Research

A Walk Through the Valley of Death

澳门十大娱乐网站的地质学家研究西南沙漠中的岩石和大地构造

April 22, 2022

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, 这说明攻击平面是垂直的.

“Doing it in the field is so much more …,” said Higgins, searching for the right word. “我是一个非常亲力亲为的学习者,所以它让我明白了.”

A female student holding her arm out at an angle, takes strike and dip measurements with a device that looks like a walkie talkie.
Sophomore Sydney Higgins taking strike and dip measurements of tilted mudstone layers in Golden Canyon in Death Valley National Park.

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)带了16名本科生和2名研究生 Death Valley National Park 和红岩峡谷一起去春假的实地考察.

“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.

“碰撞区就像推土机推石头一样.”

Tectonic Collision

当海洋板块与大陆板块碰撞时, 就像数百万年前发生在美国西部的一样, the oceanic plate will subduct (duck under) the continental plate due to its higher density. The continental plate is forced up, buckling into folds of mountains and valleys, sometimes including volcanic activity from below. Strike and dip readings allow geologists to place a particular rock formation (closeup at left) into a map that reveals the region's tectonic history.

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, 她指出,这让她想起了自己小时候为什么喜欢地球科学. His pictures and talks about Death Valley inspired her to sign up for the trip this spring.

A group of students lean against a rocky slope and take strike and dip measurements.
学生们在提图斯峡谷进行撞击和下沉测量.

Simonetti has been guiding the excursion, which is funded by CEEES, for about a decade. The group used to camp out in tents, 但一直在附近的比蒂镇开汽车旅馆, Nevada, for the last five years.

在最初的四年里,西蒙内蒂在两家公司之间交替 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, 岩浆活动引起了爆发性火山活动, and the presence of a variety of sedimentary rocks and metamorphic rocks.”

死亡谷位于两组山脉之间,越高越好 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.

A close up map of Death Valley displaying two labels: Panamint Range and to the west and Amargosa Range to the east.

死亡谷位于两组山脉之间,越高越好 Panamint Range to the west and the dryer Amargosa Range along the Nevada-California border.

A close up map of Death Valley displaying pins that show the places where the students visited.

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.

一组五名学生光着脚穿过一片多沙多山的沙漠. Two students lay on sand on their backs. 太阳就在远处的沙丘上方照耀着. 一群学生在沙丘顶上跳着拍照片.
Students hike, 躺在沙里,从Mesquite Flat sand Dunes的沙丘上跳下来, located in the center of Death Valley.

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, 西蒙内蒂说,从地质角度来看,最近大约有2个,000 years ago — a magma chamber near the surface heated up water-saturated sedimentary rocks.

“岩石中的水变成了蒸汽,”他说. “There was enough pressure that a flashpoint was created, causing a huge explosion.”

学生们一边跑一边踢沙子,沿着一条小路进入一个大坑.
学生们从770英尺深的Ubehebe火山口上沿着一条小路跑下来, which erupted approximately 2,在死亡谷国家公园的北端.
A man holds a large piece of rock up to the camera. 几块大小不一的岩石的特写.
Tony Simonetti, associate professor in Civil and Environmental Engineering and Earth Sciences, holds a piece of vesicular basalt. 岩浆房加热了上面浸透水的岩石, creating steam and a violent explosion, called a phreatomagmatic eruption.
一名女学生蹲下来检查火山口的岩石. Behind her is a large moutain formation.
Kayla Hollister, a graduate student (CEEES), examines rocks in Ubehebe Crater.

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, 熔岩中的气泡在非常轻的岩石上形成了洞. 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.

在提图斯峡谷,这群人沿着峡谷壁之间的一条狭窄通道往上爬. 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.

Inside narrow rock formations, a professor points to the side of a rock to a group of students. Vein like markings on the side of a rock formation.
Simonetti points out calcium carbonate veins present within metamorphosed limestones in Titus Canyon.

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.

A man stands with his back to the camera, looking at a group of students examine the Badwater Basin.
Simonetti and students walk through Badwater Basin, 这是死亡谷海平面下282英尺的广阔盐滩.

这个山谷平均每年只有半英寸的降雨量. 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.

Major Watersheds of North America

The rivers in the central part of the United States drain into the Gulf of Mexico, mostly through the Mississippi River Drainage Basin. The Great Basin is unique because 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, 喷发的火山和上升的山脉取代了它. Steep ranges alternate with flat, 在过去的1600万年里,干燥的沙漠不断延伸. The distance from Reno to Salt Lake City is estimated to have doubled during that time.

这种折叠拉伸过程形成的景观被称为 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. 碎石不断地从山上冲刷到山谷中, 形成类似于河流三角洲的大冲积扇的.

有几个学生把周三早上的徒步旅行取消了 Golden Canyon 这是这次旅行的亮点,尽管是最具挑战性的. 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.

学生们在光秃秃的黄色山丘间徒步,头顶是蓝天.
Students hike through the badlands of Golden Canyon in Death Valley National Park.

Silt and clay from the bottom of one of the region’s prehistoric lakes were compressed into mudstone about 6 million years ago. 最近的隆起和侵蚀使它暴露在视野中. 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. “也许峡谷岩壁的岩石应该在山谷的另一边, 但当它开始伸展和打开时就被困在这里了.”

Two female students climb down a narrow passage between yellow rock formations. A group of students and their professor pose for a photo in the Golden Canyon badlands. A student stands admiring the Golden Canyon badlands from the base of the Red Cathedral conglomerate.
研究生Kayla Hollister(前)和Sydney Herczeg, a CEEES sophomore, walk through a narrow passage. The students stop for a group photo in Golden Canyon with the Red Cathedral formation in the background. 侵蚀的泥岩脊提供了每个方向的荒地景观.

被侵蚀的黄色斜坡像皱巴巴的床单一样向四面八方折叠, 顶端是陡峭的红色悬崖,被称为“红色大教堂”. 砂岩中的铁氧化形成了红色, 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.

这一天以在自然桥峡谷徒步旅行结束, where the students examined a special rock called gneiss. Created under pressure conditions 30 kilometers below the surface and 800 degrees Celsius, 它的特点是浅色和深色的带子融合在一起. Simonetti explained why he chose this spot for their final stop in Death Valley.

Students walk through vertical canyon walls and under a rock bridge formation.
学生们徒步穿越死亡谷国家公园的自然桥峡谷.
A coarse-grained rock.
A piece of metamorphic gneiss (center), the oldest rock in the national park, sits in Natural Bridge Canyon. Gneiss is characterized by the dark and light banding of minerals segregating into separate layers.
一个男学生坐在岩石上,把手放在岩石上.
Sophomore Anthony Masso-Rivetti sits on metamorphic gneiss rocks in Natural Bridge Canyon. These are the oldest rocks in Death Valley, about 1.7 billion years old.

“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.

一群人走在一条被沙漠植物包围的多风小径上. 远处是高大的岩层,有各种颜色的层.
学生们在拉斯维加斯附近的红岩峡谷的拱心石小径上徒步.

“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. 长期的干旱导致了大坝运行的变化, 这引发了学生对水资源缓解方法的讨论.

“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.”

胡佛大坝,位于亚利桑那州和内华达州边界的科罗拉多河上.
Hoover Dam in the Black Canyon of the Colorado River, on the border between Nevada and Arizona. Construction began in 1931 during the Great Depression, and President Franklin D. 1935年9月30日,罗斯福致力于这项计划.

Mohammed Mansour, one of the civil engineers, 他说,这个项目的范围让他为自己选择的专业感到自豪. More than 3 million cubic yards of concrete were used in the dam’s construction, 如果排成一条线,足以在赤道上包裹地球. 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. “他们在修建大坝时遇到了许多挑战, but they were able to overcome those challenges. 这就是从艰苦中培养创新的真谛.”

Geological Research

对希金斯来说,重返校园并不是动手学习的结束, whose passion has led to a job in Simonetti’s lab. 这项研究显示了地质知识的许多实际用途之一.

A chemist as well as a geologist, 西蒙内蒂使用激光仪器测量同位素, 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. “基本上,澳门十大娱乐网址大全研究的是样品中发现的微量元素同位素.

“Looking at the lead or uranium signatures of nuclear materials is critical in nuclear forensic investigations.”