Hazardous environments mass movements Flashcards
Define mass movement
The large scale movement of weathered material in response to gravity. It can be in the form of slow movements such as soi creeps, fast movements such as avalanches, dry movements such as rock falls and fluid movements such as mudflows.
Factor affecting mass movement
When the slope gradient is steep, the force of gravity is strong, making mass movement for rapid.
Water acts as a lubricant, which makes it easier for material to move. Following a period of heavy rain, regolith (layer on unconsolidated material) is heavier and flows more quickly.
Humans activity: Hills are often cut during the construction of roads. This makes the hill unstable, which can lead to mass movement. Vibrations from machinery and traffic can also result in mass movement, as can deforestation.
Mining removes the overlying support of slope, undermining it internal strength, thereby contributing to mass movement.
Tectonic activity: Volcanic activity cause snow or ice covering a rater to melt during an eruption, leading to lahars. The matter mixes with soil to form mud. Strain energy released from earthquake releases seismic waves (vibrations), increasing shear stress.
Plants and trees: Roots of plants and trees bind soil particles together, increasing the slopes cohesiveness and internal strength. Slopes with unconsolidated material.
Geological structure: Rocks with faults, and potential weaknesses within it are more vulnerable to weathering and less resistant to downslope movement.
Define mass movement.
Mass movement occurs when the shear stress exceeds shear strength, as result the slope cannot overcome the forces of gravity so mass movement occurs.
What are the two effects of gravity on mass movement>
Gravity has two effects, it can move the material downslope (slide component) or stick particles to the slide (stick component)
Factors contributing to reduced shear strength.
Increases in pore-water pressure reduced cohesiveness of soil particles, reducing shear strength. Saturated water causes cohesive bonds between soil particles to break, with the slope moving similar to that of a viscous liquid.
Weathering effects: Limestone rocks have a high porosity, increasing the likelihood of infiltration into cracks/pore of the rock. Furthermore, water reactions will calcium bicarbonate (a mineral found in limestone) for form carbonic acid which is carried away in solution, wearing away the rock.
Concrete U-shaped drains can also be refered to as an….
interceptor terrace.
Vuleranbility of landlsides is a function of
location, type of human activity, use, and frequency of landslide events. The effects of landslides on people and structures can be lessened by total avoidance of landlside hazard areas or by restricting, prohibiting, or imposing conditions on hazard-zone activity.
Explain why the hazardous nature of the types of mass movements varies
