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Debris flow
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A Debris flow is a fast moving mass of unconsolidated, saturated debris that looks like flowing concrete. They differentiate from a mudflow by terms of the viscosity of the flow. Flows can carry clasts ranging in size from clay particles to boulders, and also often contains a large amount of woody debris.
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Encyclopedia
A Debris flow is a fast moving mass of unconsolidated, saturated debris that looks like flowing concrete. They differentiate from a mudflow by terms of the viscosity of the flow. Flows can carry clasts ranging in size from clay particles to boulders, and also often contains a large amount of woody debris. Flows can be triggered by large amounts of rainfall, or glacial melt, or a combination of the two. Speed of debris flows can vary from 1mph to 35mph in extreme conditions. Variables in the conditions that effect the debris flow can include slope, and avalible loose sediment. Debris flow are extremely destructive to life and property.
Debris Flow Features and Behavior
The debris flows generally form when unconsolidated material becomes saturated and unstable. Flows move downhill as from the force of gravity and are generally stay on downward slopes and mountain valleys. The front of the debris flow, or the toe, forms into a lobe, or ridge shape and marks the front of the flow. This lobe often contains a great deal of the larger sediments including cobbles and boulders. Trailing behind this lobe is the runnier mud that contains sands, silts, and sediments. Debris flows eventually become thinner muddy flood waters as they deposit their heavier components. Geological debris flows tend to move in pulses as friction or other barriers are overcome during the flow. Sometimes earlier pulses or previous debris flows form levees that channel the flow until they are breached. The presence of older levees indicates the recurrence and characteristics of debris flows in a particular area. This can be important information for developing land on what are known as alluvial fans, and alluvial fan terraces.
Different Types of Debris Flows
Lahar
A lahar is a debris flow specifically related to volcanic activity. A variety of factors can trigger a lahar including melting of glacial ice due to volcanic activity or pyroclastic flow, severe rainfall on pyroclastic material, or the out bursting of a lake that was dammed by pyroclastic material.
Jokulhlaup
A jokulhlaup is a debris flow that steams from a glacial outburst. Debris flows have the potential to form from an out burst flood if there is a lot of loose sediment that it can pick up on its descent down the mountain.
Theories and models of debris flows
Debris flows as mud flows
- Rheologically based models that apply to mud flows that are treated as a homogeneous liquid (Examples include: Bingham, visco-plastic, etc)
- The mixture theory of Iverson
- Dam break wave eg Hunt
- Roll wave Takahashi, Davies
Unsaturated 'rocky' or 'stony' debris flows
- Progressive wave-Hungr
- A type of translating rock dam-Coleman
Topographic effects in debris flows
- Curved and twisted channel: 'flow over-banking'-Pudasaini et al.
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