THE EFFECT OF TOPOGRAPHY, LATITUDE, AND LITHOLOGY ON THE DISTRIBUTION OF ROCK GLACIERS IN THE LEMHI RANGE, CENTRAL IDAHO

To investigate the development and preservation of rock glaciers in the Northern Rocky Mountains, I inspected 171 alpine valleys in the Lemhi Range of central Idaho using optical remote sensing techniques, digital topographic analysis, and field examinations. In the Lemhi Range, 48 rock glaciers were found and examined for lichen cover, evidence of ice presence, and specific signs of movement and other morphological features. In addition to recording the presence or absence of a rock glacier in each alpine valley, existing rock glaciers were classified according to their morphology. Factors such as topographic shading, lithology, relief, aspect, and elevation determine the development and preservation of rock glaciers. Analysis of the factors in the Lemhi Range show that elevation above 2600 meters, a north facing aspect (300 – 60 degrees), and less than 2300 hours of direct sunlight per year are necessary conditions for the existence of rock glaciers in any form. The majority of alpine valleys in the Lemhi Range meet these requirements. Thus, other parameters, including topographic shading and lithology, must be examined in order to determine what controls occurence of rock glaciers in the Lemhi Range. Statistical analysis of controlling parameters shows that insolation and latitude control rock glacier occurence in Lemhi Range alpine valleys. While duration of insolation is a logical controlling factor, latitude more puzzling. Further statistical analysis supports the interpretation that the latitude effect is likely the result of lithologic changes with latitude. Lithology may affect rock glacier distribution due to differences in hydrology or ventilation between differing rock types. A relationship also exists between rock glacier presence and protalus lobe presence.