Abstract
Danish glacial landscape elements such as basal till plains, hummocky moraine areas and outwash plains contain a variety of small and large depressions. They were probably formed in glacial, late-glacial or Holocene time and may represent dead-ice holes or degraded pingos, or sinkholes formed by interaction between pre-Quaternary chalk or limestone bedrock and the thin glacial co ver. The aim of this study is to map terrain depressions that might potentially be karst sinkholes by analysing digital terrain models in the geographic information system (GIS). The incentive to apply the technique for mapping of sinkholes came from an accidental acquaintance with a farmer, Jens Kirk, whose farmland is located near Thisted. Jens Kirk told us that the front end of his tractor had suddenly sunk into the ground during routine farming work, and this incident was our inspiration to start the project described here.
Highlights
Danish glacial landscape elements such as basal till plains, hummocky moraine areas and outwash plains contain a variety of small and large depressions
Sinkholes have previously been registered in mainly northern Denmark where the pre-Quaternary surface consists of chalk and limestone (Feddersen 1880)
In cliffs and limestone pits it is possible to find two types of dolines: Funnel-shaped and vertical-sided. Both types have originated as areas of intense fracturing where acid water has percolated downwards and dissolved the chalk
Summary
Danish glacial landscape elements such as basal till plains, hummocky moraine areas and outwash plains contain a variety of small and large depressions They were probably formed in glacial, late-glacial or Holocene time and may represent dead-ice holes or degraded pingos, or sinkholes formed by interaction between pre-Quaternary chalk or limestone bedrock and the thin glacial cover. Sinkholes have previously been registered in mainly northern Denmark where the pre-Quaternary surface consists of chalk and limestone (Feddersen 1880) In these areas sinkholes and other karst features including dolines, karst lakes, small caves, disappearing streams and karst springs are known (Nilsson & Gravesen 2017). The results from north of Thisted and in the planted wood of Svinkløv Plantage south of Svinkløv are presented here (Fig. 1) It should be noted, that Svinkløv Plantage has never been farmed, and the depressions found here are small compared to those in farmed areas. Sinkholes occur in the area of elevated chalk south of Fjerritslev
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