EEPS Colloquium: Suzanne Anderson
Can rock glaciers replace glacier water resources?
Rock glaciers are often cited as a water resource in alpine watersheds, yet their hydrologic behavior is understudied. These debris-mantled ice tongues number in the thousands across the western US, while numbers of true ice glaciers are declining. Can rock glaciers replace the water resources of glaciers? Specifically, does melt of the ice core of the rock generate significant streamflow, and how do rock glaciers affect water flow paths and groundwater recharge? We examine these questions in Imogene Basin, San Juan Mountains, Colorado. We have been sampling the outlet of a rock glacier, groundwater emerging from a mine adit, and nearby alpine surface streams. We combine stream gaging with measurements of water stable isotopes, specific conductivity, water temperature, and 14C ages of dissolved inorganic carbon to partition water sources over time. Multiple lines of evidence show that rock glacier ice does not contribute to runoff in the present climate. I will walk through hydrograph separation, streamflow temperatures, and water mass balance arguments to support this conclusion. The rock glacier does divert infiltrating snowmelt and rainwater through its rocky carapace to its margin, and so is efficient at generating runoff. At the same time, it is probably a barrier to groundwater recharge over its area. Nonetheless, radiocarbon water ages imply that base flow from the rock glacier and from all streams we sampled is dominated by groundwater with hundreds to thousands of years residence time in this alpine basin. Although the rock glacier stores ice, at present it acts as a permeability barrier that steers infiltrating snowmelt and rain through its rocky cover rather than as a water source.
Hosts: Claire Masteller
EEPS Colloquia are made possible by the William C. Ferguson Fund