1. Mass Wasting
Erosion
Soils
Weathering

2. Weathering: Regolith: Soil: the upper-most layer of
the physical and chemical
breakdown of rock – exposed to wind, water, ice, and living organisms
Regolith:
loose or broken rock layers
resulting from weathering
Regolith covers most of the earth.
Soil:
the upper-most layer of
regolith that supports life

3. Do “things” last for ever ? Consider :
new concrete
a 1955 Chevrolet

4. Rocks can be broken down or chemically altered on the earth’s surface.
Mechanical Weathering:
Rocks are physically broken down by various
surface processes into smaller parts without
changing physical properties.
Chemical Weathering:
Rocks are altered from one form to a
completely new form with a different
set of physical properties.

5. I weathering Discuss with a friend: Describe the difference between
mechanical and chemical weathering.
2. Give two examples of MW and CW you
have observed.
I will get an A on my exams and quizzes

6. Rock Mechanical Weathering – the breaking down of rocks
How do we expose “more surface” area for chemical
weathering to do its job ?
Let’s show some surface
Rock
More surface area
Less surface area
Increased mechanical weathering accelerates
chemical weathering.

7. Frost Wedging Repeated cycles of freezing and thawing.
Ice expands 9% of its volume.
Rock is continually broken
down over geologic time
Part of the Yosemite
weathering cycle.

8. Frost Wedging – rocks are broken into
plates and split apart.

9. Exfoliation unloading of overlying rock material releases pressure
expansion of granitic bodies
causing “sheeting” or slabbing
granite
granite “sheets” break along
planes of weakness or joints
exacerbated by frost wedging
dominant weathering force
in Yosemite

10. Exfoliation Dome – granite is
“sheeting” from loss of pressure due
to unloading processes.

11. Types of Mechanical Weathering Processes
Biological Activity – breaking down rocks through
animal burrowing
humans
plant roots
Human intervention
Animal burrowing
Plant root weathering

12. I mechanical weathering Discuss with a friend: 3. Why is MW important?
4. Briefly describe how frost wedging,
unloading and biological activity
contributes to mechanical weathering
I will get an A on my exams and quizzes

13. Chemical Weathering Rocks are chemically altered producing a new
compound
Why would a perfectly good rock want to change
it’s appearance?
STABILITY! Rocks require stability and achieve
equilibrium with it’s surroundings
Most rocks are not chemically stable at the
earth’s surface
Minerals (compositions) change to become stable
at surface conditions

14. What common agent can begin the process of chemical alteration?????
The Universal Solvent – WATER (H2O)
How would we speed up the action of water? Rain + ?????
What in the atmosphere is added to water to create a weak acid?
H2O (rain) + CO2 (atmosphere) = H2CO3 (carbonic Acid)
Let’s weather some granite with the natural acid H2CO3
Granite – the most abundant continental rock
weathering the potassium feldspar (orthoclase)
bicarbonate
potassium
silica
orthoclase
carbonic acid
water
kaolinite clay
2KAlSi2O8 + 2(H+ + HCO3) + H2O Al2Si2O5(OH)4 + 2K + 2HCO3 + 4SiO2
Granite has been
chemically weathered
and broken down into
individual grains.
in solution

15. Reduced to Clay

16. I Chemical weathering Discuss with a friend:
5. What is the universal solvent?
6. How is carbonic acid naturally
Produced?
7. How would you describe the “last” or
most reduced material the end
product of chemical weathering?
I will get an A on my exams and quizzes.

17. Soil – product of weathering containing solids,
liquids, and gas.
CLAY
What’s in your soil?
Loam – dominant soil fraction
Humus – partially decayed
organic material
CO2/Air – fills the soil voids
Water – wets the soil
and carries high
levels of dissolved
substances
SAND
SILT
50% sand, 20% silt, 30% clay
Sandy Clay Loam

18. Soil Profiles: O A E B C horizons: a layer of soil with
distinctive physical and chemical
properties.
sequence of soil horizons from
the surface to the underlying
bedrock O A
O- Organic matter (humus) E
A- Dark layer mixed with mineral
and organic matter B
E- light colored layer produced
from removal of soluble material
“leaching” C
B- accumulation of clay
C- unweathered parent rock

19. Factors that influence soil formation:
Parent Material:
residual regolith – soil forms emplace or “insitu”
Soil forms and
weathers emplace
from parent
material.
transported regolith – regolith that is moved by rivers,
wind, and ice
transported river
deposits
transported
regolith on Mars

20. Factors that influence soil formation:
Climate – soil profiles differ around the world
which is directly influenced by climate
arid soils vs. tropical soils
Living organisms – a HUGE influence on soils
Plants make organic matter.
(humus) – animals mix the soil
and recycle air and water.
Topography – the contour or “slope” of the land
Time – the longer the time the more mature a
a soil becomes ’s of years

21. Classification of soils
Soil Taxonomy – Soil classification is based on physical/chemical properties
of a soil profile, influenced by climate, living organisms,
topography, and time. --- How many different soils are there?
Six categories of soil classification:
order
sub-order
great groups
sub groups
family
series
Broadest
12-basic soil orders:
Names of soils are derived from Latin/Greek.
Latin = solum – soil
Alfisols (High-Nutrient Soil)
Andisols ((Volcanic Soil)
Aridisols (Desert Soils)
Entisols (New Soils)
Gelisols (Permafrost Soils)
Histosols (Organic Soils)
Inceptisols (Young Soils)
Mollisols (Prairie Soils)
Oxisols (Tropical Forest Soils)
Spodosols (Conifer Forest Soils)
Ultisols (Low-Nutrient Soil)
Verisols (Swelling Clay Soil)
12-orders
Specific
19,000 -series

22. What soil type (order) characterizes the
Distribution of Earth’s soils
What soil type (order) characterizes the
San Joaquin Valley?
Alfisols

23. Mass Wasting

24. Mass Wasting
What do these pictures have
common?

25. GRAVITY What is Mass Wasting ? down-slope movement of rock,
regolith, and soil under the direct
influence of GRAVITY
What force acts alone – to create
movements of the earth?
GRAVITY

26. The role of Mass wasting– What’s it good for?
Responsible for the evolution of
landforms – features of the earth
Weathering weakens rock – does
not create significant landforms
Need mass wasting to impact
weathering and shape significant
earth features

27. I mass wasting Discuss with a friend: 8. What is mass wasting ?
9. What single “force” acts alone to
produce mass wasting processes?
10. What is the sole purpose of mass
wasting?
I will get an A on my exams and quizzes.

28. So, what “triggers” a mass
wasting episode allowing gravity to
move the mass downward?
The role of water
Slopes to steep
Removal of vegetation
Earthquakes

29. The Role of Water
Saturated Sand

30. The Role of Water Water saturates surface materials.
Particles loose their cohesion (can’t
stick together).
Particles slide past one another and
slip downward under gravity forces.

31. steeper slopes exceed the “angle of
Slopes to Steep
steeper slopes exceed the “angle of
repose” and material moves downward to
stabilize or reach equilibrium.
Angle of repose:
the angle at which particles are overtaken by
gravity and move downward
angle depends on size, shape, and moisture content
of accumulated particles
Wet Sand
Dry Sand

32. Over steepening exceeding the angle of repose, nature
reacts by attempting equilibrium

33. Removal of Vegetation where plants are lacking – mass wasting
attacking
root systems bind soil
where soil is removed frequent
down slope movements occur

34. The Role of Earthquakes
Areas that have not moved in “years”,
are activated by seismic waves.
Mass slide produced by an earthquake
dammed a river forming a lake.

35. How would you describe the angle of repose?

36. I Mass Wasting Discuss with a friend:
11. Describe the 4 triggers that enable
mass wasting process.
12. What the angle of repose?
13. What is the most dominant “trigger”
causing the onset of mass wasting?
I will get an A on my exams and quizzes

37. How do geologists classify various mass wasting processes?
Classification is based on
Unconsolidated:
debris, mud, earth
Material
Bedrock:
rock
Fall: freefall of material
Slide: material moves cohesively along
well defined surface
Flow: material moves down-slope as
a viscous fluid
Motion

38. I Mass Wasting. Discuss with a friend:
14. What two criteria do geologist use to
classify mass wasting movements?
I will get an A on my exams and quizzes

39. Mass Wasting Processes
Classification of
Mass Wasting Processes

40. SLUMP downward movement of a sliding
mass, rock or unconsolidated material
that moves as a single unit along a
curved surface
moves very slow
over-steepened slopes (T)
water saturated (T)

41. Rockslide Debris slide blocks of bedrock break loose and slide
down a slope
Over steepness (T)
Debris slide
unconsolidated material break loose and
slide down a slope
Debris slide
Rockslide

42. Debris Flow rapid mass movement containing soil
and regolith with large amounts of
water
Water saturation (T)

43. Lahars debris flows composed largely of volcanic
material from the flanks
flows down existing stream valleys
extremely destructive events’
water saturation (T)
Lahars buried
a village

44. Earth Flow form on hillsides in humid areas with
abundant precipitation
water saturated – hill may break away
under gravity and weight of soil
water saturated (T)
rich in clays and silt
slow moving flows

45. Soil Creep the gradual downhill movement of soil and regolith.
soil moves extremely slow
soil disturbed by rain, roots
water saturation (T)