Mount Churchill is a volcano in the

Saint Elias Mountains The Saint Elias Mountains (french: Chaîne Saint-Élie) are a subgroup of the Pacific Coast Ranges, located in southeastern Alaska in the United States, Southwestern Yukon and the very far northwestern part of British Columbia in Canada. The range ...

and the

Wrangell Volcanic Field The Wrangell Volcanic Field is a volcanic field stretching from eastern Alaska in the United States to the southwestern Yukon Territory in Canada. The field includes the four highest volcanoes in the United States, Mount Bona, Mount Blackburn, ...

of eastern

Alaska Alaska ( ; russian: Аляска, Alyaska; ale, Alax̂sxax̂; ; ems, Alas'kaaq; Yup'ik: ''Alaskaq''; tli, Anáaski) is a state located in the Western United States on the northwest extremity of North America. A semi-exclave of the U.S., ...

. Churchill and its higher neighbor

Mount Bona Mount Bona is one of the major mountains of the Saint Elias Mountains in eastern Alaska, and is the fifth-highest independent peak in the United States.This counts both the North and South Peaks of Denali (Mount McKinley), which is not a universal ...

about to the southwest are both large ice-covered

stratovolcano A stratovolcano, also known as a composite volcano, is a conical volcano built up by many layers (strata) of hardened lava and tephra. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile with a summit crater and per ...

es, with Churchill being the fourth highest volcano in the

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...

and the seventh highest in

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...

Volcanic eruptions

Mount Churchill is most noteworthy as the source of the

White River Ash The White River Ash is a 1,200-year-old ash deposit. It was formed by two large ( VEI 6) explosive eruptions from the stratovolcano of Mount Churchill that occurred around 850 AD and blanketed of Yukon and Northwest Territories, Canada and the U.S ...

, deposited during two of the largest volcanic eruptions in North America during the past two millennia. This twin-lobed

tephra Tephra is fragmental material produced by a volcanic eruption regardless of composition, fragment size, or emplacement mechanism. Volcanologists also refer to airborne fragments as pyroclasts. Once clasts have fallen to the ground, they rem ...

deposit covers more than of eastern Alaska and northwestern

Canada Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tot ...

, with the northern lobe deposited 1900 years ago and extending over and the larger eastern lobe about 1,250 years ago and stretching over . The total volume of the ash exceeds , or roughly 50 times the volume of the

1980 eruption of Mount St. Helens On March 27, 1980, a series of volcanic explosions and pyroclastic flows began at Mount St. Helens in Skamania County, Washington, United States. A series of phreatic blasts occurred from the summit and escalated until a major explosive eru ...

, and ash layers up to thick can be seen just below the surface in many roadcuts along the

Alaska Highway