An earthquake (also known as a tremor or temblor) is the result of a sudden release of energy in the Earth's crust that creates seismic waves. Earthquakes are recorded with a seismometer, also known as a seismograph. The moment magnitude of an earthquake is conventionally reported, or the related and mostly obsolete Richter magnitude, with magnitude 3 or lower earthquakes being mostly imperceptible and magnitude 7 causing serious damage over large areas. Intensity of shaking is measured on the modified Mercalli scale.

A tornado is a violent, dangerous, rotating column of air which is in contact with both the surface of the earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud. Tornadoes come in many sizes but are typically in the form of a visible condensation funnel, whose narrow end touches the earth and is often encircled by a cloud of debris and dust.

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hurricanes

A tropical cyclone(hurricane) is a storm system characterized by a large low-pressure center and numerous thunderstorms that produce strong winds and heavy rain. Tropical cyclones feed on heat released when moist air rises, resulting in condensation of water vapor contained in the moist air.

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Volcanic eruptions

• An Eruption may in itself be a disaster due to the explosion of the volcano or the fall of rock but there are several effects that may happen after an eruption that are also hazardous to human life.
• Lava may be produced during the eruption of a volcano a material consisting of superheated rock. There are several different forms which may be either crumbly or gluey. Leaving the volcano this destroys any buildings and plants it encounters.
• Volcanic ash - generally meaning the cooled ash - may form a cloud, and settle thickly in nearby locations. When mixed with water this forms a concrete like material. In sufficient quantity ash may cause roofs to collapse under its weight but even small quantities will cause ill health if inhaled. Since the ash has the consistency of ground glass it causes abrasion damage to moving parts such as engines.
• Supervolcanos : According to the Toba catastrophe theory 70 to 75 thousand years ago a super volcanic event at Lake Toba reduced the human population to 10,000 or even 1,000 breeding pairs creating a bottleneck in human evolution. It also killed three quaters of all plant life in the northern hemisphere. The main danger from a supervolcano is the immense cloud of ash which has a disastrous global effect on climate and temperature for many years.
• Pyroclastic flows consist of a cloud of hot volcanic ash which builds up in the air above under its own weight and streams very rapidly from the mountain burning anything in its path. It is believed that Pompeii was destroyed by a pyroclastic flow.