SPATIAL PATTERNS AND DRIVERS OF MELT AND THERMOKARST EROSION IN GARWOOD VALLEY, MCMURDO DRY VALLEYS, ANTARCTICA

Previous work has shown that thermokarst formation in the Garwood Valley, McMurdo Dry Valleys (MDV), Antarctica, has accelerated to ~10 times the average Holocene rate. A large retrogressive thaw feature known as the Garwood ice cliff is among the thermokarst features representative of this rapid landscape evolution. Along the Garwood ice cliff, gullies are eroding alcoves into the buried ice and overlying sedimentary cap, incising channels in the ice-cored talus cones at the base of the cliff, and are depositing new fans along the Garwood River banks.

We used repeat terrestrial laser scanning to measure gully cross-sectional topography through time and tracked the evolution of gully slopes from alcove to channel to apron as the ice cliff recedes. We determined where sediment erosion and redeposition and/or ice subsidence occur across the landscape as a result of gully processes. Measurements of volume loss, scarp apex retreat, and sediment redeposition throughout time are synthesized to form a coherent understanding of hillslope evolution and the effects of gullies on that evolution.

Gullies are found to occur on hillslopes with lower slopes, higher relief, faster scarp apex retreat, and lower erosion rates. The lower erosion rates and faster scarp apex retreat indicates that fans deposited beneath gully features are relatively more stable than the ice cliff face. Gully erosion drives the scarp towards a uniform slope, which enhances sediment retention, and which may ultimately preserve underlying ice through re-burial.

Understanding gully evolution in Garwood Valley helps connect drivers of landscape change in the MDV to their effect on the landscape. Gullies are associated with lower erosion rates and faster scarp apex retreat, when compared with non-gullied portions of the ice cliff, indicating either that gullies may be drivers of unique erosional patterns or that gullies appear on hillslopes with a specific set of controls. A pattern of decelerating erosion across the ice cliff throughout time indicates the burial of the thermokarst feature as the ice cliff is insulated through redeposition of sediments. Understanding how gullies evolve contributes to the study of buried ice ablation in the Antarctic as climate change begins to influence old landscapes to evolve in new ways.