AIPG FIELD TRIP - ELEPHANTS • NATURAL WATER PARK • MONUMENTS
At Johnson Shut-Ins, the Black River has cut a number of more or less circular pot- holes into the rhyolite. These are formed in an area where stream velocity is relatively high. How might you explain the formation of such potholes? If we look carefully we may see evidence for flowbanding in the rhyolites. How might bands form in these igneous rocks?
As we leave the Park, we will drive by
exposures of the Upper Cambrian Lamotte Sandstone.
What is a Shut In? In the Missouri Ozarks, a “shut-in” refers
to a narrow, steep-walled stretch of a river where the channel is confined by erosion- resistant Precambrian igneous rock. As streams flowing across softer sedimentary units encounter the hard rhyolite and gran- ite knobs of the St. Francois Mountains, the valley abruptly constricts, forcing water through tight chutes, plunge pools, and polished bedrock corridors. Johnson’s Shut- Ins State Park provides one of the best examples of this distinctive geomorphic feature, showcasing how ancient volcanic rocks control modern river behavior.
Learn more about the Taum Sauk Dam Breach:
Association of State Dam Safety Officials. (2005). Taum Sauk Dam failure: Case study and foren- sic analysis. Association of State Dam Safety Officials.
https://damsafety.org/content/ dam-failure-case-study-taum-sauk-dam-mis- souri-2005
Barr, M. N. (2009). Effects of the Upper Taum Sauk Reservoir embankment breach on the surface- water quality and sediments of the East Fork Black River and the Black River, southeastern Missouri, 2006–07 (U.S. Geological Survey Scientific Investigations Report 2009–5111). U.S. Geological
Survey.https://
pubs.usgs.gov/ sir/2009/5111/pdf/SIR2009-5111.pdf
Missouri Department of Natural Resources. (2005). East Fork Black River: 2005 Biological Assessment Report. Missouri DNR, Environmental Services
Program.https://
dnr.mo.gov/document/east-fork-black-river- 2005-biological-assessment-report
Peterson, J., Zhang, L., Ramirez, A., & McDonnell, M. (2025). Time series analysis of vegeta- tion recovery after the 2005 Taum Sauk out- burst flood (2005–2024). Remote Sensing, 17(9), 1605.
https://www.mdpi.com/2072- 4292/17/9/1605
Rogers, J. D., Watkins, S., & Chung, J. (2010). The 2005 Upper Taum Sauk Dam failure: A case history. Missouri University of Science and
Technology.https://
mst.elsevierpure.com/en/ publications/the-2005-upper-taum-sauk-dam- failure-a-case-history
28 TPG •
Jan.Feb.Mar 2026 Taum Sauk Dam Breach
On the morning of December 14, 2005, a triangular section on the northwest side of the upper reservoir failed, releasing a billion gallons (4 million m³) of water in twelve minutes and sending a 20 foot (7m) crest of water down the Black River. According to AmerenUE, a computer software problem caused the reservoir to continue filling even though it was already at its normal level. The water overtopped the walls, leading to the failure at 5:12 a.m. In addition, preliminary indications are that minor leakage through the dam walls over a prolonged period, had carried away fine material in the walls, weakening the reservoir's holding walls. Piping ultimately creates voids in reservoir walls and causes reservoir walls to slump and fail. The failure of the reservoir occurred as the reservoir was being filled to capac- ity or may have possibly been overtopped.
There was no overflow spillway. A maximum fill level was reported to be 6 feet below the top. If the reservoir was filled in 16 hours and is 55 acres across, that would calculate to about 1 ft of water rise in 12 minutes. The reservoir would have overflowed in approximately 72 minutes, once the maximum level was exceeded. It was likely that the reservoir failed once water overflowed the reservoir as earthen levees will erode when overtopped.
The reservoir had been lined with a membrane in 2004 to minimize water leak-
age. It had been losing two feet of water for some time prior to the installation of the lining. The phenomenon of fine material being washed out of a reservoir structure is known as "piping". When piping occurs, the reservoir structure can settle in or slump, which means water may start flowing over its top – but that is because a weakened area in the reservoir has settled down.
Periodic surveys are necessary at a reservoir to identify if leakage and "piping" is occurring.
No fatalities were reported. Jerry Toops, his wife and three children were swept
away when the wall of water obliterated their home. Toops is the superintendent of Johnson's Shut-Ins State Park and Taum Sauk State Parks. They survived with injuries and suffered from exposure. The children were transported to a hospital in St. Louis and later released. One child was treated for severe burns which resulted from heat packs applied by rescue workers as treatment for hypothermia.
Low cloud levels prevented medical helicopters from flying to aid victims. It
wasn't until the clouds cleared up that the helicopters could retrieve victims. Three victims, all children, were first taken to Farmington, then they were transported by ambulance to SSM Cardinal Glennon Children's Hospital in St. Louis. A spokesperson for the family has informed the media that they do not want the conditions of the children to be disseminated.
The dam of the lower reservoir held, trapping much of the deluge. If it had given
way then towns downstream, including Lesterville and Centerville would have been in grave danger. A voluntary evacuation order was issued for those areas, but there was no damage. The high water was stopped at Clearwater Lake, the dam of which was not damaged by the rising waters.
A memo from Richard Cooper, superintendent of Ameren’s Taum Sauk
Hydroelectric Plant, indicated that the reservoir had a "Niagara Falls" style overflow on September 27 at the same spot that was breached, (caused by wave action related to winds from Hurricane Rita.) Another Cooper memo had also indicated that Cooper had warned that gauges used to monitor the water height in the res- ervoir were malfunctioning in October.
Thank you to feld trip leaders Dr. Aaron Johnson, CPG-12229, and John Bognar, CPG-08341.
www.aipg.org
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