Jan. 4, 2019– Mary Greeley News – The supervolcano, located in Yellowstone National Park, has had super eruptions three times in history – 2.1 million years ago, 1.2 million years ago and 640,000 years ago.
Volcanoes typically blow when molten rock, known as magma, rises to the surface following the Earth’s mantle melting due to tectonic plates shifting. Geologists have used data to draw a 3D model of the magma chamber, which sits on top of the magma plume, revealing its sheer size and just how close it is to the Yellowstone Caldera.
The model, which featured in the BBC’s “Supervolcano” documentary shows a U-shaped chamber containing more than 300 cubic miles of molten rock.
The 2015 series revealed: “It is just five miles below the surface. In truth it is just 3.1 miles deep.
Since its last cataclysmic volcanic eruption 640,000 years ago, the Yellowstone region has had about 40 eruptions of slow-moving lava flows of rhyolite (a variety of molten rock that is thick and sticky)
Yellowstone is underlain by two magma bodies. The shallower one is composed of rhyolite (a high-silica rock type) and stretches from 5 km to about 17 km beneath the surface and is about 90 km long and about 40 km wide. The chamber is mostly solid, with only about 5-15% melt. The deeper reservoir is composed of basalt (a low-silica rick type) and extends from 20 km to 50 km beneath the surface. Even though the deeper chamber is about 4.5 times larger than the shallow chamber, it contains only about 2% melt.
The method that scientists use to discern this information is similar to medical CT scans that bounce X-rays through the human body to make three-dimensional pictures of internal tissue. In an analogous manner, a method called seismic tomography uses hundreds to thousands of earthquakes recorded by dozens of stations to measure the speed of seismic waves through the Earth–data that allow geophysicists to make 3-D pictures of structures beneath the surface. Scientists compare these seismic velocities and infer the composition from deviations of these from average, thermally undisturbed values.
More importantly, the area of most dramatic rise is directly above the peak of the chamber.
“This suggests the magma chamber is expanding, pushing up against the Earth’s surface.”
The last major eruption of Yellowstone produced around 2,500 times more volcanic material than the 1980 eruption of Mount St Helens. There have been several smaller eruptions since then.
Non-explosive eruptions of lava and less-violent explosive eruptions have occurred in and near the Yellowstone caldera since the last supereruption. The most recent lava flow occurred about 70,000 years ago, while a violent eruption excavated the West Thumb of Lake Yellowstone around 150,000 years ago. Smaller steam explosions occur as well: an explosion 13,800 years ago left a 5 km (3.1 mi) diameter crater at Mary Bay on the edge of Yellowstone Lake (located in the center of the caldera). Currently, volcanic activity is exhibited via numerous geothermal vents scattered throughout the region, including the famous Old Faithful Geyser, plus recorded ground-swelling indicating ongoing inflation of the underlying magma chamber.
Geologists have warned, once a triggering event takes place, an eruption could happen in as little as two weeks.
Jacob Lowenstern, a researcher with the US Geological Survey in Vancouver, Washington, detailed how the last catastrophic incident may have played out.
He said: “Typically when these eruptions begin, they begin from a certain event, then they get larger as they move along the fracture system.
“The entire sequence that formed the last Yellowstone eruption may have taken as little as two weeks.”
This created an eruptive column so colossal that it covered about 60 percent of the US in a thick layer of ash.
Should the same happen again, the ground around Yellowstone National Park would rise upwards forming a swarm of earthquakes.
Then, following the eruption, enormous pyroclastic flows would blast their way across the park.
This mixture of ash, lava blebs, and superheated gas exceed temperatures of 1,000C and can move at speeds of up to 300mph. (Spatter applies to bombs, usually basaltic, formed from lava blebs that readily weld (agglutinates) upon impact and contrasts with scoria that do not stick together. Scoria (or cinder) cones, for example, are composed largely of loose particles; spatter cones are composed mainly of agglutinated blebs or larger isolated lava tongues.) http://volcanology.geol.ucsb.edu/frags.htm
They are predicted to spread more than 100 miles out from Yellowstone, burying states like Wyoming, Montana, Idaho, and Colorado in three feet of harmful volcanic ash.
If the pyroclastic flow hits anyone, they would possibly die within seconds as the air could heat up to around 300C.
Each of Yellowstone’s explosive caldera forming
eruptions occurred when large volumes of “rhyolitic” magma accumulated at shallow levels in the Earth’s crust, as little as 3 miles (5 km) below the surface.
This highly viscous (thick and sticky) magma, surface. This
highly viscous (thick and sticky) magma, charged with dissolved gas, then moved upward, stressing the crust and generating earthquakes. As the magma neared the surface and pressure decreased, the expanding gas caused violent explosions. Eruptions of rhyolite have been responsible for forming many of the world’s calderas, such as those at Katmai National Park, Alaska, which formed in an eruption in 1912. And at Long Valley California.