By Sid Perkins
Thousands of fast-growing, egg-shaped lakes—most with their pointy ends aimed toward the northwest—pepper the landscape of northern Alaska. A new study suggests that these enigmatic waters expand when their permafrost banks melt, rather than when wind-driven currents cause erosion, as scientists had proposed for decades.
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Geologists refer to these shallow bodies of water as oriented-thaw lakes because their long axes are aligned and they freeze each winter and melt each spring, says Jon D. Pelletier, a geologist at the University of Arizona in Tucson. They occur throughout an area about the size of New Hampshire and Vermont combined. An individual lake occasionally measures dozens of kilometers in length.