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