英语达人帮一下~有关自然灾害的问题~~急~

A natural disaster is caused by nature, such as floods, volcanic eruptions, earthquakes, tsunamis, avalanches, lahars (volcanic mudslides), landslides, sinkholes, blizzards, drought, hailstorms, heat waves, hurricanes, tropical storms, typhoons, Ice Ages, tornadoes, and wildfires。 Epidemics caused by bacteria or viruses are sometimes considered natural disasters, but sometimes put into a different category。 A biological threat such as locusts or toxic fungi could also be considered a natural disaster。Some disasters are on the edge of natural and non-natural。 Famines, the chronic lack of food, may be caused by a combination of natural and human factors。 Two space-originating categories of natural disaster, both of which rarely effect humans on the surface, include asteroid impacts and solar flares。 Although the risk of asteroid impact in the short term may be low, some scientists argue that in the long term, the likelihood of death by asteroid is similar to that of death by traditional natural disasters such as disease。The deadliest natural disasters are famines, which claimed 70 million people during the 20th century alone, with 30 million dying during the famine of 1958–61 in China。 In the Soviet Union there were several man-made famines that killed millions, blamed on the collectivist policies of Stalin, the leader of the country at the time。 Famines have a history of bringing out the worst in people, including atrocities and cannibalism。Another of the deadliest natural disasters are epidemics, most notably the Spanish flu of 1918-1919, which killed 50 million — more than World War I, which had occurred just before。 Rather than killing infants or the aged, the Spanish flu struck down people in the prime of life。 Having a good immune system was no protection against this virus — in fact, it was a liability。 The virus is believed to have killed its victims primarily through overactivating the immune system in a process called a cytokine storm。Historically, volcanoes may have been the biggest type of natural disaster。 Some scientists believe that the eruption of Mt。 Toba in Indonesia over 73,000 years ago may have killed off most of the human species, leaving behind only 1,000 - 10,000 breeding pairs。 This phenomenon, called a population bottleneck, has been confirmed through genetic analysis。