Three Calderas | Still Active | Explosion Explanation | Comparisons
Caldera (k
l-dâr’
)
- a volcanic crater that has a diameter many times that of the vent and is
formed by the collapse of the central part of a volcano or by explosions of
extraordinary violence.-Merriam Webster 2005
The Three Calderas
There have been three of these super volcanic, caldera-creating eruptions that have happened in Yellowstone's past. All of them overlap and cover portions of three states, Idaho, Montana and Wyoming. These catastrophic eruptions are estimated to have occurred 2 million, 1.3 million and 0.6 million years ago. They were absolutely huge! The 2 million year old eruption released 2500 km3 of material, followed by the 0.6 million year old eruption which released 1000 km3 of material and finally the 1.3 million year old eruption released 250 km3 of rock. Today's Yellowstone caldera was created by the most recent of explosions, occurring 0.6 million years ago. Its spans roughly 70 kilometers long and 50 kilometers wide. Ash from the eruptions can be found as far away as Iowa, Missouri, Texas, and even parts of northern Mexico.
Move Mouse Over This to see where the calderas near Yellowstone are.
Still Active [Back to Top]
The large caldera area is still volcanically active today. It is one of the largest and most active hydrothermal systems in the world. This is because magma can be as close to the surface as 5-13 meters. The ground seems to breathe meaning that it rises and falls. It slowly rises or uplifts approximately 1.5 centimeters annually. Most likely it will erupt again, but not in our lifetime at its current rate.
An important clue was found along the South shore of Yellowstone Lake. The boat dock had once become overtaken by water and trees on that edge of the lake began dying because their bases were under the water. But at the same time the water levels at the North shore had little change. Scientists hypothesized that these odd occurrences could be explained by a southward tilt of the area in and around Yellowstone Lake, including the lake basin itself. If the entire area was being pushed up, perhaps the ground at the north end of the lake was rising more than the south end, like lifting a bath tub at one end. In this way, the water level of Yellowstone Lake would appear to rise along the south shore.
The idea was tested from 1975-77 by the University of Utah and by the U.S. Geological Survey or the U.S.G.S. By using benchmarks gathered in 1923 that measured precise elevation and new measurements, they discovered that the center of the park had risen 72 cm! This explained the shift in waters of the lake.
Mouse Over to see the vertical change in the Yellowstone caldera from 1996-2000.
Mouse Over to see the GPS apparatus used in measuring elevation and horizontal shifts.
"A new satellite-based technique known as Interferometric Synthetic Aperture Radar (InSAR) allows direct and precise measurement of the vertical changes in ground level. This InSAR image of the area around the Yellowstone Caldera (black line) shows vertical changes during the 4-year period 1996–2000. The ringed pattern centered northwest of Yellowstone Lake is a prominent area of dome-shaped uplift. Each complete cycle of colors in the color bands represents a little more than one inch (28.3 mm) of vertical change. Yellow triangles are continuous GPS stations; white dots are locations of earthquakes in the period 1996–2000." - U.S.G.S. Fact Sheet 100-03
Why do these explosions occur? [Back to Top]
1) The hot spot or magma plume below the calderas
2) The properties of the magma
Some magma contains a large amount of silica, like the magma beneath Yellowstone, so the caldera is filled in with tuff, rhyolite, and other igneous rocks. Silica-rich magma is extremely thick and slow-moving.
