Volcanoes are orifices or fissures where melted rock can come out, called magma, as well as gasses like steam, carbon dioxide, methane, sulfur, among others, from within the Earth.
They are mainly formed at the edges of the continental plates (fault zones), where it is easier for magma to find a way out towards the surface when an eruption is produced. The most important chain of volcanoes is the one that surrounds the Pacific ocean and it is known as the «Ring of Fire».
A volcano is made up of several parts:
– Volcanic cone: it is formed by the accumulation of magma material, expulsed through the pipe from within the Earth.
– Crater: it is the upper and visible part of the volcano through which magma emerges in the form of lava.
– Pipe: it is the duct through which the magma ascends in its trajectory towards the exterior.
– Magma chamber: it is found at great depths within the Earth and is where the magma accumulates before coming out to the surface.
Types of volcanoes
Volcanoes can have different shapes and sizes. The most common are:
– Shield volcanoes: they have slight slopes and their base is very wide. They are formed in zones where lava is expulsed from within is very fluid.
– Cinder cones: they are in places where eruptions of gasses and magma are very violent.
– Volcanic necks: extinct volcanoes that have become eroded in such a way that only the petrified pipe remains where the magma once came from. Some of these volcanoes are located in the Arizona desert in the U.S.A.
– Stratovolcanoes: volcanoes with very steep slopes that alternate between explosive and soft eruptions.
– Volcanic domes: the edges of the domes are very abrupt and are often found in zones where the terrain is quite uneven. In addition, the lava mass is very dense, so it doesn’t go down the sides of the volcanoes and accumulates in the crater.
– Volcanic furnaces: they are volcanoes that are born after explosions, landslides or erosive agents and can be circular or horseshoe shaped. In the first case they are formed when a volcano explodes or collapses at the center or when its walls cave in symmetrically. In the second case, the destruction only causes the collapse of one side of the volcano, forming an opening that, seen from the air, tends to be shaped like a horseshoe, hence its name.
– Sea volcanoes: they are formed due to the contact of magma with deposits that contain great amounts of water, which mix together and create eruptions that come out at high temperatures with toxic gasses.
It is a set of processes through which solid, liquid and gaseous materials from within the Earth are forced out to the surface through fissures or cracks in the Earth’s crust that are deep enough (sometimes 100 to 200 km). It is produced because of an increase in temperature at the lower layers of the lithosphere, which causes magma to melt. The latter accumulates in magma chambers and, when pressure increases, it tends to come out to the surface. Although this increase in temperature can be due to local phenomena, the main zones of volcanic activity on the Earth’s crust are:
– Subduction zones: the rubbing together of tectonic plates causes an increase in temperature that melts the material in the lithosphere, causing magma chambers. This type of zone is found in the Andes mountain range and on the islands near Japan.
– Obduction zones: the heat of the magma trying to rise to the surface as a consequence of convection currents heats up the material found on the ocean floor, sometimes resulting in the emergence of volcanoes in the zone of dorsal mountain ranges (marine or terrestrial). An example of this is Easter island (Pacific Ocean) and Iceland (Atlantic Ocean).
– Heat spots or hotspots: they are zones in which matter coming from very deep layers of crust rises quickly.
Sometimes, this causes the piercing of the lithosphere and the magma material comes out to the surface.
Volcanoes are formed thanks to the displacement of the lithospheric plates over these points. A known hotspot in the Pacific ocean is the island of Hawaii.
Magma and lava
These two terms are often confused because they are closely related, but are really different. Magma is a mass of melted rock that accumulates in magma chambers at the depths of the Earth. Sometimes magma opens a path for itself beneath the crust, where it starts to cool, forming solid rock called igneous. However, the weak points of the crust let the magma go up towards the surface through the pipe of a volcano. When it rises, the dissolved gasses it carries separate from the magma and cause an enormous increase in pressure right before the eruption, heightening the explosion upon release.
Lava is the name given to magma when it comes out to the surface from the pipe of a volcano during an eruption. It is red and its density depends on the temperature and composition of the magma.
The flow of lava that slides out of a volcano has three shapes:
– A’a: the current of lava is characterized for having an irregular, wrinkly surface. It advances at a speed of 5 to meters an hour as it solidifies quickly.
– Pahoehoe: liquid lava is at a high temperature and has a slick appearance. Gasses escape slowly.
– Pillow lava: it is formed at deep marine depths or when lava slides down slopes and enters into contact with the sea, rivers or lakes. When it slides, the lava acquires a pillow shape, hence the name. Most of these volcanoes are located near or under water.
Types of eruptions
The temperature magma exits from within a volcano determines the amount of gasses that accompany the lava, its flow and density.
There are four types of volcanic eruptions:
– Hawaiian: it is a volcano with a round crater. It comes to be thanks to passive eruptions. When lava comes out of the volcano’s pipe, it easily slides down the slopes, traveling great extensions. These volcanoes are typically found on the islands of the Pacific ocean.
– Strombolian: it has fluid lava, but of a higher density than Hawaiian; the gasses ascend to the surface forming bubbles that explode irregularly. When it descends, the lava does not travel great distances.
– Vulcanian: it has a cone shape caused by eruptions that expulse great ash clouds. The magma released through the pipe is highly viscous , does not flow easily and solidifies quickly.
– Pelean: the magma that rises from the throat is extremely dense and takes time to emerge. For this reason, sometimes the material solidifies during its ascension and blocks the crater. If it reaches the surface, the enormous pressure of these gasses causes extremely violent eruptions, for which reason the volcanic apparatus ends up exploding.
Unfortunately, the majority of eruptions leave serious damage. Some of the effects produced by volcanic activity are:
– The towns and cities near volcanoes can be buried by lava and rocks, due to the velocity that these reach when descending.
– Flora and fauna die as a result of the chemical composition of the ash.
– Ash can also damage large infrastructures, such as bridges and highways.
– Volcanic gasses can poison natural and artificial water sources, causing a serious risk for human health, agriculture and cattle farming. Also, rocks and lava can block river beds and artificial canals, causing flooding in some sectors and drought in others.
– Submarine volcanoes near coasts can cause a tsunami.