When most geologists do field work, they hike around to collect rock samples. But what if your “field” is tilted 90 degrees, over half a mile high, and composed of solid granite? Roger Putnam, a graduate student in geology at UNC-Chapel Hill, suggests just climbing it.
Putnam is a scientist who happens to be an extreme rock climber. He is studying the face of El Capitan, a vertical rock formation in Yosemite Valley in California, by scaling its walls to collect data. The work aims to settle a hot debate related to how mountain ranges are formed.
El Capitan is a behemoth, the largest chunk of granite in the world. It was 1958 before someone climbed its face, taking over a year and several efforts to complete the task. Today the team’s route, known as “the Nose,” is considered a rite of passage among serious climbers. The best can climb it in under three hours, but most take about three days.
There are about 100 established climbing routes that ascend 3,000 feet. None are easy, all are straight up or overhung.
Putnam’s project was kicked off before he came to UNC as a graduate student. He was working on a hydrogeology internship at Yosemite when three football fields’ worth of rock fell off the face of El Capitan, perhaps triggered by an earthquake.
The stuff that came off didn’t match what geologists thought was there.
Further, the historical record for El Capitan was crude and outdated. Its face had been mapped with binoculars in 1920, and the composition of the rock deduced simply by its appearance.
It was clear the map needed to be updated.
When he got to graduate school, Putnam discussed this with his adviser, UNC geology professor Allen Glazner.
Quickly they realized they had a much bigger opportunity than simply updating a map. If they could detect whether the composition of the rock changes as you ascend, they could provide the first test of two competing geological theories.
How El Capitan formed
When El Capitan was initially formed, around 100 million years ago, the Yosemite Valley looked like the Pacific Northwest today. There were volcanoes caused by a subduction zone, where two plates that make up the Earth’s crust come into contact. For subduction, an ocean plate goes under and pushes against the continental plate. The conditions in the zone are extreme: temperature in the thousands, pressure thousands of times atmospheric pressure.
The stress of the plates’ contact deforms them and occasionally breaks them. Magma, the molten rock under the earth’s crust, can rise to the surface and cool. The deforming plates and rising magma create a landscape of mountains and rock formations.
The granite that makes up El Capitan is cooled magma. The scientific debate centers around how the cooling occurs.
Liquid granite is a mineral soup, dominated by silica, the stuff in glass and sand, but also containing minerals such as iron and magnesium.
One theory of how granite bodies form, the big blob theory, says that a blob of hot liquid rock emerged from the ground. Like a microwave burrito, the outside would have cooled first. So the material with high melting points, such as iron, should have solidified first, on the outside. The material with lower melting points, like magnesium, would be pushed into the hot middle, eventually cooling.
Big blob models show that, for El Capitan, this cooling should take only about 100,000 years, a blink in geological time. But this violent cooling would create huge cracks in the material, which geologists don’t see.
An alternate theory, fracture propagation, proposes that magma rises slowly and surely in tiny cracks. This creates a less stressful cooling process of millions of years. It also means the minerals won’t separate.
A risky enterprise
Regardless of the beginning, the formation of El Capitan has one more chapter. Glaciers came to Yosemite a million or so years ago. They are a powerful force of erosion, and carved through the rock like a knife through cheddar, leaving the vertical walls of El Capitan. That allows Putnam to see inside the original rock.
“Here we have a cross section,” he said. “That’s so rare.”
Putnam is studying the chemical composition of the rock as he ascends. If the composition changes, a point goes to Big Blob. If not, a point goes to fracture propagation.
Each ascent takes about 3 days of climbing. Every 100 feet, he takes 15 minutes to chip away at rock, putting the samples in a baggie. He also takes pictures of the face, and marks in his notebook. When not in use, the notebook dangles from a rope attached to his belt.
His climbing partner has to wait patiently while he does this. His partners are climbing buddies, not geologists.
“I can’t just get another geologist. You really have to be an excellent climber to do this,” Putnam saud. “And I have to be able to trust my climbing partner. You’re literally within feet of the other person for days on end, often in perilous situations.”
The work is no cakewalk, either. Usually a climber’s pack gets lighter during an ascent, as food and water are consumed. This can help lessen fatigue.
But Putnam’s pack gets heavier. He adds about 25 pounds of rock each day.
“I grew up working on fishing boats, I know a hard day of work,” said Putnam. “This is ten times harder than anything I’ve ever done.”
It’s also stressful. “I’m often scared out of my brains,” said Putnam. “The consequences of slipups are huge.”
Reports of climbing deaths remind him of the stakes, including the death this month of Eric Metcalf, a 19-year old UNC student and Cary native, with whom Putnam sometimes climbed recreationally. “He will be truly missed,” Putnam said.
‘The most glorious thing’
About 200 pounds of rock will qualify for further study. Putnam lugs it to the post office. Then he hops on a plane and reunites with the samples at UNC. A good deal can be learned from simple visual inspections. If you’ve purchased a new countertop, you know that different kinds of granite have different coloring, and can be smooth, speckled, or chunky.
But the proof comes from chemical analysis. One method is X-ray fluorescence. Putnam grinds up some of the rock, and shines X-rays on it. The X-rays excite different minerals in unique ways, and the powder will send back a signal. He can then fingerprint this signal for different minerals.
Other climbers contribute to Putnam’s work, too. Putnam himself does not feel comfortable doing this on the most difficult routes, but he can often convince better climbers to take pictures on their climbs, if not also take samples. The pictures are not only used for rock analysis. The research also intends to update the old map. To create a full map of El Capitan, Putnam and colleagues will combine these close-ups with high-resolution images taken across the valley.
Putnam also uses LIDAR to sense the topography of the face. LIDAR, short for Light Detection And Ranging, uses laser light to measure distances.
With all of this information they are building a 3D map of the entire face. Square kilometers of face will be mapped down to the centimeter. The work is certainly inspiring, so much so that National Geographic is funding part of the research.
“It really is the most glorious thing, to explore,” Putnam says. “It’s the center of the mountaineering ethos.”