Unit 52

DEFINING PHYSIOGRAPHIC REALMS AND REGIONS: THE SPA TIAL VARIATION OF LANDSCAPES

Unit Overview

This unit examines the spatial distribution of landscapes of North America through discussions of physiographic realms and regions. The main sections are as follows:

  • Defining physiographic realms and regions
  • Physiographic realms and regions of North America
  • The physiographic imprint

The surface characteristics of the landmasses can be divided into physiographic realms, with each realm subdivided into physiographic regions. The following are the six physiographic realms of North America: Canadian Shield, Interior Plains, Appalachian Highlands, Western Mountains, Gulf-Atlantic Coastal Plain, and Central American Mountains.

Often the regions are further classified. The Appalachian Highlands, for example, consists of the following physiographic regions: Appalachian Plateau, "Newer" Appalachians, Blue Ridge Section, Piedmont, and New England/Maritime Province.

Within the Western Mountains, the physiographic regions consist of the Southern Rocky Mountains, Middle Rocky Mountains, Northern Rocky Mountains, Columbia Plateau, Colorado Plateau, Basin-and-Range Province, and Pacific Mountains and Valleys.

Unit Objectives

  • To introduce physiographic realms and regions
  • To briefly discuss the six physiographic realms of North America
  • To discuss in greater detail the regions that constitute two of the physiographic realms of North America, especially in Canada


Glossary of Key Terms

Appalachian Highlands Extend northeastward from Georgia and Alabama through New England into Maritime Canada; actually a complex of several physiographic provinces.
Appalachian Plateau Eastern edge defined by the Allegheny Front in the north and the Cumberland Escarpment in the south; area of coal deposits and irregular topography.
Basin-and-Range Province Lies south of the Columbia Plateau in the intermontane region between the Rocky Mountains to the east and the Pacific Mountains and Valleys to the west; a region of basins and arid climate.
Blue Ridge Mountains Lie east of the Great Valley, extend north from Georgia to Gettysburg, Pennsylvania; underlain by much older crystalline rock than the other areas of the Appalachians.
Canadian Shield The original core of the North American landmass, heavily glaciated; characterized by low relief, unproductive soils, and large mineral deposits.
Central American Mountains Area to the south and west of the southern extension of the Gulf- Atlantic Coastal Plain; the contact zone between the Cocos and Caribbean lithospheric plates, dominated by volcanic landforms.
Colorado Plateau Area to the west of the Southern Rockies; exhibits few strong topographic contrasts, and is underlain by flat-lying sedimentary strata.
Columbia Plateau Area wedged between the Northern Rockies and the Cascade Range; one of the largest lava surfaces in the world, lies as high as 1800 m (6000 ft) above sea level.
Gulf-Atlantic Coastal Plain Extends along North America's eastern seaboard from New York City southward to the Caribbean coast of Costa Rica; lies below 300 m (1000 ft) in elevation, underlain by gently sloping, sedimentary rocks.
Interior Plains Extend eastward from the Rocky Mountains to the western edge of the Appalachians; generally an area of low relief.
Middle Rocky Mountains Area of ranges and wide valleys, less congested topography than in the Southern Rockies.
New England Maritime Province The rugged northeastern region of the Appalachians; strongly affected by glaciation and dotted with lakes.
"Newer" Appalachians Contains ridge-and-valley topography and the fertile Great Valley.
Northern Rocky Mountains Area northwest of Yellowstone Park; a confused topography of generally lower relief than the Middle and Southern Rockies.
Pacific Mountains and Valleys Lies west of the Columbia Plateau and the Basin-and Range province; orientation is north-south, a region of complex physiography, containing the Sierra Nevada and Cascades as well as California's central valley and other major lowlands.
Physiographic realm A first-order subdivision of the North American continent at the broadest scale; characterized by an appropriate uniformity of landscapes, landforms, and other physiographic elements.
Physiographic region A second-order subdivision of the North American continent at a more detailed scale than the physiographic realm; characterized by an appropriate uniformity of landscapes, landforms, and other physiographic elements. Also sometimes called physiographic provinces, an older geographic term still in use.
Physiography Literally means landscape description; refers to all of the natural features on the Earth's surface, including landscapes, landforms, climate, soils, vegetation, and hydrography.
Piedmont Low, hilly area east of the Blue Ridge section of the Appalachians.
Regional concept Used to classify and categorize spatial information; regions are artificial constructs developed by geographers to delineate portions of the Earth's surface that are marked by an overriding sameness or homogeneity (in our case, physiography) .
Southern Rocky Mountains Province lying across the center of Colorado; mountains rising sharply out of the western border of the Great Plains.
Western Mountains Region bordering the Interior Plains to the west that extends to the pacific coast; an area of rugged mountain topography and high plateaus.


Unit Outline

  • Defining physiographic realms and regions
    • Largest physiographic subdivisions are called realms (first-order units)
    • Realms subdivided into regions (second-order units)
    • Regions further subdivided into subregions (third-order units)
    • Physiography relates to all natural features on Earth, including
      • landforms
      • climate
      • soil
      • vegetation
      • hydrography
    • Boundaries of physiographic regions established by whatever criteria (as mentioned above) are being used to define a region; broad transitional zones much more common than sharp borders
  • Physiographic realms and regions of North America
    • The Canadian Shield
      • low relief, igneous and crystalline rock, thin soils
    • The Interior Plains
      • from Rocky Mountains to Appalachians, sedimentary rock, rich soils for agriculture
    • The Appalachian Highlands
      • from Georgia to Maritime Canada, rolling and rugged hills, folded sedimentary rock
    • The Western Mountains
      • dominated by high relief, varied topography, from New Mexico to Alaska, igneous, sedimentary, and metamorphic rock; Pacific region is mostly marked by rugged, high-relief terrain
    • The Gulf-Atlantic Coastal Plain
      • seaboard coastal North America, running south from New York City to Costa Rica; barrier islands, lagoons, beaches; low relief, little topographic variety
    • The Central American Mountains
      • Gulf-Atlantic Coastal Plain reaches southward to Mexico and Central America; to the south and west are the Central American Mountains volcanic landforms, earthquakes, altitudinal zonation of environments
  • The Physiographic Imprint
    • Today's landscape reflects all of the building forces and erosional systems covered in this text.


Review Questions

  1. Draw a generalized diagram of the six physiographic realms of North America, using Fig. 52.1
  2. Compare and contrast the various physiographic provinces within the Appalachians.
  3. What is the extent of the Gulf-Atlantic Coastal Plain?