A Sturzstrom (from the German '' Sturz'' (fall) and ''Strom'' (stream, flow)) or ''rock avalanche'' is a large

landslide Landslides, also known as landslips, are several forms of mass wasting that may include a wide range of ground movements, such as rockfalls, deep-seated slope failures, mudflows, and debris flows. Landslides occur in a variety of environmen ...

consisting of

soil Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former ...

and rock which travels a great horizontal distance (as much as 20 or 30 times) compared to its initial vertical drop. Sturzstroms have similarities to the flow of

glacier A glacier (; ) is a persistent body of dense ice that is constantly moving under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires distinguishing features, such a ...

mudflow A mudflow or mud flow is a form of mass wasting involving fast-moving flow of debris that has become liquified by the addition of water. Such flows can move at speeds ranging from 3 meters/minute to 5 meters/second. Mudflows contain a significa ...

s, and

lava flow Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or un ...

s. They flow across land fairly easily, and their mobility increases when

volume Volume is a measure of occupied three-dimensional space. It is often quantified numerically using SI derived units (such as the cubic metre and litre) or by various imperial or US customary units (such as the gallon, quart, cubic inch). ...

increases. They have been found on other bodies in the

Solar System The Solar System Capitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar ...

, including the

Moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...

Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury. In the English language, Mars is named for the Roman god of war. Mars is a terrestrial planet with a thin at ...

Venus Venus is the second planet from the Sun. It is sometimes called Earth's "sister" or "twin" planet as it is almost as large and has a similar composition. As an interior planet to Earth, Venus (like Mercury) appears in Earth's sky never f ...

, Io, Callisto,

Iapetus In Greek mythology, Iapetus (; ; grc, Ἰαπετός, Iapetós), also Japetus, is a Titan, the son of Uranus and Gaia and father of Atlas (mythology), Atlas, Prometheus, Epimetheus (mythology), Epimetheus, and Menoetius (mythology), Menoetius. ...

, and Phobos.

Movement

Sturzstroms may be triggered, similarly to other types of landslides, by heavy rains,

earthquake An earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can range in intensity, fr ...

s, or

volcanic activity Volcanism, vulcanism or volcanicity is the phenomenon of eruption of molten rock (magma) onto the surface of the Earth or a solid-surface planet or moon, where lava, pyroclastics, and volcanic gases erupt through a break in the surface called a ...

. They move rapidly, but do not necessarily require

water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as ...

to be present to move, and there is no definite explanation for their kinematic characteristics. One

theory A theory is a rational type of abstract thinking about a phenomenon, or the results of such thinking. The process of contemplative and rational thinking is often associated with such processes as observational study or research. Theories may ...

, the

acoustic fluidization Soil liquefaction occurs when a cohesionless saturated or partially saturated soil substantially loses strength and stiffness in response to an applied stress such as shaking during an earthquake or other sudden change in stress condition, i ...

theory, hypothesizes that vibrations caused by the collisions among the rock fragments reduce

friction Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. There are several types of friction: *Dry friction is a force that opposes the relative lateral motion of ...

and allow the mass to travel great distances. Another theory involves air pockets forming under the slide and providing a cushion that the slide rides over with very low friction, although the merit of this theory has been called into question by the presence of sturzstroms in

vacuum A vacuum is a space devoid of matter. The word is derived from the Latin adjective ''vacuus'' for "vacant" or " void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressure. Physicists often ...

s such as on the Moon and Phobos. Observation of slides on Iapetus suggests that tiny contact points between bits of ice debris may heat up considerably during the movement, causing melting and forming a more fluidand thus less friction-limitedmass of material. Kofelsite (impactite or frictionite) Kofels Structure Austria

Kofelsite (impactite or frictionite) Kofels Structure Austria

The amount of energy in a sturzstrom is much higher than in a typical landslide. Once moving, it can ride over nearly any terrain and will cover much more horizontal ground than downward-sloped ground. Its

momentum In Newtonian mechanics, momentum (more specifically linear momentum or translational momentum) is the product of the mass and velocity of an object. It is a vector quantity, possessing a magnitude and a direction. If is an object's mass ...

can even carry the sturzstrom up small

hill A hill is a landform that extends above the surrounding terrain. It often has a distinct summit. Terminology The distinction between a hill and a mountain is unclear and largely subjective, but a hill is universally considered to be not a ...

s. The process of detachment, movement and deposition of a sturzstrom can be recorded by seismometers tens of kilometers away. The peculiar characteristics of this seismic signal make it distinguishable from that of small earthquakes. In the large

Köfels landslide Umhausen is a municipality in the Imst district of state of Tyrol in western Austria. It and is located 17 km southeast of Imst at the Ötztaler Ache in the Ötztal. It has 3078 inhabitants. Geography The municipality consists of six vill ...

, which flowed into the

Ötztal The Ötztal is an alpine valley located in Tyrol, Austria. The Ötztaler Ache river flows through the valley in a northern direction. The Ötztal separates the Stubai Alps in the east from the Ötztal Alps in the west. The valley is long. The no ...

valley in

Tyrol Tyrol (; historically the Tyrole; de-AT, Tirol ; it, Tirolo) is a historical region in the Alps - in Northern Italy and western Austria. The area was historically the core of the County of Tyrol, part of the Holy Roman Empire, Austrian Emp ...

Austria Austria, , bar, Östareich officially the Republic of Austria, is a country in the southern part of Central Europe, lying in the Eastern Alps. It is a federation of nine states, one of which is the capital, Vienna, the most populous ...

, deposits of fused rocks, called "frictionite" (or "impactite", or "hyalomylonite"), were found in the landslide debris. This has been hypothesized to be volcanic in origin or the result of a meteorite impact, but the leading hypothesis is that it was due to the large amount of internal friction. Friction between static and moving rocks can create enough heat to fuse rocks to form frictionite.

References

{{Authority control Landslides

Movement

See also

References