Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Pinatubo’s rivers show the danger isn’t over when volcanic eruption ends

06.01.2005


Erupting volcanoes are among the most destructive forces in Mother Nature’s arsenal. But where many people live on or near the flanks of such mountains, the real disaster often doesn’t start until the eruption has subsided and the world has stopped paying attention. It is then that rain-swollen rivers emanating from volcanic peaks can send massive lahars – large waves of mud made up of water, ash and volcanic rock – careening down the mountainsides, often burying everything in their paths, even entire towns and villages. Such lahars can occur for years after an eruption, depending on how much debris the volcano deposits and how much rain falls, until the sediment has either been cleaned off the mountain or has stabilized so that it doesn’t erode easily.



Mount Pinatubo, northwest of Manila on the Philippine island of Luzon, erupted with devastating force in June 1991 and now is proving to be an ideal laboratory for studying the "hydrologic aftermath" of a volcanic eruption, said Karen Gran, a University of Washington doctoral student in Earth and space sciences.

Gran has been studying data compiled from 1997 through 2003 from five rivers on Pinatubo’s flanks. The streams are in various stages of recovery, with one almost back to its pre-eruption state because it didn’t become as clogged by sediment. But others traverse areas that still have vast amounts of sediment that can be washed away easily. Pinatubo’s location, in the tropics not far north of the equator, makes it subject to torrential rains from monsoons and typhoons.


"In one of the streams we’re studying, nothing can live. If a big storm hits, the whole riverbed moves," Gran said. That means that more than 13 years after the eruption, some of the rivers studied have not recovered to the point of having stable channels, which are necessary for a return of aquatic species and a general ecological recovery.

Gran is a lead author of a paper detailing the research on how streams on volcanoes recover, published Jan. 5 in the Geological Society of America Bulletin. David Montgomery, a UW Earth and space sciences professor, is co-author.

Mount Pinatubo’s eruption, the second largest recorded in the 20th century, deposited nearly 1.5 cubic miles of volcanic ash and rock on its flanks, about 10 times more than Mount St. Helens in Washington state deposited in its eruptions in 1980. The town of Bacolor at the edge of Pinatubo was buried repeatedly by major lahars. Today a large church in Bacolor must be entered through the choir loft – everything below is filled with sediment.

"The thing about a mud flood is that it doesn’t recede. It just stays," Montgomery said.

Eventually, all the river channels will stabilize and lahars will occur infrequently, Gran said. That’s because the fine-grained ash and pumice typically are the first to be carried away by water. As a river cuts deeper into the sediment, coarser material eventually will form a more solid streambed and the amount of sediment in the water will decline steadily.

Sediment runoff comes from three primary areas, Gran said. One is the vast amount of material hundreds of feet thick deposited in a river valley, which the river can wash away as it meanders across the valley. Another is high terraces formed from a combination of fine and coarse material, which stand above the river level but erode into the river during heavy rainfall and eventually can be stabilized by vegetative growth. The third source is high cliffs that are unstable and can drop large chunks of sediment into the water at any time.

The frequency of lahars is much lower now than in the first five years after the eruption, she said, and the indigenous Ayta people are moving back to their ancestral home on the mountain’s uplands. But the large amount of sediment remaining on Pinatubo’s flanks still poses danger. Some of the rivers still can flood wide areas, making it difficult to site and build bridges. And in some places, the water flows at a much higher elevation than it used to, placing the streambeds above where people live.

"There’s been more loss of life and property at Pinatubo from lahars than from the eruption itself," Gran said. "And recovery comes slowly, in stages. It could be years before we start to see ecological recovery on some rivers."

Vince Stricherz | EurekAlert!
Further information:
http://www.washington.edu

More articles from Earth Sciences:

nachricht Weather extremes: Humans likely influence giant airstreams
27.03.2017 | Potsdam-Institut für Klimafolgenforschung

nachricht Sun's impact on climate change quantified for first time
27.03.2017 | Schweizerischer Nationalfonds SNF

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Giant Magnetic Fields in the Universe

Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.

The results will be published on March 22 in the journal „Astronomy & Astrophysics“.

Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...

Im Focus: Tracing down linear ubiquitination

Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.

Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...

Im Focus: Perovskite edges can be tuned for optoelectronic performance

Layered 2D material improves efficiency for solar cells and LEDs

In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...

Im Focus: Polymer-coated silicon nanosheets as alternative to graphene: A perfect team for nanoelectronics

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...

Im Focus: Researchers Imitate Molecular Crowding in Cells

Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to simulate these confined natural conditions in artificial vesicles for the first time. As reported in the academic journal Small, the results are offering better insight into the development of nanoreactors and artificial organelles.

Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

International Land Use Symposium ILUS 2017: Call for Abstracts and Registration open

20.03.2017 | Event News

CONNECT 2017: International congress on connective tissue

14.03.2017 | Event News

ICTM Conference: Turbine Construction between Big Data and Additive Manufacturing

07.03.2017 | Event News

 
Latest News

Big data approach to predict protein structure

27.03.2017 | Life Sciences

Parallel computation provides deeper insight into brain function

27.03.2017 | Life Sciences

Weather extremes: Humans likely influence giant airstreams

27.03.2017 | Earth Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>