Miners with mule-drawn cart
Southern Iowa coal mine
Central Iowa coal mine
The Bering Land Bridge
Humans Cross the Bering Land Bridge
Glaciers in Iowa
Simonsen Excavated Site Profile
Spring Hollow Incised PotteryIowa’s Geology
The
story of Iowa started long before people ever lived on the land. Iowa’s
land has formed through a slow and never-ending process. Geologists believe
that earthquakes, volcanoes, floods and ice helped form and change Iowa
for over 1 billion years. These processes formed the base for Iowa’s
farming success, mining industries and even some art forms.
Waves of Change
Iowa is far from an ocean or vast lake, but water still has played an important role in shaping its land. Water has at least three major roles in geology.
- Water erodes rocks. Rain, ice, waves and creeping glaciers break rocks into smaller pieces.
- Fast moving water carries away eroded rocks and soil as sediments.
- When moving water slows, it deposits the sediments in new areas.
Iowa has been under water in one
form or another for much of its history. Ancient seas covered Iowa while it
was located near the equator. For millions of years, the continental plate
on which Iowa sits has slowly wandered around the globe. At one time the plate
split apart, creating a rift. Then it moved back together. Several other times,
it crashed into other plates. These crashes caused parts of the land to get
pushed up out of the water. These earth-quaking events often formed mountains.
The oldest mountain remnants in Iowa are found as Sioux Quartzite in the northwest
corner of the state.
When the land was above water, waves and rain worked to wear away the rocks.
When plates crashed together again, the land often got pushed back down. While
underwater, the land became covered with layers of sediment. Each layer of
sediment holds clues to the past. Some layers have fossil crinoids, trilobites
or even tree pollen. Most of these layers are buried under newer rocks and
soil. But the bluffs that line the Mississippi River in northeast Iowa are
an exposed outcrop of ancient sea sediments.
Frozen in Time
Although the plate became more stable
as it moved close to its current location, it hasn’t stayed dry for
long. Frozen water in the form of mile-thick glaciers creeped across parts
of Iowa at least four different times. The glaciers pushed a mix of loose
gravel and soil, called till, across Iowa. This glacial till forms the base
of Iowa’s rich farming soils.
When the climate warmed, the glaciers melted. Enormous amounts of water and
ground up rocks rushed across the land, cutting new river valleys. After the
water moved on, the sediments dried. Strong winds picked up the sediments
and carried them across the land. Much of Iowa is covered by this wind blown
sediment, called loess. But the hills along Iowa’s western edge are
among the deepest deposits of loess found anywhere in the world.
Iowa seems pretty stable today. There have been only 12 earthquakes with their
epicenter in Iowa in historic times. And polar glaciers are getting smaller,
not larger. However, water is still at work in Iowa, eroding the soils and
rocks. Humans have increased the rate of erosion
by removing plant cover and leaving the ground bare. So right now, some of
Iowa’s geologic history and its farming productivity are headed down
river to be deposited in the Gulf of Mexico.
Mining Iowa’s Treasures
The rocks and soil of Iowa have provided the raw materials for many occupations. Native Americans found chert in the Nishnabotna River valley in western Iowa. They chipped this sedimentary rock to make arrowheads and spear points. Early European explorers discovered deposits of lead and zinc near Dubuque. These ores were mined and refined.
Coal was mined in southeastern Iowa as early as the 1840s. Most of it was
burned to heat homes and businesses. When the railroads arrived in the 1860s,
more coal was needed to fuel the trains. In 1880 there were over 200 coal
mines in the southern and central part of the state. By 1900 there were more
than 400 mines. However, by the 1920s more people were using cleaner burning
coal that was mined in Illinois. The coal mines of Iowa shut down.
During the times that Iowa was slowly lifting up from underwater, the salt
from the seas became concentrated. These sea salts settled as thick deposits
which became gypsum. Gypsum is mined to make plaster, cement and wallboard.
A huge piece of gypsum taken from the Fort Dodge area in the 1860s was carved
into the figure of a giant. This “fake fossil” was then buried
near Cardiff, New York. After it was “discovered,” people paid
fifty cents each to see the giant. Although the hoax was soon uncovered, the
Cardiff Giant is still on display in a New York museum.
Mining is important for the building industry in other ways too. Limestone quarries are found across the
state. Limestone is used as gravel for roads, as an ingredient in cement and lime is used to enrich Iowa farm fields.
Buildings around the state feature actual stones including glacial erratics,
limestone blocks and Sioux Quartzite.
On a much smaller scale, local artists have mined Iowa’s geologic treasures
for use in their work. Andrew Clemens found over 42 colors of sand in the
bluffs near his home in McGregor. He used this sand to create pictures in
clear glass bottles from 1878-1894. From the 1950s through the 1970s, sculptor
Isabel Bloom of Davenport collected interesting rocks she found in the Mississippi
River. She used them as accents in her concrete creations. And in 2002 Andrew
Goldsworthy used limestone from Stone City to create a huge sculpture at the
Des Moines Art Center.
Recreation
Geology is not all about work—it has also created some of Iowa’s most interesting places to play. Iowa’s great lakes in the north central part of the state were formed when huge hunks of ice broke off and melted slowly in one place. Caves with stalactites and stalagmites are common in the limestone rocks near the surface in northeast Iowa. Geode hunters search for the state rock in southeastern Iowa. And some limestone quarries allow fossil hunters to search for specimens at unused portions of their sites.
Geology Today
A lot is known about Iowa’s
geologic history, but there is still much to be studied. Water washed away
much of the evidence from millions of years ago. Geologists working with the
Iowa Geologic Services Bureau and many universities are trying to piece together
what happened during that time. Farmers study their soil to determine how
to best use it. Homeowners and water districts want information about their
water supply and quality. Construction companies examine land before they
build on it. Geology always has, and always will play an important role in
what Iowans see and do.
Sources:
- Pierre, Amanda. “Artist Lays Groundwork for Des Moines Sculpture” Des Moines Register. May 1, 2002.
- http://www.igsb.uiowa.edu/ Iowa Geological Services Bureau, 6/11/05
- Iowa Association of Naturalists. Iowa Geology and Fossils: Iowa Physical Environment Series. Ames, Iowa: ISU Extension Service, 1999.
- Land Between Two Rivers: A Guide for Teachers. Iowa Public Television, Johnston, IA
- Prior, Jean C. Landforms of Iowa. Iowa City, IA: University of Iowa Press, 1991.
- Schwieder, Dorothy. Iowa: Past to Present. The People and the Prairie. Second Edition. Iowa State University Press, Ames, IA. 1991
- Troeger, Jack Clayton. From Rift to Drift: Iowa’s Story in Stone Ames, Iowa: Iowa State University Press, 1983.
