Regional Overview of Interior Alaska

From continental macroclimate to microalluvial salt crusts, geology is a dominant factor that influences patterns and processes in the Alaskan boreal forest. In this chapter, we outline important geologic processes as a foundation for subsequent chapters that discuss the soil, hydrology, climate, and biota of the Alaskan boreal forest. We conclude the chapter with a discussion of interior Alaska from a regional perspective. Alaska can be divided into four major physiographic regions. The arctic coastal plain is part of the Interior Plains physiographic division of North America, analogous to the great plains east of the Rocky Mountains. The arctic coastal plain is predominantly alluvium underlaid by hundreds of meters of permafrost, resulting in many thaw lakes and ice wedges. South of the arctic coastal plain lies the Northern Cordillera, an extension of the Rocky Mountain system dominated by the Arctic Foothills, Brooks Range, Baird Mountains, and Delong Mountains. These mountains were glaciated during the Pleistocene. South of the Brooks Range lies interior Alaska, which is an intermontane plateau region analogous to the Great Basin/Colorado Plateau regions. This extensive region is characterized by wide alluvium-covered lowlands such as the Yukon Flats, Tanana Valley, and Yukon Delta, as well as moderate upland hills, domes, and mountains. Largely unglaciated, this region served as a refugium for biota during glacial periods. With the Northern and Southern Cordilleras acting as barriers, the major rivers of this region have long, meandering paths to the Bering Sea. The Southern Cordillera is composed of two mountain ranges: the Alaska Range to the north and the Kenai/Chugach/Wrangell-St. Elias Mountains to the south. The lowland belt between these mountains includes the Susitna and Copper River lowlands. The entire Southern Cordillera was glaciated during the Pleistocene and today has extensive mountain glaciers. Much of Alaska is made up of multiple geologic fragments that have been rafted together by the movements of the major plates called tectonic terranes (Thorson 1986, Connor and O’Haire 1988). Plate-tectonic theory explains such observations as the changing distribution of fossils with geologic time, the deep Aleutian Trench, high Alaskan mountain barriers, and mountain glaciers.

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