Imagine living near a volcano that once produced an explosion ten times more powerful than that of Mt. St. Helens in 1980, an eruption that covered an immense area with ash and possibly forced people living in the region to pack up and move.

One would think that such a volcano would be a household name, but that is not the case with Mt. Churchill. Located about 25 kilometres west of the Alaska-Yukon border in Wrangell-St. Elias National Park, this 4,766-meter volcano is the source of the White River Ash.

Mt. Churchill first exploded about 1,900 years ago, followed by a second much larger explosion about 1,200 years ago. These two events produced more ash than any other eruptions of their type in North America during the last 2,000 years. In total the White River Ash covers about 540,000 square kilometers of land in Alaska and northern Canada.

While the ages of the ash deposits were determined long ago with radiocarbon dating, their exact source was not traced to Mt. Churchill until 1990. This is at least partly due to the fact that this peak is both remote and covered with glaciers, making research in the area difficult.

Kim West, a graduate student at Carleton University, has been studying deposits of White River Ash. Along with her supervisor, Allan Donaldson, she has been trying to determine the season in which the volcano exploded as this timing could have affected people living in the area.

"A winter eruption could have made travel more difficult if people wanted to move out, and their food supply might also have been depleted at that time of the year. The ash would have killed vegetation in the area, making it difficult for people living on the land," says West.

Anthropologists have suggested that the second eruption could have caused the migrations that eventually led to the formation of Athapaskan cultures such as those of the Apache and Navajo in the southwestern United States. Stories from the Athapaskan oral tradition refer to a fiery explosion and a collapsing mountain.

West has been studying how the ash was deposited. While working near the Donjek River and Destruction Bay, she found pristine frozen layers of "pure airfall ash" that would not have been preserved intact unless they were deposited in winter, immediately frozen, and then protected by a blanket of snow.

Ash from the first deposit was blown north as far as Eagle, Alaska. An east wind was blowing during the second eruption, scattering the ash over much of the southern Yukon.

Some ash has been found as far away as Great Bear Lake in the Northwest Territories; closer to the volcano, the ash could have been up to one metre thick in places.

Today the White River Ash can be seen in roadcuts and riverbanks throughout the southwest Yukon, and is particularly well preserved along the Alaska Highway between Tok, Alaska, and Burwash Landing.

Along roadways it usually appears as a thin white line close to the surface of the soil, though closer to the volcano it can be 60 centimetres thick.

Mt. Churchill is a pyroclastic volcano, and can remain inactive for long periods of time before exploding again unexpectedly. These explosive volcanoes tend to erupt in 100 to 1,000 year cycles.

"Pyroclastic volcanoes may have a long dormancy period; they have thicker magma and sometimes build up pressure for a long time before they explode. Some volcanoes, such as the ones in Hawaii, have more fluid magma and tend to erupt more frequently," says West.

The U.S. Geological Survey has started a hazards assessment of Mt. Churchill, as another explosion could obstruct air travel, trigger mudslides and floods in the region, and cover a large area with ash. Monitoring equipment has also been installed recently on Mount Wrangell, the only other historically active volcano in the general area.

No one knows whether Mt. Churchill will ever explode again. Evidence of past eruptions is used to predict future hazards from volcanoes, but on Mt. Churchill, such evidence is buried by snow and ice.

West and Donaldson think that Mt. Churchill blew its top off during the last eruption, so one should expect any future explosions to be significant as well.

The researchers have put together a brochure on Mount Churchill and the White River Ash that should be available in tourist information centers in the near future. They think that Yukoners and other people living within range of this volcano should be more aware of its existence.

"Mt Churchill is very remote, and I do not know if a lot of people realize its violent eruptive history. I want people to know about this volcano because it could affect them in their lifetime," says West.

For more information, Kim West can be contacted at (306) 652-7809 or by email at kwest3@chat.carleton.ca.