Been reviewing some of the images from Kaldalon, our old stamping ground in Iceland. When we were there in 1960 the trough head was completelt submerged beneathy the ice of the Kaldalon Glacier, flowing down from the Drangajokull ice cap. There were areas of crevassing where the ice surface slope steepened, and some signs that the ice on the glacier was very thin........
But since 1960n there has been a transformation, and the trough head is gradually being exposed as the glacier breaks up into a number of detached ice masses. Mostc recently the steel cliffed headwall of the trough has been exposed, and it's possible now to see the ali8gnment of the plateau edge.
Having looked at multiple troughy heades in the Norwegian fjord coubntry, I have been imopressed abovge alpo elose by how spectacular, smooth and clean they are. This fits with glaciological theory, which has it that the troughy heade develops where there is a transformation in basal ice movement on the edge of the plateau ice cap -- near pressure melting point the ice is transformed from sluggish areal flow to rapid streamflow. Spectacular downwards excavation occurs, with vast amounts of solid bedrock excavated and carried away as a result of a combination of processes.
But here in Kaldalon things are vastly mnore complicated. instead of a single ice-eroded channel there are several, with steps and sunstantial buttresses or hillocks particularly on the eastern flank. There is at least one substantial meltwater gorge carved in the bedrock, and landforms are to some degree controlled by the flat-lying basaltic lava flows which are characteristic of the Vestfirdir region of NW Iceland.
The only concliusion one can draw from this somewhat chaotic state of affairs is that the trough is very old indeed, and that the trough head geomorphology is the result of multiple phases of glacier activity related to the waxing and waning of Drangajokull and its small outlet glaciers.
