Scree
Encyclopedia
Scree, also called talus, is a term given to an accumulation of broken rock
fragments at the base of crag
s, mountain cliff
s, or valley shoulders. Landforms associated with these materials are sometimes called scree slopes or talus piles. These deposits typically have a concave upwards form, while the maximum inclination of such deposits corresponds to the angle of repose
of the mean debris
size.
The term scree comes from the Old Norse
term for landslide
, skriða.
The term talus is a French word meaning slope.
The terms scree and talus are often used interchangeably, though scree commonly refers to smaller material like mixed gravel and loose dirt, talus to rocks larger than scree. Talus is usually the preferred term in scientific writing.
and erosion
al processes acting on a rock face. The predominant processes that degrade a rock slope depend largely on the regional climate
(temperature, amount of rainfall, etc.). Examples include:
Scree formation is commonly attributed to the formation of ice
within mountain rock slopes. During the day, water can flow in joints and discontinuities in the rock wall. If the temperature drops sufficiently, for example with the onset of evening, this water may freeze
. Since water expands by 9% when it freezes, it can generate large forces that either create new cracks or wedge blocks into an unstable position. Special boundary conditions (rapid freezing and water confinement) may be required for this process to be effective. Freeze-thaw scree production is thought to be most common during the spring and fall, when the daily temperatures fluctuate around the freezing point of water, and snow melt produces ample free water.
The efficiency of freeze/thaw processes in scree production is the subject of some debate in the scientific community. Many researchers believe that it is unrealistic to assume that ice formation in large open crack systems can generate large pressures, instead suggesting that the water and ice simply flow out of the cracks as pressure builds. Many argue that a frost heaving
process, like that known to act in soil in permafrost
areas, may in fact play an important role in cliff degradation in cold environments.
Scree drains rapidly. Only in reliably moist climates does talus support mature forest (illustration, right). With sufficient time, a rock slope may become completely covered by its own scree so that production of new material ceases. This slope is said to be mantled with debris.
Scree can also be the result of human activity, such as the scree beneath the sculpture Mount Rushmore
in South Dakota
.
Rock (geology)
In geology, rock or stone is a naturally occurring solid aggregate of minerals and/or mineraloids.The Earth's outer solid layer, the lithosphere, is made of rock. In general rocks are of three types, namely, igneous, sedimentary, and metamorphic...
fragments at the base of crag
Cliff
In geography and geology, a cliff is a significant vertical, or near vertical, rock exposure. Cliffs are formed as erosion landforms due to the processes of erosion and weathering that produce them. Cliffs are common on coasts, in mountainous areas, escarpments and along rivers. Cliffs are usually...
s, mountain cliff
Cliff
In geography and geology, a cliff is a significant vertical, or near vertical, rock exposure. Cliffs are formed as erosion landforms due to the processes of erosion and weathering that produce them. Cliffs are common on coasts, in mountainous areas, escarpments and along rivers. Cliffs are usually...
s, or valley shoulders. Landforms associated with these materials are sometimes called scree slopes or talus piles. These deposits typically have a concave upwards form, while the maximum inclination of such deposits corresponds to the angle of repose
Angle of repose
The angle of repose or, more precisely, the critical angle of repose, of a granular material is the steepest angle of descent or dip of the slope relative to the horizontal plane when material on the slope face is on the verge of sliding. This angle is in the range 0°–90°.When bulk granular...
of the mean debris
Debris
Debris is rubble, wreckage, ruins, litter and discarded garbage/refuse/trash, scattered remains of something destroyed, or, in geology, large rock fragments left by a melting glacier etc. The singular form of debris is debris...
size.
The term scree comes from the Old Norse
Old Norse
Old Norse is a North Germanic language that was spoken by inhabitants of Scandinavia and inhabitants of their overseas settlements during the Viking Age, until about 1300....
term for landslide
Landslide
A landslide or landslip is a geological phenomenon which includes a wide range of ground movement, such as rockfalls, deep failure of slopes and shallow debris flows, which can occur in offshore, coastal and onshore environments...
, skriða.
The term talus is a French word meaning slope.
The terms scree and talus are often used interchangeably, though scree commonly refers to smaller material like mixed gravel and loose dirt, talus to rocks larger than scree. Talus is usually the preferred term in scientific writing.
Formation
Formation of scree or talus deposits results from physical and chemical weatheringWeathering
Weathering is the breaking down of rocks, soils and minerals as well as artificial materials through contact with the Earth's atmosphere, biota and waters...
and erosion
Erosion
Erosion is when materials are removed from the surface and changed into something else. It only works by hydraulic actions and transport of solids in the natural environment, and leads to the deposition of these materials elsewhere...
al processes acting on a rock face. The predominant processes that degrade a rock slope depend largely on the regional climate
Climate
Climate encompasses the statistics of temperature, humidity, atmospheric pressure, wind, rainfall, atmospheric particle count and other meteorological elemental measurements in a given region over long periods...
(temperature, amount of rainfall, etc.). Examples include:
- Mechanical weathering by ice
- Chemical weathering by mineral hydration and salt deposition
- Thermal stresses
- Topographic stresses
- BioticBiotic componentBiotic components are the living things that shape an ecosystem. A biotic factor is any living component that affects another organism, including animals that consume the organism in question, and the living food that the organism consumes. Each biotic factor needs energy to do work and food for...
processes
Scree formation is commonly attributed to the formation of ice
Ice
Ice is water frozen into the solid state. Usually ice is the phase known as ice Ih, which is the most abundant of the varying solid phases on the Earth's surface. It can appear transparent or opaque bluish-white color, depending on the presence of impurities or air inclusions...
within mountain rock slopes. During the day, water can flow in joints and discontinuities in the rock wall. If the temperature drops sufficiently, for example with the onset of evening, this water may freeze
Freezing
Freezing or solidification is a phase change in which a liquid turns into a solid when its temperature is lowered below its freezing point. The reverse process is melting....
. Since water expands by 9% when it freezes, it can generate large forces that either create new cracks or wedge blocks into an unstable position. Special boundary conditions (rapid freezing and water confinement) may be required for this process to be effective. Freeze-thaw scree production is thought to be most common during the spring and fall, when the daily temperatures fluctuate around the freezing point of water, and snow melt produces ample free water.
The efficiency of freeze/thaw processes in scree production is the subject of some debate in the scientific community. Many researchers believe that it is unrealistic to assume that ice formation in large open crack systems can generate large pressures, instead suggesting that the water and ice simply flow out of the cracks as pressure builds. Many argue that a frost heaving
Frost heaving
Frost heaving results from ice forming beneath the surface of soil during freezing conditions in the atmosphere. The ice grows in the direction of heat loss , starting at the freezing front or boundary in the soil...
process, like that known to act in soil in permafrost
Permafrost
In geology, permafrost, cryotic soil or permafrost soil is soil at or below the freezing point of water for two or more years. Ice is not always present, as may be in the case of nonporous bedrock, but it frequently occurs and it may be in amounts exceeding the potential hydraulic saturation of...
areas, may in fact play an important role in cliff degradation in cold environments.
Scree drains rapidly. Only in reliably moist climates does talus support mature forest (illustration, right). With sufficient time, a rock slope may become completely covered by its own scree so that production of new material ceases. This slope is said to be mantled with debris.
Scree can also be the result of human activity, such as the scree beneath the sculpture Mount Rushmore
Mount Rushmore
Mount Rushmore National Memorial is a sculpture carved into the granite face of Mount Rushmore near Keystone, South Dakota, in the United States...
in South Dakota
South Dakota
South Dakota is a state located in the Midwestern region of the United States. It is named after the Lakota and Dakota Sioux American Indian tribes. Once a part of Dakota Territory, South Dakota became a state on November 2, 1889. The state has an area of and an estimated population of just over...
.