Stephen Baxter - Longtusk

In fact, Longtusk saw, the lake had been created by the melting of the ice sheet as it crumbled into this hollow in the rock.

"This lake is just a huge meltwater pond," Longtusk said, realizing. "It is fed by melting ice. There are no fish here, because there is no way for a fish to get here. And the water is kept from draining away by that —" The plug of ice in the rocky cleft on the lake’s southern side. "Fed by meltwater from the north, trapped by the ice plug to the south, this bowl in the land will gradually fill up—"

"Until," Rockheart growled, "that chunk of ice gives way."

"Yes. And then the lake will empty itself across the land, all at once — and wash away the soil and vegetation, scouring down to the bedrock."

Rockheart rumbled. "Like Kilukpuk’s mighty tears."

"Yes. No wonder the land is so damaged. But then the ice plug forms again, and the lake begins to fill once more."

Rockheart grunted. "If that’s true, we’re lucky. We’re in no danger here."

"What do you mean?"

"The water has some way to rise before it tops that ice dam."

"You’re right. We’ll be long gone by then." Good for Rockheart, Longtusk thought: practical as always, focusing on the most important issue — the mammoths’ safety.

They left the lake, calling to the others.

A few more days and he could sense the broadening of the land to north and south, and he knew they had passed the narrowest point of this neck of Earth that stretched between the continents.

Thus, the mammoths walked from Asia to America.

Soon after that he could see the icecap.

It was a line of light, straight and pure white, all along the eastern horizon, as if etched there by the ingenious paw of a Firehead. He could hear the growl and scrape as the ice flowed over the rocky land, gouging and destroying, the mighty cracks as the ice itself split and crumbled, and the steady roar of the blunt katabatic winds which spilled from its chill domed heart.

It was a frozen sheet that covered half a continent, pushing far to the south, much farther south than in the land they had fled, on the far side of the land bridge. And it was this monster of ice that they must challenge before they reached safety.

He tried to maintain the pace and enthusiasm of his little group. But as they drew closer he could feel his own footsteps drag, as if the icecap itself was drawing out his strength, just as it sucked the moisture from the air.

They reached land that had clearly been uncovered only recently by the ice.

The rock was scoured clean, laced here and there with low dunes of glacial till and sand. Only lichen grew here: patches of yellow and green, bordered by black, slowly eroding the surfaces of the rock. The lichen might be extremely ancient; it took ten years for a new colony to become visible to the eye. He wondered what slow encrusting dreams these vegetable colonists shared, what slow cold memories of the surging ice they stored.

The land became steadily more treacherous. They worked their way past moraines, heaps of rubble left by the retreating ice. The rubble was of all sizes, from gritty sand to boulders larger than a mammoth. The moraines were cut through by meltwater rivers that varied unpredictably from trickles to mighty, surging flows, and the rubble heaps were unstable, liable to slump and collapse at any time.

As they pressed farther, a great wind rose, katabatic, pouring directly off the ice sheet and into their faces. It was a hard time. There was little to eat or drink and every step required a major effort, but they persisted. And Longtusk was careful to encourage his charges to gather as much strength as possible, for he knew that only harder days, if anything, lay ahead of them all.

At last they encountered the ice itself.

They reached the nose of a glacier. It was a wall of ice, cracked and dirty and forbidding. Blocks of broken ice, calved off the glacier like miniature icebergs, lay unmelting on rock that was rust-red, brown and black. Tornado-like columns of ice crystals spun across the barren rock in the wind, whipping up small lumps of sandstone that flew through the air, peppering the mammoths’ hides.

This was the terminus of a huge river of ice that poured, invisibly slowly, from the vast cap that still lay to the east.

The mammoths paused to gather breath, hunted without success for food, and then began the ascent.

Longtusk picked his way onto the great ice river, stepping cautiously over a shattered, chaotic plain of deeply crevassed blue ice. The glacier was a river of raw white, its glare hurting his eyes, shining under the sky’s clean blue. He could see the glacier’s source, high above him, at the lip of the ice sheet itself. Where he could he chose paths free of crevasses and broken surfaces, but he could usually find easier ground near the glacier’s edges, hugging the orange rock of the valley down which the glacier poured.

It was difficult going. Sometimes loose snow was whipped up by the wind and driven over the surface, obscuring everything around him up to shoulder height. But, above the snow, the sky was a deep blue.

At last the ice beneath his feet leveled out, and he realized he had reached a plateau.

It was the lip of the ice sheet.

He was standing on a sea of gleaming ice, which shone in every direction he looked, white, blue and green. The ice receded to infinity, flat white under blue sky — but perhaps his poor eyes could make out a shallow dome shape as the ice rose, sweeping away from him toward the east.

It was utterly silent and still, without life of any kind, the only sound the snort of his trunk, the only motion the fog of his breath.

He turned, ponderously, and looked back the way he had come.

This edge of the ice was marked by mountains, heavily eroded and all but buried, and he could see how the glacier spilled between the peaks toward the lower ground. Though locked into the slow passage of time, the glacier was very obviously a dynamic river of ice. Huge parallel bands flowed neatly down the valley’s contours. The bands marked the merging of tributaries, smaller ice rivers that flowed into the main stream, each of them keeping their characteristic color given them by the rock particles they had ground up and carried. Where the glacier reached the lower land it spread out, cracking, making the jumbled surface of crevasses he had struggled to cross.

Everything flowed down from here, down to the west and the lower ground, as if he had climbed to the roof of the world. He was cold, exhausted, hungry, and thirsty; and he was still not confident of surviving this immense venture. But, standing here, looking down on the great frozen majesty of the icecap and its rivers, he felt exhilarated, privileged.

He turned to face the east, ready to go on.

He stepped forward experimentally. The ice was unforgivingly cold, seeming to suck his body heat out through the thick callused pads on his feet. It was harder than any rock he had encountered — but it was not smooth. It was choppy, rippled, like the surface of a lake under the wind. But the ripples were frozen in place, and the footing was, surprisingly, quite secure, thanks to those scalloped ripples.

There is nothing to eat here, he thought dryly. There is no shelter, and if I stay too long I will surely freeze to death. But at least I won’t slip and fall.

He began to walk, and the others followed him. He could feel the ice’s flow in his belly, a deep disturbing subsonic murmur as it poured with immense slowness toward the lip.

The cap was one of a string of great domes of ice that littered the northern hemisphere of the planet. As its center the icecap was kilometers thick, as humans would have measured it, and the bedrock beneath — ground free of life and locked in darkness — was crushed downward through many meters.