CHAPTER 17 Focus Points

• Permafrost: Permafrost covers about 25% of the Northern Hemisphere.

• Release of carbon: Permafrost is thawing in response to climate change, releasing methane and carbon dioxide into the atmosphere.

• Glacier formation: Glaciers form through snow accumulation. Snow is compressed by gravity to form granular snow, then firn, and then glacial ice.

• Glacier movement: Glaciers move downslope at an average rate of a few centimeters per day through basal sliding and plastic deformation. At times, they move faster in glacial surges.

• Toe position: The position of a glacier’s toe largely reflects the mass balance of the glacier.

• Glacial retreat: Most alpine glaciers are retreating in response to atmospheric warming.

• Types of glaciers: Glaciers can be categorized as alpine glaciers or ice sheets.

• Glacial erosion: Glaciers are important agents of erosion. They cut into bedrock by plucking it and abrading it with plucked rocks.

• Glacial transport: Glaciers transport rock fragments downslope by means of ice flow and subglacial streams.

• Glacial landforms: Glaciers make many unique landforms, including cirques, tarns, horns, and U-shaped valleys.

• Glaciers and streams: Glaciers, like streams, deposit sediments where they stop flowing.

• Moraines: Glaciers deposit till to form moraines.

• Ice sheet deposits: Much of northern North America is covered by glacial sediments deposited by ice sheets of the Wisconsin glaciation.

• Loess: Glacial sediments on outwash plains are an important source of loess deposits.

• Distribution of ice: About 99% of the cryosphere is found in the ice sheets of Greenland and Antarctica.

• Ice loss: Greenland and Antarctica are losing about 344 billion tons of ice each year as a result of melting and an increased rate of outlet glacier flow to the sea.