The Age and Origin of Block Deposits in the Victorian Alps, Australia

ABSTRACT Large periglacial block deposits are found in the mountains of southeastern Australia. Despite their widespread distribution, their mode of formation and age are poorly understood. These landforms hold considerable potential to shed light on the nature of cooling during glacial periods. In this paper we present a new study of block deposits in the mountains of Victoria, Australia. We describe the surface architecture, microrelief, slope profiles, texture, block shape and morphology of the blockstreams and block aprons. We present 14 new cosmogenic nuclide exposure ages ( 10 Be and 36 Cl) from four sites to extend existing chronologies and explore the use of weathering rinds to establish relative age. We find that formation of the deposits spans the last glacial cycle, with ages ranging from 93.1 ± 13.5 to 10.5 ± 2.0 ka. Weathering rind thickness showed no relationship with age or distance downslope and is likely saturated. We present a conceptual model where a combination of frost creep and hydraulic pressure explain the flow and the morphology of the blockstreams. Based on analogs in North America, mean annual air temperature was 10.2°C ± 1.3°C colder than present. The high magnitude of temperature change is similar to Australian continental and Antarctic estimates and indicates that the LGM had a significant impact on the landscape.