Distribution and palaeoenvironmental significance of mountain blockstreams in the southern hemisphere

Openwork mountain block deposits (blockfields, blockstreams) have received much research interest globally given their visual appeal as prominent cold-region landforms. However, studies have shown that these landforms in both glaciated and non-glaciated environments are probably of considerable age (pre-Quaternary), yet the environmental conditions of their formation (such as the presence of permafrost) and associated processes remain poorly understood. This paper focuses on consolidating and critically analysing current knowledge on mountain blockstreams found in the southern hemisphere. This is achieved by reviewing past published work on such landforms, from the Falkland Islands, Marion Island, southern Africa and southeastern Australia. By presenting a variety of previously proposed landscape evolutionary models, we demonstrate that southern hemisphere blockstreams are products of a range of weathering and material mobilization processes over long multiple warmer/wetter and colder/drier pre-Quaternary and Quaternary climatic cycles. Although most southern hemisphere mountain blockstreams have some association with periglacial processes, they are not exclusively periglacial in their developmental history. This can be tested through field geomorphic, sedimentary and ecological methods; the use of remote sensing; radiometric and relative-age dating; seismic and other subsurface methods; and modelling. However, many research questions remain unanswered, such as the potential role of permafrost in blockstream formation and dynamics, or their sensitivity to ongoing climate change.