The Mississippi is All Locked Up!
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In order to count this Earthcache as a find, you must complete the following tasks and email the answers to me.
1. What is the elevation of the river at this point?
2. Estimate the width of the Mississippi River.
3. As best as you can, describe what the locks system looks like.
4. Describe Saint Anthony Falls (i.e., height, how the falls look like, power behind the falls).
5. How fast is the river moving at this location?
Hundreds of Native American tribes have depended on the Mississippi River and its tributaries for thousands of years. Although they knew the river by many different names, it was the Ojibwe word misi-ziibi, meaning Great River, that ultimately gave the river its present-day name. This Earthcache is located in Mill Ruins Park in downtown Minneapolis. This area, right along the river, provides vistas of Saint Anthony Falls, a view of the lock and dam system set up on the River, and history of the flour milling industry in the area. Enjoy!
The Mississippi River, like all rivers, is in a constant state of change. Various forms of the Mississippi River have flowed through this area for more than a million years. The Upper Mississippi River Valley, which flows through the majority of Minnesota, was primarily shaped during the most recent glacial stage of the Ice Age - The Wisconsin Period.
The Wisconsin glaciation period started about 75,000 years ago and ended about 12,000 years ago when the North American climate began to warm. It was a world hardly recognizable today. Minnesota was populated by a variety of very large animals called megafauna, which lived in the cold climate on the margins of the glacial ice. Many of the ancient fish species that had populated the Upper Mississippi River had moved south as the waters grew too cold, and then expanded back into the northern portion of the river as the glaciers retreated. Ancient fish that predate the glaciers and still live in the waters of the Mississippi River include long-nosed and short-nosed gar, sturgeon, and paddlefish.
The melting of those enormous ice sheets that, at their maximum, were 5000 to 10,000 feet thick and covered hundreds of thousands of square miles, released tremendous amounts of water, forming huge glacial lakes. The largest of the glacial lakes, Lake Agassiz, covered northwest Minnesota, parts of North Dakota, and the Canadian provinces of Manitoba, Saskatchewan, and Ontario. The southern discharge outlet to this lake was called Glacial River Warren, which eventually excavated the valley now occupied by the Minnesota River. The Mississippi River flows into this valley carved by the River Warren at St. Anthony Falls in Minneapolis.
The St. Croix River which drained Lake Duluth, a glacial lake the covered the western Lake Superior basin, joined the River Warren about thirty miles downstream from the present confluence of the Mississippi and Minnesota Rivers. In Wisconsin, another glacial lake drained first into what is now the Black River and later the Wisconsin River, both of which emptied into the River Warren. During the 3000 years that River Warren carried water from these and other smaller glacial lakes, the Mississippi River valley was carved bluff to bluff, and the resulting valley was approximately 250 feet deeper than it is today.
Glaciers also left their mark on the land by carving parts of the Mississippi River that cuts through this area. When the ice sheet began to recede, hundreds of feet of rich sediment were deposited, creating the flat and fertile landscape of the Mississippi Valley. During the melt, giant glacial rivers found drainage paths into the Mississippi watershed, creating the Minnesota, James, and Milk River valleys. With the disappearance of the ancient glacial lakes and Glacial River warren, the tremendous flow of water was diminished and the Mississippi River became the most important stream in the area.
Because of the power of the river flowing through this downtown area and through Saint Anthony Falls, a dam was constructed as a use for power. The first dam was constructed in 1847 and sawmills, powered by the dam soon followed. As the Minneapolis area continued to develop, several industries (i.e., sawmills, textile mills, flour mills) used the water power from the Mississippi River at the falls as their main source of power. The activity of the industry and dams caused significant damage to the falls. Prior to human activity in this area, the falls receded a foot each year; however, the industry use of the falls in this area caused the falls to recede ten to twenty feet a year. With the diversion tunnel collapsed in 1869, the falls nearly crumbled into the resulting whirlpool. The unique geography of the falls along this stretch of the river is unique and allows the falls to migrate north. Leaving the falls unstable after this collapse would mean the river would turn into a pile of rock and impassible rapids at this point.
As a result, the US Army Corps of Engineering moved in to stabilize the falls. They built a large apron to cap the rock layer, built a spillway for the main channel to prevent further erosion, and stabilized the area around the power plant. In 1956, the lower St. Anthony Falls dam was completed by the United States Army Corps of Engineers. The upper dam was finished in 1963. Together, these two hydro-electric dams help provide power to the industry in the area and stabilize the Mississippi River.
A series of twenty-six locks were also constructed on the river at between 1948 and 1963. The locks help control navigation along the Mississippi River. At Minneapolis, the locks, also constructed by the US Army Corps of Engineering to stabilize the falls, help make commercial navigation possible on the River above Minneapolis; however, since the locks in Minneapolis are small than most of the locks on the river, few barges go past St. Paul simply because of size. The locks at Saint Anthony Falls is the uppermost lock and dam system on the Mississippi River. The drop created by the lock and dam system here is the largest of all the Mississippi River locks and dams. Above the dam, the elevation of the Mississippi is 799 feet; below the dam, the elevation drops to 750 feet. The origin of the forty-nine foot drop is a waterfall preserved adjacent to the lock under an apron of concrete. The elevation continues to drop as the Mississippi continues its southern course. By the time the River reaches St. Paul, below the lock and dam at Saint Anthony Falls, the elevation has already dropped to 687 feet.
What we see at Saint Anthony Falls is a result of the efforts to stabilize the Mississippi River and falls after being abused by human activity. While the natural fall of water over a rock ledge has been lost, the falls have been preserved for generations to come.
NOT A LOGGING REQUIREMENT: Feel free to post pictures of your group at the area or the area itself - I love looking at the pictures.
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