The Earth Story

Working on class materials for tomorrow and found this wonderful demonstration of how different types of loose, sedimentary materials form different "Angles of repose" depending on the friction between grains - the angle of repose is the natural angle that material makes with the horizontal where the forces of gravity pulling downwards and frictional resistance are in balance.

Rockfalls

Like most scientists, geologists are classifiers. We break all sorts of features into different groups based on their properties; soils, weather patterns, volcanoes, you name it we can classify it.

This image is a particular type of a mass movement called a rockfall. Mass movements start with the basic rule of gravity – when something goes up it is likely to eventually come down. That rule obviously works on Earth, including with rocks that are built into mountains.

Rocks that have been thrust upwards in mountain ranges feel the force of gravity, but the resisting forces of chemical bonds that hold rocks together and the friction between one rock and another balance that force.

When rocks are broken by eroding forces such as cracking due to ice and water flowing over them, they can break away and move. It is this process that determines what we call the resulting mass movement. If everything moves chaotically while the mass slides along the ground, it would be classified as a rock avalanche. If everything moving downward moves as a fast, coherent mass, without much shifting of the rocks and dirt in-between, that would be a slide (landslide, mudslide, etc.). Finally, if a single rock or a handful of rocks break away and bounce, spending most of their time in the air with nothing around them, that would be called a “rockfall”

This is a huge example of a rockfall from near Jalalabad in Afghanistan. The areas in Southeast Asia dominated by mountains are obviously a common site for any type of mass movement, including rockfalls. The combination of high peaks and in some areas high rainfall causes lots of material to become unstable every year, and there tends to be a peak in dangerous falls, slides, and avalanches in the summer and early fall, just as the heavy rains from the monsoon arrive.

-JBB

Image credit: http://commons.wikimedia.org/wiki/File:Jalalabad_Road_rock_fall.jpg

Read more: http://bit.ly/1el8LjQ http://bit.ly/1dpnIBc http://itc.gsw.edu/faculty/bcarter/physgeol/mass/type1.htm http://bit.ly/1Ftb6Sr

ROCK AND ROLLLLLL…

Generally, when a rock falls from its position on a mountain it’s called a rockfall. In the case of this fall from Termeno, Alto Adige (Northern Italy), I think we are justified in calling it a case of rock-in-roll.

Rockfalls are one of many geologic phenomena that come under a broader category called “mass wasting.” Seriously. Mass wasting includes any sort of phenomena in which rocks, soils, sands, and muds move downslope, generally under the influence of gravity and/or water saturation. The downslope movement can be pretty instantaneous as in a landslide, or it can drag on (and on and on) over days or years or centuries in a process known as “creep.”

The speed of a rockfall is in part controlled by the retarding capacity of the surface material involved: this is expressed mathematically as the “coefficient of restitution.” I’m serious here. To reduce risks from rockfalls, engineers can construct configurations on the hill slopes above a roadway, dig trenches alongside the road to catch stray boulders before they try to cross the road, erect catchment or barrier fences armed with Geobrugg ring nets that can include the nefarious Geobrugg energy absorbing rings. (I’m sure you've seen these things alongside steep mountain roads, and now you know what they’re called.) They also put up signs warning of rockfalls, which don't deter them in the slightest.

Rockfalls occur for a variety of reasons: they become dislodged during earthquake tremors, or they may split from their neighboring rock because of ice wedging during cold temperatures, they may get washed away with torrential rains or floods or melting snow, they may be disturbed by use of dynamite in road construction or even by the vibration caused by suspiciously large trucks passing by…

Some rocks, possibly this Italian one I think, become rockfalls because they are intrinsically mean. And mass wasted.

Annie R

Thank you Giuseppe Di Capua for location. Photo taken by anonymous photographer who urges us to visit: https://www.facebook.com/IloooveClimbing Watch the Video: https://www.youtube.com/watch?v=QNBBvkzrE2s Everything scientific you want to know about rockfalls and engineering at: http://www.rocscience.com/hoek/corner/9_Analysis_of_rockfall_hazards.pdf_ _

This is stop-motion photography of the Fox Glacier, a valley glacier in New Zealand that retreated by about 300 m during the 2014-2015 year captured in this video. You can also see some tour groups paying a visit to the glacier and how the sides of the slopes are destabilized by the decay of the glacier.

Good chance this will be the slowest mass movement/avalanche you've ever seen. This is a 2 year time-lapsed video of a landslide near Val Parghera in Switzerland. Watch how the mass flow surges and stops, how it moves at the bottom sometimes, at the top others, and how they're interlinked, and how the motion of the slide changes as snow arrives.

Probably some cool fluid flow modeling that could be done here.

Video capture of the start and development of a landslide in Dagestan, triggered in part by a car getting stuck it appears.

Watch how the earth movement starts by creeping and then rapidly accelerates out of control into a mass-movement phase.

ROCK AND ROLLLLLL… Generally, when a rock falls from its position on a mountain it’s called a rockfall. In the case of this fall from Termeno, Alto Adige (Northern Italy), I think we are justified in calling it a case of rock-in-roll. Rockfalls are one of many geologic phenomena that come under a broader category called “mass wasting.” Seriously. Mass wasting includes any sort of phenomena in which rocks, soils, sands, and muds move downslope, generally under the influence of gravity and/or water saturation. The downslope movement can be pretty instantaneous as in a landslide, or it can drag on (and on and on) over days or years or centuries in a process known as “creep.” The speed of a rockfall is in part controlled by the retarding capacity of the surface material involved: this is expressed mathematically as the “coefficient of restitution.” I’m serious here. To reduce risks from rockfalls, engineers can construct configurations on the hill slopes above a roadway, dig trenches alongside the road to catch stray boulders before they try to cross the road, erect catchment or barrier fences armed with Geobrugg ring nets that can include the nefarious Geobrugg energy absorbing rings. (I’m sure you've seen these things alongside steep mountain roads, and now you know what they’re called.) They also put up signs warning of rockfalls, which don't deter them in the slightest. Rockfalls occur for a variety of reasons: they become dislodged during earthquake tremors, or they may split from their neighboring rock because of ice wedging during cold temperatures, they may get washed away with torrential rains or floods or melting snow, they may be disturbed by use of dynamite in road construction or even by the vibration caused by suspiciously large trucks passing by… Some rocks, possibly this Italian one I think, become rockfalls because they are intrinsically mean. And mass wasted. Annie R Thank you Giuseppe Di Capua for location. Photo taken by anonymous photographer who urges us to visit: https://www.facebook.com/IloooveClimbing Watch the Video: https://www.youtube.com/watch?v=QNBBvkzrE2s Everything scientific you want to know about rockfalls and engineering at: http://www.rocscience.com/hoek/corner/9_Analysis_of_rockfall_hazards.pdf