters and steaming mountains are compelling clues that something special is happening.
"If you want to learn about a planet, you have to go where the action is," said John Eichelberger, a volcanologist and professor at the Geophysical Institute of the University of Alaska Fairbanks.
Alaska has more than its share of Earth's violent geological action; Alaska is home of the largest volcanic eruption on the planet this century (at Katmai, in 1912) and the second-largest earthquake (the 9.2 magnitude earthquake of 1964) recorded.
The restless nature of Alaska is related to the processes that formed and continue to drive the pyrotechnic displays of the Aleutian Arc. The Aleutian Arc is just what it sounds like, a curve of mountains and volcanic islands extending like a smile from the Alaska Range west to Russia's Kamchatka Peninsula. The most visible part of the arc is the Aleutian Islands, home to about 100 volcanoes.
The curving symmetry of the Aleutians is not a coincidence; it's due to a process called subduction, which acts with near-textbook form beneath the Aleutian Arc. In subduction as it applies in Alaska, the Pacific plate, powered by heat from Earth's core, dives below the North American plate beneath the Aleutian Islands. As one plate grinds its way beneath another, mountains are pushed up on the other side. "Although many planets are geologically active, this is the only one eating and regurgitating its own crust," Eichelberger said. "When you shove a plate into a sphere, you get an arc. The Aleutian Arc is one of the simplest and most visible subduction zones on the planet."
And it's getting to be one of the most important. Fishermen and freight captains sail the waters surrounding the Aleutian Arc every year. Dozens of passenger and cargo airplanes fly over the Aleutian Arc every day. Sometimes the volcanoes of the Aleutian Arc interfere with peoples' travel plans, spitting ash into jet travel lanes. Sometimes the abrasive ash from volcanoes causes jet engines to seize and quit. "Twenty-thousand air passengers a day are sitting right above those 100 volcanoes," Eichelberger said. "Potentially lethal ash clouds wander into their air space about four or five times a year."
This hazard is a good reason to learn more about the Aleutian Arc, one of the frontiers of Earth science. Nobody knows, for example, why Mt. McKinley is not a volcano, even though it sits directly above where one should be: a region about 60 miles beneath the ground where the Pacific plate is sliding beneath the North American plate. In areas farther west where the Pacific plate meets the North American plate at the same depth, the interaction produces the molten rock that forms a volcano. Mt. McKinley is not the only oddball. Eichelberger said many of the Wrangell Mountains should be volcanoes but are not.
Though the Aleutian Arc is rich with potential information about the planet, it has been largely ignored by scientists because of its remoteness, its distance from Moscow and Washington D.C., and past tension between the U.S. and Russia, Eichelberger said. After a recent meeting with more than 100 Russian scientists and 30 American and Japanese scientists in Russia, Eichelberger hopes the door is now open for further study of the Aleutian Arc, a frontier of geophysics that's right in our own backyard.
