Thursday, March 12, 2015

Icelandic Tsunami: unexpected danger

 It might surprise you to learn that Iceland experiences flood waves, or tsunami fairly regularly. Icelandic Met office tsunami hazard assessment The government is as aware of the eventuality of another tsunami as it is of the potential for volcanic eruptions. Iceland actually has two causes of tsunami to fear. Both the immense power of a sea-borne tsunami that any nation with a coastline (particularly an island) faces, as well as inland tsunami, caused by rapid flooding. A sea-borne tsunami is much less likely, although still a very real possibility. The only recorded tsunami wave to reach Iceland's shores happened in 1755, and was caused by an earthquake near Lisbon, Portugal. While this earthquake and tsunami caused significant damage along European coasts, even as far as Ireland, Iceland is quite far away and the wave had lost most of it's power before striking the island. Tsunami risk-appraisal for Iceland. Tsunami are most often caused by earthquakes at subduction faults. Iceland's location atop a divergent fault, and it's distance from any subduction zones, means there is less chance for one of these devastating waves coming from the sea.
Of the two, Iceland is more at risk from this second type due to the nature of it's glacial volcanoes. These inland waves are caused by what the Icelandic people call a Jökulhlaup, a flood caused by a volcanic eruption under a glacier. This video shows the resulting Jökulhlaup from the famous 2010 eruption that halted all air traffic in Europe. Video of glacial flood.

Friday, March 6, 2015

Iceland: Volcanic jewel in the ring of fire

Iceland is known as "The Land of Ice and Fire". With a name like Iceland, and it's location near the arctic circle, the ice part might not come as a big surprise. The "fire" nickname comes from Iceland's extensive volcanic activity. Iceland is straddling a divergent plate boundary in the ring of fire called the Mid Atlantic ridge. It is also traveling over a "hot spot" in the mantle, the layer of the earth below the crust. Volcanic History of Iceland. A volcano erupts in Iceland every 3 years, on average.



 The divergent plate boundary accounts for the fissure eruptions (as seen at the right from the 2014 Holuhraun eruption) which are very common on Iceland.









The hot spot, or "plume" in the mantel is responsible for the more classically cone shaped volcanoes, and high volcanic mountains on the island. Kerlingarfjoll: Rhyolitic cinder cone
Snaefellnes: Rhyoltic cinder cone. A geographic position just outside the arctic circle causes glaciers to form on the slopes of these volcanoes. This combination of "fire and ice" is one of the most common features in iceland. These rhyolitc cones are much more dangerous than the fissure volcanoes. The type of magma which erupts from them is much more viscous, or thicker. The additional weight of the glacial ice that forms on top of them also compresses and delays eruptions, making them more violent and explosive.



This also causes extensive flooding when a sub-glacial eruption happens. While Iceland has an eruption warning system, it places much more importance in it's Flood warning system. The volume of water discharged in one of these floods can be greater than that of the flow of the Amazon river.





This combination of volcanic features gives Iceland it's unique terrain. Hot spots alone generally form island chains like Hawaii. It also explains why there is such a high volume of volcanoes on such a small island.