Raet Protected Landscape
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Raet Protected Landscape Arendal kommune, Aust-Agder Raet Protected Landscape There are three main criteria that form the Five methods for the protection of the area: basis for the protection of Raet Protected Raet (1) Protected Landscape, including Landscape. the flora and fauna, was protected by Royal Decree on 15 December 2000. The pro- These are: tected area stretches from, and includes, • sediments Jerkholmen in the west to Tromlingene in • geomorphology the east – a distance of about 15 kms. The • fresh water dammed up by the moraine protected area covers about 5,400 acres, of which about 4,600 acres is sea. The many bare outcrops of rock shaped by glacial erosion that we find in the area are The aim of the protection is «to preserve the examples of geomorphological shapes. specific character of the natural landscape These are bedrock bumps that have been and the cultivated land with geological ground smooth and fine on the stoss faces occurrences from the Quaternary period towards the ice and torn up on the lee faces. and distinctive animal and plant life linked with Raet in the coastal area of Aust-Agder». Front page photo from Bjellandsskjær, Tromøy. Photo: Ove Hetland Tromlingene Tromøysund Alvekilen Arendal Tromøya Bjelland Galtesund Spornes Hisøya Hove Gjesøya Merdø Havsøya Gjervolds Ærøya øya Lille Torungen Halvors holmene Store Torungen Jerkholmen 2 Within the area there are three (2) nature final spasms of the Ice Age. Probably the reserves which is a «stricter» form of pro- glacial front of the inland ice towered like a tection than protected landscapes. These steep wall in the sea, with proportions that are not included in the protected landscape are similar to those we find along the coasts but act as «islands» in the protected lands- of Antarctica and Greenland today. The ra cape area. These three nature reserves are, moraine stretches from Finland, through from west to east, Indre Halvorsholmen, Sweden, Østfold county in Norway and Store Torungen and the western part of crosses the Oslofjord at Moss. In Vestfold Tromlingene. The first two are intended to county it comes to the surface at Horten and take care of nesting seabirds and therefore provides the fertile soil for the country’s no one is permitted to go ashore from 15 largest beech forest Fagus sylvatica at April to 15 July. The western part of Larvik, amongst other things. After that it Tromlingene is protected to preserve the disappears into the sea again at Mølen, but wetlands. The eastern part of Tromlingene appears here and there as islands like has so-called bird-life protection as a part of Stråholmen and Jomfruland in the county the protection regulations in Raet protected of Telemark. In Aust-Agder county we first landscape. notice it in the east, just off Flosta, where the cobblestone island of Målen appears. After On the outer edge of Tromøya the (3) forest that we see the islands called Tromlingene, was protected by a Forest Act as early as and it is here that Raet Protected 1914, the purpose of this was to create Landscape begins. We can clearly see the shelter for the areas within. The forest is still large amounts of boulders and cobbles- protected, but it no longer has the same tones that the sea has washed out from function as it had previously since large the moraine material at Spornes outside parts of Tromøya now have considerably Tromøy, on the outer side of Merdø and more vegetation. further west in the protected area on Jerkholmen, and on Målen. From here it Within Raet Protected Landscape the appears on land at Hasseltangen, where following areas have been set aside for (4) again it is covered in beech forest, and can outdoor recreational activities: from west then be traced up to Feviktoppen, Grimstad, to east – Jerkholmen, Skjelbergholmen, Birkenes and then onwards in a westerly Flatskjær, Tvisteinen, Ærøya, parts of direction. Raet, and similar end moraines in Havsøya, parts of Merdø, Hove and neighbouring countries, clearly illustrate the Spornes. Areas set aside for outdoor distribution of the inland ice at an important recreational activities are either owned by period when the ice surface was melting the government, the municipality or there during the last Ice Age. are agreements between the government and private landowners, such as the (5) The moraine in the protected landscape was Coastal Park («Skjærgårdsparken»). deposited entirely underwater. After the ice withdrew, the sea swamped low-lying land areas. Following that the glacio-isostatic End moraine Raet uplift of the land gradually took place. The Raet – which is the name of the largest highest level of the sea after the last Ice Age continuous end moraine in Scandinavia – is known as the marine border and in the is an end moraine after the last Ice Age, and Arendal area it reaches up to 65-70 metres is one of the criteria for the protection of the above the present sea level. Tromlingene area. Raet moraine is an enormous gravel islands were raised above sea level 3-4,000 ridge that was deposited by advancing years ago, and Jerkholmen somewhat later. inland ice 10-11,000 years ago in one of the 3 Topography, Geology and Sediments The visible topography in the protected landscape area is relatively flat. Islands like Tromlingene (14 m above sea level), Jerkholmen (9 m above sea level) and The Allerød period 11-12,000 years ago. The inland ice Målen (about 2 m above sea level) consist has receded and the border of the ice lies further in than the present-day coastline. The glacier has deposited mainly of sediments. However, if we dip scattered moraine deposits on the sea bottom, and in down beneath the surface of the sea, the this period silt and clay from the sea are also deposited. picture is rather different. There we see the Sand and stones are dropped from passing icebergs. highest ”mountains” of underwater reefs, sunken rocks and islands, whilst the largest ”valleys” form dark depths. Between Jerkholmen and Store Torungen we find some depths of 157 metres. Between Havsøya and Merdø there is also a distinct deep ”valley” that continues in Galtesund. In the Younger Dryas period between 11-10,600 before the present time, the front of the glacier advances to the Raet Protected Landscape consists pre- Ra-line. Sediments on the sea bottom are pushed together and deposited, together with moraine materials dominantly of bedrock although there are that the ice carries with it, as an end moraine (Ra-mor- local occurrences of diabase dikes. enen). The sea level is about 61 metres higher than today. Large amounts of sediments have been deposited. On the side facing the sea, waves have washed out the small particles over a very long period and therefore we find the coarsest material like cobblestone and large stone boulders on the surface. The advance and retreat of the front of the glacier has Under the upper ”erosion skin” we find fine created smaller ridges parallell to the Ra-line. In post- particles like sand, silt and clay that are only glacial time, following the glacio-isostatic uplift of the a metre or two beneath the surface. Also in land, the moraine was subject to erosion by the waves. the surf zones you can see a number of Surface material is sorted and moved around. Stones and blocks are washed out and cobblestone areas are well-developed beach ridges of gravel and formed. stone that today cover large areas of the moraine in this area. After several thousand years of vegetation that has deposited leaves, needles etc, a thin layer of humous has formed on the surface. In the lower-lying parts, damp and swampy areas have been formed. In addition to Botnetjern on Tromøy, we can find smaller occurrences of open Today, the Ra moraine, which largely consists of silt and moraine material containing clay (moraine clay), has a freshwater on several of the smaller islands. layer of beach-washed material, partly with large blocks and cobblestones on the surface. Sandy marine beach deposits have settled over the fine grained sea deposits on both sides of the Ra. The characteristic glacially- Climate and vegetation shaped smooth whale-back rocks on the outside of the Raet Protected Landscape lies far south in Ra form an effective barrier against continued erosion of Norway and entirely in the beach area, part- the sediments. ly under the sea and partly on land. The climate is typically governed by the ocean. Formation of the Ra. Illustr.: Ivar Johan Jansen Throughout the protected landscape area 4 seaspray is driven in by the strong wind. achieved by having a certain amount of The proximity to the sea and the area’s weight placed in the bottom of the boat as relatively flat topography mean that it is oft- ballast. Earth and other deposits were used en windy. There is seldom much snow in the for this purpose and in this way foreign area. The sea modifies the temperature plants and seeds were imported – known throughout the year so that the winters are as ballast plants. Raet Protected Landscape relatively mild and summers are cool, even has several species that have been though Sørlandet is the district in Norway imported like this. that has the most sunny days during the year. Of the many botanical curiosities to be found we would mention the following: On Because Raet Protected Landscape lies so Merdø there is a large holly tree Ilex aqui- far south, you can find species that normally folium growing in the thicket. This is further belong to more southerly latitudes, and that east than we usually find this species.