QUAKE SHAKES UP GEYSER ACTIVITY

No one could argue that Yellowstone National Park’s geysers aren’t wondrous sights. But imagine most of the park’s best-known geysers, plus many hot springs that usually bubble quietly, all erupting at once. Anyone who had been standing in the geyser basins along the Firehole River at 11:37 p.m. on Aug. 17, 1959, would not have had to imagine it. On that date, one of the most powerful earthquakes to rock North America in modern times struck near Hebgen Lake west of the national park and, almost simultaneously, turned Yellowstone’s dancing waters wild.

Viewing the quake’s effects

Former park geologist George Marler surveyed the geysers as soon as daylight allowed the following morning.

“Scores of hitherto quiescent springs with no previous record of geyser activity were either boiling or showed clear evidence of having erupted,” Marler wrote in a scientific paper later published by the U.S. Geological Survey.” Large fragments of sinter scatteredaround the craters of some springs indicated a major increase of activity and forceful eruption.”

It was one of the most dramatic examples of the way seismic activity can force changes in Yellowstone’s famous hot springs and geysers, a principle that would prove itself again and again in later years– and which today offers geologists a possible tool for predicting earthquakes.

The 1959 tremor is now widely known as the Hebgen Lake Earthquake. Its magnitude was first estimated at 7.1, but was later revised upward to 7.5, making it the strongest earthquake that has shaken the Yellowstone region in modern times. Outside the national park, the temblor turned a peaceful summer night into tragedy.

A massive slide of 80 million tons of rocks and other debris in the Madison River Canyon west of Hebgen Lake buried and killed 19 people. Including those fatalities and others killed by falling rocks and other quake-related violence, the earthquake’s entire death toll was 28.

Great quake-induced cracks split roads and mountainsides. Automobiles caught by loosed rocks looked like crushed sardine cans. Houses tumbled into the waters of Hebgen Lake.

In Yellowstone Park, the quake caused damage, but the only reported injury was to a woman who hurt her ankle jumping out of bed. At the massive, log-lined Old Faithful Inn, a stone chimney crashed into the dining room, which only a few hours earlier had been filled with visitors.

Roads, buildings damaged

The earthquake caused an estimated $2.6 million in damage to park roads and $1.7 million worth to buildings. Crews clearing rocks off park road near Madison Junction freed a bear that had apparently become trapped within fallen rocks and timber. But the quake’s most striking effects were within the park’s geyser basins, fueled by heat from the same subterranean hot spot that twists and torments the earth in ways that cause such massive earthquakes.

Nearly 300 geysers erupted immediately after the Hebgen Lakeearthquake, and, of those, 160 were springs that had no previous record of eruption, Marler found. He counted 334 park thermal features that were more active after the earthquake than they had been before.

In the Lower Geyser Basin, Morning, Clepsydra and Fountain geysers had been known to erupt in sequence, one after the other. All three erupted simultaneously after the earthquake and erupted continuously throughout the next day.

Incredible geyser activity The earthquake’s “jarring served as a trigger to start discharge from hundreds of springs,” Marler wrote. “Had this happened in the daytime, the spectator would have witnessed geyser activity on a scale never even closely approximated since Yellowstone’s discovery. Even so, during the days following August 17, a spectacle without precedent was observed.”

A new geyser erupted 100 feet high from a fissure near Fountain Geyser and was promptly named Earthquake Geyser. Several days later, a steam explosion along the same fissure created another outlet for water and steam, and Earthquake Geyser’s activity declined in succeeding weeks. Today it is no longer considered a geyser but is visible as a spring, spouting only a slight bit of water.

Seismic Geyser is also a creation of the 1959 earthquake, but its last known eruptions were in 1974.

Geologists believe that the earthquake rattled the underground plumbing that supplies hot water to Yellowstone’s geyser basins. The shaking may have increased pressure on water in some of the conduits, driving water out of the ground like a squirt gun.

It may have also rearranged the minute cracks believed to make up that hidden plumbing system, sending water to surface features that had
previously had little or none.

“Throughout the basins there was evidence that the earthquake had acted like a giant hand which suddenly applied enormous pressure to the rocks beneath the hot springs, forcing water from their conduits in a manner comparable to the squeezing of a sponge,” Marler wrote.

Supporting evidence was the earthquake-caused cracks that appeared in the mineral deposits of many geyser basins. Nearly two miles worth of cracks appeared around Firehole Lake. Robert Smith, a geophysicist at the University of Utah, now says that earthquakes are a necessary element for geyser systems because the quakes open fractures that funnel hot water to the surface.

Seismic influences on Yellowstone geysers would reappear in 1983, when a magnitude 7.3 earthquake hit Borah Peak, Idaho, about 240 kilometers from Yellowstone. Park geologist Roderick “Rick” Hutchinson at the time recorded changes in the geyser basins that were more subtle than those triggered by the Hebgen Lake quake 24 years earlier.

A total of 37 thermal features exhibited changes after the quake.

“In 15 cases the physical changes of vent enlargement, rupturing of the siliceous sinter sheet, or extensive wash may be long-term or permanent,” Hutchinson wrote in a report.

One of the clearest changes was a sudden lengthening in the interval between eruptions of Old Faithful, which had been similarly affected by the 1959 earthquake.

The effects of the distant Borah Peak Earthquake on Yellowstone have since interested geologists and geophysicists looking for signs of impending earthquakes. Because geyser systems such as those in Yellowstone appear to be sensitive to seismic activity, the researchers suspect, watching the geysers may provide details about temblors that hit many miles away.