The West Old & New Vol. III Issue III March 2014 | Page 12

A Natural Monster Lurks in the Wild Beauty of the West
Yellowstone Parks Caldera Volcano

I grew up believing that I lived in one of the safest places in the world, aside from the threat of grizzly bears and mountain lions. However, in 2006 I discovered that I was actually living next to one of nature’s most powerful volcano’s, a caldera locate in
Yellowstone Park.
The caldera located in Yellowstone National Park in the United States is often referred to as a super volcano. The caldera is
located in the northwest corner of Wyoming, in which the vast majority of the park is contained. The major features of the caldera
measure about 34 by 45 miles (55 by 72 km). The caldera formed during the last of three supereruptions over the past 2.1 million
years.
Volcanism at Yellowstone is relatively recent with calderas that were created during large eruptions that took place 2.1 million, 1.3 million, and 640,000 years ago. The calderas lie over a hotspot where light, hot, molten rock from the mantle rises toward
the surface. While the Yellowstone hotspot is now under the Yellowstone Plateau, it previously helped create the eastern Snake
River Plain (to the west of Yellowstone) through a series of huge volcanic eruptions. The hotspot appears to move across terrain in
the east-northeast direction, but in fact the hotspot is much deeper than terrain and remains stationary while the North American
Plate moves west-southwest over it.
Over the past 18 million years or so, this hotspot has generated a succession of violent eruptions and less violent floods of basaltic lava. Together these eruptions have helped create the eastern part of the Snake River Plain from a once-mountainous region.
At least a dozen of these eruptions were so massive that they are classified as supereruptions. Volcanic eruptions sometimes empty
their stores of magma so swiftly that they cause the overlying land to collapse into the emptied magma chamber, forming a geographic depression called a caldera.
The oldest identified caldera remnant straddles the border near McDermitt, Nevada-Oregon, although there are volcaniclastic
piles and arcuate faults that define caldera complexes more than 60 km (37 mi) in diameter in the Carmacks Group of southwestcentral Yukon, Canada, which is interpreted to have formed 70 million years ago by the Yellowstone hotspot. Progressively
younger caldera remnants, most grouped in several overlapping volcanic fields, extend from the Nevada-Oregon border through
the eastern Snake River Plain and terminate in the Yellowstone Plateau. One such caldera, the Bruneau-Jarbidge caldera in southern Idaho, was formed between 10 and 12 million years ago, and the event dropped ash to a depth of one foot (30 cm) 1,000 miles
(1,600 km) away in northeastern Nebraska and killed large herds of rhinoceros, camel, and other animals at Ashfall Fossil Beds
State Historical Park. The USGS estimates there are one or two major caldera-forming eruptions and 100 or so lava extruding
eruptions per million years, and "several to many" steam eruptions per century.
The loosely defined term 'supervolcano' has been used to describe volcanic fields that produce exceptionally large volcanic
eruptions. Thus defined, the Yellowstone Supervolcano is the volcanic field which produced the latest three supereruptions from
the Yellowstone hotspot; it also produced one additional smaller eruption, thereby creating West Thumb Lake 174,000 years ago.
The three super eruptions occurred 2.1 million, 1.3 million, and 640,000 years ago, and