1. Changing Earth’s Surface
Mass Movement

2. RATES OF WEATHERING Factors of Rates of Weathering
1. Parent Material (The rocks themselves) - Igneous and metamorphic most resistant, sedimentary least resistant because of pores.
2. Surface Area
3. Climate - Warm and wet = chemical weathering
Cold and Dry = mechanical weathering

3. Risk factors to increase likelihood of mass movement
Gravity - hill slopes more vulnerable (on top of a hill, on the slope, or at the bottom of a hill), modified slopes (road cut, cut flat area to build on, coastal erosion, etc.)
Water - risk is higher when ground is saturated and/or during heavy rains, El Niño events
Earth Materials - loose soils (particularly clay-rich) or fractured rock, and old landslides pose greater risk
Triggering Events - heavy rain during storm, rain after big storms or fires, earthquakes (when ground is saturated?)…are all triggers

4. EROSION
EROSION - The breakup and removal of rock by moving natural agents (rivers, glaciers, wind, water)

5. Mass Movements
General term used for rock fragments moving down a slope
What is causing this erosion to occur?
Can happen either fast or slow.

6. Toppling Failure
TOPPLES: Toppling failures are distinguished by the forward rotation of a unit or units about some pivotal point, below or low in the unit, under the actions of gravity and forces exerted by adjacent units or by fluids in cracks

7. Rockfall - Rocks falling from a steep cliff
Rockfall - Rocks falling from a steep cliff. This is the most rapid type of mass movement.

11. Talus Slopes - Large piles of rock that break off and pile up at the bottom of a hill

13. Debris flows or mud flows
Mass movements that behave like fluids
Unlike slides, flows are not controlled by a failure surface, but instead are dominated by internal movements

14. Debris flows or mud flows
Factors that allow the force of gravity to overcome the resistance of earth
material to landslide movement include:
saturation by water
steepening of slopes by erosion or construction
alternate freezing or thawing
earthquake shaking
volcanic eruptions

15. Landslides Sudden movement of masses of loose rocks. Triggered by:
Earthquakes
Rainfall
Thaws
Volcanoes

16. magnitude 7.1? West Yellowstone
11:37 am on August 17, 1959
magnitude 7.1? West Yellowstone
Produced waves in Hebgen Lake
that swept over dam
Triggered landslide of
85 million tons of rock
Sped downslope at 150 km/hr
and produced hurricane force winds
• cars blown into air
• valley floor covered by 45 m
of rubble
• 28 people (campers) were
killed
Madison Canyon slide

23. Mudflow - Fast movement of large masses of mud.
Occur in dry, mountainous regions during fast, heavy rainfalls or volcanic eruptions

28. Creep - very slow down hill movement of weathered rock material.
Usually goes unnoticed unless it hits a building or something.
Creeps can include rocks, plants, buildings, etc.

30. MASS MOVEMENTS Speed of movement and water flow.
On left have mass movement speed versus moisture content.
On right have rates of travel for mass movements

31. water: two effects 1) small amounts of water
• glues particles by surface tension--”sand castles”
2) excessive amounts of water
• reduces friction between surface
material and underlying rock
• counteracts normal component
of gravity
…water pushed upward…

32. Water decreases rock/soil cohesion

33. Water decreases rock/soil cohesion

34. Water decreases rock/soil cohesion
Water circulating underground can dissolve cements
that hold sedimentary rocks together

35. The Weight of Water
Sedimentary rocks commonly have porosities of %
If pore spaces fill with water, the weight of the material is increased substantially, creating instability

36. SOILS Soils - soil science = PEDOLOGY
Most important result of weathering and erosion is soil
Two general classes of soil: A. residual soil - soil made from local bedrock B. Transport soil - soil that was moved by wind, or glacier

37. Factors determining soil makeup and Formation
1. Climate - Rainfall amount and temperature (most important)
2. Parent Rock - Type and chemical composition
3. Vegetation - Roots and Leaves
4. Topography - hilliness, etc.
5. Time - how long to develop

38. vegetation …removal (by fire or clear-cutting) leads to mass movement
roots stabilize loose, unconsolidated material
…removal (by fire or clear-cutting) leads to mass movement

39. prevention
water, weight of house, road cut

40. improve drainage -- leads to less creep

41. modify slopes (where layering dips into roadway)