Le 3

• Geohazard is a potentially destructive process that could harm man and his resources
• Disaster = f{hazard, people, & resources at risk
• Earthquakes are the vibration of the earth, caused by the rupture and sudden movement of rocks that have been strained beyond their elastic limits
• Elastic strain is recoverable portion
• Stress is the rupture or slip and elastic rebound
• Tectonic Earthquakes include plate boundaries and active faults
• Earthquake Hazards includes ground rupture, ground shaking, liquefaction, fire, landslides and related downslope movements, subsidence, flooding due to dam failure
• Shear wall and use of reinforced concrete & steel is one of engineering solutions for earthquake
• Preparedness is emerging as an alternative such as seismic risk map, strict building code, and zoning and land use
• Hot spots can be either oceanic (Hawaii) or continental (CRB, Yellowstone)
• Plates move as hot spots remain
• Internal factors that causes volcanic eruptions includes vesiculation or degassing of magma and influx of fresh magma supply
• External factors that causes volcanic eruptions includes load pressing, tectonic pressures, and ocean tides and earth tides
• What comes out of a volcano? Lava, Pyroclast = tephra, Volcanic gases
• Eruption products includes lava flow, pumice, ash, pyroclastic flow, and volcanic gases
• Types of eruption: Explosive and Effusive
• Caldera is the volcano with a crater greater than 2km in diameter
• Volcanic Hazards includes lava flows, tephra fall/ash fall & ballistics, pyroclastic flows & pyroclastic surges, volcanic gases, lahars, debris avalanches, landslides, and tsunamis, crater lake/ mountain lake breaching
• Landslides is the general term for rapid downslope movements/failure
• Mass Wasting is even more general and includes slow movements (creep, slow flows)
• Mass wasting / slope failure / landslides are all downslope movement of rock and sediment that occurs at the surface of the earth (also underwater) in response to gravity. Speeds range from extremely fast to extremely slow.
• Classification of Landslides: Type of Materials, Speed, Type of downslope movement
• Types of Downslope Movements: Fall, Topple, Flow, Slide, Subsidence
• Types of Material: Rock and Soil
• Rock is a hard or firm mass that was intact and in its natural place before the initiation of movement
• Soil is an aggregate of minerals and rocks that either was transported or was formed by the weathering of rock in place
• How fast does a landslide move? Very Slow - e.g. Creep, Moderate - e.g. Slumps and earthflows, Rapid to Very Rapid - e.g. Rockfalls and avalanches
• Slope table includes angle of repose, driving forces, and resisting forces
• Angle of repose is the maximum slope angle at which the material is stable
• Driving forces includes mass, gravity, pore pressure
• Resisting forces includes inertia, friction, cohesion
• Water plays an important role in controlling the stability of a slope
• A small amount of water in pore space that is mostly occupied by air produces a capillary force which holds particles together, resulting in more cohesion, and allowing a greater angle of repose
• A large amount of water occupying all the pore space exerts pressure on the particles (pore pressure), keeping them apart and allowing them to flow more readily, reducing cohesion
• Small amounts of moisture in unconsolidated deposits increase cohesion and the angle of repose
• Another effect of adding water to a slope is to increase the mass of material and hence, the gravitational pull on the slope, which favors mass movement
• If the Factor of Safety is greater than 1, then the Resisting Force is greater than the Driving Force and the slope is stable
• Modern building codes require a F.S. of 1.5 or greater
• Water infiltrating into unstable slope increases pore pressure (loosens particles) and adds more weight to slope, favoring failure
• Ground shaking due to earthquake activity can facilitate slope failure