Explanation texts about natural phenomena

Tsunami

The term of “tsunami” comes from the Japanese which means harbour ("tsu") and wave ("nami"). A tsunami is a series of waves generated when water in a lake or a sea is rapidly displaced on a massive scale.

A tsunami can be generated when the sea floor abruptly deforms
and vertically displaces the overlying water. Such large vertical movements of the earth's crust can occur at plate boundaries.

Subduction of earthquakes are particularly effective in generating tsunami, and occur where denser oceanic plates slip under continental plates.

As the displaced water mass moves under the influence of gravity to regain its equilibrium, it radiates across the ocean like ripples on a pond.

Tsunami always bring great damage. Most of the damage is caused by the huge mass of water behind the initial wave front, as the height of the sea keeps rising fast and floods powerfully into the coastal area.

(simplified from www.panda.org)

How Venus Eclipse Happens

On May 16, 2010, people in most regions in the world have seen a very rare natural phenomenon. It was Venus eclipse. It was very rare amazing natural event. It was reported that the Venus eclipse will seen again in the future in 2050. Do you know how this rare Venus eclipse happens?

Well, actually Venus eclipse is like Sun eclipse. Venus eclipses occurs when the position of the earth, moon and Venus is parallel. Venus planet will slowly disappear for a moment because it is covered the surface of the Moon. Venus planet seems to move to the back side of the Moon.

The moon and planets are sharing a similar apparent path in the sky. That is why, it is not unusual for the moon to appear to pass close to Venus. In fact, the moon appears somewhere near it about once a month. However, most people don’t see these events because they are visible in the evening sky only half the time, and then only for a short period after sunset. The apparent closeness varies from month to month as well.

How Earthquakes Happen

Earthquake is one of the most destroying natural disasters. Unluckily it often happens in several regions. Recently a horrible earthquake has shaken West Sumatra. It has brought great damages. Why did it occur? Do you know how an earthquake happens?

Earthquakes are usually caused when rock underground suddenly breaks along a fault. This sudden release of energy causes the seismic waves. It make the ground shake. When two blocks of rock or two plates are rubbing against each other, they stick a little. They don't just slide smoothly. The rocks are still pushing against each other, but not moving. After a while, the rocks break because of all the pressure that's built up. When the rocks break, the earthquake occurs.

During the earthquake and afterward, the plates or blocks of rock start moving, and they continue to move until they get stuck again. The spot underground where the rock breaks is called the focus of the earthquake. The place right above the focus is called the epicenter of the earthquake.

Mainly taken from: www.geo.mtu.edu/UPSeis/why.html

How does Rain Happen?

Rain is the primary source of fresh water for most areas of the world, providing suitable conditions for diverse ecosystems, as well as water for hydroelectric power plants and crop irrigation.

The phenomenon of rain is actually a water circle. The concept of the water cycle involves the sun heating the Earth's surface water and causing the surface water to evaporate. The water vapor rises into the Earth's atmosphere. The water in the atmosphere cools and condenses into liquid droplets. The droplets grow until they are heavy and fall to the earth as precipitation which can be in the form of rain or snow.

However, not all rain reaches the surface. Some evaporates while falling through dry air. This is called virga, a phenomenon which is often seen in hot, dry desert regions.

(http://mypages.iit.edu/~smart/abduima/lesson2.htm)

How do seasons happen?

Seasons come to us regularly. We have probably noticed that it gets warmer in summer or dry season while it get colder in the winter or wet season. However do we know how these seasons change?

Seasons happen and change every year. This happens because the earth tilts back and forth as it goes around the sun. During the summer, the earth tilts toward the sun. It makes half of the earth hotter. this condition is what we call summer. During the other half of the year, the earth tilts away from the sun. As a result, it makes that half of the earth cooler. This cool condition is then what we call winter.

The different parts of the world have the same season at different times. In the northern half of the world , winter happens during the months of December, January and February. The regions are such North America and Europe. In the other hand, the southern half of the world have winter during the months of June, July and August.The regions are like South America and Australia. How does this difference happen? The same season happens at different times because the top and bottom halves of the earth tilt away from the sun at different times.

Source: kidscientist.com/5/why-do-seasons-happen

How Day and Night Happen 

 

The sun seems to rise in the morning, crosses the sky during the day and sets at night. However the sun does not actually move around the earth. Earth's turning on its axis makes it look as if the sun is moves.

The earth makes a complete turn on its axis for 24 hours. It is called as rotation. It causes day and night. The earth also moves around the sun. It takes 365 days or a year. This process is called revolution. The revolution process causes the changes of the season .

Why Summer Daylight is Longger than Winter Daylight

 

In the summer, the amount of daylight that we get is more than we get in winter. This is not because as much people think we are closer to the sun but because of the tilt of the earth.

The earth is actually closer to the sun in winter than it is in summer but you would be forgiven for thinking that this can not be true after looking out of your window on a cold and frosty morning.

It seems strange that as the earth get closer to the sun during its orbit then the amount of daylight that we get decrease. But that is the case. It is the tilt of the earth that determine the amount of daylight that we get and so the length of time that for us the sun is above the horizon.

(Taken from: www.ictteachers.co.uk)