1: It may help scientists better understand why Yellowstone 's previous eruptions , in prehistoric times , were some of Earth 's largest explosions in the last few million years . 2: Volcanic activity triggers 2,000 to 3,000 small earthquakes per year , and the shake and shock waves travel at different speeds through molten , hot and other rock . 3: Scientist measured the thousands of small earthquakes in Yellowstone to scan the earth underneath it .
1: Yellowstone 's previous eruptions 2: 2,000 to 3,000 small earthquakes per year 3: small earthquakes in Yellowstone