The Pleistocene History of Some Rivers in Western Iceland

Abstract

Little detailed work has been carried out so far on the profiles of Icelandic rivers, mainly because of lack of survey information. During the course of a geomorphological investigation in Western Iceland in the summer of 1961 an area which included parts of two rivers was surveyed in detail (Ashwell, 1964) and the results of this survey have interesting implications both for Icelandic Pleistocene history and for the study of worldwide marine levels. The surveyed area (Fig. 1) covers the boundary between the highland plateau of Central Iceland, which in this district forms a Pliocene erosion surface at 3-400 m above sea-level (Einarsson, 1958, pp. 19-20) and the coastal lowland of Western Iceland. Structurally it forms part of the Tertiary basalt province of Western Iceland, in which the beds of lava dip at about 5? to the SSE. Although the amount of dip is small, horizontal erosion surfaces show up well against it. The structure exerts an important control on the relief (Fig. 2) in that outstanding rock features can often be traced to the same hard beds of basalt, while the rivers have in some cases cut along the strike of the basalt beds where intercalations of tholeeite basalt or soft sandstone occur. Faulting may have been widespread since many landscape features run parallel to the strike of the basalts. One of these is important to this study, since it forms a cliff, about 40 m in height, between the highland valley of Flokadalur, running between the ridges of Kroppsmuli in the north and Varmalaekjarmuli in the south, and the coastal lowland. This cliff is referred to as the Brekkurl cliff. This type of threshold occurs in two of the other valleys running parallel to Flokadalur. It does not appear, however, that the valley of Fl6kadalur or most of the landscape features in