Pressure valves in many places in the earth’s crust
Volcanoes are a kind of pressure valve in the earth’s crust. When magma accumulates and pressure becomes high, a volcano is formed – or an old volcano starts erupting again.
Volcanoes are on every continent, including Antarctica.
Geographically, however, the distribution is uneven because the vast majority of volcanoes are at the intersections of the earth’s crustal plates, which cover the globe like puzzle pieces. The volcanoes are most densely located around the Pacific Ocean on the so-called “eldhring” or “Ring of fire”.
The total number of fireplaces is an unknown quantity, as it is a matter of definition what counts as an active and independent fireplace and what is part of a larger system.
It is estimated that 1,300-1,500 volcanoes have erupted in the last 10,000 years. To this must be added, however, a large number of volcanic eruptions on the ocean floor. Volcanoes can range from fissures on flat land to high volcanoes, which have been built up in numerous eruptions. Ojos del Salado in South America is the highest volcano in the world, nearly 6,900 meters high.
Volcanic eruption
The heart of an active volcano is the magma chamber, where the magma accumulates. An eruption begins when the pressure in the magma chamber becomes so great that the magma pushes up to the surface, where it often rises to great heights.
Just like height and shape, the “temper” of volcanoes is determined by the underlying magma.
Sometimes the magma is thin-flowing and flows easily down a small slope (flow eruption). In other cases, the magma is much thicker and more viscous and can cause a blockage in the eruption station (whipping eruption).
Volcanoes that erupt thick magma can be compared to a ticking time bomb. When the pressure builds up, it blows off the plug in the vent, and from it erupts glowing magma and pyroxene.
Rain causes eruptions
Weather, climate and volcanic eruptions interact in various ways. If a volcanic eruption is very powerful, a lot of ash is carried high up into the atmosphere, where the ash particles reflect sunlight and can lower the temperature on the ground for many years.
On the other hand, the weather also seems capable of unleashing volcanic eruptions. Proof of this can be found in the volcano Soufrière on the island of Montserrat in the West Indies.
The mountain often erupts following heavy rains. The rainwater seeps down through cracks and forms steam when it comes into contact with the lava magma. The steam takes up many times more space than water and therefore the pressure in the dynamic chamber increases.
The seasons also seem to have an effect. In the Northern Hemisphere, volcanic eruptions are much more frequent in winter than in summer. This has been explained as the effect of the enormous amount of water that annually flows from the Northern Hemisphere to the Southern Hemisphere and back again. This is thought to have a rhythmic pressure effect on the magma chambers beneath the volcanoes.
