Featured Research

from universities, journals, and other organizations

Not so fast! Andes rise was gradual, not abrupt

Date:
April 4, 2010
Source:
University of Michigan
Summary:
Trailing like a serpent's spine along the western coast of South America, the Andes are the world's longest continental mountain range and the highest range outside Asia, with an average elevation of 13,000 feet.

Jirishanca, Yerupaja and Siula mountains in high Andes.
Credit: iStockphoto/Steve Estvanik

Trailing like a serpent's spine along the western coast of South America, the Andes are the world's longest continental mountain range and the highest range outside Asia, with an average elevation of 13,000 feet.

The question of how quickly the mountains attained such heights has been a contentious one in geological circles, with some researchers claiming the central Andes rose abruptly to nearly their current height and others maintaining the uplift was a more gradual process.

New research by U-M paleoclimatologist Christopher Poulsen and colleagues suggests that the quick-rise view is based on misinterpreted evidence. What some geologists interpret as signs of an abrupt rise are actually indications of ancient climate change, the researchers say. Their findings are scheduled to be published online April 1 in Science Express.

The confusion results when ratios of oxygen's two main isotopes, oxygen-18 and oxygen-16, are used to estimate past elevation, said Poulsen, an associate professor with appointments in the departments of Geological Sciences and Atmospheric, Oceanic, and Space Sciences.

"In the modern climate, there is a well-known inverse relationship between oxygen isotopic values in rain and elevation," Poulsen said. "As a rain cloud ascends a mountain range, it begins to precipitate. Because oxygen-18 is more massive than oxygen-16, it is preferentially rained out. Thus, as you go up the mountain, the precipitation becomes more and more depleted in oxygen-18, and the ratio of oxygen-18 to oxygen-16 decreases."

Geologists use the ratio of these isotopes, preserved in rock, to infer past elevations.

"If the ratio decreases with time, as the samples get younger, the interpretation would typically be that there has been an increase in elevation at that location," Poulsen said. In fact, that's exactly the conclusion of a series of papers on the uplift history of the Andes published over the past four years. Using oxygen isotopes in carbonate rocks, the authors posited that the central Andes rose about 8,200 to 11,500 feet in three million years, rather than gaining height over tens of millions of years, as other geologists believe.

But elevation isn't the only factor that affects oxygen isotope ratios in rain, Poulsen said. "It can also be affected by where the vapor came from and how much it rained---more intense rainfall also causes oxygen-18 to be preferentially rained out." Skeptical of the rapid-rise scenario, he and his colleagues performed climate modeling experiments to address the issue.

"The key result in our modeling study is that we identified an elevation threshold for rainfall," Poulsen said. "Once the Andes reached an elevation greater than 70 percent of the current elevation, the precipitation rate abruptly increased. In our model, the increased precipitation also caused the ratio of oxygen-18 to oxygen-16 to significantly decrease. Our conclusion, then, is that geologists have misinterpreted the isotopic records in the central Andes. The decrease in the ratio is not recording an abrupt increase in elevation; it is recording an abrupt increase in rainfall."

This conclusion is backed up by geochemical and sedimentological data, Poulsen said. "There is evidence that the central Andes became less arid at the same time that the isotope records show a decrease in the ratio of oxygen-18 to oxygen-16."

Poulsen's coauthors are Todd Ehlers of the University of Tuebingen in Germany and U-M graduate student Nadja Insel.

Funding was provided by the National Science Foundation, the U-M Graham Environmental Sustainability Institute and the Alexander von Humboldt Foundation.


Story Source:

The above story is based on materials provided by University of Michigan. Note: Materials may be edited for content and length.


Journal Reference:

  1. C. J. Poulsen, T. A. Ehlers, N. Insel. Onset of Convective Rainfall During Gradual Late Miocene Rise of the Central Andes. Science, 2010; DOI: 10.1126/science.1185078

Cite This Page:

University of Michigan. "Not so fast! Andes rise was gradual, not abrupt." ScienceDaily. ScienceDaily, 4 April 2010. <www.sciencedaily.com/releases/2010/04/100401143119.htm>.
University of Michigan. (2010, April 4). Not so fast! Andes rise was gradual, not abrupt. ScienceDaily. Retrieved September 18, 2014 from www.sciencedaily.com/releases/2010/04/100401143119.htm
University of Michigan. "Not so fast! Andes rise was gradual, not abrupt." ScienceDaily. www.sciencedaily.com/releases/2010/04/100401143119.htm (accessed September 18, 2014).

Share This



More Fossils & Ruins News

Thursday, September 18, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Egypt Denies Claims Oldest Pyramid Damaged in Restoration

Egypt Denies Claims Oldest Pyramid Damaged in Restoration

AFP (Sep. 17, 2014) Egypt's antiquities minister denied Tuesday claims that the Djoser pyramid, the country's first, had been damaged during restoration work by a company accused of being unqualified to do such work. Duration: 00:56 Video provided by AFP
Powered by NewsLook.com
King Richard III's Painful Cause Of Death Revealed

King Richard III's Painful Cause Of Death Revealed

Newsy (Sep. 17, 2014) King Richard III died in the Battle of Bosworth in 1485, and now researchers examining his skull think they know how. Video provided by Newsy
Powered by NewsLook.com
Researchers Explore Shipwrecks Off Calif. Coast

Researchers Explore Shipwrecks Off Calif. Coast

AP (Sep. 16, 2014) Federal researchers are exploring more than a dozen underwater sites where they believe ships sank in the treacherous waters west of San Francisco in the decades following the Gold Rush. (Sept. 16) Video provided by AP
Powered by NewsLook.com
Museum Traces Fragments of Star-Spangled Banner

Museum Traces Fragments of Star-Spangled Banner

AP (Sep. 12, 2014) As the Star-Spangled Banner celebrates its bicentennial, Smithsonian curators are still uncovering fragments of the original flag that inspired Francis Scott Key's poem. (Sept. 12) Video provided by AP
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