It’s difficult to find solace after any disaster, and the December reservoir breach at AmerenUE’s Taum Sauk Hydroelectric Plant is no exception.
The breach sent more than a billion gallons of water rushing down the side of Proffit Mountain in southeast Missouri. It endangered people, killed wildlife, scoured the forest and polluted the Black River.
And it devastated one of the state’s natural prizes, Johnson’s Shut-Ins State Park.
It was by all accounts a catastrophe, unlike anything Missouri has seen. The cleanup will be expensive, challenging and time-consuming. Lives will change; some already have. Full recovery appears beyond reach.
Yet scientists are cautiously excited, for out of the tumult there might arise the unprecedented opportunity to learn more about what makes the St. Francois Mountains, and their popular shut-ins, unique.
Cheryl Steeger, of the Geology and Land Survey Division at the Missouri Department of Natural Resources, toured the area on Jan. 12 with a team of fellow scientists.
“It’s pretty much overwhelming,” Steeger said of the fresh exposure. She said it was fascinating “just in terms of the amount of what you can see geologically showing up there, as opposed to what you find at some small outcrops scattered around the St. Francois Mountains. ... You really get a really nice, clear view of what has happened there geologically.”
Plenty of visitors know how special a visit to Reynolds County can be. Lazy floats down the cold Black River. Long days crawling about stream-slickened, sun-warmed shut-ins. Easy nights camping in pristine Ozark forest.
Few, however, are aware how the region came to be what it is. The shut-ins’ location at the heart of the St. Francois range gives it a unique geological status. Their formations tell tales of a time so long ago few can contemplate it. For all the wistful days spent frolicking in the shut-ins’ pools today, there were millennia of violent change.
The St. Francois Mountains already are a treasure trove for those who study igneous rock, which elsewhere is usually buried beneath 1,500 to 3,000 feet of sediment. In the St. Francois range — and especially at the shut-ins — there is an opportunity to examine igneous rocks formed by volcanic eruptions almost 1.5 billion years ago.
It’s a rare find for geologists, such as MU’s Peter Nabelek. He studies Precambrian geology, which examines the period from almost 4.5 billion years ago to roughly 500 million years ago.
“It’s one of the few places in the midcontinent where you can see igneous volcanic rock, or much of what we call the continental basement,” Nabelek said of the shut-ins park. “That’s the hard rocks of the continent that are buried in other places throughout the Midwest.” For 40 years geologists in Nabelek’s field have relied on remote rock outcrops or the relatively compact shut-ins to catch a glimpse of stone that originated deep within the Earth’s mantle. It’s an effort they’ve been willing to make. But the Taum Sauk breach, its undisputed ill effects aside, has inadvertently created a wondrous new and accessible laboratory in which to examine the evolution of the landscape.
Steeger is one of many looking forward to the opportunity.
“I think it’s just going to give us such a big exposure that we’re going to be better able to see how some things fit together.”
The emergence of the St. Francois Mountains began about 1.7 billion years ago as island arcs collided with the craton, an old and stubbornly stable section of the continental crust. The merger deposited new material along the continent’s southern border, Nabelek said, setting the stage for a geological blockbuster.
“You can just imagine a whole bunch of islands smacking into the continent and it growing in size,” Nabelek said. “We think that’s probably how the volcanism started.”
Nabelek said mountain-building events most often result in a very thick crust beneath, which later collapses and spreads “to create a whole bunch of volcanism.”
But the crust where the St. Francois range formed was thinner than usual, allowing a thick mix of silica-rich magma and gases to form an explosive boil, called a caldera, just beneath the surface. When the caldera blew, it spewed searing clouds of ash and pyroclastic lava flows.
“They’re the kind (of eruptions) that have the gigantic clouds that go up 15 to 30 kilometers high,” said Gary Lowell, a geologist at the University of Texas-Arlington who studied the St. Francois Mountains for 35 years while at Southeast Missouri State University in nearby Cape Girardeau. “At the same time, they produce these foamlike flows that spread out over time (and) fill out the topography.”
Such eruptions explain the prevalence of ash-flow tuffs and igneous rocks — including rhyolites, basalts and granites — at the shut-ins. Yet there’s nothing left today of the volcanoes that produced them.
Syracuse University geology professor Pat Bickford, who conducted the first thorough research of the shut-ins while working at the University of Kansas beginning in the 1960s and up until the early 1980s, said what we see today is only the product of eruptions.
“The volcanic edifices were eroded away, and all we have left is the crystal products of those eruptions,” Bickford said. “So when you talk about Proffit Mountain being the core of an old mountain, it’s actually what’s left of an old knobby hill and the result of a process of erosion that took place over 500 million years ago.”
Bickford spoke of a rise in sea level during the Cambrian period that covered the southern portion of the present-day United States, including the St. Francois region. As the seas receded, they left behind a layer of sediment known as the LaMotte Sandstone. Softer than rhyolite or granite, it was more vulnerable to erosion by wind and water.
Once the Black River carved through that sandstone to reach the harder igneous, it began to cut deep instead of wide, creating the narrow, twisted and pockmarked channels characteristic of Johnson’s Shut-Ins State Park. It’s those vertical cuts that geologists crave.
“In this area we don’t have much of a (vertical) topography,” Nabelek said. “But ideally a cut through the rocks is what we like to have.”
Lowell said Johnson’s Shut-Ins is an ideal place for researching Precambrian rock.
“Johnson’s Shut-Ins is one of the best — maybe it is the best — certainly when you combine accessibility. You can see a good part of the story of the St. Francois Mountains.
“You have your oldest rocks forming your highest outcrops in the state,” Lowell said. “The highest point in the state is Taum Sauk Mountain, and the rock there is close to 1.5 billion years old. That’s what the St. Francois Mountains are famous for, and everybody knows that.”
It took just 12 minutes for the torrent from the Taum Sauk reservoir to uncover formations nearly 1.5 billion years old.
Steeger, of the DNR’s geology team, said the impact of the flow was obvious during her tour of the shut-Ins and the Proffit Mountain scour, which extends 6,000 feet down the slope. Generally, she said, about five feet of topsoil has been washed away.
“It varies quite a bit,” Steeger said. “...Pretty much everything is gone on the upper part (of the scour), and then down where it flattens out is where everything that washed downhill is deposited.”
While impressed by the size of the exposure, Steeger said she was fascinated by the colorful layers of rhyolite and granite it revealed.
“In some areas the rhyolite tends to go from a dark brown to red,” she said. “Then the granite is the next thing you see, and it’s kind of that pinkish color that it’s well known for. And then you finally get down to the base of the sedimentary sequence, and there (are) some boulders of rhyolite and granite that have a kind of greenish color.”
Steegar said she thinks the scour carries abundant opportunities for research, and she’s not alone. Scientists from several universities, including the University of Missouri-Rolla, have already inquired about access.
“(They’ve) been asking, ‘How soon can we get down there? And if we can’t right now, do you have any idea when we can?’” Steegar said. “We have no idea, though. It’s pretty much up to (AmerenUE) to make that decision.”
AmerenUE spokesman Tim Fox said the primary concern right now is to stabilize the area so the Federal Energy Regulatory Commission can continue its investigation of the breach and determine whether the upper reservoir should be rebuilt.
“In the past, experts have been allowed on the site on a very select basis,” Fox said of researchers. “However, going forward, access will be extremely limited. And concerns about safety rule that we can’t allow anyone but crews attached to the project to be up in the upper reservoir area where the breach occurred Dec. 14.”
The Taum Sauk plant was built atop Proffit Mountain in 1963 and supplied power during peak daytime demand by releasing water from the upper reservoir down a 7,000-foot tunnel to spin turbines. At night, the turbines pumped the water back up the mountain to be released again. Over the years AmerenUE has contemplated building more such power plants in the region.
On Tuesday, the utility company announced it had submitted a plan for stabilizing the upper reservoir dam; it awaits a DNR permit to begin the work. The plan calls for removing concrete parapet panels so that heavy equipment can get in to stabilize slopes, rebuild existing roads and construct new ones; remove all silt and remaining liner material; and Install a cover and hatch on top of the vertical shaft that carries water back and forth between the upper and lower reservoirs.
“What’s most important to keep in mind is this is not a plan for the reconstruction of the Taum Sauk facility,” Fox said. “It was mandated by the FERC that we submit a plan so the site could be secured for further investigation and analysis of what caused the breach.”
Engineers appointed to oversee the FERC investigation recommended this month that any new dam be built entirely of concrete. Fox said it’s too early for any decision.
“The FERC will go in and look for any further causes of the incident, see if rebuilding the reservoir is feasible and, if it is, (tell) what options are available to do that.”
If and when AmerenUE stabilizes the dam and grants access to the Proffit Mountain scour, geologists will have a field day.
“It really can have something for everybody in geology,” Steeger said. “Both for people who look at Precambrian or some of the Cambrian sedimentary rocks, and (for) those who are looking at modern depositional systems.”
But if a vertical cut is ideal when investigating St. Francois geology, what benefits would scientists gain from a scour that reveals only the surface of the rock? Nabelek said the scour could reveal how pyroclastic flows and lava flows behaved once belched from the Earth.
“You could see how the lava flows were coming out of the volcano and how the ash flows began piling up,” he said. “It would give an idea of what volcanic processes were like at the surface, and what is was like after the processes which drive a volcano had acted.”
Lowell said that until all the debris is removed from the scour, its true value to geologists remaIns a mystery.
“You don’t care about what debris may have been transported down the channel,” Lowell said. “But at any rate, the breach of the dam did stir up a predictably large and widely distributed channel. Whether there any good exposures in that channel is something I don’t know, but it’s something worth looking for.”
Steeger remaIns optimistic, confident some good can come from the tragedy.
“I think if it becomes accessible for research to be done, it is really going to give us some decent Insights,” Steeger said. “More so than saying it’s just a nice big exposure of what we’ve already seen.”
Glossary of Johnson’s Shut-Ins terms
Turbidity is a measure of the cloudiness of water. Water cloudiness is caused by material, such as dirt and residue from leaves, that is suspended in the water.
The fine-grained volcanic or extrusive equivalent of granite, light brown to gray and compact.
A coarse-grained, intrusive igneous rock composed of quartz, orthoclase feldspar, sodic plagioclase feldspar and micas. Also sometimes a metamorphic product.
A fine-grained, dark, mafic igneous rock composed largely of plagioclase feldspar and pyroxene.
One and a half billion years ago, hot volcanic ash and gases spewed into the air, then cooled, forming igneous rock. Later, shallow seas covered the rock, depositing sedimentary rock. The land rose. The sea fell. The weather began tearing down the land, exposing the volcanic rock beneath it. Waters of the Black River became confined, or “shut-in,” to a narrow channel. Water-borne sand and gravel cut deeply even into this erosion-resistant rock, swirling, churning and carving potholes, chutes and spectacular canyonlike gorges.
A rock formed by the accumulation of fragments of volcanic rock scattered by volcanic explosions.
The Precambrian is an informal name for the eons of the geologic timescale that came before the current Phanerozoic eon. It spans from the formation of Earth around 4,500 million years ago to the evolution of abundant macroscopic hard-shelled fossils.
Any of various devices that convert the energy in a stream of fluid into mechanical energy. The conversion is generally accomplished by passing the fluid through a system of stationary passages or vanes that alternate with passages consisting of finlike blades attached to a rotor.