HR: 0800h
AN: C21C-1111    [Abstracts]
TI: The Role of Firn Pack in Melt Season Drainage From Temperate Glaciers
AU: * Henry, H M
EM: hiramhenry@hotmail.com
AF: Portland State University, Depts. of Geology and Civil Engineering, P.O.Box 751, Portland, OR 97207 United States
AB: The densifying firn atop temperate glaciers presents a perched unconfined aquifer. The firn/glacier-ice transition represents the approximate depth of pore closure and relative impermeability. Vertical infiltration of melt season precipitation and meltwater reaches this aquitard and results in pooling, liquid water storage, and horizontal flow. The majority of aquifer water is believed to drain via crevasses, which are internal sinks. The rate and timing of water flow through the firn aquifer plays a role in the seasonal runoff cycle of glacierized catchments. Here, a three dimensional numerical model has been developed to study that cycle with the intent to 1) simulate variation of the water table during the annual melt season, 2) study the response of aquifer discharge to storm events, and 3) examine the role of crevasses and the englacial drainage network in the flow of liquid water through the firn aquifer. The model uses a finite element technique to solve standard equations for infiltration into, and flow through, an unconfined aquifer. Crevasses are treated as transient internal boundary conditions, which have different form depending on the relative magnitudes of flow through the aquifer and drainage capacity of the crevasses. Preliminary results suggest that the response time of the water table to surface storm events ranges 3-5 days. The model indicates that most liquid water drains from the aquifer by early winter, leaving the firn unsaturated until late spring. Water table thickness in the aquifer ranges 2-6 m. This represents a maximum liquid water storage of 0.64m³ per m² of the glaciers accumulation area. These values agree with observations published in the literature.
DE: 0720 Glaciers
DE: 0740 Snowmelt
DE: 0776 Glaciology (1621, 1827, 1863)
DE: 0798 Modeling
SC: Cryosphere [C]
MN: Fall Meeting 2005