Wednesday, June 5, 2013

Death Valley field trip


Another term rolled around and it was time for a geology field trip! This time, to Death Valley. Despite living in the states for nearly 3 years, I'd never explored Death Valley, and was looking forward to it. Then the trip was postponed and a bunch of people had to drop out. Suddenly, I was getting frantic emails "Are you permitted to drive the geology vehicles?". Indeed I had been preparing for this moment for a long time. I was on the hook.

We packed up and headed out by 2pm on Friday. The 210 was slow until we got off at the 15, and shortly thereafter took old route 66 to an exposure of the San Andreas fault. It last ruptured in 1857, and is the next chunk of the fault 'due' to rupture. That'll be exciting when it happens. Back into the car and forward-ho to Barstow, which I changed lanes before continuing to Baker. At Baker we watered the horses, which, being Ford Expedition ELs, were rather thirsty. I gave my presentation on the history of the Garlock fault, despite being nowhere near it at the time. It forms the southern boundary of the Sierra range and the Sierra microplate, and is but the latest instance of a much older weakness in the crust, derived from the flat-slab subduction of the Shatsky conjugate. With all that out of the way we headed to The Mad Greek for a memorable gyro dinner, then pressed on north towards Death Valley.

The road wound through successive rift basins and eventually approached the town of Shoshone, where we parked for the evening. We avoided the rattle-snakes and headed for the pool. Here M and I worked out how to do various flips into the pool, while everyone else chilled in the shallow end. The sun set and I set out my sleeping bag in the grass. The day was still hot, but I thought better of getting cold at 4am. As night fell the stars popped out. Despite ambient light pollution from Vegas and the campsite they were still pretty good.

I woke up the next morning before dawn and the day was lovely. By the time we packed the sun was over the hills and the temperature was steadily rising. We paused in the area for coffee and to check out some old underground houses and fossilised elephant tracks. I snaffled some wifi for one last round of emails, and we were off! 

First up was the Confidence Hills just after entering Death Valley. Pushed up by a transform fault in the center of the valley, and just to the north was a mesa with paleo-shorelines, marking the altitude of the former lake. On the other side of the valley was a series of old sediments predating the initiation of subduction on the west coast of North America, and outrageously faulted hills. On the same transform fault just down the valley was a small cinder-cone volcano. Fault movement had split it in half, now separated by about 600m. Assuming slip rates stay constant, that implies an eruption about a hundred thousand years ago. Study of various paleo shorelines show that the valley has continued to deepen and to deepen rapidly.

The next stop was at Badwater, the lowest place in North America, at 86m below sea level. In the middle of a salt pan was a small brine lake. We stopped in the shade to talk about it, but even then the temperate was about 118F or 46C. Later in the summer, the Badwater ultramarathon begins here and stretches 135 miles across three valleys to Mt Whitney. Apparently they have to run on the white lines or else their shoes melt.

The next stop was Devil's golf course, a region of peculiar salt-created shapes forming insanely rough cobbles. Not far away was Mars Hill, a small hill covered in basalt cobbles worn angular by the wind. The site was selected as an analogue to the Vastitas Borealis on Mars, to enable comparative studies during the Viking missions. The rocks had all sorts of cool wind-created features, called ventifacts.

Zabriskie wash emerges from the Amargosa range. In the 1950s, road building accidentally diverted another wash into it, greatly increasing the flow. Now, during big storms, chunks of road (known in the trade as 'urbanite' or 'anthropocite', a conglomerate with a bituminous, organics-based matrix) get washed down.

Next up was lunch at Furnace Creek, an oasis and former Borax mining center. Here the temperature had dropped a few degrees, but it was still too hot for the trucks AC to have any meaningful effect. Not far away was the preserved remains of a failed Borax mining venture, complete with some crumbling walls and an iron boiler. The desolation was perfect. S and I speculated about the similarities and differences working here or on Mars. Mars is colder and the air isn't breathable, but otherwise it was pretty similar. At some point we vied with a coyote for room to examine the effect of salt leeching on boulder destruction.

The next stop was salt creek. When the climate changed here at the end of the last glaciation, most of the plants and animals died off. A few, however, managed to survive, some in increasingly isolated populations. One such creature is the pup fish. Now existing in perhaps 2 dozen different locations, these hardy fish are about the size of my pinky and live in the dried up hollows of the former lake system. One population of about 50 lives on a narrow rock shelf in a sinkhole in Nevada. 

The heat made the stops short, and as a result the trip was proceeding ahead of schedule. Next, we stopped at some sand dunes, where one person asked an interesting question. Sand grains are tiny, and their interactions with wind and each other are turbulent, scale independent, and non-linear. Why then, do sand-dunes form with regular sizes. It turns out there's a body of scholarship on the matter and it's possible to derive a dispersion relation that demonstrates certain wavelengths are preferable. J shared an anecdote about a sand dune expert who ended up fighting the Nazis in North Africa. Because he understood the sand dune dynamics, his platoon was able to conduct daring raids of various outposts, blow up the ammo dump, and then scoot off into the desert. Of course, the enemy gave pursuit, but would invariably get stuck in the sand and he would make his escape.

By now we were approaching the northern end of Death Valley. We stopped off at the Ubehebe crater, formed by a series of phreatic eruptions. With a co-conspirator I took advantage of the wind and slightly lower temperature to run through the outer craters and get a sense of the scale of the system. I was unable to find out, however, if there was a water table present in the floor of the crater. In other respects, it looked very similar to the crater in Vesuvius, only without the surrounding mountain.

From there, a few miles on bumpy dirt tracks took us to Racetrack playa. At about 40 miles an hour, the effects of the bumps are much reduced, but the ability to steer also diminishes... 

Racetrack playa is a dried up lake bed of absurd smoothness. About 4km long, the northern end is only 4cm higher. Funnily enough, it may be that tectonic actions tilt the bed faster than infrequent rain and flooding can level it again. We arrived at a campsite near an ancient mining venture and set out the deck chairs. The day had cooled off, and I went for a walk in the surrounding hills. Later that evening I found a few fluorescent rocks (possibly some fluorite) and a glowing green spider. I had never seen anything like it before. Its pedipalps were enlarged to the point of being legs, while its second pair of legs were tiny. In the meantime, S, Ge 136 TA of considerable legend, showed up and joined the evening's festivities. 

I set up my sleeping gear on top of the truck I was driving (so as to avoid wind-blown grit in the face), and with two able-bodied accomplices set off for an evening stroll to the playa. On the way I found a scorpion which glowed bright green under the UV light. The night was moonless and the stars were incredible. Less milky way than the southern hemisphere, perhaps, but certainly bright enough to see by. From the hill, the distance seemed to be about a mile. In reality it was closer to 2, but eventually we arrived on the unearthly surface and had a walk around. I brought some binoculars, with which the rings of Saturn were readily visible. Sadly, the other planets were still underground. There were plenty of meteors, satellites, nebulas, and so on to go around, however. At length we returned to the camp and, surprised to find everyone asleep, went to bed.

The next morning, I was confronted with a problem, how to get down from the trucks roof. In the end I opted for the simplest option; fall. Breakfast, packing up, and found another spider, this one less peculiar looking. My chocolate biscuits were still all melted from the day before. We got on the road and drove back down to the playa. In the light of day, we quickly found what we were looking for.

Racetrack playa is covered in rocks that have fallen from nearby hills. That, in itself, is not unusual. What is unusual is that these rocks move. Almost all of them have left tracks behind that reveal sliding across the surface, often in opposite directions, or with sharp changes in direction. This phenomenon has been studied, but since the rocks have never been observed while moving, it is not known for sure what happens. Spirits, transdimensional spaces, warp drives, energy vortexes, and so on can be safely ruled out. The general hypothesis is that during winter storms it gets a bit muddy and very windy and they get blown along. The idea that they get surrounded by rings of frozen ice seems to have been disproven. I threw my aerobie around, but the general setting was supremely unearthly.

We returned to the cars to find one had been appropriated by a grad student who wanted a sample of the local pluton contact. We squeezed into the remaining cars and headed off to find them. "Were you guys clever enough to take a radio" was, incredibly, greeted with an answer, and before long we had a visual. Two tiny specks crawling down a wash, dwarfed beneath the hills and cliff that towered overhead. One of them showed me a metamorphic rock excitedly. It bears mentioning that the geochemistry of metamorphism is still not at all well understood.

From here we bore west on rather bumpy (but still surprisingly good roads) past ghost towns and through a series of progressively wetter valleys. One was ringed with incredible wavey rock strata. One was filled with Joshua trees. Eventually we stopped at an outcropping of the Hunter mountain pluton - a rather large igneous intrusion and one of (if not) the first intrusions related to the beginning of subduction off the continental margin during the Jurassic. J found an impressive looking xenolith, or rock that got stuck in the middle of the plume from somewhere else.

We paused for lunch at the head of the Panamint valley, with a long view beneath a cloud of haze. We crossed the basalt flows of the Darwin plateau and joined the Owens valley just near Owen's (former) lake. The Owens valley was the last of the series to dry out. Prior to LA stealing all the water, it still had lakes, agriculture, and wildlife. We zoomed south. As we crossed the Garlock fault near Red Rock Canyon at the top of the Mojave, it became apparent that the haze was smoke from a few wildfires near La Crescenta. It was pretty surreal, as the desert vanished into white nothingness.

Soon we had fueled up and shooting south, crossed the San Andreas fault once more and entered the LA basin. I played hopscotch with a few semi-trailers on the ramp connecting the 5 and the 210. Fortunately I was able to sneak through a gap and up onto the ramp with only minimal squealing of tires and the bobbing of snoozing heads in the back. Once my heart rate returned to normal I set the cruise control to 0.01% below the speed limit and before long we were back in Pasadena. We had arrived at 4pm - one of the earliest field trip arrivals I've ever seen!

Post Script:

The following day (Monday), a few friends and I climbed Echo mountain, as one of our number was soon to be leaving forever. Since moving about 6 months ago I hadn't done the walk, and I found I was slightly unaccustomed to insanely long walks, despite my generally greater fitness. No matter, we proceeded upwards. About half way up the trail we entered a cloud layer. On the moonless night it became seriously dark. I usually walk without a flashlight/torch to enjoy the use of my other senses, but at times even my existing tricks weren't much use! Toward the top of the trail we popped out above the clouds and were rewarded with one of the best skies I've ever seen near LA. The milky way was visible! We milled around taking photos and screaming at the echo mountain. One of us managed to get 14 echoes! Soon two of the girls who hadn't brought a warm top got cold and began to giggle hysterically. We began the walk/stumble down through the darkness. I was tempted at times to crack out my flashlight and take longer steps, but at length we all made it down safely. Then it was just another 5 miles of trooping down Lake Street before getting back to the office some time after 3am. Some photos are also in the death valley album.

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