Figure 10.46: The slope of underlying materials must be considered when making road cuts.
( 43 )
One well known cause of landslides is from the ground shaking. Sometimes the ground
shakes from an earthquake, a volcanic eruption or even just a truck going by. We can’t
control earthquakes or volcanoes and some of the most devastating landslides have been
started by these other natural hazards. Skiers and hikers need to be aware of the ways they
disturb the snow they travel over or through to avoid setting off anavalanche.Most people
buried by an avalanche do not survive, either because they freeze, are crushed by the weight
of the snow or are unable to breathe. If you ski or snow board in deep powder, you should
carry a small shovel in your backpack and attach a long, red lightweight cord to your waist
or carry a GPS radio transmitter to help rescuers locate you in the event of an avalanche.
Types of Movement Caused by Gravity
Mechanical weathering loosens pieces of rock as water seeps into cracks in the rock and
freezes. As these rocks fall, they form a big pile of angular rocks at the base of a cliff called
atalus slope(Figure10.48). If you travel along a road or highway through regions such
as these, you may see signs warning of the danger along the road side. Sometimes as one
rock falls, it hits another rock lower down, which hits another and so on and so forth. This
is one way that a landslide or an avalanche can begin.
Landslides and Avalanches
Landslides and avalanches are the most dramatic, sudden and dangerous examples of earth
materials moved by gravity. Usually the term landslide is used to mean solid rock that falls
suddenly, whereas an avalanche is formed from snow. Most landslides happen along con-
vergent plate boundaries, in regions of the world that are tectonically active. These regions
are often mountainous and are places of frequent earthquakes and volcanic eruptions. When
large amounts of rock suddenly break loose from a cliff or mountainside, they move quickly