Shingle ridges

Abstract

Coral shingle ridges form where coral reefs lie close to shore. Waves during intense storms or tropical cyclones break fragile coral species into fragments that can accumulate as a (shingle) deposit landward of the high tide mark or as an offshore deposit that may or may not be transported landward at a later date. The onshore deposits of coral shingle are shaped into a ridge by the marine inundation constituting a storm surge, tide, wave set-up, wave action and wave run-up. Successive ridges are deposited with time so that multiple shore parallel ridges can eventually form into a ridge plain. Each new ridge is deposited seaward of the previous ridge and often, but not always, one ridge can be deposited during a single tropical cyclone event. The ridge plains can provide a valuable record of the frequency and intensity of tropical cyclones for that region over several millennia. Recent examination of several ridge plains along the Great Barrier Reef region show that these ridges are often emplaced during intense tropical cyclones and these events occur on an average every two to three centuries. This is an order of magnitude greater than that suggested by the short historical record of these events in this region.