contoh explaination text

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.

The effects of acid soil

phenomenon identification : Soils with a pH of less than 7.0 are acid. The lower the pH, the more acid the soil. When soil pH falls below 5.5, plant growth is affected. Crop yields decrease, reducing productivity. explanation sequence : Soils provide water and nutrients for plant growth and development.

Essential plant nutrients include phosphorus, nitrogen, potassium and sulfur. Plants require other elements such as molybdenum, in smaller quantities. Some elements eg aluminium and manganese, are toxic to plants. Nutrients become available to plants when they are dissolved in water. Plants are able to take up phosphate, nitrate, potassium and sulfate ions in solution.
The solubility of nitients changes with pH. In acid soils (low pH), molybdenum becomes less soluble and aluminium becomes more soluble. Therefore, plant growth may be affected by either a deficiency of molybdenum or too much aluminium.

Both crop and pasture plants are affected by acid soils. there may be a range of symptoms. Crops and pastures may be poorly established resulting in patchy and uneven growth. Plant leaves may go yellow and die at the tips. The root system of the plant may be stunted. Crops may yield less.

Plants vary in their sensitivity to low pH. Canola and lucerne are very sensitive to acid soils so do not grow well. Lupins and triticale are tolerant to soils of low pH so they still perform well. Land can become unproductive if acid soil is left untreated. Incorporating lime into the soil raises the pH. Therefore, liming soil can reverse the effects of acid soil on plants and return a paddock to productivity

Types of Volcanic Eruptions

Volcanic eruptions have caused some of the worst disasters in the world. They can wipe out entire cities and kill thousands of people. The name of volcano comes from Roman term. It derives from VULCAN which is the name of Roman fire god. Romans believed that Vulcan lived on a volcanic Italian coast. Romans called the island VULCANO.

According to scientists, volcanic eruptions are divided in to four basic groups. They are commonly known as Hawaiian, Strombolian, Vulcanian and Peleean. The term of Hawaiian eruptions are named after the volcanoes in Hawaii. These volcanic eruptions are the least violent type. They produce highly fluid lava which flows quietly. This gradually builds up a shield volcano.

Strombolian eruptions are named after Stromboli. These result from the constant release of gas from the magma. As the gas escapes, it produces tephra that piles up, turning into a cinder cone. Strombolian eruptions happen when sticky magma plugs the central vent. This makes the magmatic gas build up pressure until it blasts. The magma is turned into volcanic dust and bombs.

Vulcanian eruption which comes from the ancient Roman belief, are more violent than the strombolian eruption. Vulcanian eruption happens and brings magma which is more viscous. Vulcanian explosions are usually larger and noisier than the Strombolian eruptions.

Paleean eruptions are famous as the most violent kind of volcanic eruptions. The name of paleean comes from the eruption of Mount Pelee, Martinique in 1902. It killed almost 38 thousands people. A Peleean eruption occurs when the magmatic gas build up tremendous pressure. This causes violent explosions with glowing clouds of hot ash and dust.

Volcano Explotion

A volcano is an opening in the crust of a planet from which lava flows. A volcanic mountain forms when magma from the planet's mantle forces its way through the crust in the form of lava or ash and then forms a cone on the planet's surface. On the Earth, volcanoes form near hot spots within the Earth's crust or in regions over subduction zones at the boundaries of tectonic plates.

Volcanic eruptions occur when magma, or molten rock, rises from deep within Earth. The magma, combined with volcanic gases, creates pressure beneath the surface. When the pressure becomes great enough, the volcano erupts and spews a range of materials, including liquid lava, volcanic gas, cinders and ash, and large rock fragments that are sometimes called bombs.

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.

How is a Kite Flying?

A kite is an object which is made from a light material stretched over a frame. Due to its light material a kite will lift off the ground and fly when it is tilted into the wind.

A kite is uses wind to make it fly because it is heavier than air. When wind travels over the surface of the kite, it is split into two streams of air. One stream of the air goes over the kite while the second stream goes under the kite.

The upper stream creates an area of low pressure above the kite. The lower stream hits the kite at a shallow angle and creates an area of high pressure.

The high pressure area has a pushing effect while the low pressure area has a pulling effect. The combination of push and pull can creates enough force to lift the kite into the air.

Kites have been known for thousand of years. They are used for military or scientific purposes. Todays kites are much used for leisure and competition.

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 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.