Periglacial Processes and Landforms at Deception Island volcano, maritime Antarctica

Abstract

Ice-free areas in the South Shetland Islands and in the northern Antarctic Peninsula region have periglacial conditions that are characteristic of the maritime Antarctica. This region shows one of the highest temperature increases on Earth in the last fifty years. Therefore the study of processes and landforms in this region is of special interest. The climate of the South Shetland Islands is cold maritime, with summer rains and high cloudiness. Permafrost is sporadic on the lowest beaches, but on higher platforms and slopes, permafrost extends over wider areas. Therefore an active layer and processes related to the presence of permafrost are frequent. The study in Deception Island, the south-westernmost island of the Bransfield Strait (Mar de la Flota), is of special interest because the soils are affected by the interaction between cryogenic processes and anomalous warm terrains because of recent volcano activity. Respect to the island´s geomorphology, glaciers cover approximately 50 % of the island surface. The rest of the island is affected by volcanic, landslide, fluvial, aeolian, periglacial and marine processes. Periglacial activity is represented by hummocky terrains, nivation hollows, patterned ground, rock falls, debris and mudflows generated by water saturation of active layer, slopes with gelifluction processes, gelifluction lobes and terraces and thermokarst hollows. Hummocky terrains are continuous surfaces with decimetre to meter wide and decimetre depth bumps located mainly in the lower section of sloping lapilli and scoria terrains. Patterned grounds are represented by stripes and circles. In some places the polygonal mesh is unsorted. But in elevated sites, such as Mount Irizar, well-defined circles and stripes are found, showing a few centimetres diameter. Along the island there are low to moderate slopes without evidence of water streams but with the occurrence of ploughing boulders due to freezing-thawing processes. Gelifluction lobes and terraces appear as isolated, tongue- or linear-shaped features with a steep front and a smooth upper surface. Examples are found in Kendall Terrace and in Cerro de la Cruz. Thermokarst hollows appear as irregular depressions, caused by local melting of ground ice. Their diameters vary from a few meters to up to ten meters. They are common at Crater Lake and Refugio Chileno. The origin of many termokarst hollows is associated with past fumarole activity during the 1967, 1969 and 1970 eruption. For this reason its location and differentiation can help us to infer old fumarole places. On the other hand, debris and mudflows processes are common around the island at present time, but during the past eruptions they were more active processes.