PARTS OF A VOLCANO, STRUCTURE AND CHARACTERISTICS - ENVIRONMENT - 2024

The parts of a volcano are the crater, caldera, volcanic cone, chimney and magma chamber. The volcano is a geological structure formed by the outlet pressure of the magma contained within the Earth.

Magma is the molten rock in the Earth's mantle that forms due to the high temperatures of the planet's core. This is composed of cast iron at high temperatures (4,000 ºC).

The parts of a volcano

The upper layer of the mantle is made of silicates (asthenosphere) and they are found in solid, semi-solid and molten states (magma). This generates high outlet pressures that, when encountering a weak geological point, pushes the magma towards the earth's surface.

The process of exiting the magma to the outside forms the volcano, whose name comes from the Latin Volkanus. It is the name that the Romans gave to Hephaestus, the Greek god of fire and blacksmithing, also known as Vulcan.

The structure of a volcano is determined by the type of magma, the eruption process, the vent system, and environmental conditions. Regarding the latter, it must be taken into account if the volcano acts under air, under glaciers or under water.

Also, there are various types of volcanoes, ranging from a crack in the ground to huge stratovolcanoes. These types of volcano are identified depending on either their location or their morphological structure.

Due to their location there are terrestrial, subglacial and submarine volcanoes and their morphology is defined by the geology and physiography of the place where they arise. In this sense, the parts of the volcano and their characteristics will vary from one type to another.

Parts of a volcano and characteristics

- Magmatic chamber

The origin of a volcano is the accumulation of magma and gases in an underground chamber, called a magmatic chamber. In this chamber, the pressure necessary to push the magma upwards is generated, breaking the earth's crust.

Magma

Magma is molten or partially molten rock due to the high temperatures inside the planet, plus associated gases. The molten rocky material is essentially silica from the earth's mantle.

Magma from a volcano in Hawaii (United States). Source: Hawaii Volcano Observatory (DAS)

This can reach temperatures of up to 1,000 ° C (very fluid), forming basalt on cooling. It can also be a less hot material (600-700 ° C) that crystallizes into granite form on cooling.

There are two fundamental sources of magma as it can come from molten material in the subduction of the earth's crust or from greater depths.

Subduction

It consists of the sinking of the earth's crust from the ocean floor below the continental plates. This occurs when the oceanic plates collide with the continental plates, the first being pushed towards the Earth's interior.

Inside the Earth, the crust is melted into the mantle and then part of that material returns to the surface through volcanic eruptions. The determining force of subduction is the push of the oceanic plates by the rocks arisen in the volcanoes of the oceanic ridges.

- Chimney and ventilation system

The rise of the magma due to the pressure generated due to the high temperatures, forms an outlet conduit which is called the chimney. The chimney is the main duct of the volcano's ventilation system and will flow through the weakest parts of the earth's crust.

Chimney structure

A volcano can have one or more chimneys, which can branch out, this makes up the volcano's vent system or ventilation system. In some cases the chimney is made up of a set of small fissures that connect.

Secondary chimneys

A volcano can have a series of secondary chimneys that arise laterally in relation to the main chimney that opens in the crater of the volcano.

- Crater

When the magma reaches the surface, it breaks the superficial crust and is projected outside and this opening is called a crater and it can be a cavity of greater or lesser diameter.

Crater. Source: USGS / D. Roddy

The shape of the crater is determined by the type of lava, type of volcanic eruption, environment and geology of the terrain.

- Boiler

It is a depression formed in the center of a volcano in the shape of a cauldron or pot inside which is the crater. It is formed by the collapse of the volcanic structure over a shallow magma chamber.

Caldera of a volcano. Source: M. Williams, National Park Service

Not all volcanoes have a caldera as such, especially young volcanoes that are not very developed.

Origin

It can be formed by the collapse of the magmatic chamber, already emptied by previous eruptions due to the weight and instability of the structure. An example of this type is the caldera de las Cañadas del Teide in Tenerife (Canary Islands, Spain).

It can also be caused by a phreatic explosion in the magmatic chamber, collapsing the upper structure. The phreatic explosion occurs when magma comes into contact with groundwater, generating a huge vapor pressure.

This type of boiler is the one that the Caldera de Bandama presents in Gran Canaria (Canary Islands, Spain).

- Volcanic cone

You can see the volcanic cone in the dark part of the volcano. McGimsey, Game

As the pressure of rising magma builds up, the Earth's surface rises. When the volcanic eruption occurs, that is, the exit of the magma to the outside, the lava radiates from the crater and cools.

In this process, a cone is formed that gains height with successive eruptions. The classic volcanic cone is observed in stratovolcanoes. Not so in shield volcanoes, maars and even less so in yours.

Types of volcanoes and volcanic structures

The forms, products and scales of volcanic eruptions vary considerably from case to case. This generates a diversity of types of volcanoes, with their own structures depending on their process of origin.

It is important to consider these elements to understand the structural variations of volcanoes.

Effusive eruptions and explosive eruptions

In the case of the effusive eruption, the magma rises from the inside of the magma chamber and comes out as a coherent fluid called lava. It is basalt lava that reaches high temperatures and is not very viscous, so gases do not accumulate and explosions are reduced.

As lava flows outside like rivers, it cools and forms rock bodies called lava flows.

In turn, in the explosive eruption, the magma is very viscous due to the higher content of silica and clogs the conduits, accumulating gases which generate explosions. The magma is fragmented into more or less solid pieces (pyroclasts) and thrown violently outside by the pressure of the accumulated gases.

These gases are made up of volatile compounds that generate expansive bubbles that end up bursting.

Stratovolcano

It is formed by random layers of lava and highly consolidated pyroclasts reaching great heights. It represents the classic image of a volcano, as seen from Mount Fuji in Japan.

Mount Fuji (Japan). Source:

They form a raised volcanic cone with a central crater at the top of a proportionally narrow diameter.

Shield volcano

Here it is very fluid lava, so it reaches great distances before cooling away from the crater. Because of this, a cone with a broad base and relatively low elevation is formed.

Eyjafjallajo ̈kull volcano (Iceland). Source: Current at

Examples of these types of volcanoes are the Hawaiian shield volcanoes and the Eyjafjallajökull volcano in Iceland.

Somma volcano

It is a volcano with a double volcanic cone, due to the fact that a second cone is formed inside the caldera. A classic volcano of this type is Monte Somma, which is a stratovolcano in whose caldera is the famous Vesuvius.

Tuya volcano

These are subglacial volcanoes, that is, they erupt under a glacier, so the lava comes into contact with the ice. This causes the ice to slowly melt as the lava cools, forming layers of hyaloclastite (volcanic rock formed under water).

Herðubreið volcano (Iceland). Source: User en: User: Icemuon, cropped by User: Seattle Skier

The end result is flat-topped lava mountains with nearly vertical flanks like the subglacial Herðubreið volcano in Iceland.

Slag cone

They are formed by fragments of lava ejected by a single chimney that accumulate forming a small cone with a bowl-shaped crater. A typical slag cone is that of the Macuiltepetl volcano (Veracruz, Mexico).

Lava dome

When lava is very viscous, it does not flow long distances, accumulating around the ejection cone and above the chimney. An example is the Dome of Las Derrumbadas in Puebla (Mexico).

Maars or explosion craters

They are also called tuff ring or tuff cone and are formed by a phreatomagmatic eruption. That is, a violent expansion of water vapor when the rising magma meets groundwater.

Three maars Duan (Germany). Source: Martin Schildgen

This generates an accumulation of water vapor that violently breaks the surface forming a wide circular or oval boiler. Here the edges of the cone are low with the large diameter caldera generally filling with water after the eruption as in the Tres maars Duan in Germany.

In the following video you can see an active volcano:

References

1. Carracedo, JC (1999). Growth, structure, instability and collapse of Canarian volcanoes and comparisons with Hawaiian volcanoes. Journal of Volcanology and Geothermal Research.
2. Duque-Escobar, G. (2017). Geology Manual for Engineers. chap. 6. Volcanism. National university of Colombia.
3. National Geographic Institute (Seen on 19 Nov. 2019). Volcanology Madrid Spain. ign.es
4. Macías, JL (2005). Geology and eruptive history of some of the great active volcanoes in Mexico. Bulletin of the Mexican Geological Society Centennial Commemorative Volume Selected Topics of Mexican Geology.
5. Parfitt, EA and Wilson, L. (2008). Fundamentals of physical volcanology. Blackwell Publishing.
6. Thordarson, T. and Larsen, G. (2007). Volcanism in Iceland in historical time: Volcano types, eruption styles and eruptive history. Journal of Geodynamics.