The flanks of Erebus are spiked with ice towers, hundreds of them, called fumaroles. Gas and heat seeping through the side of the volcano melt the snowpack above, carving out a cave. Steam escaping from the cave freezes as soon as it hits the air, building chimneys as high as 60 feet.

The scientists who work on Mount Erebus say that its ice caves are every bit as much fun to explore as you might expect. But the scientists are more interested in the volcano's crater, with its great pool of lava -- one of the few of its kind. Most volcanoes have a deep central chamber of molten rock, but it's typically capped by cooled, solid rock that makes the hot magma inaccessible. On Mount Erebus, the churning magma is exposed at the top of the volcano, in a roiling 1,700-degree Fahrenheit lake perhaps miles deep.