The evolution of sea cliffs over multiple eustatic cycles in high energy, temperate environments

Abstract

Sea cliffs are steep, erosional features carved out of rocks by marine and subaerial erosive processes. They are defined as a surface at the coast with a slope angle of greater than 20°. The broad morphology of these cliffs is determined by the relative magnitude of the erosive processes and the resistance of the lithology in which they are formed. In this study, an integrated aerial LiDAR and multibeam dataset from +20 to −80 m water depth is used to precisely quantify sea cliff morphology. Over 260 km of cliffed coastline was identified and analyzed along the high-energy temperate coast of Victoria, Australia, with cliffs occurring down to 60 m depth. Cliffs at present sea level were found to range in average slope from 20.8 -53.0° with their base occurring within 6.8 m of mean sea level. Cliffs were also discovered below modern sea level in three locations, each set tending to be lower in height and slope than the contemporary active landforms. Marine erosion acting over the entire face during transgressive events is proposed that as a cause of the more gentle slopes of these landforms as upper parts of the profile are eroded in surf zone as it moves landward during a transgression. As a result, the accuracy of these drowned landforms as sea level proxies (<14.2 m within expected sea level) is less reliable than cliffs formed during the current highstand (<11.3 m within sea level).