What is the difference between a slump and a debris slide

Mudflow: A mudflow is an earthflow consisting of material that is wet enough to flow rapidly and that contains at least 50 percent sand-, silt-, and clay-sized particles. In some instances, for example in many newspaper reports, mudflows and debris flows are commonly referred to as "mudslides.

Creep: Creep is the imperceptibly slow, steady, downward movement of slope-forming soil or rock. Movement is caused by shear stress sufficient to produce permanent deformation, but too small to produce shear failure. There are generally three types of creep: 1 seasonal, where movement is within the depth of soil affected by seasonal changes in soil moisture and soil temperature; 2 continuous, where shear stress continuously exceeds the strength of the material; and 3 progressive, where slopes are reaching the point of failure as other types of mass movements.

Creep is indicated by curved tree trunks, bent fences or retaining walls, tilted poles or fences, and small soil ripples or ridges fig. The dominant mode of movement is lateral extension accompanied by shear or tensile fractures. The failure is caused by liquefaction, the process whereby saturated, loose, cohesionless sediments usually sands and silts are transformed from a solid into a liquefied state.

Failure is usually triggered by rapid ground motion, such as that experienced during an earthquake, but can also be artificially induced. When coherent material, either bedrock or soil, rests on materials that liquefy, the upper units may undergo fracturing and extension and may then subside, translate, rotate, disintegrate, or liquefy and flow.

Lateral spreading in fine-grained materials on shallow slopes is usually progressive. The failure starts suddenly in a small area and spreads rapidly.

Often the initial failure is a slump, but in some materials movement occurs for no apparent reason. Combination of two or more of the above types is known as a complex landslide. Geological causes a. Weak or sensitive materials b. Weathered materials c.

Sheared, jointed, or fissured materials d. Adversely oriented discontinuity bedding, schistosity, fault, unconformity, contact, and so forth e. Morphological causes a. Tectonic or volcanic uplift b. Glacial rebound c. Fluvial, wave, or glacial erosion of slope toe or lateral margins d.

Subterranean erosion solution, piping e. Deposition loading slope or its crest f. Vegetation removal by fire, drought g. Thawing h. Freeze-and-thaw weathering i. Shrink-and-swell weathering. In Maltman, A.

London: Chapman and Hall, pp. Extensional and compressional zones in slumps and slides in the Namurian of County Clare, Ireland. Middleton, G. Mechanics of Sediment Movement. Prior, D. Depositional characteristics of a submarine debris flow. Journal of Geology , 92 : — Disintegrating retrogressive landslides on very low-angle subaqueous slopes, Mississippi delta.

Marine Geotechnology , 3 : 37— Active slides and flows in underconsolidated marine sediments on the slopes of the Mississippi delta. In Saxov, S. Schack Pedersen, S. Comparative studies of gravity tectonics in quaternary sediments and sedimentary rocks related to fold belts. In Jones, M.

Stow, D. Deep clastic seas. In a slump, the earth moves as a great block or series of blocks and moves along a basal glide plane or multiple glide planes in complex slumps. The landscape at the toe of a slump is typically chaotic, displaying a lumpy structure, sometimes with transverse ridges, ponded areas, and in forested areas the trees may be leaning or fallen over from slump movement the name deranged forest or drunken forest is used to describe forested areas affected by landslides.

Slumps typically move quite slowly, measurable in inches to many feet in a year. Slumps can also fail rapidly, potentially contributing to an debris flow , earthflow, mudflow , or debris flood. Debris flows are a type of landslide where a moving mass of rock fragments, soil, and mud with 70 to 90 percent of the material consisting of sediment the rest is water and trapped gasses. Slow debris flows may only move a few feet per year, whereas rapid ones can reach speeds greater than miles per hour.

Debris flows typically consist of a mix of mud, sand, and typically contain rock fragments ranging in size from fine gravel to massive boulders. The general term earthflow is a type of landslide where material detaches from a hillside and moves downslope to form lobe-shaped accumulations at the base of the slope.

In the summer of , a large block of rock slid rapidly from a steep slope above Highway 99 near Porteau Cove between Horseshoe Bay and Squamish.

The block slammed into the highway and adjacent railway and broke into many pieces. The highway was closed for several days, and the slope was subsequently stabilized with rock bolts and drainage holes. As shown in Figure However, it is not actually known what triggered this event as the weather was dry and warm during the preceding weeks, and there was no significant earthquake in the region.

The Hope Slide Figure The slide at Mt. Meager west of Lillooet was also a rock avalanche, and rivals the Hope Slide as the largest slope failure in Canada during historical times Figure Creep , which normally only affects the upper several centimetres of loose material, is typically a type of very slow flow, but in some cases, sliding may take place. Creep can be facilitated by freezing and thawing because, as shown in Figure The same effect can be produced by frequent wetting and drying of the soil.

In cold environments, solifluction is a more intense form of freeze-thaw-triggered creep. Creep is most noticeable on moderate-to-steep slopes where trees, fence posts, or grave markers are consistently leaning in a downhill direction Figure