Náttúrufræðingurinn - 1954, Side 21

SÉÐ FRÁ ÞJÖÐVEGI
15
uðu jöklarnir í sjó fram þeim bergskriðum, sem fallið höfðu á næsta
hlýviðrisskeiði á undan og sköpuðu með svörfun sinni skilyrði fyrir
nýjum skriðuföllum, er þá leysti aftur. Hefur þetta ni'i gengið svo í
fjórar rennur, og margt bendir til þess, að svo muni enn fara, er
tímar líða. En þar um skal ekki meira rætt í þessu greinarkorni.
SUMMARY :
The author discusses the important role played by rockslides especially in the
valleys of the Icelandic basalt regions. He mentions the rockslides that can be seen
from the auto-road between Reykjavik and Akureyri. The three biggest rockslides
along this road are Vatnsdalshólar, the rockslide between Fremstagil and Geitaskarð
in Langidalur (Figs. 1 and 2), the front of which is on the opposite slopes of the
valley, and the famous rockslide at Hraun in Öxnadalur. The author points out that
judging from tephrochronological studies (cf. Fig. 4) most of the rockslides seem to
be of late glacial and early postglacial age. These rockslides were caused mainly by
oversteepening of the valley sides by glacial erosion, and probably favoured by fre-
quent earthquakes at the time when the rate of the isostatic land upheaval was at
its maximum. The geological structure has also played its part. Fig. 5 explains why
the rockslides are often only on one side of the valley in the basalt areas.