A discussion of the physics of flight, interspersed with birds of prey swooping just centimeters from the tops of your head, made for a captivating presentation on avian aerodynamics by the people at the World Bird Sanctuary that’s just west of St. Louis.
Lift
The presentation started with the forces involved in flight (thrust, lift, drag and gravity). In particular, they focused on lift, talking about the shape of the wings and how airfoils work: the air moves faster over the top of the wind, reducing the air pressure at the top, generating lift.
The shape of a bird's wing, and its angle to the horizontal, generates lift. Image adapted from Wikipedia User:Kraaiennest.
Then we had a demonstration of wings in flight.
Terror from the air.
We met a kestrel, one of the fastest birds, and one of the few birds of prey that can hover.
Kestrel.
Next was a barn owl. They’re getting pretty rare in the mid-continent because we’re losing all the barns.
Barn owl.
Interestingly, barn owls’ excellent night vision comes from very good optics of their eyes, but does not extend into the infrared wavelenghts.
Barn owl in flight.
Finally, we met a vulture, and learned: why they have no feathers on their heads (internal organs, like hearts and livers, are tasty); about their ability to projectile vomit (for defense); and their use of thermal convection for flying.
The ground warms when it absorbs sunlight (e.g. parking lots in summer) and in turn warm the air near the ground. Hot air rises, creating a convection current, or thermal, that the vultures use to gain height.
The Sanctuary does a great presentation, that really worth the visit.
The quarry's primary purpose is to extract limestone for construction.
The landfill/quarry we visited was originally a limestone quarry; once they had the hole in the ground they needed to fill it with something so why not trash (and why not get paid to fill it).
Shoveling boulders. The rock pieces look small but only because the shovel is so big.
The limestone bedrock is blasted daily to create some massive boulders. The boulders are then loaded on some equally massive dumptrucks. There are scarce few minutes between trucks, so a lot of rocks are being moved.
Dumptruck moving rocks. Massive boulders in the foreground. Unloading dumptruck.
The trucks then dump their load into a large building where the rocks are crushed. Our guide made us stop the bus to watch the process. While watching a dumptruck unloading might seem mundane, the enormous size of the truck and its boulder load did seem to captivate the students.
Once the rocks are crushed, the resulting sediment is sorted by size (sand, pebbles and gravel, I think) and piled up. The piles are massive. I’ve been wanting a good picture that shows the angle of repose; I got several.
The angle of repose of a pile of sediment. Also notice the greenish color of the water in the pond to the bottom left. Water with lots of fine limestone particles (silt) and dissolved limestone, tends to have that color.
The pebbles and gravel are used for road construction and provide a matrix for concrete.
Since limestone dissolves fairly easily in rainwater, the sand-sized and smaller particles (< 2mm diameter) aren't used for construction -- hard, insoluble quartz sand is preferred.
Limestone: calcium carbonate (CaCO3)
However, the limestone sediment piles sit out in the open and some the finer grains (silt sized particularly), and any dissolve calcium carbonate, get washed into the nearby ponds, which turn a beautiful, bright, milky green.
Finally, in addition to the limestone sediment piles, there is also one enormous pile of broken up concrete. One of the things that stuck with the students was that fact that you can recycle concrete.
Methane in a landfill. It's produced by decomposing organic material, is extracted via wells, and is then burned to produce heat (for a school and a set of greenhouses) and electricity (soon anyway).
Decomposing waste in landfills produces quite a lot of methane gas (CH4). Perhaps better known as natural gas, methane is one of the simplest hydrocarbons, and a serious atmospheric pollutant (it’s a powerful greenhouse gas). In the past the methane produced was either released into the atmosphere or just burned off.
Greenhouses that are warmed by methane produced by the landfill. It's a cheap, close source of energy.
I remember seeing the offshore oil rigs burning natural gas all night long — multiple miniature sunrises on the horizon — in the days before the oil companies realized they could capture the gas and sell it or burn it to produce energy. The landfill companies have realized the same thing. So now, wells pockmark modern landfills and the methane is captured and used.
Looking down the slope of the landfill to see the Pattonville High School, which uses natural gas from the landfill for heating.
First, of course, the hydrogen sulfide gas (H2S), is separated from the methane — H2S produces acid rain, so it’s emissions are limited by the EPA — then, the gas from the landfill we visited, is piped to:
greenhouses, where it’s burnt to produce heat;
the Pattonville High School, which is right next to the landfill and burns the gas for heating;
and (soon) to a electricity generating power plant that will burn the gas to produce heat which will boil the water that will produce the steam that will turn the turbines that will generate the electricity.
Electric power plant -- still under construction -- that's fueled by methane from the landfill.
You may have noticed the common theme of all these uses of natural gas: it has to be burned to be useful. The combustion reaction is:
CH4 (g) + 2 O2 (g) —-> CO2 (g) + 2 H2O (g)
which produces carbon dioxide (CO2) that is also a greenhouse gas, but is, at least, not nearly as powerful at greenhouse warming as is methane.
The limestone walls of the quarry were stained red with iron precipitate.
The cliffs of the quarry were stained red. Blood, seeping out from between the bedding planes between layers of rocks, might have left similar traces down the sides of the near-vertical cliffs’ faces. But these stains are actually made of iron.
Rain falling on the land above the quarry, seeps into the ground. There it moves downward through the soil, leaching out some of the minerals there, but going ever downward. Downward until it meets a layer of soil or rock that it can’t get through. Clay layers are pretty impermeable, though in this case it’s a layer of coal. The water can’t move through the near-horizontal coal seam very fast, so instead it moves sideways across, and eventually seeps out onto the cliff face.
The red on the walls of the cliffs are an oxidised iron precipitate (rust). The iron most likely was dissolved out of the pyrite in the coal seams.
The seeping water still has those minerals it dissolved in the soil. It also has more dissolved minerals from the coal it encountered too. Coal forms in swamps when trees and other plants fall into the waters and are buried before they can completely decompose. Decomposition is slow in stagnant swampy waters because most of the insects and microorganisms that do the decomposing usually need oxygen to help them with their work. Stagnant water does not circulate air very well and what little oxygen gets to the bottom of the swamp-water is used up pretty fast. You could say that conditions at the bottom of the swamp are anoxic (without oxygen), or reducing.
Coal formation. Image from the National Energy Education Development Project.A shiny pyrite crystal in a lump of coal (happy holidays). Image via USGS.
Iron in air will rust as it reacts with water and oxygen — rust is the red mineral hematite (Fe2O3) that you see on the walls of the quarry. Iron in a reducing environment, on the other hand, will form minerals like pyrite (FeS2). According to our guide, the thin coal seam in the quarry has a fair bit of pyrite. In fact, because of the pyrite, the coal has too much sulfur for it to be economical to burn. Like the landfill gas, hydrogen sulfide, burned sulfur turns into sulfur dioxide, which reacts with water droplets in the air to create acid rain so sulfur emissions are regulated.
The water that seeps along and through the coal seam will dissolve some of the pyrite, putting iron into solution. However, the iron will only stay dissolved as long as the water remains anoxic. As soon as the high-iron water is exposed to air, the iron will react with oxygen to create rust. Thus the long stains of rust on the cliff walls show where the water emerges from underground and drips down the cliff face.
Diagram showing the coal seam, and the seeping water that creates the iron (rust) staining.
Iron precipitate in other environments
On our Natchez Trace hike we found it quite easy to stick fingers into the red precipitate at the bottom of the stream.
We’ve seen the precipitation of iron (rust) as a result of changes in redox (oxidizing vs reducing) conditions before: on the sandbar on Deer Island in the Gulf of Mexico; in the slow streams along the Natchez Trace Park‘s hiking trails in Tennessee. Iron precipitation is an extremely common process in natural environments, and it’s easily noticeable. Just look for the red.
The rich black of decaying organic matter, sits just beneath the rusty-orange surface sediment. The red is from hematite (rust) and shows that the surface is oxidizing, while the black shows that just a few centimeters beneath the surface, there is no oxygen to decompose the organic matter (a reducing environment). This image was taken on Deer Island on the Gulf Coast.
70 million year old shell and its imprint in a clay matrix, collected at the Coon Creek Science Center.
Collecting the amazingly well-preserved Cretaceous molluscs and arthropods at the Coon Creek Science Center was an excellent way to learn about fossils and the geology of the Mississippi Embayment.
Consider: the actual shell of an actual organism that actually lived 70 million years ago; not the form of the shell, petrified in silica; not the silent imprint of ridges and grooves in the mud of some bivalve’s test, long dissolved by the silent flux of millenia of groundwater flow, although you can find those, too; but to stand in the daylight, on the gravel bar of a creek, and hold the actual shell of an actual marine organism that lived here when it was six meters under water.
When we got to Coon Creek, Pat Broadbent did her typical, excellent presentation, starting with the very basics question of, “What are fossils?” Apart from the aforementioned actual preserved shells, you can also find trace fossils, like, for example, where the imprints of the an organism is left in the mud while the shell itself has long dissolved away. They can be imprints, or molds of the shells. One of my students found the mold of a crab’s claw along the creek bed; the mud filling in the claw had solidified into rock but you could clearly see where the pincer once articulated.
Pat also talked about the Mississippi Embayment, which is the long, broad valley through which the Mississippi River flows.
The breakup of the supercontinent, Pangea. Notice how the North Atlantic Ocean is opening as North America pulls away from Europe and Africa. You can also see the flooded Mississippi Embayment. (Image from Scotese, C.R., 2002, http://www.scotese.com, (PALEOMAP website)).
When the supercontinent Pangea started to break up, North America pulled away from Europe and Africa. This created a rift that eventually became the North Atlantic Ocean. At about the same time, North America tried to split into two as a second rift was created, right where the Mississippi Embayment is today.
How the coastline of North America, has changed over the last 100 million years. The sediments at Coon Creek were deposited in the Cretaceous (black line). The current coastline is shown in blue. (Image from Wikipedia).
But the rift failed (Cox and Van Arsdale, 2007). It did, however, stretch and thin the continental crust enough to create a large inland sea running up the middle of North America. Over the 100 million years since, the rift formed, the Mississippi Embayment has filled in, first with oceanic sediment, but then with terrestrial sands and silts as the mountains to the east and west were eroded away and washed into the inland sea.
The layer of silt and glauconite clay that encases the fossils at Coon Creek is called the Coon Creek Formation. Pat was very clear that we should refer to this material surrounding the fossils as “matrix”. The “d” word was prohibited. These sediments were deposited while the sea still flooded the embayment. They formed a sand bank, several kilometers offshore.
I vaguely remember doing some research on glauconite a long time ago. Glauconite pellets are found in shallow marine waters, usually far enough away from the coastline so that sediment is deposited slowly, and it’s the finer materials, such as silts and clays, that are deposited. The water also needs to be deep enough to protect the fine sediment from the force of the waves. These are ideal conditions for clams, mussels, conchs, and their Cretaceous relatives.
A simple smear of the sediment across a microscope slide is enough to show that the matrix is has a lot of quartz. You need a microscope because the mineral grains are tiny, silt sized or smaller.
But the best part of looking at the slides is finding the microscopic fossils. They’re not as ubiquitous as you might think, but they’re there if you look. I found a couple of forams, a snail-like one and another that looks like a bolivina species.
What looks like a type of bolivina foraminfera. It's benthic, which means that it lives in the sediments not in the water. It is surrounded by silt-sized grains of quartz.
However, the smear slides came later. After Pat’s talk, she took us out to a small mound of matrix that had been excavated for sampling. Everyone grabbed chunks of matrix and pared away at them until they found something promising. These promising samples were wrapped in aluminum foil so we could clean them up under more controlled conditions.
Cleaning samples.
Cleaning takes time and patience, so Pat showed us how to do it, and each student worked on a single sample. The main idea is to create a display of the fossil using the matrix as a base. The general procedure is to:
Use a small pick, paintbrush and spray-bottle of water, to wash and wipe away the matrix from the fossil.
Let it dry out well, which usually takes about five days.
Paint the entire thing with a 50-50 mix of acrylic floor wax and water. Pat recommends Future Floor Wax, but that seems to have been rebranded out of existance.
Repeat that last step three times (let it dry for about 15 minutes inbetween) to get a well preserved, robust sample.
After the instructions on cleaning, we broke for lunch. For most of us lunch could not have come early enough, not because we were particularly hungry, but because it was quite cold outside. Just the week before the temperature had been above 20 °C, t-shirt weather. Now students were clustering around a couple space heaters trying to ward off frostbite (or at least that’s what they claimed). I did offer that they could stay inside after lunch while the rest of the class walked along the creek, but no-one took me up on it. I don’t know if it’s specific to this group or just to adolescents in general, but if there a chance to walk through water, and get dirty and wet, they’ll take it no matter what the consequence.
Students looking for fossils in gravel bar.
Walking the creek, pulling shells and molds out of the gravel bars, was the best part of the visit.
Students standing in the creek, testing their rubber boots.
The water was shallow, not getting up above the shins, despite the rain showers of the preceding days. A few students borrowed rubber boots, which half of them proceeded to fill with water.
There were quite a lot of fossils. Some of the bivalves have really thick strong shells that not only survived the 70 million years since the Cretaceous, but being washed out of the matrix and tumbled down a stream bed with all sorts of sand and gravel. Some of the casts, like the aforementioned arthropod claw, are also pretty robust.
Snail shell that's been in the ground for millions of years and then got washed out into a gravel bar.
A couple of the more interesting finds are the rather elongate tube like structures that are believed to be either fossilized burrows, or fish feces (coporolite). The material in the coporolite has been replaced by minerals, which is why it survived, but it still retains a little of the ick factor.
There’s an awful lot to learn at Coon Creek. I did not even mention the mesosaur skeletons that have been found there, but there is a nice IMAX movie, Sea Monsters, that’s a nice complement to the field trip because it’s set at the same time, and in the same marine environment as the Coon Creek Formation.
This short hike that follows a limestone bedded creek, will likely take a while because there’s quite a bit of geology to see.
The start of the hike is on the eastern side of the bridge between the villas and the hotel. Head north (left in the image) toward the lake.
This year, it was on a chilly, rainy morning in February, that we started on our hike. We took a left off the concrete stairway onto the trail that runs parallel to the river flowing in the ravine just below our cabins.
We’d stayed at the villas at Montgomery Bell State Park, which is about an hour east of Nashville. The villas are quite nice. Built into the side of the valley, sitting just across a small river from the park’s hotel/conference center, and designed to be energy efficient, they’re quite comfortable with their geothermal heating and vaulted ceilings.
They’re so nice that some wanted to stay in the warm. Others, however, were eager to get outside, despite, or perhaps even because of, the rain. I gave them the choice, but everyone came.
With the rain, we soon ran into trouble. Runoff from the road and building uphill converted part of the trail into a small stream. The first few brave souls committed to wet feet, and waded through.
The dam and lake at Montgomery Bell.
But the stream along the trail did not last long. Pretty soon we left it behind, and coming out of the valley the lake and dam opened up to the right and left. Though it had been raining for much of the previous night, the lake was still very low after the dry autumn and winter. The line of grass that marks its usual shoreline was over a meter above the level of the water.
Short concrete wall that acts as the outlet level for the dam.
So we crept along the southern edge of the dam to follow the path of the overflow channel. It was quite interesting to see the sediment and debris that choked the reservoir side of the concrete wall that regulates the level of the lake. The other side of the wall, where the water must accelerate as it overtops the barrier, was clean, bare and smooth, looking a lot like concrete until you get close enough to see that it’s hard, dark, limestone bedrock.
Drill-hole with radial shatter pattern.
But not hard enough. Small, round holes pockmark the rock. Clearly artificial, with radial cracks diverging from the center, they remind me of Sarajevo roses.
They’re probably contemporaneous with the building of the dam. In order to have their outflow channel, the dam builders needed to blast away some of the rock, so they drilled holes and filled them with explosives. The blasts crushed the upper layers of rock, but the bedding plane, upon which we are walking, dissipated the force and remained, mostly, intact.
Following the reservoir outflow channel.
The bedding plane is a bit slippery with the rain and light coating of moss, so we take a bit more care with our footing. The sides of the outflow channel are steep, with nice exposures of horizontal layers of limestone rocks.
Though I don’t go into it in detail, the different layers, with their different colors, hardness, and fossils, show the changing environment in which the sediments that created these rocks were deposited. The more friable, tan-colored layers were likely formed at a time when sea-level was lower, when this area was closer to the coastline so more sand and clays could settle out of the muddy waters emerging from fecund deltas. On the other hand, the dark, dense, grey limestone rocks are much more typical of deeper seas, offshore environments.
Tree roots prying apart the bedrock: biological weathering.
I did take the time to elaborate on the topic of weathering when my students pointed out the tree growing on the side of the cliff, with its roots entwining and pulling apart the limestone rock. It’s a part of the rock cycle that we had not spent a whole lot of time talking about in the classroom so I was glad for the opportunity.
Joints in limestone. Notice how the layers on either side of the joint line up.
Weathering also plays a part in the widening of joints, and the joints we saw were obvious and important in shaping the course of the channel. Joints are simply breaks in the rocks. When this region was uplifted, the rocks were squeezed and fractured by tectonic forces. There was not enough tectonism to seriously deform the region, the rocks are after all still close to horizontal, but they did break, creating joints that cut right through the bed of our channel and straight through the wall.
You’ll notice that the layers on either side of the joint line up, so this is just a fracture in the rock. Often, the rock will break and one side will be pushed up relative to the other; that would be considered a fault.
Runnoff from the rain, flowing along and widening joint in limestone.
One of the nice things about being out in the rain, was that you could see the water in action. Gliding along the joints, picking up and eroding small pieces of debris, while slowly, imperceptibly, dissolving away the rock and enlarging the joints. It’s the same process that created the caves we saw last year at Merimec; the reprecipitation of dissolved calcium carbonate from the limestone rocks is what creates the stalactites, stalagmites and other cave formations.
Looking up the channel at exposed bedding planes and joints.
It took a bit of care to follow the channel down. It also took teamwork. We’ve been practicing all year and it’s under these conditions that all the teambuilding, from the challenge course onward, really pays off.
Committing to wet feet.
At the bottom of the bedrock traverse was a big puddle. The water from the regular outflow of the dam creates pushes up sediment that blocks the free flow of the runoff from the current rainfall. Undoubtedly, this gets washed away when the reservoir overflows through the outlet channel, but today there was just a big puddle.
Here we faced a choice. We could have taken a hard right and walked back up to the dam along the edge of the small cliff that overlooked the outlet channel we’d just come down. It’s a nice walk, through last year’s leaf litter, and the overhang is just high enough to provide a small taste of vertigo. But the students wanted to push on, past the confluence, and follow the stream downhill. A second set of students had made the full commitment to wet feet, and any initial reluctance to be outside on a rainy day had disappeared. We followed the stream.
Convergence of the overflow channel and the drainage stream for the reservoir.
Just a few meters downstream from our decision puddle, we ran into the confluence of the regular outflow from the dam and the ephemeral, rainfall driven stream we’d been following. It’s a good place to talk about tributaries, deltas, and sediment transport, deposition and erosion, because the channel deepens into a little pool with lots of small scale features.
Following the stream.
Past the confluence the stream straightens out. It’s remarkably straight. If it weren’t for the fact that we’re in limestone rocks, it would be easy to assume, given the dam and all, that the lack of sinuosity is artificial. But it seemed like the stream was flowing parallel to the joints we’d seen earlier, so it’s not unlikely that the water is following a fracture in the rock. When convergent, tectonic forces fracture rocks, the rocks tend to break at an angle to the direction of the forces (somewhere around 60 degrees to the direction of the forces, if I remember correctly).
Climbing up to the trail that follows the ridge.
Following the stream brought us close to the picnic shelter near the entrance to the park. Just across the water is a pathway up the rocks on the side of the valley that takes you up to the trail that follows the ridge that parallels the valley.
Looking down at the stream and its floodplain from the top of the ridge.
It’s quite peaceful, standing on the ridge while water droplets drip through the sparse winter canopy, with last fall’s leaf litter beneath your feet.
Looking back down into the valley you could see (and talk about) the stream and its flat flood plain. It’s a chance to anthropomorphize. The stream “wants” to meander. It has to be constrained to one side for a reason.
Crossing the dam on the way back to the cabins (upper left).
The ridge trail takes us back to the reservoir and dam, which are quite noticeable if you’re paying attention. We traipsed down the hill and walked a narrow path between the tall, reddish-tan grass that tops the dam, and the bouldery rip-rap that protects the earthen structure from the force of the waves.
Along the edge of Pickwick Lake are outcrops of sedimentary rock being slowly broken apart by the action of the waves on the reservoir. We stopped for lunch at Shelter #6 in Pickwick Landing State Park (see map) before finding our cabins for this immersion. Located at the eastern edge of a triangular ridge of land girded by drowned river valleys on two sides the shelter is almost surrounded by water. On a beautiful, clear day at the beginning of spring, with temperatures verging on t-shirt weather, tiny flowers blooming in the grass and tree leaves just sprouting, it was an almost perfect time and place to take a break after a long drive.
Shelter #6.
Yet despite the fact that we were eating later that we normally do, half the class walked right past the shelter and down the rough slope to the lake’s edge. There they found fossils. Beautiful crinoids were weathering out of thin (4cm thick) alternating layers of sandstone and limestone, their long fossilized necks resisting while the limestone around them slowly dissolved away. They also found bivalves partially exposed on the face of the broken cliff and in the small pile of tallus. There were even a few thin sandstone wedges sitting on the rocks at the edge of the water that looked like fossilized burrow molds. It was quite fascinating.
View from inside the shelter.
Neither the word “science” nor the phrase “natural world” was used, and they brought the questions to me, which I always consider better than me asking them. Next year when we study Earth History perhaps the subject will be considered boring when we see it in the classroom, but today, out there on the rocks at the edge of the water, they got a great primer.
This stop, planed solely as a lunch break was so successful that I now wonder if I should plan the immersion trips to introduce the topics we cover in class rather than using them to integrate what we’ve already seen. Let the outdoor experience be the “spark the imagination” part of the lesson. I’m not sure, but it’s something to think about.
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