Featured Research

from universities, journals, and other organizations

Researchers Show Why Active Mountains Don’t Get Taller

Date:
September 20, 2002
Source:
National Science Foundation
Summary:
Active mountain ranges like the Olympic Mountains, Taiwan Central Range or the Southern Alps are still growing, but they are not getting any taller. According to an international team of geoscientists River cutting and erosion keep the heights and widths of uplifted mountain ranges in a steady state. The team reports the results of nearly two years of monitoring in this week's (Sept. 20) issue of Science.

Active mountain ranges like the Olympic Mountains, Taiwan Central Range or the Southern Alps are still growing, but they are not getting any taller. According to an international team of geoscientists River cutting and erosion keep the heights and widths of uplifted mountain ranges in a steady state. The team reports the results of nearly two years of monitoring in this week's (Sept. 20) issue of Science.

"These mountains grew to 2.5 to 3 miles high over the past few million years and then they stopped increasing," says Rudy Slingerland, a geologist at Penn State University.

Mountain ranges form near the border of two tectonic plates, the large moving sheets of rock that cover the earth's surface. 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 transported away to the oceans.

"People of many cultures inhabit the world's high mountain regions, and for these people, understanding unstable landscapes is a key for their survival and for the preservation of fragile mountain ecology," says Herman Zimmerman, director of NSF's earth sciences division, which funded the research. "But the importance of mountain landscapes goes far beyond the immediate region. These earth processes are also critical factors for the water supply of people living in cities and towns many hundred of miles from the mountains."

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

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.

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.

"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 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."


Story Source:

The above story is based on materials provided by National Science Foundation. Note: Materials may be edited for content and length.


Cite This Page:

National Science Foundation. "Researchers Show Why Active Mountains Don’t Get Taller." ScienceDaily. ScienceDaily, 20 September 2002. <www.sciencedaily.com/releases/2002/09/020920071256.htm>.
National Science Foundation. (2002, September 20). Researchers Show Why Active Mountains Don’t Get Taller. ScienceDaily. Retrieved July 28, 2014 from www.sciencedaily.com/releases/2002/09/020920071256.htm
National Science Foundation. "Researchers Show Why Active Mountains Don’t Get Taller." ScienceDaily. www.sciencedaily.com/releases/2002/09/020920071256.htm (accessed July 28, 2014).

Share This




More Earth & Climate News

Monday, July 28, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Asteroid's Timing Was 'Colossal Bad Luck' For The Dinosaurs

Asteroid's Timing Was 'Colossal Bad Luck' For The Dinosaurs

Newsy (July 28, 2014) The asteroid that killed the dinosaurs struck at the worst time for them. A new study says that if it hit earlier or later, they might've survived. Video provided by Newsy
Powered by NewsLook.com
The Carbon Trap: US Exports Global Warming

The Carbon Trap: US Exports Global Warming

AP (July 28, 2014) AP Investigation: As the Obama administration weans the country off dirty fuels, energy companies are ramping-up overseas coal exports at a heavy price. (July 28) Video provided by AP
Powered by NewsLook.com
Raw: Sea Turtle Hatchlings Emerge from Nest

Raw: Sea Turtle Hatchlings Emerge from Nest

AP (July 27, 2014) A live-streaming webcam catches loggerhead sea turtle hatchlings emerging from a nest in the Florida Keys. (July 27) Video provided by AP
Powered by NewsLook.com
Trees Could Save More Than 850 Lives Each Year

Trees Could Save More Than 850 Lives Each Year

Newsy (July 27, 2014) A national study conducted by the USDA Forest Service found that trees collectively save more than 850 lives on an annual basis. Video provided by Newsy
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins