Debris flow

Debris flow channel with deposits left after 2010 storms in Ladakh, NW Indian Himalaya. Coarse bouldery levees form the channel sides. Poorly sorted rocks lie on the channel floor.
Scars formed by debris flow in Ventura, greater Los Angeles during the winter of 1983. The photograph was taken within several months of the debris flows occurring.
Ancient debris flow deposit at Resting Springs Pass, California
A debris flow in Ladakh, triggered by storms in 2010. It has poor sorting and levees. Steep source catchment is visible in background.
Almaty, Kazakhstan, after the catastrophic debris flow of 1921. A number of facilities, including the Medeu Dam, have been built since to prevent flows of this kind from reaching the city.

Debris flows are geological phenomena in which water-laden masses of soil and fragmented rock rush down mountainsides, funnel into stream channels, entrain objects in their paths, and form thick, muddy deposits on valley floors.

- Debris flow

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Alluvial fan

Accumulation of sediments that fans outwards from a concentrated source of sediments, such as a narrow canyon emerging from an escarpment.

Alluvial fan in the French Pyrenees
Alluvial fan in Death Valley
Large alluvial fan in Death Valley showing a "toe-trimmed" profile
Alluvial fan in the Taklamakan Desert in Xinjiang showing active left and inactive right sectors
Pebble bed in the New Red Sandstone
Large alluvial fan at the base of the rim of Gale crater, Mars

The flow can take the form of infrequent debris flows or one or more ephemeral or perennial streams.


A lahar travels down a river valley in Guatemala near the Santa Maria volcano, 1989
Excavated 9th century Sambisari Hindu temple near Yogyakarta in Java, Indonesia. The temple was buried 6.5 metres under the lahar volcanic debris accumulated from centuries of Mount Merapi eruptions.
Mudline left behind on trees on the banks of the Muddy River after the 1980 eruption of Mount St. Helens showing the height of the lahar
The aftermath of a lahar from the 1982 eruption of Galunggung, Indonesia
The lahar from the 1985 eruption of Nevado del Ruiz that wiped out the town of Armero in Colombia
A before-and-after photograph of a river valley filled in by lahars from Mount Pinatubo

A lahar (, from ꦮ꧀ꦭꦲꦂ) is a violent type of mudflow or debris flow composed of a slurry of pyroclastic material, rocky debris and water.


A landslide near Cusco, Peru, in 2018
The Mameyes Landslide, in the Mameyes neighborhood of barrio Portugués Urbano in Ponce, Puerto Rico, was caused by extensive accumulation of rains and, according to some sources, lightning. It buried more than 100 homes.
The landslide at Surte in Sweden, 1950. It was a quick clay slide that killed one person.
The Costa della Gaveta earthflow in Potenza, Italy. Even though it moves at a rate of just a few millimeters per year and is hardly visible, this landslide causes progressive damage to the national road, the national highway, a flyover, and several houses that are built on it.
A rock slide in Guerrero, Mexico
Hotel Panorama at Lake Garda. Part of a hill of Devonian shale was removed to make the road, forming a dip-slope. The upper block detached along a bedding plane and is sliding down the hill, forming a jumbled pile of rock at the toe of the slide.
Deep-seated landslide on a mountain in Sehara, Kihō, Japan caused by torrential rain of Tropical Storm Talas
Landslide of soil and regolith in Pakistan
A Wireline extensometer monitoring slope displacement and transmitting data remotely via radio or Wi-Fi. In situ or strategically deployed extensometers may be used to provide early warning of a potential landslide.
Rhine cutting through Flims Rockslide debris, Switzerland
Global landslide risks
Ferguson Slide on California State Route 140 in June 2006
Trackside rock slide detector on the UPRR Sierra grade near Colfax, CA
Before and after radar images of a landslide on Venus. In the center of the image on the right, the new landslide, a bright, flow-like area, can be seen extending to the left of a bright fracture. 1990 image.
Landslide in progress on Mars, 2008-02-19

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.

Vargas tragedy

A part of Vargas state after the 1999 mudslides
A section of Los Corales, one of the neighborhoods in the Vargas state that suffered the heaviest destruction
Isohyet (contour of equal precipitation) map of the 14–16 December 1999 storm draped over a shaded relief map of north-central Venezuela
Oversteepened hillslopes failed during the rainstorm, sending landslides of soil into the channels (such as the braided river at bottom) and supplying sediment to flash floods and debris flows. The transmission tower on the right side of the image is 30 m tall.
A 2.9 m thick debris flow deposit from December 1999 is exposed by river incision during late-stage floods.
Damage from the debris flow on the Caraballeda fan. The main channel (at left) avulsed to a new course that led it through the houses to the right. These avulsion deposits are up to 6 m thick and total about 1.8 million cubic meters of boulders and other material.
Partially collapsed building; the collapsed area was undercut when debris flows destroyed the bottom floor

The Vargas tragedy was a natural disaster that occurred in Vargas State, Venezuela on 14–16 December 1999, when torrential rains caused flash floods and debris flows that killed tens of thousands of people, destroyed thousands of homes, and led to the complete collapse of the state's infrastructure.

Armero tragedy

The Armero tragedy (Tragedia de Armero ) occurred following the eruption of the Nevado del Ruiz stratovolcano in Tolima, Colombia, on November 13, 1985.

Lahars covering the town of Armero
Nevado del Ruiz seen from space. The summit ice cap and glaciers surround the dark Arenas crater.
A recent hazard map prepared for Nevado del Ruiz and vicinity, showing all of the major disaster zones affected by the eruption
The summit of Nevado del Ruiz in late November 1985
Armero after the eruption, December 1985
Armero was located in the center of this photograph, taken in late November 1985
Only a few buildings and structures remained standing after the mud and debris flows ravaged the town of Armero
The Armero tragedy occurred just after the 1985 Mexico City earthquake, responsible for the destruction of buildings such as this one
Nevado del Ruiz roughly two weeks after the eruption took place
Nevado del Ruiz seen from Manizales, 2006

As pyroclastic flows erupted from the volcano's crater, they melted the mountain's glaciers, sending four enormous lahars (volcanically induced mudflows, landslides, and debris flows) down its slopes at 50 km/h.


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.

Mailboxes caught in a mudflow following the May 1980 Mount St. Helens volcanic eruption.
The Mameyes mudflow disaster, in barrio Tibes, Ponce, Puerto Rico, was caused by heavy rainfall from Tropical Storm Isabel in 1985. The mudflow destroyed more than 100 homes and claimed an estimated 300 lives.

Mudflows contain a significant proportion of clay, which makes them more fluid than debris flows; thus, they are able to travel farther and across lower slope angles.

Sorting (sediment)

Sorting describes the distribution of grain size of sediments, either in unconsolidated deposits or in sedimentary rocks.

Sediment consisting of well sorted grains (left) compared with poorly sorted grains (right).

The degree of sorting may also indicate the energy, rate, and/or duration of deposition, as well as the transport process (river, debris flow, wind, glacier, etc.) responsible for laying down the sediment.

Turbidity current

Most typically an underwater current of usually rapidly moving, sediment-laden water moving down a slope; although current research indicates that water-saturated sediment may be the primary actor in the process.

Turbidites are deposited in the deep ocean troughs below the continental shelf, or similar structures in deep lakes, by underwater turbidity currents (or "underwater avalanches") which slide down the steep slopes of the continental shelf edge, as illustrated in the diagram. When the material comes to rest in the ocean trough, it is the sand and other coarse material which settles first followed by mud and eventually the very fine particulate matter. It is this sequence of deposition that creates the Bouma sequences that characterize these rocks.
Longitudinal section through an underwater turbidity current
Laboratory images of how convective sedimentation beneath a buoyant sediment laden surface can initiate a secondary turbidity current.
Turbidite interbedded with finegrained dusky-yellow sandstone and gray clay shale that occur in graded beds, Point Loma Formation, California.

Within minutes after the 1929 Grand Banks earthquake occurred off the coast of Newfoundland, transatlantic telephone cables began breaking sequentially, farther and farther downslope, away from the epicenter. Twelve cables were snapped in a total of 28 places. Exact times and locations were recorded for each break. Investigators suggested that an estimated 60 mile per hour (100 km/h) submarine landslide or turbidity current of water saturated sediments swept 400 miles (600 km) down the continental slope from the earthquake's epicenter, snapping the cables as it passed. Subsequent research of this event have shown that continental slope sediment failures mostly occurred below 650 meter water depth. The slumping that occurred in shallow waters (5–25 meters) passed down slope into turbidity currents that evolved ignitively. The turbidity currents had sustained flow for many hours due to the delayed retrogressive failure and transformation of debris flows into turbidity currents through hydraulic jumps.

Hyperconcentrated flow

A water molecule consists of two hydrogen atoms and one oxygen atom

A hyperconcentrated flow is a two-phase flowing mixture of water and sediment in a channel which has properties intermediate between fluvial flow and debris flow.

Landslide classification

Influential narrower definitions restrict landslides to slumps and translational slides in rock and regolith, not involving fluidisation.

Location: Castelmezzano – Italy. Rock on a road resulting from a rock fall
Location: Jasper National Park- Canada. These blades of rock are about to topple
Location: Canada. A rock slide deposit.
A large, rotational landslide near Cusco, Peru in 2018.
Location: Pozzano (Castellammare di Stabia) – Italy. A debris flow scar is visible on the right flank of the incised channel.
Location: Quindici – Italy. Debris flow deposits
Location: Quindici – Italy. Debris flow damage
Location: Sarno – Italy. Debris flow channel scoured out by the passage of a debris flow.
Location: Positano, Sorrentine Peninsula – Italy. Scar and deposit of a rock avalanche.
Debris avalanche in Auckland Region, New Zealand
Location: Castelfranci – Italy. An earth flow.
Intense rain triggered widespread landslides in southern Thailand during the last week of March 2011.
A: Diagram illustrating the resistance to, and causes of, movement in a slope system consisting of an unstable block
B: Diagram illustrating the resistance to, and causes of, movement in a slope system consisting of an unstable block
Groundwater conditions when the river level is stable
Groundwater conditions on the falling limb of the hydrograph. If the fall in river levels is sufficiently rapid then the high water levels in the slope can provide a hydraulic push that destabilises the slope, sometimes triggering bank collapse

Description: "Debris flow is a very rapid to extremely rapid flow of saturated non-plastic debris in a steep channel" (Hungr et al.,2001)