Natural Hazards

1. Natural Hazards

2. What is Natural Hazard? • A natural hazard is an unexpected or uncontrollable natural event of unusual intensity that threatens people's lives or their activities. • Atmospheric hazards are weather-related events, whereas geologic hazards happen on or within the Earth's surface. However, it is important to understand that atmospheric hazards can trigger geologic hazards, and geologic hazards can trigger atmospheric hazards.

3. Why are we concerned about natural hazards? • Unfortunately, the losses caused by natural hazards are increasing dramatically, mostly due to the rapid increase in human population. This unprecedented number of people has reduced resource availability and forced people to live in marginal areas where natural hazards occur more frequently.

4. Besides the direct impacts of natural hazards, such as a flood destroying a house, there are usually many indirect impacts, such as a flood spreading disease for weeks after the initial destruction. These indirect impacts can cause as much loss and add years to the recovery time from a disaster. Often, there is no such thing as a complete recovery - natural disasters can forever change our way of living.   Human activities can increase how often a natural hazard occurs and how severe a natural hazard can become. Understanding when, where, why, and how natural hazards occur is the first step in minimizing their impacts on our lives.

5. Geologic Hazards

6. Earthquake The term "earthquake" refers to the vibration of the Earth's surface caused by movement along a fault, by a volcanic eruption, or even by manmade explosions. The vibration can be violent and cause widespread damage and injury, or may be barely felt. Most destructive earthquakes are caused by movements along faults. Earthquakes can occur at the surface of the Earth or as deep as 400 miles below the surface. An earthquake can trigger additional hazards such as landslides or tsunamis.

7. Cause of Earthquake • An earthquake is caused by a sudden slip on a fault. Stresses in the earth's outer layer push the sides of the fault together. Stress builds up and the rocks slips suddenly, releasing energy in waves that travel through the earth's crust and cause the shaking that we feel during an earthquake. An EQ occurs when plates grind and scrape against each other.

9. Effects of earthquake • Earthquakes produce various damaging effects to the areas they act upon. This includes damage to buildings and in worst cases the loss of human life. The effects of the rumbling produced by earthquakes usually leads to the destruction of structures such as buildings, bridges, and dams. They can also trigger landslides. • Besides producing floods and destroying buildings, earthquakes that take place under the ocean can sometimes cause tsunamis, or tidal waves. Tsunamis are high and long walls of water which travel at a very rapid rate.

10. Safety Precautions Before Earthquake 1. Potential earthquake hazards in the home and workplace should be removed and corrected. Top-heavy furniture and objects, such as book cases and storage cabinets, should be fastened to the wall and the largest and heaviest objects placed on lower shelves. 2. Supplies of food and water, flashlight, a first-aid kit and a battery-operated radio should be set aside for use in emergencies. 3. One or more family members should have a working knowledge of first-aid measures because medical facilities nearly are always overloaded during an emergency or disaster, or may, themselves, be damaged beyond use. 4. All family members should know what to do to avoid injury and panic. They should know how to turn off the electricity, water and gas. They should know the locations of the main switch valves. This is particularly important for teenagers who are likely to be alone with smaller children.

11. During an earthquake 1. The most important thing to do during an earthquake is to remain CALM. If you can do so then you are less likely to be injured. Also, those around you will have a greater tendency to be clam if you are calm. 2. Make no moves or take no action without thinking about the possible consequences. Any irrational movement may be an injurious one. 3. If you are inside stay there. Stand in a doorway or crouch under a desk or table, away from windows or glass fixtures. 4. If you are outside, stay there. Stay away from objects such as light poles, buildings, trees and telephone and electric wires, which could fall and injure you. 5. If you are in an automobile, drive away from underpasses/overpasses, and stop in the safest place possible and stay there.

12. After an Earthquake 1. After an earthquake the most important thing to do is to check for injuries in your family and in the neighborhood. Seriously injured persons should not be moved unless they are in immediate danger of further injury. First-aid should be administered, but only by someone who is qualified or has a working knowledge of first-aid. 2. Evacuate the building as soon as the shaking stops. Carefully inspect the exterior of the building for cracks in walls, shifted posts and pillars. If you see anything other than minor cracks do no re-enter the building until it has been inspected for safety by a professional. 3. Check for safety-hazards - gas, water sewage breaks; downed power lines and electrical short circuits, damaged and weakened buildings and foundations, fires and fire hazards

13. 4. Turn off appropriate utilities. Do not use matches, lighters or open flame, appliances or electrical switches until you are sure that there are no gas leaks. 5. Do not use the telephone except in extreme emergency. 6. Wear shoes and protective clothing, for example, hard hats and gloves, to avoid injuries while clearing debris. 7. Keep battery-operated radios and listen for emergency bulletins. 8. If electrical power is off for any length of time use the foods in your refrigerator and freezer before they spoil. Canned and dry foods should be saved for last. 9. Co-operate with all public safety and relief organizations. Do not go into damaged areas unless authorized by appropriate personnel. 10. Be prepared for additional earthquake shocks.

14. Avalanche

15. An avalanche is a massive slide of snow, ice, rock or debris down a mountainside. Provoked by an earth tremor, extreme precipitation or man-made disturbances (such as a loud noise or the heavy movement of a skier or snowboarder), an avalanche can reach speeds of over 200 m/h (300 km/h). The impact of the falling material and the winds produced by the flow can cause extensive damage to anything in its path. According to experts, there are some 1 million avalanches yearly.

16. Causes of Avalanche • Weather: Avalanches are more likely to occur after a heavy snowstorm. The 24 hours following a storm are the most critical. • Snowfall: Recent snowfall puts extra stress on the existing snow pack, especially if the new snow does not adequately bond with the layer of snow already there. Snowfall amounts of one foot or more create the most hazardous situation, producing avalanches that are large enough to block highways and cause major destruction. • Temperature: Because snow is a good insulator, small changes don't have as much effect as larger or longer changes do. Changes that last several hours or days, such as a warm front moving through can seriously weaken some of the upper layers of snow.

17. Wind Direction: Wind usually blows up one side of the slope of the mountain(the windward side), and down the other(the leeward side). When blowing up the windward side, wind will scour snow off the surface and drop it on the leeward side. This packs snow unevenly on the leeward side, making it more prone to avalanches. Cornices are caused by wind scouring. • Snow Pack Conditions: Perhaps the most significant factor is how the snow pack has developed over the season. Understanding the history of snow pack for that season can reveal several clues about slope stability. Snow pack conditions can change not only over the course of the winter season but over the course of a day. This is why constant awareness and frequent slope testing are necessary. 

18. Slope Angle: Most avalanches occur on slopes between 30 and 45 degrees. You can measure the slope angle with an inclinometer, or you can "eyeball" it by dangling a ski pole by the strap and estimating the angle. • Slope Orientation: Although avalanches will run on slopes facing any direction, most avalanches run on slopes facing north, east, and northeast. Because the sun is at such a low angle, particularly during the winter, a colder and deeper snow pack develops.

19. Vegetation: On a snow covered slope, heavily forested areas are much safer than open spaces. Lone trees, bushes, or large rocks on a mountainside can sometimes weaken the stability of the snow pack. A fracture line (the break-off point for an avalanche) may run from a lone tree to a rock to another tree. Tree line (above which conditions make it to harsh for trees to grow) and smooth surfaces such as a rock face or grassy slope can effect the probability of an avalanche.

20. Effect of Avalanche • Most avalanches have been known to destroy crops, homes and people. They can do this by either burying them, or crushing them. They are very deadly.

21. Sinkholes

22. Sinkholes are depressions or holes in the land surface . They can be shallow or deep, small or large, but all are a result of the dissolving of the underlying limestone.

23. A sinkhole is just what the word implies, the sinking of an area of the earth's surface forming a hole. Sinkholes vary in size but can be large enough to allow a roadway or house to sink with them. In many places sinkholes are unheard of, but in areas where they are common they need to be taken seriously. Sinkholes usually occur where rock below the surface is limestone.

24. Causes of sinkholes • Sub-Surface Soil Disturbances Sinkholes develop when sub-surface rock develops a hole or void due to erosion. Gradually soil from above seeps down to fill the void in the rock, creating an open area or void in the sub-surface soil. As surface soil washes down, the void in the soil moves toward the surface. Eventually, the hole is just below the surface and there is a collapse, creating a sinkhole.

25. Changes in Sub-Surface Water Changes in the sub-surface water play a major role in the development of sinkholes. Water both causes the voids in rocks and washes away the residue from the voids, setting the development of a sinkhole into motion. Changes in groundwater, either from naturally occurring droughts or heavy rains, or from changes in the water table brought about by seasonal freezing and thawing, contribute as well. Human intervention to raise or lower groundwater is also sometimes a factor.

26. Human Activity Human activity that alters ground water can play a major role in sinkhole development. Sub-surface water helps keep surface soil in place, so any artificial alteration of ground water drainage can create problems, as can changes in the land surface such as creation of runoff-storage ponds. The weight of man-made construction can also cause a collapse.Human constructions can also provide clues to the development of sinkholes before they occur. Some of these signs are uneven floors or pavement, cracks in pool decks, a stair step pattern of cracks in the wall of a building and depressions in an open area such as a yard or park.

27. Volcanic Eruption

28. Volcanic eruptions are one of Earth's most dramatic and violent agents of change. They pose significant geologic hazards because their eruptions and associated activities can affect large areas and go on for extended periods of time. Many kinds of volcanic activity can endanger the lives of people and property, and the affects of these activities are felt both close to and far away from the volcano

29. Cause of Volcanic Eruption • A volcano erupts when magma escapes from inside the earth. As the magma is escaping from a confined space, a lot of energy is released with it, as happens with any other explosion. This is why many eruptions also produce huge quantities of gases and dust. Magma sometimes rises under enormous pressure, so it not only finds cracks in the earth’s crust, it can also create them. When magma reaches the earth’s surface it is called lava.

30. Safety Precautions During Volcanic Eruption • Residents living around an erupting volcano are faced with volcanic hazards that may ensue. These include pyroclastic flows, ash fall and lahars. • Hazard maps that show areas likely to be affected by any of these hazards are available from proper authorities prior to eruption. Follow all advisories and warnings, as these can save your lives. • Avoid the declared permanent danger zones in your locality. Also, rivers where hazardous volcanic substances can flow should be avoided.

31. Should ashfall occur, cover your nose with a wet cloth to allow for better breathing. • Should ashfall occur, cover your nose with a wet cloth to allow for better breathing. • Always clean your roof when heavy ashfall occurs to prevent collapse. • If you are inside a moving vehicle, seek shelter immediately. If you are along the path of potential lahar flows, move to higher ground or to a designated evacuation site.

32. Hydrological Hazards

33. FLOODS The term "flood" is a general or temporary condition of partial or complete inundation of normally dry land areas from overflow of inland or tidal waters or from the unusual and rapid accumulation or runoff of surface waters from any source. Flooding and flash flooding are the deadliest of natural disasters. Floodwaters claim thousands of lives every year and render millions homeless. One of the more frightening things about flooding is that it can occur nearly anywhere, at any time.

34. Causes of Floods 1.High rainfall Heavy rainfall raises the water level. When the water level is higher than the river bank or the dams, the water comes out from the river, there will have a flooding. 2.Snowmelt because of the global warming, the temperature of this year is higher than the temperature of many years ago. The ice caps melt in spring, many water go into the sea. The water raises the sea level, and makes the river level raise. When river level raises, flooding may cause. 3.Relief flooding often occurs in lowland. This is because rivers flow more slowly in low-lying area. If the water volume increases suddenly, floods occur. 4.Coastal flooding Flooding always occur in coastal areas. Because there have high tides or storms, the sea level will raise. If the sea level is higher than the level of the coastal lowland, flooding will occur.

35. Effects of Flooding • 1. Economy • Resources used in reconstruction • After flooding, government has to input many resources for aiding or reconstruction, e.g., police force, fire control, aid worker, resources used for resisting flood, etc. This also brings loss to society. • 2. Environment • Traffic • Flooding will lead to the damages of roads, collapse of bridges or traffic congestion, which may affect the daily operation. • Damaging the farmland • Flooding brings too much water which will cause damage to farmland. • 3. Human Beings • People died and lose their homes.

36. Flooding Precautions • BEFORE A FLOOD • Before building, check the area for signs or history of flooding and find out how many feet above flood level you need to build your house. • Do not throw garbage into drains and rivers. • Put sandbags by exposed openings. • Turn off gas and electricity. Unplug electrical appliances. • Put dangerous, flammable or explosive liquids in a safe place and close containers securely. • Seal important personal, legal and business documents in watertight containers and place above flood height. • Take furniture to upper floors or raise on a sturdy table. • Secure vehicles.

37. DURING A FLOOD • Turn on a battery-powered radio. • Evacuate and avoid flooded areas. • Do not try to cross water courses. • If your car gets stuck, abandon it immediately.

38. TSUNAMI Tsunamis are usually formed when there is an underwater earthquake, volcano, or other seismic event. The word tsunami comes from Japanese (one of the most common locations for tsunamis), "Tsu", meaning "harbor" and "nami" meaning "wave".

39. Causes of Tsunami • An Undersea Earthquake- is the most common form of tsunami formation, typically generating the most destructive tsunamis.  The earth is constantly moving on large tectonic plates.  When these tectonic plates move past each other, collide and/or slide under one another (subduction), an earthquake results. • Landslides – resulting in rockfalls, icefalls, or underwater (submarine) landslides or slumps can generate displacement of water to create a tsunami.  • Volcanic Eruption - Although relatively infrequent, violent volcanic eruptions represent also impulsive disturbances, which can displace a great volume of water and generate extremely destructive tsunami waves in the immediate source area.    Volcanic disturbances can generate waves by the sudden displacement of water caused by a volcanic explosion, by a volcano's slope failure, or more likely by a phreatomagmatic explosion and collapse and/or engulfment of the volcanic magmatic chambers.

41. Atmospheric Hazards

42. Drought A drought is a climate event marked by a prolonged period of decreased rainfall. Droughts are in fact part of the natural climate cycle in many regions of the world, but they can still be extremely disruptive, especially when the impact of the drought is increased by human activities. Drought conditions are of interest socially, politically, economically, and environmentally, and at any given time, several regions of the world are often experiencing dry conditions.

43. Causes of Drought • It could be a lack of rainfall. • It could be a lack of snowfall from mountains far away (not in India but in colder regions of the world); or • It could be caused when water supplies are not sufficient to meet every body's needs.

44. Effects of Drought Lack of water means less irrigation for the crops, less drinking water, less water for hygiene, and less hydro-electricity. In developing countries droughts cause bad disease, famine, and death.

45. Hail storm Hail is a form of solid precipitation which consists of balls or irregular lumps of ice, that are individually called hail stones. Hail stones on Earth consist mostly of water ice and measure between and in diameter, with the larger stones coming from severe thunderstorms.

46. Causes of Hailstorm A hailstorm occurs when you have a cold air mass, high in the atmosphere, meets a warn, moist air mass or front. The warm air will cool rapidly and lose its water in the form of rain. If the cold air is cold enough or high enough in the atmosphere that rain will freeze and fall to the ground as ice.

47. Effects of Hailstorm • Housing Damage • Vehicles • Crops

48. Tornado A tornado is a powerful column of winds spiraling around a center of low atmospheric pressure. It looks like a large black funnel hanging down from a storm cloud. The narrow end will move over the earth, whipping back and forth like a tail. The winds inside a tornado spiral upward and inward with a lot of speed and power. It crates an internal vacuum that then sucks up anything it passes over. When the funnel touches a structure, the fierce winds have the ability to tear it apart.

49. Causes of Tornado • Instability refers to unusually warm and humid conditions in the lower atmosphere, and possibly cooler than usual conditions in the upper atmosphere. • Wind shear in this case refers to the wind direction changing, and the wind speed increasing, with height.

50. Effects of tornado People who live in tornado prone regions know about the destructive effects of tornadoes; but those who have never experience this weather phenomena may not really understand how devastating they can be. Tornadoes are usually short lived, but in that short period of time they can cause unbelievable havoc on anyone or anything that is in their path. It is common for tornadoes to lift buildings from their foundations, roll vehicles and mobile homes around as if they were toys, and even propel animals and people great distances.