ESTIMATED WATER STORAGE WITHIN GLACIER COMPEXES IN ROCKY MOUNTAIN NATIONAL PARK

Mappable perennial firn and ice covers an area of approximately 3075 ha (7,597 ac) within Rocky Mountain National Park (RMNP). This consists of about 95 ha (234 ac) of firn, 223 ha (552 ac) of exposed ice, and 2757 ha (6811 ac) of debris-mantled ice mapped using several vintages of aerial photographs. Field checking during the drought years of 2001 and 2002 revealed glacier ice beneath much of the firn cover observed in previous years. Direct ice thickness measurements are currently limited to observed depths of crevasses and the height of the margins of debris-mantled tongues and lobes above adjacent basal surfaces. These sources have provided little information on minimum ice thicknesses and none on maximum thicknesses. However, ice plasticity increases abruptly at a pressure equivalent to a load of about 30 meters of ice resulting in much higher ice creep rates. Applying this information, structural features indicative of differential motion provide clues that can be used to estimate the minimum thickness of ice both in exposed and debris-mantled portions of ice masses. Using these minimum thicknesses, the inventoried ice masses in RMNP are estimated to contain roughly 6.7x108 m³ (5.4x10⁵ ac-ft) of water in perennial storage, approximately twice the annual water use in the city of Denver. Approximately 88% of the water is stored in ice tongues and lobes insulated beneath debris.