Debris flows are fast moving, liquefied landslides of mixed and unconsolidated water and debris that look like flowing concrete. They are defined by their non-newtonian flow dynamics, and behave as Bingham plastics. This characteristic can lead to the formation of levees at the margins of unconstrained debris flows as the margins of the flow freeze. They are differentiated from mudflows by their coarser and more poorly sorted sediment load. Flows can carry material ranging in size from clay to boulders, and may contain a large amount of woody debris such as logs and tree stumps. Flows can be triggered by intense rainfall, glacial melt, or a combination of the two. Speed of debris flows can vary from 5 km/h to up to 80 km/h in extreme cases. Volumes of material delivered by single events vary from less than 100 to more than 100,000 cubic metres. Variables considered important in debris flow initiation include slope angle, available loose sediment, and degree of land disturbance by activities such as forest harvesting. Debris flows are often more frequent following forest and brush fires, as experience in southern California clearly demonstrates. Debris flows are extremely destructive to life and property, and claim thousands of lives world-wide in any given year. They are a particular problem in steep mountainous areas subjected to intense rainstorms, and have received particular attention from researchers in Japan, Western USA, Western Canada, New Zealand, the European Alps, and Kazakhstan.
Features and behavior 
Debris flows generally form when unconsolidated material becomes saturated and unstable, either on a hillslope or in a stream channel. Flows are accelerated downhill by gravity and tend to follow steep mountain channels. The front, or 'head' of debris flow often contains a great deal of coarser material such as boulders and logs. Trailing behind this frontal lobe is the less viscous, main part of the flow that contains sand, silt and clay. Debris flows eventually become 'thinner', or less viscous, muddy flood waters as they deposit their coarser components in areas of reduced gradient. Debris flows tend to move in pulses, or discrete surges, as friction or other barriers are overcome during the flow. Sometimes earlier pulses or previous debris flow deposits form levees which confine the flow until they are breached by later, larger flows. The presence of older levees (a.k.a. lateral deposits) provides some idea of the magnitudes of previous debris flows in a particular area, and through dating of trees growing on such deposits, may indicate the approximate frequency of destructive debris flows. This is important information for land development in areas where debris flows deposit material, known as a debris cone or colluvial fan. The big debris flow or landslide is called yamatsunami (山津波), literally mountain tsunami in Japan.
Other geological flows can also be described as debris flows, though are typically given more specific names. These include:
A lahar is a debris flow related in some way to volcanic activity, either directly as a result of an eruption, or indirectly by the collapse of loose material from the flanks of a volcano. A variety of factors may trigger a lahar, including melting of glacial ice due to volcanic activity or climate change, intense rainfall on loose pyroclastic material, or the out bursting of a lake that was previously dammed by pyroclastic or glacial material. The word lahar is of Indonesian origin, but is now routinely used by geologists world-wide to describe volcanogenic debris flows.
A jökulhlaup is a debris flow that originates from a glacial outburst flood. Jökulhlaup is an Icelandic word which refers specifically to floods having a glacial trigger. In the case of Iceland, many such floods are triggered by sub-glacial volcanic eruptions, since Iceland sits atop the Mid-Atlantic Ridge. Elsewhere, a more common cause of jökulhlaups is the breaching of ice-dammed or moraine-dammed lakes. Such breaching events are often caused by the sudden calving of glacier ice into a lake, which then causes a displacement wave to breach a moraine or ice dam. Downvalley of the breach point, a jökulhlaup may increase greatly in size through entrainment of loose sediment and water from the valley through which it travels. Travel distances may exceed 100 km.
Theories and models of debris flows 
Debris flow is an example of granular convection which occurs in many different environments and scales. Numerous different approaches have been used to model their properties and kinematics, some of which are listed here.
Debris flows as mud flows 
- Rheologically based models that apply to mud flows that are treated as a homogeneous liquid (Examples include: Bingham, viscoplastic, Bagnold-type dilatant fluid, thixotropic, etc.)
- The mixture theory of Iverson
- Dam break wave, e.g. Hunt, Chanson et al.
- Roll wave, e.g., Takahashi, Davies
Unsaturated "rocky" or "stony" debris flows 
Damage prevention 
|This section requires expansion with: examples. (January 2013)|
In order to prevent debris flows reaching property and people, a debris basin may be constructed. Debris basins are designed to protect soil and water resources or to prevent downstream damage. Such constructions are considered to be a last resort because they are expensive to construct and require commitment to annual maintenance.
See also 
- Illhorn below which lies Illgraben a popular debris flow tourist spot
- Landslide classification
- Jakob, Matthias; Hungr, Oldrich (2005). "Debris-flow hazards and related phenomena". Debris-Flow Hazards and Related Phenomena (Springer): 38–39. Bibcode:2005dfhr.book.....J. ISBN 3-540-20726-0
- Pierson, Thomas C. Distinguishing between debris flows and floods from field evidence in small watersheds. US Department of the Interior, US Geological Survey, 2005.
- Iverson, R.M., 1997, The physics of debris flows, Reviews of Geophysics, 35(3): 245-296.
- Hunt,B. (1982). "Asymptotic Solution for Dam-Break Problems." Jl of Hyd. Div., Proceedings, ASCE, Vol. 108, No. HY1, pp. 115-126.
- Hubert Chanson, Sebastien Jarny & Philippe Coussot (2006). "Dam Break Wave of Thixotropic Fluid". Journal of Hydraulic Engineering, ASCE, 132 (3): 280–293. doi:10.1061/(ASCE)0733-9429(2006)132:3(280).
- Takahashi, T., 1981. Debris flow, Annu. Rev. Fluid Mech., 13, 57–77.
- Davies,T.R.H. 1986. Large debris flows: a macro-viscous problem. Acta Mechanica, 63, 161-178.
- Hungr,O. 2000. Analysis of debris flow surges using the theory of uniformly progressive flow. Earth Surface Processes and Landforms, 25, 483-495
- Coleman, P. F., 1993. A new explanation for debris flow surge phenomena (abstract), Eos Trans. AGU, 74(16), Spring Meet. Suppl., 154.
- "Debris Basins". U.S. Fish & Wildlife Service. Retrieved 30 January 2013.
Further reading 
- McPhee, John. The Control of Nature. New York: Noonday Press (Farrar, Straus & Giroux, 1989 ISBN 0-374-12890-1)