Mass Movements Wasting 2 Presented By Dr Rahul

Mass Movements/ Wasting 2 Presented By Dr. Rahul Pardeshi

4 Contents Introduction Effects Controls of mass wasting Causes of mass wasting Classification Types of mass wasting Preventions Destruction by Mass Wasting Conclusion Reference

5 Mass Wasting “It is downslope movement of masses of bedrock, rock debris, regolith or soil, under the direct influence of gravity”

Mass Wasting 6 The downslope transfer of material through the direct action of gravity Component of erosion and transport of sediment Follows weathering, which weakens and breaks the rock

7 Effects Of Mass Wasting The combined effects of mass wasting and running water produce stream valleys, which are the most common and conspicuous of Earth’s landforms. If streams alone were responsible for creating the valleys in which they flow, the valleys would be very narrow features. Most river valleys are much wider than they are deep, is a strong indication of the significance of mass-wasting processes in supplying material to streams.

8 Effects of Mass Wasting Mass movements affect the following elements of the environment The topography of the earth's surface, particularly the morphologies of mountain and valley systems, both on the continents and on the ocean floors The character/quality of rivers and streams and groundwater flow The forests that cover much of the earth's subaerial surface Habitats of natural wildlife that exist on the earth's surface, including its rivers, lakes, and oceans.

9 MASS WASTING SLUMP NEAR BISMARCK, N. d

12 Controls of Mass Wasting Gravity Angle of repose Water Time Type of material Climate Vegetation

13 Role of Gravity causes the downward movement of rock body R A If gravity pull is greater than resistive force then body will move downward R A

14 Forces due to gravity Two opposing forces determine whether the body will remain stationary or will move. These two forces are shear stress and shear strength. Shear Stress force acting to cause movement of a body parallel to the slope. There are two components of gravity: (a) Perpendicular component (acts at right angles to the slope) (b)Tangental component (acts parallel to the slope)

15 Forces due to gravity As the slope becomes steeper, the tangental component of gravity increases relative to the perpendicular component and the shear stress becomes larger. Shear Strength internal resistance of the body to movement. This internal resistance includes: (a) frictional resistance (b) cohesion between particles (c) binding action of plant roots

Angle of repose 16 Steepest angle at which material remains stable Depends upon Particle size Particle shape Moisture Content Angle varies from 25 to 40 degrees Larger and more angular particles maintain steepest angle Small and round particles do not maintain steep angle

19 Role of Water Sedimentary rocks commonly have porosities of 10 30% If pore spaces fill with water, the weight of the material is increased substantially, creating instability

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21 Role of Time Physical and chemical weathering can weaken slope materials decreasing resisting force. This causes the rock to become very weak and mass wasting occurs

22 Role of Earth Materials Weak rocks(sedimentary) will weather quickly than hard rocks(igneous, metamorphic)

23 Role of Climate plays a vital role in weathering of material Climate influences the amount and timing of water in the form of rain or snow Influences type and amount of vegetation

24 Role of Vegetation Plant roots provide a strong interlocking network to hold unconsolidated rocks and sediment Vegetation removes moisture from the soil

25 ROLE OF TREES IN STABILITY

26 Causes Of Intstability Factors that either weaken cohesion forces or increase downslope force 1. Heavy rainfall 2. Over-steepening of the slope 3. Slope Modification 4. Ground vibrations 5. Expansion/contraction cycles of soil/regolith

28 Over-steepening of the Slope Can be human-induced or by natural processes – increases the downslope force. Stream undercutting a valley wall (headward erosion, bank erosion, etc. ). Waves cutting cliffs on a shoreline. Construction of roads, buildings, homes etc.

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30 Slope Modification Removal of Vegetation Roots of plants and trees hold regolith together Plants and trees remove water from the soil Removal decrease cohesive force Building of structures decrease in cohesive force or increase downslope force due to added weight will cause movement

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32 Ground Vibrations Earthquakes – triggers the rock and initiates its movement Human induced – blasting for construction, large equipment, etc.

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40 Types of Mass Wasting Slump Rockslide Mudflow (Lahar, Debris Flow) Earthflow Creep Permafrost & Solifluction

41 Slump Downward slipping (slide) of a mass of rock or unconsolidated material moving as a unit Rock or unconsolidated material move in a curved path Does not move very fast or far away May be single or multiple blocks Caused by overloading, excess of water, over steeping, removal of anchoring material

Slump (a type of slide) 42 Indicators: Scarp earthflow Anchoring material

43 Rockslide Sliding of blocks of bed rock along a defined slippage plane Sudden, rapid and destructive movement Takes place where rock strata are inclined(steep slopes), joints or fracture exist parallel to slope, underlying layer is thin layer of clay or river cut the anchoring material Can be triggered by rain falls or ground vibration

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45 Mudflow Rapid movement of debris containing large amount of water Water get mixes with rock debris, soil or regolith and forms a mud which flow downward stream or mountain Characteristic of semiarid mountainous area Caused when snow melts quickly creating a flood or cloud burst rapidly Mudflow is of two types: Lahar Debris Flow

46 Lahar WHEN debris flows composed mostly of volcanic materials on the flanks of volcanoes are called lahars. Unstable layers of ash and debris becomes saturated with water They can occur either during an eruption or when a volcano is quiet. They cause mass destruction of land life.

47 Debris Flow Mixture of rocks debris or soil & water Moves as a viscous fluid Common after heavy rains Rapid movement – up to 50 km/hr, the more water present the faster the rate of movement Common in semi-arid regions and along volcanoes (lahars)

48 Earthflow A type of debris flow, generally move slower Forms on hillside humid areas as a result of excessive rainfall Water saturates the clay-rich regolith and material break away and flow a short distance downslope Speed of earthflow vary from few meters per hour to several meters per minutes Can remain active over periods of years

49 Creep Gradual downslope movement of soil or regolith– mm/yr Expansion/contraction, freezing/thawing or wetting/drying cycles play a key role Process so slow one cannot observe it in action Enhanced by burrowing organisms, periods of prolonged rains or snow,

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51 Permafrost Layer of permanently frozen ground, known as permafrost, occurs where summers are too cool to melt more than a shallow surface layer It refers to the permanently frozen ground that occurs in climates in which annual air temperature is low enough to maintain a continuous surface temperature below 0 C Depth to which water freezes exceeds the depth of summer thawing The water in soil underlining does not melt

Solifluction 52 Special type of creep Occurs in regions underlain by permafrost (permanently frozen, water-bearing ground) During warm periods top portion (active layer) thaws and becomes saturated Melt waters are unable to percolate into permafrost layer below Saturated (active) layer flows over frozen layers It can occur on slopes as gentle as 2 -3 degree

53 SOLIFLUCTION In mat of vegetation Solifluction move downward in welldefined lobes or overriding folds

Destruction caused by mass 56 wasting year 1916 1920 1945 1949 1954 1962 1963 1970 1985 1987 Location Italy, Austria China Japan USSR Austria Peru Italy Peru Columbia Ecuador Type Landslide Earthquake triggered landslide Flood triggered landslide Earthquake triggered landslide Landslide Earthquake related debris avalanche Mudflow related to volcanic eruption Earthquake related landslide Fatalities 10, 000 200, 000 1, 200 12, 000 -20, 000 200 4, 000 -5, 000 2, 000 70, 000 23, 000 1998 Nicaragua Debris avalanche and mudflow tirggered by heavy rains during Hurricane Mitch ~2, 000 2001 El Salvador Earthquake-induced landslide 585 2006 2009 2010 2013 Philippines Taiwan Gansu, China Northern India Rain triggered debris avalanche Typhoon Marakot triggered landslide Rain triggered mud flows Heavy rain triggered landslides >1100 397 1287 5700

57 Conclusion Mass wasting is the movement of earth material under influence of gravity It is responsible for shaping the earth and forming different land forms It causes destruction to humans beings if it occurs in living areas