All shook up!

An earthquake in Alaska didn't just rock the locals. It caused a shake-up 3,100 kilometers (2,000 miles) away in Yellowstone National Park. Scientists found that the quake jolted the park's geysers (springs that spout jets of hot water and steam) off schedule.

Alaska's Denali fault (boundary along which rocks slide past each other) suddenly shifted, generating powerful seismic waves (vibrating energy waves that travel through the ground). The fault sent its shuddering waves on a collision course with the Western U.S. "[Yellowstone] happened to be right in the path," says Robert Christiansen of the U.S. Geological Survey.

The vibrations passed through the park. Hundreds of smaller local quakes were triggered, rattling underground cracks that feed hot water to the park's geysers. "Geysers are very sensitive to changes in their underground plumbing systems," says Henry Heasler, Yellowstone's park geologist. The rattling loosened minerals that block pipes and keep eruptions in check. Result: Some geysers blew their tops more often, and others less frequently.

But one famous geyser was unfazed. Old Faithful lived up to its name--erupting right on schedule.

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