The Mammoth Hunters - Jean M. Auel [129]
Ayla signaled Whinney with pressure of legs and shift in position, so second nature she hardly thought of it as guiding the mare. They turned and started up the slope.
The trip back was not the leisurely one they had made on their way out. They traveled steadily, making no exploratory side trips or hunting forays, no early stops to relax or enjoy Pleasures. Expecting to return, they had noted landmarks as they were traveling from the valley, certain outcrops, highlands, and rock formations, valleys and watercourses, but the changing season had altered the landscape.
In part, the vegetation had changed its aspect. The protected valleys where they had stopped had taken on a seasonal variation that caused an uneasy sense of unfamiliarity. The arctic birch and willow had lost all their leaves, and their scrawny limbs shivering in the wind seemed shriveled and lifeless. Conifers—white spruce, larch, stone pine—hale and proud in their green-needled vigor, were prominent instead, and even the isolated dwarfs on the steppes, contorted by winds, gained substance by comparison. But more confusing were the changes in surface features wrought, in that frigid periglacial land, by permafrost.
Permafrost—permanently frozen ground—any part of the earth’s crust, from the surface to deep bedrock, that remains frozen year-round, was brought on, in that land far south of polar regions so long ago, by continent-spanning sheets of ice, a mile or two—or more—high A complex interaction of climate, surface, and underground conditions created and maintained the frozen ground. Sunshine had an effect, and standing water, vegetation, soil density, wind, snow.
Average yearly temperatures only a few degrees lower than those that would later maintain temperate conditions, were enough to cause the massive glaciers to encroach upon the land and the formation of permafrost farther south. The winters were long and cold, and occasional storms brought heavy snows and intense blizzards, but the snowfall over the season was relatively light, and many days were clear. The summers were short, with a few days so hot they belied the nearness of any glacial mass of ice, but generally it was cloudy and cool, with little rain.
Though some portion of the ground was always frozen, permafrost was not a permanent, unchanging state; it was as inconstant and fickle as the seasons. In the depths of winter when it was frozen solid all the way through, the land seemed passive, hard, and ungiving, but it was not what it seemed. When the season turned, the surface softened, only a few inches where thick ground cover or dense soils or too much shade resisted the gentle warmth of summer, but the active layer thawed down several feet on sunny slopes of well-drained gravels with little vegetation.
The yielding layer was an illusion, though. Beneath the surface the iron-hard grip of winter still ruled. Impenetrable ice held sway, and with the thaw and forces of gravity, saturated soils, and their burden of rocks and trees, crept and slid and flowed across the water-lubricated table of ground still frozen below. Slumps occurred and cave-ins as the surface warmed, and where the summer melt could find no outlet, bogs and swamps and thaw-lakes appeared.
When the cycle turned once more, the active layer above the frozen ground turned hard again, but its cold and icy countenance disguised a restless heart. The extreme stresses and pressures caused heaving, thrusting, and buckling. The frozen ground split and cracked and then filled with ice, which, to relieve stress, was expelled as ice wedges. Pressures filled holes with mud, and caused fine silt to rise in silt boils and frost blisters. As the freezing water expanded, mounds and hills of muddy ice—pingos—rose up out of swampy lowlands reaching heights up to two hundred feet and diameters of several hundred.
As Ayla and Jondalar retraced their steps, they discovered that the relief of the landscape had changed,