Earthquakes rumbled near Old Faithful on October 14, 2006. The largest quake was a magnitude 2.4, barely strong enough to be felt. The swarm of 74 quakes lasted several hours, according to information released by the Yellowstone Volcano Observatory.

The tight cluster of earthquakes was moderate compared with others in Yellowstone’s past, including one in April 2004 in which more than 400 earthquakes were recorded over three days.

“It piques our curiosity, but it’s not out of the range of normal behavior,” Henry Haesler, Yellowstone’s principal geologist, said of the October 14th activities.

Park officials said the earthquakes were more likely caused by the underground movement of hot water and gas, rather than the migration of magma.

The largest swarm recorded in Yellowstone Park was in fall 1985, when about 1,800 earthquakes were registered, ranging in magnitude from 1 to 4.9. At about the same time, the huge Yellowstone caldera stopped slowly rising and began slowly falling.