PALSAS IN THE HANGAY MOUNTAINS, CENTRAL MONGOLIA

The valleys of the Chuluut Gol (47.29°N, 100.07°E, 2283m) and Tsarang Sairin Gol (47.23°N, 100.02°E, 2446) contain palsas and other periglacial landforms. The palsa mounds contain an interior lens of segregated ice beneath a 60-cm thick peat-rich active layer, measure between 15 and 20 m in diameter and up to 2 m high, and are clustered in fields; the palsa fields of this study are in different stages of decay. The Chuluut Gol palsa field has four active palsas on a 6% slope and is located in an open valley covered with grass and sedge peat, and adjacent to patterned ground. Radiocarbon dating of the basal peat just above the permafrost boundary yielded an age of 4,970 ± 20 yrs BP. The Tsarang Sairin Gol field has one active palsa with segregated ice and numerous inactive palsas without subsurface ice; this field lies on the floor of a narrow glacial valley with dwarf willows and sedge peat. Field data collected from both palsa fields were used to determine what factors and/or processes contributed to the stage of palsa degradation. These factors include: (1) type and extent of vegetative cover, (2) thickness and density of the peat-rich active layer, (3) climatic factors such as temperature, (4) growth rate of the segregated ice, and (5) exposure of the subsurface ice due to growth (expansion) cracks. Field data suggests that growth cracks and the insulating properties of the active layer are important factors affecting the thermal stability of palsas in the study area. Preliminary lab experiments indicate that peat density does affect heat transport, with more compact peat transmitting heat more quickly, perhaps leading to more rapid palsa decay during the summer season.