THE AEROSPATIALE ALOUETTE light utility helicopter threading its way through the deep alpine valleys appeared as insignificant as a gnat against the backdrop of towering peaks. As the helicopter approached a mountain whose summit was crowned with three uneven knobs, Hank Thurston, seated in the front passenger's seat, tapped the shoulder of the man sitting beside him and pointed through the canopy.

“That's ”Le Dormeur,“ ” Thurston said, raising his voice to be heard over the thrashing rotor blades. “ ”The Sleeping Man.“ The profile supposedly resembles the face of a sleeper lying on his back.”

Thurston was a full professor of glaciology at Iowa State University. Although the scientist was in his forties, his face exuded a boyish enthusiasm. Back in Iowa, Thurston kept his face clean-shaven and his hair neatly trimmed, but after a few days in the field he began to look like a bush pilot. It was a look he cultivated by wearing aviator sunglasses, letting his dark brown hair grow long so gray strands would show and by shaving infrequently, so that his chin was usually covered with stubble.

“Poetic license,” said the passenger, Derek Rawlins. “I can see the brow and the nose and chin. It reminds me of the Old Man of the Mountain in New Hampshire before it fell apart, except that the stone profile here is horizontal rather than vertical.”

Rawlins was a writer for Outside magazine. He was in his late twenties, and with his air of earnest optimism and neatly trimmed sandy-blond hair and beard, he looked more like a college professor than Thurston did.

The crystal clarity of the air created an illusion of nearness, making the mountain seem as if it was only an arm's length away. After a couple of passes around the crags, the helicopter broke out of its lazy circle, scudded over a razorback ridge and dropped down into a natural bowl several miles across. The floor of the mountain basin was covered by an almost perfectly round lake. Although it was summer, ice cakes as big as Volkswagens floated on the ipirrorlike surface.

“Lac du Dormeur,” the professor said. “Carved out by a retreating glacier during the Ice Age and now fed by glacial waters.”

“That's the biggest martini on the rocks I've ever seen,” Rawlins said.

Thurston laughed. “It's as clear as gin, but you won't find any olive at the bottom. That big square structure built into the mountain off to the side of the glacier is the power plant. The nearest town is on the other side of the mountain range.”

The aircraft passed over a wide, sturdy-looking vessel anchored near the shore of the lake. Cranes and booms protruded from the boat's deck.

“What's going on down there?” Rawlins said.

“Some sort of archaeological project,” Thurston said. “The boat must have come up the river that drains the lake.”

“I'll check it out later,” Rawlins said. "Maybe I can pry a raise out