The Interior Plains is a vast physiographic region that spreads across the Laurentian craton of central North America, extending along the east flank of the Rocky Mountains from the Gulf Coast region to the Arctic Beaufort Sea. In Canada, it encompasses the Canadian Prairies separating the Canadian Rockies from the Canadian Shield, as well as the Boreal Plains and Taiga Plains east of the Mackenzie and Richardson Mountains; while in the United States, it includes the Great Plains of the West/Midwest and the tallgrass prairie region to the south of the Great Lakes extending east to the Appalachian Plateau region. [1]
A series of tectonic plate collisions in the crust that formed the center of the North American continent laid the groundwork for the modern-day interior plains. Mountain building and erosion around the plains as well as flooding from inland seas provided sediments that make up the rock strata of the interior plains.
Between 2.0 and 1.8 billion years ago the Hearne-Rae, Superior, and Wyoming cratons were sutured together to form the North American craton, Laurentia, in an event called the Trans-Hudson Orogeny (THO). [2] This event was like the Indian plate colliding with the Eurasian plate, which formed the Himalayas. After initial collisions during the THO, tectonic activity at the edges of the four main cratons sparked mountain building. The interior of Laurentia remained relatively flat and became a basin for eroded sediment from mountains at the beginning of the current time period, the Phanerozoic Eon. [3] The only remaining outcrops from this orogeny in the interior plains are in the Black Hills of South Dakota. The sediments that formed the Black Hills were granite and different types of igneous rocks, which make up the basement of bedrock in central North America. However, much of the Black Hills sediment has been metamorphosed and deformed, so it is uncertain what the conditions were like at the time of their formation. [2]
This period has a large importance in Earth's history as it saw the Cambrian explosion and Permian extinction. When global sea level rose and continents became partially submerged, the oceans had an explosion of complex life, which was the first time an event like this occurred on Earth. However, the center of Laurentia remained above sea level and as the continent moved east towards other supercontinents like Gondwana, the Appalachian Mountains began to form around 400 MYA. [4] This coincided with the formation of Pangea around 300 MYA, when the Appalachians were at their peak height. The central plains of Laurentia were subjected to deposition of eroded sediment from these mountains. [5] The oldest sediments from this period are felsic igneous rocks and granite that have since been metamorphosed, while the younger sediments are made up of sandstone, shale, limestone, and coal. Sediments deposited in the interior plains from this era are currently buried deep beneath the surface where they are difficult to study. [6]
Around 220 MYA, the supercontinent Pangea broke apart, and the North American continent began to move west and isolate itself. For much of this period the interior plains were covered by inland seas. [7] During the Jurassic period, the Sundance Sea formed along the western coast of the North American continent and extended from northern Canada to the interior plains, covering parts of Wyoming, Montana, North Dakota, and South Dakota. Coquina and sandstone layers from marine deposition were deposited on top of rock layers from the Paleozoic Era. [8] During the Cretaceous period, another inland sea called the Western Interior Seaway was formed. This body of water extended from present-day Alaska to the Gulf of Mexico and covered almost all the interior plains west of the current boundary of the Mississippi River. Limestone-shale couplets, as well as carbonate layers, are commonly found in sedimentary deposits from this inland sea. [9] Towards the end of this period, the inland seas began to drain due to uplift from the formation of the Rocky Mountains. [7]
The Laramide Orogeny event was when the western Cordillera was formed due to the flat-slab subduction of the Farallon Plate under the North American Plate. This created the frontal range of the Rockies from Montana through New Mexico. The outcrops seen at the surface of the Rockies are made up of sandstone, granite, and limestone; as well as metamorphic rocks uplifted from the Proterozoic Period. The interior plains have remained relatively flat during this period and recent sedimentation is from erosion of the newly formed Rocky Mountains as well as continued erosion from Appalachia. In general, Rocky Mountain sediment is deposited on the plains west of the Mississippi River, and Appalachian sediment is deposited to the east of the Mississippi River. [10]
2.6 million years ago at the start of the Pleistocene Epoch, the Laurentide Ice Sheet began to spread southwards to cover North America down to the northern Great Plains on the western side of the Interior Plains and down into most of Minnesota and Wisconsin. [11] The Laurentide Ice Sheet had a large influence on the morphology of the Interior Plains during the end of the Pleistocene. During the retreat, the Laurentide scoured numerous pockets of sediment. Upon the plate's melting, those pockets were filled, resulting in the kettle lakes. The Great Lakes [12] and both Great Slave Lake and Great Bear Lake [13] of Canada were formed by the Laurentide. During the retreat, the Laurentide gouged and filled the glacial paleolake McConnell in northern Canada. [14] As the region uplifted and rebounded isostatically from the mass of the ice sheet, paleolake McConnell was split into Great Slave Lake and Great Bear Lake. Great Slave Lake's basin formed under the 4-kilometer thick Keewatin Dome that today is the deepest lake in North America. [15] A vast amount of smaller lakes were formed as well and serve an integral part of ethos in the surrounding regions. For example, Minnesota is often referred to as “the Land of 10,000 Lakes” [16] due to the number and widespread recreational use of the state's lakes.
Much of the loess distributed within the Interior Plains has its origin in glaciers. In glaciated conditions, sand and silt-laden meltwater originating from alpine glaciers in the Rocky Mountains generated alluvial deposits at their base. This alluvium was then distributed throughout the Interior Plains by strong winds. [11]
Sediment transport within the Interior Plains occurs primarily by aeolian and fluvial processes. [17] Due to climate change, the average temperature of the Interior Plains is increasing and the region is becoming more arid. Because of the increase in rainstorm intensity, rain-driven erosion will grow as a factor of soil erosion in the Interior Plains. [18]
Civil engineering projects have altered the fluvial geomorphology of the Interior Plains. Normal sediment transport by river and channel systems is interrupted by river-blocking structures such as dams and flow regulators. Before 1900, the estimated annual sediment transport by the Mississippi River to the Gulf of Mexico was 400 million tons. [19] However, in the early 20th century, engineering projects including dams were created on the Missouri River, meander cutoffs, river training, bank revetments, and soil erosion control have reduced the annual transport rate to between 100 and 150 million tons of sediment per year. The artificial structures trap suspended sediment from traveling as it would in an un-engineered river. [17]
While average annual temperatures vary significantly between the northern and southern portions of the Interior Plains, the climate is characterized by susceptibility to droughts due to generally low annual precipitation. [20]
Due to a warm climate and evapotranspiration rates surpassing precipitation rates, [20] the southern Interior Plains are highly susceptible to droughts and soil erosion. A significant feature of aeolian erosion in the Interior Plains is the ubiquitous loess deposits. The deposits were placed by winds during the Pleistocene epoch. [21] The Nebraska Sand Dunes are an example of the sand and loess during the epoch. [22] These dunes were formed during the Pleistocene by Northwesterly winds depositing alluvial silt and sand. That loess is so prevalent in the Interior Plains is evidence of significant aeolian erosion, as deposits are generally accumulations of wind-blown dust. [23]
Following World War I, wheat farming in the fertile loess soil of the Interior Plains swelled. The expansion of farmland eliminated many prairies containing soil-stabilizing grasses. [24] While droughts in the region were common, [20] during the following drought, aeolian soil erosion was exacerbated by the reduced soil-holding prairie grasses. Dust storms eroded hundreds of millions of tons of topsoil, causing dust storms for months in the historical region known as the Dust Bowl. On May 12, 1934, alone, an estimated 200 million tons of wind-eroded topsoil were transported to the Atlantic Ocean. [24]
In response to the rapid aeolian erosion, soil preservation methods were implemented. In the years following the Dust Bowl, 18,500 miles (29,800 km) of shelterbelt were planted by the Works Progress Administration to reduce wind intensity. [25]
Grassland and shrubland make up the largest portion of the Interior Plains within the United States, at 44.4 percent. [26] The western margin is mainly shortgrass prairie dominated by blue grama and buffalograss. Prairies on the eastern side of the Interior Plains are dominated by tall grass varieties including big bluestem and switchgrass. The two regions are separated by mixed-grass prairie, which contains both short and long grass varieties as well as little bluestem and western wheatgrass. [27] Land used for cattle-grazing is included under this classification, which sustains nearly 50 percent of all United States beef cattle. [28]
In Canada, provinces located within the Interior Plains produce nearly 60 percent of all beef cattle. [28]
Much of the land in the Interior Plains is used for agriculture. In the year 2000, 43.8 percent of the Great Plains portion of the Interior Plains were used for agriculture. [26] By far, wheat comprises the largest portion of the agricultural yield in region; combined, wheat exports from the Interior Plains make up more than half of the world's exports. [28] Other significant crops produced in the region include barley, corn, cotton, sorghum, soybeans, and canola, which is particularly important to Canadian exports. [28]
Other sources comprise much smaller portions of the land. In decreasing percentage, forests make up 5.8%, wetland makes up 1.6%, developed land makes up 1.5%, barren land makes up .6%, and land used for mining makes up .1%. [26]
The Interior Plains physiographic area stretches across Canada and the United States, and the two governments each use a different hierarchical system to classify their portions. In Canada, the Interior Plains makes up one of seven physiographic areas included in the highest level of classification - defined as a "region" in that country. In the United States it is one of eight physiographic areas (of the contiguous 48 states) included in the highest classification, defined as a "division" there. [29] [30]
The Interior Plains of Canada are one of seven physiographic areas included in the highest level classification in that country. That country calls this primary classification level "region." For some of the seven regions, a subregion schema is provided. For other physiographic regions (such as the Interior Plains and Appalachian Uplands) subregions are not developed, but the tertiary level (called "division" in Canada) is used in the mapping data. [31]
The following list is of the 14 physiographic divisions in the Interior Plains of Canada. Further information can be found at https://atlas.gc.ca/phys/en/index.html
The following is a breakdown of the secondary (provinces), and tertiary (sections) physiographic areas of the Interior Plains portion in the United States: [32]
In geography, a plain, commonly known as flatland, is a flat expanse of land that generally does not change much in elevation, and is primarily treeless. Plains occur as lowlands along valleys or at the base of mountains, as coastal plains, and as plateaus or uplands. Plains are one of the major landforms on earth, being present on all continents and covering more than one-third of the world's land area. Plains in many areas are important for agriculture. There are various types of plains and biomes on them.
The Great Plains are a broad expanse of flatland in North America. The region is located just to the east of the Rocky Mountains, much of it covered in prairie, steppe, and grassland. They are the western part of the Interior Plains, which include the mixed grass prairie, the tallgrass prairie between the Great Lakes and Appalachian Plateau, and the Taiga Plains and Boreal Plains ecozones in Northern Canada. "Great Plains" or Western Plains also describe the ecoregion of the Great Plains, or alternatively the western portion of the Great Plains.
Prairies are ecosystems considered part of the temperate grasslands, savannas, and shrublands biome by ecologists, based on similar temperate climates, moderate rainfall, and a composition of grasses, herbs, and shrubs, rather than trees, as the dominant vegetation type. Temperate grassland regions include the Pampas of Argentina, Brazil and Uruguay, and the steppe of Ukraine, Russia, and Kazakhstan. Lands typically referred to as "prairie" tend to be in North America. The term encompasses the area referred to as the Interior Lowlands of Canada, the United States, and Mexico, which includes all of the Great Plains as well as the wetter, hillier land to the east.
The Appalachian Mountains, often called the Appalachians, are a mountain range in eastern to northeastern North America. The term "Appalachian" refers to several different regions associated with the mountain range, and its surrounding terrain. The general definition used is one followed by the United States Geological Survey and the Geological Survey of Canada to describe the respective countries' physiographic regions. The U.S. uses the term Appalachian Highlands and Canada uses the term Appalachian Uplands; the Appalachian Mountains are not synonymous with the Appalachian Plateau, which is one of the provinces of the Appalachian Highlands.
The geology of the Appalachians dates back more than 1.2 billion years to the Mesoproterozoic era when two continental cratons collided to form the supercontinent Rodinia, 500 million years prior to the development of the range during the formation of Pangea. The rocks exposed in today's Appalachian Mountains reveal elongate belts of folded and thrust faulted marine sedimentary rocks, volcanic rocks, and slivers of ancient ocean floor—strong evidences that these rocks were deformed during plate collision. The birth of the Appalachian ranges marks the first of several mountain building plate collisions that culminated in the construction of Pangea with the Appalachians and neighboring Anti-Atlas mountains near the center. These mountain ranges likely once reached elevations similar to those of the Alps and the Rocky Mountains before they were eroded.
A loess is a clastic, predominantly silt-sized sediment that is formed by the accumulation of wind-blown dust. Ten percent of Earth's land area is covered by loesses or similar deposits.
Crowley's Ridge is a geological formation that rises 250 to 550 feet (170 m) above the alluvial plain of the Mississippi embayment in a 150-mile (240 km) line from southeastern Missouri to the Mississippi River near Helena, Arkansas. It is the most prominent feature in the Mississippi Alluvial Plain between Cape Girardeau, Missouri, and the Gulf of Mexico.
The richly textured landscape of the United States is a product of the dueling forces of plate tectonics, weathering and erosion. Over the 4.5 billion-year history of the Earth, tectonic upheavals and colliding plates have raised great mountain ranges while the forces of erosion and weathering worked to tear them down. Even after many millions of years, records of Earth's great upheavals remain imprinted as textural variations and surface patterns that define distinctive landscapes or provinces.
Aeolian processes, also spelled eolian, pertain to wind activity in the study of geology and weather and specifically to the wind's ability to shape the surface of the Earth. Winds may erode, transport, and deposit materials and are effective agents in regions with sparse vegetation, a lack of soil moisture and a large supply of unconsolidated sediments. Although water is a much more powerful eroding force than wind, aeolian processes are important in arid environments such as deserts.
The Dissected Till Plains are physiographic sections of the Central Lowlands province, which in turn is part of the Interior Plains physiographic division of the United States, located in southern and western Iowa, northeastern Kansas, the southwestern corner of Minnesota, northern Missouri, eastern Nebraska, and southeastern South Dakota.
The Loess Hills are a formation of wind-deposited loess soil in the westernmost parts of Iowa and Missouri, and the easternmost parts of Nebraska and Kansas, along the Missouri River.
North America is the third largest continent, and is also a portion of the third largest supercontinent if North and South America are combined into the Americas and Africa, Europe, and Asia are considered to be part of one supercontinent called Afro-Eurasia. With an estimated population of 580 million and an area of 24,709,000 km2 (9,540,000 mi2), the northernmost of the two continents of the Western Hemisphere is bounded by the Pacific Ocean on the west; the Atlantic Ocean on the east; the Caribbean Sea on the south; and the Arctic Ocean on the north.
The U.S. state of Georgia is commonly divided into four geologic regions that influence the location of the state's four traditional physiographic regions. The four geologic regions include the Appalachian foreland, Blue Ridge, Piedmont, and Coastal Plain. These four geologic regions commonly share names with and typically overlap the four physiographic regions of the state: the Appalachian Plateau and adjacent Valley and Ridge; the Blue Ridge; the Piedmont and the Coastal Plain.
The geology of Kansas encompasses the geologic history and the presently exposed rock and soil. Rock that crops out in the US state of Kansas was formed during the Phanerozoic eon, which consists of three geologic eras: the Paleozoic, Mesozoic and Cenozoic. Paleozoic rocks at the surface in Kansas are primarily from the Mississippian, Pennsylvanian, and Permian periods.
The geology of Saskatchewan can be divided into two main geological regions, the Precambrian Canadian Shield and the Phanerozoic Western Canadian Sedimentary Basin. Within the Precambrian shield exists the Athabasca sedimentary basin. Meteorite impacts have altered the natural geological formation processes. The prairies were most recently affected by glacial events in the Quaternary period.
New England is a region in the North Eastern United States consisting of the states Rhode Island, Connecticut, Massachusetts, New Hampshire, Vermont, and Maine. Most of New England consists geologically of volcanic island arcs that accreted onto the eastern edge of the Laurentian Craton in prehistoric times. Much of the bedrock found in New England is heavily metamorphosed due to the numerous mountain building events that occurred in the region. These events culminated in the formation of Pangaea; the coastline as it exists today was created by rifting during the Jurassic and Cretaceous periods. The most recent rock layers are glacial conglomerates.
The geology of North America is a subject of regional geology and covers the North American continent, the third-largest in the world. Geologic units and processes are investigated on a large scale to reach a synthesized picture of the geological development of the continent.
The Mississippi Alluvial Plain is a Level III ecoregion designated by the Environmental Protection Agency (EPA) in seven U.S. states, though predominantly in Arkansas, Louisiana, and Mississippi. It parallels the Mississippi River from the Midwestern United States to the Gulf of Mexico.
The Chinese Loess Plateau, or simply the Loess Plateau, is a plateau in north-central China formed of loess, a clastic silt-like sediment formed by the accumulation of wind-blown dust. It is located southeast of the Gobi Desert and is surrounded by the Yellow River. It includes parts of the Chinese provinces of Qinghai, Gansu, Shaanxi and Shanxi. The depositional setting of the Chinese Loess Plateau was shaped by the tectonic movement in the Neogene period, after which strong southeast winds caused by the East Asian Monsoon transported sediment to the plateau during the Quaternary period. The three main morphological types in the Loess Plateau are loess platforms, ridges and hills, formed by the deposition and erosion of loess. Most of the loess comes from the Gobi Desert and other nearby deserts. The sediments were transported to the Loess Plateau during interglacial periods by southeasterly prevailing winds and winter monsoon winds. After the deposition of sediments on the plateau, they were gradually compacted to form loess under the arid climate.
Interior Plains