Mass Wasting Causes of mass wasting Types of mass wasting slumps slumps falls falls slides slides flows flows

Mass Wasting

Causes of mass wasting

Types of mass wasting

slumps

falls

slides

flows

Mass Wasting – downslope movement of debris in response to gravity.

http://students.washington.edu/cdcdcd/

http://jan.ucc.nau.edu/~wittke/GLG100/Wasting.html

Maximum angle with a stable slope.

The coarser the clast size, the more steeply sided a stable pile can be.

Angle of Repose

http://www.tulane.edu/~sanelson/geol204/masswastproc.htm

Toe-Cutting and Restabilization

Removing the toe of a hill destabilizes it. Material will slide, slump, and creep downhill until the original angle of repose is reestablished. The hill will then be stable.

http://jan.ucc.nau.edu/~wittke/GLG100/Wasting.html

The Role of WaterA little water in the pore spaces of a sediment make the particles “sticky”

Too much water between particles force particles apart, and the sediment lose cohesion.

Heavy rain and snowmelt are frequently associated with mass wasting.

Landscaping and Landslides

Development can lead to mass wasting due to:

Removal of slope toes

Adding extra weight to a slope

Removing vegetation, which encourages erosion

Other problems are also common. The slope may look fine, at least until the first heavy rain.

Flow

Slide Slump

Fall

Types of Mass Wasting

Rotational slide, movement occurs along a curved surface so that foot of slump slides outward while the top slides down


Slumps


Slumps have a “scooped out” appearance, with a scarp at the top and debris piled in front of the slump.

Slump

“Child Discovers Ice”

http://www.na.fs.fed.us/spfo/ncfpw/ncfpw00/contest/fun.htm

icy patch

Slump


http://landslides.usgs.gov/html_files/landslides/program.html

Slump


The car and guard rail were at the top of the slump, and

dropped almost straight down.


La Conchita, CaliforniaLandslide and debris flow (1995)

Many people were evacuated because of the slide and the houses nearest the slide were completely destroyed. Fortunately, no one was killed or injured.

Photograph by R.L. Schuster, U.S. Geological Survey

Slump



Slump


Toe of slump moved outward, bulldozing

this house

Toe of slump moved outward, bulldozing

this house

La Conchita, California1995

http://www.opl.ucsb.edu/grace/lc/lc12.html

The 2005 disaster started with a mud flow over US 101

The 2005 disaster started with a mud flow over US 101La Conchita, California

http://www.opl.ucsb.edu/grace/lc/lc12.html

La Conchita, California

“The previous photos were from the morning, before the mudslide occurred in our town.

It was the most incredible thing I have ever been a witness to. I heard a huge thundering noise, then I made the mistake of looking out my back window only to see a rushing stream of mud and debris flow into a 2-story house, buckling it at the joints and eventually taking it down.”

“The previous photos were from the morning, before the mudslide occurred in our town.

It was the most incredible thing I have ever been a witness to. I heard a huge thundering noise, then I made the mistake of looking out my back window only to see a rushing stream of mud and debris flow into a 2-story house, buckling it at the joints and eventually taking it down.”

2005

http://www.opl.ucsb.edu/grace/lc/lc12.html Photos by Frank Spada

“My neighbor's house. It has been shifted an entire lot down the street. They both got out safely.”

“My neighbor's house. It has been shifted an entire lot down the street. They both got out safely.”

“There used to be about 8 houses here.” “There used to be about 8 houses here.”

“This house is actually pitched forward and up on a pile of mud. ““This house is actually pitched forward and up on a pile of mud. “

“The mud flowed right around Ernie's house. Lucky guy...”“The mud flowed right around Ernie's house. Lucky guy...”

La Conchita, California2005


Rock and Debris Falls


Dislodged rocks and debris fall and bounce down cliff.



Rock and Debris Fall



Yosemite National Park, California Rock fall, 1996

A huge rock weighing 200 tons broke away from Granite Point, near Happy Isles, a popular trailhead and concession stand. The rock disintegrated when it landed, creating an air blast that was so powerful that it flattened as many as 2,000 trees in the area.

One person was killed at the concession stand, and 14 people were seriously injured. The dust kicked up from the pulverized granite blocked out the sun and coated tents and recreational vehicles, not unlike ashfall from a volcano.

Photograph by Edwin Harp, U.S. Geological Survey.



Slides


Dislodged rock moves down along a pre-existing surface

Slides


Fig. 09.17

Slides


A massive rock slide occurred after heavy rain, blocking the Gros Ventre River, and causing all kinds of damage to roads and other structures


Slides

http://landslides.usgs.gov/html_files/landslides/nationalmap/national.html

Cincinnati, Ohio

http://www.natlengr.com/unique.htm

ODOT Project No. 643Mt. Adams Slide Repair

Location: Hamilton County, Ohio

Owner: Ohio Department of Transportation

Approximate Value: $22,200,000

Duration of Work: 1979 - 1983

Description: Slide correction consists of installation of 97 - 2' diameter soldier piles ranging from 20' to 50' deep with rock anchors; 161 caissons (4', 5', 6', 7' diameters) ranging from 20' to 80' deep with rock anchors and tendons to a tunnel bored in rock approximately 100' behind the caisson wall; 1,100 lf of 9' diameter tunnel access shafts in rock.

Mt. Adams is the “Rodeo Drive” of

Cincinnati

Friday, June 18, 1999

Anti-landslide rules suggested BY ALLEN HOWARDThe Cincinnati Enquirer

ANDERSON TOWNSHIP — A landslide that caused expensive houses to slip off their foundations in Lawyer's Pointe might not have occurred had the county's improved regulations on hillside development been in effect.

[…]

The landslide in Lawyer's Pointe caused houses with average values of $350,000 to slip off their foundations.

To correct the slippage, the township received $1 million from the Federal Emergency Management Agency (FEMA). FEMA has requested that the township adopt hillside regulations that would prevent such slippage on future hillside developments.

http://www.enquirer.com/editions/1999/06/18/loc_anti-landslide_rules.html

Huffman Court

http://www.eas.purdue.edu/engeomap/8_three_flowslides.htm

A low-cost housing project of single story, single-family homes built in the 1960’s. The original steep (but stable) hillside was greatly altered to make a suitable platform for 15 new houses.

Note the position of the creek at the base of the slope adjacent to the development.


Huffman CourtA flat area was created by slicing off the top of a steep hill and dumping the fill on one side.

The homes were constructed on concrete platforms, i.e., without basements.

Problems started to surface about 5 years after construction was completed.

Man-made Fill

Lake Clay


The overburden of man-made fill pressed on the lake clay, causing it to squeeze out into the creek.

Huffman Court

Huffman Court


Lake Clay squeezes out into creek, where it is removed by erosion. The land beneath the house sinks, occasionally with visible deformation of the land surface.

At some point (usually after a heavy rain), the slope simply gives way, and down goes the house.


Huffman CourtBy 1971, the land beneath the project had begun to slide,

damaging some houses and lots.

Over the next 25 years, the landslides claimed three houses, and threatened all the rest. As of 1991, several more houses were already showing signs of damage.

A visit in August, 2003 confirmed that another

house had been destroyed.



Documents

Mass Wasting Causes of mass wasting Types of mass wasting slumps slumps falls falls slides slides flows flows