Page 602 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

566 part III The earth–atmosphere interface
the margins of glaciers, past and present. When soil or rock temperatures remain below 0°C for at least 2 years, permafrost (perennially frozen ground) devel- ops. Note that this defining criterion for permafrost is based solely on temperature and has nothing to do with how much or how little water is present. The active layer is the zone of seasonally frozen ground that exists between the subsurface permafrost layer and the ground surface. In regions of permafrost, frozen subsurface water forms ground ice. Patterned ground forms in the periglacial environment where freezing and thawing of the ground create polygonal forms of circles, polygons, stripes, nets, and steps.
periglacial (p. 550) permafrost (p. 550) active layer (p. 551) ground ice (p. 551) patterned ground (p. 552)
15. In terms of climatic types, describe the areas on Earth where periglacial landscapes occur. Include both higher-latitude and higher-altitude climate types.
16. Define two types of permafrost, and differentiate their occurrence on Earth. What are the characteristics of each?
17. Describe the active zone in permafrost regions, and relate the degree of development to specific latitudes.
18. What is a talik? Where might you expect to find taliks, and to what depth do they occur?
19. What is the difference between permafrost and ground ice?
20. Describe the role of frost action in the formation of various landform types in the periglacial region, such as patterned ground.
21. Explain some of the specific problems humans encounter in building on periglacial landscapes.
■ Describe landscapes of the Pleistocene ice-age epoch, and list changes occurring today in the polar regions.
An ice age is any extended period of cold. The late Cenozoic Era featured pronounced ice-age conditions dur- ing the Pleistocene. Beyond the ice, paleolakes formed because of wetter conditions. Lacustrine deposits are lake sediments that form terraces along former shorelines.
The 10°C isotherm for July defines the Arctic region. This line coincides with the visible tree line—the bound- ary between the northern forests and tundra. The Antarc- tic convergence defines the Antarctic region in a narrow zone that extends around the continent as a boundary between colder Antarctic water and warmer water at lower latitudes. This boundary follows roughly the 10°C isotherm for February, the Southern Hemisphere summer, and is located near 60° S latitude. Changes occurring in the polar regions are causing positive feedback loops re- lated to changes in surface albedo. Warming temperatures are causing the collapse of ice shelves.
ice age (p. 553)
paleolake (p. 555) lacustrine deposit (p. 555) Arctic region (p. 558) Antarctic region (p. 558)
22. Define an ice age. When was the most recent? Explain the terms glacial and interglacial in your answer.
23. Explain the relationship between the criteria defin- ing the Arctic and Antarctic regions. Is there any coincidence between the Arctic criteria and the distribution of Northern Hemisphere forests?
24. Based on information in this chapter and elsewhere in Geosystems, summarize a few of the changing conditions under way in each polar region.
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