You Betcha, it's Breccia: Some Otherworldly Pictures

I'll be back to vagabonding in the next few posts, but it's a busy week and I have lots of photos to work through. In the meantime, I have two photos that crossed my desk this week, one a few years old, and one that has been recently acquired. The thing about them is that they both made my jaw drop, even though without context they look...almost mundane.

Courtesy of JAXA (Japan Aerospace Exploration Agency)

Take this first picture, for instance. It looked to me like the surface of a mudflow in a desert environment, judging from the lack of finer sediments, and the relative sheen of the rock surfaces. A simple explanation is that it is an example of desert pavement with desert varnish, taken by someone who was using some archaic black and white film (does anyone know what film is? I have vague memories...).

But it's not. Not even close...close to Earth, that is. This is the surface of another object in the Solar System, and it's not a planet either. It's an asteroid called Itokawa. I somehow missed these pictures in 2005-2006 when the Hayabusa satellite arrived there, landed, and returned to Earth with some small particles of the asteroid (it arrived back in June of 2010). Asteroid Itokawa is small (about 600-700 meters long), and is barely a single object. It is a fairly loose agglomeration of chunks and pieces of rock...a space breccia

I appreciate blogger Glacial Till, who brought this picture to my attention last week (by coyly putting a picture of Titus Canyon in Death Valley to distract me). For more info on the Hayabusa mission to Itokawa, check out this site.

The next picture is similar; it could have been taken in practically any desert environment. It looks like some wind has cleared off another piece of breccia of some sort. What's special is that this rock isn't on Earth either, it's on Mars. The Rover mission, slated to last for 90 days, has been continuing for seven years. This picture is hot off the press, taken just a short while ago (September 7) by the Opportunity Rover on the edge of Endeavour Crater. You can read a NASA press release about the rock here. The rock is called Chester Lake.

I can hardly speculate on the composition of the breccia. The Rover is doing some serious analysis of Chester Lake because it is an outcrop of bedrock, rather than crater impact debris.

The Rover, like any geologist working an outcrop, has to look up once in a while to gain some context for the area they are working in. Here is a shot of the view from the site. The researchers have to be very selective about which rocks to test. I feel such a powerful desire to wander across this landscape, picking up and collecting all kinds of samples. Many thanks to Joel Hagen for bringing these photos to my attention.

I can't begin to describe what incredible times we live in. When I was a young boy, I was fascinated with astronomy, and my most valued possession was a small telescope. Mars was such a compete mystery! It was a little red dot in my telescope, and little more in the largest telescopes in the world. We could barely distinguish surface details on the planet, even though there were those who were sure they could see canals on the surface, evidence of some kind of civilization (who invaded us in the War of the Worlds and in Buckaroo Bonzai). I was a college student by the time our satellites started sending clear pictures of the surface, and today we are trolling about on the surface. We carry incredible pieces of technology in our pockets and purses that allow us to gaze on the surface of another planet (when we can pull our attention away from cute cat pictures!). Incredible times.

When Rhyolite Breccia makes more sense than Granite

Breccia? You betcha! Looking for Detachment has a fondness for breccias, and mentions a few others who think likewise. My field trip season never seemed to end this year (that's not a complaint), as I had two lab field trips to see the Del Puerto Canyon ophiolite this week, and a Saturday field trip to Pinnacles National Monument in the California Coast Ranges. It was a great trip for breccia bloviating.

Pinnacles is a marvelous, if widely unrecognized little park about 30 miles south of the town of Hollister. It was established as a national monument in 1908 by Teddy Roosevelt for the tower-like peaks of rhyolite lava flows and breccias that are quite out of character with the normally rounded hills of the Coast Ranges. Those who sponsored the park for protection were unaware of the deeper geological significance of the park.

The great San Francisco Earthquake of 1906 brought worldwide attention to the San Andreas fault. Extending from the Imperial Valley of southern California to Mendocino on the northern California coast, it is one of the more extensive fault systems on the globe, and it has generated two major historical quakes (1906 and 1857), and a more recent "moderate" quake (Loma Prieta in 1989). Paleoseismicity studies have revealed dozens of major earthquakes during the last few thousand years.

Prior to the advent of plate tectonics theory in the 1960's, large scale lateral movements were not considered possible on faults like the San Andreas, though it was clear that the most recent movements had indeed been lateral. A seminal paper in 1953 by Hill and Dibblee argued that the fault had shifted hundreds of miles since Cretaceous time, a highly controversial assertion for the time. In the decades that followed, the San Andreas came to be understood as a continental transform boundary between the North American and Pacific Plates. Still, the fault researchers hoped to find an unequivocal piercing point that would allow a direct measure of the exact amount of movement on the fault.

The Pinnacles volcano was a rhyolite composite cone that happened to erupt on the San Andreas fault about 22 million years ago. The San Andreas ripped the volcano apart, and the two halves began moving apart, 10 or 15 feet at a time during large earthquakes. In 1976, V. Matthews demonstrated that the Pinnacles rocks were virtually identical to the Neenach Volcanics in the Transverse Ranges of Southern California. The two halves were separated by 195 miles!

The park has a lot of offer visitors. An extensive trail system bisects the park, including two sections that explore underground caves formed by boulders piling into the narrow slot canyons carved into the rhyolite. The vertical rock faces are a climber's paradise, as shown in the photo above. The rhyolite breccia (formed from volcanic mudflows, also known as lahars) makes for lots and lots of toe-holds!

I once was privileged to introduce the famous rock-climber Royal Robbins when he spoke to a group of geology teachers in Modesto. I made a point that geologists know a great deal about the properties of rocks, but how many of us stake our lives on our understanding of those rocks? Rock climbers do that every day...

Hill, M.L. and Dibblee, T.W. Jr., 1953, San Andreas, Garlock, and Big Pine faults, California - A Study of the character, history and tectonic significance of their displacements: Geological Society of America Bulletin, volume 64, pp. 443-458.

Matthews, V., 1976, Correlation of Pinnacles and Neenach volcanic formations and their bearing on San Andreas Fault problems AAPG Bulletin 60: 2128-2141