Above are two images of strandlines (raised beaches) in the Varanger Peninsula, on the extreme north coast of Norway -- on the shore of the Arctic Ocean / Barents Sea. The top image is a satellite image, showing the little ridges of old beaches far inland. You can pick out the highest strandline and see how the coastline has changed shape as relative water level has fallen; what that actually means is that the land has risen faster than sea-level over this episode of landscape transformation.
The bottom photo shows what these raised beaches look like at ground level. The numbers refer to altitudes; click on the photo if you want to see them more clearly. The highest strandline marked is 79m -- but the highest shoreline here is at about 100m. We are not sure, but that marine limit is probably about 12,000 years old. When we bear in mind that sea-level at the time was probably between -100m and -80m, that gives us an isostatic rebound of almost 200m since the ice of the Scandinavian Ice Sheet melted from this coastal strip. Using the usual conversion ratio of 1:3 we conclude that the ice over this area was AT LEAST 600m thick. It was probably much more than that, because we do not know how much melting and ice wastage had already happened before the sea actually broke through onto this coastline and started to allow coastal processes to operate......
It's all fairly simple really...... and it all goes to show how elastic the earth's crust really is, and why we get faults and cracks all over the place, in all sorts of different rocks.
No comments:
Post a Comment