Jökull

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Jökull - 01.12.1985, Qupperneq 14

Jökull - 01.12.1985, Qupperneq 14
Fig. 3. Block-field on the high plateau 5 km northeast of Látrar in Adalvík. The altitude is about 500 m and the plateau lacks any sign of active glacial erosion or deposition. A small perennial snowfield can be seen in the back- ground. 3. mynd. Stórgrýtisdreif í um 500 m yfir sjó, um 5 km norðaustan við Látra í Aðalvík. A hásléttunni eru engin ummerki eftir virka jökla. unglaciated enclaves or plant refugia during the Weichselian, anywhere in lceland. Contrary to this, Sigbjarnarson (1983) emphasized the importance of alpine-type glacial erosion on Vestfirdir and stated that ice-free areas probably existed there throughout the Pleistocene. Only limited work has been done on the deglaciation of the northern parts of Vestfirdir. Thoroddsen (1892a) suggested two major stages in the deglaciation. During an earlier phase the glaciers had retreated and the sea transgressed to 60—70 m above present sea level, with shorelines and terraces at those altitudes forming in the outermost coastal areas while the glaciers still remained in the valleys and fjords. During a later phase, when the glaciers retreated from the lowlands, shorelines and terraces were formed at 16—30 m above present sea level. Thoroddsen (1892a) reported features indicating ancient sea levels at 63 m above the present one in Rekavík, at 30 m at Látrar in Adalvík and at 16 m in Hornvík. Kjartansson (1969) observed raised beaches in Horn- vík and on the eastern flank of Kögur. He mapped outcrops of till in Haelavík and Hlöduvík, and alluvial and eolian deposits on most of the Hornstrandir low- lands. He also observed glacial striae around Hornvík, showing downvalley movements of the glaciers. John (1974) stated that the highest marine terraces in the area north and west of Jökulfirdir reached only 10 m above present sea level, but Símonarson (1979), who reviewed the geology of Hornstrandir, reported a marine terrace at 16-20 m above the present sea level in Hornvík, and suggested a similar elevation for a marine terrace in Adalvík. The present study The maximum glaciation As mentioned above, the morphology of Hornstrand- ir is characterized by unconnected short U-shaped vall- eys, with cirques in their sides and at their heads. The morphology indicates that cirque glaciers coalesced to form outlet glaciers which reached beyond the present coastline. But the high plateaux show no sign of having been inundated by active glaciers and are usually cover- ed by mature block fields consisting of local bedrock (Fig. 3). The very flat surfaces of these plateaux cont- rast sharply with extensive lower areas which have been intensely eroded by glaciers (Fig. 4), and with cirques and different nivation features below the plateau edges (Figs. 4 and 7). Today most of the shelf around Hornstrandir is shallower than 100 m. Thus it may have been dry, or at least under very shallow water, during the Weichselian maximum glaciation — provided that this coincided with the maximum glaciation elsewhere around the North Atlantic and with the contemporaneous global sea level low. An empirically derived absolute upper limit of actively eroding ice at sites near the present coast, defined as plateau surfaces without signs of glacial erosion, plus the assumption that the ice was grounded, allows us to approximate the outer edge of the glaciated area at the maximum situation. Giving the large outlet glacier from the Vestfirdir ice cap, which must have existed in ísafjardardjúp, an Antarctic type B overall gradient and a surface profile of a 60—100 km long Greenland outlet glacier (Buckley 1969; as used for central North Iceland by Norddahl 1983), it can be 12 JÖKULL 35. ÁR
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