• The Mississippi: A Visual Biography by Quinta Scott

    "Great book and great blog - thanks for the first book I have seen that addresses the contemporary river, headwaters to gulf." Dan McGuiness, Audubon, St. Paul, Minnesota

    Click to order

  • Catagories

  • Archives

  • August 2019
    M T W T F S S
    « Oct    
     1234
    567891011
    12131415161718
    19202122232425
    262728293031  
  • Meta

  • Advertisements

Low Water on the Mississippi and Thebes Gap

Thebes Gap:

Alexander County, Illinois

“Here is a vast ledge of rocks, which stretch across the river in a direct line. The best channel in the middle of the river, in which place in low water, there is not more than six feet over the rocks.”–Zadoc Cramer, 1814

Rock Formation in the Middle Mississippi at Thebes Gap, 2006

Rock Formation in the Middle Mississippi at Thebes Gap, 2006

The Mississippi is running very low. After the Flood of 2011, the river drained away very quickly and the rain stopped. By the Summer of 2012, we in the Midwest were well into the Drought of 2012 and the river was showing the effects. Now in January 2013, the Upper Mississippi is frozen and the system of locks and dams is retaining water north of Alton, Illinois. On the Missouri a similar system of dams is retaining water in South Dakota and too little water is flowing into the Mississippi to maintain water levels for the 9-foot navigation channel on the Middle River.

Look at any aerial photograph of the confluence of the Missouri and Mississippi. The muddy Missouri spews a flume of silty water into the relatively clear Mississippi. They flow side by side downstream--the Missouri on the west, the Mississippi on the east--for several miles. During the very cold winter of 2000-2001 it was possible to see this phenomenon from the Illinois bank near the spot where Lewis and Clark started their journey up the Missouri: Lock and Dam 26 at Alton trapped ice coming down the Mississippi. South of the dam the river flowed free of ice, but ice did flow out of the mouth of the Missouri. At the confluence the two rivers, the icy Missouri and the ice-free Mississippi flowed side by side in the Mississippi channel.

Look at any aerial photograph of the confluence of the Missouri and Mississippi. The muddy Missouri spews a flume of silty water into the relatively clear Mississippi. They flow side by side downstream–the Missouri on the west, the Mississippi on the east–for several miles. During the very cold winter of 2000-2001 it was possible to see this phenomenon from the Illinois bank near the spot where Lewis and Clark started their journey up the Missouri: Lock and Dam 26 at Alton trapped ice coming down the Mississippi. South of the dam the river flowed free of ice, but ice did flow out of the mouth of the Missouri. At the confluence the two rivers, the icy Missouri and the ice-free Mississippi flowed side by side in the Mississippi channel. In the Winter of 2013 too little water is spewing out of the Missouri to feed the Middle Mississippi.

 Thebes Gap is the geological break point between the Upper Mississippi and the Lower Mississippi. The Upper Mississippi flows through a rocky gorge from Minneapolis to Thebes Gap. South of there the Lower Mississippi meanders across an alluvial plain.

At the beginning of the glacial age, the Lower Mississippi flowed along the western valley wall through an alluvial floodplain in the Western Lowlands along the Black, White, and St. Francis Rivers.

From The Mississippi: “Geologists have speculated that the river abandoned its alluvial valley and diverted through Thebes Gap, a narrow bedrock canyon in the Benton Hills, through the series of glacial floods at the end of the Wisconsinan age. At the beginning of the twenty-first century, seismologists questioned why the Mississippi would abandon its comfortable alluvial valley to ream a new course through bedrock. They noted that fault lines in the Benton Hills were active 10,000 years ago, and speculated that an earthquake along fault lines in the Benton Hills opened the canyon that is Thebes Gap. Glacial River Warren, which broke out of a glacial lake that covered northern Minnesota and North Dakota and reached north into Canada,  thundered through it, and deposited a classical alluvial fan at the mouth of the canyon.”

 “Thebes at the head of the Grand Chain and Commerce at the foot of it were towns easily rememberable as they had not undergone conspicuous alteration. Nor the Chain, either–in the nature of things; it is a chain of sunken rocks admirably arranged to capture and kill steamboats on bad nights.–Mark Twain, Life on the Mississippi

Thebes Gap, where the Mississippi takes a wide turn into the narrow reach of Thebes Gap.

Thebes Gap, where the Mississippi takes a wide turn into the narrow reach of Thebes Gap.

Mark Twain knew Thebes Gap, and while it is no longer killing steamboats, this winter modern tows can’t get through this narrow gorge between the Upper Mississippi and the Lower Mississippi.

The U.S. Army Corps of Engineers have contracted with Newt Marine and Kokosing, a marine engineering firm out of Iowa and Michigan,  to remove the rocks from Thebes Gap. When they are done there on January 11, they will move on to Grand Tower.

A tow steams passed Tower Rock at the beginning of December.

A tow steams passed Tower Rock at the beginning of December.

The river level today at Chester, Illinois is -0.6 feet, which means it is possible to walk out to Tower Rock and see just how low the Mississippi is.


[i]             Cramer, 173; Harrison, Richard W., “Report on Investigations of the Benton Hills, Scott County, Missouri, in Midwest Friends of the Pliestocene, 42nd Annual Meeting, 19-21 May 1995, 7.3; Harrison, Richard W., “Mid-Continent Urban Corridor Mapping Project,” USGS Project No.: 7160-11, U.S. Geological Survey, http://erp-web.er.usgs.gov/reports/annsum/vol40/cu/harrison.htm; Elfrink, Neil, “Gujarat Analog Response,” Archives of Central U.S. Earthquake Hazard MailList, March 21, 2001, http://clifty.com/hazard/archives/1010302-021954.html; Guccione, Margaret, “Re: ‘Gujarat Analog,’” Archives of Central U.S. Earthquake Hazard MailList, Feb 16, 2001, http://clifty.com/hazard/archives/1010216-111758.html.

Advertisements

Low water on the Mississippi and Missouri Rivers Threatens Navigation on the Middle Mississippi below St. Louis, Part 1

The Jefferson Barracks Reach of the Middle Mississippi, where the river is wide and shallow and causes the Corps of Engineers no end of headaches. July 2012.

We in the midwest have had a terrible drought this summer and even though we have had some rain since the beginning of August, that rain has not flowed to the Mississippi River. The river is very low and navigation is threatened.  And navigation on the Middle Mississippi depends on water flowing from the Missouri. Let’s start with the Missouri, which in normal years supplies the Middle Mississippi south of St. Louis with 60% of its water. This year the Mississippi has drawn 78% of its water from the Missouri.

Low water at the Confluence of the Mississippi and Missouri Rivers, between the west bank and Duck Island, 2009.

Governor Jay Nixon has asked the U.S. Army Corps of Engineersto trash its plan to reduce the amount of water it releases from 17,000 cubic feet per second to 12,000 cfs from the Gavins Point Dam in South Dakota in order to maintain water levels for navigation on the Middle Mississippi. He fears economic catastrophe is the Middle Mississippi River has to be closed to navigation for want of water from the Missouri.

Gavins Point Dam at Yankton, South Dakota

This morning, the flood gage at St. Louismeasured 0.1 foot, Over the next several days it is projected to go up, and down and then way down to -0.6 feet. Any closing could happen when the Mississippi reaches -5 feet at St. Louis.

The Middle Mississippi at Tower Rock just south of Perryville, Missouri.

When the gage at Chester, Illinois gets down to about 1 foot, it is possible to walk out to Tower Rock, just south of Perryville, Missouri. The gage at Chester was a 2.4 feet this morning, which means you cannot walk out to Tower Rock without getting your feet wet.

In the late winter and early spring and extending through the summer of 2003, the Mississippi was so low it was possible to walk out to Tower Rock, south of Perryville, Missouri. Once the flood gage at Chester gets down to about 1.0 foot, it is possible to make the hike.

Should the river fall below 5 feet at St. Louis the Corps of Engineers would consider blasting away rock formations in the bed of the river at Tower Rock and at Thebes Gap.

Update: On the bright side of the drought: with less water running off the land, fewer nutrients are making it to the river, and the dead zone in the Gulf of Mexico has shrunk this years.

Fountain Bluff and Tower Rock and the Mississippi River

Fountain Bluff and Tower Rock in red

Fountain Bluff and Tower Rock in red

Before Illinoian ice sheet pushed south through Illinois, the Mississippi flowed along the eastern valley wall. The ice blocked the flow of the Mississippi between the eastern valley wall and Fountain Bluff.

Fountain Bluff at Gorham

Fountain Bluff at Gorham

The river eroded a new channel around the the west side of the bluff and along the western valley wall, leaving Fountain Bluff as a free-standing element, rising more than two hundred feet above the ancient channel. It’s named for the numerous springs that flow from it.

Where the Mississippi carved a new course into bedrock, it left behind a rocky channel that the Corps of Engineers cleared during the 1870s. The engineers left Tower Rock as  a free-standing element in the river, thinking that one day it might serve as the foundation for a bridge. The rock, protected from quarrying, is now as the  smallest national park in the country. If you dare, negotiate the currents that swirl between the rock and the eastern shore, and take a boat out to the rock for a picnic.

Tower Rock

Tower Rock on the West and Fountain Bluff on the East

When the river runs low, at 0.1 on the Chester, Illinois gage, it is possible to hike out to Tower Rock.

Tower Rock

Tower Rock

Early nineteenth century geologists ignored the “broad belt of low, wet bottom, five miles in width, and mostly covered with ponds of water, except in the very dryest portions of the season, and over which for countless ages rolled the mighty currents that formed the valley in which the turpid waters of the Mississippi new find their way to the gulf.”

Wetland between Fountain Bluff and the Eastern Valley Wall of the Mississippi River

Wetland between Fountain Bluff and the Eastern Valley Wall of the Mississippi River

“From the fact that the waters of the Mississippi are restricted to an area much less than its average width, at what is called the Grand Tower, and are hemmed by precipitous limestone bluffs on either side, the theory has been entertained that at a former period these limestone cliffs extended quite across the river, forming an immense fall which has be gradually cut away by the current of the river.” —Amos Henry Worthen


[i] Wiggers, Raymond, Geology Underfoot in Illinois, Missoula, Montana, Mountain Press Publishing Company, 1997,  233; McDonald, Timothy A., “Illinoian Glacial Boundary,” Esling, Steven P. and Blum, Michael D., eds., Quaternary Sections in Southern Illinois and Southeast Missouri, Midwest Friends of the Pleistocene, 42nd Annual Meeting, 19-21 May 1995, 2.4; McDonald, Timothy A., “Quaternary Geology around Fountain Bluff,” Esling, Steven P. and Blum, Michael D., eds., Quaternary Sections in Southern Illinois and Southeast Missouri, Midwest Friends of the Pleistocene, 42nd Annual Meeting, 19-21 May 1995, 5.14; Hajic, Edwin R., Personal communication, July, 1999; Worthen, Amos Henry, Economical Geology of Illinois, Illinois State Geological Survey, 1882, 503