Mass Movement Hazards PDF

1.What is mass movement? 2. What is landslide? How does water aid this process? 3.What are the factors that contribute to the subsidence and collapse of land surface? 4. What are ways of reducing the effects ofmass movement? Lesson 7.1 Maim Id...

1.What is mass movement? 2. What is landslide? How does water aid this process? 3.What are the factors that contribute to the subsidence and collapse of land surface? 4. What are ways of reducing the effects ofmass movement? Lesson 7.1 Maim Idea: The geological features of the Philippines make us prone to hazards of mass movement. Mass Movement EQ:What are the different types of mass movement that we are prone to? Mass movement is the downward movement of surface materials caused by gravity. It could classified as downslope movement or vertical movement. A landslide is an example of a downslo movement. The USGS defines landslide as a wide variety of processes that result in the downwa and outward movement of slope-forming materials such as rock, soil, artificial fill, or a combinati of these. Ground subsidence is an example of a vertical movement. Ground subsidence and collaj could lead to a very slow to rapid sinking of the land surface, usually forming a depression. It is m commonly referred to as a sinkbole. 150 Exploring Life Through Science-Disaster Readiness and Risk Reduction Chapter 7 From Under our Feet 151  Geological hazards can also be grouped into sudden and slow phenomena based on their onset.sudden phenomena include earthquakes, landslides, mud flows, pyroclastic flows,tsunamis,flash floods,rolcanic eruptions, tephra, and lahar. Slow pbenomena, on the other hand, include the formation of rolcanoes,sinkholes,liquefaction,sand dunes, and shoreline and stream erosions. The Philippines is prone to geographical hazards dueto its location in the tropics and the presence of communities at the bases of mountains and hills. The Philippines, being an archipelago, also experiences the effects of global warming firsthand.In recent years, the country has experienced another humanmade disaster which came to be known as the Payatas Trash Slide. Tons of trash as high as 50feet came sliding down after several days of heavy rain,burying shanties that lay on its side and killing approximately 500 persons. Fig. 7-1. The Payatas Trash Slide or Payatas Tragedy occu Sadly,trash slide cases are not isolated in Payatas; there were other solid waste landfills that are mishandled in the Philippines such as the infamous Smokey Mountain. A similar situation occurred in Baguio City when Typhoon Mina hit the country in 2011. Incessant raining made the flooded area near the retaining wall of the Irisan dumpsite to collapse, causing the trash to slide. The flow of water and trash took the lives of at least five people who were buried alive. Fig. 7-2. The wall of trash that slid down to the residential area in Baguio City during Typhoon Mina It is therefore not just the natural geological hazards that people should be wary of, but also several humanmade hazards that could cause loss of lives as well. Unless concrete steps are taken to prevent or mitigate the possible losses from geological hazards, the country will continue to lose a lot in terms of lives, properties, and money for rehabilitation-money which could be used to jumpstart the economy or to pay off foreign debts. Chapter 7 From Under our Feet 151 52 Exploring Life Through Science-Disaster Readiness and Risk Reduction  One of the many hazards that the Philippines faces is the downslope land movement,commonly known as landslides. The following lists some of the landslides that happened in our country: 1. November 1991-Ormoc, Leyte (6000 people killed) 2. September 2003-Mining Village in Southern Philippines (22 miners dead) 3. December 2003-Panaoan Island in Southern Leyte (at least 160 people dead) 4. February 2006-Guinsaugon,Leyte (139 dead and 973 missing) The numbers might seem small compared to the other disasters that befell our country in recent years due to other causes (Typhoon Ondoy and Super Typhoon Yolanda), but just the same, their toll on human life to properties and to the environment was insurmountable. One of the primary reasons why landslides cannot be averted is because it is a natural process of the Earth's changing landscape. Just as mountains are slowly formed and shaped as they move upwards,they would naturally come down once the balance between the forces acting on them is disrupted.Gravity affects everything on Earth, including the rocks and other materials on top of mountains. This causes their downslope movement, which could become catastrophic when a large volume of materials is displaced. There are two forces that determine the ability of a slope to resist sliding. These are the force of gravity acting on a material (referred to as the driving force), and the force acting on the material and the friction holding it in place (referred to as the resisting force). The steepness of the slope and the weight of the material on top of the slope are key factors in slope failure. The steepness of the slope is directly proportional to the likelihood that the slope will fail. During the Cherry Hills Landslide, investigators determined that on average, the slope is inclined at 20°.This is steep enough for unstable materials to slide downward. Ironically, evidence and warning signs for a slope failure were already present months before the incident. If only the developers and authorities have recognized the natural signs, lives could have been saved. Over the years, authorities have worked on creating hazard maps to make the population more informed. Agencies such as PAGASA,MGB,MMDA,Manila Observatory, and PHIVOLCS have mapped out the country's hazard risks and made the maps available to the masses to download and study. These agencies worked on Project READY, Project AGOS,and Project NOAH, to name a few-all of which were put up to aid the government and the people to be nore prepared in the event of a disaster. The color convention used in the hazard maps are the following: 52 Exploring Life Through Science-Disaster Readiness and Risk Reduction Red areas have high susceptibility to landslides. These areas have active landslides and tension cracks that would directly affect nearby communities. Green areas have inactive landslides and tension cracks located away from the community. Yellow areas have low to gentle slopes and lack tension cracks; hence, they have low landslide susceptibility rating. Violet areas have high susceptibly to flooding. These are areas with over one-mneter-high flood and usually remain flooded for several hours during heavy rains. Light pink areas have low susceptibility to flooding. Flood height is usually below 1 m. Fig. 7-3. A hazard map of the Quezon City quadrangle for susceptibility to landslide and flood  Project READY Project Ready is a project aimed at providing and conducting hazard mapping and assessment for effective community-based disaster risk management. It was implemented from 2006 to 2011 by the NDRRMC in collaboration with other government agencies (MGB, NAMRIA, PAGASA, and PHIVOLCS)and funded by the United Nations Development Programme, AusAid, and Asian Development Bank. The project addresses the problems encountered by local government units in handling disaster risk management. For it to work, there must be national and local involvement. The national government will institutionalize and come up with standard measures and process for disaster risk management. On a local or community level, the project would empower the municipalities and cities in the country which are most vulnerable, and guide them in developing and preparing their disaster risk management plans. The target of the project are the 27 high-risk provinces of the country. The three major componen of the project are (1) multi-hazard and risk assessment, (2) community-based disaster risk mitigation through development of community-based early warning system and conduct of information, education, and communication campaigns, and (3) mainstreaming disaster risk reduction into the local development. Truly, Project READY will be very helpful in making the Philippines a safer country to live in, and make its residents more aware of the risk that the hazards have on their lives and properties. During the summer months, when you are most likely to visit the beach, you might have experienced building a sand castle. The amount of water added to the sand should be just enough. Too much water will make it impossible to mold the sand, and it would just fall on its side because the force of attraction among the sand particles is negligible.The right amount of water would provide the proper surface tension between loose soil grains; this is called cobesion. This results from the static charges between small particles or from the surface tension of water between grains. Fig. 7-4. The grains in wet sand are held together by the surface tension provided by the thin film of water. The grains in water-saturated sand is completely surrounded by water, eliminating contact and causing the sand to fall. 154 Exploring Life Through Science-Disaster Readiness and Risk Reduction Causes of Landslides As we move around on the surface of Earth, we are kept from flying into space by gravity and the balance of forces that act on our body. The same could be said of an airplane in flight-the balance of forces acting on it is what enables it to stay on air. The balance between the angle of a slope and its load is key to preventing landslides from happening. There are several factors that can lead to the disruption of this balance. Construction of a structure over a slope increases load. Road-widening projects can make the slope angle steeper. Deforestation can make the soil absorb more water. A perfect example of overloading in a slope can be seen in somne mountainous parts of the country,particularly in Baguio City. On one of your vacation trips, you might have seen houses that seem to have jotted out of the mountainside, as if they were placed there like pieces of a building block toy. Fig. 7-5. High density of houses built on a slope in Baguio City Exploring Life Through Science-Disaster Readiness and Risk Rediiction  Constructioncan also contribute in the oversteepening of a slope. Oversteepening may occur when the upper layer of the slope is filled with soil, increasing its angle. It could also occur when the slope is undercut from below. Oversteepening of a slope can occur naturally via erosion on the base of a slope, or it can also be induced through excavation and filling. Buying properties located on hillsides and building houses on steep slopes often undercut and add additional load to the slope, making the ground more likely to slide. More often than not,these houses are built with swimming pools, which increases the moisture of the soil-another factor which contribute to the likelihood of a landslide. Water saturates slopes, making them heavier and more loose. This reduces the bond between soil particles. Water also facilitates weathering, which reduces the strength of rocks. This is particularly more likely to occur in the Philippines for two reasons: 1. The frequency of typhoons often unload large amounts of water on the areas they pass through. 2. Forests are cleared to make way for housing projects or farmlands through kaingin. The absence of a natural absorber of water in the soil makes the water saturated,effectively weakening the bond between soil particles and increasing the likelihood of slide.This has been exemplified by the Leyte Landslide in 2006, which occurred shortly after Typhoon Seniang. The same typhoon caused portions of the Trans-Central highway in Cebu to be destroyed by erosion and eventually, collapse. Although the factors mentioned are independent of each other, it is not impossible for these to occur simultaneously at any time. When this happens, the effects would be catastrophic. An example occurred when Mount Pinatubo erupted. The rains brought about by Typhoon Diding resulted in the lahar flows that killed around 300 people. This should become a constant reminder of the importance of mitigating the effects of these disasters. After the August 1999 Cherry Hills Landslide, the Philippine Government issued DENR Administrative Order 2000-28 as its long-term response to the urgent need of protecting lives and properties from destruction brought about by geological hazards. It requires all land development projects to undertake an Engineering Geological and Geohazard Assessment (EGGA), which assesses all natural hazards that may affect the project development and recommends the necessary mitigating measures. It is an additional requirement for Environmental Compliance Certificate (ECC) applications in order to strengthen the geological component of the Environmental Impact Assessment (EIA) System. Exploring Life Through Science-Disaster Readiness and Risk Rediiction  This is a good example of the importance of the implementation of policies in order to save lives and reduce damage to properties caused by geological hazards. Exploring Life Through Science-Disaster Readiness and Risk Rediiction Chapter 7 From Under our Feet15  Lesson 7.3 Main Idea: Landslides are classified according to their composition, movement, Types of Lamdslides and rate of movement. EQ:What are the different types of landslides or downslope movements? Downslope movements or landslides are generally dassified according to three prevailing factors: type of miterial, type of movement, and rate of movement. The types of material are classified as debris that are coarser than2mm,and soil that is finer than 2 mm. The types of movement may be falls, lateral spreads, flows, and topples. The rate of movement varies on the steepness of the slope,grain size,moisture, thickness of the moving mass, type of clay mineral,and clay content. This could range anywhere from 0.3 mm/year (extremely slow) to 360 km/hour or roughly the average speed of a race car. Moving masses could be described by their movement Fig, 7-6. A section of Kennon Road leading to Bagui incessant rains of Typhoon Ineng. and the material. These are rockfall, rockslide,debris slide, debris flow, earthflow, mudflow, and, in other countries,snow avalanche. Rockfalls Rockfalls develop in zones of weaknesses or in steep mountainous regions with cliffs which are nearly vertical.Large masses of rocks that are pried loose by water separate from a steep slope or cliff, causing them to fall and break into smaller fragments and sweep downslope. Rocks such as granite, sandstone, and metamorphic rocks are most likely to cause rockfalls because they break easily into fragments. Rockfalls can be Fig. 7-7. Rockfalls occur when fragments of large triggered by earthquakes,slope undercutting, and blasting from doing mining works. Cliffs with slopes of at least 40° also increase the likelihood of rockfalls. When the rocks slide down, they collect in a fan-shaped pile of rock fragments at the base of a cliff called talus slopes. Large boulders may bounce or roll away from the base of a slope, making them dangerous to settlements at the base because of their size and speed. The kinetic energy generated by these boulders as they travel is often enough to demolish residential houses. Rockfalls can also be dangerous to highways because roads are often built following the base of precipitous cliffs, without proper mitigating measures for falling rocks. Chapter 7 From Under our Feet15  Flow When water saturates the ground, the materials become heavier, resulting in debris floww or mudflow. Flou is a type of landslide involving the movement of material down a slope in fluid form.The combination of rock and mud is capable of lifting objects along its path, including cars, trees,and even houses. The debris flow can cause flooding when it blocks streams or other waterways. Flow often leaves a distinct upside-down funnel-shaped deposit where the landslide material has stopped moving. Debris Avalanches Downslope movements of rocks and soil with extremely rapid velocity are called debris avalanches.Many of the deadliest landslides in history started off as ordinary rockfalls or rockslides that became debris avalanches. Debris avalanches are dangerous because they flow at a speed of 100 to 300 km/h and may contain boulders as big as a house. The debris avalanche that happened in Yungay, Peru on May 31,1970 traveled at a speed of almost 270 km/h. This avalanche contained 50 to 100 million m3 of granite,glacial debris, and ice, and fell at a distance of 400 to 900 m down a valley. Midway down the slope, the boulders hit a deposit of sediment which was launched into the air upon impact. Boulders that weighed several tons flew to as far as 4 km and generated a blast of wind strong enough to knock anyone off their feet and shred bare skin. This combination of events led to the burial of the entire city of Yungay under 30 m of mud and the death of 18000 people. In the Philippines, one of the most recent catastrophic disasters caused by a landslide happened in Guinsaugon, Leyte.The event started off from the detachment of three massive blocks from the slope face of Mount Can-abag. People saw a landslide that traveled 4.1 km from the source and covered an area of 3.2 k㎡.Scientists estimated the velocity of the landslide to be from 120 to 130 m/s. The almost-five-minute event resulted in 139confirmed deaths and 980 individuals unaccounted for. Chapter 7 From Under our Feet 159  Karl von Terzaghi Karl von Terzaghi developed an interest in aslronomy and geography at an early age. In 1900, he entered Technical University in Graz where he took up mechanical engineeringand developed an interest in theoretical mechanics, geology,and highway and railway engineering. Karl worked as a junior design engineer for Adol Baron Pittle, a firm involved with the newfield of generating power using hydroelectric sources. He went to the United States in 1912 for an engineering tour of major dam construction sites and gather reports and firsthand knowledge of many different projects, which he was able to apply upon his return to Austria. After World War I,he became a professor at the Royal Ottoman College of Engineering (lstanbul Technical University) where he began a new revolution in standardized testing of soil as an engineering material. In 1919, he published his work on measuring and analysing the force of retaining walls, which was quickly regarded as an important contribution to the scientific understanding of soil behavior. He also did a study on the various experimental and quantitative aspects of the permeability of soils to water. Through this, he was able to work out some theories that helped explain his observations. It was also during this time that he invented a new apparatus for measurements of his work and spent long days performing the measurements himself. In 1924, he published Erdbaumechanik (Soil Mechanics) which was considered revolutionary in the field of soil mechanics. Slides and Slumps Slide is a downslope movement of a soil or rock mass occurring dominantly on defined surfaces of rupture or thin shear zone. There is a distinct zone of weakness separating the slide material from more stable underlying materials. Translational slides move along a surface of rupture that is curved and concave-upward. It is also referred to as slump. It occurs most frequently in homogenous, cohesive materials such as soil or artificial fill.Translational slides are characterized by movements on weak surfaces that are more or less parallel to a slope. Translational slides are shallower compared to rotational slides, as evidenced by the fact that when trees slip down a surface, they remain vertical and do not rotate with the sliding surface. This, however,adds speed to translational slides, making them faster and more dangerous compared to rotational slides.Internally,it is very hard to predict what is going to happen to the materials on the slide; some may move as a coherent mass, some may break up and become debris slides. Clearing areas in steep slope for residential projects or farming often result in translational slides. One example is the debris avalanche in Guinsaugon, Leyte, which started off as a rockslide. The intersecting fractures in the rock have fractures that are related to the movement of the Philippine Fault.Illegal logging and the heavy downpour of rain for 10 days on the slope above the village were identified as the cause of the slide. It buried an elementary school where there were almost 250 children and 7teachers and presumably buried more than a thousand who were missing under the mud. The sliding block originated at about a 800 m high slope. It gained momentum as it traveled downslope and became debris. The source area is a very steep slope covered with trees. Tree roots that grow on the fracture contributed to the instability of the slopes. Chapter 7 From Under our Feet 159 160 Exploring Life Through Science-Disaster Readiness and Risk Reduction  Trees and Landslides Did you know that bended trees can be a sign of a landslide? Curved tree trunks are characteristics of areas with an ongoing creep. It can also be a precursor to a larger, faster landslide. If you happen to live near a steep slope where almost all tress are curved in one direction, have your area assessed by an engineer or geologist. Creep Creep is a relatively less dangerous mass movement involving the slow downslope movement of soil and weak rocks on the surface. This movement is able to tilt fences,power lines, and trees. Conventionally,the greater the tilt angle is, the longer the object has been subjected to soil creeping. There is lesser movement as the depth increases because majority of the movement operates or occuars on the surface. An accelerant of the creeping process is the combination of expansion and shrinking processes-wetting and drying or freezing and thawing. When the soil Fig, 7-9. A tree trunk that was deformed because of creep expands, it moves out perpendicularly to the slope; and when it shrinks, gravity pulls it straight down. The effect of this is a slight movement down the slope.Trees with trunks appearing to be tilted downslope are also an end product of creep. Creep is an indication that the slope is unstable. Movement could accelerate and could transform into a fast-moving and more dangerous slide. Avalanches An avalanche is an example of a very deadly downslope movement. Avalanches are mostly associate with snowcapped mountains. An avalanche that is almost 12 inches deep is able to move tons of sno at high speed as it goes down a slope-enough to sweep people and animals, and bury them unde snow. An avalanche can gain momentum as it goes down a slope. Sadlly, avalanches are mostly due t human actions. Factors that make an avalanche form are slope steepness, weather, temperature,slop orientation, wind speed and direction, and vegetation. Slopes that are inclined at 30° to 45° are mo prone to avalanching, but may also develop into gentler slopes if the weather conditions are just righ 160 Exploring Life Through Science-Disaster Readiness and Risk Reduction Chapter 7 From Under our Feet 161  New layers of snow also affect the formation of an avalanche. A huge snowstorm adds layers of loose snow on the surface. Snow that is 10 cm deep is favorable to skiers, but snowfall more than 30 cm is already dangerous. The movement of this loose snow may accelerate as it moves downslope and drags more materials into the snowpack as it conatinues to rolls. The risk of avalanche also increases with higher temperatures because as the snow on the top layers melt, the water may fill the pore spaces between soil grains. This water also creates a weak spot in the packed layers of snow Fig.7-10. Snow avalanche which makes it prone to sliding. If the ground is frozen, water may run downslope under the snow. This effectively weakens the friction between the soil and the snow, creating an avalanche. Landslide Vulnerability Picture Survey on page 166A Lesson 7.4 Main Idea: Ground subsidence also causes Collapse damage to properties. Ground Subsidence and subsidence and collapse?What are the warning signs of ground The hazardous vertical ground movement associated with subsidence and collapse is mostly due to human activities which change environmental conditions. Subsidence is the slow lowering of the land surface.Collapse is the relatively fast opening of the land surface and movement of surface materials into the underlying cavities. When the overlying ground collapses into the soil cavities underground over the limestone, the collapse will result in a sinkbole. Sinkholes vary in size-from ten to hundreds of meters wide; they can "swallow" houses and roads, or drain streams, lakes, and other forms of wetlands.Another danger with sinkholes is that they may allow contaminants to bechanneled to underground water sources, making the water unfit for consumption. There are sedimentary rocks in nature which are highly soluble in water (e.g., salt and gypsum), while others are soluble in a slower rate in acidic rainwater.When water droplets in the atmosphere take in carbon dioxide, a weak carbonic acid is formed. This acid slowly reacts with the Chapter 7 From Under our Feet 161 limestone under the bedrock, dissolving it to widen cracks and cavities. This reaction is made faster when it occurs in warm, moist conditions; this is the reason sinkholes are common in tropical or subtropical places. Chapter 7 From Under our Feet 161 162Exploring Life Through Science-Disaster Readiness and Risk Reduction  There are three common types of processes in sinkhole formation: dissolution, cover subsidence,and cover collapse. Dissolution occurs when the soil cover is thin and highly permeable. Acidic groundwater can easily seep through it and dissolve the underlying milestone or widen the upper parts of the soil fracture to form lumps or jagged karst surfaces. The overlying soil can slowly create a depression. Over time, when the groundwater level is high or the fracture becomes clogged with sediment, the depression may fill up and form a pond. This is generally shallow and not considered to be dangerous. Cover subsidence forms when sandy,permeable sediment sits on top of limestone bedrock. As the soil slowly fills the expanding fractures and cavities in the limestone, numerous sinkholes may occur. Cover collapbse can occur suddenly and without warning. When overlying sediments contain a significant amount of clay, this cover becomes more cohesive and less permeable, making it difficult for fractures in the cavities of the limestone to be filled. Over time,this makes the cavities grow larger and more unstable, leading to the sudden collapse of the thinning roof.Since cover collapse occurs suddenly, sinkholes open with little to no warning. It could take with it roads,cars,houses and buildings, making it the deadliest type among the three. Fluctuations on the level of groundwater contribute to the formation of sinkholes. Heavy rainfall tends to loosen soil and enlarge underground cavities, promoting sinkhole formation. More sinkholes tend to form during dry season because excessive pumping drops the levels of groundwater. In urban areas, leaking water mains and storm drains can enhance the formation of sinkholes. A large flow of water can flush soil from above fractured limestone to form large sinkholes. Structures built on top of such limestone bedrock are vulnerable to severe damage. Another contributor in the formation of sinkholes are construction activities which may increase loads on the surface. Other factors may come from the dehydration of foundation soils and drilling of wells. In the Philippines, there are five sinkhole-prone areas that have been identified by the-Mines and Geosciences Bureau: Bantayan Island and Badian in Cebu,Kabankalan City in Negros Occidental,Baguio City,Bohol, and Dadiangas in General Santos City. After the magnitude-7.2 earthquake that shocked the province of Bohol in October 2013, a hundred sinkholes were seen on the surface as the earthquake forced the 5.3-million-year-old sinkholes onto the surface. However,authorities were quick to state that the sinkholes were not dangerous as long as there were no houses built on top of them. The National Capital Region has a very low risk for sinkholes as it sits on adobe rock and not on limestone as the five provinces previously mentioned. Fig. 7-11. Personnel from MGB taking morphometric measurement of 162Exploring Life Through Science-Disaster Readiness and Risk Reduction  sinkholes 162Exploring Life Through Science-Disaster Readiness and Risk Reduction Chapter 7 From Under our Feet 16  Civil Engineer Civil engineering is concerned with designing, building, and maintaining public works. They focus on structures and facilities such as roads, tunnels, flyovers, airports, dams, and government buildings.To be a civil engineer, one must be good in mathematics, possess a creative mind for the design of structures,and is skilled and knowledgeable in the sciences. Civil engineers are also expected to be good team players and have good oral and written communication capabilities, have a high level of responsibility,and high regard and respect for authorities. In short, a civil engineer must be a well-rounded individual. In general, civil engineering requires a four- or five-year bachelor's degree and alicense given by the Professional Regulations Commission. Civil engineering also has several fields of specialization such as coastal engineering,geotechnical engineering, environmental engineering, traffic and transportation engineering, and structural engineering. Lesson 7.5 Mass Movement Main Idea: The effects of mass movement can be mitigated. Preventing and Mitigating effects of mass movement?What actions may be done to mitigate the Over the years, people have resorted to building their homes in less suitable areas due to lack of land or the inability to purchase suitable land to build on. Without the proper hazard zoning and hazard evaluation, landslides are disasters just waiting to happen. As with all hazards, knowledge about the process in downslope movements enables scientists, engineers, and even ordinary persons to understand the risks involved when exposed to these hazards. As with other hazards, records of past events can be useful. The likelihood of a landslide reoccurring in the same place is very high. The existence of landslides in an area highlights the fact that the local conditions are favorable to landslides. Some hillsides covered with vegetation may be the remnants of a landslide; roads which usually crack or exhibit broad waves in pavement suggests a sliding terrain.Old landslides can be reactivated by the same factors that can cause new landslides: adding water,steepening the slope, removing top material, loading the top part of a slope, removing vegetation, or earthquakes. The first strategy in prevention and mitigation is the use of the susceptibility maps provided by the MGB. Building structures should be avoided in steep slopes and mountainous areas, slopes which exceed 30 to 45 degrees on a hiIlside, areas abundant of loose debris on a slope, slopes with fine-grained soil,areas where a large amount of rainfall can seep through the ground, and locations of previous landslides. Shallow Chapter 7 From Under our Feet 16 slides are more likely to develop on slopes with little vegetation and lack of tree to hold surface material in place. Relocation and evacuation should be made if there are structure identified as unsafe for the risk. Chapter 7 From Under our Feet 16 64Exploring Life Through Science-Disaster Readiness and Risk Reduction  Engineering solutions may also be employed to mitigate the effects of landslides.When there is a slope with heavy structures on top, adding load to the lower part, called buttras, can help the slide resist movement. The resisting mass may also be increased by piling heavy boulders on the toe area. This may be done to stop a slope from moving. Slope angle can also be lowered to lessen the risk of movement.Sometimes, sbotcrete, a cement mixture, is used to restrict water and slow down weathering. Rock net, rock fence, or rock ditch can also be used to prevent falling rocks from reaching buildings or highways. Some resort to removing water out of the soil to increase the strength of cohesion-trees and shrubs are very helpful for this purpose.An artificial method is to drill holes, which are slightly upward into the slope, and insert perforated pipes. The water drains into the pipe and trickles out onto the surface. Rocks with many fractures can be strengthened by drilling rock bolts Fig. 7-12. Soil nails (steel bars) are inserted into the slope to s is sprayed with shotcrete. and rock anchors. Landslide Preparedness Realizing the damage that a landslide may cause, it is therefore important to know how to recognize the signs of an imminent landslide, what are the things to be observed, and what can be done in case a landslide occurs. Knowing how to look for warning signs will enable one to make safety considerations in the planning and building of structures, or being able to make split second decisions in the event of a landslide. In dry lands, the appearance of springs, seeps, or saturated grounds is a warning sign. The existence of new cracks or unusual bulges on the street pavements and sidewalks, and depressions in the road beds should be looked out for. Watch out for leaning telephone lines, poles, and retaining walls and fences. Utilities which are coursed underground, such as water, may also be broken. Look at the doors and windows to see if the frames are out of plumb. Other signs of landslide include unusual sounds like cracking wood from trees, or faint sounds of rock rolling that increases in intensity. The increasing sound also indicates how far the landslide is. 64Exploring Life Through Science-Disaster Readiness and Risk Reduction 64Exploring Life Through Science-Disaster Readiness and Risk Reduction Chapter 7 From Under our Feet 165  The first and foremost step in preventing landslides is to have ground assessment before buying exposure. Look at the history of the location; if there have been prior events of landslides in the area,the chances of it happening again is very high. Ask for information of landslide hazards in your area from authorities like the local officials, the Mines and Geosciences Bureau, or the Department of Environment and Natural Resources. They will be able to give you sound advice on the area concerned and can give you corrective measures that can be done if any. In the household, utilities such as gas or water lines should use flexble pipe fittings, which are more resistant to breakage. It is also advisable to plant ground cover on slopes and to build retaining walIs. You may opt to build deflection walls to divert the flow of debris in the event of a slide to let it flow around your structure, but it must be employed carefully so as not todamage other households. What to do during a landslide After long periods of heavy rainfall, be wary of intense short bursts of rain which may be particularly dangerous. Be on the loop with thelatest updates from radio or television broadcasts for rainfall warnings, and try to stay awake and be on alert. Early evacuation or preemptive measures declared by the authorities must be heeded; when it is safe to do so, evacuate immediately. Stay out of the path of a landslide or debris flow. Moving debris will always generate unusual sounds due to the cracking of trees or boulders which are knocking one another. Also look out for small flows or trickles of mud; they are usually signs of an incoming larger mudflow which could happen at any time. If you are situated close to a stream or channel, be cautious of any sudden change in the amount of water flow.A change in the color of the water from clear to muddy might indicate a landslide activity upstream.If you have suspected a possible landslide to happen based on your prior observations, inform the authorities who can provide a more accurate assessment immediately. Inform affected neighbors,so that they may start evacuation procedures when needed-the sooner you get out of harm's way,the more chances that you wouId get out unharmed. What to do after a landslide Stay away from where landslides have occurred as there might be a danger of additional slides from happening. Continue keeping yourself updated by listening to the emergency broadcasts on the television and radio. Watch out for any incidence of flooding that may have been triggered by landslides and debris flows. If you are trained in doing emergency response,provide help to those who are in need of it and inform the responding search-and-rescue teams regarding the locations of survivors.Be aware of any elderly people or person with disabilities (PWVD) in the neighborhood who might need special assistance and extra attention. Be on the lookout for broken utility lines and roadways; report such incidents immediately to the utility companies so that repairs can be made right away and resupply procedures will be made. Also note that erosion caused by loss of ground cover can lead to flash floods and additional landslides in the future. Chapter 7 From Under our Feet 165  Chapter Recap Mass movement is the downward movement of surface materials due to gravity. Geological hazards may be classified as sudden (landslides, mudflow, and lahar) or slow (mountain formation, liquefaction, and erosion). Humanmade disasters occur because of irresponsible actions against nature. Hazard maps are available for the public to view and use. The amount of water in the soil affects the cohesion forces that determine if the soil would compact or slide. There are several causes of landslides. Some of these are load on the slope, oversaturation of the soil, and oversteepening of the slope. Sinkholes are common, especially if the bedrock is made of limestone. World of Wonders in the Web For more information about the chapter topics, scan the QR code below. 168 Exploring Life Throuch c_.  As explained in the chapter, the government already made steps to map out the hazards that the country is subjected to in light of the Cherry Hills Tragedy and the Guinsaugon Landslide in Leyte.Nowadays,the agencies tasked to do such jobs have produced different hazard maps which are specific.When these hazard maps are used to carefully lay out the master plan for any future developments or the zoning of a certain area,we can be certain that we would be constructing on stable lands. Information and adherence to the law is the key to lowering the disastrous effects of mass movements. The effects of global warming also significantly contribute to the acceleration of our land being susceptible to these mass movements. Since there are fewer trees on our mountains, there are no more natural ways to keep the moisture of the soils in its optimum level to maintain cohesion and prevent sliding. Pollution also increases the production of acid rain that eats up the limestone-rich bedrocks in some Philippine provinces, thereby increasing the likelihood of sinkhole formation. Unless due diligence is done both by the community and the local government units, there is no way that the effects of disasters can be lessened. QUESTIONS: 1.How does the composition of the soil surface affect the likelihood of landslide? 2.Why are hazard maps essential in preventing or minimizing the effects of landslides? 3.What is the role of the community in ensuring little to no casualty and damages caused by landslides? 168 Exploring Life Throuch c_. 168 Exploring Life Throuch c_.