Glacier and glaciatio chapter 12

CHAPTER 12 – GLACIERS AND GLACIATION
Today glaciers cover nearly 10 percent of Earth’s land surface; however, in the recent geologic past ice sheets were three times more extensive, covering vast areas with ice thousands of meters thick. Many regions still bear the mark of these glaciers. The basic character of such diverse places as the Alps, Cape Cod, and Yosemite Valley was fashioned by now-vanished masses of glacial ice. Moreover, Long Island, the Great Lakes, and the fiords of Norway and Alaska all owe their existence to glaciers. Glaciers, o course, are not just a phenomenon of the geologic past. As you will see, they are still sculpting and depositing debris in many regions today.
GLACIERS: A PART OF TWO BASIC CYCLES
Glaciers are a part of two fundamental cycles in the Earth system, the hydrologic cycle and the rock cycle. Earlier you learned that the water of the hydrosphere is constantly cycled through the atmosphere, biosphere, and solid Earth. Time and time again, the same water evaporates from the ocean into the atmosphere, precipitates upon the land, and flows in rivers and underground back to the sea. However, when precipitation falls at high elevations or high latitudes, the water may not immediately make its way toward the sea. Instead, it may become part of a glacier. Although the ice will eventually melt, allowing the water to continue is path to the sea, water can be stored as glacial ice for many tens, hundreds, or even thousands of years. During the time that the water is locked up in a glacier, it can be a powerful erosional force. Erosional processes are an important part of the rock cycle. Like rivers and other erosional processes, the moving ice modifies the landscape as it accumulates, transports, and deposits sediment.
TYPES OF GLACIERS
EXTERNAL PROCESSES
GLACIERS
A glacier is a thick ice mass that originates on land from the accumulation, compaction, and recrystalization of snow. Because glaciers are agents of erosion, they must