Augustine Volcano is Behaving like a Percolator

Six weeks after its major eruption on March 26, Augustine Volcano continues to grumble and steam. Recently, however, it is displaying a type of behavior that is mystifying volcanologists.

It is characteristic for the ground to vibrate continuously during an eruptive cycle when magma from below is moving toward the vent and flowing out onto the surface. Indeed, this was observed at Augustine prior to all the larger eruptive events of the recent cycle, and it continued for several weeks afterward. During this time, seismograph records from stations on the island were never at rest; a typical record was an indecipherable mess of wildly swinging lines.

Beginning the last week of April, however, something different happened. The constant seismic background began to die away and was replaced by small, discrete seismic events which repeated with remarkable regularity. These small events (each equivalent to about a magnitude 1 earthquake) were occurring regularly at about 15-second intervals. Dr. Juergen Kienle, volcanologist with the Geophysical Institute, observes that there are no other examples of this type of activity documented in the scientific literature. Augustine's "putt-putt" behavior (as it has been labeled) thus appears to be unique among the world's volcanoes--at least among those which have been studied in any detail.

This mysterious behavior is almost certainly due to steam explosions which result when subterranean water comes into contact with hot magma. But why do the explosions occur with such regularity? The volcano is behaving almost like a percolator coffee pot, with its characteristic "blurps" at regular intervals.

But there are other complexities. The water source cannot be the basal water table extending into the island from sea level, because the events are occurring near the summit. (Of the five seismograph stations on the island, four are on the flanks and one is near the summit--these events are picked up by the summit station first.)

Kienle therefore feels that the water must be coming from surface runoff seeping through cracks and fissures in the mountain. He likens each explosion to a drop of water falling onto a hot plate. Why this continues with such metronome-like regularity is not understood.

Augustine's present bizarre behavior is more than just a geological curiosity. It is certain that the data being gathered will lead to a better understanding of the plumbing and internal workings of a volcano. Already, more information has been gathered from this single eruptive cycle than previously existed for all other Alaskan eruptions combined.