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Supplementary GeoSite Anholt and Østerrev

Theme:  Holocene coastal develoment 

Locality: Anholt and Østerrev
Description of a supplementary GeoSite


Primary identification


1. GeoSite no.:
GS - 5-4.

2. National locality no.:
NGI 39.

3. GeoSite name:
Anholt & Østerrevet.

4. Location:
Denmark; Kattegat.

5. Co-ordinates UTM:
System ED50, Zone 32, x=659078, y=628998.

6. Type of locality:
Island.


Primary geological features


7. Main topic:
Coastal evolution.

8. Geo(morpho)logy:
Simple spit, cuspate foreland and beach ridge plain influenced by prevailing wind direction.
The island of Anholt offers a beautiful and instructive example of coastal development under the influence of prevailing winds and waves, as the island is freely exposed to all directions. The island has a triangular, 3 km2 core of clayey till in the West, and a 19 km2 marine foreland extending eastward in the lee of the core.
The core has been subjected to wave erosion, mainly during the maximum Holocene relative sea level stand (+ 8 m), and cliffs have been formed on all three sides. Erosion of this core has provided the material for forming the marine deposits.
The marine foreland consists of three main elements: A beach ridge plain, a simple, or trailing spit, and a cuspate foreland:
The beach ridge plain, which forms the major part of the island, has an elevation of about 12 m in the lee of the core and dips Eastward. It consists of two main sets of divergent beach ridges. One set in the Western part which is oriented N-S, and a discordant set in the East which is oriented NE-SW. The two contrasting orientations may stem from two separate Holocene transgressions. The plain is superimposed by up to 25 m high inactive (parabolic) dunes which are oriented according to the prevailing W-E wind direction.
A simple, or trailing spit, "Totten", forms the eastern extremity of the island and continues into the submerged reef called Østerrev. The spit and the reef have been formed by longshore sediment transport along the northern and southern sides of the island as a result of the dominant wave directions from West.
A cuspate foreland, "Flakket", is situated in the Northwestern corner of the island. This feature emerged mainly during the period 1887-1935 and its position is determined by a stony and gravelly reef, the "Nordvestrev". The reef and a small island which has now disappared provided a wave shadow and resulted in a decreasing littoral drift in the lee of the reef.

9. Frame / context:
Sedimentology, Geomorphology

10. Chronostratigraphy:
Holocene, Recent.

11. Primary value:
Major beach ridge plain, with active simple or trailing spit, and cuspate foreland.

12. Comparative evaluation:
Anholt is a conspicuous example within a number of Danish islands, penninsulas and coasts exhibiting the genesis of marine foreland. The site is a particularly focus of ongoing formation of spits and beach ridges.

13. Comparable GeoSites:
In Denmark: Skagen spit. Outside Denmark: ???? Supplementary data in support of the locality.


Supplementary data in support of the locality


14. Delineation on a map:
Location, delineation and suggested access are marked in red. Map base: Kort & Matrikelstyrelsen. Map courtesy DN 2005 ©, Also shown are habitat and bird protection areas.

15. Higth of the GeoSite:
~8 m (beach plane), dunes up to 28 m

16. Area of the GeoSite:
22 km2

17. Subordinate geological interests:
None

18. "Non"-geo interests:
Holiday resort. Bathing. Bird and wildlife reserve. Fishing.

19. References:
Jessen, A. (1897). Beskrivelse til geologisk kort over Danmark. Kortbladene Læsø og Anholt. Danmarks Geologiske Undersøgelser, I Rk. 4, 48pp.
Schou, A. (1969). Kystudligningen. In: A.Nørrevang & T.J.Meyer (eds.) Danmarks Natur, vol.4, 81-85. Politikens Forlag, København. Christensen, S.N. & Johnsen, I. (2001) The lichen-rich coastal heath vegetation on the isle of Anholt, Denmark – description, history and development. Journal of Coastal Conservation, 7, 1-12.

20. Data sources, collections:
None

21. Illustrations:
Photo: Ole Malling. Sand dunes at the edge of the "desert".

22. Proposers:
Dansk Geologisk Forening & Det Kongelige Danske Geografiske Selskab/Troels Aagaard, Jørgen Nielsen & Niels Nielsen.

23. Description by:
Troels Aagaard.

24. Recommandation:
The location is a GeoSite.

25. Comments:
...

26. Supplementary description:
Anholt is a 22 km2 large island, divided into a 3 km2 morainic core in the west, and a 19 km2 marine foreland extending eastward in the lee of the core. The triangular island is elongated in a W-E direction. The core was formerly significantly larger but it has been subjected to wave erosion . The maximum relative sea level during the Holocene was + 8 m and the core has been cliffed on all three sides. Erosion of this core has provided the material for the construction of the marine deposits. The marine foreland consists of three main elements: A beach ridge plain, a simple, or trailing spit, and a cuspate foreland. The beach ridge plain, which forms the major part of the island, has an elevation of about 12 m DNN in the lee of the core and slopes eastward. It consists of two main sets of divergent beach ridges: One set in the western part which is oriented N-S and a discordant set in the east which is oriented NE-SW. These two contrasting orientations could be a result of two separate Holocene transgressions. The plain is leached and poor in nutrients and the vegetation consists mainly of Ammophila, Calluna, and Juniperus. It is superimposed by up to 25 m high (parabolic) dunes which are oriented W-E and originated in the 17th century due to forest clearing and cattle/sheep grazing. The dunes are now stabilized by vegetation. The eastern extremity of the island is made up of a simple, or trailing spit, Totten which continues into the submerged reef called Østerrev. The spit and the reef have been formed by longshore sediment transport along the northern and southern sides of the island as a result of the dominant westerly wave directions. The spit has been eroding during the past century; the erosion may be related to the construction of groynes (to protect the lighthouse) and possible the formation of Flakket. Flakket is a cuspate foreland situated in the NW corner of the island. This feature emerged mainly during the period 1887-1935 and its position is determined by the stony, gravelly Nordvestrev. The reef and a small now-disappared island provided a wave shadow and resulted in a decreasing littoral drift in the lee of the reef. A contributing factor to the formation of Flakket was extraction of stones and gravel from the reef. This extraction made sand available for onshore transport along the reef. Comparative evaluation The island offers a beautiful and instructive example of coastal development under the influence of the prevailing winds and waves as the island is freely exposed to all directions.

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List of localities
Jylland
BoerupBovbjerg KlintFroeslev PlantageGram LergravHanklitKalksøjler ved HirsholmeneKarlby klintKongens Mose Lille VildmoseLønstrupSilstrup, Northern, Mors and Ertebølle HovedSkagens OddeStensbaek PlantageUrhøje og Myrhøje PlantagerVadehavetFur (Stolleklint and Knudeklint)

Theme: Holocene coastal development
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Last modified : Sunday 07. Jan. 2007 Erik Nygaard
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