Spring

Welcome to the Spring 2015 LPL Newsletter. As we finish off another academic year, there is, as always, lots to talk about.

The most exciting news is that Professor Renu Malhotra has been named a member of the National Academy of Sciences, one of the highest honors an American scientist can receive. For good measure, she also was named a member of the American Academy of Arts & Sciences.

The other big piece of faculty news is that two long-time LPL faculty members, Randy Jokipii and Rick Greenberg, are retiring over the summer. Rick has been at LPL for roughly a quarter of a century, but Randy has been here longer—he was one of the early hires when the Lunar and Planetary Laboratory added an academic component and the Department of Planetary Sciences was born.

In addition, our talented graduate students continue to accrue honors. Most notably, Jamie Molaro won the UA College of Science award for the most outstanding effort in public outreach, based on the very successful Art of Planetary Science event that she designed and organized. The College gives out one award each for Research, Teaching and Service each year—an LPL  grad has won one of those three each of the last four years, and the award-winners have been in all three categories, a testament to our students' performance.

We also have several items of personal interest involving the LPL family, ranging from births and graduations to just introductions to the people you might see in the hallway (if you work at LPL) or hear about from LPL friends (if you’re part of LPL’s extended family).

But perhaps the most impressive thing about LPL is still the work that is done here. This newsletter includes more than two dozen articles with an LPL twist from various news outlets, covering a broad range of topics. Reading those will give you some sense of the amazing range of interesting things going on at LPL, from flying kites in Hawai’i to study Mars to using “leftover” data from Catalina Sky Survey to study black holes. And because not every excellent paper generates a press release, you’ll have to use either your imagination or a database of the scientific literature to understand the full scope of the science that goes on at LPL.

Enjoy the newsletter, and as always, if you have news about you, your career, or your family, please let us know, so that we can pass it along to all the people who would be interested.

by Shane Byrne

This semester, the LPL field trippers returned to a site previously visited on our fieldtrips several years ago—Canyonlands in southeast Utah. This national park contains many features familiar to planetary geologists such as graben (tectonically formed trenches where the floor has dropped in elevation) and an impact crater (although previously this was argued to be a salt diapir).

Driving up to Canyonlands from Tucson takes a day in itself, but there was plenty to see along the route. We stopped at Walnut Canyon in Flagstaff to view some of the Colorado Plateau Stratigraphy and spectacular cross-bedding within the Coconino sandstone. Driving further, we passed through exposures of the Chinle formation and later Monument Valley, which all expose different portions of the enormously thick stratigraphic record within the Colorado Plateau. Hundreds of millions of years of history are on display here, containing chapters from marine environments and inland deserts. More recently, volcanic activity has been common on the plateau, some of these volcanoes have been removed by erosion and the vertical conduit through which magma and brecciated rock moved to the surface is often preserved. Agathla Peak in northern Arizona is one such feature (known as a diatreme) that we stopped to survey. The Plateau is no longer collecting sediments as it has been uplifted to great height. This uplift had other effects such as prompting previously slow-moving meandering rivers to erode downwards. Deeply incised meanders near the Arizona-Utah border are a testament to the uplift that has occurred here and the power of water to quickly erode though rock when the situation demands.

Our first stop in Canyonlands was Upheaval Dome, a circular structure with upward tilted layers at its center. The origin of this feature has been debated for decades. There is a thick layer of salt buried deep beneath Canyonlands. In similar locations (like Iran), this salt rises buoyancy through the rocks in a diapir and leads to circular surface features (circular features in Triton’s “cantaloupe terrain” are also thought to be due to icy diapirs).  Lately though, it’s been recognized that this is probably a heavily eroded impact crater. Certain types of fractures that we observed in the surrounding rocks require very large pressures to form, which can only realistically be produced during an impact event.

The next day, our group drove around to the southern entrance to the park. This is a little used access point through Beef Basin—little used because the roads in question are frequently impassible even to 4WD vehicles. One particularly notorious stretch known as Bobby’s Hole provided the biggest challenge, which luckily we navigated without significant incident. The reward for this rather arduous drive was to be able to drive through the Canyonlands Graben. This is a set of normal faults that allow blocks of rock a few hundred meters wide to drop downward and form steep walled trenches that we can drive through. We see graben on many solar system bodies where the surface is being stretched apart. In the case of the Canyonlands Graben, the surface rocks are being stretched because the Colorado River has eroded a deep canyon and the rocks to the east of this canyon (no longer buttressed) can now glide westward on the buried salt layer. Moving past the Graben, we stopped at the joint trail, where incredible examples of jointed rock are visible. The joints themselves are about 10 meters deep here and wide enough to walk through at the bottom. Indeed, they are wider at the bottom than the top as the lower rock layers are more easily eroded so that only a thin strip of sky is visible overhead.

Canyonlands is a truly unique place with a mix of tectonic and impact features alongside a detailed stratigraphy that records long periods of Earth’s environmental conditions. In those respects, it is similar to areas on Mars currently being explored by rovers and orbiting spacecraft.  It was certainly a long drive to get to Canyonlands and then back from Tucson, but it was certainly worth every mile.

Photos courtesy of Ali Bramson.

by Shane Byrne

As rovers crawl across the surface of Mars, they can investigate small-scale structures in sedimentary rock that can’t be seen from orbital datasets. These structures can tell us a lot about the environment within which the rocks were deposited. Terrestrial geologists have been interpreting these features for a long time, but it is a relatively new tool in planetary science. On this trip we journeyed to southern New Mexico where we saw examples of deposits from volcanic base surges and aeolian material that contain some of these sedimentary structures.

Our first stop for this LPL field trip was Kilbourne hole and the neighboring Aden lava flow (a good example of an inflated flow with polygonal fractures).  Kilbourne hole is a Maar crater i.e., where subterranean magma encounters ground water and generates repeated explosions. These explosions throw out debris and generate base surges that can mobilize these particles into cross-bedded patterns. Later erosion at Kilbourne Hole allows us to see cross-sections of this stratigraphy and occasional volcanic bombs that are embedded within it. Kilbourne Hole is also famous for its mantle xenoliths—chunks of almost pure olivine carried to the surface from great depth. They are hard to find these days as the site was been thoroughly picked over by geo-tourists, but we were lucky enough to discover a large one (~40 pounds). It is also well known for its large rattlesnake population, which we fortunately failed to discover.

After leaving Kilbourne Hole, we traveled to the White Sands dune field. Cross-bedding in the making can be observed here as gypsum sand avalanches down dune slipfaces. White Sands has many types of dunes (from parabolic to barchan) and a wide range of dune migration rates, which can be clearly measured in orbital imagery and airborne LIDAR datasets (dune migration rates can now also be routinely measured on Mars through HiRISE orbital imagery). We hiked out to Alkali Flats to see the source of the dunefield—gypsum crystalizes on the surface of a playa here before blowing eastward towards the dunes. One non-geologic highlight of the trip was the permission to camp overnight within the park. Incredibly dark skies even allowed for views of the zodiacal light and the white dunes illuminated by starlight gave this terrestrial analog an unearthly quality.