The geography of Iowa includes the study of bedrock, landforms, rivers, geology, paleontology and urbanisation of the
U.S. state
In the United States, a state is a constituent political entity, of which there are 50. Bound together in a political union, each state holds governmental jurisdiction over a separate and defined geographic territory where it shares its sove ...
of
Iowa
Iowa () is a state in the Midwestern region of the United States, bordered by the Mississippi River to the east and the Missouri River and Big Sioux River to the west. It is bordered by six states: Wisconsin to the northeast, Illinois to th ...
. The state covers an area of 56,272.81 sq mi (145,746 km
2).
Bedrock features
Iowa's bedrock geology generally increases in age from west to east. In northwest Iowa
Cretaceous
The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...
bedrock is ca. 74 million years old, in eastern Iowa
Cambrian bedrock dates to ca. 500 million years ago.
Meteor impact structures
Manson impact structure
Seventy-four million years ago, a large asteroid crashed into what is now southeast
Pocahontas county creating the
Manson crater. Nearly 22 miles in diameter,
it would have killed most animals within 650 miles, roughly an area from modern Denver to Detroit. This was originally thought to have been one of the causes of the
dinosaur
Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...
extinction, but recalculation of the impact's age indicates it occurred some 12 million years before the mass extinction. Although
glaciation
A glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age that is marked by colder temperatures and glacier advances. Interglacials, on the other hand, are periods of warmer climate be ...
has erased all surface evidence of the impact, the bedrock associated with this impact is unique in Iowa.
Decorah crater
A much older meteorite strike created the
Decorah crater during the
Middle Ordovician
The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya.
Th ...
Period, 470 million years ago. The crater is estimated to be 3.5 miles (5.6 km) in diameter, covered by Winneshiek Shale.
There is no surface evidence of the impact, as the Winneshiek Shale is more than 50 feet below the bottom of the
Upper Iowa River
The Upper Iowa River is a U.S. Geological Survey. National Hydrography Dataset high-resolution flowline dataThe National Map, accessed May 13, 2011 tributary of the Mississippi River in the upper Midwest of the United States.
Its headwaters rise ...
. The impact, equivalent to
1,000 megatons of TNT,
did not appear to penetrate the Earth's mantle, but it did push down the underlying Ordovician and Cambrian bedrock several hundred feet. It may be one of several Middle Ordovician meteors that fell roughly simultaneously 469 million years ago, part of a proposed
Ordovician meteor event
The Ordovician meteor event was a dramatic increase in the rate at which L chondrite meteorites fell to Earth during the Middle Ordovician period, about 467.5±0.28 million years ago. This is indicated by abundant fossil L chondrite meteorites in ...
.
Midcontinent rift
Buried deeply within Iowa's bedrock, the
Midcontinent Rift System
The Midcontinent Rift System (MRS) or Keweenawan Rift is a long geological rift in the center of the North American continent and south-central part of the North American plate. It formed when the continent's core, the North American craton, ...
can be seen clearly in magnetic anomaly maps of Iowa. This is a billion-year-old tectonic plate scar that extends from Kansas through
Lake Superior
Lake Superior in central North America is the largest freshwater lake in the world by surface areaThe Caspian Sea is the largest lake, but is saline, not freshwater. and the third-largest by volume, holding 10% of the world's surface fresh wa ...
. This rift is not seismically active.
Seismic activity
No major active
fault lines exist in Iowa, and Iowa is one of the most
seismic
Seismology (; from Ancient Greek σεισμός (''seismós'') meaning "earthquake" and -λογία (''-logía'') meaning "study of") is the scientific study of earthquakes and the propagation of elastic waves through the Earth or through other ...
ally stable states in the U.S. With the exception of the
1968 Illinois earthquake which caused the water tower at
Lineville to leak, no injuries or significant damage has ever been caused by
earthquake
An earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can range in intensity, fr ...
s in Iowa. Occasional small earthquakes occur near
Fremont County in the far southwest, and the
Sioux City
Sioux City () is a city in Woodbury and Plymouth counties in the northwestern part of the U.S. state of Iowa. The population was 85,797 in the 2020 census, making it the fourth-largest city in Iowa. The bulk of the city is in Woodbury County ...
area can occasionally be shaken by nearby tremblors. Large earthquakes associated with the
New Madrid Fault of far southern Illinois and Missouri can occasionally be felt in eastern Iowa. Recent earthquakes centered in Oklahoma have also been felt in Iowa, but have caused no damage.
Fossil fuels
Historically, Iowa was a significant
coal
Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen.
Coal is formed when ...
producer, particularly the
Des Moines River
The Des Moines River () is a tributary of the Mississippi River in the upper Midwestern United States that is approximately long from its farther headwaters.U.S. Geological Survey. National Hydrography Dataset high-resolution flowline dataThe Na ...
valley from
Coalville
Coalville is an industrial town in the district of North West Leicestershire, Leicestershire in the East Midlands of England, with a population at the 2011 census of 34,575. It lies on the A511 trunk road between Leicester and Burton upon Tr ...
south. Much of the greater City of
Des Moines area was mined.
Boone and
What Cheer were important in the late 19th century. In the 20th century, the most important mines were farther south around
Albia,
Centerville,
Lucas and
Oskaloosa. Iowa coal tends to be too high in
sulfur for modern applications, and the last commercial mine closed in 1994.
Iowa has very limited
natural gas
Natural gas (also called fossil gas or simply gas) is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane in addition to various smaller amounts of other higher alkanes. Low levels of trace gases like carbo ...
and
oil
An oil is any nonpolar chemical substance that is composed primarily of hydrocarbons and is hydrophobic (does not mix with water) & lipophilic (mixes with other oils). Oils are usually flammable and surface active. Most oils are unsaturated ...
production.
Sioux quartzite
Although Iowa's bedrock is generally younger in western parts of the state, one exception is a small part of far northwest Iowa where
Precambrian Sioux quartzite bedrock is found in northwest
Lyon County. Sioux
quartzite
Quartzite is a hard, non- foliated metamorphic rock which was originally pure quartz sandstone.Essentials of Geology, 3rd Edition, Stephen Marshak, p 182 Sandstone is converted into quartzite through heating and pressure usually related to tec ...
is a very hard rock of ruddy pink color used extensively in the region for road and railroad beds. Sioux quartzite has been dated to have been laid between 1.64 and 1.76 billion years ago.
Geodes
Geode
A geode (; ) is a geological secondary formation within sedimentary and volcanic rocks. Geodes are hollow, vaguely spherical rocks, in which masses of mineral matter (which may include crystals) are secluded. The crystals are formed by the fill ...
s are found in southeast Iowa and are the official state rock. They consist of grey to pink cobbles within
limestone
Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...
that when cut or smashed open reveal a hollow crystal-filled interior. Geodes are common around
Geode State Park in
Henry County.
Landforms and topography
Despite popular perception, Iowa is generally not flat; most of the state consists of rolling hills. Prior divides Iowa into eight
landforms based on
glaciation
A glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age that is marked by colder temperatures and glacier advances. Interglacials, on the other hand, are periods of warmer climate be ...
,
soil
Soil, also commonly referred to as earth or dirt
Dirt is an unclean matter, especially when in contact with a person's clothes, skin, or possessions. In such cases, they are said to become dirty.
Common types of dirt include:
* Debri ...
s,
topography
Topography is the study of the forms and features of land surfaces. The topography of an area may refer to the land forms and features themselves, or a description or depiction in maps.
Topography is a field of geoscience and planetary sc ...
, and
river
A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and becomes dry at the end of its course without reaching another body of w ...
drainage:
Paleozoic plateau
Also known as the
Driftless Area
The Driftless Area, a topographical and cultural region in the American Midwest, comprises southwestern Wisconsin, southeastern Minnesota, northeastern Iowa, and the extreme northwestern corner of Illinois.
Never covered by ice during the las ...
, this region of scenic, high relief landscapes includes such features as resistant, bluff-forming bedrock
outcrop
An outcrop or rocky outcrop is a visible exposure of bedrock or ancient superficial deposits on the surface of the Earth.
Features
Outcrops do not cover the majority of the Earth's land surface because in most places the bedrock or superficia ...
s, deep V-shaped valleys, caves, springs, and
sinkhole
A sinkhole is a depression or hole in the ground caused by some form of collapse of the surface layer. The term is sometimes used to refer to doline, enclosed depressions that are locally also known as ''vrtače'' and shakeholes, and to openi ...
s. Glacial deposits and
loess are thin or absent over most of the region.
Des Moines lobe
Often called the
Prairie Pothole Region
The Prairie Pothole Region (PPR; french: Région des cuvettes/fondrières des prairies) is an expansive area of the northern Great Plains that contains thousands of shallow wetlands known as potholes. These potholes are the result of glacier ac ...
, the Des Moines Lobe was glaciated up until 12,000 years ago during the
Wisconsin glaciation
The Wisconsin Glacial Episode, also called the Wisconsin glaciation, was the most recent glacial period of the North American ice sheet complex. This advance included the Cordilleran Ice Sheet, which nucleated in the northern North American Cord ...
. The area is marked by rolling terrain and ridges. Historically, this area was peppered with small interconnected swamps, most of which were drained for farmland. The
Iowa Great Lakes
The Iowa Great Lakes, often referred to as ''Okoboji'', is a group of natural lakes in northwestern Iowa in the United States. There are seven lakes in the region totaling with the three principal lakes of the group being Big Spirit Lake, West O ...
occur along the western edge of the Des Moines lobe.
Southern Iowa drift plain
The southern Iowa drift plain covers most of the southern half of Iowa. This is probably the most familiar landscape to travelers, since most of
Interstate 80 in Iowa runs through the SIDP. The classic Iowa landscape, consisting of rolling hills of Wisconsin-age loess on Illinoian (or earlier)
till
image:Geschiebemergel.JPG, Closeup of glacial till. Note that the larger grains (pebbles and gravel) in the till are completely surrounded by the matrix of finer material (silt and sand), and this characteristic, known as ''matrix support'', is d ...
. The SIDP is some of the most productive agricultural land in the world.
Mississippi alluvial plain
Generally level areas of stream terraces, paleochannels, backwater sloughs, and
oxbow lakes are found within the broad
Mississippi River
The Mississippi River is the second-longest river and chief river of the second-largest drainage system in North America, second only to the Hudson Bay drainage system. From its traditional source of Lake Itasca in northern Minnesota, it fl ...
valley.
Loess hills
The
Loess Hills
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.
Geology
The Loess (, , or ) Hills are generally located bet ...
consist of very thick deposits of loess in far western Iowa deposited during the Wisconsin and Illinoian periods. Highly eroded, leaving stark, beautiful "golden hills".
Iowan surface
Northeast Iowa is covered with eroded Pre-Illinoian till with moderate loess formation, frequently in the form of
paha ridges, muted relief except for steep rolling hills near river valleys, and deeper valleys. These picturesque hills are depicted in many of the landscapes of
Grant Wood.
Northwest Iowa plains
Like the Iowan Surface, the Northwest Iowa Plains are rolling hills consisting of eroded soils developed since pre-Wisconsinan glaciation, but with significant amounts of loess.
Missouri alluvial plain
Perhaps the only truly flat region of Iowa, the Missouri Alluvial Plain contains areas of terraces, sloughs, and oxbows. Its valley trench is not as deep as the Mississippi River system, and the
Missouri River is contained in a much narrower channel. In Iowa, the eastern border of the Missouri Plains is the Loess Hills, forming steep rounded bluffs.
Climate
Iowa has a
humid continental climate
A humid continental climate is a climatic region defined by Russo-German climatologist Wladimir Köppen in 1900, typified by four distinct seasons and large seasonal temperature differences, with warm to hot (and often humid) summers and freezing ...
throughout the state (
Köppen climate classification
The Köppen climate classification is one of the most widely used climate classification systems. It was first published by German-Russian climatologist Wladimir Köppen (1846–1940) in 1884, with several later modifications by Köppen, notabl ...
''Dfa'') with extremes of both heat and cold. The average annual temperature at Des Moines is ; for some locations in the north, such as Mason City, the figure is about , while
Keokuk, on the
Mississippi River
The Mississippi River is the second-longest river and chief river of the second-largest drainage system in North America, second only to the Hudson Bay drainage system. From its traditional source of Lake Itasca in northern Minnesota, it fl ...
, averages . Snowfall is common, with
Des Moines getting about 26 days of snowfall a year, and other places, such as
Shenandoah getting about 11 days of snowfall in a year.
Spring ushers in the beginning of the
severe weather
Severe weather is any dangerous meteorological phenomenon with the potential to cause damage, serious social disruption, or loss of human life. Types of severe weather phenomena vary, depending on the latitude, altitude, topography, and atmos ...
season. Iowa averages about 50 days of
thunderstorm
A thunderstorm, also known as an electrical storm or a lightning storm, is a storm characterized by the presence of lightning and its acoustic effect on the Earth's atmosphere, known as thunder. Relatively weak thunderstorms are some ...
activity per year.
[US Thunderstorm distribution](_blank)
src.noaa.gov. Retrieved February 13, 2008. The 30-year annual average of tornadoes in Iowa is 47.
In
2008
File:2008 Events Collage.png, From left, clockwise: Lehman Brothers went bankrupt following the Subprime mortgage crisis; Cyclone Nargis killed more than 138,000 in Myanmar; A scene from the opening ceremony of the 2008 Summer Olympics in Beijing; ...
, twelve people were killed by tornadoes in Iowa, making it the deadliest year since
1968
The year was highlighted by protests and other unrests that occurred worldwide.
Events January–February
* January 5 – " Prague Spring": Alexander Dubček is chosen as leader of the Communist Party of Czechoslovakia.
* Janu ...
and also the second most tornadoes in a year with 105, matching the total from 2001.
Iowa summers are known for heat and humidity, with daytime temperatures sometimes near and occasionally exceeding . Average winters in the state have been known to drop well below freezing, even dropping below . Iowa's all-time hottest temperature of was recorded at Keokuk on July 20, 1934, during a nationwide heat wave; the all-time lowest temperature of was recorded in
Washta on January 12, 1912.
Iowa has a relatively smooth gradient of varying
precipitation
In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravitational pull from clouds. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hail. ...
across the state, with areas in the southeast of the state receiving an average of over of rain annually, and the northwest of the state receiving less than . The pattern of precipitation across Iowa is seasonal, with more rain falling in the summer months. Virtually statewide, the driest month is January or February, and the wettest month is June, owing to frequent showers and thunderstorms, some of which produce hail, damaging winds and/or tornadoes. In Des Moines, roughly in the center of the state, over two-thirds of the of rain falls from April through September, and about half the average annual precipitation falls from May through August, peaking in June.
Climate data
Water
As in most of the U.S., surface water in Iowa is never safe to drink untreated, contamination by agricultural runoff including
nitrates,
herbicides,
pesticides, and
animal waste
Manure is organic matter that is used as organic fertilizer in agriculture. Most manure consists of animal feces; other sources include compost and green manure. Manures contribute to the fertility of soil by adding organic matter and nu ...
is common, though the
Clean Water Act has helped. Municipal water supplies are typically heavily chlorinated, this chlorine, combined with high nitrate levels, often give municipal water a strong smell, and the limestone bedrock in much of the state causes hard water. Some communities, such as
Iowa City resort to additional carbon filtration and
lime softening Lime softening (also known as lime buttering, lime-soda treatment, or Clark's process) is a type of water treatment used for water softening, which uses the addition of limewater (calcium hydroxide) to remove hardness (deposits of calcium and magnes ...
coagulation-sedimentation to make the water more palatable. Water treatment can be surprisingly effective; Des Moines' advanced filtration system has led to water quality ranked among the nation's best.
Jordan Aquifer
The Jordan Aquifer is the largest source of groundwater, extending from northeast Iowa to south central Iowa, and is ultimately the source of much of Iowa's agricultural and industrial water. In addition to pollution threats, the aquifer is threatened by overuse in well-source irrigation,
ethanol
Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an alcohol with the chemical formula . Its formula can be also written as or (an ethyl group linked to a ...
production, and the diminishment of resupply caused by extensive field tilling. The aquifer has dropped by as much as 300 feet since the 19th century, resulting in dry wells, the disappearance of natural surface springs, and the diminishment of water quality.
Soils
The
NRCS divides Iowa into 23 soil regions. In general, soils of southern, eastern, and western Iowa are loess-derived, while soils of northern and central Iowa are till-derived. Most level areas of Iowa have soils highly suitable for agriculture, making Iowa one of the most productive farming regions of the world.
Radon
Like most Upper Midwest and Plains states,
radon
Radon is a chemical element with the symbol Rn and atomic number 86. It is a radioactive, colourless, odourless, tasteless noble gas. It occurs naturally in minute quantities as an intermediate step in the normal radioactive decay chains through ...
is a common problem in Iowa, especially in areas with clay-rich soils.
Radon is the highest in the southern and the western parts of Iowa.
Paleontology
Devonian Fossil Gorge
Floods in 1993 washed away all the soil and unconsolidated bedrock along the spillway of the
Coralville Lake Dam in
Johnson County, exposing a rich collection of
Devonian-age
fossil
A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...
s. This area has been transformed into a visitors' center, where hikers can tour the bedrock. Unfortunately, looters have illegally removed many of the better fossils. The June 2008 floods expanded the fossil bed floor, and removed some of the weathered overburden.
Dinosaurs
Jurassic
The Jurassic ( ) is a geologic period and stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The Jurassic constitutes the middle period of ...
and
Cretaceous
The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...
bedrock in western Iowa have potential to contain dinosaur remains, and in nearby parts of Nebraska
Hadrosaurid (“duck-billed”)
ornithopod
Ornithopoda () is a clade of ornithischian dinosaurs, called ornithopods (), that started out as small, bipedal running grazers and grew in size and numbers until they became one of the most successful groups of herbivores in the Cretaceous wo ...
dinosaur remains have been recovered in Cretaceous bedrock similar to that of Iowa. The deep loess that covers much of western Iowa typically conceals the bedrock, limiting opportunities to finding dinosaurs to mining and quarrying operations.
Paleofauna
Archaeological and
paleontological
Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of foss ...
sites in Iowa have produced an extensive collection of
Pleistocene
The Pleistocene ( , often referred to as the ''Ice age'') is the geological epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was finally confirmed in ...
and
Holocene
The Holocene ( ) is the current geological epoch. It began approximately 11,650 cal years Before Present (), after the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene togeth ...
animals; these have been used to reconstruct past environmental conditions in the Midwest. Some of the earliest paleoclimatic reconstructions of the midcontinent were made from Iowa collections, such as the
Cherokee Sewer Site.
A Pleistocene giant
sloth
Sloths are a group of Neotropical xenarthran mammals constituting the suborder Folivora, including the extant arboreal tree sloths and extinct terrestrial ground sloths. Noted for their slowness of movement, tree sloths spend most of their l ...
is under excavation along West Tarkio Creek near
Shenandoah, Iowa
Shenandoah is a city in Page and Fremont counties in Iowa, United States. The population was 4,925 at the time of the 2020 U.S. Census. Once referred to as the "seed and nursery center of the world," Shenandoah is the home to Earl May Seed Compa ...
. Three individuals of ''
Megalonyx
''Megalonyx'' (Greek, "large claw") is an extinct genus of ground sloths of the family Megalonychidae, native to North America during the Pliocene and Pleistocene epochs. It became extinct during the Quaternary extinction event at the end of th ...
jeffersonii'', or Jefferson's Ground Sloth, have been identified so far, including one adult and two juveniles of different ages.
Notable Iowa geologists
Samuel Calvin (1840–1911) was Iowa's first systematic geologist, who helped to make the first bedrock and landform maps of Iowa, as well as lead geological research throughout the state.
[Calvin obituary, ''The Journal of Geology'', July 1911, pp. 385-391.] Calvin Hall at the
University of Iowa
The University of Iowa (UI, U of I, UIowa, or simply Iowa) is a public research university in Iowa City, Iowa, United States. Founded in 1847, it is the oldest and largest university in the state. The University of Iowa is organized into 12 col ...
is named for him.
Clair Cameron Patterson (1922–1995) developed the lead-lead dating and calculated an age for the Earth of 4.55 billion years; a figure far more accurate than those that existed at the time and one that has remained unchanged for over 50 years.
Charles Rollin Keyes
Charles Rollin Keyes (1864–1942) was a U.S. geologist and in 1918 was a U.S. Senate candidate in Iowa. Born in Des Moines, Iowa, he graduated from the State University of Iowa in 1887. He worked for the United States Geological Survey. He earne ...
was also an early Iowa geologist who helped map the soils and bedrock of southeast Iowa; he, with Calvin, was a founder of the Iowa Geological Survey.
Notes
References
External links
*Iowa Geological Survey, http://www.igsb.uiowa.edu/
*Iowa Geographical Map Server, https://web.archive.org/web/20080513085937/http://cairo.gis.iastate.edu/
*U.S. Geological Survey Iowa Overview, http://www.usgs.gov/state/state.asp?State=IA
*Web Soil Survey, http://websoilsurvey.nrcs.usda.gov/app/WebSoilSurvey.aspx
*NRCS Soil Survey, https://web.archive.org/web/20061113181444/http://soils.usda.gov/technical/classification/osd/index.html
*Geological Society of Iowa, https://web.archive.org/web/20081004055910/http://www.iowageology.org/
*Loess Hills Geology, http://pubs.usgs.gov/info/loess/
*University of Iowa Geoscience, https://web.archive.org/web/20080605050513/http://www.uiowa.edu/~geology/
*Iowa Geological Society Annual Report, http://ir.uiowa.edu/igsar/
*Iowa Geological Survey Publication on coal, http://ir.uiowa.edu/igs_pubs/
*Samuel Calvin geological photographs, http://digital.lib.uiowa.edu/cdm4/index_calvin.php?CISOROOT=/calvin
{{Iowa, expand
Iowa
Iowa () is a state in the Midwestern region of the United States, bordered by the Mississippi River to the east and the Missouri River and Big Sioux River to the west. It is bordered by six states: Wisconsin to the northeast, Illinois to th ...
Natural history of Iowa