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EnvironmentOntology / envo

A community-driven ontology for the representation of environments
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Upgrade debris flow semantics for wildfire use cases #987

Open pbuttigieg opened 3 years ago

pbuttigieg commented 3 years ago

Proposed definition fro Gary Berg-Cross

debris flow – debris flows occur when masses of poorly sorted sediment, agitated and saturated with water, surge down slopes in response to gravity.

from https://www.usgs.gov/natural-hazards/landslide-hazards/science/landslides-glossary?qt-science_center_objects=0#qt-science_center_objects

Katherine Rowden notes this is compliant with their defintions.

First order modification: A debris flow is a mass wasting flow which occurs when masses of poorly sorted sediment are saturated with water and agitated into motion.

Garybc commented 3 years ago

Garybc Orcid 0000-0002-2282-7215

Garybc commented 3 years ago

More extensive definition: Debris Flows A form of rapid mass movement in which loose soil, rock and sometimes organic matter combine with water to form a slurry that flows downslope. They have been informally and inappropriately called “mudslides” due to the large quantity of fine material that may be present in the flow. Occasionally, as a rotational or translational slide gains velocity and the internal mass loses cohesion or gains water, it may evolve into a debris flow. Dry flows can sometimes occur in cohesionless sand (sand flows). Debris flows can be deadly as they can be extremely rapid and may occur without any warning Source The Landslide Handbook— A Guide to Understanding Landslides By Lynn M. Highland, United States Geological Survey, and Peter Bobrowsky, Geological Survey of Canada https://pubs.usgs.gov/circ/1325/pdf/Sections/Section1.pdf

Garybc commented 3 years ago

More background on debris flow from the same source: Occurrence Debris flows occur around the world and are prevalent in steep gullies and canyons; they can be intensified when occurring on slopes or in gullies that have been denuded of vegetation due to wildfires or forest logging. They are common in volcanic areas with weak soil. Relative size/range These types of flows can be thin and watery or thick with sediment and debris and are usually confined to the dimensions of the steep gullies that facilitate their downward movement. Generally the movement is relatively shallow and the runout is both long and narrow, sometimes extending for kilometers in steep terrain. The debris and mud usually terminate at the base of the slopes and create fanlike, triangular deposits called debris fans, which may also be unstable. Velocity of travel Can be rapid to extremely rapid (35 miles per hour or 56 km per hour) depending on consistency and slope angle. Triggering mechanisms Debris flows are commonly caused by intense surface-water flow, due to heavy precipitation or rapid snowmelt, that erodes and mobilizes loose soil or rock on steep slopes. Debris flows also commonly mobilize from other types of landslides that occur on steep slopes, are nearly saturated, and consist of a large proportion of silt- and sand-sized material. Effects (direct/indirect) Debris flows can be lethal because of their rapid onset, high speed of movement, and the fact that they can incorporate large boulders and other pieces of debris. They can move objects as large as houses in their downslope flow or can fill structures with a rapid accumulation of sediment and organic matter. They can affect the quality of water by depositing large amounts of silt and debris.

smrgeoinfo commented 3 years ago

There are two concepts here: Debris flow process Debris flow deposit

A definition of these two concepts should enable an observer to determine if an event involves a debris flow process, or whether a deposit is a debris flow deposit. The definition needs to differentiate from potentially related concepts like mudflow, landslide, rock avalanche, and lahar.

e.g. Neuendorf et al 2005 (AGI Glossary of Geology) (process) a moving mass of rock fragments, soil, and mud, more than half of the particles being larger than sand size

dr-shorthair commented 3 years ago

more than half of the particles

by mass, volume, or count?

smrgeoinfo commented 3 years ago

Interesting question.... since the definition was written by a geologist, there's probably different answers, depending on who you talk to. I'll ask around.

pbuttigieg commented 3 years ago

There are two concepts here: Debris flow process Debris flow deposit

This thread is focusing on the process, but we can deal with the deposit in passing as we do for related terms like flood.

A definition of these two concepts should enable an observer to determine if an event involves a debris flow process, or whether a deposit is a debris flow deposit.

Yes, as we do with other classes, this will be clear from both the textual def and the positioning in the hierarchies.

The definition needs to differentiate from potentially related concepts like mudflow, landslide, rock avalanche, and lahar.

Yes, that's where we need a bit of help.

e.g. Neuendorf et al 2005 (AGI Glossary of Geology) (process) a moving mass of rock fragments, soil, and mud, more than half of the particles being larger than sand size

Noting @dr-shorthair 's point above, we would need a couple more definitions to see if there is convergence / difference of opinion.

Thanks for asking around @smrgeoinfo !

smrgeoinfo commented 3 years ago

This is what I got. The AGI glossary definition with the grain size criteria doesn't seem consistent with the literature. Thanks to Ann Youberg (AZGS) and Nancy Riggs (NAU) for discussion and leads.

Synthesis

A type of sediment-water flow in which the sediment and water mixture becomes a slurry, similar to wet concrete, capable of holding gravel-sized particles in suspension when flowing slowly or stopped. Debris flows are usually confined to the dimensions of the steep gullies that facilitate their downward movement. Generally the movement is relatively shallow and the runout is both long and narrow, sometimes extending for kilometers in steep terrain. Velocity of travel can be rapid to extremely rapid (35 miles per hour or 56 km per hour) depending on consistency and slope angle. Debris flows are non-Newtonian viscoplastic or dilatant fluids having laminar flow and uniform sediment concentration profiles, sediment concentrations ranging 70-90 % by weight (47-77% by volume), and shear strengths greater than about 400 dynes/cm2. In debris flows solid particles and water move together as a single viscoplastic body. Sediment entrainment is irreversible, water and solids move at the same velocity, and debris flows cannot deposit any but the coarsest particles as flow velocities decrease. Shear is concentrated in a thin zone at the flow boundaries.

Synthesized from