Shallow Thoughts : tags : geology

Akkana's Musings on Open Source, Science, and Nature.

Sat, 29 Nov 2008

Upheaval Dome: New research confirms impact theory

Kurt Fisher wrote to draw my attention to the latest Lunar Photo Of the Day (LPOD), a lovely shot he made of one of my favorite places anywhere, Upheaval Dome in Utah's Canyonlands National Park.

Upheaval Dome has long been strongly suspected to be a massive, eroded impact crater, but the LPOD highlights a study that finally puts this (non-)controversy to rest, Elmar Buchner and Thomas Kenkmann's Upheaval Dome, Utah, USA: Impact origin confirmed, documenting shocked quartz grains in the Kayenta sandstone of Upheaval's outer ring.

[Upheaval Dome] It's about time -- it's been pretty clear for many years that this structure was an impact formation, not a collapsed salt dome (the relative lack of salt in the core might have been a clue) but the park service doesn't seem to have gotten the message, giving equal weight to the salt-dome theory in all its Canyonlands literature and signs. Perhaps the Buchner and Kenkmann paper will finally convince them.

Reading about this gave me the push I needed to update my own Upheaval Dome page, adding links to the latest research and to the excellent Upheaval Dome Bibliography Kurt has put together. My page also badly needed a bigger view of the crater itself, so I stitched together a quick panorama of the view from the rim that I'd shot on a trip several years ago but never assembled.

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[ 12:15 Nov 29, 2008    More science/geology | permalink to this entry ]

Thu, 18 Sep 2008

The Alum Rock Narrows

On a trip a couple years ago, Dave and I sought out an interesting geologic phenomenon: the Victorville Narrows of the Mojave river, after reading the discussion of it in Geology Underfoot in Death Valley and Owens Valley by Robert P. Sharp.

The Mojave river is interesting because for most of its length it flows entirely underground. Looking at the wide, sandy, dry washes along the many miles of its length you'd never suspect that a year-round river was flowing beneath the surface.

One of the few places it comes to the surface is near Victorville, CA, where a big chunk of rock gets in the way and forces the water to the surface for a short distance before it disappears back into another sandy wash.

That's all background to the interesting discovery we made at Alum Rock park yesterday, where Penitencia creek and its tributary, Aguage creek, have been looking progressively drier over this past month.

[big fish in Penitencia Cr] Walking upstream along the creek trail, we saw a fairly normal looking lower creek up to the bridge at the last parking lot. Just a little further upstream beyond that parking lot, the creek follows a series of little cascades and pools. The pools are only a few feet deep at this time of year ... but in one, we saw quite a large fish, about a foot long and looking vaguely catfishy. How does something that big live in a stream this shallow and ephemeral?

Not only that, but just upstream, as the stream crossed under the park road near Sycamore Grove, it disappeared. We knew there had to be water because something was feeding those pools and the lower creek -- but it was all underground here. We continued upstream, and discovered ... the Alum Rock Narrows! Right by the steel bridge over the creek, the dry Penitencia and Aguage creeks become wet as water is forced to the surface at their confluence, only to disappear again some fifty feet downstream of the bridge.

It was very like the Victorville Narrows in miniature ... right here in the big city. Not for the first time, I wish I could find a decent geologic map of this fascinating park!

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[ 21:26 Sep 18, 2008    More nature/trails | permalink to this entry ]

Sat, 29 Apr 2006

The Hayward Fault -- Exposed!

Today was opening day for the Hayward fault!

Well, okay, the fault itself has been there a while, but it was opening day for the Hayward Fault: Exposed! exhibit in Fremont. They've dug a trench into the Hayward fault as part of the 1906 San Francisco Earthquake Centennial activities, so people can walk a stairway and stand right in a fault and see what it looks like.

I'm a volunteer docent for the exhibit: one of the people who help answer questions about the fault, the trench, and earthquakes in general, and who also help with details such as setup, safety, and getting people to sign the liability waiver as they enter the exhibit. (My photos and fault facts here.)

Opening day was a bit hectic even aside from the usual opening-day flutters because it was a big day in Fremont Central Park: there was a huge manga festival at the Teen Center right next to the fault trench, complete with live band all day, and over at Lake Elizabeth at the other end of the park was the annual "Splashdown" rubber ducky race.

We expected chaos. But we didn't get it: everything went surprisingly smoothly. We got lots of visitors who were there specifically to see the fault, not just spillover from the other events: apparently it had gotten press on the TV news and several newspapers. There may also have been word of mouth advertising: a surprising number of the visitors I talked to were CERT volunteers or otherwise actively involved in bay area disaster preparedness programs. They were already very well informed about seismic hazards and earthquakes, and eager to see the fault for themselves.

We ended up with about 600 visitors (perhaps a fourth to a third of them teens from the manga festival). Everyone was very well behaved, asked good questions and seemed to appreciate the exhibit. It's lovely to volunteer at exhibits where you spend all your time answering questions, chatting with people and explaining the exhibit, not worrying about policing people and enforcing rules.

(Well, maybe there was a little bit of chaos. The band at the manga festival included karaoke. It's not every day that one gets the opportunity to try to explain paleoseismology and radiocarbon dating while someone a few feet away is belting out "Bohemian Rhapsody" over a loudspeaker but forgetting the words.)

We were pleased to see that everyone spent a lot of time around the (excellent) poster displays from the USGS, which cover everything from earthquake preparedness to stratigraphy of this particular trench to geologic maps of the Hayward fault and the bay area. Most people missed the parking lot displays on the way in (a sign pointing to cracks in the pavement and an offset curb, highlighted with orange spray paint), but we told them what to look for so they could catch them on the way out.

The exhibit will get more press tonight: two or three different TV channels showed up today and interviewed Heidi Stenner, the USGS geologist organizing the exhibit, as well as some of the visitors. So with any luck we'll continue to get good turnouts. The trench will be open through the end of June.

Most of the other docents are either seismologists or seismology graduate students. It wasn't a problem: the questions most people were asking were straightforward questions I could answer easily. But it was fun listening to the other docents and learning from them, and when someone asks a tricky question, you sure can't beat being able to turn to the researcher who did the original study on this trench in 1987 (Jim Lienkaemper) and get the straight scoop! (He also developed the USGS Virtual Tour of the Hayward Fault web site).

The Hayward fault last let go in 1868, a magnitude-6.9 event called "The Great San Francisco Quake" until the 1906 earthquake on the San Andreas took over that title. Trench studies like Lienkaemper's have shown that historically this fault has a large earthquake every 130 to 150 years. Our visitors didn't need a calculator to do the math.

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[ 22:46 Apr 29, 2006    More science/geology | permalink to this entry ]

Tue, 18 Apr 2006

Mr. Sid Meets Linux

Every now and then I search for a map (usually a geologic map) and end up at a USGS page like this one.

The web viewer is impossible, so that link over on the left -- Download Image Now (16M) -- looks awfully tempting, and I always go for it.

What they don't tell you is what sort of image you're getting; after you download that 16M, you end up with a file called something like q250_1388a_us_c.sid, which no image viewer I've ever found considers to be an image file. Even ImageMagick, which can handle almost anything, is baffled by .sid files.

It turns out that .sid stands for "Mr. Sid", a file format for very large raster images. The format is controlled by a company called LizardTech, and it's apparently so scary that no one has ever managed to reverse engineer it. The only way to read a Mr. Sid file is to use one of the programs (available in binary form only) from LizardTech.

Fortunately LizardTech does provide at least one of their programs, mrsisddecode, as a Linux binary. Get it from their download page. Then you can type a command like mrsiddecode -i q250_1388a_us_c.sid -o q250_1388a_us_c.jpg to convert the file into some other image format (which will be quite large -- this particular map is 17170 x 9525).

(Apparently there's an SDK which is also available for Linux, available here. The gdal toolkit used by MapServer and certain other GIS applications make use of this SDK. I hear it's somewhat picky about GCC version, but otherwise works.)

I'm happy that I've found something that will convert MrSid files to a format I can use, but it's a little discouraging that the USGS is restricting its public maps to a format that can be read only with software from a single company. I wonder if the USGS has a contingency plan concerning all these Mr. Sid maps in case anything ever happens to LizardTech? Aren't open formats safer in the long run?

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[ 21:50 Apr 18, 2006    More science/geology | permalink to this entry ]

Wed, 12 Apr 2006

Dream Jobs and Mars Rocks

Driving home from dinner, watching the alpenglow fade from the gleaming domes of Lick Observatory, I found myself thinking about the talk last night: a wonderful geology seminar by Michael Carr of the USGS on the subject of "Water on Mars".

I had a chance to chat briefly with the speaker before the meeting. We got to talking about the moon. It turns out that he spent some of his early career at Lick, working with a few colleagues to make a geologic map of the moon. How? By sketching the terminator every night from the eyepiece of the 36" refractor, and trying to deduce the geology from the topography they sketched. Talk about dream jobs!

It was interesting to compare Carr's talk to the SJAA talk on the same subject earlier this year by Jeff Moore of NASA/Ames (always one of my favorite SJAA speakers). Carr's talk was quite a bit more detailed and heavier on the geologic details, not surprising since he was speaking to a room full of geologists and geology students. He even showed a stratigraphic column of the Burns Cliff area that the Opportunity rover investigated near Meridiani.

I learned quite a bit that I can apply toward my "Mars Rock" collection. I have a set of rocks that are similar to the various interesting rocks on the moon (I finally found some anorthosite a few months ago). I use them when I give presentations on the moon. It goes over very well: I think people get a better idea of what the moon is made of and how its surface looks when they get a chance to handle the rocks and look at them up close.

I have a start on a similar collection for Mars, but of course the most interesting Mars-like rocks to show people aren't the boring black and red basalts; they're the ones the Rovers have been discovering that point to a history of water. So those are the rocks I'm most interested in adding: the sulfates and other evaporites, sandstones made of evaporite sediments, hematite "blueberries" (Moqui Marbles, on Earth), and jarosite.

I'd never heard of jarosite before, but from a bit of web research the day after the talk, it turns out to be one of the minerals implicated in the controversy that was in the news last year about modern-day generation of methane on Mars. Some people attributed the extra methane to the presence of biological organisms, though others were quick to point out that there are plenty of non-biological ways to release methane.

Interestingly, one of the audience members at the talk commented that in the Sierras jarosite is a weak biological indicator (because the biological organisms prevent formation of carbonates, if I understood him correctly). So it's a pretty interesting mineral even for someone who doesn't hold out much hope for finding life on Mars.

Here's a good summary of the rocks found in the Burns Cliffs.

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[ 21:27 Apr 12, 2006    More science/geology | permalink to this entry ]

Tue, 31 May 2005

Geological Society of America (GSA) Conference

The GSA conference happened back when I was too caught in the whirl of events to write about them. It's been a over month now, but I did want to save a couple of impressions.

The field trips all started way too early. Sure, this is the whining of a non-morning person: but really, when your field trip starts with 45 minutes of everybody standing around because the rental agency that rents the vans isn't open yet, maybe that's a sign that starting a little later might be a good idea. Even aside from the wisdom of scheduling all your travel time for the height of rush hour.

The field trips were worthwhile, though. The most interesting parts were often topics that hadn't sounded interesting at all ahead of time.

The talks at the conference were terrific, total information overload, with maybe six sessions going at once. There are lots of people doing interesting research in geology, often fairly junior people (grad students or postdocs), and many of them are even able to talk enthusiastically about their research using words that make sense to a mere student of the subject. Dry jargon-laden talks did exist, but they were the exception, not the rule.

Everybody was friendly, too, and very willing to talk to students and explain their research or chat about other topics in geology. I went to one of the "Roy J. Shlemon student mentoring lunches" featuring a round-robin of geologists moving from one student table to another to share insight and stories: very helpful and interesting!

The conference organizers obviously worship at the altar of Bill Gates. There was apparently a conference-wide dictum that Thou Shalt Use Powerpoint and Thou Shalt Display On Our Windows Boxen, Not Your Own Machine.

The unsurprising result was that roughly 80% of the talks had at least some problems displaying slides, resulting in cursing, then apologies, with the speaker assuring the audience that it would make much more sense if only we could see the slide the way it had been written. Perhaps half of these followed up with a mutter about having to use Windows rather than a Mac. Macs are clearly big with geologists (though alas there was no sign of Linux use).

That said, the conference ran aggressively on time, each session having an appointed watchdog to sit in front and remind the speaker when time was running out. I've never seen a conference stick to a schedule so well, especially when filled with short (20-minute) talks. I had been prepared for the worst after problems getting schedule information before the conference, but the organization on site (except field trips) was flawless.

All in all, quite a good time. I'm only sorry next year's conference isn't back in San Jose. (It's in Alaska; I'd love to go, but finances will probably prevent it.)

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[ 23:04 May 31, 2005    More science/geology | permalink to this entry ]

Mon, 23 May 2005

Geology of Red Rock Canyon

I just finished writing up the final project for my field geology class.

The project involved discovering and mapping the geology of Red Rock Canyon. I'll probably upload the paper and other documents later; for now, just a few notes about the field trip, weekend before last.

Red Rock Canyon is in the Mojave desert, near Ridgecrest. I'd been through a few times before, since it's more or less on the way to Death Valley, but of course didn't know any of the geologic details, other than "Ooh, look at the pretty red and white layers and the eroded hoodoos!"

Actually, it's not technically in the Mojave. One of the reasons Red Rock Canyon is interesting is that it sits at the junction of three of California's geomorphic provinces, at the junction of the Garlock fault (dividing the Mojave from the Basin and Range) and the Sierra Front fault (dividing the Sierra from the other two). The Mojave is bounded on its south end by the transverse section of the San Andreas, but Red Rock Canyon is north of the Garlock fault, in the Basin and Range.

Our four day camping trip (two days of hiking, measuring, and mapping, two days devoted mostly to travel) covered a few square miles around the visitor's center, but we ended up with a surprisingly complete map and stratigraphy. Several people had trouble with the temperatures, which were somewhere in the nineties, combined with the pace of the hikes. That's not really all that hot, especially for desert, but it's hot for a group of people coming out of a bay area winter and an unusually rainy spring, especially the students unused to hiking. (This was all rather ironic since we'd switched our mapping project to Red Rock after being concerned about too much snow at the first choice location, June Lake. Those concerns were probably justified; it was snowing up until a few days before we left, so despite the heat, Red Rock was the right choice.)

Nevertheless, Red Rock is a great location to learn geologic mapping. The structure is fairly simple and easy to see (especially from the top of Whistler's Peak), with a series of cuestas of sedimentary layers each capped with basalt, and a couple of other interesting and distinctive layers in between. Luckily for us, there isn't much complex folding, just a fairly continuous tilt caused by uplift due to the El Paso fault (a branch of the Garlock). The rocks themselves are interesting, with lots of olivine and other crystals in one of the basalt layers, and an area at the base of the other basalt layer containing lovely rocks such as opals -- the area used to be an opal mine.

It's also a fairly nice place to camp, with campsites nestled back among towering cliffs (of the Tr5 fluvial member of the Ricardo formation, if you're curious for details) which provides a bit more privacy and separation from other campers than a lot of parks allow. I'm not really much of a camper (I'm a poor sleeper, and I do like my morning shower) but out campsite converted even the timid non-campers in the class.

White-throated swifts play in the turbulence along the face of the cliffs, calling loudly to each other. Their calls woke me up at daybreak each morning, but setting aside sleep deprivation, it wasn't all bad. It's mating season for the swifts, and it turns out they mate in midair. Two birds come together, and locked together they spiral hundreds of feet downward, finally separating just short of the ground. We have white throated swifts here in the bay area, but I'd never seen anything like their aerial mating dance before; let alone seen it set against towering desert cliffs in the stillness of dawn light.

Other interesting natural phenomena observed on the trip: a barn owl flew over the campsite every night, visible against the campfire light. Zebra-tailed lizards were ghostly white except for their black-ringed tails and some ghostly markings on their backs. We saw lots of jackrabbits and several alligator lizards (the latter have been numerous in the bay area as well, this spring). And we saw a lovely horizontal "rainbow" at mid-day of the first day which turned out, after much research, to be a "circumhorizontal arc". I took a telescope along, but we didn't have very good skies (haze, thin clouds, and disturbed seeing, and with all the campfires it was smoky and not even very dark) so we mostly looked at Jupiter, Saturn, and the moon (we did get good seeing at dusk one night for the moon, and we got a good look at the Mare Nectaris shock rings and the beginnings of Rima Ariadaeus).

A few of our group were disturbed to learn on the way down that they wouldn't have cellphone reception at Red Rock. Horrors! They rushed to tie up loose ends, and managed it before we finally lost reception passing by Mojave.

All in all, a very successful trip, although most of us were awfully glad to get home and jump in the shower. I'm even gladder to have my final report finished. Nevertheless, geologic mapping is fun: I'm happy that I had the chance to complete a map of an area like this. I may even be back to Red Rock some day, to try to trace out the extent of that mystery fault at the north end of the pink tuff breccia layer ...

5/25/2005: photos and report are up.

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[ 19:11 May 23, 2005    More science/geology | permalink to this entry ]