This unique addition to reference literature provides an introduction to the major concepts and contemporary issues that are essential for students of environmental science and environmental studies to know. With over 200 entries authored by world-class names like Anthony Brazel, John Day and Edward Keller, this text is divided into six sections: Environmental Science, Environments, Paradigms & Concepts, Processes & Dynamics, Scales & Techniques, and Environmental Issues.
Permafrost is ground in which a temperature lower than 0° has existed continuously for two or more years whether water is present or not. In areas of severe winters the depth of permafrost can be greater than 1400 m in Siberia (Lena and Yara river basins), more [Page 130]than 700 m in the Canadian Arctic islands, and more than 600 m in Alaska (Prudhoe Bay). The lower limit of permafrost is determined by the increase of temperature with depth beneath the Earth's surface (the geothermal gradient). There are spatial variations in permafrost so that in the Northern Hemisphere a zone of continuous permafrost occurs everywhere except under deep lakes in the northern part of the zone; a discontinuous permafrost zone occurs with mean annual soil ...