Thirlmere Lakes, N.S.W.: geomorphic environment and evolution

Thirlmere Lakes, N.S.W., are located in an incised former river valley which has undergone considerable infilling with sediments prior to, and possibly during the formation of the lakes. -- Research into the geomorphic processes operating in and around the lakes has shown that organic sediment, in the form of sedge peat, is the main type of deposit accumulating in the lakes at the present time. Past lake level changes are indicated by, firstly, alternation of fine with coarse inorganic sediment in the marginal areas of the lakes reflecting oscillations in the location of the littoral zone; secondly, changes in the aquatic vegetation zonation; and, thirdly, the formation of peat islands. Bushfire appears to be a major influence on the initiation of sediment transport on the surrounding hillslopes and alluvial fans. -- Lacustrine facies at depth in the valley fill indicate more extensive lacustrine deposition in the valley in the past, and lake formation may be related to tectonic uplift of the area since the Late Tertiary period.