When people think of tall volcanoes within the United States, they tend to think of towering
volcanoes such as Mount Hood or Mount Rainier. However, there exists another active volcano
which climbs above these two peaks to more than 15,000 feet in elevation. This volcano
I am referring to is Mount Churchill, which has produced the two of the largest volcanic
eruptions in the United States of the last 5,000 years. This video will discuss this volcano,
and mention what its future hazards are. Mount Churchill is located in the southeastern
portion of Alaska. Specifically, it can be found 40 miles east of McCarthy,
or 24 miles west of the border with Canada. Despite how prominent Mount Churchill is,
we don't know much about its early geologic history or even how old the volcano is. What
we do know is the age of several other volcanoes in the region, so we can estimate how old it is
based on levels of erosion. An educated guess would put the age of this stratovolcano at
about 200,000 years old. The initial eruptions from this volcano produced numerous overlapping
layers of viscous lava flows of dacite rock. Some of these layers were then overlaid by ash
deposited from highly explosive eruptions. As the volcano continued to build a tall
cone, it is likely that several partial summit collapses took due to the slope of the mountain.
During one of the recent glacial periods, a thick glacier began growing on the
massive complex of Mount Churchill. During the subsequent growth and retreat of this glacier,
it greatly carved the nearby mountains and produced numerous very steep cliffs.
After the end of the last ice age, Mount Churchill was likely about 16,000 feet tall. However,
as glaciers began melting on top of the volcano, the crust rebounded upwards, and
magma traveled to the surface. (pause 2 seconds) As a result, in 60 AD, a massive eruption began
from the central cone of this volcano. This initially melted part of the glacier overlying
Mount Churchill, after which pyroclastic flows emerged and raced down the mountain.
As the eruption continued, a towering plume of ash was carried 25 miles into the atmosphere.
The vast majority of ejected material was erupted via this plume,
and as a result a thick layer of ash began falling over a vast area.
Soon, 3000 square miles north of the mountain was coated with more than a foot of ash. One area
along what is now Yukon Highway 1 was especially hard hit, and was blanketed with 2 feet of ash.
The amount of ashfall decreased with distance, but a measurable amount of strikingly white ash
from the eruption has been found at numerous sites more than 300 miles north of the volcano.
Afterwards, Mount Churchill became quiet once again. Then, in 847 AD, a second massive eruption
began. This eruption was larger and more violent than its predecessor, and caused ejected ash to
drift in an eastward direction. Ash rained down across eastern Alaska, a majority of the Yukon
Territory, and even reached the Northwest Territories. Due to prevailing winds at the time
of this eruption, ash even reached Iceland and the United Kingdom. As this eruption continued,
the lava chamber was slowly drained. Eventually, this caused the summit of the volcano to collapse
and form a 2 mile wide caldera. Although largely buried beneath a glacier, you can still make out
the outline of the caldera rim. The two eruptions which had taken place were truly massive;
and were each between 20 and then 30 times larger than the 1980 eruption of Mount Saint Helens.
Since then, no additional eruptions have occurred. However, shallow earthquakes have
been detected nearby which hints at the possibility of future volcanic activity.
Although unlikely in the short term, this volcano will erupt again. In addition to ashfall,
its next major eruption could pose another deadly threat, lahars. Since Mount Churchill
is covered by a thick glacier, a future eruption could melt a significant amount of ice to melt,
generating a phenomena similar to a flash flood. This wall of water would cause flooding several
hundred miles away, and could hypothetically even effect Dawson City in Yukon. However,
what I just described represents an incredibly unlikely worst case scenario. The next eruption
will likely be thousands of times smaller than the previous two eruptions, and only cause ashfall and
glacial melt within a few miles of the mountain. I hope that you enjoyed this video. If
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