One of the most fascinating maps I've seen are the Ancient Courses of the Mississippi River by cartographer Harold Fisk for the Army Corps of Engineers.
The maps (they run up and down the Lower Mississippi River), show the present (c.1944) course of the river, as well as how that course has changed over time through stages.
The Mississippi River has not remained static over time. It has been constantly shaped by natural forces such as erosion, sedimentation, floods, earthquakes, natural and anthropogenic climate change, tectonic movements, and glacial cycles. These forces have caused the river to change its course, width, depth, and speed over time. The river changes course continuously, as do all rivers.
Along the way from Lake Itasca, MN to the Gulf of Mexico, the Mississippi River shapes the landscape, culture, and history of 10 states and countless communities. But how did this mighty river come to be? And how has it changed over time? These maps help to answer that question, although their beauty and complexity create even more questions in the process.
|1944 Fisk Map of the Mississippi River (Plate 32, Sheet 6) (Amazon Link)|
The maps represent the Meander Belt of the Mississippi, according to Public Domain Review, and are primarily focused on the last several millennia of changes. As the Mississippi and Missouri Rivers are the primary rivers of the third largest river system in the world, the stage changes of the Mississippi are immense, and viewing these maps for the first time gave me a profound sense of wonder for how natural processes change.
The Mississippi River has a long and complex geologic history that spans millions of years. According to recent research by geologists, the river began flowing through the Mississippi Delta, a gap in the ancient mountains that once spanned the southern portion of the continent, about 70 million years ago. This was during the late Cretaceous period, when dinosaurs still roamed the planet.
|A scale for how many maps exist in the series, each created by Harold Fisk.|
In the book Twain's Feast, author Andrew Beahrs wrote of the Mississippi, "It transformed under the stars and in pitch blackness, in gray mist and by the light of a multitude of moons ... [it] had a new story to tell every day." (NPR)
NASA provides context below for the Fisk maps and its comparison to 1999 satellite imagery. Even going back very recently in geologic time shows the complexity of the River!
Less poetically, as the landscape around them changes, rivers, or the waters that make them up, take the path of least resistance, which changes as rocks and sediment move around or are eroded over time. This process can create new channels of flow, and abandon old ones, resulting in natural phenomena like oxbow lakes, or in the case of Kaskaskia, islands within the river, which is why the once former capital of Illinois is now West of the Mississippi River.
Another example of these channels was Glacial River Warren
, a much larger glacial river that flowed south from Lake Agassiz (a massive glacial lake that covered parts of Canada and Minnesota) to join the Mississippi near present-day Minneapolis. Glacial River Warren carved out a deep valley that is now occupied by the Minnesota River. When Lake Agassiz drained away about 9,500 years ago, Glacial River Warren ceased to exist and the Mississippi became a small tributary to it.
|You can see remnants of the Mississippi's ancient courses on Google Maps. Floods in 1844 and 1881 created the main channel of the river today, while older flows mark up where the boundary between Illinois and Missouri were settled.|
While rivers change their flows, state boundaries do not, and thus there are several examples across the US of a state boundary that was decided where the river flowed at that time that have since created examples like Kaskaskia above, where the main course of the river does not match the boundary of the state.
As you can see, the Mississippi River is a continuously evolving natural being, and while in the last couple hundred years humanity has straightened, dammed and changed the river, much like with most bodies of water, without human intervention it would continue to change and evolve naturally. Mark Twain compared the river being straightened for navigation to the change going on throughout his lifetime, "everything was changed... That world which I knew in its blossoming youth is old and bowed and melancholy now; its soft cheeks are leathery and wrinkled, the fire is gone out of its eyes and the spring from its step. It will be dust and ashes when I come again."
Seeing these maps made me want to begin mapping the changing courses of rivers, much like how the changing alignments of railroads is one area of focus on our Abandoned Railroad Map, but the sheer complexity and time that the river has existed make that a nearly impossible task. Finding all the abandoned railroads and realignments is difficult enough, on a system that has existed for just about 200 years at this point.
The Mississippi River, on the other hand, is many millions of years old, and thus the scale of change on even a thousand year timeline speaks to the level of change that has taken place over the course of geologic time.
Since Fisk's maps, LiDAR imagery has allowed us to further visualize changes in river courses, as shown below by Dan Coe Carto:
|"Lidar-derived image of the Mississippi River along the border of Arkansas and Mississippi, southwest of Memphis, Tennessee." (Dan Coe Carto)|
|The same area as the above LiDAR image from the Fisk map.|
The Mississippi River is still changing today as it responds to natural and human-induced factors. Some of these factors include sea level rise, subsidence (sinking) of land due to sediment compaction and oil extraction, sediment starvation due to dams and levees that trap sediment upstream, erosion due to storms and floods, and pollution due to agricultural runoff and industrial waste. These factors pose various challenges and opportunities for the river and its surrounding ecosystems and communities. For example, sea level rise and subsidence threaten to drown coastal wetlands that provide habitat for wildlife and protection from storm surges. Sediment starvation reduces the ability of the river to build new land and replenish existing land in its delta. Erosion exposes more land to saltwater intrusion and increases vulnerability to flooding. Pollution degrades water quality and affects human health and aquatic life.
The Mississippi River's past offers a glimpse into its future as well. Another example of a channel change is the Atchafalaya River, a distributary of the Mississippi that branches off near Simmesport, Louisiana. The Atchafalaya River has been capturing more and more water from the Mississippi over time due to its shorter and steeper route to the Gulf of Mexico. If left unchecked, this process could eventually divert most of the Mississippi’s flow into the Atchafalaya River, creating a new delta and leaving New Orleans stranded on a dry riverbed. To prevent this from happening, engineers have built structures such as dams and levees
to control and regulate the flow of both rivers.
Thanks as always for reading!
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