SGER: Iceberg Lake: A High Resolution Glacial Record Exposed in an Outburst-Drained Proglacial Lake

University Of California-Santa Cruz, Santa Cruz CA

Investigators

Abstract

A high resolution neoglacial record of glacial sediment yield exposed in a jokulhlaup-drained proglacial lake Documentation of the production of sediment by glaciers is critical to our understanding of the roles of glaciers in the topographic evolution of mountain ranges and in global geochemical cycles. While proglacial lakes offer an excellent opportunity to investigate the relationship between sediment source and sink in a non-tidewater glacier environment, access to their sedimentary record is often poor. We will examine sediments impounded by "Iceberg Lake," a large, stable, long-lived proglacial lake in Alaska's Chugach Mountains. Iceberg Lake unexpectedly drained in 1999 and again in 2000, offering a tremendous (but ephemeral) opportunity to characterize the lake's accumulated sediments in three dimensions. Although glacier-dammed, there is no historical record of Iceberg Lake draining prior to 1999. The lake's apparent stability over hundreds of years resulted in 1) a series of four well-developed shoreline deposits ringing the lake, 2) a series of four sandy deltas, and 3) strongly-varved lacustrine sediments. As the lake's main inlet stream is now rapidly cutting down through all of these deposits, virtually all of Iceberg Lake's neoglacial sedimentary record is currently exposed. In this small glacial basin, with very tight coupling between source and sink, these deposits promise a centuries-long sediment record with annual resolution. By mapping the sediments, and by detailed sampling of the varve record, we will produce a detailed time-series of coarse and fine-grained sediment delivery to Iceberg Lake. This will document year-to-year variability in the volume and type of sediment deposited in Iceberg Lake over hundreds of years, and will provide insight into glacier dynamics, sediment production and evacuation, and fluvial transport during, after, and possibly even prior to the Little Ice Age.