Occurring most commonly in North America, tornadoes occur in conjunction with thunderstorms. When bodies of warm and cool air suddenly collide, the result can be an upward spiral of fast-moving wind. These winds can reach speeds exceeding 200 miles per hour. At such speeds, the wind alone becomes a danger to human lives and structures. When carrying sharp and heavy debris, tornadoes become even more dangerous.
In various parts of the world, massive rotating storms form in tropical areas and drift to subtropical and temperate areas. These storms are called hurricanes in the Americas, typhoons in East Asia and the Pacific islands and cyclones in areas bordering the Indian Ocean. According to the Hurricane Facts website, these storms are "the most destructive natural weather occurrences on Earth." Hurricanes are so destructive because they often initiate other kinds of natural disasters and hazards, such as tornadoes, lightning, floods and mudslides.
Avalanches, landslides, and mudslides are all characterized by a large amount of a particular substance suddenly flowing down a steep slope and covering objects in its path. Avalanches occur due to excessive amounts of snow accumulated on a mountainside. They are sometimes caused by seismic activity. Landslides occur mostly due to seismic activity disrupting a mass of loose soil or rock on a slope. Mudslides are usually caused by excessive rain combined with deforestation.
The crust of the Earth is composed of seven major tectonic plates that are constantly shifting and rubbing against one another. When these plates push together or pull apart, an earthquake will often result. Most earthquakes occur without anyone noticing except scientists, but some earthquakes are so powerful that they knock people off their feet and level buildings. Most of the planet's earthquakes occur in the Pacific Rim.
Tsunamis are huge ocean waves usually started by underwater earthquakes. Tsunamis can occur suddenly and reach speeds of up to 500 mph. The shock wave of a tsunami may not even be noticeable in the open ocean, but as the wave or waves approach the shallower water near land, they can suddenly grow to 100 feet and can wipe out coastal communities.
