22/08/2008 Iceland: A Force of Nature

We arrived 9:20 at the mechanics. Considering their day started at 9:00, we were slightly surprised to find that they had already gone for coffee. Anyway, we left the car and keys, and went to look down at the harbour for some fish for James. After a futile search and an hour attempting to see a whale near one of the tourist boats, we picked up the car with its brand new window, and drove to Ásbyrgi, where an old river channel cascaded down old basalt flows in what must have once been a tremendous waterfall. Only the river notch and plunge pool survive, remnants of an ancient wonder of nature now inhabited only by fulmars.

Setting off along the gravel road we had arrived on yesterday, we visited Hljóðaklettahringur, where lavas once flowed into a river valley, preserving as immortal proof that columnar basalts need not always be vertical. Most of the columns intersected the large blocks at right angles to the surface, suggesting:

1. Very little erosion, and
2. Jointing perpendicular to isotherms whilst still hot

i.e. the river likely cuased significant erosion to subhorizontally flowing lava flows during initial cooling. Many regions appeared glassy, even well within the large forms, suggesting extremely rapid, fluid-aided cooling.

After leaving the site, we returned via the route we had come along, then travelled east to join the Dettafoss road on the other side of the river.

Our final stop of the day was Dimmuborgir ('Dark Fortresses' in Icelandic), where lava had once flowed over marshland, heating the water and forcing steam up through vents during solidification. Apparently the lake then breached its lava-dam, causing the molten material to flow between the vents and into a lava channel, resulting in subsidence of the upper cooled crust and leaving columns and ridges of lava where the vents were once active, or the lava was unable to drain.