Mass Movements

Essential QuestionsWhat are mass movements?

What factors trigger mass movements?

Mass movements/mass wasting→• Mass movements occur when

masses of soil, bed rock, rock debris, soil, or mud fall downhill due to gravity– usually occur along steep-

sided hills and mountains

• We know these as landslides, mud slides, and avalanches

http://education-portal.com/academy/lesson/major-triggers-for-mass-wasting-water-slopes-vegetation-removal-earthquakes.html#lesson

Mass movements can be triggered by the following triggers1. Water saturation occurs when the soil is too wet and

acts as a liquid• Usually due to too much rain

2. Oversteepening of slopes occurs when the slopes are too steep to retain material

• Think about mountains3. Roots of vegetation act to hold down the soil. When

the vegetation is removed the soil is more likely to slip

4. Earthquakes shake the soil causing it to move

• There are five types of mass movements.1. Rockfalls2. Slides3. Slumps4. Flows5. Creep

• The types are broken down into different groups due to difference in material, speed, and distance

• Slides– Blocks of material move

suddenly down flat, inclined surface

– Exp: rock slides– One of the fastest mass

movements• Rockfalls

– Occurs when rocks fall freely – Common on slopes that are too

steep to retain loose materials – Frequently caused by frost-

wedging

British Columbia, Canada. (- Geoscape Vancouverhttp://www.youtube.com/watch?v=uOJfcTZME0U

The rock slide at Frank, Alberta, Canada (1903) moved 33 million m3 of rock from Turtle Mountain over the town of Frank in less than two minutes killing 70 people, NOAAhttp://www.youtube.com/watch?v=hMlt-xcpNSo

• Flows– mass movements of material

containing large amounts of water > move as thick fluids

– Earthflows• move 1 mm/day to several

meters/day• Occur on hillsides in wet regions• Creates tounge-shaped mass

– Mudflows-can move up to 80 km/h• Common in semiarid

mountainous regions

Mount St. Helen, WAhttp://www.youtube.com/watch?v=d2vxCDgO6oM

• Slumps– Downward motion of block of

material along curved slope– Not a large change in distance

or fast– Common on oversteepened

slopes with thick accumulations of clay

Creep Slowest type Moves few mm- few cm/ year Freezing and thawing

contributes to creep Cause structures to tilt

Sometimes our preventive measures do not work.

Prevention/Protection→ Mass movement can have a

tremendous impact on the infrastructure and economics status of a community. People try to reduce the impact of mass movements by Digging Trenches/ditches Building Walls Building fences Moving buildings Adding vegetation

Writing Assignment:• What is the impact of mass movements on the social and

economic status of an area? – At least one page and at least three paragraphs– Have to have at least three facts/points

Yungay, Peru before and after landslidehttp://www2.fiu.edu/~longoria/natural/mass/mmain.htm