scholarly journals Dynamic rock fragmentation: thresholds for long runout rock avalanches

2014 ◽  
Vol 8 (30) ◽  
pp. 7-13
Author(s):  
E.T. Bowman
Keyword(s):  
Rock Fragmentation ◽  
Long Runout ◽  
Rock Avalanches ◽  
Fragmentation Thresholds

A fragmentation-spreading model for long-runout rock avalanches

1999 ◽  
Vol 36 (6) ◽  
pp. 1096-1110 ◽  
Author(s):  
T R Davies ◽  
M J McSaveney ◽  
K A Hodgson
Keyword(s):  
Rock Mass ◽  
High Velocity ◽  
Rock Fragmentation ◽  
Front Part ◽  
Long Runout ◽  
Spreading Model ◽  
Rock Avalanches ◽  
Rear Part ◽  
Dispersive Stress

Based on the observation that deposits of large rock avalanches consist predominantly of intensely fragmented rock debris, it is proposed that the processes of rock fragmentation are significant causes of the peculiar distribution of mass in these deposits, and of the correspondingly long runout. Rock fragmentation produces high-velocity fragments moving in all directions, resulting in an isotropic dispersive stress within the translating rock mass. A longitudinal dispersive force consequently acts in the direction of reducing mass depth and tends to cause the rear part of the avalanche to decelerate and halt and the front part to accelerate. The result is greater longitudinal spreading of the travelling mass compared with nonfragmenting granular avalanches. The longer runout results from this additional fragmentation-induced spreading.

scholarly journals Investigation of rock fragmentation during rockfalls and rock avalanches via 3‐D discrete element analyses

2017 ◽  
Vol 122 (3) ◽  
pp. 678-695 ◽  
Author(s):  
Tao Zhao ◽  
Giovanni Battista Crosta ◽  
Stefano Utili ◽  
Fabio Vittorio De Blasio
Keyword(s):  
Discrete Element ◽  
Rock Fragmentation ◽  
Rock Avalanches

Rock Avalanches

2018 ◽  
Author(s):  
Tim Davies
Keyword(s):  
Rock Avalanche ◽  
Long Runout ◽  
Runout Distance ◽  
Glacier Terminus ◽  
Rock Avalanches ◽  
Landslide Volume ◽  
Long Duration ◽  
Wide Range ◽  
The 19Th Century ◽  
Scientific Questions

Rock avalanches are very large (greater than about 1 million m3) landslides from rock slopes, which can travel much farther than smaller events; the larger the avalanche, the greater the travel distance. Rock avalanches first became recognized in Switzerland in the 19th century, when the Elm and Goldau events killed many people a surprisingly long way from the origin of the landslide; these events first posed the “long-runout rock-avalanche” problem. In essence, the several-kilometer-long runout of these events appears to require low friction beneath and within the moving rock mass in order to explain their extremely long deposits, but in spite of intense research in recent decades this phenomenon still lacks a generally accepted explanation. Large collapses of volcano edifices can also generate rock avalanches that travel very long distances, albeit with a different runout–volume relationship to that of non-volcanic events. Even more intriguing is the presence of long-runout deposits not just on land but also beneath the sea and on the surfaces of Mars and the Moon. Numerous studies of rock avalanches have revealed a number of consistencies in deposit and behavioral characteristics: for example, that little or no mixing of material occurs within the moving debris mass during runout; that the deposit material beneath a meter-scale surface layer is pervasively and intensely fragmented, with fragments down to submicrometer size; that many of these fragments are agglomerates of even finer particles; that throughout the travel of a rock avalanche large volumes of fine dust are produced; that rock avalanche surfaces are typically covered by hummocks of a range of sizes; and that, as noted above, runout distance increases with volume. Since rock avalanches can travel tens of kilometers from their source, they pose severe, if low-probability, direct hazards to societal assets in mountain valleys; in addition, they can trigger extensive and long-duration geomorphic hazard cascades. Although large rock avalanches are rare (e.g., in a 10,000 km2 area of the Southern Alps in New Zealand, research showed that events larger than 5 × 107 m3 occurred about once every century), studies to date show that the proportion of total landslide volume involved in such large events is greater than the proportion in smaller, more frequent events, so that a large proportion of the total sediment generated in mountains by uplift and denudation originates in large rock avalanches. Consequently, large rock avalanches exert a significant influence on mountain geomorphology, for example by blocking rivers and forming landslide dams; these either fail, causing large dam-break floods and long-duration aggradation episodes to propagate down river systems, or remain intact to infill with sediment and form large valley flats. Rock avalanches that fall onto glaciers often result in large terminal moraines being formed as debris accumulates at the glacier terminus, and these moraines may have no relation to any climatic change. In addition, misinterpretation of rock avalanche deposits as moraines can cause underestimation of hazard risk and misinterpretation of paleoclimate. Rock avalanche runout behavior poses fundamental scientific questions, and rock avalanches have important effects on a wide range of geomorphic processes, which in turn pose threats to society. Better understanding of these impressive and intriguing events is crucial for both geoscientific progress and for reducing impacts of future disasters.

Physical models of rock avalanche spreading behaviour with dynamic fragmentation

2012 ◽  
Vol 49 (4) ◽  
pp. 460-476 ◽  
Author(s):  
E.T. Bowman ◽  
W.A. Take ◽  
K.L. Rait ◽  
C. Hann
Keyword(s):  
High Speed ◽  
Rock Avalanche ◽  
Physical Models ◽  
Cube Root ◽  
Long Runout ◽  
Dynamic Fragmentation ◽  
Solid Coal ◽  
Rock Avalanches ◽  
Average Position ◽  
Degree Of Fragmentation

The dynamic fragmentation of rock during avalanche motion has been postulated as a mechanism explaining the long runout of large rock avalanches or Sturzströme. This paper investigates whether test conditions that produce dynamic fragmentation can lead to greater runout or spreading of physical model rock avalanches. Model avalanche experiments were carried out under enhanced acceleration to generate breakage in coal, a fragmentable, brittle solid. Coal blocks were released from a stationary position on a slope to run out on a plane. The motion of the ensuing fragmenting debris was captured using a high-speed camera placed above the horizontal plane. The average position of the front was tracked and the degree of fragmentation of the model avalanches was quantified. The paper presents results of the frontal velocity of the avalanches, corrected for centrifuge Coriolis effects. Comparison is made between the peak and impulsive front velocities, the final runout, and the degree of fragmentation of the model avalanches. Strong relationships are found between runout normalized by the cube root of volume, impulse velocity, and Hardin’s relative breakage parameter, BR. Results are discussed in light of the mechanics involved and are compared with field-scale events.

Source characteristics of long runout rock avalanches triggered by the 2008 Wenchuan earthquake, China

2011 ◽  
Vol 40 (4) ◽  
pp. 896-906 ◽  
Author(s):  
Shengwen Qi ◽  
Qiang Xu ◽  
Bing Zhang ◽  
Yuande Zhou ◽  
Hengxing Lan ◽  
...  
Keyword(s):  
Wenchuan Earthquake ◽  
Long Runout ◽  
2008 Wenchuan Earthquake ◽  
Source Characteristics ◽  
The 2008 Wenchuan Earthquake ◽  
Rock Avalanches

Dynamic simulation of the motion of fragmenting rock avalanches

2002 ◽  
Vol 39 (4) ◽  
pp. 789-798 ◽  
Author(s):  
T R Davies ◽  
M J McSaveney
Keyword(s):  
Field Data ◽  
Mass Movement ◽  
Rock Avalanche ◽  
Earth Pressure ◽  
Long Runout ◽  
Analogue Model ◽  
Pressure Coefficients ◽  
Rock Avalanches ◽  
Internal Pressures ◽  
Rapid Mass

A mass-referenced continuum model for dynamic analysis of rapid mass movement (DAN) is verified by laboratory and field data. Increased earth pressure coefficients are used in this model to represent the dispersive pressures caused by fragmentation within a translating rock avalanche. The numerical model demonstrates that increased runout in large rock avalanches can occur with normal friction coefficients if higher than normal internal pressures, such as those believed to be generated by fragmentation, are present. The extent of the Falling Mountain rock-avalanche deposit in New Zealand is reproduced in the model with normal friction and high earth pressure coefficients to represent by analogy the additional internal pressures due to fragmentation. It appears that if internal friction is changed by fragmentation, it is only by a small amount and may increase rather than decrease. To test this, and to move beyond the present analogue model, requires a better understanding of the rheology of fragmenting rock.Key words: rock avalanches, long runout, fragmentation, simulation model, dispersive stresses, earth pressure coefficients, Falling Mountain.

Mobility of long-runout rock avalanches

Landslides ◽  
2013 ◽  
pp. 50-58 ◽  
Author(s):  
Tim Davies ◽  
Mauri McSaveney
Keyword(s):  
Long Runout ◽  
Rock Avalanches
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