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Q&A With Jim Zimbelman: Iceland

By | March 9, 2010

Iceland's Namaskard geothermal area

Smithsonian Journeys: Of all the terrestrial and extra-terrestrial imaging and mapping that you’ve done, how does Iceland’s landscape compare in beauty, drama, violence?


SJ: The huge volume of water that surges over the Dettifoss and Iceland’s other waterfalls and powers down the glacial rivers – where does it come from? Is it “young” water from recent precipitation? Is it ancient water from glacial melt? What “pumps” it to the surface with such force? Is it the volcanoes under the glaciers and lakes?

JZ:The water in the rivers of Iceland is both young and old.  Every winter the country is blanketed in new snow that in the spring then feeds large runoffs. However, the glaciers are also melting, releasing water that fell as snow tens of thousands of years ago. Both water sources mix together to make the dramatic rivers of Iceland.  The ‘force’ comes from the sheer volume of snow and ice available to feed the rivers; the volcanic bedrock does not need to add additional force (although, when an eruption occurs directly beneath a glacier, the resulting enormous flood when the melt water finally bursts out from beneath the glacier has an Icelandic name – jokullaupe).

SJ:  When and how did scientists realize that Iceland straddles two tectonic plates?




SJ: Iceland’s fjords seem to be limited to the north and west coasts. Why?


SJ: How many times in geologic history has the crust of Iceland been recycled? And how old is Iceland?

JZ: I don’t know the age of the very oldest rocks in Iceland, but I have heard discussions of some rocks that are millions of years old.  Over 99% of the rocks in Iceland are volcanic in origin, and the rocks at the surface are typically tens to hundreds of thousands of years old.  Few of the rocks on the island have been ‘recycled’ in that Iceland does not experience subduction (where the moving plates get shoved into each other), which leads to classic steep-sided volcanoes like Mt. Fuji in Japan or the large volcanic cones along the west coast of the U.S.

SJ:Would you please elaborate on the Icelandic plume, which seems to persist through geologic time, yet wander (or is it the “subaerial” surfaces such as Iceland and Greenland which have wandered?).

JZ: Iceland does indeed sit atop a particularly strong ‘plume’ of magma rising up from the interior of the Earth.  The coincidence of this plume with the mid-Atlantic ridge system is, we think, just that, a geologic coincidence.  Greenland does ‘wander’ in the sense that it is entirely on the North American plate and it moves along with that plate.  Iceland is literally growing as it is pulled apart along the ridge system that runs across the middle of the country.  Each year roughly 2 centimeters of new ‘Iceland’ is formed as the two plates spread apart  along that ridge.

Dr. Jim Zimbelman


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