Geological Hazards PDF

GEOLOGICAL HAZARDS naturally occurring earth phenomena that can potentially cause danger can cause disruption on economic and social activities 1. Landslide 2. Ground Subsidence Landslide: Possible Causes Landslide - downslope bulk displacement of soils and rock...

GEOLOGICAL HAZARDS naturally occurring earth phenomena that can potentially cause danger can cause disruption on economic and social activities 1. Landslide 2. Ground Subsidence Landslide: Possible Causes Landslide - downslope bulk displacement of soils and rocks due to the action of gravity Natural Artificial weathering (due to human activity) slope angle (steepness) soil pro le and its components deforestation presence of ground water adding weights on slopes (building activity infrastructures) earthquakes and aftershocks vibrations due to traf c and other human volcanic eruption activities extreme and/or prolonged mining and quarrying rainfall Landslide: Slope stability and equilibrium slope stability depends on: failure to achieve a slope equilibrium is slope angle (steepness) caused by: slope's load increase in the slope angle slope equilibrium must always be (oversteepening) achieved increase in the slope's load weight (overloading) Landslide: Oversteepening ~happens when a section of the lower ~happens arti cially by putting land part or of the base of a slope is cut, ll that is not equally distributed excavated or eroded throughout the slope ~happens naturally due to ~occurs naturally due to weathering weathering ~weakens the support of the slope's lower section/ base on its load fi fi fi fi  Landslide: Overloading ~happens faster due to arti cial causes: ~naturally increases due to rainfall constructing buildings and other ~increases the load and weakens the hold structures on a slope of the soil putting a land ll on the slope ~heavy and prolonged rain commonly cause a rain-induced landslide ~happens when the lower part or the base of the slope is cut through or ~slopes with no vegetation increases excavated for the construction of roads the chance of landslide by: or other structures permitting more water to seep into the ~happens when the water content of the ground ground increases allowing water to saturate the soil and occurs arti cially when water leaks from: push its particles apart *pool *water and sewer pipe *septic tank *irrigation canal Landslide: Vegetation ~brush and trees reduce the water moisture ~balances the slope equilibrium by lessening the slope's load ~vegetation are usually removed by: *wild re *intentional burning *deforestation. Landslide: Oversteepening and Overloading Overloading of the slope by erecting a building and putting a land ll. ~leaking septic tank ~Steep slope due to base undercut and land ll. ~Potential Slip Surface Oversteepening Overloading weathering of the lower part excavation of the base construction of or the base of the slope buildings and other structures adding a land ll on top of the addition of water: leaking pool, water and sewer pipes, septic tank, and irrigation canal *rain fi fi fi fi fi fi fi GEOLOGICAL HAZARDS naturally occurring earth phenomena that can potentially cause danger can cause disruption on economic and social activities 1. Landslide 2. Ground Subsidence Geological Hazards: Ground Subsidence ~settling or subsiding of earth's surface below the natural ground surface level ~usually occurs through a very long period of time ~less dangerous than other hazards Ground Subsidence: Carbonate Dissolution and Collapse ~a slow natural process that usually cause ground subsidence ~very common in places where the land feature is mostly composed of limestones Limestones are rocks that are mainly made of calcium carbonate. Limestones can be easily dissolved by acidic water. Acidic water is naturally produced in the environment when carbon dioxide (COz) in the atmosphere combine with water vapor (H20). The product carbonic acid (H, CO3) fall down to the ground as acid rain. The acidic water seeps into the soil which can react with the existing limestones underground. This reaction will dissolve the calcite (CaCo3) in the limestone, breaking the rock apart. This will eventually create a void underground. Acidic water dissolves the limestone under the ground and creates a void. The other soil and rock materials above will fall and ll these open spaces. The void will A depression on the surface will be formed. become larger and larger over a long period of time. The underground erosion of rocks and soil can create cavity as they move downward to ll the void below. This small cavity will increase in size over time and can create a cave. The roof of the cavity can suddenly collapse, creating a sinkhole. fi fi Ground Subsidence: Groundwater Abstraction ~withdrawal of water from an underground source (aquifer) ~lessen the pressure between rock layers that support and pushes them apart ~normal ground level (before abstraction) ~surface depression (after abstraction) ~A deep well can extract too much ground water causing rock layers to be compressed. ~Rock materials are compacted very closely to each other. Ground Subsidence: Oil and Natural Gas Extraction oil and natural gas ~acts the same as underground water ~exert pressure that support the rock layers ~occupy the small voids, cracks, and spaces between rock layers Oil and natural gas extraction lessen the pressure holding the rock layers apart. Pressure supporting the upper rock layers becomes very weak because of the extraction. empty oil reservoir Ground Subsidence: Underground Mining it causes ground subsidence due to the removal or displacement of large amount of underground materials its effects can be controlled and predicted Ground Subsidence: Change of Season ~natural cause of ground subsidence ~common in areas where the ground is mostly composed of clay Areas with abundant clay soil can experience ground subsidence during the dry season because the clay becomes dry, causing it to shrink. *wet season water table *dry season water table is lower *less amount of water in surface stream/river *clay soil shrink causing ground to subside dissolution and collapse of limestone (carbonate dissolution and collapse) excessive groundwater withdrawal groundwater abstraction oil and natural gas extraction underground mining change of season HYDROMETEOROLOGIC HAZARDS Typhoon A typhoon is a violent tropical cyclone that forms over warm waters, North of the equator in the Western Paci c Ocean. It contains winds rotating counterclockwise, with a speed of 118-220 kilometers per hour. It could also develop into a super typhoon if the wind speed exceeds 220 kilometers per hour. The impending signs of a typhoon are felt when it is close to landfall. These include the following: 1. increased ocean swell– A swell is a series of ocean waves brought about by strong winds. An incoming typhoon would cause a swell of about a meter in height that hit the shore every 10 seconds. As the typhoon approaches the waves to come in much faster and may also increase in height. 2. changes in clouds – Cumulus clouds may ll the sky about 36 hours before a typhoon. As the storm approaches, the sky could be clear of clouds and may later have a mass of cirrus clouds which appear as a veil covering the horizon, eventually covering a large portion of the sky. A few hours before the typhoon landfall, low-lying clouds form which slowly become thick and dark, usually accompanied by rain. 3. barometric pressure drop – the atmospheric pressure may start to drop about 36 hours before typhoon landfall. This will continue as the storm approaches. 4. abrupt changes in wind speed – wind speed increases due to the drop in atmospheric pressure as air moves from an area with high pressure to low pressure. The increase in wind speed also increases the height of the ocean swell. Thunderstorm A thunderstorm is a small-scale storm accompanied by lightning and thunder. A typical thunderstorm only lasts about 30 minutes to an hour and may cover an area as small as 5 kilometers in diameter. However, they bring about other hazards such as strong winds and heavy rainfall. In extreme cases, they may be accompanied by hail or tornado. The impending signs of a thunderstorm include the following: 1. system of cumulonimbus clouds – unequal heating of the Earth’s surface cause the upward movement of moist air, forming a tower of cumulonimbus clouds that continuously accumulate in the sky, signaling an incoming thunderstorm 2. the sky turns dark – the cumulonimbus clouds lled with water droplets serve as a barrier for sunlight. The sky darkens with a greyish tint or may also have hues of green, yellow, or violet. As clouds start to have dark bases, they may be in the process of becoming thunderstorm clouds. 3. lightning and thunder– flashes of lightning followed by thunder may be observed. This may occur even before the rain falls. In some cases, thunder that follows the lightning is inaudible which could mean that the thunderstorm is approaching or forming from a distance. As the atmosphere is becoming electrically charged, a radio static may also be experienced. fi fi fi  4. gusts of wind and change in wind direction – Figure 1 shows downdrafts which are rapidly descending air columns. Downbursts descend even faster Storm surge Storm surge is a rapid rise of seawater above normal sea level on the coast, generated by strong winds brought about by typhoons and thunderstorms. This means that the impending signs of storm surge are similar to that of the two aforementioned hazards. Unlike a tsunami that has visual signs such as receding water level, a storm surge is a rather fast and unexpected hazard that can sneak in anytime during a storm. It is advised that residents of low-lying coastal areas should evacuate upon observing signs of an incoming storm. Flood and Flashflood The flood occurs when land areas which are normally not covered with water are being submerged, often after heavy and continuous rainfall. In some cases, heavy rainfall may cause temporary overflow from bodies of water, adjacent lands, or floodplains causing the flood. The impending signs of the flood are similar to that of typhoons or thunderstorms as they are usually accompanied by rain. People should also watch out for overflowing water from manholes as this could mean that the area may be flooded soon. Flooding may last for days and even weeks. 1. weather forecasts typhoon or thunderstorm – they may bring intense and prolonged rainfall. 2. water collecting in puddles and rapidly rising water – this could mean that the ground is saturated with water and flooding may follow. Water could be stocked up in a distant area and a flash flood could occur anytime soon. 3. muddy water – this may mean that calm water has been disturbed and the dirt has mixed with the water. 4. roaring sound from upstream – this may be from stones, branches, or logs being carried in the water. 5. floating debris in water – twigs, leaves, and sticks may be from bigger Hydrometeorological hazard maps A hydrometeorological hazard map is a guide that highlights areas that are vulnerable to potential hazards like storm surge, typhoon, and flood. They are created to identify the areas that are prone to or affected these hydrometeorological hazards. Hazard maps can also help prevent serious damage and deaths. Tools for Monitoring Hydrometeorological Hazards Philippine Atmospheric, Geophysical & Astronomical Services Administration (PAGASA), as the National Meteorological and Hydrological Services (NMHS) of the Philippines is authorized in providing the warning for the public safety of the people. They used various instruments to monitor environmental conditions. Tools used to monitor the weather Barograph – a barometer that reads and records atmospheric pressure continuously. Thermograph – an instrument that measures and records air temperature continuously. Ceiling light projector - an instrument that projects a light beam to the clouds. Clinometer - an instrument that determines the height of the cloud base by measuring the distance of the cloud base to the ground. Ceiling balloon - a balloon lled with hydrogen or other gas lighter than air, which is used to determine the height of the cloud base. This is done by measuring the time that the balloon disappears into the clouds from the time that it is released. Theodolite - an instrument that determines wind speed and direction. It is attached to a hydrogen- lled pilot balloon and is allowed to float in the atmosphere at different heights to reach its different levels. Radiosonde - an instrument attached to a balloon and is used to measure temperature, pressure, and relative humidity in the atmosphere. It is equipped with a transmitter that sends data to a radiosonde receiver on the ground. rawinsonde - is like a radiosonde, but it is also capable of measuring wind velocity Wind finding radar - it measures wind speed and direction thru radar echoes. It works by attaching a radar target to a balloon that is sent to the atmosphere. The time interval and bearing of the radar echoes are evaluated by a receiver ground radar. Weather Surveillance Radar - it detects and monitors the track of typhoons and cloud masses within 400 kilometers. Doppler Radar - calculates the motion of precipitation, estimates its type, and determines the structure of storms and their potential to cause severe weather. Weather Satellite - provides the synoptic view and coverage area of a weather disturbance and the capability to relay weather data from remote automatic weather stations. FOR RAIN-INDUCED LANDSLIDE PRONE AREAS, THERE ARE THREE COLORS: Yellow: low susceptibility-less likely to be experience landslide; Be prepared. Green: moderately susceptible; Be cautious. Red: highly susceptible; Be alert and ready to evacuate. FOR FLOOD-PRONE AREAS: Pink: Low to moderately susceptible. Be cautions. Violet: Highly susceptible; Be alert and ready to evacuate. fi fi THE ELEMENTS OF FIRE TRIANGLE Fire rapid oxidation of a flammable material accompanied by the production of light and heat has brought signi cant advancements to people and industries. used as an external source of heat and light used as a power source may bene t the environment and restore ecological balance through the removal of pests and plants that compete with other species for nutrients. The elements of Fire Oxygen Heat fuel The 4 Stages of a Fire 1. Incipient: Ignition has occured but there has been no spread 2. Growth: Fire is self sustaining 3. Fully Developed: Fire is at its hottest point, burning all its available fuels 4. Decay: Fire is running out of fuel but is still very dangerous. This is the longest stage. Causes of Fires 1. Faulty electrical wiring or connection 9. Neglected electrical appliances or devices 2. LPG-related 10. Unchecked electrical types of machinery 3. Neglected cooking or stove 11. Flammable chemicals 4. Lighted cigarette butts 12. Incendiary device or ignited flammable liquid 5. Left unattended open flame: torch or sulo 13. Spontaneous combustion 6. Left unattended open flame: candle or 14. Under planned pyrotechnics gasera 15. Bomb explosion Danger zone 1 16. Lightning 7. Matchstick or lighter kept near flammable 17. Others (forest re, vehicular re, etc. materials 8. Direct flame contact or static electricity fi fi fi fi