Natural hazard

  • A threat of a naturally occuriring event that will have a negative effect on people or the environment.
  • Natural hazards are severe and extreme weather and climate events that occur naturally in all parts of the world, although some regions are more vulnerable to certain hazards than others. Natural hazards become natural disasters when people’s lives and livelihoods are destroyed. (WMO)


  • Avalanche
    • Snowslide or snowslip
    • Sudden drastic flow of snow down a slope, occuring when either natural triggers, such as loading from new snow or rain, or artificial triggers, such as explosives or snowmobilers.


  • Earthquake
    • Quake, tremor, temblor
    • The result of a sudden release of energy in the earth’s crust that creates seismic waves.
    • An earthquake’s point of initial rupture is called its focus or hypocenter. The epicenter is the point at ground level directly above the hypocenter.
    • Tsunami – soo-nah-mee
    • A series of water waves caused by the displacement of a large volume of a body of water.
    • Earthquakes, volcanic eruptions, and other underwater explosions, landslides, glacier calvings, meteorite impacts all have potential to generate tsunami.


  • Lahar
    • Lahar is an Indonesian term that describes a hot or cold mixture of water and rock fragments that flows down the slopes of a volcano and typically enters a river valley.
    • A moving lahar looks like a rolling slurry of wet concrete, and as it rushes downstream, the size, speed and amount of material carried can constantly change.
    • Eruptions may trigger lahars by melting snow and ice or by ejecting water from a crater lake.
    • Pyroclastic flows can generate lahars when extremely hot, flowing rock debris erodes, mixes with, and melts snow and ice as it travel rapidly down steep slopes.


  • Sinkholes
    • Sink, snake hole, swallow hole, swallet, doline, or cenote.
    • Natural depression or hole in the earth’s surface caused by chemical dissolution of carbonate rocks.
    • Usually caused by the collapse of a subterranean structure such as a cave.
    • Sinkholes are common where the rock below the land surface is limestone, carbonate rock, salt beds, or rocks that can naturally be dissolved by groundwater circulating through them.


  • Volcanic eruption
    • The point in which a volcano is active and releases its power. Lava, tephra, and various gases are expelled from volcanic fissures.
    • Eruptions can be effusive, where lava flows like a thick, sticky liquid, or explosive, where fragmented lava explodes out of a vent.
    • In explosive eruptions, the fragmented rock may be accompanied by ash and gases; in effusive eruptions, degassing is common but ash is usually not.
    • Types of eruptions:
      • Hawaiian eruption
      • Strombolian eruption
      • Vulcanian eruption
      • Plinian eruption
      • Lava domes
      • Surtseyan eruption
    • note: refer to


  • Landslide
    • Landslide is the movement of rock, debris or earth down a slope. They result from the failure of the materials which make up the hill slope and are driven by the force of gravity.
    • Landslides are known also as landslips, slumps, or slope failure.
    • Landslide movements:
      • Fall – rapid rate of descent
      • Topple – abrupt falling, sliding, bouncing and rolling.
      • Flow – lose cohesion, turns slurry due to water.
      • Slide – slumps, move with rotation
      • Spread – caused by liquefaction, gradual lateral displacement.



  • Blizzard
    • Severe snow storm characterized by strong winds causing blowing snow that results in low visibilities.
    • Blizzards can bring whiteout conditions, and can paralyze regions for days at a time, particularly where snowfall is unusual or rare.
    • Blizzard conditions of cold temperatures and strong winds can cause wind chill values that can results in hypothermia or frostbite.

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  • Drought
    • A period of below-average precipitation in a given region, resulting in prolonged shortages in the water supply, whether atmospheric, surface water or ground water.
    • A drought can last for months or years.
    • It can have substantial impact on the ecosystem and agriculture of the affected region.
    • Causes of drought: precipitation deficiency, dry season, El Nino, erosion and human activities, and climate change.


  • Hailstorm
    • A natural hazard where a thunderstorm produces numberous hailstones which damage the location in which they fall.
    • Hail formation requires environments of strong, upward motion of air with the parent thunderstorm and lowered heights of the freezing level.


  • Heatwave
    • A hazard characterized by heat which is considered extreme and unusual in the area in which it occurs..
    • Is a prolonged period of excessively hot weather, which may be accompanied by high humidity, especially in oceanic climate countries.
    • A heat wave is considered extreme weather, and a danger because heat and sunlight may overheat the human body.
    • Temperatures that people from a hotter climate consider normal can be termed a heat wave in a cooler area if they are outside the normal climate pattern for that area.


  • Cyclonic storms
    • Cyclonic storms develop when an advancing cold front pushes into a region of lighter, warmer air.
    • As the warm air is pushed away, the resulting low atmospheric pressure will sometimes create complex wind storms that spiral in toward the center of the disturbance. These storms primarily develop in low pressure areas over tropical or sub-tropical waters.
    • The warm temperatures and the spiraling effects of the winds combine to create the huge storms that periodically sweep the Atlantic and Pacific oceans.
    • Tropical cyclones are like giant engines that use warm, moist air as fuel. That is why they form only over warm ocean waters near the equator. The warm, moist air over the ocean rises upward from near the surface. Because this air moves up and away from the surface, there is less air left near the surface. Another way to say the same thing is that the warm air rises, causing an area of lower air pressure below.
    • they generally develop in different regions only at certain times of the year: in the northern hemisphere, tropical cyclones–with winds that spin counterclockwise–develop between May and November, while in the southern hemisphere– where the winds spin clockwise–they are generally found between December and June.


  • Ice storm
    • An ice storm is a type of winter storm characterized by freezing rain, also known as a glaze eventor in some parts of the United States as a silver thaw. From 1982 to 1994, ice storms were more common than blizzards and averaged 16 per year.
    • Ice storms occur when a layer of warm air is between two layers of cold air. Frozen precipitation melts while falling into the warm air layer, and then proceeds to refreeze in the cold layer above the ground. If the precipitate is partially melted, it will land on the ground as sleet.
    • However, if the warm layer completely melts the precipitate, becoming rain, the liquid droplets will continue to fall, and pass through a thin layer of cold air just above the surface. This thin layer of air then cools the rain to a temperature below freezing (0 °c or 32 °f). However, the drops themselves do not freeze, a phenomenon called supercooling (or forming “supercooled drops”).
    • When the supercooled drops strike ground below 0 °c (32 °f) or anything else below 0 °c (32 °f) (power lines, tree branches, aircraft), they instantly freeze, forming a thin film of ice, hence freezing rain


  • Tornado
    • A tornado is a violent, dangerous, rotating column of air that is in contact with both the surface of the earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud. They are often referred to as a twister or a cyclone.
    • The word tornadois an altered form of the spanish word tronada, which means “thunderstorm”. This in turn was taken from the latin tonare, meaning “to thunder”.
    • Twisters are born in thunderstorms and are often accompanied by hail. Giant, persistent thunderstorms called supercells spawn the most destructive tornadoes.
    • These violent storms occur around the world, but the United States is a major hotspot with about a thousand tornadoes every year. “Tornado alley,” a region that includes eastern South Dakota, Nebraska, Kansas, Oklahoma, northern Texas, and eastern Colorado, is home to the most powerful and destructive of these storms. US tornadoes cause 80 deaths and more than 1,500 injuries per year.


  • Sand storm
    • Or dust storm, is a meteorological phenomenon common in arid and semi-arid regions. Dust storms arise when a gust front or other strong wind blows loose sand and dirt from a dry surface.
    • Particles are transported by saltation and suspension, causing soil to move from one place and deposition in another. The sahara and drylands around the arabian peninsula are the main terrestrial sources of airborne dust


  • Geomagnetic storm
    • Is a temporary disturbance of the earth’s magnetosphere caused by a disturbance in the interplanetary medium.
    • Is caused by a solar wind shock wave and/or cloud of magnetic field which interacts with the earth’s magnetic field. The increase in the solar wind pressure initially compresses the magnetosphere and the solar wind magnetic field will interact with the earth’s magnetic field and transfer an increased amount of energy into the magnetosphere.

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  • Wildfire
    • A wildfire is any uncontrolled fire in combustible vegetation that occurs in the countryside or a wilderness area. Other names such as brush fire, bushfire, forest fire, desert fire, grass fire, hill fire, peat fire, vegetation fire, and veldfire may be used to describe the same phenomenon depending on the type of vegetation being burned.
    • Wildfires can cause extensive damage, both to property and human life, but they also have various beneficial effects on wilderness areas. Some plant species depend on the effects of fire for growth and reproduction, although large wildfires may also have negative ecological effects.

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