Natural Disasters Topic 7 Drainage Basins & Mass Wasting)
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Overview of drainage basins and mass wasting for a GE-level course in natural disasters.
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Natural Disasters Topic 7 Drainage Basins & Mass Wasting)
- 2. Hydrologic System Some of the water evaporated from the ocean falls onto continental surfaces. This water makes its way back to the ocean, in part, by surface runoff.
- 3. Drainage Basins A drainage basin is the area that collects water and sediment for a particular river system.
- 4. Drainage Basin Zones Mostly erosion Erosion & deposition balanced Mostly deposition Drainage basins can be divided into three zones based on the relative dominance of erosion and deposition.
- 5. Drainage Basins & Hydrologic System The collecting zone consists mostly of mountainous regions. Transportation takes place primarily across the stable platform. Deposition occurs predominantly along the coast.
- 6. Graded Profile River systems strive toward a state of equilibrium, in which a smooth curve flattens from mountain peaks to the sea shore.
- 7. Base Level Base level is the lowest level to which a stream can flow and is controlled by lake or sea level.
- 8. Graded Profile Changes Any change to a graded profile eliminates earlier conditions of equilibrium, and a new profile is developed. Changes are related mostly to tectonic movements or fluctuations in base level.
- 9. Photo by W. W. Little
- 10. Photo by W. W. Little
- 13. Photo by W. W. Little
- 15. Collecting Zone The collecting zone is found mostly in mountainous regions and is dominated by erosional processes, such as downcutting, headward advancement of channels, and slope retreat.
- 16. Downcutting Downcutting is the vertical entrenchment (deepening) of a channel. Downcutting typically represents tectonic uplift but can reflect the lowering of base level.
- 18. Photo by W. W. Little
- 19. Photo by W. W. Little
- 23. Headward Erosion Photo by W. W. Little Headward erosion is the lengthening of a channel due to the concentration of runoff at the point where the channel begins.
- 27. Landscape Dissection Headward erosion proceeds until the landscape, typically a plateau, becomes completely dissected. Once streams from opposite sides meet, headward erosion ceases.
- 28. Headward Erosion & Base Level Either faulting or a change in base level can disrupt stream equilibrium. A new profile will develop, in part, through headward erosion.
- 31. Slope Retreat Slope retreat is the widening of a channel, due primarily to processes of mass wasting (e.g. landslides).
- 32. Mass Wasting Slump Slide Fall Flow Creep Mass wasting (or movement) is the downslope movement of rock material under the influence of gravity and can take the form of falls, slides, slumps, flows, or creep.
- 33. Falls Falls occur when rock breaks loose from a steep to vertical rock face and drops to the ground.
- 35. Talus Rock falls form cone-shaped accumulations at the base of the slope – called talus.
- 36. Pueblo Bonito, CO 1941
- 37. Rock Avalanches Large masses of rock can break loose and move at high velocities as they ride over a cushion of compressed air, in a manner similar to snow avalanches.
- 43. Slides Slides take place when rock breaks loose and slips down an inclined surface, such as a bedding plane or a joint.
- 48. Slumps Slumps are large blocks of rock that break and rotate as a single mass along curved surfaces that resemble faults. Flows often occur at the toes of slumps.
- 61. Flows Flows develop when the rock body becomes completely saturated with water and moves as a fluid.
- 62. Deforestation Removal of vegetation from muddy slopes is a major cause of mud flows.
- 68. Debris Flows Debris flows consist of a fluid mixture of mud to boulder-size material.
- 75. Solifluction Solifluction is a slow type of flow that takes place in thin layers of soil that overly frozen ground.
- 76. Creep Creep is a slow downslope movement of rock material in response to freeze-thaw cycles.
- 77. Creep Processes If the ground is damp, freezing will cause it to expand perpendicular to the surface. Gravity then pulls it vertically downward. The result is a gradual down slope movement of sediment.
- 80. Deflection Walls
- 81. Drainage Systems
- 83. Rock Bolts