Презентация "Опасна ли наша планета для жизни"

Is the Earth a Dangerous Place?

Problems:

• To prove or to disapprove the statement.
• To know what natural powers can threaten us.
• How can we prevent the danger.
• The project was made up by students of the 11-th form Danilova Katya, Svistyakova Anna,Kelareva Tanya

Tornadoes

Tornadoes are the most violent of all storms. Nobody can predict what they might do.

Tornadoes destroy houses, carry away cars and telephone boxes. Tornadoes consist of very strong winds. They can teach speeds of up to 320 kilometers on hour. That is why they are so dangerous?

In Russia during one tornado, people saw money falling from the sky. At least a thousand coins fell from the clouds. The wind had removed the earth from some buried treasure and picked up the coins.

Tornadoes occur throughout the world, but mostly in the USA. The central states of the country have probably more tornadoes than any other place in the world.

Tornadoes occur in the spring. A hot day in the afternoon or in the early evening is the most likely time for this dangerous storm. Large cloud appear in the sky. They become darker and darker. There are sounds of thunder in the distance. Bright flashes of lighting are seen. A cloud then forms a funnel and begins to twist. It moves faster and faster. The faster the winds, the louder the noise. If the funnel touches the ground, it picks up everything it can. The violent winds of tornadoes blow down almost everything on their way.

Fortunately tornadoes can be predicted, and these people have a much better chanse of protecting themselves.

Volcano

A volcano is an opening, or rupture, in a planet's surface or crust, which allows hot, molten rock, ash, and gases to escape from below the surface. Volcanic activity involving the extrusion of rock tends to form mountains or features like mountains over a period of time.

Volcanoes are generally found where tectonic plates are diverging or converging. A mid-oceanic ridge, for example the Mid-Atlantic Ridge, has examples of volcanoes caused by "divergent tectonic plates" pulling apart; the Pacific Ring of Fire has examples of volcanoes caused by "convergent tectonic plates" coming together. By contrast, volcanoes are usually not created where two tectonic plates slide past one another.

Volcanoes can also form where there is stretching and thinning of the Earth's crust (called "non-hotspot intraplate volcanism"), such as in the African Rift Valley, the Wells Gray-Clearwater volcanic field and the Rio Grande Rift in North America and the European Rhine Graben with its Eifel volcanoes.

Volcanoes can be caused by "mantle plumes". These so-called "hotspots" , for example at Hawaii, can occur far from plate boundaries. Hotspot volcanoes are also found elsewhere in the solar system, especially on rocky planets and moons.

Plate tectonics and hotspots

Map showing the divergent plate boundaries (OSR – Oceanic Spreading Ridges) and recent sub aerial volcanoes.

Divergent plate boundaries

At the mid-oceanic ridges, two tectonic plates diverge from one another. New oceanic crust is being formed by hot molten rock slowly cooling and solidifying. The crust is very thin at mid-oceanic ridges due to the pull of the tectonic plates. The release of pressure due to the thinning of the crust leads to adiabatic expansion, and the partial melting of the mantle causing volcanism and creating new oceanic crust. Most divergent plate boundaries are at the bottom of the oceans, therefore most volcanic activity is submarine, forming new seafloor. Black smokers or deep sea vents are an example of this kind of volcanic activity. Where the mid-oceanic ridge is above sea-level, volcanic islands are formed, for example, Iceland.

Lava enters the Pacific at the Big Island of Hawaii

Convergent plate boundaries

Subduction zones are places where two plates, usually an oceanic plate and a continental plate, collide. In this case, the oceanic plate subducts, or submerges under the continental plate forming a deep ocean trench just offshore. Water released from the subducting plate lowers the melting temperature of the overlying mantle wedge, creating magma. This magma tends to be very viscous due to its high silica content, so often does not reach the surface and cools at depth. When it does reach the surface, a volcano is formed. Typical examples for this kind of volcano are Mount Etna and the volcanoes in the Pacific Ring of Fire.

Hurricane

A tropical cyclone is a storm system characterized by a low pressure center and numerous thunderstorms that produce strong winds and flooding rain. Tropical cyclones feed on heat released when moist air rises, resulting in condensation of water vapour contained in the moist air. They are fueled by a different heat mechanism than other cyclonic windstorms such as nor'easters, European windstorms, and polar lows, leading to their classification as "warm core" storm systems.

The term "tropical" refers to both geographic origin of these systems, which form almost exclusively in tropical regions of the globe, and their formation in Maritime Tropical air masses. The term "cyclone" refers to such storms' cyclonic nature, with counterclockwise rotation in the Northern Hemisphere and clockwise rotation in the Southern Hemisphere. Depending on its location and strength, a tropical cyclone is referred to by many other names, such as hurricane, typhoon, tropical storm, cyclonic storm, tropical depression, and simply cyclone.

While tropical cyclones can produce extremely powerful winds and torrential rain, they are also able to produce high waves and damaging storm surge as well as spawning tornadoes. They develop over large bodies of warm water, and lose their strength if they move over land. This is the reason coastal regions can receive significant damage from a tropical cyclone, while inland regions are relatively safe from receiving strong winds. Heavy rains, however, can produce significant flooding inland, and storm surges can produce extensive coastal flooding up to 40 kilometres (25 mi) from the coastline. Although their effects on human populations can be devastating, tropical cyclones can also relieve drought conditions. They also carry heat and energy away from the tropics and transport it toward temperate latitudes, which makes them an important part of the global atmospheric circulation mechanism. As a result, tropical cyclones help to maintain equilibrium in the Earth's troposphere, and to maintain a relatively stable and warm temperature worldwide.

Many tropical cyclones develop when the atmospheric conditions around a weak disturbance in the atmosphere are favorable. Others form when other types of cyclones acquire tropical characteristics. Tropical systems are then moved by steering winds in the troposphere; if the conditions remain favorable, the tropical disturbance intensifies, and can even develop an eye. On the other end of the spectrum, if the conditions around the system deteriorate or the tropical cyclone makes landfall, the system weakens and eventually dissipates. In spite of this, it is not possible to artificially induce the dissipation of these systems with current technology.

Floods

A flood is an overflow of an expanse of water that submerges land, a deluge. In the sense of "flowing water", the word may also be applied to the inflow of the tide. Flooding may result from the volume of water within a body of water, such as a river or lake, exceeding the total capacity of its bounds, with the result that some of the water flows or sits outside of the normal perimeter of the body. It can also occur in rivers, when the strength of the river is so high it flows out of the river channel, particularly at bends or meanders.

The word comes from the Old English flod, a word common to Teutonic languages (compare German Flut, Dutch vloed from the same root as is seen in flow, float).

The term "The Flood," capitalized, usually refers to the great Universal Deluge described in the Bible, in Genesis, and is treated at Deluge.

Tsunami

A tsunami is a series of waves created when a body of water, such as an ocean, is rapidly displaced. Earthquakes, mass movements above or below water, some volcanic eruptions and other underwater explosions, landslides, underwater earthquakes, large asteroid impacts and detonation of nuclear weapons at sea all have the potential to generate a tsunami. Due to the immense volumes of water and energy involved, the effects of tsunami can be devastating. Since meteorites are small, they will not generate tsunami.

The Greek historian Thucydides was the first to relate tsunami to submarine quakes, but understanding of the nature of tsunami remained slim until the 20th century and is the subject of ongoing research.

Many early geological, geographic, oceanographic etc., texts refer to "Seismic sea waves"—these are now referred to as "tsunami(s)".

Some meteorological storm conditions—deep depressions causing cyclones, hurricanes—can generate a storm surge which can be several metres above normal tide levels. This is due to the low atmospheric pressure within the centre of the depression. As these storm surges come ashore the surge can resemble a tsunami, inundating vast areas of land. These are not tsunami. Such a storm surge inundated Burma (Myanmar) in May 2008.

Earthquake

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.

At the Earth's surface, earthquakes manifest themselves by shaking and sometimes displacing the ground. When a large earthquake epicenter is located offshore, the seabed sometimes suffers sufficient displacement to cause a tsunami. The shaking in earthquakes can also trigger landslides and occasionally volcanic activity.

In its most generic sense, the word earthquake is used to describe any seismic event—whether a natural phenomenon or an event caused by humans—that generates seismic waves. Earthquakes are caused mostly by rupture of geological faults, but also by volcanic activity, landslides, mine blasts, and nuclear experiments. An earthquake's point of initial rupture is called its focus or hypocenter. The term epicenter refers to the point at ground level directly above this.

We are convinced that on the earth there are dangerous forces. But the reasons for a panic are not present. All these acts of nature don’t occur often.

Вывод : мы убедились ,что Земля- это опасное место для жизни. Но нет причин для паники. Все вышеперечисленные природные явления случаются редко .

We can not interfere with forces of the nature. But if we are warned, we will be protected.

Thanks for attention.

The End