Page 462 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

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A slope, like the recently disturbed slope in GIA 14.1, is an open system that tends toward dynamic equilibrium. If the forces acting on slope materials
—shown in GIA 14.2—are balanced, the slope remains stable. If the forces become unbalanced, the slope changes until a new equilibrium is reached. Over time, this equilibrium-seeking process gives slopes a characteristic structure, or “anatomy” (GIA 14.3).
14.1
14.2
A SLOPE IN DISEQUILIBRIUM
Unstable, saturated soils gave way on this hillslope, leaving a debris dam partly blocking the river. The hillslope, river, and forest ecosystem are in disequilib- rium as adjustments to new conditions proceed. [Robert Christopherson.]
Potential energy:
Forces opposing motion:
Forces promoting motion:
Visit the Study Area in MasteringGeographyTM to explore slopes and the dynamic equilibrium model.
Visualize: Study a geosciences animation of mass Assess: Demonstrate understanding of slopes and movement. the dynamic equilibrium model (if assigned by
instructor).
FORCES ON A SLOPE
Directional forces (noted by arrows) act on materials along an inclined slope. If the forces opposing motion fall below the force of gravity, the slope is destabilized and material moves downhill. A
Particles on a hillslope have potential energy because of their position.
variety of events can destabilize a slope, including heavy rain, a wildfire that destroys protective plant
cover, or an earthquake.
Exogenic processes
Friction, cohesion of
particles, inertia
Weathered materials added to slope
Endogenic processes
Gravity, aided by endogenic and exogenic events that disturb slope equilibrium
Gravity
Infer: What events or processes could reduce the degree of cohesion of particles on a slope?
geosystems in action 14HiLLsLopEs As opEn systEms
Frictional resistance
Movement at geomorphic threshold
Potential energy becomes kinetic energy
Weathered materials removed from slope
Push of surface
Degree of cohesion
Weight of rock