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Voyage inside the Earth

By: Daniele Souza

 Mt. Rinjani, Indonesia. Photo: Oliver Spalt/Wikipedia

Mt. Rinjani, Indonesia. Photo: Oliver Spalt/Wikipedia

Every year, people travel around the world to visit volcanoes, and curiosity over them is not recent. The name “Volcano” is associated to Vulcanus, that is, Vulcan, the Greek-Roman God, the creator of lightnings. In the movies, volcanos expel lava, cause earthquakes and throw bits of themselves very far away.

However, volcanos have a very important role in nature. Four billion years ago, thousands of active volcanos, released large volumes of water, which formed the first oceans. The gases in this primitive atmosphere also  came from volcanic emissions. Besides that, a few elements necessary for life to emerge - like heat, chemical elements, water and atmosphere - appeared due to volcanic activity.

A volcano is no more than a crack in the ground; a communication between the magma inside the crust and the surface from which gases, ashes, solids, lava, etc, are expelled. They are also an important source for scientific observation, since the deepest ever reached through research was on only 6.8 miles, whereas the earth’s radius is 3,960 miles.

When people think about volcanos, they think of a cone, which is the accumulation of ejected material. But volcanos come in many shapes, depending on the kind of volcanism. But what is it that causes volcanic activity?

Most sorts of volcanism are the result of the movement of tectonic plates (“tectonic” comes from the Greek: “pertaining to building”). Continents are not stationary. The world map shows us that South America and Africa fit on each other. This process was at first called “Continental Drift”, but has now been dubbed “Plate Tectonics”. It says the crust of the Earth is divided in plates, huge solid blocks, which are constantly moving over the Earth’s melted mantle.
Either when plates collide - that is, when they move underneath each other - or when they are torn apart from each other, magma tends to rise up, because heat always goes up. This heated material might either come up through fissures in the middle of plates or through borders of plates. That’s what originates volcanoes.

Only around five percent of active volcanoes on Earth are not located along the borders of these plates, but in the middle of them. That happens in the so called “hotspots”, which are fixed columns of heated rocky material that rises to the surface and dissipate heat. Hawaii is an example of a complex of volcanoes formed over a hotspot. The hotspot feeds a volcano for millions of years until the plate moves away from that spot, thus making the volcano inactive and forming a new one by continuing to bring material to the surface.

Volcanism and the environment

Volcanoes are a great source of both short-time and extended climate change, such as global warming. Two or three eruptions have more power to increase the temperature of the Earth than dozens of years of industrial activity. Volcanoes produce around 110 million tons of CO2 every year, besides ashes and SO2. Most metallic minerals, like gold, are connected to magma found near extinct volcanoes.

Without Volcanoes, there wouldn’t be any atmosphere, nor water on the surface, which was originated in the so-called “magmatic water” or “juvenile water”, which comes from vapor expelled by volcanoes. There is a “water cycle”, which includes rain and evaporation, but some of it is lost in the atmosphere in the form of water vapor. If volcanoes didn’t constantly add magmatic water, our planet would end up dry in the long run. This water also transports and works as solvent for many chemicals.

Anak Krakatau. Photo: Thomas Schiet/Wikipedia

Anak Krakatau. Photo: Thomas Schiet/Wikipedia

Accounts of the explosion of the Krakatoa show that the volcano released approximately 5,000 times more energy than the bomb dropped on Hiroshima. The explosion was heard in Australia, more than 1,200 miles away, triggered tsunamis (waves taller than 130 feet), rendered exotic colors to dusk and dawn (due to material spread in the atmosphere), besides partially blocking sun.

In 1927, new submarine eruptions occurred. Soon after, a new island volcano, named Anak Krakatau or Child of Krakatoa, rose above the waterline. Since the 1950s it has grown at an average rate of 6.8 meters per year. The island is still active. Quiet periods of a few days have alternated with almost continuous low-level eruptions since then, with occasional much larger explosions.

With time, the billion tons of lava and volcanic ash become fertile soils. Other products are used as ingredients in the Pharmaceutical industry and in cleaning products. Geothermal fields are also used to produced geothermal energy.

Volcanoes are one more factor changing the environment. By studying it, we might answer important questions concerning life and the Earth.

Find out more about:

What volcanoes expel and volcanic phenomena

Types of eruptions

Morphology of a Volcano

Volcanoes in Brazil

Preventing volcanic activity

Geothermal energy

The Pacific Ring of Fire

Changes on Earth


Toli, Fabio et al. Decifrando a Terra. Oficina de Textos, USP

Thanks to:

Mguel Tupinambá, professor at UERJ’s School of Geology.

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