Mount Churchill is a dormant volcano in the Saint Elias Mountains and the Wrangell Volcanic Field (WVF) of eastern Alaska.

Subduction of the Pacific Plate beneath southeastern Alaska has largely ceased during the last one million years, causing a decline of the volcanic activity in the WVF.

Churchill appears to be fed by melts derived from a stagnant slab in the mantle, left over by the previous subduction.

The White River Ash covers vast expanses of Alaska and western Canada and has been found as far as Europe, and there is evidence that the Athabaskan people migrated out of the region and into the present-day United States as a consequence of the eruption.

[3] The mountain was first ascended in 20 August 1951 by R. Gates and J. Lindberg[8] and named in 1965 after the English politician Winston Churchill[9] and is also known as Klutlan Glacier, Churchill-Bona, or White River volcano.

[17] The mountain is mostly covered by[18] ice hundreds of meters thick,[19] but lava flows with columnar jointing and tephra deposits form outcrops,[20] indicating that Mount Churchill may be a stratovolcano.

[28] A 90-metre-high (300 ft) pumice mound on the other side of the glacier,[29] 16 kilometres (9.9 mi) from Mount Churchill,[30] was formed by tephra building up on a bedrock bench.

[60] There is a moderate quantity of phenocrysts, including biotite, hornblende, ilmenite, hypersthene, magnetite and plagioclase, with little apatite and orthopyroxene.

[61][62][63] Several different rock chemistries contribute to each of the White River Ash lobes,[26] which are otherwise very similar to each other[64] and thus difficult to distinguish.

[4] The Wrangell slab[67] left over from the subduction may have stalled in the mantle, and was heated by asthenosphere flowing through a slab window until it melted and gave rise to the Mount Churchill magmas,[68][69] which thus have an adakitic composition typical for melts derived from subducted basalts at high temperatures.

[68][69] Several ice cores have been taken from the Bona-Churchill massif[73] and are an important source of information on the climate of the Pacific Northwest.

[84] The appearance and height of Mount Churchill (and neighbouring Bona) imply that they were constructed in recent time.

[94] Mount Churchill is the source[f] of two of the largest volcanic eruptions of the past two millennia in North America.

[104][105] The present-day towns of Dawson City and Whitehorse, Canada, are within the 25-millimetre (1 in) thickness area of the northern and eastern lobe, respectively.

[122] The ash deposits have been used as a time marker in tephrochronology to obtain dates for natural events and archaeological sites[123] from Alaska and Yukon[124] as well as Greenland (correlation of ice cores)[125] and Ireland in Europe.

[65] The widespread "PWS tephra" in Prince William Sound was emplaced between 2,039 and 1,520 years ago and resembles the northern White River Ash.

[159] Burial of food sources and ingestion of ash and fluoride would have impacted caribou, goats, moose and sheep populations,[160] forcing them to move away; genomic data indicate a large shift in caribou populations after the eastern White River Ash eruption,[161] although this theory is not uncontested.

[99] Local hunter-gatherer populations probably left the worst-hit areas and sought refuge in unaffected regions, returning only when conditions had improved[164] or not at all.

[170] Other Dene people migrated south and east[l] after the eruption, driving the Athabaskan expansion and spreading the Na-Dene languages across the continent.

By the arrival of the Europeans,[142][172][173][99] Athabaskans like the Apache[m] and Navajo[174][175] had spread between subarctic Canada and the Great Basin of the southwestern United States, bringing their languages with them.

[176] The eruption produced sulfate aerosols,[177] which can dim the Sun and cause a cooling of Earth's climate, creating a volcanic winter.

[182] There are widespread reports of bad weather and resulting hardships such as famines during that decade in Europe,[183] and a clear link to the Mount Churchill eruption is not established;[184] at worst, it would have aggravated a pre-existent climate disturbance.

[185] A link between the White River Ash and the mid-6th century cooling (Late Antique Little Ice Age) has been ruled out.

[189] Similar flood hazards exist in the Chitina and Copper River valleys south of Mount Churchill.

[37] The United States Geological Service ranks Mount Churchill as a "high threat" volcano.

[37] In addition, the intercontinental spread of ash would cause severe disruption, similar but on a larger scale to the 2010 eruptions of Eyjafjallajökull, with resultant consequences to transportation and the airline industry.

[152] Aircraft routes between Asia, Europe and North America pass through the extent of the White River Ash plume.