Urgent problems of mankind

Earthquake,vibrations produced inside the earth. The vibrations can range from barely noticeable to catastrophically destructive. There are six kinds of shock waves generated in the process. Two are classified as body waves and the other four are surface waves.
The general classes of earthquakes are: tectonic,vulcanic and artificially. The tectonic is the most devastating but scientists find ways to predict them.
The tectonic earthquake is situated in zones where one plate slides past another,for example at the San Andreas fault in California.If one plate will slide below the other at a sharp angle the earthquakes in these areas are not so strong,but if two plates are sliding beside each other,one plate will often be forced under the other at a shallow angle so these eartquakes are more frequent and stronger.In these regions they can cause great loss of life by destroing structures, buildings, bridges and they can also devastating nature

Seismologists have devised two scales to desribe earthquakes quantitatively. One is the Richter scale-named after american seismologist CH.F.Richter, which measures the motion of the land from the epicenter to focus.The Richter scale is open-ended.The other scale was invited in 20th century by the italian seismogolist Giusseppe Mercalli.This scale measures the intensity of shaking from 1 to 12.
The strongest earthquakes were in 1906 in San Francisco 8.3-9.2 and in 1964 the Alaskan earthquake 8.4-9.2 richter´s scale, but the biggest one was in Tokyo
with the loss of 200 000 lives. It was past but now we can predict the earthquakes and it help´s people in stricken areas..

Drought, condition of abnormally dry weather within a geographic region where some rain might be expected. Drought is quite different from a dry climate,which
designates a region that is normally, or at least seasonally dry. Catastrophic droughts generally occur at latitudes 15-20. The characteristic of these areas
is warm dry weather with tropical air.The biggest area of dry weather is in Africa called the Sahel.The statistics indicate that every 22 years with a precision of three to four years a mayor drought occur in the United States.
Although drought cannot be predicted,certain precautions can be taken in drought areas.These include construction of water towers,emergency water supliess,education to overcropping,and programs to limit setlement in drought-prone areas.

Global warming-it is an increase in earth´s temperature caused by using the fossil fuels and other industrial processes leading to buildup of greenhouse gasses in
the atmosphere.Since 1896 it has been known that all these gasses help to stop the earth´s infrared radiation from escaping into space.This is called the greenhouse effect.Since 1850 there has been a rise in global temperature of
approximately 1 Celsius degree.It was thought that this rise could be a part of a naturalfluctuation.Such fluctuation have been recorded for tens of thousands of years.Because of the difficulty of distinguishing human-made causes carbon dioxide emissionfrom natural sources,govermental legislation regarding control of these emissions has slowed in coming.However 1995 was the warmest year on record,according to the British Meteroroligical Office.A United Nations panel of scientist atributed the warming to human influence and predicted that if the greenhouse-gas emissions are not reduced,the average global temperature will rise by 1 to 3.5 Celsius degrees,with a best estimate of 2 Celsius degrees,by 2100.Some scientists predict that the global warming will cause the polar ice caps to melt.Because of it sea-level will rise about 22cm by 2050. So many peoples from low-lying areas now move to the higher grounds

Huricanes-this name is for migratory tropical cyclones,which originate over oceans in certain regions near the equator.Huricanes in the western Pacific are known as typhoons.Most huricanes originate in the doldrums.They´re narrow equatorial areas characterized by intermittent calms,light variable breezes and fequent squalls.They´re lying between the northeast and southeast trade winds.Atlantic doldrums are situated more to the north from the equator,so the huricanes don´t occur in the South Atlantic Ocean.Huricanes consist of high-velocity winds blowing circularly around a low-presure centre,called the eye of storm.The diameter of the area affected by winds of destructive force may be 240 km.The strength of huricane is rated from 1 to 5.The mildest category 1, has got winds of 150 km/h.The strongest category,Category 5,has winds that exceed 250 km/h.Huricanes usualy move in path looking like the curve of a parabola.Since 1943 U.S. military aircraft have been flying into huricanes to measure wind velocities and directions,the location and size of the eye.The centre of huricanes
is in Florida.They are able to minimiye loss of life in huricanes,but property damage is still heavy, especially in coastal regions.

Floods-when it rains or snows,some of the water is retained in the soil,some is absorbed by vegetation,some eveporates and the rest is called runoff.Floods occur when the soil and vegetation can´t absorb all the water.
Water runs the off the land in quanties, that can´t be carried in steam channels or caught in natural ponds or dams.Periodic floods occur naturally on many rivers.These floods are often results from heavy rain,sometimes combined with melting snows.It causes the riverbank overflow.A flood that rises and falls rapidly is called flash flood.Flash floods are usualy results of intensive rainfalls over a relative small area.Floods don´t only damage property and manace the live of people and animals,but have also other effects.Rapid runoff causes soil erosion as well as sediment deposition problems downstream.Spawning grounds for fish and other wildlife habitat are often destroyed.High velocity currents increase flood damage.Prolonged high floods delay traffic and economic use of lands.Bridges abutments,bank lines,outfalls and other structures are damaged.Financial losses are caused by floods are comounly milions of dollars each year