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 GPM sees deadly tornadic storms moving through US Southeast
01.12.2016 | NASA/Goddard Space Flight Center

nachricht Cyclic change within magma reservoirs significantly affects the explosivity of volcanic eruptions
30.11.2016 | Johannes Gutenberg-Universität Mainz

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Novel silicon etching technique crafts 3-D gradient refractive index micro-optics

A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.

Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...

Im Focus: Quantum Particles Form Droplets

In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.

“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...

Im Focus: MADMAX: Max Planck Institute for Physics takes up axion research

The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.

The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...

Im Focus: Molecules change shape when wet

Broadband rotational spectroscopy unravels structural reshaping of isolated molecules in the gas phase to accommodate water

In two recent publications in the Journal of Chemical Physics and in the Journal of Physical Chemistry Letters, researchers around Melanie Schnell from the Max...

Im Focus: Fraunhofer ISE Develops Highly Compact, High Frequency DC/DC Converter for Aviation

The efficiency of power electronic systems is not solely dependent on electrical efficiency but also on weight, for example, in mobile systems. When the weight of relevant components and devices in airplanes, for instance, is reduced, fuel savings can be achieved and correspondingly greenhouse gas emissions decreased. New materials and components based on gallium nitride (GaN) can help to reduce weight and increase the efficiency. With these new materials, power electronic switches can be operated at higher switching frequency, resulting in higher power density and lower material costs.

Researchers at the Fraunhofer Institute for Solar Energy Systems ISE together with partners have investigated how these materials can be used to make power...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ICTM Conference 2017: Production technology for turbomachine manufacturing of the future

16.11.2016 | Event News

Innovation Day Laser Technology – Laser Additive Manufacturing

01.11.2016 | Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

 
Latest News

UTSA study describes new minimally invasive device to treat cancer and other illnesses

02.12.2016 | Medical Engineering

Plasma-zapping process could yield trans fat-free soybean oil product

02.12.2016 | Agricultural and Forestry Science

What do Netflix, Google and planetary systems have in common?

02.12.2016 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>