Major tectonic plates (from USGS).Seafloor topography around the Hawaiian Hotspot (from NOAA)
The question came up about where are good places for geothermal energy, and the answer, of course, was to introduce plate tectonics. It was a quick introduction, and a refresher for the 8th graders, but the interest was there and it seemed impactful.
It also provided a link to talk about the Icelandic volcano that’s been disrupting air traffic in Europe. NASA has an amazing picture of the eruption on its Picture of the Day for April 19th.
Google Maps is a great tool for showing features like the mid-ocean ridges (use the satellite view), zooming in and out of the mountain ranges, tracing the Hawaii hotspot and watching East Africa split apart.
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.
[googleMap name=”Picnic Shelter #6, Pickwick Landing State Park” description=”The picnic shelter is located at the point due west of this marker.” width=”480″ height=”400″ mapzoom=”15″ mousewheel=”false”]35.055555, -88.232[/googleMap]
Blood Falls, Antarctica. Note the tent in the lower left for scale. From the U.S. Antarctic Program.
For millions of years, cut off from the atmosphere and the sun by an immense continental glacier, microbes survived in a lake of salty water under the ice. No air and no sunlight means no oxygen, so the water became anoxic and able to dissolve iron out of the rocks and sediment beneath the lake. But sometimes the lake breaches and the iron rich water comes to the surface where it is exposed to the air once again and the iron reacts with the oxygen to form a red mineral, hematite (rust). A template for life on Europa? Maybe. Blood Falls, Antarctica.
On the last morning of our immersion trip we had a choice between going to Hot Springs, Arkansas, with its geothermal springs and another museum, or hiking at Lake Catherine where we had spent the night. Since we’d been to two museums on the previous day, we pretty unanimously chose the hike. And it was great.
Conchoidal fracture in quartz (image by Eurico Zimbres FGEL/UERJ via Wikimedia commons)
We took the Falls Branch Trail, which follows a couple of young, boulder-choked creeks that have are carving steep-sided valleys through nice clean limestone bedrock. The students were constantly bringing me rocks to identify, and they were almost invariable limestone, with a few pieces of quartz thrown in. The limestone was so clean that it was near translucent (fairly close to marble) and the cobbles in the stream bed were easy to mistake for smoky quartz, particularly if they were rounded enough that you could not look for quartz’s characteristic, curved, conchoidal fracture. Quartz also tends to be a lot harder than limestone, but the ultimate test, which the students really wanted to see, is to put acid on the rock. Limestone fizzes. I did not have any limestone on this trip (note to self: get some HCl for next time), but this little experiment is a nice follow up for our discussions of ionic bonding in chemistry. We have some limestone samples back at school so I plan on doing this as a follow-up.
Quartz vein (white) cutting through a limestone boulder.
Because Lake Catherine is very close to Hot Springs, it would not be surprising to find some quartz. The hot water that’s coming out of the springs flows up through cracks (faults) that extend deep beneath the surface. The deeper basement rocks are silicates, the granitic rocks that make up the continental crust, so the hot water dissolves some of that silicate material, and when the water cools down, ever so slightly, as it approaches the surface, some of those silicates will precipitate out to coat the walls of the faults with quartz. Sometimes they even fill up the faults entirely, leaving quartz veins.
The stream bed, being of young geological age, was a series of small waterfalls culminating in the five meter high drop that gives the trail its name. The water was clear and cold but with that beautiful aquamarine tint of dissolved limestone. There’s a whole lot more I could say about plunge pools and migrating nickpoints, but I’d probably go on too long. Besides we did not take the time to talk about those since there was so much else to see.
Interference pattern in ripples.
When we reached estuary of Falls Creek and Lake Catherine, the lake’s water was so calm that the kids started trying to skip stones. This of course provided a beautiful opportunity to look at water waves and interference patterns. As the ripples from each skip of the stone expanded, they melded. The constructive interference was easier to see in the field because it made for bigger ripples. But the photos show the destructive interference very nicely.
This was an excellent hike. We were a little pressed for time since we needed to get back to school before the end of the school day, but next time, I think, I’ll have us pack our food in and have lunch on the trail overlooking the waterfall and the lake. The ability to use these types of outdoor experience to integrate the academic work is one of the main reasons I enjoy the Montessori approach to middle school. All through the trip back though I kept thinking about how I could organize things so that we would never need to see the inside of the classroom again.
