Minnesota

Introduction The state of Minnesota was named after the river that runs across the state and flows into the Mississippi. Native Americans (Dakota) who lived along the river called it the "minnesota" from the words "minne" (water) and "sota" (smoke) meaning whitish water. Over the years, the official interpretation and translation of the name has come to be "sky-tinted water" due to the appearance of the water resembling a clouded sky. Note: since Native Americans north of the Rio Grande (Mexico) didn't have a system of written language, many spelling variations exist as Euro-Americans tried to interpret, translate, and write their words. There are four geographic topics with highlights about Minnesota which help explain its particular geologic and human history. Location and terrain Lakes and rivers Rocks and minerals Ecology The rest of this page will describe these topics. Many of the pictures can be seen in a larger format by clicking on the image.

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Location and Terrain Minnesota is located near the center of the North American continent - a low relief area about midway between the two major mountain ranges of the Rockies and Appalachians. North America (120 kbytes) Topographic relief (55 kbytes) In Minnesota's geologic past, there were three times (about 2.7, 1.8, and 1.1 billion years ago) when the land was mountainous and volcanic. As the North American continent formed beyond its "Canadian" core, "Minnesota" assumed its more central location and the land became relatively stable and quiet with no major volcanic, earthquake, or land building activity. For about the last billion years or more wind, water, and ice (glaciers) have eroded, leveled, and altered the land to its present topography. The Appalachians which formed about 225 million years ago (climax), and the Rockies (formed about 65 million years ago) still exist due to their relatively young age. The highest point in Minnesota is Eagle Mountain (701 m / 2301 ft) located in the Sawtooth Mountains north of Lake Superior (see Minnesota map). The lowest point is Lake Superior (183 m / 602 ft). The rest of the state doesn't vary much and averages 340 m (1200 ft). The latitude of Minnesota extends from 43.5° to 49.45° N - a distance of 653 km (406 mi). The longitude extends from 95.35° W (w. border) eastward along the northern border for a distance of about 575 km (357 mi). For most of Minnesota's geologic history in the last billion years, the land was on or near the equator and sometimes surrounded by tropical seas as they periodically advanced and receded. About 280 million years ago, a landmass (Pangea) that included "Minnesota" started drifting north and then split a couple times (about 170 and 120 million years ago) forming North America as a result. North America is continuing to drift at a rate of a few centimeters per year (mostly west relative to Europe).

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Lakes and Rivers About 5.7 % of Minnesota's 217735 sq. km (84068 sq. mi) area is inland water (excluding Lake Superior). This inland water includes many streams, rivers, and more than 15000 lakes (at least 11800 greater than 10 acres). Historically, three of the most important bodies of water have been: Minnesota (41 kbytes) Lake Superior - the largest fresh-water lake in the world (surface area) and the chain of lakes and rivers along Minnesota's northern border. Mississippi River - the largest river basin system in North America (3rd in world) with its source in north-central Minnesota and two of its tributaries - the Minnesota river and the St. Croix. Red River of the North - and its wide valley is one of the most fertile farm lands (e. g. spring wheat) in the world due to its history of once being the bed of the ancient Glacial Lake Agassiz (see below).

Lakes and rivers have always been important to support life for Native Americans since some of the last glacial ice started receding from "Minnesota" about 12000 years ago. Wild rice, the only native cereal in North America, has been harvested from northern lakes for at least 1300 years. Note: corn (maize) is American but is a cultivated hybrid. In the 17th century, the two primary tribal groups were the Dakota and the Anishinabe (Ojibwe) who had started moving toward the northern part of "Minnesota" in the early 17th century from the east side of Lake Superior. The population in the mid 17th century was perhaps 10000 to 15000 but not well known.  The first known non-native visitors to "Minnesota" were French-speaking people from France and eastern "Canada" who Fur trade (83 kbytes) initially explored inland areas from Lake Superior (ca. 1655) and canoed along northern lake / river routes primarilly for two reasons - both economic. One reason was to find the "Northwest Passage" - an all water route through North America to establish trade with Asia. The other was to obtain and transport furs (mostly beaver - initially) which were plentyful in "Minnesota" and were highly valued in European fashions during the 17th and 18th centuries. When Minnesota was named as a US territory in 1849 (which included land as far west as the Missouri River), there was a Euro-American population explosion from less than 5000 in 1849 to about 150000 in 1857. Rivers became an important source of transportation and power for the primary industries of lumber, wheat, milling, and iron ore. The present borders of Minnesota were established when it became a state in 1858 and were based to a large extent on natural river and lake boundries. The population in 1860 was about 172000.

All of the water in Minnesota's river system flows out of the state in three general directions from eight major river basins. No water flows into the state. A three-way divide is located in the northeast near the center of the Mesabi iron range (Hibbing). three-way divide    (20 kbytes)    North - Water from the Rainy River and the Red River of the North basins flow north from the Laurentian continental divide (blue line) to Lake Winnipeg, the Nelson River, Hudson Bay, and on to the Arctic and Atlantic Oceans. South - Water from the Mississippi River and its tributary basins flow south from the Laurentian continental divide (blue line) to the Gulf of Mexico. East - Water from the Great Lakes basin flow east to the Great Lakes, St. Lawrence River, and on to the Atlantic Ocean.

Most of the many lakes and rivers in Minnesota and southern Ontario were created after the most recent glaciers (up to 3000 m thick) in the Wisconsin glaciation period started receding about 13000 years ago until about 11000 years ago when most of the ice had disappeared from the state. Wisconsin glaciation (maximun extent) The maximum southern extention of the glacier (called the Laurentide Ice Sheet) in this area was a lobe into central Iowa but the southeast and southwest corners of Minnesota were not covered.  As the glacier melted, a huge lake was created called Glacial Lake Agassiz (after Louis Agassiz 1807-1873 Swiss-American naturalist). A large river also formed from the southern arm of the lake called the Glacial River Warren (after G. K. Warren 1830-1882 military topographical engineer). Glacial Lake Agassiz (maximum extent) The Glacial River Warren carved out a wide valley which later became the much smaller Minnesota River. A few other much smaller glacial lakes were also created in the area including Glacial Lake Duluth which later became Lake Superior. As seen on the map, there are still remnant lakes from Glacial Lake Agassiz which was mostly drained from "Minnesota" by about 9000 years ago and from "Canada" about 7500 years ago. The Wisconsin glaciation period started about 75000 years ago. There were also earlier glaciation periods starting about 2 million years ago in the latest ice age and even a few earlier ice ages but most of the topography in Minnesota today is due to the Wisconsin period. Some of the effects of the glacier, lake, and river can be seen on the relief map above.

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Rocks and Minerals Minnesota contains rock that is among the oldest found in the world - at least 3.6 billion years old. The state also contains one of the largest concentrations of iron-ore deposits in the world and is famous for its Lake Superior Agates. The geologic history of Minnesota starts with the earliest aspects of the formation of North America and includes 6 major events and processes related to local rocks and minerals - the formation of the Canadian Shield, iron-formations, Penokean mountain-building, erosion, the Keweenawan (mid-continental) rift, and sedimentation from surrounding seas.

The oldest exposed part of the North American continent is a core landmass called the Canadian Shield. Canadian Shield About 2.7 billion years ago, large-scale volcanic activity started building this land in the ocean and then above sea level, a total thickness of at least 10000 m, to create mountains which quickly started to erode. Within a few million years, subsequent foldings of rock layers and intrusions of different rock types created a mountainous environment with peaks and valleys of several km each including bands of a basaltic based rock called greenstone due to large percentages of green minerals. Some of the rock that was incorporated into the shield included small pockets of granitic gneiss formed in an earlier time from an unknown (but perhaps North American basement rock) landmass. This gneiss has been dated at least 3.6 billion years in the Minnesota River Valley area and at least 4.0 billion years in the northern Great Slav Lake area in northwest Canada. The Canadian Shield has generally been the high ground of North America, usually above sea level as seas periodically advanced and receded.

North America can very generally be divided up into 5 geomorphic regions according to a chronological development history. Minnesota lies on the border between the Canadian Shield and a second region of central plains and lowlands. Geomorphic regions Region 2 was formed as a result of eroding rock from the Canadian Shield being carried by water, gravity, ice, and wind and deposited on an existing platform of continental rock. Another land altering process ongoing was periodic splits and "welds" of proto-North America with smaller landmasses called microcontinents.  About 2.1 billion years ago, the area around the present Lake Superior was below sea level in shallow waters which had filled a large east-west subsided zone called the Animikie Basin. Iron Ranges (17 kbytes) After about 100 meters of sandstone had been deposited, iron-formation precipitation and sedimentation began probably due to an increase in atmospheric (and shallow sea) oxygen levels. Over time (depending on the area), circulating waters oxidized and concentrated the iron-formations to create a natural iron ore. From 1844 to 1904 iron ore deposits were discovered and started as mining operations which soon became the primary US production area (ca. 90 %). The largest mine is the Mesabi Range in northeast Minnesota where a high grade ore was discovered in 1890. Through 1977, about 58 % of all US iron ore production came from the Mesabi mine. After the late 1940's, a low grade ore called taconite started to be mined and processed as the higher grade ores started to diminish.  Another event occuring in Early Proterozoic time (starting about 1.9 billion years ago), was the formation of the Penokean Mountains. Geomorphic regions and Provinces Note: for a general review of geologic time and terminology, see the Geological Time Scale. The Penokean Mountains were formed as a result of the convergence of the Canadian Shield with a smaller "microcontinent" landmass in an area perhaps extending from present South Dakota or beyond to near Lake Huron. The extent is not well known because most of the mountains have eroded away but once they were similar in height to the present Rocky Mountains. As in other continental convergences, volcanic activity and land uplifting with folding were involved in the mountain building period. About 1.1 billion years ago during Middle Proterozoic time, after the Penokean Mountains had eroded down, the proto-North American continent nearly split in half along a zone called the Keewenawan Rift. The area affected extended from present Kansas through the Lake Superior area to about Lake Erie and is the largest known continental rift in the world. The rift started as a "hot spot" of basaltic magma below the Lake Superior region and ended up extruding layers of lava up to about 20 km thick and sometimes extending at least 100 km on either side of the main rift zone. The continent probably would have split completely but about this time, proto-North America was converging with another "microcontinent" (Grenville Province) in the east which applied some compressional forces to the rift. Lake Superior Agates common along the north shore, were created after the volcanic activity subsided and formed inside lava cavities (left from gas bubbles) after the lava had mostly cooled. Silica and small amounts of iron oxides were transported to the cavities by warm waters and deposited in layers of varying iron concentrations. After the surrounding lava weathered away, individual agates remained. The Keewenawan Rift event was the last of any volcanic or mountain building activity in present Minnesota. Sagging, tilting, and faulting of lava flows did however create a basin of up to 5000 m deep along the rift zone which soon started to be filled with eroding sediments carried from rivers in the surrounding highlands. The first proto-Lake Superior was created in the basin during this time. The next phase of rock formation occurred long after the rifting event. About 550 million years ago during the Cambrian period, the proto-North American continant started subsiding enough that oceans advanced inland to the extent that present southeast Minnesota was a shoreline. Periodic advances and recessions also occured in later periods up to the late Cretaceous period (ending 65 million years ago). Each advance left sedimentary deposits of differing compositions including the sandstones, shales, and limestones found in southern Minnesota. Fossils are common in these sedimentary rocks. The shallow sea which covered Minnesota and the adjoining region contained a variety of marine organisms including corals, bryozoans, brachiopods, clams, snails, cephalopods, trilobites, and various plants. During the Permian, Triassic, and Jurassic periods, "Minnesota" was mostly above sea level and no rocks were formed. As a result, no fossils exist from life at that time (e.g. dinosaurs). Some Cretaceous fossils have been found (e.g. crocodile and shark remains) but any non-marine vertebrate fossils have not been discovered.  exposed bedrock       The rocks described above constitute the bedrock of Minnesota. bedrock   (29 kbytes)   The distribution can be seen on the bedrock map of the state but actually most of these rocks are covered by sediments up to 150 m thick left by glaciers. Direct observation of Minnesota bedrock is mostly limited to the northeast and southeast corners of the state and along parts of the Minnesota River. The southeast is exposed because parts were not covered by glaciers in the Wisconsin glacial period and perhaps not in earlier periods either. This area along with corners of Iowa, Illinois, and a larger area in southwest Wisconsin is known as the "driftless area". Places along the Minnesota River are exposed because of erosion from the river and the earlier Glacial River Warren. The northeast is exposed because glaciers there were eroding more and depositing less than in other areas.

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Ecology The US has been divided up into a system of hierarchcical regions based on similar ecologies. Regions are established by integrating climatic, geologic, hydrologic, topographic, soil, and vegetation data. The most general regions are called domains and are further subdivided into divisions, provinces, and more specific units. Provinces Within the 48 contiguous states, 3 of the 4 global domains are present and are grouped into 11 divisions and 34 provinces. Three divisions converge in Minnesota - Warm Continental, Hot Continental, and Prairie. Three divisions in one non mountainous state is unusual and indicates the diversity of Minnesota's ecology. In Minnesota, there are three provinces (same boundries as for the 3 divisions in this state) - Laurentian Mixed Forest Eastern Broadleaf Forest (Continental) Prairie Parkland (Temperate) Maps and descriptions of Minnesota's regions are on divisions and provinces pages. pre-settlement ecology   Some aspects of the ecology of Minnesota were different before 19th century settlement. The biggest differences are fewer trees and less wetlands today mostly due to land conversion for ecomomic purposes. Wetlands were drained, prairies plowed, forests logged, and habitat and food chain systems dramatically altered. The central band of hardwood trees used to be known as the "Big Woods" but now the number of trees is considerably less.   Minnesota's climate varies across the state - both north to south and east to west. The climate page contains maps for statewide variations in temperature, precipitation, and growing season.   More detailed information about the climate in Minneapolis / St. Paul can be seen in the following charts. Charts Temperature & Sunshine - US or metric Precipitation & Snow - US or metric Dew Point & Wind Speed - US or metric ^ Top