YELLOWSTONE NATIONAL PARK, Wyo. – A swarm of more than 70 small earthquakes shook the ground near Old Faithful geyser earlier this month. The largest was a magnitude 2.4, barely enough to be felt.

An earthquake swarm hit a region of flood-stricken Yellowstone on Sunday ahead of the closure of the National Park due to unprecedented floods. Data from the University of Utah's seismograph ...