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Flying circus of physics

Rockfalls

Monday, June 01, 2015

 

Video series

The second episode of my Flying Circus of Physics video series with Cleveland State has now been posted. https://www.youtube.com/channel/UChrOvC-DFkPNxKIxe-XKD3g

Rockfalls
Jearl Walker  www.flyingcircusofphysics.com
June 2015  A rockfall is where a rock or a collection of rocks fall from the side of a mountain, usually the face of a cliff. If you are in or near the path, you suddenly feel small and defenseless. Here are three examples:

Near the beginning of this first video, watch the top of the mountain --- part of it moves! And that is the part that ends up hitting the road.

https://www.youtube.com/watch?v=uOJfcTZME0U

There was not quite enough energy left in the boulder for its center of mass to come up over its contact point on the road, and so the boulder rotated back down onto the road instead of down onto the car. Very lucky physics there.



In this next one, the cameraman was knocked down but hopefully was not hurt.

https://www.youtube.com/watch?v=qcrRf8wY8YE

This next video is tough to watch because as the people escape their vehicles, one person is hit and then needs help escaping. Note that toward the end, the windshield in front of the video camera is broken.

https://www.youtube.com/watch?v=1TppfeZzsn4 one person hit

Most rockfalls are due to weathering of bedrock: (1) Fissures that collect water can be widened and extended when the water freezes, because the water expands. (2) The rock is weakened by chemical weathering, especially when moisture is available. Although any rock can undergo weathering, rockfalls occur only when the bedrock face is steep and when a section continues to be supported while fissures are driven into the face. At some point, the section’s attachment or support is overwhelmed, and the rock breaks free.

Depending on circumstances, the freed rock can fall through the air, bounce down a fairly steep slope, tumble down a moderate slope, or slide down a shallow slope. It can also shatter into smaller rocks. With any of these outcomes, it loses much of its energy in the collision. It can also lose energy if it collides with trees, and thus a stand of trees is often grown as a rockslide barrier.

When a rockfall involves many rocks of various sizes, the rocks can become segregated along a slope because the larger rocks reach the bottom of the slope whereas smaller rocks tend to catch in the low points (the crannies) along the slope. In general, material along a slope tends to vary from fine grade at the top to coarse grade at the bottom. The foremost rock in some rockfalls ends up at a surprisingly large distance from the other rocks, presumably because it gains energy as other rocks hit it from the rear during the sliding and rolling portion of the fall. Here is an example:

https://www.youtube.com/watch?v=yZtxHlProWo damage to house, long trails

Other videos:

https://www.youtube.com/watch?v=8FJwIHdVue8 rock wall gradually falls

https://www.youtube.com/watch?v=39LCzBS8yOM news video

https://www.youtube.com/watch?v=afI58PRmTJ0 helicopter causes rockfall

https://www.youtube.com/watch?v=zANdPKczdlk earthquake rockfall

https://www.youtube.com/watch?v=j84SD55cuPg

References
Dots · through ··· indicate level of difficulty
Journal reference style: author, title, journal, volume, pages (date)
· Porter, S. C., and G. Orombelli, “Alpine rockfall hazards,” American Scientist, 69, No. 1, 67-75 (January-February 1981)
· Scheidegger, A. E., “A review of recent work on mas movements on slopes and on rock falls,” Earth-Science Reviews, 21, No. 4, 225-249 (1984)
· Uhrhammer, R. A., (abstract) “Seismic analysis of the Yosemite rock fall of July 10, 1996,” EOS, 77, 508 (1996)
· Wieczorek, G. F., and S. Jager, “Triggering mechanisms and depositional rates of postglacial slope-movement processes in the Yosemite Valley, California,” Geomorphology, 15, 17-31 (1996)
· Day, R. W., “Case studies of a rockfall in soft versus hard rock,” Environmental & Engineering Geoscience, 3, No. 1, 133-140 (spring 1997)
· Peila, D., S. Pelizza, and F. Sassudelli, “Evaluation of behaviour of rockfall restraining nets by full scale tests,” Rock Mechanics and Rock Engineering, 31, No. 1, 1-24 (1998)
·· Morrissey, M. M., and W. Z. Savage, “Air blasts generated by rockfall impacts: analysis of the 1996 Happy Isles event in Yosemite National Park,” Journal of Geophysical Research, 104, No. B10, 23189-13198 (10 October 1999)
·· Matsuoka, N., and H. Sakai, “Rockfall activity from an alpine cliff during thawing periods,” Geomorphology, 28, 309-328 (1999)
· Wieczorek, G. F., J. B. Snyder, R. B. Waitt, M. M. Morrissey, R. A. Uhrhammer, E. L. Harp, R. D. Norris, M. I. Bursik, and L. G. Finewood, “Unusual July 10, 1996, rock fall at Happy Isles, Yosemite National Park, California,” Geological Society of American Bulletin, 112, No. 1, 75-85 (January 2000). Photos 1 and 2 in Fig. 11 are reversed; correction on page 959 (June 200)
··· Okura, Y., H. Kitahara, T. Sammori, and A. Kawanami, “The effects of rockfall volume on runout distance,” Engineering Geology, 58, 109-124 (2000)
·· Dorren, L. K. A., “A review of rockfall mechanics and modelling approaches,” Progress in Physical Geography, 27, No. 1, 69-87 (2003)


Are you looking for the stories from last five months? They are in the archives:

Loop-the-loop with cars, bikes, skateboards, and simply running, 1.270
Pub  trick --- spoon into mug, 1.271
Transparent when wet, 6.86
Hula-hoop, 1.84


Lethal upward streamers in an electric storm, 5.1
Floaters in your eye, 7.5
Pub trick --- musical wineglass, 3.43
Standing and walking in a strong wind, 1.227
 

Pub trick --- beer bottle tapping prank, 2.76
Bull riding, 1.92
Mianus Bridge collapse, 1.71
Sliding stick across outstretched fingers, 1.172

Café wall illusion, 7.58
Tire explosions, 4.114
Pub trick --- using thermal stress to open a wine bottle, 4.113
Giant Leg towers, 1.272

Pouring tea in an airplane during a barrel roll  2.197
Pub trick --- water from nowhere  6.166
Survival strategies of emperor penguin huddles   1.197
Racing over a rail crossing  7.59

V1 flying bombs tipped by Spitfire airplanes  1.273
Smallest electric train  5.61
Whispering bench in New York City's Central park  3.63
Pub trick --- separating salt and pepper  5.60

Tesla coils  5.62
Royle's self-pouring teapot  2.198
Self-righting of overturned turtles and the toy known as gomboc  1.274
Pub trick --- the self-righting bottle  1.106

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