Geomorphology and geomorphological responses to climate change in the interior of sub-Antarctic Marion Island

by Hedding, David William.

__________________________________________________________________________ i University of Pretoria etd – Hedding, D W (2007) Geomorphology and geomorphological responses to climate change in the interior of sub-Antarctic Marion Island David William Hedding Supervisors: Prof. K.I. Meiklejohn and Dr P.D. Sumner Department of Geography, Geoinformatics and Meteorology Master of Science Abstract The influence of climate change on the geomorphology of the interior of Marion Island (above 750m a.s.l.) is investigated as climatic amelioration is thought to be responsible for the observed rapid melt out of the summit regions. Records have shown that the climate on Marion Island is warming and, as it represents a maritime periglacial environment characterised by small seasonal temperature ranges and steep temperature profiles, it is particularly sensitive to climate change. Marion Island is, therefore, an ideal location to address the poor understanding of periglacial environments in the Southern Circumpolar Region in the context of environmental conditions governing permafrost, seasonally frozen ground, and frost processes. To ascertain the influence of climatic amelioration on the geomorphology of Marion Island’s interior, thermokarst, periglacial, and rudimentary aeolian features were identified and mapped. Geomorphological features were documented to determine the extent of landscape response to climate change in the island’s interior. In addition, identification and mapping of geomorphological features were, in some cases, used to provide evidence for the previous existence of permafrost. Ground temperatures were also monitored to determine the present state and possible existence of permafrost above 750m a.s.l. Landscape development in the certain areas of the interior of Marion Island where glacial ice persists beneath sediment (scoria) and where permafrost previously existed has resulted in the manifestation of thermokarst features and the creation of a unique undulating topography. In parts of the study area, thermal erosion and subsidence of the thermokarst are identified as processes that are important agents of landscape evolution. Thermokarst processes, indicative of climate change are, however, limited to areas where buried glacial ice persists and permafrost existed. Thermokarst features studied were also noted to be ephemeral and easily destroyed through erosion by wind and water. Aeolian erosion, in particular, has a significant influence on thermokarst as the interior of the island represents a polar desert where almost no vegetation survives. Persistence of thermokarst features is further limited due to the nature of local sediment, namely scoria, being cohesionless, Abstract University of Pretoria etd – Hedding, D W (2007) ii __________________________________________________________________________ thereby limiting the retention of water that can be frozen. The disappearance of the former permanent snowline sub-aerially exposing much of the interior suggests interaction between frost and aeolian processes will provide potentially relevant avenues for future geomorphological research. Furthermore, interactions between frost and aeolian processes are extremely important for plant colonisation in an area that is almost entirely devoid of vegetation.