Yellowstone Relief Map (University of Utah, Robert B Smith)
Three times during the past two million years, the Yellowstone supervolcano has erupted, leveling mountains and covering half of North America with ash.
As described in the notice for a lecture to be delivered earlier this year by the University of Utah’s Robert B. Smith — The Yellowstone Supervolcano: Past, Present and Future — “the energy responsible for creating these geologic features comes from a 50-mile-wide ‘hotspot’ or ‘mantle plume’ of molten rock that originates at least 400 miles below the Idaho-Montana border, and then angles eastward and rises until it is only 30 miles beneath Yellowstone. There, the plume hits cooler rock and spreads out to a width of 300 miles.
“The buoyancy of the hot plume lifts Yellowstone and the surrounding region into a 500-mile-wide ‘topographic swell’ that pushes the ground well above 7,000 feet elevation, or about 1,600 feet higher than it would be without the underground plume.
“The volcanic plume also fuels a shallow ‘magma chamber’ of hot and partly molten rock that extends from about five miles beneath Yellowstone to a depth of at least 10 miles.”
This immense powerhouse is the source for all the amazing wonders which attract hundreds of thousands of visitors to the nation’s first National Park. “The crustal magma body continues to fuel Yellowstone’s geysers and power a restless caldera, which, like others on Earth, huffs upward and puffs downward for millennia without erupting — often by many feet over the decades. The caldera floor rose 40 inches during 1923-1984, fell 8 inches during 1985-1995, rose a few inches maximum during 1995-2000, mostly sank about an inch during 2000-2003, then mostly rose more than 3 inches since mid-2004 — three times faster than its historic rate of uplift.
“Movement of magma and hydrothermal fluids cause these ups and downs. Studies have revealed Yellowstone’s hydrothermal systems release 100 watts per 36 square feet — in other words, a square of ground measuring 6 feet on a side emits enough heat to power a 100 watt light bulb. That’s more than 20,000 times the heat emitted by the average rock in North America.
“During late December 2008 and early January 2009, Yellowstone experienced its second-largest earthquake swarm in recorded history, and it was well-documented by the University of Utah real-time seismic network. The sequence consisted of about 1,000 earthquakes, including a dozen quakes of magnitude 3.0 or higher, and one as large as 3.9 on the Richter scale.”
Now, a new study of the Yellowstone supervolcano has determined that the magma chamber is 20 percent larger than previously believed, and verified that it reaches deep beneath the earth’s crust into the mantle.
The three historical eruptions, which took place 2.05 million years ago, 1.3 million years ago, and 642,000 years ago, were respectively 2,500, 280, and 1,000 times larger than the eruption of Mount Saint Helens in 1980.
Yellowstone Plume (University of Utah)