Cheating Death One More Time: Home from the Field

Sunset in Death Valley near Badwater

Hey, I'm back, after five days in the wilds with no wi-fi access, and no television. Did anything happen while I was gone? What about that asteroid that was making a close pass...did it cause any problems? I sure wouldn't want to be around if a big chunk of space rock actually entered the atmosphere...

Okay, I actually did hear about the Russian near miss, and because our media access was really limited, we first thought we were hearing that 400 people had DIED. It just goes to show how stories can get out of hand. What an extraordinary event however, and what a relief that no one actually was killed.

Meanwhile, I've had a delightful weekend doing what I love: teaching geology in the field, this time mostly in Death Valley National Park. There is such a difference between drawing lines on a chalkboard to represent rock layers, and standing in front of the real thing.

Our group included a fair number of geology majors, but most were new to the science, with only a few weeks of a lecture class completed before we tossed them, kicking and screaming, onto an outcrop of rock (actually, this was a stand-alone class, and all the students had chosen to be there).

To get our new students up to speed, we started in the Renaissance, reviewing the basic rules of stratigraphy as described by Nicolas Steno in the 1600s: superposition, original horizontality, and lateral continuity (I described these principles in detail last year, in this post). These principles allow us to start discerning the sequential story of these rocks. We did some basic rock identification so the students could start determining the ancient environments that were responsible for these sediments. Note the preponderance of reds and browns; these rocks were exposed to oxygen at the time of their formation and burial. The region was also subject to occasional volcanic activity, as shown by the white ash layers (which also provide a means of accurately dating the rock).

The sedimentary sequences were cut by a series of minor faults, providing us with an introduction to tectonic processes, as well as offering a fine example of cross-cutting relationships. Ultimately, the students were able to work out a reasonably complete sequence of events that produced the spectacular red cliffs.

Although we couldn't see any at this locality, we talked about the rich fossil record at this site, a group of animals that included early species of horses and camels, large predatory ancestors to wolves and bears, and large grazing species similar to rhinos.

All in all, Red Rock Canyon State Park in the Mojave Desert of California is a great place to introduce basic principles of geology. When we finished up here, we were ready to take on the much more complex landscape of Death Valley National Park.

Strangers in a Strange Land: Discerning the Story in the Rocks at Red Rocks

In the last post, we were introduced to the basic rules of stratigraphy as they stood exposed in the spectacular cliff faces of Red Rock Canyon State Park in California's Mojave Desert. A classroom chalk board can only provide a cartoon of these concepts, so there is nothing quite like being there and laying your hands on these records of the Earth's past. We were on the road with 30 community college students, most of whom were seeing this landscape for the first time. After an introduction to the stratigraphic principles of superposition, original horizontality, lateral continuity, and cross-cutting relationships, I sent the students forth to test their newly acquired knowledge against the cliffs above. We weren't quite to the point where we could do geologic mapping, but I provided them with an outlined photo of the scene (below) and asked them to describe the rocks, and identify any structures.

This is one of the finest moments a teacher gets to have. I wasn't teaching at all; my students were teaching themselves. They were crawling up and down the slopes, taking notes, and discussing what they were seeing. OK, it's true there was no cell phone service, so what else were they gonna do?

The layers were readily labeled on the basis of color alone, and most of the students developed some version of the picture below (click to enlarge):

I climbed up the slopes to have a closer look at some the exposures. What happened here 8-12 million years ago? The red and brown layers (A, C, and D) proved to be arkosic sandstones, the kind of thing one might find in river channels and alluvial fans in a region of relatively high relief (lots of rapid erosion). Some of the finer-grained brown sediments formed in river floodplains. These rocks had clearly formed on land.

The white layers (B) with puffy deposits that kind of looked like ground hamburger were ash deposits, evidence of regional volcanic activity. The ancient environment here was beginning to look a little bit dangerous!

The upper cliffs and slopes (layer F), proved to be evidence of the greatest geological violence possible, a rhyolitic tuff breccia. The rock formed when hot ash rolled over the landscape, picking up gravel and debris and incorporating the material in the nearly molten tuff deposit. This was no place to be hanging about...but plenty of animals did. The layers of the Dove Springs Formation are a treasure trove of Miocene fossils, one of richest beds found in California (or pretty much anywhere, really).

The animals found in the sedimentary sequences here include include extinct elephants, rhinos, three-toed horses, giraffe-like camels, saber-toothed cats, and bone-crushing dogs as well as smaller animals like ancestral skunks, martens, alligator lizards, rodents, and shrews. (follow the links to descriptions of each type of animal on the Los Angeles Natural History Museum website).

Faults in a cartoon drawing on a chalkboard are a lot easier to see than most faults in the real world. A number of the students noticed how the layers ended and identified the fault that caused them to be offset (see the arrows in the diagram above). I headed up to take a closer look at the fault surface...because I think everyone should know their faults...

We only had a few precious days to see as much as possible on this trip, so we couldn't spend as much time at Red Rock Canyon as we would have liked. A fair number of geology programs do mapping exercises here, spending several days on site. It sounds like fun...if it isn't too hot. It was time for us to move on, so we loaded up the vans and drove north on Highway 14 towards our next destination at the south end of the Owens Valley. That will be part of the next post.

If postings seem sparse in the coming week, it would be because we are about to embark on part two of our Strangers in a Strange Land journey: an exploration of the Mojave Scenic Preserve in the desert south of Death Valley. We're attending the spring meeting of the Far Western Section of the National Association of Geoscience Teachers at the Desert Research Center at Zzyzx. Hope to see a few of you there!

Strangers in a Strange Land: What stories can the stones tell?

What does a cartoon tell us? I remember a time when at least certain cartoons had the purpose of communicating an important moral or story at a level that could be understood by anyone (and then there were the other 99% that represented empty brain calories...what have we done to our kids?). I spend a lot of time and effort (with varying success) drawing cartoons on a chalkboard to illustrate basic geologic principles. Part of what is missing is the context. I often draw the above picture to illustrate a fault (and some important principles), but the lines are often meaningless, because students are not yet associating lines on a board with rocks in the real world. So I try to give the picture some "realism" (below). I suppose this is a little bit like the difference between stick figures, and the more complex drawings by comic artists (Superman and Batman!). Or not...

I ask the students to imagine they are walking through a canyon, and that they see rocks in the canyon walls that are aligned like those above. Since many of them have not done such a thing, or they were not looking at the rocks at the time, this can still be a meaningless exercise. As Mrs. Geotripper has led me down the road into art history, I have become aware that artists throughout history have had a similar problem.

Source: http://en.wikipedia.org/wiki/File:Masaccio7.jpg

Understandably, art throughout history has mostly been about gods, people, and to a lesser extent, animals (I'm thinking of cave paintings and petroglyphs, for instance). If rocks were ever included in a scene, they lacked structure, at least through the Renaissance. Note, for example the mountains in the scene above by Masaccio ("Tribute Money", c. 1426). Despite the vibrant colors and the life-like rendering of the humans, the mountains in the background are little more than gray blobs, lacking any kind of detail. The mountains in the image are mere cartoons.

Source

Leonardo da Vinci is often given credit for introducing real geological details in some of his works such as the meandering river in the "Mona Lisa", and the clearly layered aspect of the stones on the water in the "Virgin of the Rocks" seen above. This had a lot to do with the fact that he had observed and studied rocks in the course of his life. He saw, comprehended, and thus recorded the structure of the rocks in his works.

So...what do Leonardo da Vinci paintings and cartoons have to do with our journey to Death Valley last week? It has to do with the intrinsic and tangible value of the field trip in geoscience education. You can show draw cartoons on a chalkboard, you can show digital images on a screen, but nothing can ever substitute for the value of students standing on a mountainside, laying their hands on the rocks and making their own observations and judgements about the story told by the rocks.

For my students, and for the first pioneers of geology, telling the story of the rocks was a huge step. The mere recognition that rocks have a story was one of the great advances in the science, because in the European worldview of the middle ages, rocks were simply created as is, and changes since their origin have been minor. They barely deserved attention unless they contained valuable ores. Nicolas Steno (1638-1686), a Danish physician who spent much of his life in Florence, changed that.

St. Nick (yes, he was beatified in 1988!) first annunciated three of the four founding principles of stratigraphy, and each of them can be connected to the cartoons I used above. Take a look again, only now with labels:

If we recognize that each layer formed uniquely from the others, then we can start to talk about the order in which things happened. Which layer formed first? If you said "A", then you understand the principle of superposition: if sedimentary layers have not been overturned, the oldest layers will be found beneath the others.

Did these sedimentary layers form originally as sloping layers? If you think layers form horizontally, in the bottom of lakes, on the bottom of the sea, or on a floodplain, then you understand the Principle of Original Horizontality: most sediments originate in horizontal layers. If the layers are tilted, some outside force put them that way.

Did layer E or F originally end in a cliff? If you think not, you are on the verge of understanding the Principle of Lateral Continuity: sediments are continuous unless they abut against the edge of the original sedimentary basin, or they thin out. We understand that one can expect to find more of layer E or F in the general vicinity, because although erosion has removed the intervening rock, the original layers continued across a larger area than just this outcrop.

When did the faulting occur? If you think it came after the sediments were deposited, than you would be right, and you begin to understand the Principle of Crosscutting Relationships: faults and intrusive rocks are younger than the rocks they cut across. Steno may have written something about this, but the principle is associated more often with James Hutton in the latest 1700's and Charles Lyell in the early 1800's.

With this basic background (oh my, this post reads like a classroom lecture, doesn't it?), you can begin to understand the enthusiasm with which I presented these topics on our Death Valley trip. I was standing in front of the cliff in the picture below:

It's all there, including a sweet looking little fault cutting diagonally across the cliff face. We had reached Red Rock Canyon State Park on Highway 14 along the Garlock Fault and the El Paso Mountains in the Mojave Desert. The park is a showcase of geological principles, and it doesn't stop with the basic ones; those sedimentary layers are chock-full of fossils, and there are lava flows nearby too.

After presenting the basic principles we walked around the corner and encountered another outcrop, as seen below:

The students set out to identify the kinds of rocks, the order of the layers, and to define any structural complications. After only a few hours on the road, they were already deciphering the story of the Earth, as exposed in this corner of the Mojave Desert. What can you discern from this photograph? Can you do as well as they did?