Lerfaldene ved Kokstad, Gretnes og Braa.

Abstract

The marine clay deposits in the South Eastern part of Norway, in the Trondheim district, and in certain valleys in Northern Norway are often distressed by landslides which make freat damages. In historical times the largest clayslide (\"lerfald\") being that occurring in Værdalen by which 292.03 ha of the land slipped and 863.87 ha were flooded by water and muddy clay. 250 people populated this flooded and slipped area where 112 people perished. During this kind of landslides, the so called clay slides (\"lerfald\"), soft clay is forcing out from the ground. As a rule the overlying firmer layers are quickly broken into flakes which in great speed float into the rivers or fjords on the liquid clay. They are not under obligation to any particular season of the year and may just as often occur in the middle of the winter while the ground is frozen and covered with snow as in the summer. In this paper three clay slides are mentioned occurring in the later years. None of them being equal to the clay slide at Værdalen as to size and violation even these three being of considerable dimensions. The clay slide at the farm Kokstad in Gjerdrum north of Oslo took place the night of October 21st 1924. The clayey deposits are here intersected by small valleys to a depth of some 50-60 meters.