Distribution, properties and origin of viscous-flow features in the McMurdo Dry Valleys, Antarctica

- Debris-covered glaciers are tongue-shaped with visible ice core.
- Gelifluction sheets occur below valley sidewalls with a shallow active layer.
- Gelifluction sheets moved by subsurface meltwater on top of permafrost
- Features comparable to alpine and arctic regions

Satellite images and high resolution air photos, coupled with field examinations, were used to examine 24 rock glaciers/debris-covered glaciers and 25 gelifluction sheets, collectively referred to as viscous-flow features, in the McMurdo Dry Valleys, Antarctica. Debris-covered glaciers are the dominant form and are longer (mean length = 2.5 km), wider (mean width = 0.8 km), and less steep (mean slope = 12°) than similar features reported in most arctic and alpine environments. The catchment areas tend to be large, averaging over 9 km2. Most of the debris-covered glaciers are tongue-shaped, and where excavation was possible, the ice core was readily observable. Gelifluction sheets primarily occur at the base of valley sidewalls below talus on slopes ranging from 5 to 30° (average = 13°) and contain a very thin active layer (normal range 20 to 40 cm). Both viscous-flow forms occur on the north- and south-facing slopes of the east-west trending valleys and are concentrated in the inland mixed zone and stable upland microclimatic zone; these lobes were not found in the coastal thaw zone. Gelifluction sheets result from the melting of snow high on the valley walls, subsurface flow of meltwater on top of the permafrost, and slow movement downslope. They are readily observable from nonsorted polygons that are stretched into rectangles that are perpendicular to the slope and contain raised polygon rims upslope. The movement of gelifluction sheets can be detected from upturned stones containing carbonate coatings. Rates of horizontal surface flow of the viscous-flow features are comparable to those reported elsewhere in Antarctica and in the alpine and arctic regions of the world. Some of the viscous-flow features appear to be inactive, possibly reflecting the recession of alpine glaciers in high elevation cirques.