Mass Movement

Rigolith: loose material weathered from the earths surface Mass Movement:the downslope movement of rigolith due to pull of gravity

Influences on mass movement

Gradient: M.M is fastest when the slope is steep water content: makes regolith heavier and acts as a lubricant. makes M.M move quickly and easily Human Activity:people make cuttings into sides of hills-leaves a steeper slope and may cause material to collapse Vegetation: roots of trees and plants bind the soil together-slows down rate of M.M

Types of M.M

slow- soil creepfast-landslides,bogbursts,mudflows

Soil Creep

DIAGRAM: trees grow at an angle-trunks are curved telephone graphs are tilted steps called terracettes develop on steep slopes soil builds up behind wall and causes them to bulge and collapse also fences tilt and break

Avalanche:very rapid downslope movement of snow or ice on a mountain side

Landslide: rapid downslope of loose soil and rock may occur because of: road cutting into a steep slope which may cause regolith to fall onto it constant erosion by waves causing undercutting of cliffs-overhanging ledges collapse as a landslide

Earth flows and mudflows(lahars):occur when soil and mud become saturated by water on steep slopes.this water may result from heavy rain or snow melted from volcanic eruptionsmudflow due to volcanic eruption is called lahar

Bogbursts: occur in mountain bogs of ireland after long periods of heavy rain-saturated peat moves quickly down slope

Nevado del Ruiz-snowcapped mountain in columbian Andes erupted in 1984

when it erupted it threw out huge amounts of ash and steam heat melted the snow meltwater descended down the mountain picking up ash soil and rocks on the way water+ash+rocks=mudflow 20 metres deep in places @ 80 km/h(heavy rain also increased flow) Armero(town built at the foot of the mountain) was in direct path of mudflow and was struck just before midnight

Impact of mudflow

worlds deadliest mudflow in the last century 21000 killed 5000 homes destroyed 6000 made homeless cost of disaster was $1bn(20% on columbias GNP)

general notes

case study: volcaneo of nevado del ruiz