Geography of Iowa
The geography of Iowa includes the study of bedrock, landforms, rivers, geology, paleontology and urbanisation of the U.S. state of Iowa. The state covers an area of 56,272.81 sq mi.
Bedrock features
Iowa's bedrock geology generally increases in age from west to east. In northwest Iowa Cretaceous 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 extinction, but recalculation of the impact's age indicates it occurred some 12 million years before the mass extinction. Although glaciation 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 Period, 470 million years ago. The crater is estimated to be 3.5 miles 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 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.Midcontinent rift
Buried deeply within Iowa's bedrock, the Midcontinent Rift System 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. This rift is not seismically active.Seismic activity
No major active fault lines exist in Iowa, and Iowa is one of the most seismically 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 earthquakes in Iowa. Occasional small earthquakes occur near Fremont County in the far southwest, and the Sioux City area can occasionally be shaken by nearby temblors. 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 producer, particularly the Des Moines River valley from Coalville 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 and oil 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 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.Image:geode angle 300x267.jpg|thumb|100px|Geode half
Geodes
s are found in southeast Iowa and are the official state rock. They consist of grey to pink cobbles within limestone 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, soils, topography, and river drainage:Paleozoic plateau
Also known as the Driftless Area, this region of scenic, high relief landscapes includes such features as resistant, bluff-forming bedrock outcrops, deep V-shaped valleys, caves, springs, and sinkholes. Glacial deposits and loess are thin or absent over most of the region.Des Moines lobe
Often called the Prairie Pothole Region, the Des Moines Lobe was glaciated up until 12,000 years ago during the Wisconsin glaciation. 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 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 till. The SIDP is some of the most productive agricultural land in the US.Mississippi alluvial plain
Generally level areas of stream terraces, paleochannels, backwater sloughs, and oxbow lakes are found within the broad Mississippi River valley.Loess hills
The Loess Hills 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".Image:Loess hills.jpg|thumb|left|250px|Loess Hills east of Mondamin, Iowa, showing the transition with the Missouri alluvial plain.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 throughout the state 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, 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 season. Iowa averages about 50 days of thunderstorm activity per year. The 30-year annual average of tornadoes in Iowa is 47. In 2008, twelve people were killed by tornadoes in Iowa, making it the deadliest year since 1968 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 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
| City | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
| Davenport | 30/13 | 36/19 | 48/29 | 61/41 | 72/52 | 81/63 | 85/68 | 83/66 | 76/57 | 65/45 | 48/32 | 35/20 |
| Des Moines | 31/14 | 36/19 | 49/30 | 62/41 | 72/52 | 82/62 | 86/67 | 84/65 | 76/55 | 63/43 | 48/31 | 34/18 |
| Keokuk | 34/17 | 39/21 | 50/30 | 63/42 | 73/52 | 83/62 | 87/67 | 85/65 | 78/56 | 66/44 | 51/33 | 33/21 |
| Mason City | 24/6 | 29/12 | 41/23 | 57/35 | 69/46 | 79/57 | 82/61 | 80/58 | 73/49 | 60/37 | 43/25 | 28/11 |
| Sioux City | 31/10 | 35/15 | 47/26 | 62/37 | 73/49 | 82/59 | 86/63 | 83/63 | 76/51 | 63/38 | 46/25 | 32/13 |