PHYSICAL CHARACTERISTICS AND BATHYMETRY OF ICE-CONTACT, PROGLACIAL SHERIDAN LAKE, SHERIDAN GLACIER, ALASKA

Sheridan Lake evolved during retreat of Sheridan Glacier from an 18th century moraine. Separation from once confluent Sherman Glacier provided space for spreading of a small, 5 km wide piedmont lobe. Since 1950 (earliest topographic quadrangle) several ephemeral basins merged, and by 1965 three distinct and separate, ice-contact, proglacial lakes had formed, each with separate outflow streams. Aerial photos show that continued retreat during the ensuing decade led to the coalescing of the western and southern basins, drained by Sheridan River, as the eastern basin filled with Sherman Glacier outwash.

The lake shore and ice front position are represented on a new 2000 GPS-based map. The ice front maintains a uniform trend where the gently sloping ice surface enters the lake, but consists of ice-wall promontories and wedge-shaped reentrants where calving along intersecting splaying crevasses occurs.

Bathymetric information reveals a common ice front depth ranging from 40-70 m. However, within a wedge-shaped reentrant reaching 400 m up glacier, the lake bottom plunges from 65 m to 130 m, thus placing the lake floor 85 m below msl. Comparison with 1999 depth data indicates negligible annual sediment accumulation. This may be related to very low turbidity (<0.01 g/L), a condition unexpected from a graywacke provenance. Low suspended sediment combined with uniform temperature values (0.4-0.6°C) throughout the water column suggest a lack of subglacial water inflow.