Interior Plains facts for kids
The Interior Plains are a huge flat area in the middle of North America. They stretch all the way from the Gulf of Mexico up to the Arctic Ocean, running alongside the Rocky Mountains. In Canada, these plains separate the Rocky Mountains from the Canadian Shield. In the United States, they include the Great Plains in the west and the Tallgrass prairie region, which is south of the Great Lakes and reaches east towards the Appalachian Plateau.
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How the Interior Plains Formed
The land that makes up the Interior Plains was shaped over billions of years. Huge movements of Earth's plates, called plate tectonics, created mountains and caused land to rise and fall. Over time, these mountains wore down, and rivers and ancient seas left behind layers of sand, mud, and other materials. These layers built up to form the rocks we see today in the plains.
The Proterozoic Period (2.5 to 0.54 Billion Years Ago)
About 2 billion years ago, several large pieces of Earth's crust crashed together. This event, called the Trans-Hudson Orogeny, was similar to how the Himalayas formed when the Indian plate hit the Eurasian plate. These collisions created the core of North America, known as Laurentia.
After these huge crashes, mountains grew around the edges of Laurentia. But the middle part stayed mostly flat, like a giant bowl. This bowl collected sediments (bits of rock and soil) that eroded from the new mountains. Today, you can still see some of these ancient rocks in the Black Hills of South Dakota. These rocks are mostly granite and other igneous rocks, which are very old and form the base layer of the continent.
The Paleozoic Era (542 to 251 Million Years Ago)
This era was a very important time for life on Earth. It began with the Cambrian explosion, when many new and complex forms of ocean life suddenly appeared. Later, it ended with the Permian–Triassic extinction event, a huge event where many species died out.
During this time, global sea levels rose, covering parts of the continents. The middle of Laurentia, however, stayed above the water. As the continent slowly moved east, the Appalachian Mountains began to form about 400 million years ago. These mountains reached their highest point around 300 million years ago, when the supercontinent Pangaea formed.
The central plains of Laurentia became a dumping ground for eroded material from these tall mountains. The oldest rocks from this period are now buried deep underground. Younger rocks include sandstone, shale, limestone, and coal.
The Mesozoic Era (251 to 65.5 Million Years Ago)
Around 220 million years ago, the supercontinent Pangaea began to break apart. The North American continent started moving west, becoming separated from other landmasses. For much of this era, the Interior Plains were covered by large inland seas.
During the Jurassic period, the Sundance Sea covered parts of Wyoming, Montana, North Dakota, and South Dakota. This sea left behind layers of coquina (rock made of shell fragments) and sandstone. Later, during the Cretaceous period, an even bigger sea formed called the Western Interior Seaway. This huge body of water stretched from modern-day Alaska all the way to the Gulf of Mexico. It covered almost all of the Interior Plains west of the Mississippi River. This sea left behind layers of limestone and shale.
Towards the end of the Mesozoic Era, these inland seas began to dry up. This happened because the land was pushed up as the Rocky Mountains started to form.
The Cenozoic Era (65.5 Million Years Ago to Today)
The Laramide Orogeny was a major event that created the western Cordillera, which includes the front ranges of the Rocky Mountains. This happened because a plate called the Farallon Plate slid underneath the North American Plate at a shallow angle. This process lifted up huge blocks of rock, forming mountains from Montana down to New Mexico.
The rocks you see at the surface of the Rockies today include sandstone, granite, and limestone. There are also older metamorphic rocks that were pushed up from the Proterozoic Period. The Interior Plains have stayed mostly flat during this time. New sediments are still being deposited on the plains from the erosion of the Rocky Mountains in the west and the Appalachians in the east.
How Glaciers Shaped the Plains
About 2.6 million years ago, during the Pleistocene Epoch, a huge ice sheet called the Laurentide Ice Sheet began to spread south. It covered much of North America, reaching down into the northern Great Plains and parts of Minnesota and Wisconsin.
As this massive ice sheet melted and retreated, it dramatically changed the landscape of the Interior Plains. The ice scraped out many hollows in the ground. When the ice melted, these hollows filled with water, creating thousands of "kettle lakes." The Great Lakes were formed by the Laurentide Ice Sheet, as were Canada's Great Slave Lake and Great Bear Lake. Great Slave Lake is the deepest lake in North America.
Many smaller lakes were also formed, especially in places like Minnesota, which is known as "the Land of 10,000 Lakes."
Much of the fine soil called loess found in the Interior Plains also came from glaciers. Meltwater from glaciers in the Rocky Mountains carried sand and silt. Strong winds then picked up this material and spread it across the Interior Plains.
How Sediment Moves Around
Sediment (bits of soil and rock) moves around the Interior Plains mainly by wind (called aeolian processes) and by rivers (called fluvial processes). Due to climate change, the Interior Plains are getting warmer and drier. However, when it does rain, the storms are often more intense. This means that rain-driven erosion will become a bigger problem for soil in the plains.
Rivers and Sediment
Human projects, like building dams and changing river paths, have greatly affected how rivers move sediment in the Interior Plains. These structures stop sediment from flowing naturally downstream.
For example, before 1900, the Mississippi River carried about 400 million tons of sediment to the Gulf of Mexico each year. But in the early 20th century, dams were built on the Missouri River, and other projects changed the Mississippi. Now, the river carries only about 100-150 million tons of sediment per year. The dams trap the suspended sediment, preventing it from reaching the Gulf.
Wind and Sediment
The Interior Plains generally have low rainfall, making them prone to droughts. This is especially true in the southern parts, where warm temperatures and high evapotranspiration (water evaporating from the ground and plants) make the region very dry. This dryness makes the soil very vulnerable to soil erosion by wind.
A common feature of wind erosion in the Interior Plains is the widespread presence of loess deposits. These fine, wind-blown dust deposits were laid down during the Pleistocene epoch. The Nebraska Sand Dunes are a good example of how wind deposited sand and loess during this time. The large amount of loess in the Interior Plains shows just how much wind erosion has happened there.
After World War I, many farmers started growing wheat in the rich loess soil of the Interior Plains. This meant that many natural prairies, which had grasses that held the soil in place, were plowed under. While droughts were common, a severe drought in the 1930s led to terrible wind erosion. Without the prairie grasses, huge dust storms, known as the Dust Bowl, swept across the region for months. On May 12, 1934, alone, an estimated 200 million tons of topsoil were blown all the way to the Atlantic Ocean.
To fight this rapid wind erosion, new methods for protecting the soil were put in place. In the years after the Dust Bowl, the Works Progress Administration planted 18,500 miles of shelterbelt trees. These rows of trees helped to slow down the wind and reduce soil erosion.
How the Land is Used Today
In the United States
In the United States, the largest part of the Interior Plains (about 44.4%) is covered by grasslands and shrublands. The western part has short grasses like blue grama and buffalograss. The eastern part has tall grasses such as big bluestem and switchgrass. In between, there's a mixed-grass prairie with both short and tall grasses, including little bluestem and western wheatgrass.
Much of this grassland is used for raising cattle. Nearly half of all beef cattle in the United States are raised here. In Canada, provinces in the Interior Plains produce almost 60% of all beef cattle.
A large amount of land in the Interior Plains is used for agriculture. In 2000, almost 44% of the Great Plains area was farmland. Wheat is the most important crop grown here. The Interior Plains produce more than half of the world's wheat exports. Other important crops include barley, corn, cotton, sorghum, soybeans, and canola (which is especially important for Canada).
Smaller parts of the land are used for other things. Forests make up 5.8%, wetlands 1.6%, developed areas 1.5%, barren land 0.6%, and land used for mining 0.1%.
See also
In Spanish: Llanuras Interiores para niños
