Rockfall

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Rockfall deposit, Afghanistan Jalalabad Road rock fall.jpg
Rockfall deposit, Afghanistan

A rockfall or rock-fall [1] is a quantity/sheets of rock that has fallen freely from a cliff face. The term is also used for collapse of rock from roof or walls of mine or quarry workings. "A rockfall is a fragment of rock (a block) detached by sliding, toppling, or falling, that falls along a vertical or sub-vertical cliff, proceeds down slope by bouncing and flying along ballistic trajectories or by rolling on talus or debris slopes." [2]

Contents

Alternatively, a "rockfall is the natural downward motion of a detached block or series of blocks with a small volume involving free falling, bouncing, rolling, and sliding". The mode of failure differs[ how? ] from that of a rockslide. [1]

Causal mechanisms

Rockfall in Utah, USA Rockfall on the Zion-Mount Carmel Highway (5895397668).jpg
Rockfall in Utah, USA

Favourable geology and climate are the principal causal mechanisms of rockfall, factors that include intact condition of the rock mass, discontinuities within the rockmass, weathering susceptibility, ground and surface water, freeze-thaw, root-wedging, and external stresses. A tree may be blown by the wind, and this causes a pressure at the root level and this loosens rocks and can trigger a fall. The pieces of rock collect at the bottom creating a talus or scree . Rocks falling from the cliff may dislodge other rocks and serve to create another mass wasting process, for example an avalanche.

A cliff that has favorable geology to a rockfall may be said to be incompetent. One that is not favorable to a rockfall, which is better consolidated, may be said to be competent. [3]

In higher altitude mountains, rockfalls may be caused by thawing of rock masses with permafrost. [4] In contrast, lower altitude mountains with warmer climates rockfalls may be caused by weathering being enhanced by non-freezing conditions. [4]

Propagation

Yosemite Valley rockfall map, indicating the type of rockfall as well as location and known date of each one in Yosemite Valley. Rockfalls tend to be common in spring and winter. NPS yosemite-valley-rockfall-map.gif
Yosemite Valley rockfall map, indicating the type of rockfall as well as location and known date of each one in Yosemite Valley. Rockfalls tend to be common in spring and winter.

Assessing the propagation of rockfall is a key issue for defining the best mitigation strategy as it allows the delineation of run out zones and the quantification of the rock blocks kinematics parameters along their way down to the elements at risk. [5] In this purpose, many approaches may be considered. For example, the energy line method allows expediently estimating the rockfall run out. [6] Numerical models simulating the rock block propagation offer a more detailed characterisation of the rockfall propagation kinematics. [7] These simulation tools in particular focus on the modeling of the rebound of the rock block onto the soil [8] The numerical models in particular provide the rock block passing height and kinetic energy that are necessary for designing passive mitigation structures.

Mitigation

Steel nets installed for rockfall protection on Sion Panvel Highway in India. Sion Panvel Highway Rock Netting.jpg
Steel nets installed for rockfall protection on Sion Panvel Highway in India.

Typically, rockfall events are mitigated in one of two ways: either by passive mitigation or active mitigation. [9] Passive mitigation is where only the effects of the rockfall event are mitigated and are generally employed in the deposition or run-out zones, such as through the use of drape nets, rockfall catchment fences, galeries, ditches, embankments, etc. The rockfall still takes place but an attempt is made to control the outcome. In contrast, active mitigation is carried out in the initiation zone and prevents the rockfall event from ever occurring. Some examples of these measures are rock bolting, slope retention systems, shotcrete, etc. Other active measures might be by changing the geographic or climatic characteristics in the initiation zone, e.g. altering slope geometry, dewatering the slope, revegetation, etc.

Design guides of passive measures with respect to the block trajectory control have been proposed by several authors. [10] [11] [12]

Effects on trees

The effect of rockfalls on trees can be seen in several ways. The tree roots may rotate, via the rotational energy of the rockfall. The tree may move via the application of translational energy. And lastly deformation may occur, either elastic or plastic. Dendrochronology can reveal a past impact, with missing tree rings, as the tree rings grow around and close over a gap; the callus tissue can be seen microscopically. A macroscopic section can be used for dating of avalanche and rockfall events. [13]

See also

Related Research Articles

<span class="mw-page-title-main">Landslide</span> Natural hazard involving ground movement

Landslides, also known as landslips, are several forms of mass wasting that may include a wide range of ground movements, such as rockfalls, mudflows, shallow or deep-seated slope failures and debris flows. Landslides occur in a variety of environments, characterized by either steep or gentle slope gradients, from mountain ranges to coastal cliffs or even underwater, in which case they are called submarine landslides.

<span class="mw-page-title-main">Avalanche</span> Rapid flow of a mass of snow down a slope

An avalanche is a rapid flow of snow down a slope, such as a hill or mountain.

<span class="mw-page-title-main">Megatsunami</span> Very large wave created by a large, sudden displacement of material into a body of water

A megatsunami is a very large wave created by a large, sudden displacement of material into a body of water.

<span class="mw-page-title-main">Chaos Crags</span> Mountain in the Cascade range in California

Chaos Crags is the youngest group of lava domes in Lassen Volcanic National Park, California. They formed as six dacite domes 1,100-1,000 years ago, one dome collapsing during an explosive eruption about 70 years later. The eruptions at the Chaos Crags mark one of just three instances of Holocene activity within the Lassen volcanic center. The cluster of domes is located north of Lassen Peak and form part of the southernmost segment of the Cascade Range in Northern California. Each year, a lake forms at the base of the Crags, and typically dries by the end of the summer season.

<span class="mw-page-title-main">Scree</span> Broken rock fragments at base of cliff

Scree is a collection of broken rock fragments at the base of a cliff or other steep rocky mass that has accumulated through periodic rockfall. Landforms associated with these materials are often called talus deposits. Talus deposits typically have a concave upwards form, where the maximum inclination corresponds to the angle of repose of the mean debris particle size. The exact definition of scree in the primary literature is somewhat relaxed, and it often overlaps with both talus and colluvium.

<span class="mw-page-title-main">Mass wasting</span> Movement of rock or soil down slopes

Mass wasting, also known as mass movement, is a general term for the movement of rock or soil down slopes under the force of gravity. It differs from other processes of erosion in that the debris transported by mass wasting is not entrained in a moving medium, such as water, wind, or ice. Types of mass wasting include creep, solifluction, rockfalls, debris flows, and landslides, each with its own characteristic features, and taking place over timescales from seconds to hundreds of years. Mass wasting occurs on both terrestrial and submarine slopes, and has been observed on Earth, Mars, Venus, Jupiter's moon Io, and on many other bodies in the Solar System.

<span class="mw-page-title-main">Rockslide</span> Type of landslide caused by rock failure

A rockslide is a type of landslide caused by rock failure in which part of the bedding plane of failure passes through compacted rock and material collapses en masse and not in individual blocks. Note that a rockslide is similar to an avalanche because they are both slides of debris that can bury a piece of land. While a landslide occurs when loose dirt or sediment falls down a slope, a rockslide occurs only when solid rocks are transported down slope. The rocks tumble downhill, loosening other rocks on their way and smashing everything in their path. Fast-flowing rock slides or debris slides behave similarly to snow avalanches, and are often referred to as rock avalanches or debris avalanches.

<span class="mw-page-title-main">Gabion</span> Cage full of rock

A gabion is a cage, cylinder or box filled with rocks, concrete, or sometimes sand and soil for use in civil engineering, road building, military applications and landscaping.

There have been known various classifications of landslides. Broad definitions include forms of mass movement that narrower definitions exclude. For example, the McGraw-Hill Encyclopedia of Science and Technology distinguishes the following types of landslides:

A slide fence is a structural fence designed to physically stop falling rocks from reaching the tracks. The fence is designed to retain a rockslide if possible, but if it is displaced by such it also can cause the signaling system to display a restrictive aspect to approaching trains.

<span class="mw-page-title-main">Avalanche control</span>

Avalanche control or avalanche defense activities reduce the hazard avalanches pose to human life, activity, and property. Avalanche control begins with a risk assessment conducted by surveying for potential avalanche terrain by identifying geographic features such as vegetation patterns, drainages, and seasonal snow distribution that are indicative of avalanches. From the identified avalanche risks, the hazard is assessed by identifying threatened human geographic features such as roads, ski-hills, and buildings. Avalanche control programs address the avalanche hazard by formulating prevention and mitigation plans, which are then executed during the winter season. The prevention and mitigation plans combine extensive snow pack observation with three major groups of interventions: active, passive and social - sometimes more narrowly defined as "explosive", "structural", and "awareness" according to the most prevalent technique used in each. Avalanche control techniques either directly intervene in the evolution of the snow pack, or lessen the effect of an avalanche once it has occurred. For the event of human involvement, avalanche control organizations develop and train exhaustive response and recovery plans.

<span class="mw-page-title-main">Val Pola landslide</span>

The Val Pola landslide happened in Valtellina, Lombardy, Northern Italian Alps, on 28 July 1987 and resulted in the Valtellina disaster with a total cost of 400 million euros. The calamity affected the province of Sondrio, but also other Alpine valleys in the provinces of Brescia, Bergamo, Lecco, and Como.

<span class="mw-page-title-main">1958 Lituya Bay earthquake and megatsunami</span> Geologic events off the Alaska coast

The 1958 Lituya Bay earthquake occurred on July 9, 1958 at 22:15:58 PST with a moment magnitude of 7.8 to 8.3 and a maximum Mercalli intensity of XI (Extreme). The strike-slip earthquake took place on the Fairweather Fault and triggered a rockslide of 30 million cubic meters and about 90 million tons into the narrow inlet of Lituya Bay, Alaska. The impact was heard 80 kilometers (50 mi) away, and the sudden displacement of water resulted in a megatsunami that washed out trees to a maximum elevation of 524 meters at the entrance of Gilbert Inlet. This is the largest and most significant megatsunami in modern times; it forced a re-evaluation of large-wave events and the recognition of impact events, rockfalls, and landslides as causes of very large waves.

<span class="mw-page-title-main">Randa rockslides</span>

In April and May 1991, two consecutive rockslides occurred from a cliff above the town of Randa in the Matter valley of Switzerland. The rockslides released a cumulative volume of approximately 30 million cubic meters of debris, with each of the rockslide stages occurring over several hours. Slide debris buried key regional transportation lines including the road and railway leading to Zermatt, and dammed the Mattervispa river which eventually flooded a portion of the town of Randa upstream. There were no fatalities resulting from either of the rockslide events, though livestock, farmhouses and holiday homes were destroyed.

Protection forests are forests that mitigate or prevent the impact of a natural hazard, including a rockfall, avalanche, erosion, landslide, debris flow or flooding on people and their assets in mountainous areas. A protection forest generally covers the sloping area between a hazard potential and the endangered or exposed assets. In the Alps, protection forests are increasingly considered equal to engineered mitigation measures against natural hazards. In French, German, Italian and Slovenian protection forests are called respectively, Forêt de protection, Schutzwald, foreste di protezione, varovalni gozdovi, and even their maintain function is to protect soil and to prevent it from eroding or blowing away.

<span class="mw-page-title-main">Scarp retreat</span>

Scarp retreat is a geological process through which the location of an escarpment changes over time. Typically the cliff is undermined, rocks fall and form a talus slope, the talus is chemically or mechanically weathered and then removed through water or wind erosion, and the process of undermining resumes. Scarps may retreat for tens of kilometers in this way over relatively short geological time spans, even in arid locations.

<span class="mw-page-title-main">Rock shed</span> Road protection structure

A rock shed is a civil engineering structure used in mountainous areas where rock slides and land slides create highway closure problems. A rock shed is built over a roadway that is in the path of the slide. They are equally used to protect railroads. They are usually designed as a heavy reinforced concrete covering over the road, protecting the surface and vehicles from damage due to the falling rocks with a sloping surface to deflect slip material beyond the road, however an alternative is to include an impact-absorbing layer above the ceiling. A further use of this type of structure may be seen protecting the A4 road; although constructed primarily to alleviate risk from falling rocks from a limestone seam it also serves to protect against objects or persons falling from the Clifton Suspension Bridge where the height differential of approximately 70 metres from the bridge to the bottom of the Avon Gorge would give sufficient kinetic energy to even a relatively small item to cause injury on impact.

<span class="mw-page-title-main">Mount Cayley</span> Mountains in British Columbia

Mount Cayley is an eroded but potentially active stratovolcano in the Pacific Ranges of southwestern British Columbia, Canada. Located 45 km (28 mi) north of Squamish and 24 km (15 mi) west of Whistler, the volcano resides on the edge of the Powder Mountain Icefield. It consists of massif that towers over the Cheakamus and Squamish river valleys. All major summits have elevations greater than 2,000 m (6,600 ft), Mount Cayley being the highest at 2,385 m (7,825 ft). The surrounding area has been inhabited by indigenous peoples for more than 7,000 years while geothermal exploration has taken place there for the last four decades.

A rockfall protection embankment is an earthwork built in elevation with respect to the ground to intercept falling rock fragments before elements at risk such as roads and buildings are reached.

A rockfall barrier is a structure built to intercept rockfall, most often made from metallic components and consisting of an interception structure hanged on post-supported cables.

References

  1. 1 2 Whittow, John (1984). Dictionary of Physical Geography. London: Penguin, 1984. ISBN   0-14-051094-X.
  2. Varnes, D.J., 1978, Chapter 2, Slope Movement Types and Processes
  3. google.at, U.S. Geological Survey Professional Paper, Issue 1606 Debris Flows from Failures of Neoglacial-Age Moraine Dams in the Three Sisters and Mount Jefferson Wilderness Areas, Oregon Eisbacher & Clague, 1984, p.48
  4. 1 2 Temme, Arnaud J. A. M. (2015). "Using Climber's Guidebooks to Assess Rock Fall Patterns Over Large Spatial and Decadal Temporal Scales: An Example from the Swiss Alps". Geografiska Annaler: Series A, Physical Geography . 97 (4): 793–807. doi:10.1111/geoa.12116. ISSN   1468-0459. S2CID   55361904.
  5. Dorren, Luuk K. A. (2016-08-18). "A review of rockfall mechanics and modelling approaches". Progress in Physical Geography. 27: 69–87. doi:10.1191/0309133303pp359ra. S2CID   54653787.
  6. Jaboyedoff, M.; Labiouse, V. (2011-03-15). "Technical Note: Preliminary estimation of rockfall runout zones". Natural Hazards and Earth System Sciences. 11 (3): 819–828. Bibcode:2011NHESS..11..819J. doi: 10.5194/nhess-11-819-2011 . ISSN   1684-9981.
  7. Agliardi, F.; Crosta, G.B. (June 2003). "High resolution three-dimensional numerical modelling of rockfalls". International Journal of Rock Mechanics and Mining Sciences. 40 (4): 455–471. doi:10.1016/S1365-1609(03)00021-2.
  8. Bourrier, Franck; Hungr, Oldrich (2013), "Rockfall Dynamics: A Critical Review of Collision and Rebound Models", Rockfall Engineering, John Wiley & Sons, Ltd, pp. 175–209, doi:10.1002/9781118601532.ch6, ISBN   978-1-118-60153-2 , retrieved 2021-01-18
  9. Volkwein, A.; Schellenberg, K.; Labiouse, V.; Agliardi, F.; Berger, F.; Bourrier, F.; Dorren, L. K. A.; Gerber, W.; Jaboyedoff, M. (2011-09-27). "Rockfall characterisation and structural protection – a review". Natural Hazards and Earth System Sciences. 11 (9): 2617–2651. Bibcode:2011NHESS..11.2617V. doi: 10.5194/nhess-11-2617-2011 . ISSN   1561-8633.
  10. Ritchie, A.M. (1963). Evaluation of rockfall and its control. Highway Research Record, No. 17, pp. 13-28.
  11. Pierson, L.A., Gullixson C.F., Chassie R.G. (2001) Rockfall Area Design Guide. Final Report SPR-3(032), Oregon Department of Transportation and Federal Highway Administration, FHWA-OR-RD-02-04.
  12. Pantelidis, L. (2010). Rock catchment area design charts. In Proceedings of GeoFlorida 2010 (ASCE) Conference on Advances in Analysis, Modelling and Design (pp. 224-233). doi : 10.1061/41095(365)19
  13. Favillier, Adrien; Mainieri, Robin; Saez, Jérôme Lopez; Berger, Frédéric; Stoffel, Markus; Corona, Christophe (2017-07-30). "Dendrogeomorphic assessment of rockfall recurrence intervals at Saint Paul de Varces, Western French Alps". Géomorphologie: Relief, Processus, Environnement. 23 (2). doi:10.4000/geomorphologie.11681. ISSN   1266-5304.