The urban geology of Cairns, Queensland, Australia

Abstract

The urban geology of Cairns, on the northeast tropical coast of Australia, is dominated by Quaternary sediments. These sediments provide a record of sea-level change, alluvial and slope response to late Quaternary climatic changes and millennial scale occurrences of various natural hazards. Drying of climate and consequent retraction of rainforest into refugia just prior to and after the Last Glacial Maximum resulted in the construction of extensive high-level alluvial fans and slope deposits which were incised following the amelioration of climate during the early Holocene. The Holocene sea-level record of the region is best shown by coral micro-atolls which suggest that hydro-isostatic rebound following flooding of the continental shelf resulted in a sea-level fall of approximately 1 m since 5.5 ka . Coastal progradation following sea-level stabilisation at approximately 6 ka has occurred with the deposition of sandy beach ridges and cheniers on a mud substrate. These and other ridges on offshore islands along the Great Barrier Reef were likely a result of deposition by storm surge and waves during tropical cyclones. These millennial scale records highlight that extreme intensity tropical cyclones occur an order of magnitude more frequently than that suggested by the short (∼100 yr) historical record of tropical cyclones from the region.