1. September 29 Course Website: http://glg110.asu.edu Today: Chapter 8 Mass Movements

2. GLG 110 Fall 2003 Overview Mass Wasting Definitions Slope Processes Slope Stability Types and Examples of Mass Movements Human Activity and Landslides Minimizing the Hazard

3. GLG 110 Fall 2003 What examples of mass movements can you think of? Land slides Mud slides Avalanche Slump and creep Where in the US do we hear about landslides?

4. GLG 110 Fall 2003 Landslide hazard map, USA

5. GLG 110 Fall 2003 Definitions Mass Wasting = comprehensive term for any type of downslope movement of Earth materials –More precisely = downslope movement of rock or soil all together Includes: –Landslides, earthflows, mudflows, rockfalls, debris and snow avalanches, and subsidence

6. GLG 110 Fall 2003 Mass Wasting Downslope movement of rock, regolith, soilDownslope movement of rock, regolith, soil Force of gravity dominatesForce of gravity dominates Often initiated by heavy rainfall or earthquakeOften initiated by heavy rainfall or earthquake Distinct from erosional processesDistinct from erosional processes Follows weatheringFollows weathering Mass-wasting + running water = stream valleysMass-wasting + running water = stream valleys Mass wasting & erosion sculpt Earth’s surface

7. GLG 110 Fall 2003 Slope Processes Slopes are the most common landforms Most appear stable but really are dynamic and evolving –Material on slopes is constantly moving Slope form depends on: –Underlying rock type –Climate –Regional tectonics –Regional drainage pattern

8. GLG 110 Fall 2003 Slope Processes Concave Slope Cliff Face Straight Slope Hard Granite Weak Rock Soil Talus Slope (rock fall debris)‏ Convex Slope Note – the slopes on this figure in your text are mislabeled!

9. GLG 110 Fall 2003 Slope Stability Slope = how steep the inclination of the hillside is Slope stability depends on the driving and resisting forces that act on the slope –As angle of slope increases, driving forces increase

10. GLG 110 Fall 2003 Slope Stability Image: University of Minnesota Gravity Weight of Material Friction Upward force of supporting materials Driving ForcesResisting Forces Driving Forces and Resisting Forces Driving forces move material down the slope (Most common = weight of slope material, vegetation, and structures on slope)‏ Resisting forces oppose downward movement (Most common = strength of slope material)‏

11. GLG 110 Fall 2003 Slope Stability Slope stability is evaluated by computing safety factor Safety Factor = ratio of resisting forces to driving forces –If S.F. > 1 the resisting forces are stronger and the slope is stable –If S.F. < 1 the driving forces are stronger and the slope is unstable Resisting Forces Driving Forces S.F. =

12. GLG 110 Fall 2003 Slope Stability Slope stability changes over time as conditions change causing ratio to change Driving and resisting forces are determined by interactions between: –Type of earth materials –Slope angle and topography –Climate –Vegetation –Water –Time

13. GLG 110 Fall 2003 Role of Slope Material Affects type of mass movement –Shale or weak volcanic material slopes tend to creep, flow, or slump Affects falls when strong, resistant rock is underlain by weak, easily erodable rock, can result in undercutting and subsequent rock fall

14. GLG 110 Fall 2003 Role of Slope Material Affects type and frequency of slides Patterns of movement: –Rotational = occurs along curved slip surface, produces terrace-like structures –Translational = planar, along slip planes within the slope Slip planes include fractures, layers, bedding planes, foliation, etc.

15. GLG 110 Fall 2003 Role of Slope & Topography Angle of Repose = maximum angle at which unconsolidated material on slope is stable ~30-35° The larger and more uniform the size of fragments the steeper the angle of repose Controlled by: –Coarseness, shape, size and uniformity of size of fragments –Water content Steep slopes often associated with rockfalls and debris avalanches

16. GLG 110 Fall 2003 Role of Climate Climate = characteristic weather at specific place over time Includes: –Average temperature –Amount and timing of precipitation Which then infiltrates slope thus affecting stability Affects vegetation which influences slope stability –Seasonal weather patterns Common mass movements in arid and semiarid regions = fall, debris flow, shallow slips

17. GLG 110 Fall 2003 Role of Vegetation Vegetation is a function of climate, soil type, topography, and fire history Can increase or decrease the chances of mass movement –Shields soil thus mitigates runoff during heavy precipitation –Roots help fix soil in place –Adds weight to the slope In subhumid to humid areas vegetation is abundant, thick soil develops so mass movements = complex landslides, flows, and creep Image: Geolith Consultants

18. GLG 110 Fall 2003 Role of Water Almost always directly or indirectly involved with mass movements Water fills pore spaces between sediments, reduces internal resistance, adds weight Affects: –Decreasing stability when slope becomes saturated –Slumps or slides can occur years after deep water infiltration –Can erode base or toe of slope decreasing stability

19. GLG 110 Fall 2003 Role of Water Water & Erosion –Stream or wave erosion may remove material creating steeper slope thus reducing safety factor May reactivate old landslides Liquefaction –Some clays behave as liquid and flow when disturbed Does not always require earthquake, can occur through toe erosion

20. GLG 110 Fall 2003 Role of Time Forces on slopes often change with time –Driving and resisting forces can change seasonally as water content changes Chemical weathering introduces elements into soils which change properties A slope that is becoming less stable with time may exhibit increasing creep until failure occurs

21. GLG 110 Fall 2003 Types of Mass Movements Important variables in classifying downslope movement of Earth materials are: –Types of mass movements slide, slump, fall, flow, subsidence, or complex –Slope material –Amount of water –Rate of movement

22. GLG 110 Fall 2003 Carson and Kirby, 1972 in Ritter, et al., 2002 Classification of Mass Movements based on water content and speed of movement Types of Mass Movements

23. GLG 110 Fall 2003 Carson and Kirby, 1972 in Ritter, et al., 2002 Types of Mass Movements Slide/ Fall

24. GLG 110 Fall 2003 Types of Mass Movements Slide = downslope movement of coherent block of Earth material

25. GLG 110 Fall 2003 Types of Mass Movements Blackhawk Landslide, California Started as slide Rode on blanket of air Was pulverized when hit the base of slope Created debris blanket 10-30 m thick

26. GLG 110 Fall 2003 Types of Mass Movements Fall = free fall of Earth material Image: USGS/Lloyd DeForrest Yosemite National Park, California

27. GLG 110 Fall 2003 Rock falls and rock slides

28. GLG 110 Fall 2003 Rock falls Falls are the free-fall of pieces of rock from a mountain or cliff face. On mountains, ice wedging is the main contributor. As water from snowmelt finds its way into the cracks and joints of the rock face, it may refreeze and being to expand. This expansion widens the cracks in the rock. Over time, the cracks have been widened enough so that they are a point of structural weakness.

29. GLG 110 Fall 2003 Image: NOAA Types of Mass Movements Debris Avalanche = very rapid downslope movement of soil, rock, & organic debris In <2 minutes 40 million cubic yards of rock covered the town of Frank, Alberta, Canada, in 1903

30. GLG 110 Fall 2003 Types of Mass Movements Avalanche –Rapid downslope movement of snow and ice sometimes with rock, soil, and trees –Often begins with slab weighing millions of tons, falling from an overloaded slope –Can travel as much as 62 mph –Tend to travel down chutes where previous avalanches have flown

31. GLG 110 Fall 2003 Carson and Kirby, 1972 in Ritter, et al., 2002 Types of Mass Movements Flow

32. GLG 110 Fall 2003 Image: USGS Types of Mass Movement Lahar = mudflow produced when large volume of volcanic ash and ejecta becomes saturated with water Armero, Nevado Del Ruiz, 1985

33. GLG 110 Fall 2003 Image: NOAA Flow = downslope movement of unconsolidated Earth material saturated with water –particles within also move with respect to each other Mudflows (or debris flows) are rivers of rock, earth, and other debris saturated with water. Types of Mass Movements Debris Flow = >50% of particles coarser than sand Mudflow = >50% of particles finer than sand

34. GLG 110 Fall 2003 Slumgullion mudflow, San Juan Mtns., Colorado

35. GLG 110 Fall 2003 Types of Mass Movement Rock Glacier = mass or rock and ice frozen together and flowing downslope Image: NOAA Mt. Sopris, Colorado

36. GLG 110 Fall 2003 Carson and Kirby, 1972 in Ritter, et al., 2002 Types of Mass Movements Creep/ Heave

37. GLG 110 Fall 2003 Types of Mass Movements Creep & Heave = slow, ~imperceptible downslope movement of unconsolidated Earth material –Often related to seasonal effects and/or precipitation rates Slow Flow Image: NOAA

38. GLG 110 Fall 2003 Carson and Kirby, 1972 in Ritter, et al., 2002 Types of Mass Movements Slump/ Subsidence

39. GLG 110 Fall 2003 Image: NOAA Types of Mass Movements Slump = rock or soil moving downslope along curved slip plane producing slump blocks Black Hills, N.D.

40. GLG 110 Fall 2003 Types of Mass Movements Subsidence = sinking of mass of Earth material below level of surrounding material –can occur on slopes or flat ground Image: NOAA San Joaquin Valley, California

41. GLG 110 Fall 2003 Types of Mass Movement Subsidence can occur as a result of: –Withdrawal of groundwater –Withdrawal of oil and gas –Dissolution of limestone –Mining (coal, ore, salt)‏ See Lake Peigneur example in book Subsidence can cause earth fissures and sinkholes

42. GLG 110 Fall 2003 Carson and Kirby, 1972 in Ritter, et al., 2002 Types of Mass Movements Complex Landslide

43. GLG 110 Fall 2003 Types of Mass Movements Landslides occur when masses of rock, earth, or debris move down a slope. They may be very small or very large, and can move at slow to very high speeds. However slow movement is also seen in the gradual downhill creep of soil on gently sloping land. La Conchita, California, 1995

44. GLG 110 Fall 2003 Image: USGS La Conchita Complex Landslide Image: USGS

45. GLG 110 Fall 2003 Aerial photos of complex landslide at La Conchita, California Do you see the landslide scarp? La Conchita Complex Landslide 19271967

46. GLG 110 Fall 2003 Aerial photos of complex landslide at La Conchita, California Do you see the landslide scarp? La Conchita Complex Landslide 19271967

47. GLG 110 Fall 2003 Note how quickly the vegetation is returning and how it helps conceal the slide scar La Conchita Complex Landslide 1998 Image: Jeffrey J. Hemphill

48. GLG 110 Fall 2003 Types of Mass Movement: Soil creep A very, very slow form of mass wasting. The effect is the way the grass covered slope seems to ooze downhill forming little bulges in the soil. This heaving of the soil occurs in regions subjected to freeze-thaw conditions.

49. GLG 110 Fall 2003 Mass movements are caused by various conditions: Volcanic activity many times causes huge mudflows when the icy cover of a volcano melts and mixes with the soil to form mud as the magma in the volcano stirs preceding an eruption. Mudslides can also develop when water rapidly accumulates in the ground, such as during heavy rainfall or rapid snow melt, changing the earth into a flowing river of mud or "slurry.". Earthquake shocks cause sections of mountains and hills to break off and slide down.

50. GLG 110 Fall 2003 Mass movements are caused by various conditions: (cont.)‏ Human modification of the land or weathering and erosion help loosen large chunks of earth and start them sliding downhill. Vibrations from machinery, traffic, weight loading from accumulation of snow; stockpiling of rock or ore; from waste piles and from buildings and other structures. However, the force behind mass movements is the gravitational pull of the earth on soil, rocks, and mud.

51. GLG 110 Fall 2003 Effects of human activities The rock slide that covered the town of Frank, Alberta, Canada on April 29, 1903 was in part caused by human activities. The sedimentary rock layers in Turtle Mountain dipped away from the valley containing the mining town of Frank. However, joints in the limestone layers did dip toward the town. The mountain was also composed of some structurally weak limestone, shale, siltstone, and coal layers that were deformed by the weight of more massive limestone located above. The mining of coal at the Turtle Mountain's base reduced the support to overlying materials. Together these factors lead to the sudden movement of 33 million cubic meters of rock in approximately two minutes.

52. GLG 110 Fall 2003 Project: You are a concerned land owner in Malibu, CA. You own a nice little beach house near the beach. Developers have been building mansions on the hillside behind your property. Write a letter to the building commissioner with your concerns for your property. List the reasoning for your concerns. Explain how the hillside development could effect you. Give an example of what could eventually happen (use a real example from your text). Should be at least 5 sentences in the format of a letter.