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
Electrons use the zebra crossing
17.12.2018 | Universität Stuttgart
Data storage using individual molecules
17.12.2018 | Universität Basel
Researchers from the University of Basel have reported a new method that allows the physical state of just a few atoms or molecules within a network to be controlled. It is based on the spontaneous self-organization of molecules into extensive networks with pores about one nanometer in size. In the journal ‘small’, the physicists reported on their investigations, which could be of particular importance for the development of new storage devices.
Around the world, researchers are attempting to shrink data storage devices to achieve as large a storage capacity in as small a space as possible. In almost...
The more objects we make "smart," from watches to entire buildings, the greater the need for these devices to store and retrieve massive amounts of data quickly without consuming too much power.
Millions of new memory cells could be part of a computer chip and provide that speed and energy savings, thanks to the discovery of a previously unobserved...
What if, instead of turning up the thermostat, you could warm up with high-tech, flexible patches sewn into your clothes - while significantly reducing your...
A widely used diabetes medication combined with an antihypertensive drug specifically inhibits tumor growth – this was discovered by researchers from the University of Basel’s Biozentrum two years ago. In a follow-up study, recently published in “Cell Reports”, the scientists report that this drug cocktail induces cancer cell death by switching off their energy supply.
The widely used anti-diabetes drug metformin not only reduces blood sugar but also has an anti-cancer effect. However, the metformin dose commonly used in the...
A research team from the University of Zurich has developed a new drone that can retract its propeller arms in flight and make itself small to fit through narrow gaps and holes. This is particularly useful when searching for victims of natural disasters.
Inspecting a damaged building after an earthquake or during a fire is exactly the kind of job that human rescuers would like drones to do for them. A flying...
12.12.2018 | Event News
10.12.2018 | Event News
06.12.2018 | Event News
17.12.2018 | Studies and Analyses
17.12.2018 | Life Sciences
17.12.2018 | Power and Electrical Engineering