Physiographic regions are geographic areas that share distinct properties like landforms, rock type, and evolutionary history. This lesson will look at some of the ways these regions are classified and look at examples in the USA.
What Is a Physiographic Region?
When you look at a satellite image of the United States, you probably notice differences across the landscape. There are mountains, rivers, plains, rolling hills, and low-lying coastal lands. When scientists try to categorize regions based on their physical characteristics, we get the development of physiographic regions.A physiographic region has a distinct type of landscape, landforms, rock type, and evolutionary history. If you then compare two different regions together, you’ll see that they vary based on each of these categories.
Physiographic Regions in the USA
The first attempt to classify the United States into physiographic regions was published in a scientific journal back in 1917, and there have been many discussions and attempts at fine-tuning this method to find the best way to categorize land types.At the broadest scale, the USA is split into 8 regions that vary in size.
- The Appalachian Highlands
- The Atlantic Plain
- The Interior Highlands
- The Interior Plains
- The Intermontane Plateaus
- The Laurentian Uplands
- The Pacific Mountain System
- The Rocky Mountain System
This is a great first step at classification, but we can take this one step further and look at more detailed physiographic regions.Currently, the USA can be split into 24 distinct physiographic regions (which are sometimes called physiographic provinces), and each of these can be sub-divided into more specific groups that are still related to the broad categorization we started with.
Some maps show 25 categories because they include the continental shelf currently under water, but for the purposes of this lesson, we’ll stick with 24.
The 24 regions found within the contiguous USA are as follows:
- Appalachian Plateaus
- Basin and Range
- Blue Ridge
- Cascade-Sierra Mountains
- Central Lowland
- Coastal Plain
- Colorado Plateaus
- Columbia Plateau
- Great Plains
- Interior Low Plateaus
- Lower Californian
- Middle Rocky Mountains
- New England
- Northern Rocky Mountains
- Ozark Plateaus
- Pacific Border
- Southern Rocky Mountains
- St. Lawrence Valley
- Superior Upland
- Valley and Ridge
- Wyoming Basin
This is pretty cool to look at, right? So how were these physiographic regions defined?
Classification Features & Factors
The study of landforms and landscapes is a field called geomorphology, and this field underlies the classification of physiographic regions. The earth is over 4.5 billion years old, and an awful lot has happened during that time.
The last Ice Age ended around 10,000 years ago, and the retreating glaciers definitely had an impact on the landscape.Knowing that there is such a rich history affecting geomorphology, scientists look at five things when trying to determine how to classify a physiographic region:
- Morphology is the shape and appearance of the landscape.
- Morphometry is the measurement and slope of a landform.
- Morphogenesis is the chemical and biological processes that historically occurred to form a landform.
- Morphochronology is the age of a landform.
- Morphodynamics is the land-forming process currently active in shaping a landscape.
These factors consider both historical and current influences on the landscape. Additionally, variables like climate, ecological communities, wetlands, and watersheds may be used to describe regions. Based on a scientist’s interest, they may choose a different metric to use for classification, especially if the area of focus is a smaller region like an individual state.
Washington, for example, uses their mountains, rivers, and lowland/coastal areas to categorize 10 physiographic regions within the state.
As you’ve probably figured out, there’s no one right way to classify physiographic regions, those that share the same landform types, geology, and evolutionary history. The study of landforms is called geomorphology, where scientists use morphology (shape), morphometry (measurement), morphogenesis (origin), morphochronology (age), and morphodynamics (current affecting processes) to help with the classification.
Ultimately, the USA has been split into 24 general physiographic regions, and states can break these into more specific regions.