Jomfruland is an island in the Kragerø archipelago, a characteristic formation, the outermost piece of land before reaching the waves of Skagerrak.
Despite the relatively modest size of the island (ca.7, 5 km long and 1 km wide), there is a very large variation in the landscape, from Precambrian gneisses without vegetation, coastline with large boulders, sandy shores with eolian dunes, shady deciduous forests andagricultural areas.
The island is a ridge with low relief, the result of an ice advance under the last phase of last ice age, about 12 500 years ago. In fact, the island is a part of the Ra moraine. North and south of Jomfruland, the moraine is a submarine formation. At Mølen in the north, another Geopark locality, we meet the Ra moraine again, as an onshore formation. The Ra moraine surrounds the Scandinavia and Kola peninsulas, and represents an ice-advance from the Younger Dryas time (12 800-11 500 years ago).
The glacier stood more or less still for 300 years, piling up a large amount of stones, boulders, sand and clay in front of it, on the sea bottom. When the glacier retreated, the moraine material was left as a pronounced ridge, at a depth of about 135 meters. The land started rising immediately after the ice retreat, first quite fast, then slowing down, but still active today (some millimeters a year). The top of the marginal moraine eventually reached the zone of wave action, and the material was re-worked and sorted, a process that is still going on today.
On the outside of Jomfruland you can see the shoreline made of boulders. In between the boulders, close to the sea, you may discover some of the finegrained marine clays from the arctic seabottom, some 12 000 years old. If you look carefully, you will notice some marked shorelines or raised beaches, the remnants from old great storm waves, eroding the island when the sea was much higher. Man has reworked the beaches a lot of places, though, in need of boulders for buliding material, houses and walls, or just to make the shoreline easier to pass.