Desert Geology course at The College of Wooster

The 2015 Wooster Desert Geologists!

Geology in the News –

The evidence is now clear that Mars once had a very large ocean of water, and it lasted far longer than anyone had previously imagines. One of the clever ways NASA scientists have deduced this was to look at the amount of deuterium in the remaining ice. Vast amounts of water simply escaped to space, concentrating the “heavy water” (that included deuterium) that was left behind. Here’s another article on the vanished Martian seas.

Big news in the field of human evolution: a new lower jawbone of Homo habilis has been found in sediments in Ethiopia dating back 2.8 million years. This pushes back the range of this species by about 500,000 years. This is very close to the latest date known for Australopithecus afarensis (“Lucy”). I’ve seen these articles before that claim the human family tree will be “redrawn”, so I’ll withhold judgement until other experts have their say.

This is a fun BBC article on the diversity of flying organisms. I didn’t know that there are flying squid, nor that it is more energetically costly to fly over water than land. Who would have guessed that 20% of all the particles between 0.25 and 1 micrometer in size 8-15 km up in the air are flying bacteria?

This session will be brief. We will review the “bring list”, schedule, regulations, expectations … and the latest Mojave Desert weather reports!

2013 Mojave Desert Field Trip Group

Geology in the News –

Great “astronomical sleuthing” shows that a newly-discovered dwarf start brushed our Solar System about 70,000 years ago. It seems to have passed through the outer parts of the Oort Cloud. If it “perturbed” some icy bodies to become comets, we’ll see them in about 1.3 million years. There has long been speculation that something similar happened in the Cretaceous to release comets, at least one of which may have struck Earth.

Now we can watch in real time as the oceans slowly acidify. You know the story, which is repeated in the article, about the rise in atmospheric carbon dioxide that produces more carbonic acid in rain, freshwater and the oceans. Depressing indeed.

My friend Mary Droser and her colleagues have found some very cool vertebrate trackways in the Early Triassic of Utah. A tantalizing glimpse of life after the Great Dying.

Dr. Judge and Dr. Pollock will lead a “virtual field trip” today highlighting the places we will visit with new imagery and other technological wonders. This gives us a chance to repeat our schedule again, with links. Prior to class, be sure to examine the web resources for each site. Bring your laptop.

Geology in the News –

Remember the hypothesis of the Moon’s origin that involves a planet-sized body crashing into the early Earth? I just learned that planet has a name: Theia. Now isotopic evidence is telling us more about Theia, including that it had a composition similar to Earth, but not quite the same.

An extensive survey of the fossil record (and living organisms) shows conclusively that evolution favored larger animals in the sea. “In the past 542 million years, the average size of a marine animal has gone up by a factor of 150.” That’s cool. Bigger is almost always better in the ocean, and changing environmental conditions may have played a role.

More often than you think we find specimens squirreled away in museums that someone forgot to properly identify, and they turn out years later upon rediscovery to be new to science. The latest case is a fantastically-preserved ichthyosaur from the Jurassic of England. Museum collections are absolutely critical to our continuing enterprise of describing life’s diversity.

Dr. Meagen Pollock, our esteemed petrologist, is our guest speaker today. She would like us to visit the Mojave National Preserve Geology Field Trip website and read the pages on Cima Dome, Hole-in-the-Wall, Cinder Cones, and the Granite Mountains. (Lovely places, all.) We will take the virtual field trip in class and view some representative rock samples from our collection. Petrologists are warned that Dr. Pollock expects you to be able to identify and describe the rocks!

(Remember that you can click on the Mojave Desert tag of our Wooster Geologists blog to see lots of photos and stories from our previous field trips in this area.)

Geology in the News –

Remember the hypothesis of the Moon’s origin that involves a planet-sized body crashing into the early Earth? I just learned that planet has a name: Theia. Now isotopic evidence is telling us more about Theia, including that it had a composition similar to Earth, but not quite the same.

An extensive survey of the fossil record (and living organisms) shows conclusively that evolution favored larger animals in the sea. “In the past 542 million years, the average size of a marine animal has gone up by a factor of 150.” That’s cool. Bigger is almost always better in the ocean, and changing environmental conditions may have played a role.

More often than you think we find specimens squirreled away in museums that someone forgot to properly identify, and they turn out years later upon rediscovery to be new to science. The latest case is a fantastically-preserved ichthyosaur from the Jurassic of England. Museum collections are absolutely critical to our continuing enterprise of describing life’s diversity.

Deserts are such dry places that when the rain does come it can have dramatic effects. Desert soil sheds water quickly, and there are relatively few plants to retard runoff. The result is often a flash flood. Here is a NOAA page on predicting flash floods, not all of which are in deserts (thanks in part to deforestation), and here is a NOAA page where you can get the latest flash flood warnings by zipcode. And please, young geologists, never end up in a narrow canyon during a flash flood.

Alluvial fans and debris cones are dramatic water-formed features, and they are well displayed in deserts. They are characterized by their fan shapes (they’re really deltas on land) and poorly-sorted sediments.

On our field trip we will see that wadis (also known as arroyos, washes, or dry river beds) will be our pathways into the desert wilderness. Here’s a USGS page about wadi (wash) development in the Mojave. Note how important it is to understand past climate conditions and geomorphology before interpreting present geomorphic features. This is especially true for the Mojave River, which you will soon get to know well.

Want to see beautiful photographs of Death Valley? They are very cool, as are these. Here’s to sunshine, flowers, and rocks as far as you can see!

Speaking of desert water, I just found a series of blog posts on the recent history of Zzyzx. It is a good introduction to Curtis Howe Springer. You can also check out the Wikipedia entry on Rev. Springer.

Geology in the News –

Here’s an extinct South American rodent that was the size of a buffalo and had incisors that could inflict some serious damage. Josephoartigasia monesi was a kind of monster guinea pig. Impressive.

This short BBC time-lapse film of the Vermillion Cliffs in Arizona is beautiful and soothing. You’ll also see superposition, dune cross-bedding in a Jurassic sandstone, entrenched meanders, and a stunning starry confirmation of the Earth’s rotation.

Could there now be “hundreds of billions of Earth-like planets in our galaxy which might support life”? The numbers of detected exoplanets is now in the thousands, enough so that some astronomers can suggest that most stars have planets. It’s not feeling so lonely any more.

This week will focus on the structural geology and tectonics of the Mojave region. Some of you have completed the structural geology course (Geology 313); others of you are in it right now; still others can only dream of it in the future. We know this and will review most terminology for you, but you want to at least visit again the structural sections of your Geology 200 notes.

Please return to the USGS Mojave National Preserve website and review the section on the general geological history of the Mojave Desert and the portion covering faults and active tectonics. We will discuss the San Andreas and Garlock faults, both of which are described at the Southern California Earthquake Data Center. The USGS also has a very brief introduction to the San Andreas fault. Both of these faults simulate strike-slip motion, but strike-slip faults can be very complex. Do you remember structural vocabulary such as flower structures, releasing vs. restraining bends and transpression vs. transtension? If not, Wikipedia has a quick vocabulary review of each. You’ll also want to become comfortable with other fault vocabulary such as normal faults, reverse/thrust faults, dip slip faults, and oblique faults.

If you have time, please review the geological history of Death Valley itself as presented by the National Park Service, along with the USGS webpages on Death Valley through time. Death Valley is a spectacular place for all kinds of geology, from the Precambrian through modern desert processes, so we will return to it often in our introductory sections.

Geology in the News –

We have so much more to learn about human evolution. We’re not even done finding the most basic fossils. The latest is a set of hominid teeth in China between 60,000 and 120,000 years old. They are not Homo sapiens. They’re not any recognizable species.

There’s a new set of survey results out on Americans and their perception of science and scientists. It is, of course, not good news when it comes to the acceptance of evolution or climate change. We’ll let a snarky British newspaper tell the story.

I didn’t think of this one: Climate change may mean more volcanic eruptions in Iceland. By melting more ice off the island, it gets lighter and rises. This in turn decreases pressure on the subterranean magma bodies, causing more to erupt lava on the surface. This can’t be good news for us.

The wind is the part of the desert that I miss the most. There is something primal in the desert wind, the way it can go from a feathery touch to hot breath to a raging dust storm in just minutes. The features the wind creates are among the most attractive images in geology. ( “Of all natural forms, sand dunes are the most elegant – so simple, severe, bare. Nature in the nude.” From Desert Images, by Edward Abbey.) Our goal for Friday’s lecture is to understand the wind in the desert: where it comes from and what it does as a geological process.

We’ll start with an overview of eolian (wind) processes, which this physical geography webpage gives us (more or less). What causes the wind in the first place? How do Mojave Desert winds differ from other wind systems? (OK, that poem isn’t so great, but at least you were entertained by the pop-ups. Maybe this Mojave poem by Sylvia Plath is better?) How windy is it in the Mojave Desert right now?

As for the effects of wind in the desert, you’ll certainly want to start with some movies of sand movement in wind tunnels (very exciting, especially the close-ups), and read how some Germans have modeled sand dunes in that classic German way. As for real sand dunes, there are many websites with spectacular photos and descriptions. We will even see one of the famous deposits of “acoustic sands” on our field trip. (Hearing the sound is another story. I’ve heard it only once doing experiments on the Kelso Dunes with my Wooster colleagues.) The movement of sand in deserts is a serious issue, especially when desertification approaches a city, like Nouakchott, Mauritania, in this example.

Finally, we’ll look at the issue of dust derived from deserts by the wind. Loess is a deposit of wind-blown silt or clay. Dust storms have increased in frequency across the globe as deserts have increased and desert soils have been disturbed. This has very worrying health implications. (I grew up, for example, with the constant threat of Valley Fever.) Desert dust storms are even implicated in the decline of coral reefs.

If we have time we may get to talk about the Mojave wind as a renewable energy source — but the topic is presently mired in much debate, with even the military entering in.

Field trip note: This is a good time to review the bring list from the Desert Studies Center. It may be updated later once we get the final paperwork from the DSC.

Geology in the News –

NASA has a great video on the structure of Greenland’s ice sheet, using a variety of techniques, most notably ice-penetrating radar. These scientists have produced a 3-D map of the age relationships of the ice, all the way back to the Eemian.

The Rosetta Probe studying Comet 67-P contnues to provide astounding images of the comet’s surface. Check out these cometary goosebumps and what they may tell us about the origin of this comet billions of years ago.

A new biophysical analysis suggests hadrosaur dinosaurs could outrun Tyrannosaurus rex, at least if given a bit of a headstart. Their engineering would allow them to outlast T. rex in a long distance race. If surprised, though, the hadrosaurs were a quick lunch.

Our topic for this day is almost impossible to summarize in a couple of web-paragraphs. I will briefly outline the geological history of the Mojave Desert, leaving plenty of room for Dr. Judge to talk about the tectonic and structural context of the Mojave next week. For your reading this week, please start at this USGS page on the Mojave National Preserve and keep reading through all the successive pages.

We will spend most of the period discussing the human history of the Mojave Desert. It in many ways is even more complex than the geology, and it is full of drama, bravery, cruelty, cowardice, creativity, surprises and mysteries — like most history! The primary characters will include the Mojave Indians, Francisco Garcés, the first of the “Spanish Fathers” (as they were always called in my California History classes of childhood), Jedediah Smith (one of my heroes), The Old Spanish Trail, emigrant wagon trains, Mormons, outlaws, the railroads, the mining industry, Route 66, and much else. Near the end we’ll view this ancient newscast about the last appearance of Curtis Springer at Zzyzx.

Calico Ghost Town near Barstow, California.

Geology in the News –

The rate of sea level rise in the past two decades has been steeper than previously thought. This means projections of the inevitable continued rise of sea level will be significantly modified upwards. Part of this story’s interest is how difficult it is to get consistent measurements of sea level over time.

Here is an excellent popular account of the Snowball Earth concept. More than once in Earth history the planet either partly or completely froze over. The geological evidence for Snowball Earth episodes is very strong. The latest interest is in how these events affected the evolution of life.

Here’s a good first-person account of finding Scotland’s first Jurassic ichthyosaur. I’m surprised there aren’t more such fossils because they are relatively common in southern England.

Deserts are extraordinary. I must tell you from the beginning that deserts are my natural environment. The world for me consists of dry, brown, dusty hills where I can see for miles under a brilliant sky. A place so dry the air plucks at your lips and the sand crackles under your feet. And there is always the wind and the sun. Every landscape is quickly divided into the shady and the sunlit, the wind-swept and the protected. The rest of the world with its trees and grass, rivers and lakes, clouds and rain, is an exception for me. The Mojave Desert is my homeland. I grew up in Barstow, California. Rainbow Basin is a place I had many childhood adventures. I have a passion for deserts, so team-teaching this course with my colleagues in the Geology Department is a rare privilege.

During this first week we will discuss the general setting of deserts and the basic geological processes which operate within them. Our initial definition of a desert is the simplest one: a place which receives less than 25 cm (10 inches) of precipitation a year. Deserts can be hot or cold (they are rarely moderate!), they can be filled with life or virtually lifeless (or actually lifeless if we consider Martian deserts), and they can be flat or mountainous. We will be considering the “non-polar” deserts, especially the large ones like the Sonoran, Sahara, Arabian, Atacama, Kalahari, Australian, Gobi, and many more which are lesser known (including the Negev in Israel where Wooster geologists have recently been working). We will often return to the starkly beautiful Death Valley of southern California.

Red Rock Canyon National Conservation Area near Las Vegas.

Geology in the News –

Tyrannosaurus rex is often in the news because it “was pretty much the most effective killing machine ever to have stomped the Earth.” An American paleopathologist claims it also played with its food. “Deductive reasoning leaves a single conclusion: the activity resulting in the tooth marks on the bones discussed herein fulfills the definition of play.” I’m not at all convinced, but it is our T. rex news of the week!

A strange “ice ring” 2 km across in Antarctica may mark a meteorite impact from 2004. What’s coolest is that infrasound measurements were used to locate a possible impact of a “house-sized” object in this region way back in 2007.

We will also have lots of fossil discoveries in China this semester, guaranteed. It is the hottest place right now for paleontological exploration. Here is the oldest flying fish ancestor from the Triassic of southern China. Wushaichthys itself may not have “flown” (we really should say “glided”), but it shows early features leading to that step.