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A Q&A with Expert Dr. Jim Zimbelman

By | April 6, 2014

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

A: 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.

Q: 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?). 

A: 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

Dr. Jim Zimbelman is a planetary geologist at the Smithsonian’s National Air and Space Museum where he has served as the chairman of the Center for Earth and Planetary Studies. Over the past 20 years at NASM, he has been involved in the analysis of high-resolution spacecraft imaging and geophysical data of the Earth and terrestrial planets, geologic mapping of Mars and Venus, and other geologic studies of terrestrial planets.

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