Greinasafni: Icelandic Times
Geology: Land of Contrasts

Iceland is a land of contrasts and diversity where beautifully colored lava, wide expanses of sand, and the power of its waterfalls all interplay. Only a short drive from Reykjavík one  finds himself in a vast wildernesswhere lava formations resemble modern sculpture, bubbling holes of mud with superheated water are found, glaciers fill valleys and geysers explode.

Geological Hot Spot

On a geological time scale Iceland is a very young country. It´s geological history reflects environmental development in the North Atlantic region since Miocene times (about 25 million years ago). Iceland is situated astride a divergent plate boundary, the Mid-Atlantic Ridge, and on top of a hotspot presumed to be fed by a deep mantle plume. The centre of the plume is generally assumed to be located under Central Iceland. At the plate boundary the two major plates, the Eurasia and North  America Plates, move apart todaywith a velocity of about 19 mm/year. The divergence of the ridge started in the north about 150 million years ago and as the plates moved apart above the Icelandic hotspot, excessive eruptions of lava constructed volcanoes and filled rift valleys. The divergence continues today and is accompanied by earthquakes, reactivation of old volcanoes and creation of new volcanoes. The best place in the world to study divergent plate boundaries is Þingvellir, a short drive from Reykjavík. Þingvellir offers the possibility of observing both faults and tension fissures related to the rifting and drifting of the North American and Eurasian plates away from each other.

 

Volcanic Eruptions Every Five Years

Iceland is one of the most active and productive sub-aerial volcanic region on Earth, with eruption frequency of ≥20 events per century. Iceland is home to more than 100 volcanoes and on average, a volcano erupts about  every 5th year. Volcanoes define a wide spectrum of forms, ranging from a crack in the ground to the stately stratovolcanoes like the Hekla  volcano. Icelanders have learned to live with natural disasters and there is a risk that eruptions of molten lava could take place at any time. Laki´s great eruption in 1783 is the largest lava eruption that the world knows of in historical times. Enormous quantities of lava poured out and devastated immense areas of land. Apart from damage caused by the lava, poisonous gases and the ashes from the eruption led to crop failure and killed the livestock. In the famine that followed one fifth of Iceland´s population died. Fortunately for Iceland such cataclysmic events are rare. The latest major eruption to take place was in 1973, when totally without warning a new volcano erupted on the eastern side of Heimaey town in the Westman Islands, south of Iceland. In 1963, to the south of the Westman Islands and to the accompaniment of columns of fire, clouds of ash and rumbles of thunder, a completely new island emerged from the   sea. This island is called Surtsey after Surtr,  the fire giant from Nordic mythology.Only scientists, keen to discover how new and isolated land is colonized by nature have access to it.

 

Melting the Ice Age Away

When the Ice Age set in three million years ago, the volcanoes kept on erupting, melting huge cavities which filled with new rock under the ice sheets. After the termination of the last Ice Age, 10.000 years ago, the land had changed and great mountain ranges had grown from the sub-glacial eruptions. Composed mainly of crumbly rocks, like easily eroded tuff and rhyolite, they are the beautifully colored mountains at Landmannalaugar, the moss-clad cliffs of Þórsmörk and the grey ridges that transect the northern desert. Where the eruptions were long enough, they broke through the ice and a hard cap of lava formed. After the ice melted, flat-topped “table” mountains appeared, of which Herðubreið is the most striking. The older parts of Iceland, the east, north and north-west of the island were eroded during the Ice Ages and steep-sided valleys and fjords were formed. Those mountains are made of many layers of basalts from eruptions that built the foundations of the island. Because of Iceland´s location, on the Mid-Atlantic Ridge, the island will be in the process of formation, of transformation, its old parts, the east and west carried away by the wind, the sea, the rain, and the ice, while new parts are created by volcanic action.
Landmannalaugar.


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