Mount Churchill is most noteworthy as the source of the White River Ash, deposited during two of the largest volcanic eruptions in North America during the past two millennia. This twin-lobed tephra deposit covers more than of eastern Alaska and northwestern Canada, 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, and ash layers up to thick can be seen just below the surface in many roadcuts along the Alaska Highway. The extensive ash deposits in the lowlands near the White and Yukon Rivers were first recognized in 1883, but their source remained a mystery for the next century. Geologists in the 1960s traced the two lobes of the ash back into the Saint Elias Mountains, and postulated that the ash may have come from a vent now buried under the Klutlan Glacier, which flows east for over from the Bona-Churchill massif into the Yukon Territory of Canada. More detailed studies in the 1990s by the U.S. Geological Survey finally produced the definitive answer. Aerial photos showed a elliptical, gently sloping, ice-filled depression at just east of the present summit of Mount Churchill. This was identified as a caldera, which had formed by the collapse of the volcano's previous summit during the cataclysmic eruptions. The geological field work revealed thick young pumice deposits along the rim of the caldera which are mineralogically and chemically identical to the White River Ash.
History
Mount Churchill was first climbed in 1951 by R. Gates and J. Lindberg, but the peak was merely an unnamed satellite of Mount Bona at the time. The mountain was named in 1965 by the Alaska State Legislature for English statesman Winston Churchill. In terms of elevation, it is a major North American peak, at well over ; however, in terms of topographic prominence or isolation, it is less significant, with less than a 1200-foot drop from its summit to the saddle with Bona. Churchill also lies on the northern, gentler side of the Bona massif, making it a less visually spectacular peak than some of the lower outliers of Bona such as University Peak or Aello Peak. The current standard climbing route is the South Ridge, usually as part of a climb of Mount Bona from the east starting from a ski-equipped bush plane landing at around on the Klutlan Glacier.
