Questions About Yellowstone Research
How fast is the hotspot moving under Yellowstone?
Actually, the source of the hotspot is more or less stationary at depth within the Earth, and the North America plate moves southwest across it. The average rate of movement of the plate in the Yellowstone area for the last 16.5 million years has been about 4.6 centimeters annually. However, if shorter time intervals are analyzed, the plate can be inferred to have moved about 6.1 centimeters per year from 16.5 million years ago until about 8 million years ago, then slowed to 3.3 centimeters a year for the past 8 million years.
How large is the magma chamber that is currently under Yellowstone?
The magma chamber is believed to be about 40 by 80 kilometers across, similar in size to the overlying Yellowstone caldera. The top of the chamber is about 8 km deep and the bottom is around 16 km deep. However, the chamber is not completely filled with fluid magma. It contains a partial melt, meaning that only a portion of the rock is molten (about 5 to 15%); the rest of the material is solid but, of course, remains hot.
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 of seismograms to measure the speed of seismic waves from earthquakes and small, intentional dynamite explosions--data that allow geophysicists to make 3-D pictures of structures within the Earth. Scientists compare these seismic velocities, and infer the composition from deviations of these from average, thermally undisturbed values.
Why is Yellowstone called Yellowstone?
Contrary to popular belief, Yellowstone was not named for the abundant yellow- colored rhyolite lavas in the Grand Canyon of Yellowstone that have been chemically altered by reactions with steam and hot water to create vivid yellow and pink colors. Instead, the name was attributed as early as 1805 to Native Americans who were referring to yellow sandstones along the banks of the Yellowstone River in eastern Montana, several hundred miles downstream and northeast of the Park.
Are earthquakes at Yellowstone related to volcanism?
Earthquakes, volcanism, and hydrothermal features go hand in hand at Yellowstone. The underground plumbing of hot water and magmas beneath Yellowstone is influenced by the same stresses that cause earthquakes. The largest historic earthquake in the Rocky Mountains occurred in the Yellowstone region. The magnitude 7.5 earthquake northwest of the National Park in 1959 was caused by the extension or stretching of the Earth's crust. The earthquake caused the land to rupture, displacing a 40-km-long fault that rose vertically up to 20 feet. The same stretching of the Earth's crust that caused the 1959 earthquake causes a reduction in the horizontal pressures on Yellowstone's magma systems, allowing them easier ascent through the crust. Thus, when earthquakes occur in or around Yellowstone, they can change the stress on hydrothermal and magma reservoirs, leading to enhanced fluid movement. Conversely, volcanic processes can induce earthquakes.
What is the relationship between volcanism and the geysers and hot springs in Yellowstone?
Heat and volcanic gases from slowly cooling magma rise and warm the dense salty water that occupies fractured rocks above the Yellowstone magma chamber. That brine, in turn, transfers its heat to overlying fresh groundwater, which is recharged by rainfall and snowmelt from the surface. Water boiling at depth below the surface is hotter than the temperature of boiling at the surface. If it rises quickly, this superheated water can flash to steam, propelling both steam and hot water to the surface as a geyser. More commonly, hot water rises and loses its heat at a steady rate, flowing to the surface as a hot spring.