YELLOWSTONE NATURE NOTES

SUMMARY

The review of Yellowstone geology emphasizes that this portion of the Rocky Mountains is an active earthquake area where mountain building forces are still at work. For the interested observer there is a multitude of evidence of dynamic earth processes from the geologic past to the present.

The 1959 earthquakes have left their impress on this region. To date we have found no evidence of fault displacements within the park with the exception of that area on the western boundary in the vicinity of Grayling Creek. Earthquake energy seems to have been channeled along old well-established faults and the major rockslides occurred along canyon walls where the rocks are jointed and deeply weathered. Fractures in the alluvial cover and in the siliceous sinter of the geyser basins appear to be surface phenomena and probably do not extend to any great depth. Future work of the U. S. Coast and Geodetic Survey will reveal what changes of level have occurred. Undoubtedly some of the earlier established elevations are no longer correct.

Rumors and tall tales are a common aftermath of every major earthquake. Yellowstone was no exception. It was reported in the press that Old Faithful Geyser, shortly before the main shock, put on a performance of power unequaled in the history of the park. Every eruption of this geyser is different and during any 24 hour period there are appreciable variations in height, interval and duration of play. It would be very difficult to correlate supposed unusual behavior of Old Faithful with events that preceded the earthquake. If caused by a minor foreshock then certainly the geyser should have been most erratic in the weeks that followed when aftershocks were being recorded daily. This is contrary to the facts.

The legendary material of seismology includes many stories of unusual animal behavior during the hours that precede a major earthquake. Some accounts must be considered as coincidence, others imaginative, and there may be a scientific explanation for some. It is true that animals are more sensitive to certain vibrations than humans and it is quite possible that they react to shocks imperceptible to man. There have been conflicting reports of water birds vacating the Hebgen Lake area shortly before the main shock. In attempting to evaluate these reports one might seriously question how many people are observant of waterfowl activity at midnight? On the other hand I have heard that a gravimeter survey party had to cease operations on August 17 apparently because this highly sensitive instrument was being disturbed. Until more factual information is available the reader must tentatively draw his own conclusions.

On the more factual side there are well documented reports* of the stampeding of elk concurrently with some of the aftershocks and it seems likely that some bear may have been buried in rock slides in Madison Canyon. One bear was trapped in a cave in the Firehole Canyon and was observed on August 23 trying to dig his way out. D. R. Hearne, Maintenance Foreman, West District, was able to pry loose some of the rock and the bear emerged apparently unharmed but with a strong desire to quench a six day thirst.

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*Earthquake Study File, Yellowstone Park Library.

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