Earthquakes and tremors are common in Yellowstone. Hundreds, sometimes, thousands, are recorded annually. Most are too small to be felt but all are capable of triggering subtle as well as dramatic transformations in the behavior of thermal features.
The plumbing of the thermal features reaches the surface through glacial gravels covering the rocks. These gravels are honeycombed by the hydrothermal passageways of the springs, making them very susceptible to the shaking of earthquakes. The jarring energy of the earthquake can make the gravels shift as they are shaken by the rock below. As the gravel particles vibrate, they move with respect to one another. The usual result is compaction. Water that is displaced from around rock particles is forced to the surface, carrying muddy material that clouds the surface pools. Fractures accompany the compaction, and water levels in some springs drop as their water supply is diverted elsewhere.
On March 26. 1994, an earthquake centered on the northwest section of Yellowstone National Park triggered some intriguing changes in some features in Norris Geyser Basin. Ledge Geyser, dormant for fifteen years, roared back to life. Monarch Geyser, which had not erupted since 1913, began spouting mud and rocks from its vent and ejected water to heights of at least 15 feet. Steamboat Geyser seemed to have experienced a shift oF the ground water supply away from its plumbing.
The Hebgen Lake earthquake of 1959 changed Leather Pool, in the Fountain Paint Pots area, once lined with leather-like brown algae growing in warm (143° F, 62° C) water, into a pool filled with boiling water. This water killed all of the brown algae. The Red Spouter spring originated in the Hebgen Lake earthquake and show tremendous changes through the seasons. During the summer it is a fumerole, but from late fall to early summer it spouts brilliant red water and mud. In the days after the earthquake, all of the changes described above were observed in various springs in the Firehole Geyser basin.
Will these changes be long lasting or just a brief variation in each feature's "normal" activity? Only time and observation will provide these answers.
This material is abstracted from brochures distributed by The Yellowstone Association for Natural Science, History & Education, Inc.
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© 1995 Karen M. Strom