About Active Volcanoes in the United States
Most people have heard of Mount St. Helens, but how many people know that Mississippi once hosted an active volcano? The volcanic history of the United States is rich and varied, with eruptions arising from the global phenomenon of plate tectonics as well as more localized geologic events. Even today's active volcanoes are unpredictable and exciting. The summer of 2008 saw hot action in the country's coldest state: Alaska. On the Aleutian Islands, three eruptions went off in a single month.
Time Frame
Fifty volcanoes in the United States have erupted since the beginning of the 19th century, which is the time frame usually used to categorize active volcanoes. Most of them are in the Aleutian Islands, an island chain off the Alaska's southwest coast. Other recent volcanic activity has visited Hawaii, California, Washington and Oregon. Mount St. Helens, in Washington, erupted destructively and famously in 1980 and is sleeping, according to geologists--but is still considered to be active. The summer of 2008 was a fiery time in the Aleutian Islands, with three volcanoes--Kasatochi, Okmok and Cleveland--exploding within a month spanning July and August.
Misconceptions
For every volcano that has erupted in the last 200 years, at least four more are ghosts of eruptions past. Wide swaths of New Mexico, Arizona and California were once as volcanically active as Alaska is today. Fewer eruptions occurred in the past in Idaho, Wyoming, Utah and Nevada. Many of those eruptions were thousands to millions of years ago, along short-lived volcanic fields unrelated to plate tectonics. In Utah and Idaho, these volcanic fields may have resulted from historic stretching of the Earth's crust in the Basin and Range Province, characterized by parallel mountain ranges.
History
Three states--Colorado, Mississippi and South Dakota--each host a single historic volcano. Colorado's, called Dotsero, is the namesake of its host town near where the Colorado and Eagle rivers join in the northwest portion of the state. The Dotsero Volcano last erupted in 2200 BC. Mississippi's Jackson Volcano is believed to have erupted 65 million years ago, and so far there is no published estimate of the last eruption of Bear Butte in South Dakota.
Identification
The most active volcanism happens where tectonic plates are in the long, slow process of colliding. The volcanism at the Aleutian Islands is part of the so-called Pacific Ring of Fire, where activity at the margins of the Pacific and smaller, adjacent tectonic plates yields earthquakes and volcanoes alike. Eighty percent of active volcanoes in the United States are in the Aleutian Islands, and almost that percentage--about 75 percent--of the world's volcanoes occur along the Pacific Ring of Fire. The Cascade Volcanoes in northern California, Oregon and Washington--Mount St. Helens is one of them--are also part of the Pacific Ring of Fire.
Potential
The U.S. Geological Survey recognizes 18 volcanoes with the potential to erupt again, all of them in Alaska and the West Coast except for two--the Kilauea and Mauna Loa volcanoes in Hawaii. Most of these volcanoes have erupted within the past 200 years. And all of them, if they do erupt, would have the ability to wreak havoc on their immediate surroundings by emitting ash and toxic gases and causing mudslides.
Tags: Aleutian Islands, United States, have erupted, Pacific Ring, Pacific Ring Fire
