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Abstract:
Merrill Cave, part of a Pleistocene lava flow within Lava Beds National Monument, is the site of ice deposits that have fluctuated widely in volume between the Pleistocene and Holocene Epochs. Remnant mineral deposition from ice levels on the walls in the lower level of the cave provides insight into the depth of the ice during this time. The disappearance of a large perennial ice deposit in the lower level of the cave was tracked using historical photographs and modern photographic and ice-level monitoring techniques. A major change in airflow patterns and temperatures in an as yet unexplored lower level of the cave are suspected to have initiated the decline in ice levels. Measurements taken of the elevation of the surface of the ice deposit show a loss of over 1.25 m of ice in eight years. Surface and interior losses of ice from evaporation and/or sublimation have resulted in the near total loss of the large main perennial ice pond in the lower level of the cave. Photographs also document a drastic change in ice volume and levels during the same period of time. Several theories for the disappearance of ice have been suggested. One possible explanation for the loss of ice is related to a significant seismic event in the region in 1993 that may have caused rock fall in another, inaccessible section of the cave and precipitated the loss of ice in the accessible lower level. The dramatic loss of ice may also be the result of climate changes that, over time, indirectly influenced ice levels in Merrill Cave. Visitor impacts to the ice deposit after a large cavity breached the surface of the deposit contributed to the decline of ice conditions. Lastly, the presence of western juniper (Juniperus occidentalis) in the terrestrial environment above the cave may influence the hydrology of the cave environment.