Category The Earth, Earth Science, Planet Earth

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.