Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Researchers show why active mountains don’t get taller

20.09.2002


Active mountain ranges like the Olympic Mountains, Taiwan Central Range or the Southern Alps are still growing, but they are not getting any taller. River cutting and erosion keep the heights and widths of uplifted mountain ranges in a steady state according to an international team of geoscientists.



"These mountains grew to 2.5 to 3 miles high over the past few million years and then they stopped increasing," says Dr. Rudy L. Slingerland, professor of geology and head of Penn State’s geosciences department. "We assumed that various erosional forces were compensating for the constant uplift of the mountains, but few observations have been available to validate this assumption."

Mountain ranges form near the border of two tectonic plates. When one plate slides beneath the other, or subducts, a veneer of rocks on the subducted plate is scraped off and piles up to form the mountains. Even though tectonic plates subduct for tens of millions of years, mountain ranges usually stay between 2.5 and 3 miles high and about 75 to 150 miles wide. This is because the slopes become steeper as the mountains grow in elevation and more material erodes away via landslides, river cutting and other forms of erosion. The higher and steeper the mountains, the greater the slope and the more material is transported away to the oceans.


"The process of river erosion redistributes the mass of the mountain and has significant influences on maintaining steady-state mountain heights and widths," says Slingerland.

Slingerland, working with N. Hovius, a former Penn State postdoctoral fellow now at Cambridge University; K. Hartshorn, graduate student; and W. B. Dade, research scientist, also at Cambridge University, looked at the LiWu River in the East Central Range of Taiwan.

The researchers monitored the site of the only water gauging station on the LiWu River. The station was established for a small, Japanese built, hydroelectric station 2.5 miles downstream. They report the results of nearly two years of monitoring in today’s (Sept. 20) issue of Science.

The LiWu River originates at 11,500 feet above sea level and drains an area of about 230 square miles of mostly quartzite and schist rocks. The researchers note that the area has a high rate of tectonic uplift, about 2 to 4 miles per million years and approximately 110 million tons of sediment move through the river each year. This is about a tenth of all the sediment that goes into the sea worldwide.

"We measured the elevation of the riverbed to plus or minus two one-hundredths of an inch," says Slingerland. "This really fine measurement allowed us to see how rapidly the water was eroding the riverbed."

The quartzite components of the riverbed eroded about a third of an inch over two wet seasons and the schist eroded a little under a quarter of an inch.

"It just so happened that the first season we were monitoring was quite dry, then in the second season there was a super typhoon, Supertyphoon Bilis," says Slingerland. "We found the wear rates differed between the two years."

During the typhoon year, there was some wear in the river bottom, but most of the wear was higher on the valley walls and in the corners, widening the river’s course. During the non-supertyphoon year, when rainfall was relatively frequent but of moderate intensity, wear occurred lower in the river valley.

"Looking at the numbers, even for only a few years, indicates that the down cutting rate fairly closely matches the rate at which rocks move up," says the Penn State researcher.

Knowing that the river cutting balances the continuous mountain up lifting answered the question of the rate of river cutting, but how that cutting takes place was another question the researchers investigated.

"While violent water discharge does pluck blocks of rocks from the riverbeds, it appears to be the abrasion by suspended particles that does most of the down cutting," says Slingerland. "It is like sandblasting a stone building. The tiny particles wear away the surface."

Andrea Elyse Messer | EurekAlert!
Further information:
http://www.psu.edu/

More articles from Earth Sciences:

nachricht Global study of world's beaches shows threat to protected areas
19.07.2018 | NASA/Goddard Space Flight Center

nachricht NSF-supported researchers to present new results on hurricanes and other extreme events
19.07.2018 | National Science Foundation

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: First evidence on the source of extragalactic particles

For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.

To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...

Im Focus: Magnetic vortices: Two independent magnetic skyrmion phases discovered in a single material

For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.

Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...

Im Focus: Breaking the bond: To take part or not?

Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.

A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...

Im Focus: New 2D Spectroscopy Methods

Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.

"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....

Im Focus: Chemical reactions in the light of ultrashort X-ray pulses from free-electron lasers

Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.

Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Leading experts in Diabetes, Metabolism and Biomedical Engineering discuss Precision Medicine

13.07.2018 | Event News

Conference on Laser Polishing – LaP: Fine Tuning for Surfaces

12.07.2018 | Event News

11th European Wood-based Panel Symposium 2018: Meeting point for the wood-based materials industry

03.07.2018 | Event News

 
Latest News

Global study of world's beaches shows threat to protected areas

19.07.2018 | Earth Sciences

New creepy, crawly search and rescue robot developed at Ben-Gurion U

19.07.2018 | Power and Electrical Engineering

Metal too 'gummy' to cut? Draw on it with a Sharpie or glue stick, science says

19.07.2018 | Materials Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>