Need to understand volcanoes

Engr Sabir Hussain

A colossal eruption of volcanoes can blow off the top of mountain up to few kilometers, resulting in scattering of fine ashes all over the globe and rock fragments into stratosphere (second lower most part of the atmosphere) to darken the skies. The volcanic processes are called Vulcanism which has literally shaped the world. These eruptions rifted the continents, raised the mountain chains, constructed islands and shaped the topography of the Earth. Furthermore, they have not only made continents but it is also believed that they have made the world’s first stable atmosphere, providing water for the oceans, rivers and icecaps. The entire bed of ocean has a basement of volcanic basalt and currently there are more than 1500 active volcanoes.

Most part of volcanoes is gases in which more than 90% is water vapours from deep Earth while rest of the gases is nitrogen, carbon dioxide, sulphur dioxide, methane, ammonia and hydrogen. According to geologists, the Earth has a molten core, surrounded by a semi-molten mantle and a dry outer skin called Crust, like a soft-boiled egg with a runny yolk, a firm but squishy white and a hard shell. If the shell is even slightly cracked during boiling, the white material bubbles out and sets like a tiny mountain chain over the crack line in archipelago of volcanic island such as the Hawaiian Islands.

Although, the Earth is so much bigger, but the mantle, below part of the Earth, is so much hotter. The mantle rocks are kept solid by overlying pressure but they can still slowly flow like thick treacle. This flow of treacle is thought to be in the form of conventional current which is powerful enough to fracture the eggshell of the crust into plates which in consequences bump and grind against each other or even overlapping at a rate of few centimeters a year. These fracture zones where collision occurs are the major earthquake happening zones with high likelihood of volcanoes too. These zones are lines of weakness or hot spots. Rocks deep in the mantle heat to 1350 degree centigrade, start to expand and rise. Therefore, the pressure drops, it expands, becomes liquid and rise more swiftly.

The biggest eruptions are deep on the mid-ocean floor, where new lava is forcing the continent apart and widening the Atlantic by approximately five centimeters a year. The maps of volcanoes, earthquakes and the island chains like Philippines and Japan represent rough outline of tectonic plates which make up the Earth crust and mantle. The most dramatic of these is the Pacific ‘ring of fire’ where there have been the most violent explosions, Mount Pinatubo near Manila, Mount St Helen’s in the Rockies, and El Chichon in Mexico.

These volcanoes are not very predictable as geological time is not like human time. During quit times, volcanoes cop with themselves with their own lava by farming a powerful cone from the molten rocks slopping over the rim of the crater. Later, the lava cools slowly into a huge, hard and stable plug which blocks further eruptions until the pressure becomes irresistible. In addition, in the case of Mount Pinatubo, this took 600 years.

On May 8, 1902, Mont Pelee in Martinique blew its top and of a town of 28,000 people only two humans survived. Similarly, in 1815, a sudden blast removed the top 1280 meters of Mount Tambora in Indonesia. The eruption was so fierce that dust thrown into the stratosphere darkened the skies, cancelling the following summer in Europe and North America. Thus, the harvest failed and obligated thousands to starve.

The writer is a satellite engineer by profession. He did B.Sc Electrical Engineering (Telecom) from the COMSATS University, Lahore Campus and M.Phil in Space Science from the University of Panjab, Lahore. He can be contacted at:

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