Deep in the heart of a lava flow

Mark Wilson March 17, 2011 9:51 pm

ZZYZX, CALIFORNIA–This morning the Wooster Geologists enjoyed an ancient lava flow from the inside. We found our way to a lava tube near the center of the Mojave National Preserve and explored the interior with flashlights and flash cameras. It helped that there were a few “windows” in the basalt roof where sunlight could stream in. As Meagen Pollock (she who lives for basalt) explained, a lava tube is formed when a flow cools on its exterior portions while the lava is still moving.  When the lava drains out at the end of the flow, the result is a long tunnel of basalt.  Lava dripped from the ceilings, making the igneous equivalent of stalactites.  As the flow receded, it left horizontal “bath tub rings” along the side of the tube. It was fun to speculate on how many lava tubes remain undiscovered beneath the many square kilometers of basalt exposed in the Mojave Desert.

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Igneous delights at Amboy Crater and in the Granite Mountains

Mark Wilson March 16, 2011 11:13 pm

Greg Wiles on the rim of Amboy Crater.

ZZYZX, CALIFORNIA–This afternoon the Wooster geologists studied two very different magma products in the southern part of our field area. After lunch we drove to Amboy on historic Route 66 and then hiked up to the rim of Amboy Crater. Here we saw the extrusive, mafic rock basalt at its finest in the cinder cone itself and the lava flows across the valley.

Desert iguana on the basalt near Amboy Crater.

After Amboy, we traveled north to the Granite Mountains and examined wonderful alkali granites weathering into rounded boulders. The feldspar crystals in these intrusive felsic rocks were extraordinarily large and numerous, and there were many xenoliths scattered throughout. The countryside here was lush with desert vegetation that made our all-too-brief stop most enjoyable.

An exposure in the Granite Mountains, California.

The feldspar-rich alkali granite in closer view.

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Structural geology and mineralogy at Calico

Mark Wilson March 16, 2011 10:58 pm

ZZYZX, CALIFORNIA–It was surprisingly cool this morning in Zzyzx as we left for our day of fieldwork, but we were not surprised by the wind at our first stop, Calico Ghost Town outside Barstow. Every time we’ve been there it has been blustery. Calico is an old silver mining site with a complex geological structure complimented by hydrothermal mineralization driven by dacite intrusions roughly 17 million years ago. Shelley Judge showed us how strike-slip faulting (ultimately a result of movement on the San Andreas Fault to the west) produced compressional folds in the Barstow Formation. Meagen Pollock talked about how the silver rich veins were formed by thermal alterations of the sedimentary rocks on the flanks of the Calico Mountains. We then spent a little time in the town itself eating our packed lunches and enjoying cold sarsparilla!

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Plunging into Lake Manix

Mark Wilson March 15, 2011 11:11 pm

ZZYZX, CALIFORNIA–East of Barstow and west of Afton Canyon was a very large pluvial lake during the Pleistocene. This Lake Manix was hundreds of feet deep, and its catastrophic drainage through Afton Canyon about 185,000 years ago must have been a great spectacle. This afternoon we explored one of the southern shores of this ancient lake, and then climbed down through its eroding bottom sediments.

Shoreline of Pleistocene Lake Manix. The dark rocks to the left apparently are remnants of an alluvial fan delta which extended into the lake shallows. The light-colored sediments below and to the right are from the lake itself. The white band in the foreground appears to be a type of coastal tufa formed by the agitated lake waters mixed with waters coming from the fan.

Lake Manix bottom sediments consisting mostly of fine silts and clays.

The plateau above the lake sediments includes windswept desert pavements and beautiful ventifacts (wind-carved stones) like this one.

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A morning with the Barstow Formation

Mark Wilson March 15, 2011 10:48 pm

Greg Wiles explores the top of a wadi in Owl Canyon. The debris here consists of blocks of Barstow Formation eroded during recent floods.

ZZYZX, CALIFORNIA–It is hard to believe that the Mojave region once had vast lakes, erupting volcanoes and a diverse mammalian fauna including camels and horses. The most important record of this time is the Barstow Formation (Miocene — about 15 million years ago). This unit contains river and lake sediments along with volcanic ash, all of which produce a diversity of colors leading to the name “Rainbow Basin” for the best exposures outside Barstow, California.

The Wooster geologists spent the morning with the Barstow Formation in Owl Canyon and Rainbow Basin. The highlights included a group analysis of dozens of rock specimens, a desert tortoise crossing the road, and meeting old friends Buzz and Phyllis Sawyer from Barstow.

The Wooster geologists in Rainbow Basin with the Barstow Syncline in the background. Image by Buzz Sawyer.

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Death Valley Day

Mark Wilson March 14, 2011 11:01 pm

ZZYZX, CALIFORNIA–Our Wooster geological crew awoke to a spectacular sunrise over the Soda Lake playa this morning. We drove north from Zzyzx through Baker and Shoshone into Death Valley by way of Jubilee Pass. The weather could not be better with daytime temperatures in the low 80s and brilliant blue skies. Shelley Judge gave us an overview of the tectonics that formed Death Valley, Meagen Pollock helped us sort out the poikilitic textures in basalts along Artists Drive, Greg Wiles discussed the declining levels of Lake Manly, and I helped out with interpretations of sedimentary structures in Miocene deposits exposed along Golden Canyon. Students kept their end of the bargain with challenging questions. A most excellent day.

Part of Death Valley's charm is in its extremes. This is Telescope Peak on the western side of the valley. It is 11,049 feet above sea level. Note the snow cover.

And here are salt deposits below Telescope Peak at 275 feet below sea level, baking in the relentless sunlight.

The Wooster students on the 2011 Mojave Desert field trip.

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Wooster Geologists return to the Mojave Desert

Mark Wilson March 13, 2011 10:59 pm

ZZYZX, CALIFORNIA–All four geology faculty members, our administrative coordinator Patrice Reeder, Jesse Wiles and eight students have safely arrived at the Desert Studies Center in the delightful Zzyzx.  We spent a few hours exploring the Jurassic sandstones exposed in the Red Rocks Conservation Area outside Las Vegas (with marvelous dune cross-bedding) and then slogged through horrible Los Angeles-bound traffic from Las Vegas to Baker, California.  (All too typical for a Sunday night here.)

Unfortunately bandwidth is highly restricted, so our posts will be infrequent until we return to Wooster.

Lichen and bits of desert varnish on the cross-bedded sandstone at the Red Rocks National Conservation Area.

Lindsey Bowman apparently saves Becky Alcorn with a dramatic backdrop of cross-bedding.

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Wooster Geologist safe in Japan

Mark Wilson March 13, 2011 3:20 am

Tsunami bearing down on a Japanese village (March 11, 2011). From the Associated Press.

HORONOBE-CHO, HOKKAIDO, JAPAN–I am relieved to report that my friend and fellow Wooster Geology classmate Kaz Aoki and his family survived last week’s devastating earthquake and tsunami. Kaz, his wife Sachiko, their four daughters and their new son-in-law all are unscathed, considering themselves “very lucky”. Their previous hometown, Kamaishi-shi was severely damaged.  They say a tsunami warning 30 minutes before the event saved many lives.

Kaz is working in crisis mode right now. He is a Principal Senior Scientist in the Japan Atomic Energy Agency (JAEA) at the Geological Isolation Research and Development Directorate. We can only imagine the stress in the face of repeated failures in several nuclear power plants.

The Wooster Geology Department, all four faculty members, our Administrative Coordinator Patrice Reeder, and a group of students are leaving this morning for our field trip in the Mojave Desert. This blog will be filled with fun posts and colorful images, as it should be. We will not forget, though, the current travails of the Japanese people and our particular friends the Aoki family.

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Wooster’s Fossil of the Week: A sweet local scallop (Lower Carboniferous of Wooster)

Mark Wilson March 13, 2011 1:56 am

The delicious scallop has a long, long history. Wooster’s variety, known as Aviculopecten subcardiformis, is about 345 million years old. The beauty above was found in the Logan Formation, a conglomeratic sandstone that underlies much of the city, including the college. This particular fossil is preserved as an external mold, meaning the shell is dissolved away and only an impression remains in the surrounding sediment. Note that this preservation is still so good that we can count all the ribs and even growth lines.

Scallops are characterized by a nearly-symmetrical shell. They have extensions along the hingeline (at the top of the image) that are commonly called “ears” and technically termed auricles. They have one large muscle (adductor) used to close the shell. It is relatively large and the part of the clam we find so tasty.

Pecten jacobaeus from the Mediterranean Sea. (Photo courtesy of Andreas Tille of en.wikipedia.)

Many modern scallops use that large adductor muscle to clap the valves together when they are threatened, enabling them to swim short distances. As an early warning system to detect predators (including us, I suppose), they have rows of tiny eyes in the soft tissue around the edge of the shell (see below).

The eyes of this living scallop are the small bluish spheres along the edge of the mantle.

We can’t tell if our ancient scallop was able to see its enemies and swim away. It does, though, take us back to a time when a warm shallow sea covered our little patch of Ohio.

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Experiential Learning in the Desert

mpollock March 11, 2011 12:00 am

As Dr. Wilson so gleefully pointed out today, the last several blog posts have been about fossils. I think it’s about time for a change of subject, don’t you?

Spring break officially begins tomorrow, and this is what Wooster looks like tonight:

A view of the snow covered street from my living room. I had to take the picture tonight because Dr. Wilson would have undoubtedly beat me to it in the morning.

The Wooster Geologists are ready to leave all of the snow behind! In a few short days, we’ll be headed to the warm and sunny Mojave Desert. The Desert Studies Center will serve as our base camp while we explore Death Valley, the Mojave National Preserve, and Barstow, CA (Dr. Wilson’s hometown). We invite you to follow us on our week-long adventure. Be on the lookout for posts that feature blue skies, stunning vistas, and geologists learning about the desert through direct experience. (It’s good to be a geologist.)

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