My Science School

Volcanoes are found primarily at the borders of the plates, where the oceanic Earth’s crust submerges below another plate, melts in the depth, and magma rises. This is generally the case all around the Pacific Ocean. Here, the Cocos and the Nazca plates submerge below the middle and South America, and the Pacific plate submerges below the small plates in Southeast Asia. 

 

Volcanoes are found in areas ranging from Italy to Turkey and Iran upto the Indonesian islands. Very rarely will we find volcanoes in the middle of a plate. These occur only in ‘hot spots’ which are areas with high volcanic activity, such as the Hawaiian Islands. 

Farmers prefer to settle near volcanoes because the soil is very fertile due to the lava and volcanic ash deposits. When the volcano erupts, people leave the place for some time, and return to the risk zone after the eruption because the safer places are already inhabited. Moreover, for many people the area around the volcano is home, which they do not want to leave.

Because volcanoes are highly erratic, it becomes very difficult to predict volcanic eruptions. But there are ways of saving lives. Early tremors and earthquakes are often signs of a volcanic eruption—gases are emitted and the volcano expands by a few centimetres to a metre. The volcanologists carefully observe these signs. In 1991, before the eruption of the Pinatubo in Philippines, these signs were interpreted correctly and over 10,000 people were moved to safer places. 

Continue reading "How can we predict volcanic eruptions? "

We can call a volcano dangerous only when it causes damage to human life. For instance, if a volcano erupts on the almost uninhabited East-Asian peninsula of Kamchatka, it is hardly reported in the news. But, if a volcano starts spewing hot gases and ash in a densely populated area, many lives are at risk. Explosive volcanic eruptions discharge huge quantities of dust and ash, often burying neighbouring areas. Thin, dark magma can flow at a fast speed of up to 1oo km/h making it impossible to escape. Volcanic eruptions can also have far-reaching consequences. When the Indonesian volcano Krakatau erupted in 1883, the volcanic ash reached up to a height of 8o km, which for some time darkened the sky worldwide.

Since the material coming out of the Earth’s core is different in different areas, the resultant changes are also different. If the magma is very hot, more than 1000°C, it is dark, thin and mostly flows quietly. The sides of such volcanoes have gradual slopes. Colder, and hence more viscous, magma often erupts in explosions. The volcanic cone is steeper. Because of the heat in the Earth’s core, geysers (water fountains), solfataras (discharge of hot sulfuric gases), and hot water sources are found near the volcano. These are often used for heating in places such as Iceland.

 

 

 

 

Volcanoes are natural phenomenon that occurs everywhere, but some places are more prone than the others. The molten rock and gas in the mantle called magma pushes its way upwards and pours to the surface through cracks in the crust. This is a volcano. There are different types of volcanoes; some are explosive others are not, and all erupt as spectacularly as we see on the television. Some eruptions take place unexpectedly, but others can be predicted, which is very important for the people living near a volcano. 

Mountains are formed in two ways. When the tectonic plates move, they collide against each other. When the heavy oceanic part of the plate collides with the continental part, it submerges below it. The Andes, for instance, were formed in this way. The other way is when two continents collide with each other; the plates bend at the point of contact and fold up steeply. The Himalayas or the Alps were formed in this way around 35 million years ago and are counted among the ‘young’ mountains of the world. Old mountains, such as Black Forest or the Harz mountains, are lower ranges because peaks have been worn down by rain, ice, and wind over time.

This discovery is credited to the German geologist Alfred Wegener. He not only discovered that the coastline of South America fits very well against that of Africa but also showed that the fossils in both the coastal regions are Similar. He also proposed another idea: about 300 million years ago there must have been a single, continuous landmass that somehow broke up and gave rise to several parts—the tectonic plates. The continents on these plates drifted away from one another and then rejoined the way they are today. Thus, landmasses were displaced, and their position is changing even today.  The tectonic plates are still moving at a speed of around 6 cm per year.

 

 

 

 

 

The relatively solid Earth’s crust - and a part of the layer that lies below it - is divided into seven large and more than ten smaller plates. These plates float over the hot, viscous layer, which is constantly in motion - like boiling soup. These flushes of heat in the Earth’s interior are known as ‘convection cells’. At places where the convection currents push the rocks upwards, the crust often breaks and gives rise to a new crust. For example, the mid-ocean ridges in the Atlantic and Pacific oceans.

 

The word ‘atmosphere’ means a gaseous cover enveloping a planet. Without atmosphere life would not have been possible on the Earth: One-fifth of the atmosphere is oxygen and four-fifths is nitrogen. Like the Earth’s interior, the atmosphere too is made up of several layers. All animals and plants live in the lowermost layer of the atmosphere called the ‘troposphere’. All weather phenomena take place in the troposphere. Even aeroplanes fly in the outer edge of the troposphere. The stratosphere, the mesosphere, the ionosphere, and the exosphere lie above the troposphere. 

 

Gravity is the force of the Earth that attracts every object towards itself. From our perspective this force always acts downwards. For a long time people did not believe that the Earth is round because then the people ‘underneath’ the sphere would have actually fallen down. In 1687, a physicist, Isaac Newton, proved that the force of gravity always acts towards the centre of the Earth. On the Earth, the force of gravitation always acts ‘downwards’ irrespective of Eskimos in the Arctic region, people in Europe or inhabitants of Australia. 

About 3000 years ago people believed that the Earth was flat. But people wondered why ships disappeared at the horizon. Sailors too returned from journeys and were proof that ships did not fall off the edge of the Earth. The simplest explanation was: the Earth must be round. The final proof came in the year 1522 after the expedition of Ferdinand Magellan, who was the first to sail around the Earth.

Caves and mines go only up to 1-2 km inside the Earth. Even the deepest wells of the world, such as the one 12 km deep in the Russian Kola Peninsula or the 9-km-deep one in the Upper Palatinate, hardly scratch the Earth’s crust. One can ‘look’ deep inside the Earth in the aftermath of earthquakes or by creating nuclear explosions. The explosions generate sound or seismic waves. They also throw off rock particles. By measuring their intensity and timings, scientists discover the composition of the Earth’s interiors. 

Like an onion, the Earth has several layers. The outermost layer, the Earth’s crust, has an average depth of about 40 km. As compared with the diameter of the Earth, which is around 12,700 km, the Earth’s crust is very small. It is primarily made up of solid rocks. Below the crust is the mantle, reaching to a depth of about 2900 km. Due to the heat inside the Earth, the mantle consists of solid and molten rocks. Below the mantle is the core, made up of iron and nickel. The deeper one travels inside the Earth, the hotter it is. The temperature in the core is between 4000 and 5000 degree Celcius.

It has been known for more than 2000 years that the Earth is round, but we were able to actually see this much later only when we flew into space. The knowledge why we do not fall off from the Earth is much more recent. A journey as described by author Jules Verne in his book Journey to the Center of the Earth was, after all, impossible. Only one thing was known: the Earth is made up of soil, rocks, and water. Today, we know that the Earth is also surrounded by an air cover called the atmosphere.