Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Amazon Basin sediment accumulation influenced by La Niña

24.11.2003


Enormous quantities of sediment are deposited in the flood-plains traversed by the Amazon and its tributaries in times of flooding. Scientists have hitherto considered the sedimentation rate to be generally constant with time.



Research conducted jointly by the IRD, the Universities of Washington1 and California2 and the Bolivian National Meteorology and Hydrology Service (SENAMHI) of La Paz, on two Bolivian rivers shows on the contrary that such events are irregular and less frequent than has been thought. These results, just published in Nature, emphasize that, in this Andean-Amazonian foreland, sedimentation is closely dependent on the flood amplitude, in turn linked to climatic variability, and particularly to La Niña, the cold phase of the ENSO (El Niño Southern Oscillation).

Continental-scale rivers can transport enormous sediment loads. In periods of flood, a proportion of these is deposited on flood-plains. In the Amazon Basin, crossed by the Earth’s largest river, great volumes of such sequestered sediment accumulations occur. This is especially so in the Llanos, the Bolivian lowland flood-plains which stretch from the foot of the Andes. An estimated 100 to 150 million tonnes of sediment are deposited each year respectively in the Rio Beni and the Rio Mamore flood-plains. These are the two Andean tributaries of the Rio Madeira, one of the Amazon’s main tributaries and source of more than half the sediment load transported by that river.


The inter-annual sediment accumulation rate has up to now been considered to be generally constant. Now a study conducted in the floodplain which receives these two tributaries refutes this. It is the first to reveal an episodic pattern. During the past century, large sediment accumulation events indeed occurred only quite infrequently (11 events recorded over 90 years of analysis), corresponding to an average recurrence interval of eight years.

These results were the fruit of investigations forming part of the HyBAm (Hydrogéodynamique du Bassin amazonien) programme, conducted by a joint research team involving the IRD (working in the combined research unit UMR LMTG-CNRS-IRD- Paul Sabatier University of Toulouse), the Universities of Washington1 and California2, and the Bolivian National Meteorology and Hydrology Service (SENAMHI) of La Paz. 210Pb3 activity profile analysis on 300 sediment cores sampled from the Beni and Mamore basin flood-plains, interpreted using a new geochronological model developed by the University of Washington,1 enabled them to date discrete sedimentary packages to near-annual resolution. They revealed evidence of an episodic pattern in the main sedimentation events.

Why does sediment accumulation in this part of the Amazon Basin show an episodic pattern? Climatic variability plays a prime role. The team established a significant correlation between these periods of mass sediment deposition and La Niña, the cold phase of the ENSO (El Niño Southern Oscillation) climatic cycle. During most La Niña years over the past century, the Andean relief has been subjected to torrential rainfall generating fierce flooding and intensive mechanical erosion on the Andean slopes. Recordings from a hydrological station situated at the foot of the Andes showed this.

Measurements were continued and followed up in the Hybam programme. When these floods occur, huge volumes of sediment are eroded from the Andean piedmont sub-basins and transported towards the floodplain. For a proportion of these sediments to have been deposited there (for example up to 40% in the Beni Basin flood-plain), the researchers estimate that the water-level rise, during these years of high sedimentation rate, must have been extremely rapid, in excess of 8 000 m3/s. The floods would then have reached the force necessary to cut crevasses in small natural levees along the main stems of the Beni and Mamore rivers and inundate a large expanse of the plain.

With the new data the research team also studied the century-long depositional history in the floodplain of mercury associated with fine particles and the role of these in trapping metal elements transported by the great Amazonian rivers and their tributaries. Also brought to light was a strong increase, over the past 30 years, of mercury concentrations in the sediment particles deposited in the Rio Beni plain. This corresponds to the recent "boom" in gold prospecting, now at an end, but also to the colonization of new arable land on the steep flanks of the Andean piedmont.

Marie Guillaume | alfa
Further information:
http://www.ird.fr/fr/actualites/fiches/

More articles from Earth Sciences:

nachricht The Wadden Sea and the Elbe Studied with Zeppelin, Drones and Research Ships
19.09.2017 | Helmholtz-Zentrum Geesthacht - Zentrum für Material- und Küstenforschung

nachricht FotoQuest GO: Citizen science campaign targets land-use change in Austria
19.09.2017 | International Institute for Applied Systems Analysis (IIASA)

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Ultrafast snapshots of relaxing electrons in solids

Using ultrafast flashes of laser and x-ray radiation, scientists at the Max Planck Institute of Quantum Optics (Garching, Germany) took snapshots of the briefest electron motion inside a solid material to date. The electron motion lasted only 750 billionths of the billionth of a second before it fainted, setting a new record of human capability to capture ultrafast processes inside solids!

When x-rays shine onto solid materials or large molecules, an electron is pushed away from its original place near the nucleus of the atom, leaving a hole...

Im Focus: Quantum Sensors Decipher Magnetic Ordering in a New Semiconducting Material

For the first time, physicists have successfully imaged spiral magnetic ordering in a multiferroic material. These materials are considered highly promising candidates for future data storage media. The researchers were able to prove their findings using unique quantum sensors that were developed at Basel University and that can analyze electromagnetic fields on the nanometer scale. The results – obtained by scientists from the University of Basel’s Department of Physics, the Swiss Nanoscience Institute, the University of Montpellier and several laboratories from University Paris-Saclay – were recently published in the journal Nature.

Multiferroics are materials that simultaneously react to electric and magnetic fields. These two properties are rarely found together, and their combined...

Im Focus: Fast, convenient & standardized: New lab innovation for automated tissue engineering & drug

MBM ScienceBridge GmbH successfully negotiated a license agreement between University Medical Center Göttingen (UMG) and the biotech company Tissue Systems Holding GmbH about commercial use of a multi-well tissue plate for automated and reliable tissue engineering & drug testing.

MBM ScienceBridge GmbH successfully negotiated a license agreement between University Medical Center Göttingen (UMG) and the biotech company Tissue Systems...

Im Focus: Silencing bacteria

HZI researchers pave the way for new agents that render hospital pathogens mute

Pathogenic bacteria are becoming resistant to common antibiotics to an ever increasing degree. One of the most difficult germs is Pseudomonas aeruginosa, a...

Im Focus: Artificial Enzymes for Hydrogen Conversion

Scientists from the MPI for Chemical Energy Conversion report in the first issue of the new journal JOULE.

Cell Press has just released the first issue of Joule, a new journal dedicated to sustainable energy research. In this issue James Birrell, Olaf Rüdiger,...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

“Lasers in Composites Symposium” in Aachen – from Science to Application

19.09.2017 | Event News

I-ESA 2018 – Call for Papers

12.09.2017 | Event News

EMBO at Basel Life, a new conference on current and emerging life science research

06.09.2017 | Event News

 
Latest News

“Lasers in Composites Symposium” in Aachen – from Science to Application

19.09.2017 | Event News

New quantum phenomena in graphene superlattices

19.09.2017 | Physics and Astronomy

A simple additive to improve film quality

19.09.2017 | Power and Electrical Engineering

VideoLinks
B2B-VideoLinks
More VideoLinks >>>