Nav: Home

SF State research reveals how climate influences sediment size

November 16, 2015

SAN FRANCISCO, Nov. 16, 2015 -- In a new paper published this week in the Proceedings of the National Academy of Sciences (PNAS), San Francisco State University Professor of Earth and Climate Sciences Leonard Sklar and colleagues show how two established geochemical techniques can be combined in a novel way to reveal both the altitude where river rocks were originally produced and the rate of erosion that led them to crumble into the river.

Geologists have long dreamed of interviewing the rocks on the bed of a river to learn the story of where they were born and how they came to be the size they are. This is because the size of river rocks influences how rivers behave, from the habitat they provide to the speed with which they carve canyons. Yet, until now, the rocks have withheld their secrets.

Sklar, along with lead author Cliff Riebe and doctoral student Claire Lukens from the University of Wyoming and David Shuster from the University of California, Berkeley, wanted to understand how climate, which varies with altitude, controls the size and flux of sediments in rivers.

The National Science Foundation-funded research team's key breakthrough came when it used two techniques to query river rocks. First, researchers used cosmogenic nuclides to trace erosion rates in sediment samples. This common method of measuring erosion rates uses rare isotopes formed in minerals exposed to cosmic rays at the earth's surface. A higher concentration of isotopes means the rock has spent a longer time exposed at the surface, indicating a slower erosion rate.

They then combined this technique with detrital thermochronometry, another sediment tracing tool, which pinpoints where on a mountain sediment was produced. This is done by laboriously isolating tiny crystals of the mineral apatite and using ultraprecise machines to count the number of helium atoms contained in the crystals. The helium is formed by radioactive decay of uranium and is more abundant in rocks at higher elevations in the study area.

The findings are significant for two reasons, Sklar said. The results show that the size of sediment that falls into rivers is larger where mountain slopes are steeper, colder and less vegetated, revealing how climate and topography influence the size of sediments in rivers. Sediment size, in turn, controls how fast rivers cut canyons into rock, which ultimately limits how high mountains can rise.

"With this new way of interrogating river rocks," Sklar continued, "we can close the circle between how hillslopes feed rocks to the river and how the river carves the landscape and creates the hillslopes in the first place."

This article titled "Climate and topography control the size and flux of sediment produced on steep mountain slopes" was published online Nov. 16. The research was conducted in California's High Sierra Mountains, which tower above Inyo Creek, a small watershed adjacent to Mt. Whitney, the highest peak in the contiguous United States.
-end-
San Francisco State University makes things happen. Founded in 1899, it is the only master's-level public university serving the counties of San Francisco, San Mateo and Marin. Its nationally acclaimed programs span a broad range of disciplines. Nearly 30,000 students enroll at the University each year, and its more than 236,000 graduates have contributed to the economic, cultural and civic fabric of San Francisco and beyond. Through them -- and more than 1,600 world-class faculty members -- SF State proudly embraces its legacy of academic excellence, community engagement and commitment to social justice. For more information, visit sfsu.edu.

San Francisco State University

Related Climate Articles:

Climate change label leads to climate science acceptance
A new Cornell University study finds that labels matter when it comes to acceptance of climate science.
Was that climate change?
A new four-step 'framework' aims to test the contribution of climate change to record-setting extreme weather events.
It's more than just climate change
Accurately modeling climate change and interactive human factors -- including inequality, consumption, and population -- is essential for the effective science-based policies and measures needed to benefit and sustain current and future generations.
Uncertainties related to climate engineering limit its use in curbing climate change
Climate engineering refers to the systematic, large-scale modification of the environment using various climate intervention techniques.
Public holds polarized views about climate change and trust in climate scientists
There are gaping divisions in Americans' views across every dimension of the climate debate, including causes and cures for climate change and trust in climate scientists and their research, according to a new Pew Research Center survey.
Incubating climate change
A group of James Cook University scientists led by Emeritus Professor Ross Alford has designed and built an inexpensive incubator that could boost research into how animals and plants will be affected by climate change.
And the Oscar goes to ... climate change
New research finds that Tweets and Google searches about climate change set new record highs after Leonardo DiCaprio's Academy Awards acceptance speech, suggesting celebrity advocacy for social issues on a big stage can motivate popular engagement.
Cod and climate
Researchers use the North Atlantic Oscillation as a predictive tool for managing an iconic fishery.
What hibernating toads tell us about climate
The ability to predict when toads come out of hibernation in southern Canada could provide valuable insights into the future effects of climate change on a range of animals and plants.
Maryland climate and health report identifies state's vulnerabilities to climate change
A new report by the University of Maryland School of Public Health and the Maryland Department of Health and Mental Hygiene details the impacts of climate change on the health of Marylanders now and in the future.

Related Climate Reading:

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Anthropomorphic
Do animals grieve? Do they have language or consciousness? For a long time, scientists resisted the urge to look for human qualities in animals. This hour, TED speakers explore how that is changing. Guests include biological anthropologist Barbara King, dolphin researcher Denise Herzing, primatologist Frans de Waal, and ecologist Carl Safina.
Now Playing: Science for the People

#532 A Class Conversation
This week we take a look at the sociology of class. What factors create and impact class? How do we try and study it? How does class play out differently in different countries like the US and the UK? How does it impact the political system? We talk with Daniel Laurison, Assistant Professor of Sociology at Swarthmore College and coauthor of the book "The Class Ceiling: Why it Pays to be Privileged", about class and its impacts on people and our systems.