Ozark Reservoir Collapse

The weekend of Father’s day 2010, my sisters and I visited the East Fork of the Black River near Lesterville, in southeastern Missouri. It’s in the heart of the St. Francois Mountains - a small region of 1.4+ billion year old igneous rocks that are home to some of the most unique natural features in MO (Elephant Rock State Park and Johnson’s Shut-ins). These small mountains contain some of the highest points in the state, and “form the core of the Ozarks.” They are the largest of only three igneous rock exposures in Missouri (bright fuchsia on the map!) Source: http://www.rollanet.org/~conorw/cwome/article6&7.htm

Wow, the pretty purple rhyolite that makes the hard-to-erode rocks of Johnson’s Shut-ins are 1.4 billion years old! The St. Francois Mountains are the exposed geologic core of the Ozarks and used to be taller than the Rockies. Here is a map of what is considered the Ozarks. Most of the light blue is in Missouri, the Ozarks extend into northern Arkansas and some in Oklahoma (source: http://www.answers.com/topic/ozark).

Ameren UE built a reservoir on top of Proffit Mountain as a pumped-storage hydroelectricity facility. The method pumps water from a lower elevation reservoir created in the Black River by a dam, to the upper reservoir at a higher elevation during low-electricity-cost off-peak times. During periods of high electrical demand, the stored water is released through turbines to generate electricity that can be sold at the higher prices. The pumping process makes the plant a net consumer of energy overall but is economical because of energy pricing. In the satellite image you can see where the wall broke on the reservoir and went down the west side of the mountain into the valley that was the popular Johnson's Shut-ins state park.

According to Wikipedia, the electic power operation started in 1963. They thought the upper reservoir was built on pure bedrock. A software glitch on Dec 14 2005 caused the pumps to keep pumping water even though the upper reservoir was full so water flowed over the top lip and eroded the soil/rock underlying the wall which collapsed at 5:14am creating a 700 foot wide breach and releasing 1.3 billion gallons of water down the mountainside. A 20-foot-high wall of water, soil, rocks and trees scoured a path down to the bedrock a mile long until it all flooded into the Johson’s Shut-ins. The rocky shut-ins dammed the water which eventually drained through, but the narrowness and strength of the igneous rocks kept all that debris from going further downstream. The superintendent of the park, his wife and three children were swept away when the wall of water obliterated their home. They survived, suffering from injuries and exposure. The children were transported to a hospital in St. Louis and later released. One child was treated for severe burns from heat packs applied by rescue workers as treatment for hypothermia (!).

The dam of the lower reservoir, which by design is able to hold much of the capacity of the upper reservoir, withstood the onslaught of the flood, but the state park was all but destroyed by rocks, trees and water. Larry’s cabin where we stayed is downstream & south of satellite image, below the lower reservoir...silt/clay is still eroding into the water that goes by the cabin making the stream less crystal clear than it used to be.

Ameren UE took responsibility for the breach and spent $40 million on restoration of the park. More than 15,000 truckloads of debris were removed from the park in the year following the disaster, according to Ameren, including 1,748 truckloads of trees, nearly 4,000 loads of rock and almost 8,500 loads of silt. Wow that is a lot of gasoline.

(Source: http://www.columbiamissourian.com/stories/2007/08/18/rebuilding-reservoir/)

The Federal Energy Regulatory Commission fined Ameren UE $15M for the breach – the 2nd largest fine in the FERC history (after a fine on Florida Power and Light for a power outage in 2008). Federal regulators approved Ameren’s plan to rebuild the reservoir, and construction began in late 2007. The rebuilt structure is made entirely of roller-compacted concrete, unlike the rock-fill original. In addition to fill-detection instrumentation it incorporates a spillway to handle any overflow and a video system to monitor the water level. The $450 million cost of rebuilding the reservoir was covered mostly by insurance. The utility is prohibited from billing customers to recoup any of the cost. I saw a wall of concrete on top of the mountain when we were driving to the shut-ins to swim, and it felt like a sci-fi movie suddenly.

The scour-path made by the rushing water and boulders has been a boon for geologists who are now able to study an ancient mountain range. A large bed of rhyolite has been uncovered as well as rocks from several other geologic eras… Some rocks 1.4 million yrs old, others 530 million years old.

"We have 900 million years of the Earth’s history right here," said Cheryl Seeger, geologist for the Missouri Department of Natural Resources. DNR owns the bottom portion of the scour path and plans to make it available for the public and create educational programs with it.

Seeger pointed to a series of tiny ridges on a section of harder rock. "These were created by waves from a huge saltwater sea that lapped the shore," she said. "This was a beach about 530 million years ago." The entire St. Francois Mountain range, once higher than the Rocky Mountains, eventually was covered by sea. That was long before the glaciers melted, fish swam in the sea or dinosaurs roamed the Earth, she explained. Almost 1.5 billion years ago, "caldera" volcanoes spewed forth hot gases and materials from under the Earth, creating mountains. Eruptions left holes underground, which eventually caused the mountains to collapse. This pattern continued for centuries. Unlike Hawaiian volcanoes that spew liquid lava, calderas erupt explosively. "Think Mount St. Helens, only huge," Seeger said. "If you think of St. Helens’ " eruption "as the size of an espresso cup, Yellowstone was a 50-gallon bag and ours was a 30-gallon bag." (Source: Monday, October 20, 2008 in the Columbia Tribune - http://www.missouristateparks.net/johnson)