Jökull


Jökull - 01.12.1978, Side 22

Jökull - 01.12.1978, Side 22
part, where intensive wind abrasion is going on. Striae are scarce on hyaloclastites because of its weak resistance to weathering. Some areas, such as to the northeast of Miklafell and south of Laugafellshnjúkur, are covered with thick fluted lodgement till, leaving few bedrock exposures. Fluted surfaces represent the last movement of the ice, and are in fact a better indicator of the direction of movement than the striations, because the former are less influenced by the local topography. The directional elements and the end moraines show that the retreat of the main ice sheet has been towards southeast. This is in a good agreement with the supposed Lateglacial ice divide on a southwest-northeast lying line from Mýrdalsjökull to Vatnajökull, to the south of the present main watershed (Kjartansson 1955). In the western part of the study area directions from N50°V to N25°V occur. In this area the variation in the direc- tions is small. On the other hand the disper- sion is greater in the eastern part of the area, where directions between N62°V and N4°E occur. This suggests that the ice retreated fas- ter and more continuously in the western part, which first was deglaciated. On the other hand, several readvances with dispersion of the ice flow near the front occurred in the castern part. Directions of flutes to the east of Miklafell indicate an ice lobe between the Hofsjökull mountain massif and the Tungnafellsjökull area. The ice lobe has been directed by these two mountain groups towards north and northeast. Farther to the south, the ice move- ment was not influenced by the above men- tioned mountain massifs, and directions of the striations are towards north and northwest (.Kjartansson 1955, 1965). ICE TERMINAL DEPOSITS The ice recession in the study area was in- terrupted by glacial stillstands and readvan- ces. They are marked by terminal moraine ridges, sandur deposits or kame terraces. Eight end moraines which have been found in the area are described below. They are listed in the order of age from north to south: The Raudhólar moraine, the Vesturbugur moraine, the Strangilækur moraine I, the Strangilækur moraine II, the Miklafell moraine, the Fjórdungsalda moraine I, the Fjórdungsalda moraine II and the Fjórdungs- alda moraine III. All the end moraines are supra-aquatic. The Raudhólar moraine is a typical stillstand- moraine formed when the glacier was stationary for some time. The moraine ridge is 100—200 m broad, 20—30 m high and often manifold. The material in the Raudhólar moraine is almost unsorted till. The moraine is fairly broad and often indistinct in the field. Most of the other end moraines are push moraines formed when the glacier margin ad- vanced. The push moraines are narrow and steep, and usually not more than 10 m high. They consist mostly of coarse till, almost without finer particles. In some places all the fine material has been washed or blown away so the ridges consist almost completely of stones and boulders. Some of the push morai- nes may represent surge moraines, in which case the advances were not of climatic origin. When the main ice sheet had retreated from the narrow Skagafjördur valleys up to the mountain plateau, the ice had become flat— shaped and the topographical conditions seem to have been similar to those which Thorarins- son (1964) described for the surging Vatna- jökull outlet glaciers in the years 1930—1964. Raudhólasandur and the Raudhólar moraine Huge fluvioglacial deposits lie to the east of Raudhólar, which is a north-south oriented hyaloclastite ridge (Fig. 2). The southern and eastern margin of this formation are terraced. The terrace is highest at the southeastern corner, where it reaches 18 m. From the appearance the southern terrace could be supposed to be erosional, formed by down- cutting of the river Bleikálukvísl, as is the case for the eastern terrace. However, closer inves- tigations showed that it is a true ice-contact 20 JÖKULL 28. ÁR
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