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Humanity hit fast forward on geological time, and there's no rewind | Popular Science
Thursday, April 18, 2019
Without much effort, humans can warm the atmosphere, turn rainforests into deserts, and bleach coral reefs. Now, according to a study published April 15 in the Proceedings of the National Academy of Sciences, we can also literally erode bedrock. David Montgomery, professor of Earth and space sciences at the UW, is quoted. Read More
Historic logging site shows first human-caused bedrock erosion along an entire river
Monday, April 15, 2019
Geologic time is supposed to be slow, and the most solid object should be bedrock. But new University of Washington research upends both concepts: Effects of logging show that human activity can significantly erode bedrock, causing geology to fast forward.
“In the last century, we have more river incision in this area than expected. Something caused these rivers to start eroding a lot more,” said lead author Sarah Schanz, a former UW doctoral student who is now a postdoctoral researcher at Indiana University. “We know the Teanaway River has eroded into bedrock before, naturally -- it has some terraces that are 1,800 years old. But this current cycle is anthropogenic, or human-driven.”
Results show that practices related to logging caused bedrock incision of up to 2 meters (6 feet) along the riverbed. As much as a half of what had been a floodplain was transformed into a new terrace abutting the river.
“This is the first time that we’ve been able to pinpoint erosion into bedrock due to human action,” Schanz said. “Most rivers are eroding at about a tenth of a millimeter per year. This is about 100 times that amount.”
The discovery means this beautiful riverbank resulted from human action, not natural forces. It could change how geologists think about landscapes in other parts of the world, such as Taiwan, with its long history of intense human activity.
The study began 20 years ago when co-author Brian Collins, a UW senior lecturer in river geology, was curious why there was so much exposed bedrock in the Teanaway.
Collins also noticed unusual river terraces, the stepped structures along the river bank resulting from cycles of the river flooding and then running more quickly, cutting a new channel deeper into the sediment. He led a 2016 study that calculated short-term changes in the Teanaway’s western fork and suggested logging may have caused the river to cut a new channel.
This site in a community forest offered good access for regular visits by the research team and undergraduate assistants to all three forks. By combining newspaper records, material from the UW Libraries Special Collections, Central Washington University and the local Kittitas County historical society, the researchers were able to piece together and confirm the full history.
Before logging roads existed, companies built temporary “splash dams” high up on the slope with all the logs and then broke up the dam with tools or explosives. Released water helped send logs shooting down to the mills.
“It was such an event that schools closed, and newspaper records show it really well,” Schanz said. “People who are still alive today, some of their earliest memories are of going to see it.”
Key to the process is that loggers would clear away debris to give the logs a clear shot down the river. This removed barriers that held back sediment and cleared out much of the gravel from the riverbed. Such events, the authors believe, caused the erosion to change dramatically.
“If you have too much sediment, you’re basically protecting the river from erosion. But if you have not enough sediment, as that sediment is moving along, it starts to hit the bedrock and erode it,” Schanz said.
David Montgomery, a UW professor of Earth and space sciences, and the other two co-authors used many techniques to analyze the four youngest terraces on the river’s edge, including LIDAR maps, carbon dating of rocks and computer models. In 1999 the team even hammered nails into the bedrock and measured the erosion rates directly.
Many rivers, including the Teanaway, have individual features that show evidence of human impact on areas of bedrock. But this is the first time an entire river basin is found to have been transformed by human activity.
“This is a direct topographic signature of the Anthropocene, the ‘age of humans’ that we now live in,” Montgomery said. “The finding that terrace surfaces in the Teanaway are recently-abandoned floodplains suggests that similar landforms around the world may also reflect the influence of human activity.”
The UW team recently published an overview paper looking at where river terraces have formed worldwide over the past 4,000 years. The authors showed that in many cases, river terrace formation coincided with deforestation.
“It’s sort of a hand-wavey linkage at this point, but I think this could be prevalent worldwide,” said Schanz. “It’s just not a signal that we’ve known to look for before.”
Schanz will start a faculty position in August at Colorado College, where she plans also to explore what the finding means for how river canyons form through natural processes.
“I think the human part is really interesting, but what has broader implications, for me, is the proof that if you change how sediment moves through a river, you can change erosion rates,” Schanz said.
The research was funded by the National Science Foundation.
Rapid Warming in Northwestern Canada
Friday, April 12, 2019
Eric Steig & Spruce Schoenemann (now at the U. Montana) co-authored a paper with the U. Toronto's Trevor Porter, showing recent warming in the Yukon has surpassed anything in the past 13600 years. Read More
North Dakota site shows wreckage from same object that killed the dinosaurs
Friday, March 29, 2019
An excavation site in North Dakota sheds new light on what happened when a giant meteorite struck planet Earth, 66 million years ago.
On that day, violent ground shaking first raised giant waves in the waters of an ancient inland sea. Then tiny beads began to fall, created from molten rock cooling at the edge of space to make glassy spheres. The rain of glass was so heavy it may have ignited much of the vegetation on land, while in the water, fish struggled to breathe as the glass beads clogged their gills.
Once the surge of water reached a river mouth, it transformed into a 30-foot wall of water, tossing hundreds if not thousands of freshwater fish -- sturgeon and paddlefish -- onto a sandbar and temporarily reversing the flow of the river.
Stranded by the receding water, the fish were pelted by glass beads up to 5 millimeters (almost a quarter of an inch) in diameter. Some beads got buried inches deep in the mud. Rocks and beads continued to rain down for another 10 to 20 minutes before a second large wave inundated the shore and covered the fish with gravel, sand and fine sediment, sealing them until the present-day discovery.
In a paper to be published April 1 in the Proceedings of the National Academy of Sciences an international team of authors, including University of Washington Provost Mark Richards, share the discovery of a site that tells another piece of the story from the day a meteor strike is thought to have led to the end of the dinosaurs.
“It’s like a museum of the end of the Cretaceous in a layer a meter and a half thick,” said Richards, who is also a professor in the UW Department of Earth & Space Sciences.
This unique fossilized graveyard - fish stacked one atop another mixed with burned tree trunks and conifer branches, dead mammals, a pterosaur egg, a mosasaur and insects, the carcass of a Triceratops and seaweed and marine snails called ammonites - was unearthed over the past six years in the Hell Creek Formation in North Dakota by lead author Ro bert DePalma.
“This is the first mass death assemblage of large organisms anyone has found associated with the KT boundary,” said DePalma, curator of paleontology at the Palm Beach Museum of Natural History in Florida and a doctoral student at the University of Kansas. “Nowhere else on Earth can you find such a collection consisting of a large number of species representing different ages of organisms and different stages of life, all of which died at the same time, on the same day.”
The new study describes the site, dubbed Tanis, and the evidence connecting it with the asteroid or comet strike off Mexico’s Yucatan Peninsula. That impact created a huge crater, called Chicxulub, on the ocean floor and sent vaporized rock and cubic miles of asteroid dust into the atmosphere.
The impact would have melted the bedrock under the seafloor and pulverized the asteroid, sending dust and melted rock into the stratosphere, darkening the sun for months if not years. Debris would have rained down from the sky.
Richards, who did the research as a professor and dean at the University of California, Berkeley, and Walter Alvarez, a UC Berkeley professor of the graduate school who first hypothesized that a comet or asteroid impact caused the mass extinction, analyzed the rain of glass beads and the tsunami-like waves that buried and preserved the fish. The beads, called tektites, formed in the atmosphere from rock melted by the impact.
Richards and Alvarez determined that the fish could not have been stranded and then buried by a typical tsunami, a single ocean wave that would have reached this previously unknown arm of the Western Interior Seaway hours after the impact 3,000 kilometers away, if at all. Their reasoning: The tektites would have rained down within 45 minutes to an hour of the impact, unable to create mudholes if the seabed had not already been exposed.
Instead, they argue, seismic waves likely arrived within 10 minutes of the impact from what would have been the equivalent of a magnitude 10 or 11 earthquake, creating a seiche (pronounced saysh) wave in the inland sea, similar to water sloshing in a bathtub during an earthquake.
Though large earthquakes often generate seiche waves in enclosed bodies of water, they’re seldom noticed, Richards said. For example the 2011 Tohoku quake in Japan, a magnitude 9.0, created 6-foot-high seiche waves a half hour later in a Norwegian fjord 8,000 kilometers away.
In the case of the Chicxulub impact, the timing works out for the seiche waves’ arrival.
“The seismic waves start arising within 9 to 10 minutes of the impact, so they had a chance to get the water sloshing before all the spherules had fallen out the sky,” Richards said. “These spherules coming in cratered the surface, making funnels -- you can see the deformed layers in what used to be soft mud -- and then rubble covered the spherules. No one has seen these funnels before.”
The tektites would have reached terminal velocity of about 200 miles per hour, according to Alvarez, who decades ago estimated the travel time of these objects through the atmosphere.
“You can imagine standing there being pelted by these glass spherules. They could have killed you,” Richards said. Many believe that the rain of debris ignited wildfires over the entire American continent, if not around the world.
Richards estimated that the seismic waves, creating the seiche waves, would arrive in North Dakota at roughly the same time as the projectiles from above.See also: “The Day the Dinosaurs Died” in The New Yorker
At least two huge seiche waves inundated the land, perhaps 20 minutes apart, leaving six feet of deposits covering the fossils. Overlaying this material is a layer of clay rich in iridium, a metal rare on Earth but common in asteroids and comets. This layer is known as the KT or KPg boundary, marking the end of the Cretaceous Period.
“When we proposed the impact hypothesis to explain the great extinction, it was based just on finding an anomalous concentration of iridium -- the fingerprint of an asteroid or comet,” said Alvarez. “Since then the evidence has gradually built up. But it never crossed my mind that we would find a deathbed like this.”
The new discovery at Tanis is the first time the debris produced in the impact was found along with animals killed in the impact’s immediate aftermath.
Jan Smit, a retired professor of paleontology from the Vrije Universiteit in Amsterdam in The Netherlands, who is considered the world expert on tektites from the impact, analyzed and dated the tektites from the Tanis site. Many tektites were found in near-perfect condition embedded in amber.
“We have an amazing array of discoveries which will prove in the future to be even more valuable," Smit said. "We have fantastic deposits that needs to be studied from all different viewpoints. And I think we can unravel the sequence of incoming ejecta from the Chicxuulab impact in great detail, which we would never have been able to do with all the other deposits around the Gulf of Mexico."
Co-authors are David Burnham of the University of Kansas, Klaudia Kuiper of Vrije Universiteit, Phillip Manning of the College of Charleston in South Carolina, Anton Oleinik of Florida Atlantic University, Peter Larson of the Black Hills Institute of Geological Research in South Dakota, Florentin Maurrasse of Florida International University, Johan Vellekoop of KU Leuven in Belgium and Loren Gurche of the Palm Beach Museum of Natural History.
Glacier growing: Melting Jakobshavn glacier in Greenland is growing again, a new NASA study finds | CBS News
Tuesday, March 26, 2019
In 2015, it lost a piece of ice the size of Manhattan. But now a major Greenland glacier that was one of the fastest shrinking ice and snow masses on Earth is growing again, a new NASA study finds. Ian Joughin, a glaciologist at the UW, is quoted. Read More
Students launch high-altitude balloon into stratosphere | Bend Bulletin
Monday, March 25, 2019
A group of home-school students got to see the effects of low air-pressure and radiation after they sent a weather balloon into the stratosphere, with a little help from NASA and the UW. Robert Winglee, professor of Earth and space sciences at the UW, is quoted. Read More
New signs on State Highway 530 | KUOW
Monday, March 25, 2019
Since the Oso landslide 5 years ago, a state joint commission has issued recommendations that could include creating a landslide hazard and risk mapping program. David Montgomery, professor of earth and space sciences at the UW, is interviewed. Read More
Explosion in Finley quarry registers on earthquake sensor | Tri-City Herald
Friday, March 15, 2019
A seismology sensor picked up an explosion that shook the ground south of Kennewick at 8:47 a.m. Thursday morning. Amy Wright, a research scientist with the UW's Pacific Northwest Seismic Network, is quoted. Read More
The Tibetan Plateau is more recent than previously thought
Thursday, February 28, 2019
A new study published this week in Science shows that the Tibetan Plateau is much more recent than previously thought. Assistant Professor Alexis Licht from ESS co-authored the article. Read More
Learning from the 2001 Nisqually Earthquake | Q13 FOX News
Thursday, February 28, 2019
There is something about earthquakes that has always intrigued UW Earth and space sciences professor Harold Tobin. Read More