Mass Movements Essential Questions What 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 mass-wasting-water-slopes-vegetation-removal- earthquakes.html#lesson

Mass movements can be triggered by the following triggers 1.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 mountains 3.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.Rockfalls 2.Slides 3.Slumps 4.Flows 5.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 Vancouver The rock slide at Frank, Alberta, Canada (1903) moved 33 million m 3 of rock from Turtle Mountain over the town of Frank in less than two minutes killing 70 people, NOAA

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, WA

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 landslide