T64 Quaternary Geology and Its Applications: In Honor of David M. Mickelson

Sunday, 9 October 2011
1:30 PM - 5:30 PM
Room L100A-C

LATERAL MELTWATER CHANNELS OBSERVED FORMING ALONG THE MARGINS OF A TEMPERATE GLACIER, GLACIER BAY, ALASKA -- IMPLICATIONS FOR INTERPRETING PALEO-THERMAL REGIMES

Paper number: T64-11
Program: Technical Sessions
Time: 4:10 PM – 4:25 PM

Authors

Abstract

Lateral meltwater channels (LMCs) form parallel to the glacial ice margin and subparallel to the contour of the land surface. LMCs commonly are used as evidence for cold-based or polythermal Pleistocene ice sheets (especially in Scandinavia). During his Ph.D. research, David Mickelson (1971) observed LMCs forming along the margins of a rapidly thinning temperate glacier (Burroughs Glacier) in Glacier Bay, Alaska. These observations, published by Syverson and Mickelson (2009), show that LMCs alone cannot be used as definitive evidence for cold-based or polythermal ice.

Mickelson observed the formation of flights of nested linear lateral meltwater channels and in-and-out channels on the sides of emerging nunataks. The nested channels are up to 200 m long, are good proxies for the slope of the ice margin along the land surface, and are terminated by subglacial chutes. Up to 8 channels/year formed as the ice wasted. The in-and-out channels are hook-shaped, and the upstream and downstream parts of the channels appear to “hang” on the hillside where no modern source of water is available.

Most workers think LMCs form where meltwater cannot flow through the frozen toe of a cold-based glacier; rather, the meltwater flows along the ice margin and incises an LMC. This is reasonable explanation, and many Pleistocene LMCs likely formed in such an environment. However, a temperate ice margin does not have a frozen glacial/subglacial barrier to water flow. At the temperate Burroughs Glacier, Syverson and Mickelson (2009) proposed that high rates of precipitation and ablation cause a perched water table in the ice. This makes the temperate ice relatively impermeable. Thus, the water flows along the margin and erodes LMCs until a subglacial chute carries the water into the subglacial water system.

Because lateral meltwater channels have been observed forming along a temperate glacier margin, lateral meltwater channels alone should not be used as definitive evidence for cold-based or polythermal ice.