Rockslide

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Rockslide at Oddicombe Beach in Devon, UK Rockslide at Oddicombe.jpg
Rockslide at Oddicombe Beach in Devon, UK

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. 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. [1] Fast-flowing rock slides or debris slides behave similarly to snow avalanches, and are often referred to as rock avalanches or debris avalanches. [2]

Contents

Definition

The term landslide refers to 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. [3] Rockslides are a type of translational event since the rock mass moves along a roughly planar surface with little rotation or backward tilting. [3] Rock slides are the most dangerous form of mass-wasting because they incorporate 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 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. [4]

Causes

Mass-wasting occurs whenever gravitational pressure exceeds the affected slopes ability to resist its pressure. Therefore, anything that erodes or impedes the mountain's ability to resist this force may be one of the causes of mass-wasting. [5] 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.

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 the resistance of the material to movement. [4] 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.

Disaster prevention

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 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. [6] Once susceptible areas are discovered, detailed analysis can be carried out at 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.

Wire meshing
A corrosion resistant material that is installed at the crest and foot of the slope. This insures that any falling debris is trapped behind the mesh.
Retaining walls
One of the oldest forms of ground engineering, retaining walls are built in order to neutralize the effects of unstable slopes by holding fallen rocks and soil back from roads and other structures.
Soil nailing
An economical method of constructing a form of retaining wall from the top of a slope down. In this process closely spaced steel tendons are drilled into the soil. These nails significantly increase the cohesion of soil through the ability of these rods to carry tensile loads. these steel beams are usually reinforced through the use of welded wire mesh.
Rock bolting
Rock bolts are always a primary means of reinforcement, Bolts are placed in a specific pattern in order to transfer the faces load from the slopes exterior, to its interior.

See also

Related Research Articles

Landslide type of natural disaster, geological phenomenon

The term landslide or less frequently, landslip, refers to several forms of mass wasting that include a wide range of ground movements, such as rockfalls, deep-seated slope failures, mudflows, 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. Gravity is the primary driving force for a landslide to occur, but there are other factors affecting slope stability that produce specific conditions that make a slope prone to failure. In many cases, the landslide is triggered by a specific event, although this is not always identifiable.

Megatsunami A 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.

Slump (geology)

A slump is a form of mass wasting that occurs when a coherent mass of loosely consolidated materials or a rock layer moves a short distance down a slope. Movement is characterized by sliding along a concave-upward or planar surface. Causes of slumping include earthquake shocks, thorough wetting, freezing and thawing, undercutting, and loading of a slope.

Engineering geology Application of geology to engineering practice

Engineering geology is the application of the geology to engineering study for the purpose of assuring that the geological factors regarding the location, design, construction, operation and maintenance of engineering works are recognized and accounted for. Engineering geologists provide geological and geotechnical recommendations, analysis, and design associated with human development and various types of structures. The realm of the engineering geologist is essentially in the area of earth-structure interactions, or investigation of how the earth or earth processes impact human made structures and human activities.

Geologic hazards

A geologic hazard is one of several types of adverse geologic conditions capable of causing damage or loss of property and life. These hazards consist of sudden phenomena and slow phenomena:

Mass wasting geomorphic process by which soil, sand, regolith, and rock move downslope

Mass wasting, also known as slope movement or mass movement, is the geomorphic process by which soil, sand, regolith, and rock move downslope typically as a solid, continuous or discontinuous mass, largely under the force of gravity, frequently with characteristics of a flow as in debris flows and mudflows. Types of mass wasting include creep, slides, flows, topples, and falls, 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, and Jupiter's moon Io.

Submarine canyon A steep-sided valley cut into the seabed of the continental slope

A submarine canyon is a steep-sided valley cut into the seabed of the continental slope, sometimes extending well onto the continental shelf, having nearly vertical walls, and occasionally having canyon wall heights of up to 5 km, from canyon floor to canyon rim, as with the Great Bahama Canyon. Just as above-sea-level canyons serve as channels for the flow of water across land, submarine canyons serve as channels for the flow of turbidity currents across the seafloor. Turbidity currents are flows of dense, sediment laden waters that are supplied by rivers, or generated on the seabed by storms, submarine landslides, earthquakes, and other soil disturbances. Turbidity currents travel down slope at great speed, eroding the continental slope and finally depositing sediment onto the abyssal plain, where the particles settle out.

Rockfall Rocks fallen freely from a cliff, roof, or quarry

A rockfall or rock-fall refers to quantities of rock falling 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 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,”. 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.

Hilina Slump

The Hilina Slump, on the south flank of the Kīlauea Volcano on the southeast coast of the Big Island of Hawaiʻi, is the most notable of several landslides that ring each of the Hawaiian Islands. These landslides are the means by which material deposited at a volcano's vents are transferred downward and seaward, eventually spilling onto the seabed to broaden the island.

Mudflow

A mudflow or mud flow is a form of mass wasting involving "very rapid to extremely rapid surging flow" of debris that has become partially or fully liquified by the addition of significant amounts of water to the source material.

Sturzstrom type of landslide consisting of soil and rock

The term sturzstrom, a German word composed of Sturz (fall) and Strom (stream), indicates some large landslides consisting of soil and rock which travel a great horizontal distance when compared to their initial vertical drop — as much as 20 or 30 times. The term is used as a synonym to rock avalanche. Sturzstroms have similarities to the flow of glaciers, mudflows, and lava flows. They flow across land fairly easily, and their mobility increases when volume increases. They have been found on other bodies in the Solar System, including the Moon, Mars, Venus, Io, Callisto, Iapetus, and Phobos.

2006 Southern Leyte mudslide 2006 major landslide in the Philippines

On February 17, 2006, a massive rock slide-debris avalanche occurred in the Philippine province of Southern Leyte, causing widespread damage and loss of life. The deadly landslide followed a 10-day period of heavy rain and a minor earthquake. The official death toll was 1,126.

There have been known various classifications of landslides and other types of mass wasting.

<i>Earth Revealed: Introductory Geology</i> US television program

Earth Revealed: Introductory Geology, originally titled Earth Revealed, is a 26-part video instructional series covering the processes and properties of the physical Earth, with particular attention given to the scientific theories underlying geological principles. The telecourse was produced by Intelecom and the Southern California Consortium, was funded by the Annenberg/CPB Project, and first aired on PBS in 1992 with the title Earth Revealed. All 26 episodes are hosted by Dr. James L. Sadd, professor of environmental science at Occidental College in Los Angeles, California.

Submarine landslide Landslides that transport sediment across the continental shelf and into the deep ocean

Submarine landslides are marine landslides that transport sediment across the continental shelf and into the deep ocean. A submarine landslide is initiated when the downwards driving stress exceeds the resisting stress of the seafloor slope material causing movements along one or more concave to planar rupture surfaces. Submarine landslides take place in a variety of different settings including planes as low as 1° and can cause significant damage to both life and property. Recent advances have been made in understanding the nature and processes of submarine landslides through the use of sidescan sonar and other seafloor mapping technology.

2005 La Conchita landslide

On January 10, 2005, a major landslide occurred in the town of La Conchita, California. The landslide killed 10 people, and destroyed or damaged dozens of houses. The landslide occurred on part of a previous landslide that occurred in 1995. The historic slides are part of the larger Rincon Mountain slide, which "started many thousands of years ago and will continue generating slides in the future."

Landslides vs. Rock strength

Landslides are a major geologic hazard in many locations around the globe. They are considered a mass-wasting process, the most common of which are debris flows, hill slides, and rock falls. These events can take place over the course of several years of creeping but powerful movement, or in a matter of a few devastatingly destructive moments. There are several factors relating to structural geology that correlate directly to landslide occurrences. One major factor pertaining to landslides is rock strength. Rock strength is defined by stress/strain relationships, pore fluid pressure, and confining pressure. Stronger, more dense rocks are not as likely to be involved in a rock slide or landslide than porous less dense rocks that can be easily saturated with water. In Utah the groundwater level is continually fluctuating, making the area particularly susceptible to landslides. As water saturates the ground, making it softer and heavier, the stress/strain relationships experienced by the rocks increases considerably. The strength of a rock can be defined by its Mohr Circle, and its corresponding failure envelope. Once conditions are reached which place a rock over its failure envelope, it will experience deformation.

Barry Voight is an American geologist, volcanologist, author, and engineer. After earning his Ph.D. at Columbia University, Voight worked as a professor of geology at several universities, including Pennsylvania State University, where he taught from 1964 until his retirement in 2005. He remains an emeritus professor there and still conducts research, focusing on rock mechanics, plate tectonics, disaster prevention, and geotechnical engineering.

2014 West Salt Creek landslide

The West Salt Creek landslide occurred on the evening of May 25, 2014 near Collbran, Colorado, along the north side of the Grand Mesa, about 30 miles (48 km) east of Grand Junction. It was the largest landslide in Colorado's history.

2010 Mount Meager landslide

The 2010 Mount Meager landslide was a large catastrophic debris avalanche that occurred in southwestern British Columbia, Canada, on August 6 at 3:27 a.m. PDT (UTC-7). More than 45,000,000 m3 (1.6×109 cu ft) of debris slid down Mount Meager, temporarily blocking Meager Creek and destroying local bridges, roads and equipment. It was one of the largest landslides in Canadian history and one of over 20 landslides to have occurred from the Mount Meager massif in the last 10,000 years.

References

  1. Whittow, John (1984). Dictionary of Physical Geography. London: Penguin, 1984. ISBN   0-14-051094-X.
  2. "Flows". California State University Long Beach. Archived from the original on 2013-08-18.
  3. 1 2 "Landslide Types and Processes". USGS. 2004-08-18. Retrieved 2015-12-17.
  4. 1 2 "What is Mass Movement?". Idaho Museum of Natural History. Retrieved 2015-12-17.
  5. "Types of Wasting: Slump, Rockslide, Debris Flow & Earthflow - Video & Lesson Transcript" . Study.com. Retrieved 2015-12-17.
  6. D. Jean Hutchinson (2008). "Rock slide hazards: Detection, assessment and warning". Geological Survey of Brazil. Retrieved 2015-12-17.