Landslides - All the different Kinds

The Difference Between Slides, Falls, and Flows Explained

Aerial View of a Landslide on road near the seaside

 

gece33 / Getty Images 

Landslides take many different forms and sizes. This photo set progresses through the following: slides, falls and flows. Each of these types of landslides may involve rock, debris (mixed rock and soil) or earth (fine-grained material). Flows of very wet earth are called mudflows, and mudflows associated with volcanoes are called lahars. At the end are photos showing various efforts to control landslides

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Parts of a Landslide

Parts of as Landslide

 U.S. Geological Survey image

This generic landslide is labeled with the names of the parts of a landslide.

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Soil Creep

Soil Creep

 U.S. Geological Survey diagram

Soil creep is a slow process based on wetting and drying (or freezing and thawing) cycles. Its signs are subtle, but building designs must account for it.

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Trees Affected by Soil Creep

Trees affected by soil creep

 SA Geography

These trees always sought to grow straight upward, but the ground beneath it was subject to creep. As its base tilted, its crown bent toward the vertical.

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Soil Creep

rocks affected by soil creep

 National Geophysical Data Center photo

Soil creep moves the fractured rock of the Hammond Formation down slope near Marathon, Texas. Creep is faster nearer the surface. The rock is not actually bent.

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Block Slide Diagram

Block slide landslide diagram

 U.S. Geological Survey

The simplest slide involves large blocks of rock that do little more than move downhill, leaving a slide surface behind them.

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Block Slide, Forest Road 19, Oregon

An Oregon road is closed
U.S. Forest Service photo

In January 2006 the road to Terwilliger Hot Springs was closed by this block slide. It included mud and wood but was predominantly rock blocks, little deformed.

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Slump or Rotational Slide

Slumping

 U.S. Geological Survey image

A slide involves slow motion along a surface of weakness above undisturbed material. Slumps leave backward-rotated blocks and a sitzmark shape in the slope.

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Berkeley Hills Slump

Berkeley Hills slump
Landslide Picture Gallery.

Andrew Alden, licensed to About.com ( fair use policy)

A wet winter put large amounts of water into this hillside, especially along the outer edge of the road. After several weeks of heavy rains, the slope gave way.

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Slump Near Morgan Hill, California

Yet another earthquake hazard
Landslide Picture Gallery.

Andrew Alden, licensed to About.com ( fair use policy)

This slump in young, upturned sedimentary rocks is near the Calaveras fault. Large earthquakes may trigger thousands of landslides at once, adding to damages.

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Slump, Panoche Hills, California

Complex slumps set in shale
Landslide Picture Gallery.

Andrew Alden, licensed to About.com ( fair use policy)

Several different slumps line Escarpada Canyon. Steep canyon walls undercut the weak shale; also, earthquakes may trigger slump events. Available in wallpaper

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Slumps, Del Puerto Canyon, California

Tilted strata contribute to slumping
Landslide Picture Gallery.

Andrew Alden, licensed to About.com ( fair use policy)

The upper slump moves down the dip of the Great Valley Sequence rocks (visible at right) and feeds the lower slump or debris flow. The stream dissects its toe.

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Translational Slide

Translational landslide

 U.S. Geological Survey image

Translational slides do not scoop out their beds but move more or less straight downhill on a flat zone of weakness. They may involve rock, debris or earth.

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DeBeque Canyon Rockslide, Colorado

Large, century-old active slide
Colorado Geological Survey

This active slide began around 1900 and has moved several times since then. It threatens Interstate 70 east of Grand Junction with slow movements of its toe.

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Tully Valley Landslide, 1993

A slump-flow in glacial deposits
USGS photo by Gerald Wieczorek

This translational debris slide occurred when saturated land slid on a layer of glacial clay. The U.S. Geological Survey prepared a report on it.

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Diagram of Rockfall

Rock fall landslide

 Wyoming State Geological Survey

A rockfall is a sudden movement of rock, separated along fractures or bedding planes. There is no fluidity in the motion, only bouncing, rolling and free fall.

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Rockfall

Chert chunks in a neat pile

Andrew Alden, licensed to About.com

This small rockfall displays the piecemeal nature and relative cleanliness of this type of landslide. Road widening destabilized this bit of strongly layered chert.

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Rockfall, Washington Route 20, 2003

Road workers and rockfall
Washington Department of Transportation

Rockfalls are common in mountains of all kinds. Sometimes road construction destabilizes slopes; other times the only feasible route crosses existing slides.

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Debris Flow

Fast-moving rocky mixtures
U.S. Geological Survey image

Debris is mixed rock and soil (but not dominantly fine material), with more or less water and air included. A debris flow acts as a fluid and moves rapidly.

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Debris Flow, Wooden Valley, California

A small example in the wine country

Andrew Alden, licensed to About.com ( fair use policy)

Faulting and folding make oversteepened, unstable slopes that spawn landslides. This slide cleared a long path across route 121 and down a forested hillside.

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Lahars in Colombia, 1994

Volcanic mudflows
U.S. Geological Survey photo by Tom Casadevall

Volcanic debris flows followed an earthquake near Nevado del Huila, smothering towns and killing thousands. They're a hazard near active or extinct volcanoes.

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Debris Avalanche Diagram

When earth turns fully fluid
U.S. Geological Survey image

Debris avalanches flow very rapidly, incorporating air or water that makes the debris behave like a liquid. "Debris" signifies the presence of rock and soil.

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Peru Debris Avalanche of 1970

Path of a catastrophe
U.S. Geological Survey photo

Snow and debris fell from Nevado Huascarán, turned into a rushing fluid and smothered the towns of Yungay and Ranrahirca on 31 May 1970. Tens of thousands died.

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Diagram of Earthflow

Earthflow diagram

 U.S. Geological Survey image

Earthflows involve fine-grained material that forms a thick slurry and has a fluid motion. The hourglass shape is typical.

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Earthflow

A thin-skinned slump

Andrew Alden, licensed to About.com ( fair use policy)

Earthflows involve fine-grained soil rather than rocks, and they ooze rather than rush. They also form lobes rather than long streams like debris flows.

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La Conchita Landslide, 1995

This was on the news
U.S. Geological Survey photo by R. L. Schuster

This earthflow of 1995 reawoke after heavy winter rains in 2005 and killed 10 in the coastal California town of La Conchita. Note the stretching of its top surface.

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Fire and Landslides

Mobilizing stripped soils

Andrew Alden, licensed to About.com ( fair use policy)

Fires that strip the soil of cover commonly are followed by debris flows and earthflows as rain mobilizes the sediment.

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Slump Affects a Bridge

Not ready for earthquakes

Andrew Alden, licensed to About.com ( fair use policy)

Sixty years after this concrete overpass was built, settling and slumping of the earth around it is disrupting the join between structure and foundation.

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Monitoring Rock Stability

Telltale tautlines

Andrew Alden, licensed to About.com ( fair use policy)

A plumb line and strain gauges housed in plastic pipes help detect motions in the walls of a former quarry. Early detection can lead to timely mitigation.

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Slide Defense with Concrete Pillars

Failure of mitigation

Andrew Alden, licensed to About.com ( fair use policy)

Concrete columns in the hillside saved the roadbed, but not the soil. Plastic sheeting (foreground) kept water out of the slope until it degraded.

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Berkeley Hills Slides and Mitigation

Small hillside slides

Andrew Alden, licensed to About.com ( fair use policy)

Earth slide at left and earthflow at right formed after heavy rains. Steel rails and stout timbers hold up the roadbed at left--for now.

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Draining a Landslide, Northern California

Reducing water content can slow its motion

Andrew Alden, licensed to About.com ( fair use policy)

Highway 128 crosses an active landslide in serpentine. Draining water is a common mitigation technique to help stabilize slides, although this one still moves.

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Gabion Wall

A strong and porous barrier

2011 Andrew Alden, licensed to About.com

Gabions, blocks of rocks wrapped in steel mesh, are commonly used to fortify vulnerable slopes. Unlike concrete walls, gabions allow free drainage through themselves, benefiting the slope from both sides.

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Bridge Footing on Active Slide, California Hwy 128

Chopping, patching and padding help save a bridge

Andrew Alden, licensed to About.com ( fair use policy)

The bridge over Capell Creek butts into the active landslide (left) shown previously. This retrofit allows the roadway to shift without endangering the bridge.