BGE 214-1 Lecture 6 Geologic Hazards.pdf

BGE 214-1 Geography Department of Applied Earth Sciences BGE 214-1, Geography  Natural Disasters Department of Applied Earth Sciences BGE 214-1, Geography What is a disaster...

BGE 214-1 Geography Department of Applied Earth Sciences BGE 214-1, Geography  Natural Disasters Department of Applied Earth Sciences BGE 214-1, Geography What is a disaster Emergency: a serious, unexpected, and often dangerous situation requiring immediate action Apocalypse: an event involving destruction or damage on a catastrophic scale. Calamity: an event causing great and often sudden damage or distress; a disaster. Cataclysm: a large-scale and violent event in the natural world. Catastrophe: an event causing great and usually sudden damage or suffering; a disaster. Disaster: a sudden accident or a natural catastrophe that causes great damage or loss of life. Department of Applied Earth Sciences BGE 214-1, Geography What is a natural disaster?? Natural disasters are catastrophic events that result from any of the Earth's natural phenomena Grave danger events occur in an area that can causes massive damage or loss of life Usually rare incidents Department of Applied Earth Sciences BGE 214-1, Geography Classification of natural disasters Department of Applied Earth Sciences BGE 214-1, Geography Biological natural disasters Biological disasters are natural scenarios involving disease, disability or death on a large scale among humans, animals and plants due to micro-organisms like bacteria or virus or toxins Biological disasters may be in the form of: Epidemic - affecting a disproportionately large number of individuals within a population, community, or region at the same time Pandemic - epidemic that spreads across a large region, that is, a continent, or even worldwide Department of Applied Earth Sciences BGE 214-1, Geography Biological natural disasters Department of Applied Earth Sciences BGE 214-1, Geography Biological natural disasters Epidemic Viral infectious diseases (Malaria, Dengue fever) Bacterial infectious diseases (Bubonic Plagues) Parasitic infectious diseases (Trypanosomiasis ) Fungal infectious diseases Prion infectious diseases Insect infestation Animal stampede Department of Applied Earth Sciences BGE 214-1, Geography Geological disasters Geological / Geophysical disasters are natural disasters that occur as a result of the movements/activities in solid earth (crust) Induce by the tectonic and seismic activities below the Earth's surface Examples for geophysical disasters Earthquakes Tsunamis Volcanic eruptions Land slides (mass movements) Department of Applied Earth Sciences BGE 214-1, Geography Geological disasters EARTHQUAKES Earthquakes are shaking of the earth’s crustal blocks due to the movement of plates and their rocks along a fault or plate boundaries The sudden release of strain energy in the Earth's crust, resulting in waves of shaking that radiate outwards from the earthquake source Department of Applied Earth Sciences BGE 214-1, Geography Geological disasters EARTHQUAKES Department of Applied Earth Sciences BGE 214-1, Geography Geological disasters EARTHQUAKES The rocks under stress accumulate strain energy over a period of time When the stress exceeds the strength of the rocks, then the rock gets broken The strain energy is released as seismic waves The longer that energy is stored up and is maintained without release, the more likely that a strong earthquake will occur Department of Applied Earth Sciences BGE 214-1, Geography Geological disasters EARTHQUAKES Department of Applied Earth Sciences BGE 214-1, Geography Geological disasters EARTHQUAKES – How to Measure Department of Applied Earth Sciences BGE 214-1, Geography Geological disasters EARTHQUAKES – How to Locate The instrument used to measure seismic waves is a seismometer. It has a heavy suspended mass as motionless as possible—suspending it by springs or hanging it as a pendulum A seismograph is a recording device permanently record of Earth motion detected by a seismometer The record of Earth vibration is called a seismogram Department of Applied Earth Sciences BGE 214-1, Geography Geological disasters EARTHQUAKES – Global Seismic network Department of Applied Earth Sciences BGE 214-1, Geography Geological disasters EARTHQUAKES – How to Locate P and S wave travel time is the key Based on what recorded on the seismogram, seismologist could determine the wave type and time and distance to the epicentre. The lag time between P and S are crucial By analyzing the x-y-z coordinates of waves, depth to focus can be determined Department of Applied Earth Sciences BGE 214-1, Geography Geological disasters EARTHQUAKES – How to Locate P-S Time lag gives the distance from the measured seismic station to the epicentre Wave amplitude gives the magnitude scale Further analysis needs to locate the focus Department of Applied Earth Sciences BGE 214-1, Geography Department of Applied Earth Sciences BGE 214-1, Geography Geological disasters EARTHQUAKES After the occurrence of a major earthquake, secondary shocks may indicate of a further earthquake Major impacts and effects come mainly from land movement, fracture, or slippage, landslides, tsunamis, fires, and fault rupture The destructive effects of earthquakes are from Due to lack of warning, a severe loss to life occurs during earthquakes Earthquakes Don’t kill!, but man made/natural objects Do! Department of Applied Earth Sciences BGE 214-1, Geography Geological disasters IMPACTS OF EARTHQUAKES Department of Applied Earth Sciences BGE 214-1, Geography Geological disasters TSUNAMIS P-S Time lag give from the measure to the epicentre Wave amplitude g magnitude scale Further analysis n the focus Department of Applied Earth Sciences BGE 214-1, Geography Geological disasters VOLCANIC ERUPTIONS A volcanic eruption is the release of gas and/or lava from a volcano explosively Department of Applied Earth Sciences BGE 214-1, Geography Geological disasters HOW VOLCANOES ERUPT Deep within the Earth it is so hot that some rocks slowly melt and become a thick flowing substance called magma Since it is lighter than the solid rock around it, magma rises and collects in magma chambers Eventually, some of the magma pushes through vents and fissures to the Earth's surface. Department of Applied Earth Sciences BGE 214-1, Geography Geological disasters VOLCANIC ERUPTIONS Department of Applied Earth Sciences BGE 214-1, Geography Geological disasters MAJOR IMPACTS OF VOLCANIC ERUPTION Volcanic blast can destroy structures and environmental surrounds, and also cause fires, possibly including forest fires Land surface cracking, resulting from volcanic explosion, may affect buildings and other structures Lava flow can bury buildings and crops. It may also cause fires and render land unusable. Department of Applied Earth Sciences BGE 214-1, Geography Geological disasters MAJOR IMPACTS OF VOLCANIC ERUPTION Ash, in its airborne form, can affect aircraft by ingestion into engines Ground deposit of ash may destroy crops and also affect land use and water supplies Ash may also cause respiratory problems Mud flows may arise from associated heavy rain Cities and people can be buried under the lava flow (Eruption of mount Vesuvius, burned the entire city of Pompeii, 24 August 79 AD) Department of Applied Earth Sciences BGE 214-1, Geography Geological disasters MAJOR IMPACTS OF VOLCANIC ERUPTION Department of Applied Earth Sciences BGE 214-1, Geography Geological disasters MASS MOVEMENTS Mass movements are massive failures of slope masses including rock, debris, soils and snow/ice These mass movements are sometimes associated with other disasters such as earthquakes, floods, thunderstorms, heavy rainstorms, etc. Mass movement hazards depend on factors such as slope, lithology, vegetation cover, rainfall, and earthquakes Department of Applied Earth Sciences BGE 214-1, Geography Geological disasters MASS MOVEMENTS Department of Applied Earth Sciences BGE 214-1, Geography Geological disasters TYPES OF MASS MOVEMENTS Rockfall Landslide Avalanche Subsidence Department of Applied Earth Sciences BGE 214-1, Geography Geological disasters ROCKFALL A rockfall is a type of fast-moving landslide that happens when rock or earth falls, bounces, or rolls from a cliff or down a very steep slope Rockfalls start from high outcrops of hard, erosion- resistant rock that become unstable for a variety of reasons The size of the falling rock depends on the source area geology (bedding thickness, bedding dip and dip direction, hardness, joint/fracture orientation), weathering, position, and steepness of the slope Department of Applied Earth Sciences BGE 214-1, Geography Geological disasters ROCKFALL Rockfalls may be triggered by, Freeze/thaw action Rainfall Changes in groundwater conditions Weathering and erosion of the rock and/or surrounding material Root growth Rockfall is the most common type of mass movement caused by earthquakes Department of Applied Earth Sciences BGE 214-1, Geography Geological disasters ROCKFALL Department of Applied Earth Sciences BGE 214-1, Geography Department of Applied Earth Sciences BGE 214-1, Geography Geological disasters LANDSLIDE Landslide is a general term used to describe the downslope movement of soil, rock, and organic materials under the effects of gravity and also the landform that results from such movement Usually caused by disturbances in the natural stability of a slope They can accompany heavy rains or follow droughts, earthquakes, or volcanic eruptions Department of Applied Earth Sciences BGE 214-1, Geography Geological disasters LANDSLIDE Mudslides develop when water rapidly accumulates in the ground and results in a surge of water-saturated rock, earth, and debris The material in a landslide may be either a rock or soil (or both). Department of Applied Earth Sciences BGE 214-1, Geography Cut Slope Failures - Sri Lanka Dec. 2015-Demodara Badulla-Bandarawela Rd Department of Applied Earth Sciences BGE 214-1, Geography Landslides – Sri Lanka Department of Applied Earth Sciences BGE 214-1, Geography Geological disasters MAJOR IMPACTS OF LANDSLIDES Damage to structures and systems can be severe (buildings may be buried or villages swept away) Rivers may be blocked, causing flooding Crops may be affected. Sometimes areas of crop-producing land may be lost altogether (e.g., in the major slippage of surface soils from a mountainside) When landslides are combined with very heavy rain and flooding, the movement of debris (e.g., remains of buildings, uprooted trees) may cause high levels of damage and destruction Department of Applied Earth Sciences BGE 214-1, Geography Geological disasters Identification of landslide (Forecast) Look for erratic boulders Look for Talus slope/ Old landslide deposit Other Eyeopeners Slanting trees Stay Alert! Slanting poles Sudden appearance/ disappearance of springs Muddy water springs Appearance of new cracks Department of Applied Land subsidence/ Cracks on buildings Earth Sciences BGE 214-1, Geography Geological disasters LANDSLIDE - PREVENTION Geotechnical Measures Avoid slip surfaces Proper drainage Bolting/Anchoring/Soil nailing Gabion walls Retaining walls Grouting Geo-textile Department of Applied Earth Sciences BGE 214-1, Geography Geological disasters LANDSLIDE - PREVENTION Geotechnical Measures Sheet pilling Geogrid/ Geotextile Department of Applied Earth Sciences BGE 214-1, Geography Geological disasters AVALANCHE Department of Applied Earth Sciences 44 BGE 214-1, Geography Geological disasters AVALANCHE Avalanches are masses of snow, ice, and rocks that fall rapidly down a mountainside They can be deadly Falling masses of snow and ice, avalanches pose a threat to anyone on snowy mountainsides Avalanches can be triggered by wind, rain, warming temperatures, snow and earthquakes Department of Applied Earth Sciences BGE 214-1, Geography Geological disasters SUBSIDENCE Subsidence is sinking of the ground because of underground material movement Most often caused by the removal of water, oil, natural gas, or mineral resources out of the ground by pumping, fracking, or mining activities Subsidence can also be caused by natural events such as earthquakes, soil compaction, glacial isostatic adjustment, erosion, and sinkhole formation Department of Applied Earth Sciences BGE 214-1, Geography Geological disasters SUBSIDENCE Department of Applied Earth Sciences BGE 214-1, Geography Department of Applied Earth Sciences BGE 214-1, Geography