Holocene landscape instability in the Dazzler Range, northern Tasmania

Abstract

At least 5m of poorly consolidated Quaternary sediments have accumulated since the mid Holocene in the lower reaches of stream channels that drain the flanks of the Dazzler Range. Radiocarbon assay of charcoal and wood fragments contained in the sediments indicate deposition during the mid to late Holocene 5.2-1.8 ka. Coarse gravels in the earliest deposits are believed to have been recycled from relict periglacial gravels in response to increased runoff and channel instability, brought about by neoglacial cooling coupled with changes in vegetation structure and associated fire frequency. The thickness of the sediments and the presence oflarge logs in the sediments along the lower reaches of Branchs Creek suggest at least one geomorphic event of high magnitude. Significant aggradation of finer calibre sediments has continued during the last two millenia. Since European settlement, deep gulleys have formed in the lower reaches of alluvial fans that flank the range, in response to land dearing for agriculture and the artificial straightening of stream channels. The earlier history of slope instability and sediment aggradation, even under natural conditions, highlights the need for careful land management.