Cyclones and Tsunamis
At times, winds blow around a central area where the atmospheric pressure is low. This causes revolving storms or cyclones. Cyclones taking place in the northern hemisphere are termed as typhoons or hurricane. The wind flows in a circle in an anticlockwise direction. Cyclones that take place in the southern hemisphere are termed as tropical storms. The winds blow in a circle in a clockwise direction.
How Do Cyclones Develop
It is near the equator that the cyclones occur over warmer seas. Air gets heated by the sun’s rays and starts rising rapidly creating low pressure areas. When the warm air keeps rising it gets filled with lots of moisture which then undergoes condensation to form massive thunderclouds. A void remains, which then gets filled in by cooled air that rushes in. However the Earth keeps rotating around its axis constantly which makes the air bend inwards and then with great force, it starts spiralling upwards. The rotation of the swirling winds becomes faster and faster and thus forms a very huge circle upwards. This huge circle can extend to about two thousand kilometres across, also. The storm also has a centre area which is cloudless and calm and termed as the eye. Winds in this central area are fairly light and there is no rain.
The cyclone starts building up and begins moving. A flow of moist and steady air, sustains the cyclone. Heavy and strong winds are found in the clouds that tower and merge into a wall present at a distance of twenty to thirty kilometres from the centre of the storm. The wind around the centre or the eye reaches a speed of around two hundred kilometres per hour and develops as a full cyclone. Per second around two million tons of air is pumped by the cyclone leading to release of more rains.
Types Of Cyclones
This is a swirling and dense pack of winds and clouds that range between half to six miles width. It appears as a vertical and thin bank of clouds spinning from under the thunderstorm. If it hits the ground it can turn into a tornado and churns up warm and wet air. Meso-cyclones take place largely in the United States with many of them turning into tornadoes.
• Tropical Cyclone
Thunderstorms and clouds emerge as a rotating system and generally originate over the sub tropical or tropical regions. These cyclones take place close to the Equator generally including the Gulf of Mexico, Caribbean, Atlantic Ocean and the East Pacific Ocean. A severe storm is created leading to a cyclone with a combination of winds and moving areas with low pressure.
• Sub Tropical And Sub Polar Cyclones
Cyclones occurring between the polar areas and tropical cyclone bands are termed as sub tropical and sub polar cyclones. Even if they form in a similar way, the main variables are durability, temperature and predictability. Cyclones are random, unpredictable and colder when they occur near the Arctic Circle and could last for long or short periods.
• Arctic Or Polar Cyclones
These cyclones occur in the polar, Arctic or Antarctic regions and can be up to 1200 miles wide. They are not seasonal and can occur any time in the year. It is difficult to predict their direction as they form quickly. Siberia and Northern Russia are more prone to such cyclones.
Regions Affected By Cyclones
Many cyclones have occurred over the years leading to a huge death toll in many countries. Galveston, Texas, USA experienced a cyclone in 1900 with a death toll of ten to twelve thousand people. Society and Cook Islands were affected in 1906 in which ten thousand people were killed. Bangladesh experienced a cyclone in 1964, 1965 and 1991 with a death toll of thirty five thousand, fifteen thousand and one hundred and thirty-nine thousand people respectively. One hundred thousand people lost their lives in the Caribbean Coast in the 1970 cyclone. In Honduras, a hundred thousand people were killed in the 1977 cyclone.
What Is A Tsunami
Tsunami is a Japanese term. It means a ‘harbour wave’ in the English translation. The two characters are tsu and nami. Tsu means harbour while the term ‘nami’ means a wave. The general public termed Tsunamis as tidal waves while the scientific community termed it as sea waves of the seismic type. The coastline is impacted by the tsunami depending upon the level of tide when it strikes. Actually tides and tsunamis are not related. Tides occur due to the gravitational, extra-terrestrial, and imbalanced influence of the planets, sun and the moon. Impact of a meteorite, landslide or any event that is non seismic in nature could lead to a tsunami.
Different Types Of Tsunamis
• Regional Tsunami
This tsunami is restricted to a particular region where the casual event occurs. Huge land masses are affected in a regional tsunami. Shorelines that are affected generally have a warning of about one to three hours.
• Ocean Wide Or Distant Tsunamis
When from the causal event, the seismic waves travel to long distance it leads to distant tsunamis. An Indonesia earthquake for example can generate seismic waves in a big series thus causing a lot of damages to the African coast. Advance warning can be obtained before a distant tsunami occurs and accordingly people could be evacuated to safety.
It is rare for meteorites to cause a tsunami, but at times they do happen. One such tsunami took place sixty five million years back. It is the belief of scientists that the K-T or the Cretaceous Tertiary impact caused a lot of flooding all over the world.
• Local Tsunamis
The local tsunami is restricted to a particular area that surrounds the place where the causal event occurs. Before this tsunami hits, there is hardly any warning received.
• Submarine Sediment Slide
When landslides occur on the floor of the ocean, it leads to submarine sediment slides.
• Earthquake Event
Earthquakes are the main cause in this type of a tsunami. Tsunamis are generated by the earthquakes occurring on the floor of the ocean. Tsunamis are not caused by earthquakes that occur over land.
Regions Affected By Tsunamis
On March 9, 1957, the Aleutian Island was affected by a distant tsunami. Wide spread damages took place at Haena Kauai. A regional tsunami took place in 1983 in the Sea of Japan causing severe damage in Russia, Korea and Japan. In the last thirty thousand years, three big submarine sediment slide tsunamis took place in the Storegga area off the Norway coast.