Towers of tufa

The next time you're passing through southwestern Greenland, don't miss the towers of tufa. These unique formations of calcium carbonate, or tufa, grow only in the chilly waters of Ikka Fjord. There are more than 500 towers clustered in less than half a square mile. Some reach 60 feet in height, their tops visible at low tide.

First described 35 years ago, they were never studied intensively until a group of Danish researchers examined them a couple of years ago. They determined that the towers are made of an unusual form of calcium carbonate called ikaite. The ikaite crystals form when carbonate-rich water from springs beneath the fjord seeps up and comes into contact with cold, calcium-laden seawater, causing calcium carbonate to precipitate out. "Because it's at such a low temperature, the movement of the water is slower," explains Bjorn Buchardt, a geologist at the University of Copenhagen. "The water can't get away during the precipitation of the mineral and is incorporated into the crystal lattice. That's why you get this weird ikaite forming." The towers shelter anemones, algae, and sea cucumbers. Buchardt has suggested that the towers be preserved as a geologic World Heritage site. "They are unique in the way they form and they are of extreme beauty," he says. "The area is small and vulnerable and deserves protection."

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