mass movements
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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 - PowerPoint PPT PresentationTRANSCRIPT
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