As far as scientists know volcanism in Yellowstone began about 2.2 million years ago. There were precursors and then there were three giant eruptions larger than anything in recorded history. The precursors began with an eruption of the Junction Butte Basalt in the northeastern part of the park. Then the Island Park area in Idaho blew its lid. These oldest postulated eruptions were followed by the three big ones: One giant eruption occurred 2.1 million years ago. The second big one occurred 1.3 million years ago. The last known big one occurred 639,000 years ago.

The big ones were followed by intermittent smaller eruptions. One of these about 180,000 years ago was filled by the West Thumb area of Yellowstone Lake. This series of eruptions continued until about 70,000 years ago while the current Yellowstone Plateau took shape.

Right now Yellowstone’s magma chamber is 5 to7 miles beneath the surface.  It heats the overlying rock which heats the water and causes the geothermal reactions and Old Faithful itself. The magma also causes the Yellowstone caldera to rise and fall every few decades. More recently the uplift has gone on at an extraordinary rate. But it probably doesn’t mean you will see an eruption this year or next year. This is the pattern of the volcano. But like all good scientists they have to admit that they don’t know for sure.

The Roadside Geology of Yellowstone Country by William J. Fritz concludes by saying, “The inescapable conclusion from all this earthquake activity is that the likelihood that another major earthquake will occur in Yellowstone Country is guaranteed; it is simply a matter of when it will happen.”

All this geology about the Yellowstone supervolcano and Yellowstone’s geothermal areas is the background of the upcoming Cheops Books LLC historical thriller the Old Faithful Plot by Dora Benley. Find out what could happen next.