Flying to Twentynine Palms

On April 1, I took my friend Vali for her first flight in a Cessna 172. Vali is a geologist who does a lot of field work in the Joshua Tree area, so we decided to fly to the Twentynine Palms airport (KTNP) which would give us some great aerial views of places she already knows well from the ground.

This was a good chance for me to do some more flying outside of the L.A. Basin. I’ve been working on trying to visit all of the L.A. airports and have now visited 17 of 26 (!). But it’s good to get some longer flights in and more experience with new locations.


Chino Hills with spring green and yellow flower fields

Starting from El Monte, we flew southeast to the Paradise VOR (PDZ), then east through the Banning pass at 7500′. That’s high enough to have some options for landing, but still below the mountain peaks to the north and south, yielding some dramatic views.


Mt. San Jacinto, south of the Banning Pass

We also got a good view of the San Andreas Fault, just east of Palm Springs.


San Andreas Fault

We continued on to the Palm Springs VOR (PSP), then turned northeast to head to Twentynine Palms.

At TNP, we found a cute little pilot’s lounge stocked with water, sodas, and snacks (honor system to pay for fridge items). It also has a microwave and a bathroom. Great place to have our picnic lunch!


TNP pilot’s lounge

TNP has the largest and most visible wind tetrahedron I’ve ever seen. It looks like a huge yellow tent and easily spins around to show the current wind direction. Next to it, the windsock looks small and ineffective.


Windsock and wind tetrahedron at TNP

TNP has runway options for north-south or east-west winds. The larger and more improved runway runs east-west, but the winds at the time of our visit were coming from the north, so we took the smaller one. That meant flying downwind south straight at the rising terrain, then turning for a left base entry to runway 35. It’s 3800′ long, which is plenty, but only 50′ wide, compared to 5500′ x 75′ for the more commonly used runway 8/26.

We returned following highway 62 through the Morongo Valley and back west through the Banning Pass at 8500′. I tried to descend a few times as we got closer to the PDZ VOR, but SoCal kept me high to deconflict with traffic. You can see that we didn’t actually reach the VOR but instead did some navigation north around it – SoCal gave us vectors to avoid traffic during that period.

TNP track
Flight track (click to enlarge).

Both flights were great! We got to see some great terrain and to visit a new airport. It took us about 1.25 hours each way, with a headwind on the way east and a tailwind coming back. It wasn’t a crystal clear day, so there was some distant haze, but still good visibility. One annoyance was that there was light turbulence throughout, which makes the ride a bit less comfortable, but nothing problematic. We overheard someone else coming through the pass who was getting 1000 fpm up- and downdrafts, and we were glad not to have anything that wild!

What is Io’s lava made of?

Jupiter’s moon Io is very active volcanically:

“A Giant plume from Io’s Tvashtar volcano composed of a sequence of five images taken by NASA’s New Horizons probe on March 1st 2007, over the course of eight minutes from 23:50 UT. The plume is 330 km high, though only its uppermost half is visible in this image, as its source lies over the moon’s limb on its far side.” (Robert Wright and Mary C. Bourke)

But what is that lava made of? What materials lie inside the moon that are being spewed out? We can’t (yet) land on Io and test its lava directly. But we can make some inferences based on remote sensing observations of the lava’s temperature. The temperature carries information about how mafic (magnesium and iron-rich) or felsic (silicon-rich) the lava may be.

The best way to test our ability to deduce composition from orbit is to do it here on Earth, where we do have the opportunity to determine the true composition by sampling the lava on the ground. Scientists Robert Wright, Lori Glaze, and Stephen M. Baloga recently reported a positive correlation between temperature observations from Earth orbit (using the Hyperion spectrometer) and ground composition observations of 13 volcanoes: “Constraints on determining the eruption style and composition of terrestrial lavas from space”. The conclusion for Io is that the lava is so hot that it is likely ultramafic: very high magnesium/iron content.

You can read more about this endeavor (and view more pictures).

Geology and Sherlock Holmes

A couple of months ago, I visited Edinburgh, Scotland, and had a glorious time exploring the local geology. One of my favorite non-geological sights in the city was the National Library of Scotland. Like the John Rylands Library in Manchester, it is not a public library, but rather one in which you can “register” to become a Reader and then do serious research, gaining access to original texts, rare manuscripts, illustrated maps, and so on. The National Library of Scotland had a wonderful exhibition, open to us non-Readers, featuring light-up displays with accoutrements associated with several famous authors, including one of my particular favorites, Isabella L. Bird, as well as Sir Arthur Conan Doyle. It occurred to me that I’d never actually read anything by Sir Arthur Conan Doyle. Back home, one day I came across this commentary on Sherlock Holmes as a forensic geologist, and all the pieces clicked together. Geology, Scotland, and Holmes—I had to sample one of those stories!

I decided to read “A Study in Scarlet” (published 1887, full text here, thank you Project Gutenberg), which is not only the first Holmes story that Doyle wrote, but also the one referenced in the context of geology. In it, Watson after meeting Holmes notes down his knowledge of geology as “Practical, but limited. Tells at a glance different soils from each other. After walks has shown me splashes upon his trousers, and told me by their colour and consistence in what part of London he had received them.” Like Andrew Alden, author of the commentary I mentioned above, I was taken by Doyle’s choice of Utah as the setting for the story behind the London murder that is unraveled by Holmes in A Study in Scarlet. His characterization of Mormons and their culture in the early settling of Utah is, um, colorful, but so is his depiction of the wide fertile valleys the settlers were so grateful to find, and the bitter steep canyons that surrounded the area. I waited for more geology to take an active role in the story, but alas.

The story itself is amusing and captivating, with a clever mystery to solve that is, happily, all explained in the end. It’s not a mystery that the reader is seriously meant to be able to solve independently, as some crucial bits of information are later revealed as being in Holmes’s possession and not available to the reader; but it is still entertaining to watch Holmes work, and above all to see what a strange, quirky, and moody character he was. (In 1891, Doyle wrote to his mother, “I think of slaying Holmes … and winding him up for good and all. He takes my mind from better things.”) I also learned a new word: jarvey (British slang for a cabdriver).

Overall, what perhaps connects Holmes most strongly to geology is his emphasis on reasoning “analytically”, by which he means working backward from evidence to deduce how things came to be the way they are now. This is equally useful in solving crimes and in understanding the long slow evolution of the rocks and structures we see around us today.

Inspiring geology at Arthur’s Seat

Edinburgh is where James Hutton delivered his landmark lectures claiming not only that the Earth was older than the then-accepted 6,000 years, but that it was “immeasurably old” given the tools available in that time (1785). (How he would have loved to have lived to the invention of radiometric dating!) Hutton was a great observer, taking careful note of the impact of regular daily erosional processes, and what they could do if extended out over aeons. He also traveled around much of Scotland and England examining interesting rock formations.

His careful observations inspired him to suggest the radical idea that molten rock from deep underground could force its way up through overlying, older sedimentary layers. (At the time, sedimentary rock was held to be the youngest rock type, as all existent rocks were believed to have precipitated out of a global ocean.) One of the formations that supported his claim is “Hutton’s Section”, lying at the base of Arthur’s Seat, just outside of Edinburgh. Naturally this was one of the highest priorities on my sights-to-see list!

Arthur’s Seat is the remnant of a volcano that erupted about 340 million years ago (see Arthur’s Seat’s formation history in sketch format). Edinburgh Castle is built on another volcanic remnant nearby. It’s a good climb up to the top of Arthur’s Seat (823 feet high), which affords an excellent view of the surrounding country. (It was gaspingly windy, although sunny, the day I climbed it, and people and dogs were stumbling around at the top, buffeted by the wind.) But one doesn’t see much geology from up on top of anything!

I found Hutton’s Section near the dip between Arthur’s Seat and the Salisbury Crags. The Crags are a volcanic sill, composed of lava that pushed its way out from the volcano’s main chamber to spread horizontally through the sedimentary layers. At Hutton’s Section, you can see a blob of volcanic rock intruding right into a sedimentary layer—from above. (See also the University of Edinburgh’s photo and description of the Section). I felt a moment of quiet, powerful awe as I stood in the same spot where Hutton had stood, seeing almost with his very eyes. (But would I have been able to interpret this evidence as ably as he did?) Later in the day, as I walked around to the north side of the Crags, I could see that there were several places where this same phenomenon occurs, not just at his Section. Repeatability lends credence!

Another stunning geological sight at Arthur’s Seat is Samson’s Ribs, a sprawling cliff on the Seat’s southwest side composed of huge basaltic columns. Such geometric (hexagonal) construction always arrests the eye, since it seems so artificially precise and angular. Yet the crystal formation processes that lead to these structures are quite natural, and the size of the columns provides clues as to the rate at which the magma cooled and formed them.

If you ever get a chance, do stop and see these beautiful structures! And pick up some geocaches while you’re there: Weir’s Way: An Edinburgh Volcano, Arthur’s Seat Earthcache, Let’s Get Radical, and Samson’s Ribs Earthcache. For more information on James Hutton and his contributions to founding geology as a science, I recommend The Man Who Found Time, a book that served as a delightful in-country guide and provided all sorts of fascinating background on Hutton and his insights.

Volcanoes in my backyard

So again, on Sunday, I drove out to explore Amboy Crater (also see wikipedia’s article). It is a fairly recent cinder cone caused by volcanic activity out in the desert between 6000 and 500 (yes, only 500!) years ago. Once you get to the parking lot (about a 3-hour drive from here, not exactly my backyard), it’s a 2-hour round-trip hike to the crater, up to the rim (250 feet high), and back down and out. You get some spectacular views from the top of the desert and the huge lava field created by the cinder cone. I’d show you some views captured by me, except that I somehow left my camera at home (with my whole daypack, including lunch, extra water, batteries, etc.). I realized this just past Barstow (halfway to Amboy) and it wasn’t worth going back. Instead, I’ll just link to other people’s photos! (Photo at right is from Golden Gate Photo.)

Between Barstow and Amboy, I couldn’t help stopping to check out a few geocaches. One was inside Siberia Crater, an even smaller cinder cone (sadly, I didn’t actually find that one!). Another one was on a Route 66 loop off of I-40 (nice detour!) and another was at Amboy Crater itself. Boy, it was fun to sit on the rim and dig through an old ammo box full of plastic toys! There’s also a totally awesome cache just east of Amboy (the town), marked by a shoe tree. No, really: an old tree is hung about with hundreds of shoes.

The path out to Amboy Crater is marked with occasional educational plaques containing little facts about the desert. Two that stood out to me:

  • Desert lizards do “push-ups” to get warm (because they cannot regulate their own body temperature). But based on my previous knowledge (and some quick googling), this is totally wrong. Push-ups are a form of display, aggression, or communication, used in competition and in mating. If you’ve ever been the target of a push-up display, you’ll have noticed that the lizard points itself at you while doing it — it’s not a mindless set of calisthenics. Maybe the BLM needs to work with factcheck.org.
  • The tarantula bite is not deadly, but in self-defense it may flick hairs off its back, to which most animals (including humans) are allergic. This seems to actually be true! There’s even a word to describe these stinging hairs: urticating (check out some awesome photos of these hairs). They can cause anything from mild rashes up to anaphylactic shock.

But about the crater itself: there are lots of interesting volcanic features, including a lava field 24 square miles in extent; pressure ridges, where the lava has buckled upward; and stretches of pahoehoe (smoother) lava (although what I saw wasn’t as smooth or distinctive as that in Hawaii). There are also reputedly “squeeze-ups” of bulbous lava and “bowl-shaped depressions” where lava surfaces sank, but I didn’t see these. The view from the crater rim was excellent, with long shadows from the winter sun even at 3 p.m., gusty wind, and waving grass and brush colonizing the lumpy black lava field. (Photo by h.seng.)

Older entries »