Friday, 1 April 2011
Iceland day 3!
We are at the moment driving across the Sandur, a vast volcanic plain, formed through glacial outbursts or Jokulhaulps. The last of these, from Grimsvotn in 1996. The landscape is littered with the remains of old bridges, that sometimes last only a few days, and are often destroyed in order to allow the flood waters to pass through. There has been much stabilization of the sandur with planting of resistant plants which aim to capture Aeolian sediments and protect the main ring road. This road is quite an accomplishment for Iceland, the vast sandur's present a significant risk to those attempting to cross the,.The villages and the towns in the East depend on it now as a main route to the capitol, but before that, the options were to cross the mountain glaciers, dangerous in the case of Vatnajokul which has the largest geothermal system in Europe underneath it, or to try to cross the hundreds of glacial fed rivers. The alternative is to drive around the rest of the coastal road to the north, not exactly a short cut! If you go it wrong, as would have been easy with Grimsvotn, as the flood occurred six weeks after the eruption, and rose to 5m high, you risk being washed away with boulders the size of houses! Here is a picture taken looking out across the Sandur that clearly shows some of the management in place for glacial floods:
The wing dykes are a means of diverting flow away from roads and bridges that would be more expensive to repair. There are many of these all over Iceland, as the ring road is often destroyed over the winter periods in different places.
After this we headed to the Glacial Lagoon, Jokulsarlon, where the Bond movie was filmed, this is a proglacial lake, formed as the glacier retreats and deposits material in a terminal morraine, then fills with water behind it. This one is connected to the sea, and creates a spectacular black beach littered with icebergs. We did manage to see some seals in the lagoon, they are to two tiny black dots in the middle!
The ice is filled with tiny bubbles, which we will be using as proxy evidence for climate change very soon in class. We can measure the relative proportions of gases in the bubbles and from that calcualte atmospheric composition and temperature. They are also remarkably pretty:
The shores of the lake, which is brackish water are also coated in smaller icebergs which can take many years to melt if they are large enough. The concern over the lake is that the coastline is eroding due to lack of fresh input of sediment from eruptions, and rising sea levels, if there is no replenishment, the river mouth will soon reach the lake, the morraines will be destroyed and the ice will be gone:
Finally, the beach, blue icebergs, black sand and white waves, enough said:
There are times in Iceland's history when these floods cause significant growth of the land, in fact they depend on much of the material as without it, coastal towns like Vik, where we stopped for souvenirs, are more at threat from coastal erosion as the sediment is removed by the high energy waves but not replenished at the same rate. The last Katla eruption in 1918 extended the southern coastline by 4km in 24 hours. Katla and Hekla are both overdue! Maybe replenishment will come soon, though preferably not while we are out here!!!