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Landslides !. Mass Wasting Downslope movement of earth materials Generally gravity driven Generally result from undercutting of a slope – Either natural.

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Presentation on theme: "Landslides !. Mass Wasting Downslope movement of earth materials Generally gravity driven Generally result from undercutting of a slope – Either natural."— Presentation transcript:

1 Landslides !

2 Mass Wasting Downslope movement of earth materials Generally gravity driven Generally result from undercutting of a slope – Either natural or human induced Landslides – General term for all types of mass wasting Not to be confused with mass wasted…

3 Landslide Factors Steepness of slope – Steep slopes are generally unstable Vegetation – Roots hold soil together and absorb water – Vegetated slopes generally more unstable than non-vegetated

4 Landslide Factors Continued... Water – Sandcastle analogy Nature of unconsolidated stuff – Angle of repose— maximum slope at which loose material remains stable – Higher for angular rocks

5 Landslide Factors Continued... Type of rock and orientation of rock layers – Sedimentary rocks dipping in same direction of slope = bad – Sedimentary rocks dipping in the opposite direction of slope = good

6 Landslide Factors Continued... Earthquakes and volcanoes – Earthquakes can destabilize slopes – A volcanic eruption can melt glaciers at summit—creating a landslide

7 “You’re just my type.” Flow – Loose, unconsolidated sediment/soil moves in a fluid-like way Slide – Movement of a coherent block of material along a fracture Fall – Rapid, free-fall motion

8 Types of Mass Wasting

9 Flows Creep – Slow downhill flow of rock or soil under the influence of gravity – Very slow—1cm/yr – Shallow stuff moves more quickly than deeper stuff – Pistol butt trees and leaning fences Natural creep Human creep…

10 Flows: mudflows A flow composed entirely of fine-grained sediment Lobe shaped deposits Can be wicked fast—60mph Two types – Lahar—volcanic ash mobilized by water – Jokulhlaup—large release of water from a sub- glacial lake

11 The Armero Tragedy Armero, Columbia: 1985 Small eruption from nearby volcano, Nevado del Ruiz melted the glacier on top of the volcano Water from the glacier mixed with volcanic ash creating a lahar “People can evacuate if they feel like it…” ~29,000 people killed 80 yrs previous, town buried by mud flows

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13 Slides Slump – Occurs when blocks of material slide downhill over a curved fracture – Rotated trees – Jumbled, hummocky front Rockslide ( aka rock avalanche – Bedrock slides downslope over a fracture plane – Breaks up—jumbled chaotic mess of rock – Fast 500 km/hr

14 Rockfall Individual blocks plummet in a free fall from a cliff or steep mountainside

15 Lituya Bay, Alaska: Rock Fall Example July 9, 1958 – 8.0 earthquake on Fairweather Fault – Rock fall (slide?) from face of Gilbert Inlet slams into Lituya Glacier removing 1,300 ft (1km fall)

16 Total volume = 30 million m 3 – Wave was generated 1720’ tall (525m) which swashed back and forth due to the Bay’s shape – 100 ft (30m) tall when reaches inlet

17 Out of 6 boaters in the bay, 2 killed, 2 tossed over the spit into the Pacific, two completely unharmed 8X greater than any tsunami Speed of wave mph

18 Lituya Bay Images Tsunami inundates 13 km 2 of woodland – Sharp line of tree inundation measure of wave height – Wave travels 1.1 km inland

19 Landslide Prevention: Intro Consequences of construction – Land more susceptible to mass wasting Undercutting—removing support for upper part of slope Vegetation removal Weight of buildings Irrigation—adding water

20 Landslide Prevention 1 Preventative measures – Retaining walls with drain pipes – Terraces – Planting fast growing grasses and shrubs – Sloping “sheds” or tunnels – Building roads in low landslide risk areas

21 Landslide Prevention 2 Radio-transmitted, real- time monitoring of areas that are prone to landslides – Especially places where roads might be affected Bedrock “stitching” – Basically drilling holes into bedrock and reinforcing with concrete and steel cable Education


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