Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Avalanches – triggered from the valley

03.12.2008
When slab avalanches thunder into the valley, winter sports fans are in danger. Researchers have now gained amazing insights into the formation of these avalanches – especially regarding how they are remotely triggered by skiers in more gently inclined areas.

Everybody knows that skiers swishing down steep slopes can cause extensive slab avalanches. But there is a less well known phenomenon: A person skiing a gentle slope in the valley triggers a slab avalanche on a steeper slope, sometimes several hundred meters further uphill. This scenario doesn’t seem to make sense – yet it claims human lives year after year.

But what exactly happens when an avalanche is remotely triggered? “In a slab avalanche, the upper layer of snow slides down into the valley. For that to be able to happen, it first has to become detached from the layer beneath it,” says Prof. Dr. Peter Gumbsch, director of the Fraunhofer Institute for Mechanics of Materials IWM in Freiburg. The view commonly held until now assumes that the layers of snow are separated by shear cracks – the upper layer shifts within a limited area. If the two layers of snow were two hands placed palm to palm, a shear crack would be equivalent to rubbing one hand against the other. The layers of snow can only shift if the slope is steep enough. Shear cracks may be a satisfactory explanation for the breakaway of snow slabs in steep terrain. But how can they be triggered from a distance?

Gumbsch and his colleagues Michael Zaiser and Joachim Heierli at the University of Edinburgh, Scotland, have developed a physical model that explains this phenomenon. “The boundary layer that connects the upper and lower layers of snow is made of ice crystals with fairly large interstices,” explains Heierli. The pressure exerted by a skier can cause the ice crystals to break, separate from one another and slip into the interstices – the layer collapses. The layer on top of it subsides. This mass collapse, which can be described as an anti-crack, releases energy that has not previously been taken into account. This energy enables the crack to propagate.

To return to our previous analogy, the anti-crack would be like pressing the two hands together. Experiments carried out by Canadian researchers at the University of Calgary confirm the theory: Whether the slope is gentle or steep, it is equally difficult to trigger the collapse. Once it has started, it propagates as an anti-crack.

It can move up or down the mountain and grow to a length of several hundred meters within a few seconds: The layers of snow lose their cohesion. Only the forces of friction can then prevent the snow from slipping. If these are insufficient, the upper layer slides off and a slab avalanche begins.

Prof. Dr. Peter Gumbsch | alfa
Further information:
http://www.iwm.fraunhofer.de
http://www.fraunhofer.de/EN/press/pi/2008/12/ResearchNews122008Topic1.jsp
http://www.fraunhofer.de/EN/bigimg/2008/rn12fo1g1.jsp

More articles from Physics and Astronomy:

nachricht Physics boosts artificial intelligence methods
19.10.2017 | California Institute of Technology

nachricht NASA team finds noxious ice cloud on saturn's moon titan
19.10.2017 | NASA/Goddard Space Flight Center

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

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

Im Focus: Neutron star merger directly observed for the first time

University of Maryland researchers contribute to historic detection of gravitational waves and light created by event

On August 17, 2017, at 12:41:04 UTC, scientists made the first direct observation of a merger between two neutron stars--the dense, collapsed cores that remain...

Im Focus: Breaking: the first light from two neutron stars merging

Seven new papers describe the first-ever detection of light from a gravitational wave source. The event, caused by two neutron stars colliding and merging together, was dubbed GW170817 because it sent ripples through space-time that reached Earth on 2017 August 17. Around the world, hundreds of excited astronomers mobilized quickly and were able to observe the event using numerous telescopes, providing a wealth of new data.

Previous detections of gravitational waves have all involved the merger of two black holes, a feat that won the 2017 Nobel Prize in Physics earlier this month....

Im Focus: Smart sensors for efficient processes

Material defects in end products can quickly result in failures in many areas of industry, and have a massive impact on the safe use of their products. This is why, in the field of quality assurance, intelligent, nondestructive sensor systems play a key role. They allow testing components and parts in a rapid and cost-efficient manner without destroying the actual product or changing its surface. Experts from the Fraunhofer IZFP in Saarbrücken will be presenting two exhibits at the Blechexpo in Stuttgart from 7–10 November 2017 that allow fast, reliable, and automated characterization of materials and detection of defects (Hall 5, Booth 5306).

When quality testing uses time-consuming destructive test methods, it can result in enormous costs due to damaging or destroying the products. And given that...

Im Focus: Cold molecules on collision course

Using a new cooling technique MPQ scientists succeed at observing collisions in a dense beam of cold and slow dipolar molecules.

How do chemical reactions proceed at extremely low temperatures? The answer requires the investigation of molecular samples that are cold, dense, and slow at...

Im Focus: Shrinking the proton again!

Scientists from the Max Planck Institute of Quantum Optics, using high precision laser spectroscopy of atomic hydrogen, confirm the surprisingly small value of the proton radius determined from muonic hydrogen.

It was one of the breakthroughs of the year 2010: Laser spectroscopy of muonic hydrogen resulted in a value for the proton charge radius that was significantly...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ASEAN Member States discuss the future role of renewable energy

17.10.2017 | Event News

World Health Summit 2017: International experts set the course for the future of Global Health

10.10.2017 | Event News

Climate Engineering Conference 2017 Opens in Berlin

10.10.2017 | Event News

 
Latest News

Electrode materials from the microwave oven

19.10.2017 | Materials Sciences

New material for digital memories of the future

19.10.2017 | Materials Sciences

Physics boosts artificial intelligence methods

19.10.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>