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A new study by a team of National Science Foundation-funded geologists has found that the Wrangell volcanic belt stretches in Alaska's Wrangell-St. Elias National Park and Preserve is older than previously recognized and determined why its volcanic field has been persistently active since it formed about 30 million years ago. The Wrangell volcanic belt, which stretches just over 300 miles from south-central Alaska to southwestern Yukon Territory in Canada. A volcanic arc is a location where an oceanic plate slides beneath another plate -- the Pacific Plate sliding under the continental North American Plate in the case of the Wrangell volcanic arc. Where the two plates collide is called a subduction zone, and the denser plate is pushed down to the Earth's mantle at an angle. Subduction zones are characterized by widespread and hazardous volcanoes and damaging earthquakes. Subduction zones are also places where continental crust essentially forms, which is the layer of igneous, sedimentary and metamorphic rock that forms the continents. The researchers collected a variety of rock samples in remote sections of the national park -- some places only accessible by light planes that can land in extremely rocky places -- and studied them under microscopes back at their universities. Some samples were pulverized into a powder that was sent to labs that evaluate element and isotope concentrations to determine what melted to form the rock. Radiometric dating also helped the researchers piece together the history of the Wrangell volcanic field, including frequency of eruptions, relative ages of its different volcanoes and the relationship between volcano formation and plate movements.