signature=cfc31ac8c76628bdea7d6b7d7ce25563,Sources of groundwater in an alpine catchment, Rocky Moun...

Abstract

Characteristic talus hydrology involves recharge of the subsurface reservoir by snowmelt and summer rain events; water with a distinct isotopic and chemical signature moves quickly through talus in response to these events due to high permeability and hydrologic heads and typically arrives in the stream minutes to hours later. Water is released more gradually from talus during base-flow conditions as the hydrologic head declines and the deposits slowly drain. Discharge, water chemistry, and water temperature were monitored throughout the year at a stream and in several springs draining talus fields during 1997 - 2001 in Loch Vale, a high-elevation catchment (3050 - 4009 m) in Rocky Mountain National Park, USA, to determine contributing sources of water. Flows in the stream and a nearby spring draining a south-facing slope exhibited similar hydrologic and chemical behavior to each other under a variety of flow conditions and seasons, suggesting a potentially strong linkage between these hydrologic systems. Hydrologic behavior at two springs draining northwest-facing slopes suggests variable sources of water through the year. Flow at one spring on a northwest-facing slope was strongly influenced by melting of a seasonal snow field that declined in size through the summer (flow ceased when the snow field disappeared). Flow at the other spring on a northwest-facing slope occurred only during summer and fall, and water temperatures were below 2°C despite a lack of snow fields in its catchment. CFC-12 measurements on water collected from each of the springs during October, 2001 indicated that the ages of the spring waters ranged from 12 to 33 years. These ages are much older than expected based on the high hydraulic conductivities of the talus material (10-3 to 10-1 cm/s). One possible explanation is that melting permafrost may contribute substantial flow to the springs during late summer and fall. Mapping of mean annual soil-surface temperatures using climate data from three weather stations in Loch Vale indicates that permafrost may exist at elevations above 3310 m on north-facing slopes and at 3612 m on south-facing slopes. Thus, melting permafrost is a plausible source of water for some talus springs.