Friday, March 16, 2018

All My Faults are Normal, But Not Really: Travels in Death Valley

Death Valley is the ultimate expression of the extensional forces that have ripped apart the crust of the western United States. The affected area reaches from northern Nevada and Oregon, east to central Utah, and south into Arizona. The broken up crust has resulted in the formation of countless fault basins and high mountain ranges (the entire region is called the Basin and Range Province). But few of those basins (really just one, the Owens Valley) approach the grandeur of Death Valley.

The valley (which is just part of the larger national park) is more than a hundred miles long, and it's deep. The vertical distance from the summit of Telescope Peak to the valley floor at Badwater is more than two miles (11,331 feet). Few places in America display greater relief. And the valley was not carved by water or any other erosional force: it is the result of faulting, the movement of the crust of the earth.

Most students of geology are taught early on that fault valleys are called grabens, and that they are formed by normal faulting. That begs the question of "what is normal?" (a concept I'm sure we all struggle with). Faults displaying vertical motion often have a sloping fault plane, and the fault block that "hangs" over the other is called the headwall (which therefore covers the footwall). When the crust is stretched, or extended, the headwall drops relative to the footwall, and that is what defines a "normal fault". If the crust is compressed, the headwall will move up relative to the footwall, forming an "abnormal fault" wait, that's my bad joke from the classroom. It's called a "reverse fault".
Death Valley is in an isolated lonely region, except for the main tourist area, which lies mostly along Highway 190 and Badwater Road which leads to...Badwater. But Badwater Road doesn't end there. It continues on to the south end of Death Valley and eventually over Jubilee Pass to the village of Shoshone. Few tourists ever venture this way. But there are things to see out there in the deep desert.
There is an odd little hill on the floor of Death Valley at the south end near the Ashford Mill (the remains of an old mine). It's a cinder cone, a small eroded pile of volcanic cinders and bombs that erupted tens of thousands of years ago. It's out on the valley floor in the midst of the alluvial fans, made up of the gravel and sands eroded from the surrounding mountains. The short climb from West Side Road provides a fine view of the graben of Death Valley. It's odd because it may be the only mountain you will ever climb whose summit is below sea level (-73 feet to be exact).
There are other reasons it is odd. Being in the middle of the valley, there seems no obvious way for lava to reach the surface of the valley. For another, it's in pieces. One half can be seen in the photo mosaic below.
From the main highway (below) it becomes apparent that the two pieces are offset from each other. It's been torn apart by faulting, but not by the kinds of faults we looked at above. The side are moving laterally. This kind with the lateral motion is caused by shearing and is called a strike-slip fault. The presence of the fault provides an explanation for the presence of the cinder cone (the magma was able to follow the fault fracture to the surface). But what are strike-slip faults doing in the Death Valley graben?

There are two kinds of strike-slip faults, right and left lateral. The type can be determined by looking at what the opposite block has done from the observers position: notice below that Pokey moved to Gumby's right. But from Pokey's point of view, Gumby has moved to Pokey's right. That's a right lateral fault.

One can therefore see that Cinder Hill in the Google Earth image below is offset in a right lateral manner, with the southwest portion moving northwest. That's a coincidence (not really) because the San Andreas fault, many miles away to the west, is also a strike-slip fault, and it is moving in the same direction. The two faults are roughly parallel. And that provides a clue about the nature of the faults in the Death Valley region.

There are other strike-slip faults in Death Valley, and they "step over" in such a way that a gap opens between the ends of the fault. In that area the crust is being stretched apart, forming a "pull-apart basin" (below). Death Valley National Park is being stretched apart to form grabens, but the overall motion is towards the northwest as the Sierra Nevada pulls away from the rest of the Basin and Range Province.
The clues to the broad forces affecting the crust of the planet show up in the way that they deform and fracture the rocks at the surface. Observations of an obscure little cinder cone at the south end of Death Valley reveals that the park is part of a much bigger process of continental motions that divide the North American plate from the Pacific plate. The faults might seem normal, but not all of them actually are.

Sunday, March 11, 2018

Waves on Fire at the Devil's Slide near Half Moon Bay

Even though Geotripper is a geology-based blog, it seems ocean waves don't make an appearance all that often in my posts. Try as I might, I don't photograph them very well, or very creatively. I love them, however, and can watch them for hours at times.
I think part of my difficulty is the point of view. Most of the time we are standing on a shoreline and the waves crash in front of us, always with the curl of the impending breaker, and the swash upon the sand beach. Always the same angle. And that's what caught my attention tonight. We had occasion to be in Half Moon Bay at sunset, and it was a truly beautiful splash of color in the sky. We had finished dinner at Miramar, where the coast is a long curving stretch of sand. Certainly pretty, but we wondered what the sunset would look like from a bit hundreds of feet higher. So, as the sun sank closer to the horizon, we headed north on Highway 1, and soon reached the new tunnels at Devil's Slide.
The Pacific Coast Highway was meant to hug the coast from Mexico to Oregon, and the effort to complete it was monumental. Regrettably, almost all of California's coastal cliffs bear the scars of road construction, and only about 25 miles of the state's spectacular shoreline remains as true wilderness. Just the same, there is no experience quite like following this highway from one end of the state to the other. It begins in the nightmare of urban traffic throughout most of Southern California, leading to winding mountain roads through immense Redwood forests in the north. Of all the spectacular stretches of highway, the one between Half Moon Bay and Pacifica has given road engineers the biggest headache of all. It's called the Devil's Slide.
The highway was built over an active landslide hundreds of feet above the shoreline. From the very beginning, the road experienced constant damage from slope failures, and the highway was often closed for expensive repairs. The powers-that-be finally gave up and eventually built the Tom Lantos Tunnels through the mountain behind the slide and closed the old highway in 2014. It was given to the county and is now operated as a trail and scenic overlook.

That's where we found ourselves tonight at sunset: hundreds of feet above the shoreline looking almost straight down on the crashing waves. I realized I was seeing something unique, the waves from above, with the dramatic light of the sun on the backside. It was an indescribable sight, so I won't even try. You'll just have to enjoy the pictures.
I've included a couple of pictures of the broader view so you can have some context for understanding the pictures above.
The waves are rolling into a narrow cove, and break as they reach shallow water. The shore is mostly bedrock with no sand, so as the waves break, they often reflect (bounce off the water's edge) and roll backwards, breaking again against the other side of the cove. The intersecting waves create an interesting tapestry.

Despite the imposing name, the Devil's Slide is one of the most spectacular stretches of the California coast, and is not to be missed if you ever find yourself in San Francisco. It's no more than 30 minutes from downtown or the airport. I've often visited there while waiting to pick up people from the airport.

Saturday, March 10, 2018

How Low Can You Go? Badwater Basin, and a Real Hell on Earth

Salt flats at Badwater, -282 feet. The snowcapped mountain in the distance is Telescope Peak, 11,049 feet.

How bad could it be? On our recent trip to Death Valley, we made the rather mandatory pilgrimage to Badwater, the lowest point in North America at -282 feet (86 meters). Although the hottest temperature ever recorded on planet Earth was measured at Furnace Creek Ranch in 1913 (56.7°C; 134°F), it is known that Badwater is often 2 degrees hotter. That's hot. Really hot.
I've regularly worked and played in temperatures as high as 105°F without ill effect at home in the Great Valley of California. I floated down the Colorado River in August of 2013 where temperatures soared as high as 118°F, and I realized that I could have been in trouble if we didn't have the river to dip in every few minutes (because it flowed from deep within Lake Powell, the water temperature was around 48°F even many miles downstream). The hottest moment I've ever experienced was in the aforementioned Death Valley when we had an occasion to be there in late May, and an early heat wave shot temperatures to a near record 122°F. It was simply intolerable outdoors...we retreated to the motel room until the sun went down before emerging to seek dinner. People no doubt adapt to such conditions, but it can't be pleasant.
Alluvial fan just south of Badwater. The terraces on the fan are fault scarps, indicating the role of faulting in the subsidence  of Death Valley.

Standing at the lowest point in North America does cause one to consider other low places on the planet. The National Park Service provides a handy guide on interpretive signs and on their websites. They note that all of the low places also tend to be exceedingly dry and hot, and that the source of the low elevation is generally tectonic in origin. Those low points are as follows:
Dead Sea (Jordan/Israel) -1360 feet (-414 m)
Lake Assal (Djibouti, Africa) -509 feet (-155 m)
Turpan Pendi (China) -505 feet (-154 m)
Qattara Depression (Egypt) -435 feet (-133 m)
Vpadina Kaundy (Kazakstan) -433 ft (-132 m)
Denakil (Ethiopia) -410 ft (-125 m)
Laguna del Carbón (Argentina) -344 ft (-105 m)
Death Valley (United States) -282 ft (-86 m)
Vpadina Akchanaya (Turkmenistan) -266 ft (-81 m)
Salton Sea (California) -227 ft (-69 m)
Sebkhet Tah (Morroco) -180 ft (-55 m)
Sabkhat Ghuzayyil (Libya) -154 ft (-47 m)
Lago Enriquillo (Dominican Republic) -151 ft (-46 m)
Salinas Chicas (Argentina) -131 ft (-40 m)
Caspian Sea (Central Asia) -92 ft (-28 m)
Lake Eyre (Australia) -49 ft (-15 m)
The Black Mountains provide the backdrop to Badwater. They rise steeply more than a mile above the salt flats.

Looking at this list, it is clear that the Dead Sea is in a class by itself as far as low elevations are concerned. At nearly 1,400 feet below sea level, it is unique in the world. To find anything deeper, we have to reach back into the depths of geologic time. The Strait of Gibraltar is narrow and shallow, and is the only connection between the Mediterranean and any other ocean. What would happen if it ever separated the two oceans? It's not totally idle turns out that this actually happened, about six million years ago. The speculation began when vast amounts of salt, gypsum and anhydrite deposits were discovered beneath the seafloor sediments of today's Mediterranean Sea.

When the cutoff occurred, the Mediterranean immediately began to dry up. And dried more. And then even more. The level of the sea dropped precipitously. It dropped past the 1,000 foot level. And then 2,000. And it kept going. Until the level of the basin reached 15,000 feet below sea level. Three miles below sea level. The implications are staggering in many ways. The Nile and Rhone Rivers would have started cutting deep channels far below their normal level. In places, the subsequent sedimentary layers hide canyons that were once 8,000 feet deep (The Grand Canyon, for comparison is 5-6 thousand feet deep). 
The climate changes would be extreme. Air sinking into the basin would increase temperatures at the dry adiabatic rate of 5.5°F per thousand feet. That amounts to conditions at the lowest reaches of the Mediterranean Basin that would be 70°F higher than they would be at sea level. In this desert environment, summertime temperatures could reach 176°F. No organisms could survive at these levels except for a few thermophiles. This is a place no human could or would be able to venture.

And imagine the end. Imagine the moment that the Atlantic Ocean began seeping over the Strait of Gibraltar. Seepage that turned into a torrent, and then a torrent that turned into a flood, and a flood that turned into a deluge beyond imagining. Some calculations suggest flows equivalent to 1,000 Amazon Rivers at once. The entire ocean basin could have filled in between a few months to two years. Sea level would have risen as much as 30 feet per day. This event is called the Zanclean Flood.

All in all, this place would have been hell on Earth, at least until the waters came...

PS: The Rhone River, not the Rhine. Correction made, thank you Olivier Malinur.

Wednesday, March 7, 2018

Yosemite's Half Dome Makes an the Central Valley

Once a week, my errands take me past the intersection of Keyes and Hickman Road on the floor of California's Central Valley. There is usually nothing much to be seen there in the late afternoon hour, just some fields of crops and almond orchards. Nothing much that is, except for the rare clear days in our usually smoggy and dusty valley. On those days, the Sierra Nevada can be seen off in the distance, and from a narrow angle, one can see the looming edifice of Half Dome, rising 4,000 feet above Yosemite Valley. Today was one of those days.
It's been a little controversial, because there are some who think it is not possible to see the dome, and indeed it is not easy to see unless you know just where to look. My pictures are at zooms ranging from 60x to 120x. The picture below provides an idea of the appearance with the naked eye. The dome itself is mostly to the left of center. One has to keep in mind that the rock is something like forty miles away, and there are even effects caused by the curvature of the earth that make it look odd.
The previous day had been clearer, but I just couldn't get away to try for the picture. I had to sharpen the contrast and play with the other settings to bring out the dome. Some are surprised that it doesn't form the skyline, but the peaks behind reach elevations of 12,000 feet or more. Half Dome isn't even 9,000 feet high. I only discovered the view because the first time it was visible to me, there were clouds obscuring the peaks behind, causing the dome to stand out as if it were on the skyline.

We'll see if the storms next week clear out some of the dust and smog...

Tuesday, March 6, 2018

The Struggle for Life in a Harsh Desert: The Living Fossils of Fossil Falls

Fossil Falls, the Bureau of Land Management site near Little Lake and south of Owens Valley, is one of the strangest sights in the California Desert. The ironic point of Fossil Falls is that it has neither fossils, nor does it have falls. It is the former path of the glacial ice age Owens River where it drained Owens Lake and spilled over into China Lake Valley. The river was quite vigorous in its time, and carved a fascinatingly complex waterfall complete with giant potholes. But except for the occasional rill formed during rainstorms, the falls have been dry for thousands of years. I've written about the falls at length several times over the years (check out a sampling by clicking here).
But that's not what I wanted to talk about today. I want to talk about something I know practically nothing about (that's my right as a blogger!!). Every time we stop at Fossil Falls and the students are exploring the labyrinth of potholes and drop-offs, I am on my belly staring at a small hole in the lava flow. What could possibly be more interesting than volcanism and glaciers and faulting and the Sierra Nevada?

Well, nothing actually. But after visiting the site for thirty years, some other things can capture my attention...such as a desperate struggle to survive in a horrifically harsh land. In the small crucible of an insignificant pothole, an entire ecosystem has been born, and has only days to grow to adulthood, reproduce, and then die. The players are small arthropod shrimp, and maybe ostracods (seed shrimp).
Arthropods were one of the earliest forms of complex multi-celled life to leave a rich fossil record. Trilobites (the fossils of which we will see in a later post) account for around three-quarters of all of the hard-shelled fossils in rocks from 530 million years ago. The arthropod phylum, which includes the insects, spiders, scorpions, crabs, lobsters and many others, is the most successful lifeform ever to inhabit Earth, both in terms of biomass and in diversity. Arthropods are found in the deepest coldest oceans and in the hottest of rainforests. But one might expect that the desert would defeat them, especially those species which have gills, and thus must live in water to survive. But here at Fossil Falls there are creatures that have adapted to the severe climate. Their secret lies in patience and speed.
Desert Shrimp and Seed Shrimp (or Ostracods?) in close up.
I'm always struck by how these small creatures cling to life in their exceedingly small habitat. They are the extreme example of how life finds a way even in the most difficult of circumstances. No water most of the time? Evolve a way for the species to survive desiccation even if an individual cannot. Water for only a short time? Evolve rapid maturing and reproduction. Long periods of drought, possibly lasting for years? Evolve eggs (or cysts) that can last for years without water. These tiny beings can show a direct line of ancestry to the first arthropods in Paleozoic seas 540 million years ago, but they are very different creatures now.
These little creatures are actually bivalves in the manner of clams, but they are far different. The unfortunate ant provides scale.
I admit to not knowing very much about the species of creatures found in this hole, and an internet search didn't yield very much information. I hope my biologist readers can shed some light on the identities of these creatures. I will gladly add the info to this post. As best I can tell, the larger animals (below) are called Desert Shrimp. The extremely small yellow creatures seem to be either a Seed Shrimp (a Branchiopod), or an Ostracod.
This close up from a previous year shows a shrimp with an egg sac
I got a bit of video showing the ghostly Desert Shrimp and the really hyperactive Seed Shrimp. I guess they all have a lot to do, and not much time to do it in...


Sunday, March 4, 2018

The Sounds of Science (with apologies to Paul Simon): Kids are More Talented Than You Think

Strange things were afoot on Saturday at Modesto Junior College, where I've been teaching for the last thirty years. There was a Tyrannosaur flipping burgers, and a very cool Triceratops taking orders for Brontoburgers and Raptor dogs.
There was a constant barrage of earthquakes recorded on our seismometer upstairs on the third floor. There was some sort of harmonic tremor going on, visible on the bottom row of the monitor below. Was a volcano about to erupt under our campus? Were we in the grips of an earthquake swarm? Nah, nothing like that. It was instead that time of year for the sounds of science to take place at our institution: the Science Olympiad.
Forty-six junior- and senior-high schools from Stanislaus County, many hundreds of students, had gathered to compete in a series of science-related events. The winning schools from our competition would advance to state-level competition.

Our county is economically moribund. It takes a long time for economic recoveries to reach our region, which regularly has an unemployment rate that is twice the national average. Recessions hit us first (we reached close to 20% unemployment in 2011). The money for education is limited to say the least. And it often seems that science is not a very high priority when budgets are proposed. But the funny thing is, our residents have better priorities than our political leaders. When we had a chance to vote for a bond issue to upgrade our community college campus, including the construction of a Science Community Center, the county voted for it. Since the center opened in 2015, with the planetarium and the Great Valley Museum of Natural History, tens of thousands of kids (and their parents) have paid a visit. Our county knows that support of science is a key to a secure economic future.
And so we witnessed the genius of our best and brightest students competing for glory in laboratories instead of football fields. There were more than forty events. I was in charge of the competition in Rock and Mineral identification, and some of the student teams had scores that rivaled those of my first- and second-year geology students.
If you are wondering about why a T-rex and a Triceratops were involved, well, what can I say? 700 or 800 hungry students were on campus, and our Geology Club stood ready to provide them sustenance to help raise funds for our field studies program.

I've been participating in the Science Olympiad now for nearly three decades. It is a privilege and an inspiration to see these very talented students in action. It gives me hope for the future.

Wednesday, February 28, 2018

Seeking the Savanna instead of Seas: "Saturday Night Live" and Geology??

Historical geology is a real head trip (remember that term?). Stick geologists in the desert against a cliff like the one above, and they will make a few observations, pick up a few stones (and/or fossils), and in their mind's eye, they will be exploring a long-ago prairie that would have looked much like the one in the picture below (a bit of the rarest ecosystem in California, the prairie at Merced National Wildlife Refuge).

There would be differences of course. This current-day prairie is populated by a diverse group of birds and small mammals like ground squirrels and rabbits. But it lacks some of the components of a healthy modern wild prairie, mainly the larger grazing animals like deer, antelope, and bison, and the large carnivores that would prey on them. Coyotes and foxes still inhabit the region, and cattle or sheep are sometimes brought onto the prairie to help maintain the quality of the grasslands. But the larger canines and cats, i.e. the wolves and the lions, are long gone, as are the bears.
We were on the first full day of our exploration of Death Valley National Park. We weren't there yet, because we had a hundred miles of Mojave Desert to cross before we reached the park. Along the way we made a stop at one of California's most spectacular state parks, Red Rock Canyon (not to be confused with the Red Rock Canyon National Conservation Area outside of Las Vegas). Red Rock Canyon is on Highway 14 between the town of Mojave and Lone Pine, southeast of the Sierra Nevada. The place will look familiar to many, as the striking red and white cliffs have formed the backdrop to dozens if not hundreds of Hollywood movies (including some the opening scenes of the original Jurassic Park).
The plain hills to the south of our parking area (in the picture above) are composed of Paleozoic and older metamorphic rocks that have been displaced and uplifted along the Garlock Fault just south of the park. The rocks have been moved some forty miles from their original location by the left lateral movements of the fault zone. They have their own fascinating story, but what catches the eye are the much more colorful sedimentary layers that were deposited on the eroded surface of the metamorphic rocks between about 8 and 12.5 million years ago, a time period called the Miocene epoch.
For many of our students, this is the first real-world example of the basic principles of stratigraphy. We spent a few minutes talking about the birth of the science of geology in the observations of Nicolas Steno (superposition, lateral continuity, and original horizontality), and James Hutton (uniformitarianism). Then I unleashed them onto the rock exposures so they could evaluate the origins of the rocks and the sequence of events that produced the spectacular cliffs in front of us.
Understanding the changes of a prairie ecosystem through time is as easy as understanding "Saturday Night Live" (which for a fact might not be that easy). For more than forty years the underlying structure of the show has remained much the same; there's a guest host, there is a cold open ("It's Saturday Night!"), there are skits, there is the weekend news, there are fake ads, there are musical numbers. But cast is constantly in flux. There have been many people over the years who have filled in the niches: those who could mimic political figures, those who could act as the "straight man/woman", those who could sing. Sometimes the actors were so unmemorable that they disappeared without a trace after a few weeks or months. Others were successful, and remained for years. Others went on to greater things, like Hollywood movies. And that's how the prairie savanna has worked over the years.
Once our students have looked closely at the rocks, they've identified that there are fine layers representing deposition in lakes, other layers that formed on floodplains or alluvial fans. The terrestrial origin of many of the layers is supported by the bright red color, formed as iron in the rocks oxidized into natural rust. What we don't have time for (or permission for that matter) is a search for fossils, because it is the fossils that tell the fullest story of these rocks. Are these fossils the John Belushi-Dan Akroyd period of the grasslands? Or the Joe Piscopo-Eddie Murphy period? Or Kate McKinnon?
Grasses emerged as a dominant plant species in the middle of the Cenozoic period around 30-35 million years ago. The low-lying plants had a novel method of survival: instead of broad leaves easily chewed by forest-dwelling animals, the blades of grass incorporated silica into their structure, and the hard silica would soon destroy the teeth of most animals that tried to subsist on it. A general warming and drying of the world climate led to the expansion of the grasses at the expense of woodlands and tropical rainforests. Animals either adapted to the new conditions or went extinct. The early part of the Oligocene and early Miocene saw many changing species, especially in the horse clan. The ancestors of the horses were small browsers in the forests. As they adapted to the open grasslands, they became larger, and their feet went from three or four toes to hooves, which gave them great speed to escape predators. Their teeth evolved to grow throughout life, allowing them to survive nicely while grazing the grasslands.
The fossil-bearing rocks at Red Canyon are called the Dove Spring Formation (formerly the Ricardo Formation). The cast of characters are familiar in the sense that they fill the roles of many species on the prairies and wetlands today, but there were some unfamiliar characters as well. More than a hundred species of plants and animals have been found, making this one of the richest and most diverse fossil assemblages in the American West. They include the smallest mammalian members of the ecosystem such as mice, ground squirrels, rabbits and even a pika. The larger grazers were represented by ten (yes, ten) species of horse (compared to the three existing in the present day), four camel species, and three species of antelope. There were the surprising ones, two rhinoceros species, and two elephant ancestors (gomphotherium). The carnivores are represented by eight species of canine ancestors (some are called the "bone-crushing dogs"), and three species of felids (cats), including an early saber-tooth. There is a fair candidate for the ancestor of bears and dogs called a "bear dog" (Amphicyon). For a complete listing of the fossils found at Red Rock, check out this technical report from 2009.
So our investigation of an ancient savanna prairie revealed some of the early players in the drama that has played out across North America over millions of years. Some of the players (genera) were diverse and widespread but ultimately died out in North America (the horses and camels, rhinos and elephants). Other lineages survived, including the deer, the pronghorns, and predators like the wolves, coyotes, mountain lions, and foxes. The bears still lurk nearby in the mountains and would no doubt reoccupy the grasslands if the farms disappeared. Like "Saturday Night Live", the show continues and hasn't suffered cancellation, but a great many changes have taken place. The prairies of 12 million years ago can still be found in California today, but with a new cast and a different look.