A spatial inventory of glacial, periglacial and rapid mass movement forms on part of Marion Island : implications for Quaternary environmental change

Abstract

While climate change is expected to have its greatest impacts in the earth's polar regions, most studies to date concentrate on Northern Hemisphere landscape changes. In contrast, Southern Hemisphere periglacial environments are poorly understood, both in terms of basic understanding of geomorphological dynamics as well as sensitivity to climate change. Marion Island constitutes such an environment and the purpose of this project was to assess the Late Pleistocene and Holocene glacial, periglacial and mass movement morphology on the island, and to use these data as indicators for climate change. A survey and thematic mapping, following an adaptation from the lTC working procedure, was used to compile an inventory of the glacial, periglacial and mass movement features for grey lavas on the eastern side of Marion Island. Glacial moraines, glacially polished and striated bedrock surfaces identified from previous research verified and mapped, while undocumented sites were added to the inventory. Data support the findings of Hall (1978; 1980a; 1982) and that the suggested palaeoreconstruction and glacial succession on Marion Island from that research is correctly interpreted. Periglacial landforms occur Qn all the grey lava areas that were surveyed on Marion Island. The features are found throughout the whole island altitudinal range, and definite trends can be discerned, where landform size increases with altitude. No significant differences, however, appear to exist between the warmer north-facing and colder south facing slopes with regards to the size distribution of periglacial features on Marion Island. Increasing periglacial activity with altitude is indicative of an increase in frequency and/or intensity of frost induced processes. Stone-banked lobes, stone-banked terraces, vegetation-banked lobes and blockstreams identified in this study and whose morphology cannot be explained by present day soil frost activity are considered relict. These features indicate and confirm conclusions from previous studies that Marion Island experienced a more severe frost environment than present. Rapid mass movement features are present in most grey lava areas, except where there is an absence of cliffs or where low slope angles are found. Screes are mostly found where high free faces exist and the extent of the screes is related to the morphology of the cliffs above. Peat slides are common in middle and low altitudinal areas between 150m a.s.l. and 450m a.s.l. where thick soil and steeper slopes are present. However, peat slides are conspicuously absent form the feldmark environments due to a lack of peaty soil. Most peat slides on Marion Island occur on the north facing slopes of the major ridgelines. It is concluded from observations that major scree production occurred during a period of more intensive periglacial activity during the early Holocene lasting from 12kBP until 7kBP. The area demarcated as Feldmark Plateau, is bounded by faults due to isostatic uplift on deglaciation, which indicates that the ice cover in this region must have been extensive. However, no irrefutable proxy evidence for glacial activity has been found in this area. Periglacial features on the Feldmark Plateau are relatively larger than the same landforms in other areas at similar altitudes and possible reasons for this could be that the Feldmark Plateau was not glaciated in the Pleistocene; the features would then have developed under a cold, but ice-free environment. It should be noted that all slopes of the Feldmark Plateau are south facing and thus receive less insolation than north facing slopes. In addition, the slopes occupy the southern sector of the island, which may further contribute towards a cooler and more intense frost environment. It is hypothesised that a period of intense scree production occurred during the early Holocene, and this is manifested in the scree on the slopes of the Feldmark. If glaciation did occur, over-steepend slopes following ice retreat, would also have been conducive to intense scree production. It can, therefore, be concluded that the Feldmark Plateau, if glaciated, became ice-free rapidly after glaciation, so that the intense periglacial activity, plus the oversteepend slopes left by the glacial activity, produced large amount of scree from the cliffs. The inventory of periglacial, glacial and mass movements on grey lava areas of Marion Island provides a useful baseline for geomorphological studies on Marion Island. Through refinement this database has the potential for palaeoenvironmental research and is a useful resource for earth and biological scientific studies.