Chapter 10 Landslides and Slope Failure 1 Mass

Chapter 10: Landslides and Slope Failure 1. Mass Wasting: The Human Impact 2. Factors Influencing Slope Failure 3. Slope Failure Processes Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

Learning Objectives • • Students will explain concepts related to slope failure. Students identify how weathering is related to mass wasting. Students will evaluate the factors that would increase or decrease the risk of landslides. Students will summarize the characteristics of slope failure processes.

Mass Wasting: The Human Impact “The term ‘natural disaster’ has become an increasingly anachronistic misnomer. In reality, human behavior transforms natural hazards into what would really be called unnatural disasters. ” - Kofi Annan, Secretary General of the United Nations Would you live here? The Good Earth/Chapter 10: Landslides and Slope Failure

Mass Wasting: The Human Impact If there is no human impact caused by a natural phenomenon, there is no disaster. Jan 10, 2005 – in a matter of seconds a 330 foot portion of the slope mobilized, flowed down, and buried homes and killed ten people. “It came down like lava down the mountains. It was explosive, like there was a stick of The Good Earth/Chapter 10: Landslides and Slope Failure dynamite in there. ” (resident of La Conchita)

Mass Wasting: The Human Impact Mass Wasting = the downslope movement of material under the influence of gravity. Thicker regolith is more likely to fail Landslide – a term used to describe many rapid forms of mass wasting Mass wasting is key in modifying landscapes in areas with significant topography Beartooth Mountains, southern Montana The Good Earth/Chapter 10: Landslides and Slope Failure

Mass Wasting: The Human Impact Where do you see the areas of highest risk for slope failure? What do those areas have in common? Orange and brown = high to moderate incidence Gold = high susceptibility but moderate incidence The Good Earth/Chapter 10: Landslides and Slope Failure

Mass Wasting: The Human Impact Self Reflection Survey Answer the following questions as a means of uncovering what you already know about landslides and slope failure. A. Are there places in your community that are characterized by steep slopes? Have landslides occurred there? The Good Earth/Chapter 10: Landslides and Slope Failure

Mass Wasting: The Human Impact Self Reflection Survey Answer the following questions as a means of uncovering what you already know about landslides and slope failure. B. Could Kofi Annan’s quote from slide 1 be applied to the events at La Conchita on Jan 10, 2005? Explain. The Good Earth/Chapter 10: Landslides and Slope Failure

Mass Wasting: The Human Impact Self Reflection Survey Answer the following questions as a means of uncovering what you already know about landslides and slope failure. C. Why do you think people choose to live in places like La Conchita, even after landslides? Ventura County has invested time and resources to clean up after both landslides at La Conchita. At what point is it fair for the taxpayers of the county to say, “Enough! Don’t use our money to bail out people who choose to live in a high risk area”? The Good Earth/Chapter 10: Landslides and Slope Failure

Go back to the Table of Contents Go to the next section: Factors Influencing Slope Failure The Good Earth/Chapter 10: Landslides and Slope Failure

Factors Influencing Slope Failure Gravity moves materials down a slope Friction acts to prevent or slow the movement of material down a slope • Steeper slopes are more likely to fail • Analogy – a slide on a playground − The steeper and smoother the slide, the faster you go Steep slopes in Sierra de Avila (Venezuela) allow material to wash into narrow canyons that funnel debris toward coastal cities. The bare patches are locations where landslides have occurred. The Good Earth/Chapter 10: Factors Influencing Slope Failure

Factors Influencing Slope Failure Gravity has two components (acts on an object in two directions): • Parallel to the slope (gs) • Perpendicular to the slope (gp) The steeper the slope the larger the component of gravity parallel to the slope, making it more likely the object will move downhill. The Good Earth/Chapter 10: Landslides and Slope Failure

Factors Influencing Slope Failure Water: A small amount of water holds grains together (cohesions) Dry sand slopes will fail above angles of about 35 degrees Too much water forces grains apart The Good Earth/Chapter 10: Landslides and Slope Failure

Factors Influencing Slope Failure Too much water promotes instability • Very wet sediment flows like a liquid • Excess water reduces cohesion between grains and allows them to move more freely • Adds weight to a slope • Water supports some of the weight of overlying material, reducing perpendicular force on slope and reducing friction that counterbalances gravity Example: Higher risk for landslides in Appalachian Mountains than in the western states where slopes are steeper. Why? More precipitation in eastern U. S. Addition of water to slopes with loose materials increases the likelihood of failure. The Good Earth/Chapter 10: Landslides and Slope Failure

Factors Influencing Slope Failure Venezuelan Landslides • The view from the Caribbean Sea − The mountains of the Sierra de Avila with the city of Caraballeda in the foreground View up a canyon from Caraballeda showing narrow canyon floor and steep sides The Good Earth/Chapter 10: Landslides and Slope Failure

Landslides and Slope Failure • What happened in Venezuela in 1999? − Unseasonable storms – 36 inches of rain on steep mountain slopes − A series of floods and landslides devastated communities along the coast and killed ~19, 000 people − The 3 -day rainfall total equaled the average annual rainfall in midwestern U. S. − Vegetation had shallow roots in the 10 ft thick soil/regolith − Cities were located on the only flat patches of ground – at the mouths of the narrow canyons, where material was funneled − Slurries of dirt, rocks, and water flowed at velocities of 6 -30 mph − Flows were fast enough to carry bus-sized particles The Good Earth/Chapter 10: Landslides and Slope Failure

Factors Influencing Slope Failure • 16 ft thick deposits on canyon floor • Caraballeda − Single story buildings were buried − Apartments partially collapsed − Over 140, 00 people homeless − Burial of main road impeded evacuation − Poor city planning, constructions standards, building inspections − Cost of damage $2 billion The Good Earth/Chapter 10: Landslides and Slope Failure

Factors Influencing Slope Failure • Human influence − Venezuela – very little urban planning − La Conchita – earlier slide blamed on overwatering of crops above the bluff − Italy 1998 – poor land management (deforestation) − Logging, forest fires remove protective vegetation List as many factors as you can that contributed to the debris flows in Venezuela in December 1999. The Good Earth/Chapter 10: Landslides and Slope Failure

Factors Influencing Slope Failure Checkpoint 10. 3 Venn Diagram: La Conchita vs. Caraballeda Landslides Use the Venn diagram to compare and contrast mass wasting events at La Conchita and Caraballeda. Write the features in the list at left, and place their corresponding numbers in either of the circles (depending on which landslide they refer to) or in the overlap (if they refer to both). La Conchita Caraballeda 1. Caused by excessive rainfall 2. Happened in an area with strict planning and construction standards 3. 4. 5. 6. 7. 8. 2 1 The Good Earth, Chapter 10: Landslides and Slope Failure

Factors Influencing Slope Failure Can we minimize slope failures? How? • Improve slope drainage • Attach the slope material to bedrock with physical restraints The Good Earth/Chapter 10: Landslides and Slope Failure

Go back to the Table of Contents Go to the next section: Slope Failure Processes The Good Earth/Chapter 10: Landslides and Slope Failure

Slope Failure Processes The Good Earth/Chapter 10: Landslides and Slope Failure

Slope Failure Processes Mass Wasting is characterized by type of material involved (rock versus regolith) and manner of movement. Rockfall – The dislodging of a rock from a steep slope. The Good Earth/Chapter 10: Landslides and Slope Failure

Slope Failure Processes Rockslides – Large-scale movements of rock traveling rapidly down a slope along a surface The Good Earth/Chapter 10: Landslides and Slope Failure

Slope Failure Processes Slump – The movement of material down a slope on a curved slip surface Debris Flow – Material flowing downhill as a chaotic mixture of soil, rock, and water The Good Earth/Chapter 10: Landslides and Slope Failure

Slope Failure Processes Checkpoint 10. 6 Examine the following diagram and answer the following questions. Assume that this diagram is from an area in the midwest (Illinois or Indiana). 1. The road cut in this diagram is likely to experience mass wasting by which process? a. Rockfall c. Slump b. Rockslide d. Debris flow The Good Earth/Chapter 10: Landslides and Slope Failure

Slope Failure Processes Checkpoint 10. 6 Examine the following diagram and answer the following questions. Assume that this diagram is from an area in the midwest (Illinois or Indiana). 2. If the swimming pool on the right side of the diagram leaks, the underlying dirt fill is likely to experience mass wasting by which process? a. Rockfall c. Slump b. Rockslided. D. Debris flow The Good Earth/Chapter 10: Landslides and Slope Failure

The End Go back to the Table of Contents The Good Earth/Chapter 10: Landslides and Slope Failure