INTRIGUING GLACIAL FLOW PATTERNS, MORAINE CANYON, ANTARCTICA

Moraine Canyon, a 25 km long and 4 km wide valley in Transantarctic Mountains, located about 300 km North of South Pole, has half of the valley floor covered by clean (debris free) glacier ice and the other half by debris covered ice. What makes this intriguing is that the division runs along the long axis of the valley; down the flow line in the middle. The differential GPS measurements on permanent markers across the valley floor (perpendicular to flow lines) over a time span of one year show that the clean ice flows at a rate of ~1.4 m/yr and the debris covered ice flows at a rate of ~0.7 m/yr. The clean ice sublimates at a rate of ~5 cm/yr. The debris cover retains patterns that indicate flow convergence from small tributaries and pooling into the main valley.

The existing data is leading to following working hypothesis: 1) there is a flow boundary between clean and debris covered ice, 2) the debris side of the valley mouth is blocked by a fast moving ice stream, 3) the differences in ice sublimation and flow rates between clean and debris covered sides lead to relatively faster surface lowering in the clean side. Eventually the higher elevation debris covered side will temporarily flow laterally to the clean side and a sliver of the debris covered ice will become incorporated into the faster flow and get evacuated from the valley.

Supporting visual evidence include the long narrow debris slivers on the clean ice, apparent thinning and stretching of the debris cover at the lower end of the glacier, and apparent flow blockage of the debris covered ice into the Amundsen glacier at the mouth of the valley.

These suggestions have interesting implications for deciphering the glacial deposits left behind by this and other glaciers. If the glacier in Moraine Canyon were to retreat today the debris side of the valley would have a lateral moraine (just like seen higher on the valley wall today) but the clean side would have none (none is found today). The cosmogenic exposure age of the boulders on the debris side moraine could yield an age that is more related to the glacial turnover rate than the depositional age of the moraine (at the above rate it takes about 30 kyrs to cover the length of the valley).

Unusual as this glacier seems today such systems may have been more prevalent in full glacial time with well-developed valley glacial networks.