A Walk Through the Valley of Death
Notre Dame geologists study rocks and Earth tectonics in southwest desert
Sydney Higgins was trying to make sense of the readings from her Brunton compass at Red Rock Canyon near Las Vegas.
Geologist Tony Simonetti had taught his Planet Earth students how to take strike and dip measurements in the classroom, but now a theory had turned into reality. He poured water on the angled rock mountainside to identify the exact direction of the dip angle, which reveals the strike plane in a perpendicular direction.
“Doing it in the field is so much more …,” said Higgins, searching for the right word. “I’m a very hands-on learner, so it just made me understand.”
Taking strike and dip readings, Simonetti said, helps a geologist understand a region’s tectonic history — the massive underground forces that thrust up the mountains and stretched out the valleys over millions of years. Seeing firsthand the results of these tectonic plate collisions is exactly why the associate professor in the Department of Civil and Environmental Engineering and Earth Sciences (CEEES) took 16 undergraduates and two graduate students to Death Valley National Park and Red Rock Canyon for a one-credit field trip over spring break.
“Older rocks are usually overlain by younger rocks,” Simonetti said of the picturesque canyon. “But this is the reverse because you’re standing on this well-developed thrust fault which hugs the western coast of the continent. These rocks may have traveled 400 to 500 kilometers.
“The collision zone acts like a bulldozer pushing rocks around.”
A sophomore from Rochester, New York, Higgins was taking her measurements at the exact point on the mountain that showed where tectonic plates had collided and shoved the older white limestone up and over the younger red sandstone. “It’s great to watch him be so excited about rocks, and rock formations, and the tectonic events that have happened here,” she said.
Higgins changed her major to Environmental Sciences after taking Simonetti’s class in the fall, noting that it reminded her of why she loved Earth science as a kid. His pictures and talks about Death Valley inspired her to sign up for the trip this spring.
Simonetti has been guiding the excursion, which is funded by CEEES, for about a decade. The group used to camp out in tents, but has been getting motels in the nearby town of Beatty, Nevada, for the last five years.
For the first four years, Simonetti alternated between Big Bend National Park in Texas and Death Valley. But he settled on Death Valley for its shorter drives and clear examples of concepts explored in the sophomore-level Planet Earth class.
“Death Valley National Park and the surrounding area is a tectonically active region of the U.S. undergoing active extension due to convection within the underlying upper mantle, which gives rise to the Basin and Range province. This results in rocks being moved around along faults that produce earthquakes, magmatic activity giving rise to explosive volcanic activity, and the presence of a variety of sedimentary rocks and metamorphic rocks.”
Death Valley lies between two sets of mountains, the taller Panamint Range to the west and the dryer Amargosa Range along the Nevada-California border.
The students stayed in a Beatty hotel and visited nine total sites in Death Valley National Park.
The park visit started Monday with a trip to Mosaic Canyon on the Panamint side.
Simonetti pointed out examples of a smooth metamorphic rock called Noonday Dolomite, which is about 800 million years old. During that tectonic collision, he explained, faults formed when plates slipped by each other, while folds formed when the two land masses collided and caused the rocks to compress.
“Imagine a fold forming by taking a sheet of paper and then pushing the ends towards one another along a flat surface like at a table,” he said. “The end result will be the formation of a fold.”
The students’ reward for a long hike was a stop at nearby Mesquite Flat Sand Dunes, where rolling waves of sand made the valley floor resemble the Sahara Desert. They jumped off dune peaks, rolled in the sand and pretended they were at the beach like many of their classmates.
Tuesday began with a visit to Ubehebe Crater, a hole 770 feet deep and half a mile wide that looks like it formed as a result of a meteor impact. Instead, Simonetti said that very recently in geological terms — about 2,000 years ago — a magma chamber near the surface heated up water-saturated sedimentary rocks.
“The water in the rocks was turned into steam,” he said. “There was enough pressure that a flashpoint was created, causing a huge explosion.”
The students kicked up clouds of dust as they ran down the steep slope to find pieces of black lava from the explosion. Patrick Cho, a graduate student from Los Angeles, showed them a piece of this vesicular basalt, where bubbles in the lava formed holes in the surprisingly light rock. He and Kayla Hollister, the other graduate student, hope to use their doctoral degrees to go into fieldwork for a government agency such as the National Oceanic and Atmospheric Administration.
In Titus Canyon, the group hiked up a narrow slot between high canyon walls. Simonetti pointed out a rock formation called breccia while the students took strike and dip measurements. This breccia looks like a spider web of small rocks criss-crossed by white stripes. It formed when high pressures underground crushed the limestone and squeezed calcium carbonate out of it, but the carbonate liquid then solidified and “froze” the limestone pieces in place.
One of the highlights of Death Valley is Badwater Basin, the lowest land point in the Western hemisphere at 282 feet below sea level. A white river of crushed salt spreads along the valley floor where people walking have made it smooth. Untouched, it looks more like recently plowed ground where white salt is emerging from the earth as the moisture in the sediment evaporates.
The valley averages only about half an inch of rain each year. What makes the region known as the Great Basin unique is that it is the only place in America where water doesn’t flow through rivers to either ocean. The small amounts of rainfall or snow run into the valleys and simply evaporate.
About 250 million years ago, tectonic collisions to the west caused a quiet, sea-covered continental margin to recede, while erupting volcanoes and uplifting mountains replaced it. Steep ranges alternate with flat, dry deserts that have continually stretched over the last 16 million years. The distance from Reno to Salt Lake City is estimated to have doubled during that time.
The landscape formed by this folding and stretching process is called horst and graben topography. The German words refer to the upraised blocks called horsts that form mountain ranges, and down-dropped fault blocks of graben, or linear valleys. Debris continually erodes and washes from the mountains into the valleys, forming large alluvial fans similar to a river delta.
Several of the students called Wednesday morning’s hike through Golden Canyon the highlight of the trip, despite being the most challenging. The trail begins in a slot canyon on the valley floor and winds into a badlands region similar to its more famous cousin in South Dakota.
Silt and clay from the bottom of one of the region’s prehistoric lakes were compressed into mudstone about 6 million years ago. More recent uplift and erosion have exposed it to view. The minerals in the mudstone are shaped like tiny plates that act as roof shingles, preventing water from penetrating the surface. Along with scant rainfall, this makes soil development and plant growth nearly impossible.
Simonetti asked how the mudstone mounds could be higher up the mountain than the rock walls at the canyon’s start, stumping the students.
“It seems illogical,” he said. “Maybe the canyon wall rocks belong on the other side of the valley, but got stuck here when it started to stretch and open.”
Eroding yellow slopes fold like crumpled bedsheets in every direction, giving way to steep red cliffs known as the Red Cathedral at the top. The oxidation of iron in the sandstone creates the red color, similar to the process that forms rust in metal. A hike up a steep slope at the end is rewarded with a spectacular view from Zabriskie Point.
The day concluded with a hike in Natural Bridge Canyon, where the students examined a special rock called gneiss. Created under pressure conditions 30 kilometers below the surface and 800 degrees Celsius, it features light- and dark-colored bands fused together. Simonetti explained why he chose this spot for their final stop in Death Valley.
“When I saw this, I got very excited because nowhere else in the park do you see the non-altered, fresh basement rocks,” he said. “It’s the oldest rock in the park, 1.7 billion years. Touch it, feel it, talk to it. Respect your elders.”
On Thursday the students headed back toward Las Vegas in their three rented GMCs. Located essentially in the city’s suburbs, Red Rock Canyon features a scenic loop through mountain faces of striking colors — bands of yellow, black and several shades of red. But Simonetti explained that millions of years of different sediment layers were not the cause of the distinctive banding.
“It’s all a bleaching effect,” he said. “After the formation of the sandstone units, at some point between now and 170 million years ago, we had some fluids percolate through the rock. As the fluid migrated through the rock, it bleached the rock by converting the oxidized iron … removing the red coating. That’s where you see the yellow bands.”
The trip’s final stop came at Hoover Dam — because it’s a perfect example of the water stress on the southwestern environment and because there were two civil engineers on the trip. Prolonged drought has led to changes in the dam’s operation, which sparked student discussion of water mitigation approaches.
“The impact of climate change in the region is easily seen with the exposure of bleached rocks contouring the Lake Mead reservoir behind Hoover Dam,” Simonetti said. “At present, the water depth at the dam is at 140 feet, which is 80 to 90 feet below the optimal level.”
Mohammed Mansour, one of the civil engineers, said the scope of the project made him proud of his chosen major. More than 3 million cubic yards of concrete were used in the dam’s construction, enough to wrap the Earth at the equator if laid in a line. The builders had to invent new concrete cooling techniques and finished ahead of schedule.
“Learning about the history of the project and how it was completed during the Great Depression makes me appreciate the project even more,” Mansour said. “They ran into a multitude of challenges when building the dam, but they were able to overcome those challenges. This is the true meaning of fostering innovation from hardship.”
The return to campus isn’t the end of hands-on learning for Higgins, whose passion has led to a job in Simonetti’s lab. The research shows one of many practical uses of geological knowledge.
A chemist as well as a geologist, Simonetti uses laser instruments to measure isotopes, the nuclear variations of a chemical element, to determine how and where rock formed.
Because uranium ore — the material used to make nuclear bombs — varies widely depending on where in the world it is mined and processed, the variation offers a unique signature that can be used to identify the material’s source. Making his research publicly available acts as a deterrent to potential traffickers or malignant actors, a warning that the source region won’t stay hidden.
“What I do is called laser ablation inductively coupled plasma mass spectrometry, which means I hit rocks with lasers,” Higgins said. “Basically, we look at the trace element isotopes that are found in samples.
“Looking at the lead or uranium signatures of nuclear materials is critical in nuclear forensic investigations.”