Preconditioning and Driving Factors of Coastal Cliff Erosion in Denmark

Abstract:

Cliffs along the Danish coastline often consist of glacial till prone to high rates of erosion. This erosion will probably increase in the future due to sea-level rise and higher wave impact. Coastal cliff erosion is an underestimated factor in the sediment balance of the Danish shores and it has probably affected the coastal evolution in the Holocene. Investigating the preconditioning and driving factors of coastal cliff erosion is crucial to understand landscape evolution. A new mapping of more than 2.500 recent coastal landslides revealed the abundance of mass movements along the Danish coastline.

We report on the preconditioning and driving factors of coastal cliff erosion all across Denmark. A dataset of recent coastal landslides is used to derive the morphometrics of the cliffs. The cliff erosion processes are linked to national datasets on topography, geomorphological landforms, Pre-Quaternary bedrock, ice sheet advances, hydrology, soils, land use and climate. Coastal cliff erosion predominantly occurs in landscapes formed under the Scandinavian ice sheet in Denmark. Neogene and Paleocene clays are important preconditioning factors for increased coastal cliff erosion. They can act as sliding planes wherever these clays are close to the current sea level. The most common cliff movements are slides, ranging from shallow translational slides to deeper seated rotational movements. The latter are also affected by the ice-flow direction of the last glacial period. We assume that base erosion and removal by waves play an important role in driving cliff erosion along the Danish North Sea coast, whereas climatically induced pore-water pressure is a more important factor along the inner-coastal waters. Moreover, land use may condition coastal cliff erosion by engaging in the natural path of water flow and inducing rills, often leading to an increase in erosion.

The investigation of the preconditioning and driving factors of coastal cliff erosion can lead to mapping of areas prone to cliff erosion in Denmark. Furthermore, we will, at a later stage, predict cliff erosion rates in the near future based on various IPCC climate predictions, and develop landscape evolution models under a changing climate.