Step-by-step explanation:
Scientists say that Yellowstone is a hotspot which is marked by anomalously high temperatures. This intense heat produced by this hotspot is responsible for melting the crust and the formation of basaltic crust.
The Yellowstone hotspot is fixed within the Earth's mantle and has been suspected to be part of the mantle plume.
Heat from the shallowest magma chamber caused an area of the crust to expand and rise. This stree on the overlying crust formed faults and eventually these faults reached the magma chamber and magma oozed from these cracks. As the underground magma emptied, the ground above it collapsed and created the first of Yellowstone's three caldera.
The second, smaller volcanic eruption occured within the western edge of the first caldera which was almost 1.3 million years ago. The third and recent massive volcanic eruption happened 640,000 years ago. Different smaller eruptions occurred, and one of these created the West Thumb of Yellowstone Lake.
I hope this helps! This is as much information I could pull together!