Chapter 22: Amazing Ice: Glaciers and Ice Ages

Beginning with Louis Agassiz's groundbreaking hypothesis that continental ice sheets once blanketed much of the Northern Hemisphere, the chapter establishes how glacial theory revolutionized our understanding of climate change. The formation process transforms atmospheric precipitation into glacial ice through successive stages of compaction and recrystallization, moving from loose snow to intermediate firn and finally to dense, flowing ice. Glaciers are classified into distinct types—alpine glaciers including valley, cirque, and piedmont varieties, and massive continental ice sheets presently found in Greenland and Antarctica. The chapter explores how glaciers flow through two primary mechanisms: plastic deformation within the ice itself and basal sliding across the bedrock interface, processes that create distinctive structural features such as crevasses and account for the brittle-plastic transition zone. Glacial erosion produces characteristic landforms including cirques, arêtes, horns, and U-shaped valleys, while deposition generates moraines, drumlins, eskers, and kettle lakes. The chapter details how glaciers influence global sea level, trigger post-glacial rebound in formerly ice-covered regions, and create periglacial environments characterized by permafrost and patterned ground. The Pleistocene Ice Age receives comprehensive treatment, including evidence from both terrestrial and marine records, the extinction of megafauna, and the oscillation between glacial and interglacial periods. The chapter concludes by integrating Milankovitch orbital cycles, atmospheric carbon dioxide fluctuations, and ocean circulation patterns as controlling mechanisms for glaciation, while addressing contemporary concerns about anthropogenic warming and its potential to extend the current interglacial interval indefinitely.