Classification of Disasters Depending on their origin, Disasters can be broadly classified as
An earthquake is a sudden, violent shaking or movement of part of the earth’s surface, caused by the abrupt displacement of rock masses, usually within the upper 10 to 20 miles of the earth’s surface.
Earthquake occurs when pressure beneath the earth’s crust builds up to such a point that giant blocks of rock start pushing against one another, and creak and groan, causing shudders on the surface. Eventually one rock plate rides on top of the other. This may cause a huge rift on the earth’s surface. When the stress exceeds the bearing capacity of the rocks, they break, suddenly releasing the accumulated stress. It is at this instant that an earthquake occurs. The impact of this gigantic rearrangement causes shock waves, which spread for miles around. breakage of rocks is spread over an area covering 40 kms.
Landslide is a descent of a mass of earth and rock down a mountain slope. Landslides may occur when an earthquake occurs or when water from rain sinks through the earth on top of a slope, seeps through cracks and pore spaces in underlying sandstone, and encounters a layer of slippery material, such as shale or clay, inclined toward the valley. The water collects along the upper surface of this layer which it softens. If the support is sufficiently weakened, a mass of earth and rock slides down along the well-lubricated layer. Some great landslide masses move slowly and spasmodically for years, causing little destruction. Earthquakes and volcanic eruptions can also cause severe, fast-moving landslides. Such masses characteristically have the appearance of hummocks, or rounded knolls, and trees growing on them are likely to be tilted at odd angles. Landslides that suddenly rush down a steep slope can cause great destruction across a wide area of habitable land and sometimes cause floods by damming up bodies of water. Landslides can assume disastrous proportions, especially the ones triggered by earthquakes (e.g. The El Salvador landslide in Central America). They are all due to loss of stability, which can be brought about by natural or man-made causes. While the landslides occur commonly in hill stations like Simla, Mussourie, etc. and on the banks of the rivers like the Alaknanda, they can also occur in densely populated towns of Mumbai, like Ghatkopar and Kandivili.
Flood is described as a situation where a normally dry land becomes inundated with water. Floods can be slow or fast rising, but they generally develop over a number of days. When flooding occurs quickly due to a calm river turning to a raging river, it catches people off-guard and is, thus, dangerous. There are different types of floods, some of which are described below
Types of Floods
- Coastal Flood
- River Flood
- Flash Flood
- Flash Floods in Arroyos
These are the large sea waves produced by an undersea earthquake abruptly moving the ocean floor. The waves move at a high velocity and can cross thousands of kilometers before they reach the shore. At sea, their low wave height gives little evidence of their existence. However, as they approach land, their velocity decreases and their height increases. In this way, a five meter crest moving at 600 kmph in the open sea becomes a devastating 30-meter high wave moving at 50 kmph when it reaches shore. Tsunamis are dangerous because areas far from the earthquake’s epicentre can be struck without warning. There are instances of earthquakes in Chile creating tsunamis that struck in Japan.
Cyclone is the result of a low pressure area developing in the atmosphere. It has two characteristics
- Atmospheric pressure, which is lowest at the centre, and
- Winds that spiral in towards the center.
They can either be warm-core or cold-core.
People in some regions call the cyclone a tornado or a twister. Cyclones are also called as a Tornado, Typhoon or a Hurricane based on their characteristics, speed and conditions in which they are created.
Droughts and Famines
Though droughts and famines are often used synonymously, they have different connotations. A drought is not a famine. Famine (fames in Latin means hunger) means severe shortage of food, generally affecting a widespread area and large number of people. Natural causes include droughts, floods, earthquakes, insect plagues, and plant disease. Man-made causes of a famine include wars, civil disturbances, sieges, and deliberate crop destruction. Widespread, chronic hunger and malnutrition may result from severe poverty, inefficient food distribution, or population rise that is disproportionate to the food producing or procuring capacity of people in a region.
On the other hand, a Drought is a condition of abnormally dry weather within a geographic region, where some rain might usually be expected. A drought is, thus, quite different from a dry climate. The term drought is applied to a period in which an unusual scarcity of rain causes a serious hydrological imbalance; water supply reservoirs become empty, wells dry up, and crop damage ensues. The severity of the drought is gauged by the degree of moisture deficiency, its duration, and the size of the area affected. If the drought is brief, it is known as a dry spell or partial drought. A partial drought is usually defined as having duration of more than 14 days, without appreciable precipitation, whereas a drought may last for years.
Drought is, thus, a meteorological phenomenon, that does not always have a direct relationship with famine, while famine is not a mere deficiency of food but an absolute lack of food.
Forest or jungle fires are classified as a type of natural fire. It happens due to severe climatic conditions, like extremely high temperatures. These fires are usually not noticed immediately, since they are in the forests, but, by the time they are detected, they have already spread in the surrounding forest areas. These fires cause a lot of ecological damage.