A rockfall or rock-fall 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."
43-537: 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 from that of a rockslide . 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
86-408: A consequence, in the description of a landslide, it can be interesting to understand in what type of climate the event occurred. In the evaluation of landslide susceptibility, causes of the triggers is an important step. Terzaghi describes causes as "internal" and "external" referring to modifications in the conditions of the stability of the bodies. Whilst the internal causes induce modifications in
129-409: A fundamental factor of the morphological evolution of a slope . Bedding attitude and the presence of discontinuities or faults control the slope morphogenesis . As the landslide is a geological volume with a hidden side, morphological characteristics are extremely important in the reconstruction of the technical model. This criterion describes, in a general way, the location of landslides in
172-402: A great importance in the hazard evaluation. A velocity range is connected to the different type of landslides , on the basis of observation of case history or site observations. Landslide dating is an interesting topic in the evaluation of hazard . The knowledge of the landslide frequency is a fundamental element for any kind of probabilistic evaluation. Furthermore, the evaluation of
215-646: A movement event). Various scientific disciplines have developed taxonomic classification systems to describe natural phenomena or individuals, like for example, plants or animals. These systems are based on specific characteristics like shape of organs or nature of reproduction. Differently, in landslide classification, there are great difficulties because phenomena are not perfectly repeatable; usually being characterised by different causes, movements and morphology, and involving genetically different material. For this reason, landslide classifications are based on different discriminating factors, sometimes very subjective. In
258-434: A relatively narrow zone", i.e., the movement is localised to a single failure plane within the subsurface. He noted landslides can occur catastrophically, or that movement on the surface can be gradual and progressive. Falls (isolated blocks in free-fall), topples (material coming away by rotation from a vertical face), spreads (a form of subsidence), flows (fluidised material in motion), and creep (slow, distributed movement in
301-412: A sudden, incredibly fast-paced release of bedrock along a uniform plane of weakness. These uniform weaknesses are key to identifying rock slides because unlike slumps, flows, or falls, the failed material moves in a fairly uniform direction over a layer of solid, pre-existing rock. Rock may break down while falling during rockslides. The sudden, rapid release of material found in rock slides combined with
344-411: A surface of rupture that is curved and concave " (Varnes, 1996) Speed: extremely slow to extremely rapid Type of slope: slope angle 20–40 degrees Control factor: morphology and lithology Causes: Vibration , undercutting, differential weathering , excavation, or stream erosion "Spread is defined as an extension of a cohesive soil or rock mass combined with a general subsidence of
387-477: A system similar to that of the denomination of formations. Consequently, it is possible to describe a landslide using the name of a site. In particular, the name will be that of the locality where the landslide happened with a specific characteristic type. These criteria give particular importance to climate in the genesis of phenomena for which similar geological conditions can, in different climatic conditions, lead to totally different morphological evolution. As
430-414: A variety of mass wasting events (geologic slope failures) that include slumps , slides, falls, and flows. The two major types of slides are rotational slides and translational slides. Rockslides are a type of translational event since the rock mass moves along a roughly planar surface with little rotation or backward tilting. Rock slides are the most dangerous form of mass-wasting because they incorporate
473-543: Is a downslope movement of soil or rock mass occurring dominantly on the surface of rupture or on relatively thin zones of intense shear strain ." (Varnes, 1996) Description: "In translational slides the mass displaces along a planar or undulating surface of rupture, sliding out over the original ground surface." (Varnes, 1996) Speed: extremely slow to extremely rapid (>5 m/s) Type of slope: slope angle 20-45 degrees Control factor: Discontinuities, geological setting Description: "Rotational slides move along
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#1732775532550516-584: Is a spatially continuous movement in which surfaces of shear are short-lived, closely spaced, and usually not preserved. The distribution of velocities in the displacing mass resembles that in a viscous liquid. The lower boundary of displaced mass may be a surface along which appreciable differential movement has taken place or a thick zone of distributed shear (Cruden & Varnes, 1996) Description: "Flow movements in bedrock include deformations that are distributed among many large or small fractures, or even microfracture, without concentration of displacement along
559-399: Is not favorable to a rockfall, which is better consolidated, may be said to be competent. In higher altitude mountains, rockfalls may be caused by thawing of rock masses with permafrost . In contrast, lower altitude mountains with warmer climates rockfalls may be caused by weathering being enhanced by non-freezing conditions. Assessing the propagation of rockfall is a key issue for defining
602-557: Is the forward rotation out of the slope of a mass of soil or rock about a point or axis below the centre of gravity of the displaced mass. Toppling is sometimes driven by gravity exerted by material upslope of the displaced mass and sometimes by water or ice in cracks in the mass" (Varnes, 1996) Speed: extremely slow to extremely rapid Type of slope: slope angle 45–90 degrees Control factor: Discontinuities, lithostratigraphy Causes: Vibration, undercutting, differential weathering , excavation, or stream erosion "A slide
645-464: Is usually made by comparing the percentage of coarse grain size fractions. If the weight of the particles with a diameter greater than 2 mm is less than 20%, the material will be defined as earth ; in the opposite case, it is debris . The classification of a landslide based on its activity is particularly relevant in the evaluation of future events. The recommendations of the WP/WLI (1993) define
688-399: Is usually possible to identify one or more landslide causes and one landslide trigger . The difference between these two concepts is subtle but important. The landslide causes are the reasons that a landslide occurred in that location and at that time and may be considered to be factors that made the slope vulnerable to failure, that predispose the slope to becoming unstable. The trigger is
731-567: 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
774-489: The McGraw-Hill Encyclopedia of Science and Technology distinguishes the following types of landslides: Influential narrower definitions restrict landslides to slumps and translational slides in rock and regolith , not involving fluidisation. This excludes falls, topples, lateral spreads, and mass flows from the definition. The causes of landslides are usually related to instabilities in slopes. It
817-671: 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. The term landslide refers to
860-519: The age of the landslide permits to correlate the trigger to specific conditions, as earthquakes or periods of intense rains . It is possible that phenomena could be occurred in past geological times, under specific environmental conditions which no longer act as agents today. For example, in some Alpine areas, landslides of the Pleistocene age are connected with particular tectonic , geomorphological and climatic conditions. This represent
903-445: The air by falling, bouncing, or rolling" (Varnes, 1996). Secondary falls: "Secondary falls involves rock bodies already physically detached from cliff and merely lodged upon it" (Hutchinson, 1988) Speed: from very to extremely rapid Type of slope: slope angle 45–90 degrees Control factor: Discontinuities Causes: Vibration, undercutting, differential weathering , excavation, or stream erosion Description: "Toppling
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#1732775532550946-454: 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. Rockslide A rockslide is a type of landslide caused by rock failure in which part of
989-422: 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. In this purpose, many approaches may be considered. For example, the energy line method allows expediently estimating the rockfall run out. Numerical models simulating the rock block propagation offer a more detailed characterisation of
1032-485: The categories that Varnes excluded are recognised as landslide types, as seen below. This leads to ambiguity in usage of the term. The following clarifies the usages of the various terms in the table. Varnes and those who later modified his scheme only regard the slides category as forms of landslide. Description: " the detachment of soil or rock from a steep slope along a surface on which little or no shear displacement takes place. The material then descends mainly through
1075-424: The concept of activity with reference to the spatial and temporal conditions, defining the state, the distribution and the style. The first term describes the information regarding the time in which the movement took place, permitting information to be available on future evolution, the second term describes, in a general way, where the landslide is moving and the third term indicates how it is moving. This factor has
1118-412: The fields of geologic science and engineering continue to perfect methods of rock slide detection, assessment, and warning. New earth observation tools have supplied a much enhanced ability to detect potential rock slide hazards. Analysis of sequential InSAR and LiDAR data provides a very valuable regional view of slope movement. Once susceptible areas are discovered, detailed analysis can be carried out at
1161-433: The following write-up, factors are discussed by dividing them into two groups: the first one is made up of the criteria utilised in the most widespread classification systems that can generally be easily determined. The second one is formed by those factors that have been utilised in some classifications and can be useful in descriptions. This is the most important criterion, even if uncertainties and difficulties can arise in
1204-476: The fractured mass of cohesive material into softer underlying material." (Varnes, 1996). "In spread, the dominant mode of movement is lateral extension accommodated by shear or tensile fractures" (Varnes, 1978) Speed: extremely slow to extremely rapid (>5 m/s) Type of slope: angle 45–90 degrees Control factor: Discontinuities, lithostratigraphy Causes: Vibration, undercutting, differential weathering , excavation, or stream erosion A flow
1247-415: 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. 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
1290-407: The geometry of a hill through excavation, can also change the stress state, contributing to slope instability. Amongst these erosional properties, water is arguably the most effective geologic agent that causes mass-wasting events to occur. Water aids in the downslope movement of surface material by adding weight to the soil and by filling pores which tends to push apart individual grains, decreasing
1333-443: The gravitational force on the rock exceeds the ability of the slope to resist that force. Therefore, anything that erodes or impedes the mountain's ability to resist this force may be one of the causes of mass-wasting. While a major event such as an earthquake can cause large rockslides to happen, a majority of slides occur due to a combination of gravitational pressure and erosional influences. Anthropogenic activities, such as altering
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1376-413: The identification of movements, being the mechanisms of some landslides often particularly complex. The main movements are falls, slides and flows , but usually topples, lateral spreading and complex movements are added to these. Rock , earth and debris are the terms generally used to distinguish the materials involved in the landslide process. For example, the distinction between earth and debris
1419-416: The material itself which decrease its resistance to shear stress , the external causes generally induce an increase of shear stress, so that block or bodies are no longer stable. The triggering causes induce the movement of the mass. Predisposition to movement due to control factors is determining in landslide evolution. Structural and geological factors, as already described, can determine the development of
1462-497: The movement, inducing the presence of mass in kinematic freedom. In traditional usage, the term landslide has at one time or another been used to cover almost all forms of mass movement of rocks and regolith at the Earth's surface. In 1978, in a very highly cited publication, David Varnes noted this imprecise usage and proposed a new, much tighter scheme for the classification of mass movements and subsidence processes. This scheme
1505-419: The physiographic context of the area. Some authors have therefore identified landslides according to their geographical position so that it is possible to describe " alpine landslides", "landslides in plains", "hilly landslides" or " cliff landslides". As a consequence, specific morphological contexts are referred characterised by slope evolution processes. With these criteria, landslides can be identified with
1548-423: The resistance of the material to movement. While these processes can cause a slide to happen, the speed and potential devastation of a rockslide is often determined by the severity of steepness presented by the failing slope. With increasing populations in rural areas around the world, the hazards presented by potential rock slides are becoming more of a pressing issue moving forward. Luckily, individuals working in
1591-433: The rockfall propagation kinematics. These simulation tools in particular focus on the modeling of the rebound of the rock block onto the soil The numerical models in particular provide the rock block passing height and kinetic energy that are necessary for designing passive mitigation structures. Typically, rockfall events are mitigated in one of two ways: either by passive mitigation or active mitigation. Passive mitigation
1634-500: The sheer size and weight of the material that is falling is what gives these events the potential to have devastating effects on human life and infrastructure. Rock slides are very common in the over steepened canyons and drainages of Idaho, particularly in those areas like the Salmon River Canyon where more than 5,000 feet of elevation may exist between the ridge tops and the canyon bottoms. Mass-wasting occurs whenever
1677-416: The single event that finally initiated the landslide. Thus, causes combine to make a slope vulnerable to failure, and the trigger finally initiates the movement. Landslides can have many causes but can only have one trigger. Usually, it is relatively easy to determine the trigger after the landslide has occurred (although it is generally very difficult to determine the exact nature of landslide triggers ahead of
1720-584: The specific site. These assessments are used to determine the amount of material that will be released as well as the speed at which this material will be transported. Once a site is deemed hazardous, different types of geologic engineering techniques are used in order to prevent the compromised slope from failing. Some of these designs are listed below. Landslide classification#Types and classification There have been known various classifications of landslides . Broad definitions include forms of mass movement that narrower definitions exclude. For example,
1763-514: The subsurface) are all explicitly excluded from the term landslide. Under the scheme, landslides are sub-classified by the material that moves, and by the form of the plane or planes on which movement happens. The planes may be broadly parallel to the surface ("translational slides") or spoon-shaped ("rotational slides"). Material may be rock or regolith (loose material at the surface), with regolith subdivided into debris (coarse grains) and earth (fine grains). Nevertheless, in broader usage, many of
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1806-400: 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
1849-455: Was later modified by Cruden and Varnes in 1996, and influentially refined by Hutchinson (1988) and Hungr et al. (2001). This full scheme results in the following classification for mass movements in general, where bold font indicates the landslide categories: Under this definition, landslides are restricted to "the movement... of shear strain and displacement along one or several surfaces that are visible or may reasonably be inferred, or within
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