Abstract
Block streams comprise linear accumulations of coarse openwork rock debris that have moved or are moving downslope in areas of past or present periglacial conditions, respectively. Thus, relict and active examples occur and are usually components of local continuums of blocky materials. Marked differences exist in block stream plan forms, dimensions, morphology, and structure and composition, and a variety of processes act in combination and/or succession during their development. Relict block streams are frequently regarded as a result of macrogelivation, mass wasting, and frost heaving/sorting, with immobilization due to removal of fine-grained matrix materials. Elements of this evolutionary sequence have been questioned, and it may be the case that not all relict block streams were subjected to the same set of processes. Where active block streams are associated with permafrost, they may be the cause of permafrost aggradation rather than a consequence of it. It has not been demonstrated that permafrost was a requirement during development of relict block streams. Many relict block streams are in areas that were adjacent to the ice margin during the Last Glacial Maximum (LGM) and they may have been active at that time. A LGM age for relict block streams in southeastern Australia has been confirmed by cosmogenic isotope dating.
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