you can learn about disasters.
2. A natural disaster is a major adverse eventresulting from natural processes of the Earth.Examples: floods, volcaniceruptions, earthquakes, tsunamis, and othergeologic processes.A natural disaster can cause loss of life orproperty damage and typically leaves someeconomic damage in its wake, the severity ofwhich depends on the affectedpopulation's resilience or ability to recover. 3. An adverse event will not rise to the levelof a disaster if it occurs in an area withoutvulnerable population. In a vulnerablearea, however, such as San Francisco,an earthquake can have disastrousconsequences and leave lasting damage,requiring years to repair. 4. Catastrophes Statistics for the year 2012Total count 905Meteorological (Storms) 45%Hydrological (Floods), 36%Climatological (Heat waves, coldWaves, Droughts, Wildfires) 12%Geophysical events (Earthquakesand Volcanic eruptions). 7%Catastrophes 93%Cost in Billion US $ 170Insured Losses US $ 7093%Between 1980 and 2011 geophysical eventsaccounted for 14% of all natural catastrophes. 5. Droughts Hailstorms Heat waves Tornadoes Wild fires Health disasters Epidemics Space disasters Impact events Solar flare Gamma-ray burst Protection by international law 6. Avalanches 7. An avalanche (also called a snowslide or snowslip)is a rapid flow of snow down a slope. Avalanches aretypically triggered in a starting zone from amechanical failure in the snowpack (slab avalanche)when the forces on the snow exceed its strength butsometimes only with gradually widening (loose snowavalanche). After initiation, avalanches usuallyaccelerate rapidly and grow in mass and volume asthey entrain more snow. If the avalanche moves fastenough some of the snow may mix with the airforming a powder snow avalanche, which is a typeof gravity current. 8. Slides of rocks or debris, behaving in a similar way to snow,are also referred to as avalanches (see rockslide). Theremainder of this article refers to snow avalanches.The load on the snowpack may be only due to gravity, inwhich case failure may result either from weakening in thesnowpack or increased load due to precipitation.Avalanches that occur in this way are known asspontaneous avalanches. Avalanches can also be triggeredby other loads such as skiers, snowmobilers, animals orexplosives. Seismic activity may also trigger failure in thesnowpack and avalanches. 9. Although primarily composed of flowing snow andair, large avalanches have the capability to entrainice, rocks, trees, and other material on the slope,and are distinct from mudslides, rock slides,and serac collapses on an icefall. Avalanches arenot rare or random events and are endemic to anymountain range that accumulates a standingsnowpack. Avalanches are most common duringwinter or spring but glacier movements may causeice and snow avalanches at any time of year. 10. In mountainous terrain, avalanches are among themost serious objective natural hazards to life andproperty, with their destructive capability resultingfrom their potential to carry enormous masses ofsnow at high speeds.There is no universally accepted classification ofavalanchesdifferent classifications are useful fordifferent purposes. Avalanches can be described bytheir size, their destructive potential, theirinitiation mechanism, their composition and theirdynamics. 11. Formation and classification Loose snow avalanches Slab avalanches Powder snow avalanches Dry snow avalanches Terrain, snowpack, weather Terrain Snowpack structure and characteristics Weather Dynamics Modeling Human involvement Prevention Mitigation Survival, rescue, and recovery 12. FormationandclassificationMost avalanchesoccur spontaneouslyduring storms underincreased load due tosnowfall. The secondlargest cause ofnatural avalanches ismetamorphicchanges in thesnowpack such asmelting due to solarradiation. 13. Loose snowavalanchesLoose snowavalanches(far left)and slab avalanches(near center)nearMountShuksan inthe North Cascadesmountains.Fracturepropagation isrelatively limited. 14. SlabavalanchesA crown fracturefrom a slabavalanche nearthe Neve Glacierin the NorthCascadesmountains.Extensive fracturepropagation isevident. 15. PowdersnowavalanchesA powder snowavalanche inthe HimalayasnearMountEverest. 16. Dry snowavalanchesDry snowavalanchewith apowdercloud 17. Terrain,snowpack,weatherDoug Fesler andJill Fredstondeveloped aconceptualmodel of thethree primaryelements ofavalanches:terrain, weather,and snowpack. 18. TerrainIn steepavalanche-proneterrain,traveling onridges isgenerally saferthan traversingthe slopes. 19. Drought is an extended period when a region notes a deficiency in its watersupply whether surface or underground water. A drought can last for months oryears, or may be declared after as few as 15 days. Generally, this occurs when aregion receives consistently below average precipitation. It can have a substantialimpact on the ecosystem and agriculture of the affected regionMany plant species, such as cacti, have adaptations such as reduced leaf area andwaxy cuticles to enhance their ability to tolerate drought. Some others survivedry periods as buried seeds. Semi-permanent drought produces arid biomes suchas deserts and grasslands. Most arid ecosystems have inherently lowproductivity.This global phenomenon has a widespread impact on agriculture. Lengthy periodsof drought have long been a key trigger for mass migration and played a key rolein a number of ongoing migrations and other humanitarian crises in the Horn ofAfrica and the Sahel.According to F. Bagouls and Henri Gaussen's definition, a month is dry when themean monthly precipitation in millimeters is equal to or lower than twice the meanmonthly temperature in C. 20. ConsequencesGlobally. Regions affectedCausesTypesProtection and relief 21. ConsequencesA Mongolian gazelle dead due to drought. Periods of droughts can havesignificant environmental, agricultural, health, economic and socialconsequences. The effect varies according to vulnerability. For example,subsistence farmers are more likely to migrate during drought because theydo not have alternative food sources. Areas with populations that depend on asa major food source are more vulnerable to famine.Drought can also reduce water quality, because lower water flows reducedilution of pollutants and increase contamination of remaining water sources.Common consequences of drought include:Diminished crop growth or yield productions and carrying capacity forlivestockDust bowls, themselves a sign of erosion, which further erode the landscapeDust storms, when drought hits an area suffering from desertification anderosion 22. Famine due to lack of water for irrigationHabitat damage, affecting both terrestrial and aquatic wildlifeHunger, drought provides too little water to support food crops.Malnutrition, dehydration and related diseasesMass migration, resulting in internal displacement and international refugeesReduced electricity production due to reduced water flow throughhydroelectric damsShortages of water for industrial usersSnake migration and increases in snakebitesSocial unrestWar over natural resources, including water and food 23. GloballyDrought is a normal, recurring feature of the climate in most parts of theworld. It is among the earliest documented climatic events, present in the Epicof Gilgamesh and tied to the biblical story of Joseph's arrival in and the laterExodus from Ancient Egypt.Hunter-gatherer migrations in 9,500 BC Chile have been linked to thephenomenon, as has the exodus of early humans out of Africa and into the restof the world around 135,000 years ago.Modern people can effectively mitigate much of the impact of drought throughirrigation and crop rotation. Failure to develop adequate drought mitigationstrategies carries a grave human cost in the modern era, exacerbated by ever-increasingpopulation densities.Regions affectedRecurring droughts leading to desertification in the Horn of Africa havecreated grave ecological catastrophes, prompting massive food shortages, stillrecurring. To the north-west of the Horn, the Darfur conflict in neighbouring 24. Sudan, also affecting Chad, was fueled by decades of drought and overpopulationare among the causes of the Darfur conflict, because the Arab Baggara nomadssearching for water have to take their livestock further south, to land mainlyoccupied by non-Arab farming peoples.Approximately 2.4 billion people live in the drainage basin of the Himalayanrivers. India, China, Pakistan, Bangladesh, Nepal and Myanmar could experiencefloods followed by droughts in coming decades. Drought in India affecting theGanges is of particular concern, as it provides drinking water and agriculturalirrigation for more than 500 million people. The west coast of North America,which gets much of its water from glaciers in mountain ranges such as the RockyMountains and Sierra Nevada, also would be affected.In 2005, parts of the Amazon basin experienced the worst drought in 100 years.A 23 July 2006 article reported Woods Hole Research Center results showingthat the forest in its present form could survive only three years of drought.Scientists at the Brazilian National Institute of Amazonian Research argue inthe article that this drought response, coupled with the effects ofdeforestation on regional climate, are pushing the rainforest towards a "tippingpoint" where it would irreversibly start to die. 25. It concludes that the rainforest is on the brink of being turned into savanna ordesert, with catastrophic consequences for the world's climate. According tothe WWF, the combination of climate change and deforestation increases thedrying effect of dead trees that fuels forest fires.By far the largest part of Australia is desert or semi-arid lands commonly knownas the outback. A 2005 study by Australian and American researchersinvestigated the desertification of the interior, and suggested that oneexplanation was related to human settlers