Seismicity

The diagram below shows that the three largest Yellowstone eruptions emitted much more material than the eruptions of Mount St. Helens (1980), Mount Pinatubo (1991), Krakatau (1883), Mount Mazama (7,600 years ago), and Tambora (1815).
Deep within the Earth it is so hot that some rocks slowly melt and become a thick flowing substance called magma. Because it is lighter than the solid rock around it, magma rises and collects in magma chambers.
The May 18, 1980 eruptive column at Mount St.
The science of forecasting a volcanic eruption has significantly advanced over the past 25 years. Most scientists think that the buildup preceding a catastrophic eruption would be detectable for weeks and perhaps months to years.
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.
Before May 18, 1980, Mount St. Helens' summit altitude of 9,677 feet made it only the fifth highest peak in Washington State.
Very hot!! Here are some temperatures recorded at different times and locations:
Ground deformation (swelling, subsidence, or cracking) is measured with a variety of techniques, including Electronic Distance Meters (EDM), the Global Positioning System (GPS), precise leveling surveys, strainmeters, and tiltmeters.
Earth's heat is released in Yellowstone by two main processes, conduction and convection: