Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

La Niña Takes Bolivian Andes on a Sedimental Journey

02.10.2003


Rolf Aalto stands on the cracked mud of a sediment deposit along the Mamoré River in Bolivia. The deposit is part of an estimated annual average of 3 billion tons of sediment washed into the Amazon River basin from the Andes Mountains.
Credit: Rolf Aalto/University of Washington

Conventional wisdom says a river’s flood plain builds bit by bit, flood after flood, whenever the stream overflows its banks and deposits new sediment on the flood plain. But for some vast waterways in South America’s Amazon River basin, that wisdom doesn’t hold water, according to scientists funded by the National Science Foundation (NSF). Results of their research are published in the October 2nd issue of the journal Nature.

Seasonal rains wash billions of tons of rock and soil from the Andes Mountains each year. But new evidence suggests that it’s only about once every eight years, when the equatorial climate phenomenon known as La Niña is in full swing, that water rises rapidly enough to move huge amounts of that sediment to the flood plains.

"Because this research provides new insights into fundamental issues of fluvial rates and processes, the results will be applicable to many of the world’s river systems," said Walt Snyder, section head in NSF’s division of earth sciences, which funded the research. "This paper wonderfully underscores that understanding Earth processes is highly dependent on our ability to measure the rates at which the processes occur and the spatial extent of their products."

Rolf Aalto, a University of Washington (UW) geologist and lead author of the Nature paper, uses a lightweight tubelike device to extract core samples of such sediment deposits across the remote, thickly forested and unspoiled flood plains of northern Bolivia. He measures the amount and activity of lead-210, a radioactive isotope produced by the decay of naturally occurring radon. The isotope is deposited on the flood plain by fresh river sediment and by rainfall, and it can be used to date successive layers of sediment, for as long as a century after it is deposited, as the lead-210 decays further.

But when Aalto examined samples from the Beni River, which flows northward from the Andes into a Mississippi-sized Amazon tributary called the Rio Madeira, he was puzzled.

"I wasn’t seeing a signal that looked anything like what I expected from previous studies on other river flood plains. I was befuddled," he said. "I would see a lot of lead-210 on the surface, and then the activity would drop down to an unchanging level of activity for a long way down, until the next big decrease."

The multitude of thin layers and gradually declining lead210 activity he expected to see simply didn’t show up. The reason: A few thick sediment layers were filling most of the core samples. Aalto devised a new dating method to better reflect a more complex flood plain environment, then analyzed new samples that showed similar large deposits at various intervals going back nearly 100 years. Each of the large layers was deposited at a time that correlated with a La Niña event in the equatorial Pacific Ocean. La Niña is the cold phase of the El Niño Southern Oscillation climate phenomenon that now is recognized as having wide affects on weather throughout the Western Hemisphere.

"The whole system is being raised," Aalto said. Sediment is moved and deposited throughout the river system in episodes orchestrated by the El Niño cycle."

Thousands of years ago, the Beni flowed into the Mamore’ near the Andes. But its course has changed many times through the millennia and the main channel now is hundreds of miles away from the Mamore’. Major floods in which a river shifts course don’t happen often on human time scales, but these Bolivian rivers still can migrate large distances during a single flood, he said.

Aalto believes such active channel migration, periodic large sediment deposits on the flood plain and large floods might all be part of the general mechanics of large rivers. However, that theory cannot be fully explored in the United States because few rivers of appreciable size still function naturally. He hopes that studying largely unspoiled rivers such as the Beni and Mamoré will help to build a better understanding of how rivers behave in completely natural conditions, and that understanding can be applied to disturbed river systems in the United States and elsewhere.

"Rivers are the arteries of continents," said Aalto. "And the Beni is about as close to the heart of the Amazon as you can get."

Other authors of the Nature paper are Laurence Maurice Bourgoin and Jean-Loup Guyot of Institut de Recherche pour le Développement (IRD) in France and Brazil, who have conducted extensive field studies in Bolivia and Brazil; Thomas Dunne of the University of California, Santa Barbara; and David Montgomery and Charles Nittrouer, both scientists at UW. The research is funded by NSF and IRD.

Cheryl Dybas | NSF
Further information:
http://www.nsf.gov/
http://www.nsf.gov/od/lpa

More articles from Earth Sciences:

nachricht Salish seafloor mapping identifies earthquake and tsunami risks
25.04.2019 | Seismological Society of America

nachricht Geomagnetic jerks finally reproduced and explained
23.04.2019 | CNRS

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Unprecedented insight into two-dimensional magnets using diamond quantum sensors

For the first time, physicists at the University of Basel have succeeded in measuring the magnetic properties of atomically thin van der Waals materials on the nanoscale. They used diamond quantum sensors to determine the strength of the magnetization of individual atomic layers of the material chromium triiodide. In addition, they found a long-sought explanation for the unusual magnetic properties of the material. The journal Science has published the findings.

The use of atomically thin, two-dimensional van der Waals materials promises innovations in numerous fields in science and technology. Scientists around the...

Im Focus: Full speed ahead for SmartEEs at Automotive Interiors Expo 2019

Flexible, organic and printed electronics conquer everyday life. The forecasts for growth promise increasing markets and opportunities for the industry. In Europe, top institutions and companies are engaged in research and further development of these technologies for tomorrow's markets and applications. However, access by SMEs is difficult. The European project SmartEEs - Smart Emerging Electronics Servicing works on the establishment of a European innovation network, which supports both the access to competences as well as the support of the enterprises with the assumption of innovations and the progress up to the commercialization.

It surrounds us and almost unconsciously accompanies us through everyday life - printed electronics. It starts with smart labels or RFID tags in clothing, we...

Im Focus: Energy-saving new LED phosphor

The human eye is particularly sensitive to green, but less sensitive to blue and red. Chemists led by Hubert Huppertz at the University of Innsbruck have now developed a new red phosphor whose light is well perceived by the eye. This increases the light yield of white LEDs by around one sixth, which can significantly improve the energy efficiency of lighting systems.

Light emitting diodes or LEDs are only able to produce light of a certain colour. However, white light can be created using different colour mixing processes.

Im Focus: Quantum gas turns supersolid

Researchers led by Francesca Ferlaino from the University of Innsbruck and the Austrian Academy of Sciences report in Physical Review X on the observation of supersolid behavior in dipolar quantum gases of erbium and dysprosium. In the dysprosium gas these properties are unprecedentedly long-lived. This sets the stage for future investigations into the nature of this exotic phase of matter.

Supersolidity is a paradoxical state where the matter is both crystallized and superfluid. Predicted 50 years ago, such a counter-intuitive phase, featuring...

Im Focus: Explosion on Jupiter-sized star 10 times more powerful than ever seen on our sun

A stellar flare 10 times more powerful than anything seen on our sun has burst from an ultracool star almost the same size as Jupiter

  • Coolest and smallest star to produce a superflare found
  • Star is a tenth of the radius of our Sun
  • Researchers led by University of Warwick could only see...
All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Revered mathematicians and computer scientists converge with 200 young researchers in Heidelberg!

17.04.2019 | Event News

First dust conference in the Central Asian part of the earth’s dust belt

15.04.2019 | Event News

Fraunhofer FHR at the IEEE Radar Conference 2019 in Boston, USA

09.04.2019 | Event News

 
Latest News

Hopkins researchers ID neurotransmitter that helps cancers progress

26.04.2019 | Life Sciences

Unprecedented insight into two-dimensional magnets using diamond quantum sensors

26.04.2019 | Physics and Astronomy

Liquid crystals in nanopores produce a surprisingly large negative pressure

26.04.2019 | Physics and Astronomy

VideoLinks
Science & Research
Overview of more VideoLinks >>>