A comprehensive presentation of subchapter 3.3 Slope Processes, from the third chapter of Physical Geography, AS Cambridge, Rocks and Weathering.

1. ASGEOGRAPHYREVISION
ROCKSANDWEATHERING
3.3 SLOPEPROCESSES

2. KEYTERMSANDDEFINITIONS
Avalanches are rapid movements of snow, ice, rock or earth down a
slope.
Climatic geomorphology refers to the different processes that operate
in different climatic zones, producing different slope forms or shapes.
Denudation is the wearing away of the Earth’s surface. It includes
erosion, weathering and mass movements.
Falls are movements of rock/debris under the effect of gravity, e.g.
after it has been prised open by freeze–thaw weathering.
Flows are movements of a mass of soil or rock that contain a significant
amount of water.
Heaves are movements of soil or ice towards the surface in a vertical
direction.

4. KEYTERMSANDDEFINITIONS
Mass movements are large-scale movements of the Earth’s surface
that are not accompanied by a moving agent such as a river, glacier or
ocean wave.
Regolith is the irregular cover of loose rock debris that covers the
Earth.
Shear strength is the internal resistance of a slope.
Shear stress is the forces attempting to pull a mass downslope.
Sheetwash is the unchannelled flow of water over a soil surface.
Slides are an entire mass of material moving along a slip plane.

6. KEYTERMSANDDEFINITIONS
Slope is an inclined surface (hillslope), and / or an angle of inclination
(slope angle).
Slope evolution is the development of slopes over time.
Slope form is the shape of the slope in cross-section.
Slope processes are the activities acting on the slopes.
Slumps are a form of mass movement which occur on weaker rocks,
especially clay, and have a rotational movement along a curved slip
plane.
Throughflow is water moving down through the soil.

7. TOPICSUMMARY
Slopes include any part of the solid land surface, including level
surfaces of 0°.
Descriptive accounts of slopes have been replaced by more detailed
process-orientated models.
Slopes are examples of open systems. Inputs to the slopes include
energy, such as insolation, and mass, such as water and sediment.
Outputs from the system also include energy (reradiated heat) and
mass (water and regolith).

8. TOPICSUMMARY
Many slopes vary with climate. In humid areas, slopes are frequently
rounder, whereas in arid regions slopes are jagged or straight.
Geological structure is another important control on slope
development. This includes faults, angle of dip and vulcanicity.
Vegetation can decrease overland runoff through the interception and
storage of moisture. Deforested slopes are frequently exposed to
intense erosion and gulleying.
Slopes can be divided into those that are time-independent and time-
dependent slopes.
Mass movements include any large-scale movement of the Earth’s
surface that are not accompanied by a moving agent such as a river,
glacier or ocean wave.

10. TOPICSUMMARY
The types of processes can be classified by speed of movement, water
content, type of movement and material.
The most important factors that determine movement are gravity,
slope angle and pore pressure.
Slope failure is caused by two factors: a reduction in the internal
resistance, or shear strength, and/or an increase in shear stress, that is
the forces attempting to pull a mass downslope.
Surface wash occurs when the soil’s infiltration capacity is exceeded.

11. TOPICSUMMARY
Sheetwash is an unchannelled flow of water over a soil surface. Heave
or creep is a slow, small-scale process.
Falls occur on steep slopes (> 70°), especially bare rock faces where
joints are exposed.
Slides occur when an entire mass of material moves along a slip plane.
Slumps occur on weaker rocks, especially clay, and have a rotational
movement along a curved slip plane.
Avalanches are rapid movements of snow, ice, rock or earth down a
slope.

13. ADDITIONALWORK
1. ‘Climate is the main factor in slope development.’ Discuss.
2. Outline the factors that influence mass movement.
3. Explain how human activities can influence mass movements.
4. Describe and explain how the slopes found in humid temperate
areas differ from those found in semi-arid areas.
5. Examine the concept of slopes as open systems.
6. Outline a classification of mass movements.
7. Describe and explain the concepts of shear strength and shear
resistance.
8. Outline the natural and human causes of landslides. Use examples to
support your answer.

14. SUGGESTEDWEBSITES
www.physicalgeography.net/fundamentals/10x.html for the
Fundamentals of Physical Geography e-book.
http://uregina.ca/~sauchyn/geog221/slope.html for some basic
information on slope processes.
http://wps.prenhall.com/esm_keller_introenvgeo_2/3/1010/258563.
cw/index.html for environmental geology. Click on ‘Understanding the
Concepts’ and ‘Applying the Concepts’ on the left to try the multiple-
choice quizzes (some of the questions are difficult); see also ‘Web
Essays’.