Title: Cliff coast collapses driven by nested biological, astronomical and meteorological activity cycles

Michael Dietze, Kristen L. Cook, Luc Illien, Oliver Rach, Niels Hovius

GFZ Potsdam, Germany

Event: GeoKarlsruhe 2021

Date: 2021

DOI: 10.48380/dggv-yeqk-7k80

Cliffs line many erosional coastlines. Localized failures can cause land loss and hazard, and impact ecosystems and sediment routing. Links between cliff erosion and forcing mechanisms are poorly constrained, due to limitations of classic approaches. Combining multi-seasonal seismic and drone surveys, wave, precipitation and groundwater data we study drivers and triggers of 81 failures along the chalk cliffs on Germany’s largest island, Rügen. We have found that marine processes are negligible in triggering failures but efficient in removing the deposits. Instead, cliff failure has been associated with terrestrial controls on soil moisture and groundwater. During the vegetative season, evapotranspiration impedes groundwater flow into the cliff face. When vegetation is dormant, failure frequency correlates with lunar-mediated precipitation. Failures are triggered by relative air moisture and rain, leading to clustered events during night time. Drier terrestrial conditions prevent smaller failures, which causes beach erosion and ultimately prepares the cliff for sector collapse.

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