Thursday, August 28, 2014

One of Geology's Little Mysteries Solved: The Sliding Stones of Racetrack Playa in Death Valley

Bonnie Claire Playa in Nevada
There are side shows that happen in the sciences. There are the big mysteries of the cosmos and earth history that take many years and the work of dozens or hundreds of the greatest minds to solve: atomic theory, quantum physics, plate tectonics, DNA sequencing and so on. In geology, there are the big picture mysteries of how the continents have moved through time, the patterns of evolution of life on the planet, the origins of rock sequences. It's the great human adventure of exploration that carries us into a fascinating future.

And then there are those nagging little mysteries. Why does bread fall with the buttered side down? Why do cats land right side up? It's the kinds of things that have kept the Mythbusters at work for years. Well, it seems that one of those nagging little mysteries in geology has been solved. For years, stones have left mysterious trackways on the surface of Racetrack Playa in Death Valley National Park. They have been noted more than half a century, and have been the subject of a number of studies, but in all those years no one has seen it happen, or provided a convincing explanation of how it could happen. There have been numerous hypotheses, and of course outlandish ideas like magnetic force lines and alien interventions.
Bonnie Claire Playa, Nevada
But now, we are learning that Richard D. Norris, James M. Norris, Ralph D. Lorenz, Jib Ray, and Brian Jackson have shed light on the mystery, and produced digital images of the rocks in action. In their just released article, Sliding Rocks on Racetrack Playa, Death Valley National Park: First Observation of Rocks in Motion, they document the conditions that resulted in the movement of numerous stones on the playa, especially during the winter of 2013-2014. The article can be read in its entirety here: (and thank you for the open access!).

In essence, the researchers marked the location of stones, and outfitted many with GPS trackers. When storms filled part of the playa surface, a thin sheet of ice formed on the water. As the ice began to melt during the day, large sheets of ice were seen moving and pushing the stones.  The winds recorded were not nearly as powerful as expected, as stones were moved when the winds were no more than 4-5 meters per second (9-11 mph). You can see the process happening in the video here:

I was sure all along that UFOs were swooping down and playing a form of ice hockey with complicated rules, but actually the phenomenon the researchers described made good sense. Racetrack Playa is not the only place where rocks have left trails. I've not been to Racetrack Playa yet, but I've seen tracks on Bonnie Claire Playa northeast of Death Valley National Park, and along Highway 50 in the Carson Sink of western Nevada. There were certain factors in common with each site: relatively high altitude, a source of rocks (the roadbed of Highway 50 was one source), and winters that occasionally have freezing conditions and high winds. Ice was suggested as a factor because many of the trails were parallel to each other as if the rocks were locked together.

I've been joking all day that my life feels empty now that the stones have been explained. But does solving the mystery of the sliding stones take away from our sense of wonder at the world? No, it doesn't. It is a marvelous example of how science works. I love to see mysteries solved by good old-fashioned hard work and persistence. 

This also allows me to say to the vandals and felons who have stolen the sliding stones from the surface of the Racetrack, thinking they have some taken possession of a magical key to the supernatural worlds encompassed within: "Guess what, moron! You've stolen a rock. You are an idiot".

Citation: Norris RD, Norris JM, Lorenz RD, Ray J, Jackson B (2014) Sliding Rocks on Racetrack Playa, Death Valley National Park: First Observation of Rocks in Motion. PLoS ONE 9(8): e105948. doi:10.1371/journal.pone.0105948

Tuesday, August 26, 2014

Northern Convergence: Stories on Trees, the Totems of the Northwestern First Nations

During the flurry of planning for our Northern Convergence journey through Canada and the Pacific Northwest, I was barely keeping up with the geology, and any background information on the anthropology/archaeology of the region fell to my colleague from our anthropology department. There were certainly some intriguing sights related to the First Nations people of  Canada, and the one of these impressed itself on me early in the trip.

We were rushing from one part of Vancouver Island to another, and I was running down the beach cliffs below Beacon Hill Park in Victoria while Mrs. Geotripper went wandering off somewhere.  I was vaguely aware that there was a really tall telephone pole or satellite receiver tower at the edge of the forest, and eventually I noticed that Mrs. Geotripper was motioning me over.
It slowly dawned on me that I was looking at one of the largest totem poles in the world. It was impossibly tall, and I had to go up and touch it to make sure it was made of wood. It was. The plaque at the base notes that the pole honors the First Nation people who fought in the world wars.
The pole was carved from a gigantic Western Cedar tree in 1956 by a team led by Mungo Martin, a Kwakiutl tribal chief. According to the city history, the pole was expected to last no longer than 50 years at which time it would return to the Earth. Major restorations a decade ago added some years, but it may not be there beyond 2020 or so. It stands 40.5 meters (133 feet) high, making it the fifth tallest in the world (or the tallest "free-standing"). The tallest in the world is in the village of Alert Bay on Cormorant Island at the north end of Vancouver Island. It is 53 meters (173 feet) high. We may not see many more poles of this height. There are few monster sized Cedar trees left to carve them from.
Totem poles haven't left much of an archaeological record for fairly obvious reasons. Wood disappears fast in this humid environment. They are known from the 1800s, and are known to have been present with some First Nation tribes prior to European contact. They are a beautiful art form, and communicate family histories, legendary stories, and clan status. They were apparently never objects of worship.
On our rainy day with the students on Vancouver Island, we made a stop at the town of Duncan in the Cowichan Valley, a region with a large First Nation presence. The town has embraced the display of totems, with around 80 in the town center. Each was carved by a local First Nation artisan..
It was an interesting area to take a break and learn a bit of local history. The town is also home to the Quw'utsun Cultural and Conference Centre run by the Cowichan tribe, the largest in British Columbia.
The rain continued (the blue skies in these pictures were from our reconnaissance trip a week earlier), and we needed to be in Nanaimo in a few hours to catch the ferry back to mainland. We drove north to Departure Bay. Our story will continue with our journey up the Sea to the Sky Highway.

Sunday, August 24, 2014

Seismogram of Napa 6.0 Magnitude Earthquake from Modesto

One of the nice things about the new Science Community Center at Modesto Junior College is that we have been given some wonderful tools for the teaching of science. We had a modest seismometer at the old facility, but the software ran off Windows 97, and had not been updated since. We purchased a new seismograph unit from Wards Science, and although it is a simple apparatus, it has been giving us some excellent data on quakes worldwide. We got a good reading on today's event in the Napa Valley, a magnitude 6.0 shaker, the largest in the Bay Area in 25 years. That was the Loma Prieta Earthquake of 1988, a magnitude 6.9 quake that killed dozens, and collapsed bridges and overpasses in Oakland and San Francisco.

The bottom image is the raw data. Each horizontal line on the screen represents one hour of recording time, and so about two days are represented. The waves reverberated through our area for about eight minutes or so. The computer program allows us to isolated the event and manipulate the appearance of the waves, so the upper image is the same data, only spread out. Modesto is located about 100 miles from Napa as the crow flies, and the largest waves were off-scale. I'm pretty sure there were people in Modesto who felt the event.

Magnitude 6.0 Quake in Northern California - Largest Bay Area Quake in 25 Years


Northern California woke up this morning to the largest Bay Area earthquake since the 1989 Loma Prieta Earthquake (magnitude 6.9). The magnitude 6.0 quake, now being called the South Napa Earthquake, was located 6 miles (9 km) SSW of the wine country town of Napa at a depth of 6.6 miles (10.7 km). Dozens of people have been injured, three severely, and there has been a lot of structural damage, including a fire that destroyed at least four mobile homes. There are numerous gas leaks and water line breaks as well.

According to the USGS Event Page, the quake occurred along the West Napa Fault, a northwest trending right lateral strike slip fault. The first motion diagram confirms the motion. I've seen in some media reports cracks in pavement  that show broken roads that appear to have right lateral offset, although the break may have been from liquefaction or landsliding.
At magnitude 6.0, this quake is classed as a strong quake, but one of the unfortunate diagrams I'm seeing in media reports is that anything between a 6.0 and a 6.9 like the Loma Prieta quake are being lumped together on a bar graph as "strong". The difference between a 6.0 and 6.9 is profound, and is a reason that we are not hearing about dozens or hundreds of people killed in the event. On the magnitude scale, the amount of energy released increases by about 30 times with each whole number. In other words, a magnitude 7.0 quake is just over 30 times more powerful than a magnitude 6.0, and a magnitude 8.0 is just over 30 times more powerful than a 7.0 (this make an 8.0 around a 1,000 times more powerful than a 6.0).

The USGS is warning that aftershocks are very likely, and there have been dozens already, including a 3.6 magnitude event. It is important to point out that there is a 5-10% chance of an even larger event. It's not likely, obviously, but this could be a foreshock to a larger event. It is a reminder to us folks in California that we do live on active faults, and we have to live with the possibility of quakes reaching 7.5 magnitude, and maybe even magnitude 8.0. If you live in the state, make sure you are prepared with water, first aid supplies, food, and most importantly, an emergency plan.

Another issue related to today's quake is in the "near-miss" category. The earthquake took place uncomfortably close to the Sacramento Delta, one of California's most vulnerable environments. It is the region where the Sacramento and San Joaquin rivers converge and flow into San Francisco Bay, forming nearly three dozen islands.  Because of groundwater withdrawals, oxidation of soils and other factors, most of these islands are now below sea level, and are protected from flooding by a series of century-old levees and dikes.

Had water levels been high, such as during spring runoff, the levees would have been saturated with water, and subject to collapse from liquefaction during the quake. The islands could have been inundated, drawing salt water from San Francisco Bay well into the delta environment. The most serious effect would be the fouling of the intakes for the California Water Project that provides water for tens of millions of people in central and southern California.

Northern Convergence: The Day We Actually Had on Vancouver Island...and Goldstream

A plan is such a wonderful thing! With a plan, one can conduct field trips smoothly, with no delays, no missed stops,  no problems. Oh, did I say plan? I meant to say "luck". I've been having fun with my recent posts, talking about the places on Vancouver Island that we intended to visit on our recent field studies course, but which we had to miss. There were plenty of reasons, all of the normal kind: it's all about what happens when you try to move 22 people from point A to point B.

But we did see some neat geology, and discovered a pretty good site for studying the regional rocks.
Photo by Mrs. Geotripper
The day started out as planned. We slept in a bit, having arrived the previous night very late on the ferry from Port Angeles. We headed out to Beacon Hill Park in the center of Victoria. The geology of the park was covered in this previous post, with the main difference being that it was seriously overcast and starting to rain. We certainly couldn't see across the Strait of Juan de Fuca. As is usual, we took longer than expected, and the situation was complicated by the fact that we couldn't find bathrooms where we expected to. And traffic was getting heavy in the downtown area. Think of the challenge of maneuvering five vehicles through heavy traffic looking for a gas station. And then finding one, which turned out to have a single bathroom. Time was ticked away, and just like that we were an hour or two behind schedule. The Sooke Potholes fell from the schedule first. East Sooke Park disappeared next. And the rain was coming down more heavily. We needed a substitute plan...
Photo by Mrs. Geotripper
We'd passed the signs for Goldstream Provincial Park during our reconnaissance trip. In the crush of trip planning, I didn't have time to consider the site carefully, but we needed someplace to stop, use a restroom, and to discuss some of the anthropology/geology topics that had been delayed by rain at our other stops. Goldstream turned out to have a really fine rain-proof picnic shelter and the all important restrooms! We caught up with class, while I ran to the visitor center and tried to learn the geology of the park in ten minutes.
Goldstream Provincial Park turns out to have a lot of important geology in only 800 or so acres! The Leech River Fault, a major terrane boundary, cuts through the park. It hosts a surprising variety of plant and animal life, due to a wide variety of habitats. Part of the value of the park is that it has not been logged, and thus preserves old-growth forests, including 700 year old Cedar trees.
The main park trail winds past some of the finest examples of old trees.
The appearance of a rainforest belies the fact that the park includes one of the northernmost examples of a dry Mediterranean climate zone on the continent, and maybe in the world. Such climates are distinguished by dry summers and mild winters. The mild climate results from the moderating effects of the Pacific Ocean and Strait of Georgia, and the dryness from the rainshadow effect of the mountains along the main part of Vancouver Island.  
The park includes an estuary complex and river (the Finlayson Arm) that hosts ten different species of fish, including three salmon species, Steelhead trout, and Coastal Cutthroat Trout. The estuary is evidence of the glacial origin of this landscape, having been carved by the continental glaciers that covered the region as recently as 13,000 years ago. The glaciers were exploiting a weakness in the rocks from a fault that ran through the valley.
Looking south from the Nature Center one can see Mount Finlayson, another feature that indicates the presence one time of glaciers. The rounded form of the mountain identifies it as a roche moutonnée, a larger-scale version of the rounded forms seen in Beacon Hill Park in Victoria. The rocks making up the peak are metamorphic volcanic rocks and granitic plutons dating from the Mesozoic Era.
One might wonder the derivation of the name of the park. The rocks on the west side of the canyon are part of the Leech River Complex, a collection of schist and slate dating from the late Mesozoic Era. The rocks at one time or another were altered by superheated mineralized water, and quartz veins with minor amounts of gold were emplaced in the area. The gold was discovered in 1858, and a minor rush involving perhaps 300 miners ensued a few years later. There was not a great deal of gold to be had, and the boom soon petered out, but the name remained. A few old tunnels and mines can still be seen in the park.
There was one more treasure for us to discover. When the ice sheet moved through the area, it preferentially eroded the north-south fault valley, and the east-west drainages were not cut so deeply. When the ice disappeared, the side drainages remained as elevated river valleys, and waterfalls were formed. A beautiful small waterfall with the somewhat pretentious name Niagara Falls can be reached by a short hike from the parking area. The name comes clearly not from the volume of the waterfall, but from the height, which at 155 feet (47.5 meters), is similar to that of its more famous cousin in New York/Canada (167 feet/51 meters).
We were there in the dry season (despite the rain that was falling on us), and the falls were at such a low ebb that the pool at the base was not flowing more than a few meters downstream. It was sinking underground instead.

Goldstream Provincial Park was a fascinating little park to visit, but by then our schedule was in serious trouble. We had to catch a 5:30 pm ferry in Nanaimo, and it was well past lunchtime (but we had not had lunch). We hit the highway and headed towards Duncan for food. And some really cool anthropology, as it turned out.

Friday, August 22, 2014

Northern Convergence: Vancouver Island, the last of the plan that was...

Our tour of Vancouver Island in British Columbia continued. I've spent several posts (here, here, and here) describing places we saw when we scouted the island a few days before the arrival of our students, and they were really fine places to learn geology. But our students never saw them, for a variety of reasons. Today is the last of the lost stops. The next post will be about the places we did get to see, and really, they are pretty neat as well.
We are looking at the rocks exposed on Newcastle Island near the town of Nanaimo, a port on the shoreline of the Strait of Georgia. With an important exception outlined below, I never got a particularly good picture of these sandstones, but the rocks are interesting and exceedingly important in understanding the reason for the existence of Nanaimo. These are sandstones and shales of the Nanaimo Group, a sequence around 4 kilometers thick (a bit over two miles) that was deposited in a basin that paralleled the coast of North America in Cretaceous and early Paleogene time (around the time of the extinction of the dinosaurs). The basin developed as the subduction zone pushed and flexed the crust along the edge of the continent.

The seaway was populated with a variety of marine reptiles, including mosasaurs, plesiosaurs, and giant turtles. There were sharks, fish, and coiled ammonites. The sediments were deposited by turbidity currents (underwater landslides) of the edge of coastal deltas. The most important aspect of the deltas and coastal plains is that they were covered with tropical vegetation, swamps, and coastal estuaries.

The vegetation that didn't decay away was compressed into coal, and coal was the economic heart of Nanaimo. From 1848 to as late as the 1950s, coal was mined underground, following seams that sloped towards the bay. Miles and miles of tunnels were carved, reaching depths of 180 meters (nearly 600 feet). Many of the tunnels reached below sea level, and below the docks. Miners were literally working under the bay, able to hear the boats above as they worked. For many years the coal was shipped to San Francisco.
The town of Nanaimo was not the first settlement at this location (as usual, the First Nations people get the Columbus treatment). The site was originally home to a Salish people called the Snunéymuxw, from which the name Nanaimo was derived. They built longhouses here, though little trace is left. The most enduring clue of their existence are the petroglyphs that dot the region. A number of petroglyph sites are known, the most accessible of which is preserved at Petroglyph Provincial Park on the south edge of town. That's where our scouting trip took us.
The park is not large, just a few acres, but it is a small island of wilderness in the urban environment. Given my recent hobby of photographing avian species, I was looking up when I first arrived, seeing a new bird (for me), a Spotted Towhee. I understand they live in my neighborhood, but I haven't seen them there yet.
The park has a simple layout. A trail leads past an interpretive center that has some good explanatory panels (although I noticed that the word "indians" has been scratched out; "First Nations" is the preferred term in Canada these days). It also has a number of simulated petroglyphs that can be used for rubbings, since doing them on the actual carvings can damage them (Unfortunately they face many threats, from vandalism or otherwise. Another site nearby was recently destroyed during construction work).
Beyond the interpretive site, the trail climbs to the petroglyphs themselves. Fences are in place to keep people off the artwork. In this near-rainforest environment, it's amazing that the carvings haven't been more severely eroded. We found the rock exposures covered with forest duff and moss.
I was frustrated for a moment that only a few petroglyphs were visible, but it was clear that this is part of what protects the rock art. Sweeping or brushing them would surely damage them within a short period of time. I thought I had seen only one carving, a "seawolf", or sea lion.
When I was processing the pictures this evening, I realized that there were actually two of them. The second can be seen at the bottom of the photo below.
During the actual field trip with our students, we arrived in Nanaimo very late in the day, and we had a ferry to catch. And it was raining. The class was a combined geology/archaeology class, so it would have been a good spot for both classes, but that's life on the road! As will be noted later on, the storm we were in actually caused some real problems farther east.

In the next post, we'll describe what our students actually did get to see. Despite the rain, we had a pretty good day, as it turned out.

Thursday, August 21, 2014

Northern Convergence: Vancouver Island, the Plan That Was, Part III

Road construction at Malahat Summit. Photo by Mrs. Geotripper.
Continuing my brief series of things my students didn't see on Vancouver Island during our Northern Convergence tour of Canada, we reach a place my students did in fact "see", as in we were there and looking around, but the students didn't see what we saw. Malahat Summit is 352 meters above sea level, about 1,155 feet, and is the local high point on this part of the Trans-Canada Highway between Victoria and Nanaimo. Several of my guidebooks called this a "must-see" stop, so I was anxiously watching for the turnoff. We then found out why scouting trips are a good idea...road construction had closed the summit rest area (above). I was disappointed, but found out I hadn't read the guides carefully enough, as the all-important viewpoint was actually a short distance down the hill.
Looking southeast from Malahat Summit towards Victoria and Saanich Peninsula. Without wildfire smoke, Mt. Baker would have been visible in the distance.
We pulled out and immediately noticed two things: the view was stunningly spectacular (I've been using those two words a lot), and there was room to park maybe half a dozen vehicles. When the students were with us in a few days, we would need a stroke of luck to have enough parking for our whole group (there would be no turning back on the narrow highway, and the viewpoint was busy).
Looking northeast from Malahat Summit.
Sometimes we don't always appreciate the scale of things. A thousand feet, 300+ meters, might not seem like all that much, but when you have been driving up a hill from sea level in a thick forest with no view, and a view suddenly opens up, it is like flying. The overlook is apparently at the top of an old marble quarry, so there is extremely steep terrain below.
The view extends across the Saanich Inlet to the Saanich Peninsula and beyond to the Strait of Georgia and the U.S. mainland north of Seattle. Though conditions were very clear, wildfire smoke obscured the distant horizon. Otherwise the volcanic edifice of Mt. Baker would have been visible (it turned out we had a bit of trouble seeing volcanoes on this trip). The Peninsula is a lowland covered mostly by glacial debris with occasional knobs of bedrock sticking out. The moderate climate makes the peninsula a good region for dairy farms and botanical gardens. Butchart Gardens were directly across the Inlet from our location, filling an old marble quarry (the marble is Triassic in age, metamorphosed from shallow marine limestone).

Do you have a sense of the scale of things yet? The barren brown field on the peninsula in the picture above is actually Victoria International Airport. And that little boat in the pictures above? It's actually a good-sized ferry.
BC Ferry in Saanich Inlet. Photo by Mrs. Geotripper.

In the near rainforest environment along the highway, rocks are sort of a rare sight. We saw lots of them, though, courtesy of some major road construction activity, but there was nowhere to stop and take a closer look.
Road construction at Malahat Summit. Photo by Mrs. Geotripper.
There were also rocks behind us at the viewpoint, which I briefly glanced at, seeing some kind of nondescript metamorphic rock of some kind. I found out later from the guidebook that this outcrop was actually granitic rock. It's simply been covered by a cement-like coating of limestone dust from the quarry activities down below. I've been fooled by this sort of thing before, most notably at Tehachapi Pass in Southern California.
Granite covered by lime dust near Malahat Summit. Photo by Mrs. Geotripper.
So...this business of what we saw and the students didn't? We actually made it here a few days later. We had time, and we even had parking! We pulled off the highway and saw...nothing. We had driven right up into the cloud cover and were surrounded by an impenetrable fog. I said nothing about what they were missing, and most of them probably don't even remember pulling out for a moment at the locality. As I've said before, the students had an interesting day and saw great things, but not this at this spot. Some days are like that.

I've mentioned guides that I was using. Two of the most useful were The Geology of Southern Vancouver Island by Chris Yorath, and Geology of British Columbia by Cannings, Nelson, and Cannings.