"Calvin Fremling has successfully described and explained a very complex river system and series of events to a general audience. To my knowledge, there has not been any attempt to address the spatial and temporal scope that is contained in Immortal River. In fact, I dare say, there is nothing even close."—Thomas O. Claflin, professor emeritus of biology, University of Wisconsin–La Crosse
Immortal River: The Upper Mississippi in Ancient and Modern Timesby Calvin R. Fremling
This engaging and well-illustrated primer to the Upper Mississippi River presents the basic natural and human history of this magnificent waterway. Immortal River is written for the educated lay-person who would like to know more about the river's history and the forces that shape as well as threaten it today. It melds complex/i>
This engaging and well-illustrated primer to the Upper Mississippi River presents the basic natural and human history of this magnificent waterway. Immortal River is written for the educated lay-person who would like to know more about the river's history and the forces that shape as well as threaten it today. It melds complex information from the fields of geology, ecology, geography, anthropology, and history into a readable, chronological story that spans some 500 million years of the earth's history.
Like the Mississippi itself, Immortal River often leaves the main channel to explore the river's backwaters, floodplain, and drainage basin. The book's focus is the Upper Mississippi, from Minneapolis, Minnesota, to Cairo, Illinois. But it also includes information about the river's headwaters in northern Minnesota and about the Lower Mississippi from Cairo south to the river's mouth ninety miles below New Orleans. It offers an understanding of the basic geology underlying the river's landscapes, ecology, environmental problems, and grandeur.
- University of Wisconsin Press
- Publication date:
- Edition description:
- Sales rank:
- Product dimensions:
- 6.00(w) x 9.00(h) x 1.20(d)
Read an Excerpt
The Upper Mississippi in Ancient and Modern Times
By Calvin R. Fremling
THE UNIVERSITY OF WISCONSIN PRESS
Copyright © 2005
The Board of Regents of the University of Wisconsin System
All right reserved.
Chapter One Majestic River Bluffs and Beautiful Valleys
The immensity of the gorge of the Upper Mississippi River awed early explorers. Viewing the precipitous bluffs and cliffs that flanked the river, many thought that they were seeing low mountain ranges. They marveled at the rugged headlands and the layered rocks filled with the shapes and shells of animals they had never seen before.
To this day, travelers and people who have lived for years along the river wonder about these same things, unaware of how the river came to occupy this deep valley. Most are surprised when they ascend the "hills" and find themselves in the midst of beautiful, flat, highly productive agricultural land that is dissected by deep valleys. There are no mountains or hills, just valleys-valleys carved through a vast plateau of soft, incredibly old, sedimentary rocks.
This chapter and the next four chapters tell how this magnificent landscape came to be, offering a "big picture" of the geologic forces that shaped this landscape from the dawn of time to the present. A basic understanding of the geology that underlies the river and the land it flows through illustrates how natural forces have dictated the locations of our cities, highways, dams, and bridges. It is the story of the natural barriers to man's navigation of the river-St. Anthony Falls, the Rock Island Rapids, the Des Moines Rapids at Keokuk, Iowa, and the Chain of Rocks at St. Louis. It explains why some sections of the river must be dredged and red redged to maintain commercial navigation, and ultimately, why the Mississippi River is here at all.
To tell of the almost six hundred million years of extraordinary earth and ecological history pertinent to the story of the Upper Mississippi River I have stood on the shoulders of giants, drawing upon the written works of legions of geologists, biologists, anthropologists, and intellectually curious river folks. As is customary in geologic literature, I denote prehistoric times in years B.P. (Before Present). To avoid confusion, times just prior and subsequent to the birth of Christ will be denoted as A.D. and A.D., the system familiar to most readers.
Ancient Seas: Formers of Sedimentary Rocks
The land was born of rock, fire, and water. The infant earth was a glowing ball of molten rock whirling around the primeval sun. Over cosmic stretches of time the earth began to cool and rain began to fall, producing the feature that makes our planet unique in all the known solar system-liquid water. Of all the earth's naturally occurring compounds water is unique, the only substance found as a liquid, solid and vapor at naturally occurring surface temperatures and pressures. In each of these physical states water carves and shapes the earth's surface, wearing away, first at bare rock, later cutting through sand and soil to create much of the landscape that surrounds us.
The entire surface of the earth began as hot rock, gradually cooling under the first rains falling on the newly formed planet. These rocks formed in fire-igneous rocks-are the ancestors of all other rocks, sand, and soil. Igneous rock is still being formed when hot magma from deep in the planetary interior rises to the surface as volcanic lava or cools and solidifies quietly in the earth's crust. We are familiar with igneous rock as granite and basalt, hard and dense.
Water-exploding into steam as it contacts molten magma; irresistibly expanding in cracks and crevasses as it freezes; swirling and polishing as it flows as a liquid-is the great destroyer of igneous rock. It fractures the rock, breaking off fragments, which are carried in its currents in an abrasive stew that wears away the rock it flows across, weathering it into ever smaller pebbles, sand grains, and flecks of clay. As the current slows or the stream dries up, these particles are deposited as sediment.
Granite, familiar to most as the stone cut and carved into cemetery markers, consists mainly of the minerals quartz and feldspar. With complete weathering quartz usually produces sand-sized sediments, while feldspar weathers to silt and clay. Silt and clay particles are so fine they can only be distinctly seen though a high-powered microscope. Silt, the coarser of the two can be distinguished from clay by a simple test-when ground between the teeth, silt is gritty, clay is not. Fine sand, predominantly quartz, is hard and stable-the most common mineral not easily dissolved in water.
Larger sediment particles are often bits of rock containing more than one mineral. Larger still are granules, pebbles, cobbles, and boulders consisting of rock fragments, usually rounded by abrasion during their transport by water or ice (Leopold 1994). Particles larger than sand are generally called gravel. Because quartz is very stable, it tends to hang around longer and to be the most common mineral at earth's surface. Most of the Mississippi's sand is made of quartz.
Sediment transported by water is described as either suspended load or bed load. Suspended load consists of clay and silt and is what makes water muddy. Due to its size it ultimately settles out in quiet areas, but it may be resuspended again and again by river currents or wave action. Bed load, in contrast, consists of larger particles that are dragged along near the streambed (Leopold 1994). Oceans are the ultimate sinks for sediments. The heavier and coarser sand particles settle out near river mouths or where there are currents produced by the pounding of the surf, but silts and clays settle out in the calm areas, either in protected shallow areas or at great depths.
Left undisturbed, deposits of sediment may be transformed into sedimentary rock. Deposits of sand may ultimately form sandstones. Silts and clays may form siltstones and shales. All sedimentary rock is formed in layers called strata. Strata can easily be seen and identified in sedimentary rock formations; therefore, sedimentary rock formations are often described as stratified, or layered. Most of our knowledge of our planet's history is derived from studies of the sedimentary rocks that blanket most of the earth's crust-the oldest rocks on the bottom and the youngest on the top.
The particles that compose sedimentary rocks such as sandstone or shale have been compacted by the immense weight of overlying strata, and are usually cemented together by minerals precipitated from ground water. Other sedimentary rocks, such as limestone and dolomite (dolostone), are composed largely of the calcareous skeletons of corals and seashells that may have been reduced to sand-sized particles. Limestone is simply calcium carbonate, but dolomite is calcium-magnesium carbonate. Technically, dolomite is the mineral and dolostone is the rock that contains it. However, the rock is still referred to as dolomite in most circles, especially in older literature.
With time, sedimentary rocks may be buried under an ever-thickening series of layers that may reach thicknesses of tens of thousands of feet. The earth becomes hotter at increasingly deeper levels, and the weight of overlying rocks exerts incredible pressure. In concert, the heat and pressure cause the deeper strata to form metamorphic ("changed form") rocks. The metamorphic rocks are a complex group that includes common rocks like slate (from shale), marble (from limestone and dolomite), and quartzite (from sandstone).
Sedimentary rocks that were formed in the depths of the sea may be uplifted by geologic forces to become mountains thousands of feet high. In the American West, the Rocky Mountains are the contorted sedimentary strata of an ocean bed that has been elevated over two miles. I was awed many years ago when I climbed one of the mountains, sat down to rest at the summit, and found it littered with fossil trilobites, oceanic invertebrates that have been extinct for 250 million years! Impossible as it seems, the crest of the world's tallest mountain, Mount Everest, is composed of limestone formed from the floor of an ancient ocean.
All of the rock formations visible along the Mississippi from St. Paul, Minnesota, to the Gulf of Mexico are sedimentary rocks. Sedimentary rocks cover a much larger area of North America and its continental shelves than igneous rocks. Shale covers 52 percent, sandstone 15 percent, limestone and dolomite 7 percent, while granite and basalt only account for 18 percent (Leopold 1994).
The Rock Cycle
The earth's crust is restless. Supported by a highly plastic mantle, plates of the earth's crust, with their raised continents, have drifted and wrinkled. Relative to sea level, their surfaces have risen and fallen. The ocean basins have changed shape, and massive continental glaciers have repeatedly scoured large areas of the Northern Hemisphere.
The continual process of destruction and rebirth of the earth's crust is called the "rock cycle." The concept of the rock cycle was probably first stated in the late eighteenth century by geologist James Hutton: "We are thus led to see a circulation in the matter of this globe, and a system of beautiful economy in the works of nature. This earth, like the body of an animal, is wasted at the same time that it is repaired. It has a state of growth and augmentation; it has another state, which is that of diminution and decay. This world is thus destroyed in one part, but is renewed in another; and the operations by which this world is thus constantly renewed are as evident to the scientific eye, as are those in which it is necessarily destroyed" (Hutton 1795, 562).
Formation and Uplifting of the Mississippi Valley's Ancient Blufflands
There is general consensus among scientists that our planet is about 4.6 billion years old. About 4 billion years ago primitive life developed in the ocean. For the next 3.5 billion years, all life on earth was confined to the ocean waters.
About seven hundred million years ago soft-bodied creatures such as jellyfish and worms appeared in the Precambrian fossil record, setting the stage for the great explosion of life that was to come in the Cambrian period. Fossils found in rocks formed about 544 million years ago document the first explosion of hard-bodied invertebrate animals in the seas. That momentous event defines the beginning of the Cambrian period of the Paleozoic Era.
At the beginning of the Cambrian period, the North American continent was smaller than it is now. As new forms of life developed, geologic forces caused the earth's crust to subside (sink) throughout much of the interior of the continent. As the land sank, there was a general worldwide rise in the level of the sea, which flooded the low-lying, bleak, barren, surface of the land now drained by the Mississippi River and its tributaries.
The burst of evolution known as the Cambrian explosion began around 530 million years ago when sea levels rose dramatically, probably due to melting of vast glaciers, creating expansive shallow seas, giving evolution a tremendous boost.
The oceans did not advance at a uniform rate. Forces deep within the earth caused mild subsidence or down warping in some areas and broad, gentle uplifts in adjacent areas, causing shorelines to advance and retreat. The seas continued to rise until the late Ordovician period, about four hundred million years ago.
As the sea advanced, pounding surf attacked the uplands, stripping rock debris from still barren, severely weathered land. As in modern times, most sediment was carried to the sea by rivers-then reworked, sorted, and cleaned by the surf.
Beach zones were high-energy environments where wave action and currents continued the disintegration of the rock debris, winnowing it, and depositing the coarsest particles in the surf areas as clean, well-sorted beds of sand that ultimately formed sandstones. Silt and clay were wafted out into quiet, deeper waters where they settled and were compressed to form shales. Abundant lime-secreting organisms produced deposits that formed limestones and dolomites in warm shallow water, with little input of sand, silt, or clay.
During the ensuing five hundred million years the shallow epicontinental sea served as a collection basin for sediments eroded and washed outward from primordial uplands and mountain ranges. As ancient rivers entered the sea, which was seldom deeper than 150 feet, they lost their velocity and their ability to carry sediments, causing the larger or heavier sediments to be deposited near sea level. Even though the sediments were of relatively low density, their great weight facilitated a commensurate subsidence of the earth's crust. Subsidence and sedimentation were concurrent. The rate of accumulation was slow, perhaps averaging only an inch every two thousand years or so.
This average is misleading, however, because it portrays scenes of tranquility. The early earth was a geologically active and often violent place. Most of the sandstones and shales seen in Mississippi River bluffs were deposited when catastrophic earthquakes and volcanic eruptions sent avalanches and mud slides crashing into swollen rivers.
A large drop in sea level took place at the end of the Ordovician when vast quantities of water were distilled from the world's oceans and bound up as ice in continental glaciers (Mossler 1999). Thus, the shallow sea did not advance at a uniform rate over the land; numerous advances were interrupted by minor withdrawals causing the shoreline to alternately advance inland (transgress) and to retreat (regress). The changes in sediment deposition that coincided with the changing shoreline caused distinctive cyclic patterns in the sedimentary rocks. A sandstone stratum laid down as an ancient beach, for example, may be bounded above and below by shale or limestone formed in deeper calmer waters. These layers of sedimentary rocks are now hundreds of feet thick in southern Minnesota and thousands of feet thick in the Far West and Deep South.
It is generally accepted that during this interval of inundation the North American Plate straddled the equator. Nearly all of the marine fossils found in central North America are of animals that flourished in warm, tropical seas. Throughout most of the Paleozoic era, which ended about 245 million years ago, North America drifted northward, to become part of the supercontinent Pangaea (all earth).
Pangaea included all of the earth's present continents. The eastern edge of the North American Plate once pushed against the African and Eurasian Plates, causing the rise of the Appalachian Mountains, while the eastern edge of the South American Plate abutted the African Plate. During the first hundred million years of this interval, land surfaces remained lifeless, barren, and easily eroded, but the seas teemed with an abundance and diversity of plants and animals (Ojakangas and Matsch 1982). Animals, plants, and fungi first came ashore about 450 million years ago, very recently in geologic time.
About two hundred million years ago, Pangaea began to break up into its constituent plates. The North American Plate, whose exposed land surface was the North American protocontinent, began to drift away from Eurasian and African Plates at about the speed that fingernails grow. This initiated the opening of the Atlantic Ocean.
As recently as 95 million years B.P., our planet was still a world of shallow seas. The landmasses no longer formed a supercontinent, but they remained close together. Sea levels were higher than now, primarily because there were no large glaciers to store water, and oceans flooded the interiors of most continents during the Cretaceous period.
Geologic forces caused the general uplifting of the North American continent from the Mississippi River to the Pacific Ocean during the westward drift of the North American plate. The Rockies, some of the continent's tallest and youngest mountains, were thrust upward as the Earth's crust, near the plate's western margin, uplifted and folded.
Subsequently, to the east of the Rockies, a great sedimentary rock plateau rose from the sea, constructing a stable platform of relatively soft sedimentary rocks, bounded on the west by the youthful Rocky Mountains and on the east by the much older southern Appalachian Mountains.
Stripped of its sedimentary rock covering by repeated glacial advances, the remaining stable nucleus of the primordial North American continent is exposed in the northern United States and Canada as the Canadian Shield, an expanse of igneous and metamorphic rocks that include some of Earth's oldest rocks.
Excerpted from Immortal River by Calvin R. Fremling Copyright © 2005 by The Board of Regents of the University of Wisconsin System. Excerpted by permission.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.
Meet the Author
Calvin Fremling is professor emeritus of biology at Winona State University and former aquatic ecologist at the Resources Studies Center, St. Mary's University of Minnesota. He has written numerous articles on the environment and the Mississippi River.
Most Helpful Customer Reviews
See all customer reviews
Dr. Fremling has given us a fascinating account of how the Mississippi was born, how it has evolved, and how we humans have tried to harness it. Full of helpful charts, graphics and photos, the book also chuckles with stories big and small about life on and in the river. Hurricane Katrina's recent ravages in Louisiana and Mississippi are readily understood after reading this book. We mess with Ol' Man River at our own risk - let the river do its job! Highly recommended reading for anyone within the watershed (and that's a lot of the country).