Jökull


Jökull - 01.01.2016, Page 66

Jökull - 01.01.2016, Page 66
Paweł Molewski and Leon Andrzejewski floated in the ice-dammed lake, as attested by drop- stone structures in the glacilacustrine sediments. The lake was feed by meltwaters, which probably formed small fan deltas. After the lake disappeared, meltwa- ters formed small alluvial fans on the terrace surface (Figure 11B). These waters flowed out between the glacier and Jökulgrindur in a south-westerly direction. A debris flow formed on the melting glacier snout. After degradation of the glacier snout the meltwater flow on the terrace surface disappeared and a lower flow system formed (Figure 11C). Since the kame ter- race was partially destroyed (Figure 11D) by the sub- sequent glacifluvial flow, the size of the lake cannot be inferred from its present size. The spatial relationships of the studied forms and the range of the moraine deposits in the study area suggest that the original width of the lake and ter- race was about 250 m. The trace of the lake shoreline preserved on Jökulgrindur’s slopes indicates that its depth was at least a dozen metres. CONCLUSIONS The geomorphological and sedimentological studies, as well as the analysis of cartographic and remote sensing materials, have resulted in a reconstruction of the main stages of the formation of relief and depo- sitional environments in the northern part of Tungna- árjökull’s marginal zone between the end of the LIA and modern times. It has been shown that the vol- canic substrate of the glacier forefield had a major impact on the landforms and sediments in this part of the marginal zone. Its main element is a system of parallel Upper Pleistocene volcanic ridges oriented northeast-southwest. The ridge of Jökulgrindur runs parallel to the northern part of Tungnaárjökull’s snout, which blocked the outflow of glacier meltwaters dur- ing its subsequent advances. The damming of meltwater outflow caused the oc- currence of ice-dammed lakes in the northern part of the marginal zone of Tungnaárjökull. The preserved lake shorelines and small wave-cut platform, fossil delta and kame terrace are evidence of their existence. Figure 11. Model of the kame terrace, modified from Molewski et al. (2005). A: Ice-dammed lake phase; B: Meltwater flow phase; C: Erosion of the kame terrace and degradation of dead glacial ice; D: Preserved kame terrace. – Líkan af þróun jökullónsins við norðvesturjaðar Tungnaárjökuls. 66 JÖKULL No. 66, 2016
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