Friday, May 30, 2014

Zion National Park

Memorial Day weekend saw another instantiation of the legendary Ge136 field trip. This trip has taken me out and about all over the south west US, and is always a blast. My recent trip to Zion was no exception!

Zion Canyon and area stratigraphy:

Friday morning I collected some food supplies, snuck (one of) my secret payload(s) into the truck, assembled a compelling team of passengers and copilot, and headed for the expressway. Even at midday on Friday before memorial day, the traffic was slow going at times, though we managed to avoid a terrible snarl on the 15 by diverting up the 215. Before long we cruised through Apple Valley, Barstow, Baker, Primm, and Vegas, continuing past a crash on the 15 to Valley of Fire state park, where, rather unusually, we arrived at the camp site well before sunset.

Caltech's master of all things culinary Tom Mannion and a few friends had come to cook us an incredible dinner that took two days to finish. Surrounded by eroded rocks eroded from the fossilised Navajo formation dune fields, crossbedded, incredibly red, and eminently climbable, we discussed the upcoming meteor shower, the possibility of monopole detection, and the slightly overcast skies. I sat on a ledge overlooking the fire and tried to imagine what Zion canyon might be like.

That evening, sleeping on a camp stretcher beneath the stars the clouds cleared for long enough to see a few meteors including a very bright fireball, but not the thousands we had anticipated! At some point an EMT van showed up convinced one of us had managed to fall off the rocks, but everyone was okay.

Next morning we woke and while stuffing ourselves with leftovers talked about rocks while I flew my video drone around and between them. Soon enough we loaded up the cars and drove north. The 15 north of Las Vegas cuts through an incredible canyon as it climbs up the Colorado plateau. A relatively stable chunk of crust, the Colorado plateau has some of the most interesting sedimentary sequences in the world, all revealed in devastating clarity within the grand canyon and others as the plateau was lifted and incised about 60mya. 

Beyond this canyon, the town of Hurricane lies next to the Hurricane fault, a normal fault that in the last few million years has resulted in relative lifting across the Virgin river of up to 800m, which caused the formation of Zion Canyon. We stopped in Hurricane for a presentation on the Pah Tempe hot springs there, sadly defunct since an earthquake and drilling project led to their abatement.

The 15 diverts through Utah before cutting east across northern Arizona above the grand canyon north rim. We turned off on the Turroweap road and followed a friendly geologist down to a breccia pipe. Some of the grand canyon sequence contains limestone, and its selective dissolution has lead to the formation of vertical pipes, somewhat like a filled sinkhole. These pipes, filled with sediment, have inward dipping bedding layers and often act like chemical reactors as different pore fluids from different levels flow up and down and mix. In particular, these breccia pipes contain a reductant that leads to the precipitation and concentration of uranium oxide, a mineral essential to the nuclear power industry. On the surface, the breccia pipe appears as a gently sloping bowl shaped area about the size of a football field, but beneath the surface disrupted rock extends for thousands of vertical feet. Over the next decade, the ore will be extracted, leaving the surface largely undistrubed.

Sadly we didn't have time to drive the 60 miles to the grand canyon rim and back, so we continued east and then north back into Utah and into Zion canyon. We arrived near the top, which are the youngest rocks dating from the early Jurassic, around 180mya. As we continued through the park, we went back in time. The campsite was near Moenkopi formation, dating from the beginning of the Triassic, right after the greatest mass extinction of all time, roughly 250mya. 

Our first stop was checkerboard butte, a large conical slab of Navajo sandstone crosscrossed with stress fractures. Unlike the rocks in Valley of Fire from the same formation, these had been bleached white by a reducing pore fluid which dissolved the iron oxide right down to the level of the water table. As it moved through the rock, the minerals occasionally formed hematite concretions, small spheres of rock stained and hardened by a hematite matrix, and thus protruding from the sandstone face. Similar features have also been found on Mars.

We continued on through the canyon to the group campground, when S, TA emeritus, showed up. We knew we were in for a treat. Later that evening, the professor Joe told us the story of how he named his eldest son 'magnetite' in Japanese (a very auspicious name - the Kanji character means literally 'power stone'), and I set up my telescope to look at moons of Jupiter, the disk of Mars, and the rings of Saturn. Despite my best efforts I couldn't find comet Panstarrs, which was supposedly underneath the flat part of Ursa Major.

Next day, we had a full day of activity in the park planned, and even better, no driving! I produced a small jar of Vegemite at breakfast, which I shared with a few brave souls, though none asked for seconds! We caught the shuttle up to the grotto, where most of us zoomed up the well maintained trail to Angel's landing. Angel's landing is a tall promontory of rock sticking out of the middle of the canyon floor, more than a thousand feet high, and accessible only via a narrow, exposed trail with a chain to hold on to. After waiting in line while some rather silly people gradually realised that their ambition outclassed their ability in the same way that my flashlight is outshone by the sun, we made it to the summit and drank in the amazing view up and down the canyon.

On our return to the canyon floor, we had located a swimming hole. Fortunately my boxer shorts that day were brand new - the elastic more than competent, so I was able to swim without fear. The water was cool and refreshing and the bath highly recommended. S found a pair of glasses on the bottom. K lost her sunglasses. While sticking my toes into the freezing mud on the bottom, I found K's sunglasses and returned them to the light. 

Soon enough it was time to return to the shuttle, where we climbed up into a cave covered with dripping water and hanging gardens. Flowers sprouted from the roof and a humming bird sipped the nectar.

Our last stop for the day was the narrows, the pointy end of the canyon, where the walls gradually close in, necessitating wet feet. We had a talk about desert varnish, a mysterious amorphous black coating on rocks, made of manganese oxide, occasionally found on Mars, and of unknown origin. I helped some canyoneers fix a rope on a waterfall for their descent. After a while we reached a good turning around point and walked back to the road, and, in due course, returned to the camp ground. I set up a timelapse, rehabilitated my drone after a recent crash, and made an alcohol fuel stove from an empty aluminium can, without covering myself blood! When dinner arrived, incredible quantities of pasta, I found to my dismay and confusion I had room for only one plate. That evening the stars shone overhead, a cool breeze blew down the canyon, and I snuggled in my sleeping bag as the events of the day played over in my mind.

The next morning, we packed our things and drove out the bottom of the canyon. Pausing near the rocket test track, we examined the lowest layers of the Zion canyon formation, including some rocks deposited during the poorly understood PT extinction. Later, near Quail Creek reservoir, we drove up an eroded anticline and had a good look at cryptobiotic soils, a common surface covering in non-sandy deserts. Built by bacteria over up to 50 years, it helps to retain surface moisture.

We drove back to Vegas. Traffic monitoring suggested the 15 and 210 from Vegas to LA would be stop and go for hours, so we diverted to the north, circling around the nuclear weapon test facility and stopping at a road-side shop that celebrated both Area 51 and one of the few legal brothels in Nevada. At Beatty, we turned west and crossed into Death valley, running around some dunes in 45C heat, then climbed a vertical mile before dropping into the desolate Panamint valley. A year ago, I saw it from the Hunter mountain saddle stretching below, and now we drove south along it. At the southern end we passed a pretty desperate looking borax mining town, reminiscent of some of the abandoned cities I saw in Russia.

From here the sun set and the story is all freeways and bad drivers. What an amazing weekend! Geologists have all the fun!