StudySpace: Chemistry 2e.

ANIMATION: Glacial Advance and Retreat

Glacial advance and retreat is determined by the balance between the accumulation of snow and the removal of ice by sublimation, melting, and calving (ablation). When the rate of ablation below the snowline equals the rate of accumulation above it, the glacier is stationary, as in View 1. During glacial retreat, View 2, the rate of ablation exceeds the rate of accumulation, and the position of the toe retreats toward the origin of the glacier. Glacial advance, View 3, occurs when the rate of accumulation exceeds the rate of ablation. For all views, pay attention to the motion of the stones. Note that in all cases, ice flows downhill. For more information, see Section 22.2 Ice and the Nature of Glaciers starting on p. 758 and Figure 22.14 on p. 768 in your textbook.

Zoomable Art: Glaciers and Glacial Landforms

Glaciers are rivers or sheets of ice that last all year and flow slowly. Continental glaciers, vast sheets of ice up to a few kilometers thick, covered extensive areas of land during times when Earth had a colder climate. For more information, see the Featured Painting on pp. 778-779 in your textbook.

ANIMATION: Milankovitch Cycles

Why do glaciers advance and retreat periodically during an ice age? In 1920, Mulutin Milankovitch showed that regular variations in the shape of Earth's orbit and the orientation of its axis create variations of solar intensity at high latitudes: warm summers in which glaciers retreat, and cool summers when they advance. These climate cycles, called Milankovitch Cycles, are determined by three factors: orbital eccentricity, shown in View 1, changes in the tilt of Earth's axis, View 2, and the precession of Earth's axis, View 3. For more information, see Section 22.8 The Causes of the Ice Age starting on p. 793 and Figure 22.46 on p. 795 in your textbook