USGS Nov. 30, 2000
Harmonic tremors have begun to rock the Yellowstone Caldera. Unlike earthquakes, characterized by an abrupt release of energy, harmonic tremors are marked by a nearly continuous stream of energy, caused in most cases by large scale movements of magma beneath the earth. Beginning the morning of November 29th, this pattern has been observed in the Yellowstone basin. Harmonic tremors have been known to precede the most violent of earthquakes; in other cases no significant activity is triggered. But the magnitude and scale of these tremors has the experts worried.
Was this a valid early warning? My friend's father is a retired Yellowstone park ranger. He says that increased geothermal activity on its own is not particularly unusual, but the bulge and displaced water in Yellowstone Lake certainly is.