What Causes a Volcano to Erupt?
Volcanoes are the geological architects of the earth. They have created more than 80 percent of the surface of our planet, laying the foundation for life to thrive. A volcano is basically an opening or crack in the earth's crust connected to a magma chamber through which glowing materials in the form of magma escape from the interior of a planet and accumulate on the planet's surface.
Read on in this article from thedailyECO where we explain what volcanoes are, how they form, and the different types of volcanoes that exist.
What are volcanoes?
A volcano is an opening in the crust of a planet or moon through which molten rock and gasses trapped beneath the surface erupt, often forming a hill or mountain.
As the descending land mass sinks deep into the earth, temperatures, and pressures rise, releasing water from the rock. As the magma chamber fills with pressure, the magma moves through channels in the rock and reaches the surface. Once it flows to the surface, the magma is called lava.
They usually form at the edge of tectonic plates and consist of lava flows and fragmented material, but they can form in different ways depending on where the volcanoes originate, as we will see below.
An erupting volcano can exhibit different types of activity, which can also vary in intensity. Volcanic activity includes earthquakes caused by magma movement, gas emissions, lava eruptions, and cataclysmic eruptions.
There are volcanoes on every continent, even in Antarctica. About 1500 volcanoes around the world are still considered potentially active today.
Volcanoes have created more than 80% of our planet's surface, laying the foundation for life to thrive. Their explosive power creates both mountains and craters. The decomposition of volcanic rock by the elements releases nutrients that result in fertile soils where civilizations can thrive.
How are volcanoes formed?
As we have already indicated, there are different ways in which a volcano can form, depending on where it is located, but the steps are generally the same. Volcanoes can form in two ways: through plate tectonics, i.e., the continuous movement of our planet's crustal plates across the molten mantle, or in so-called hot spots, where glowing material appears selectively in a particular area of the Earth. There are three settings where volcanoes typically form:
- Destructive plate boundary volcanos: destructive or convergent plate boundaries are located where tectonic plates move toward each other. In this scenario, volcanoes form either when an oceanic plate dips beneath another oceanic plate or when an oceanic plate dips beneath a continental plate.
- Constructive plate boundary volcanos: also known as divergent plate boundary, they occur when plates move apart. When this happens, magma rises from the Earth's mantle and forms (or constructs) a new crust.
- Hot-Spot Volcanos: in contrast to other volcanoes, hot-spot volcanism originates outside of Earth's tectonic plate boundaries. Instead, it occurs at unusually hot centers known as mantle plumes.
The formation of volcanoes can vary due to a number of factors, including location and process, but there are aspects of their formation that are universal.
Steps in the formation of volcanoes
- At very high temperatures, magma forms inside the planet, reducing its density.
- This change in the density of the magma causes it to rise to the top of the planet's surface.
- The magma then escapes through cracks in the Earth's crust and through the main crater in the form of an eruption.
- Pyroclastic material accumulates on the surface of the Earth's crust and creates the main cone of the volcano.
Parts of a volcano
A volcano is composed of different parts:
- Conduit: an underground passage through which magma rises until it reaches the crater.
- Crater: can be considered the mouth of a volcano, and it surrounds a volcanic vent. Lava, ash, and pyroclastic material are ejected through the crater.
- Caldera: a large depression that forms during an eruption and, because of the lack of structural support, causes instability inside the volcano so that the floor eventually collapses inward. Not all volcanoes have a caldera, and it ends up being larger than the crater.
- Parasitic cone: also known as adventive cone or satellite cone, is the cone-shaped accumulation of volcanic material that does not belong to the central vent of a volcano. Secondary vents are formed as the volcano matures through cracks that occur at the base of the volcano or along its flanks.
- Throat: entrance of a volcano. The part of the conduit that ejects lava and volcanic ash.
- Fumarole: is a vent in the surface of the Earth or other rocky planet from which hot volcanic gasses and vapors escape without being accompanied by liquids or solids. In other words, no magma is ejected.
- Magma chamber: is a large pool of liquid rock beneath the Earth's surface
- Lava: magma that comes to the surface at a high temperature and cools and solidifies on contact with air. This lava, along with the rock and ash, contributes to the formation of the cone-shaped body of the volcano formed by the many eruptions over time.
- Ash: fragments of lava or rock less than 2 mm in size that are ejected into the air during volcanic explosions.
- Ash cloud: a cloud of ash produced by volcanic explosions.
You may be interested in this other article, where we explain how mountains are created.
Types of volcanoes
Volcanologists designate volcanoes as active, dormant, or extinct, depending on how long ago they erupted and whether they are likely to do so again. Let us take a closer look at each case:
- Active volcanoes: are those that can erupt at any time, they are in a state of latency. A volcano is considered potentially active if it has erupted in the last 10,000 years.
- Dormant volcanoes: refers to a volcano that is not erupting now, but is considered likely to erupt in the future. They might also show some signs of activity. There is no precise distinction between active and dormant volcanoes. Dormant volcanoes are sometimes described as being potentially active.
- Extinct volcanoes: an extinct volcano is one that is not expected to erupt again in the future. Sometimes the determination of whether a volcano is extinct is based on the amount of time since its last eruption. Thousands of years must pass before a volcano is considered extinct, although this is no guarantee that it will ever awaken again.
Types of volcanic eruptions
An erupting volcano may exhibit different types of activity, which may also vary in intensity. Volcanic activity includes earthquakes caused by magma movement, gas emissions, lava eruptions, and cataclysmic eruptions. Most geologists use the term eruption to describe an entire period of volcanic activity interspersed with quiet intervals. Eruptions generally consist of eruptive pulses and eruptive phases.
- Eruptive pulses are single explosions that can last from a few seconds to minutes.
- Eruptive phases consist of numerous eruptive pulses that create a pulsating eruption column or lava flow, and can last from several hours to days.
An eruption may consist of many eruptive pulses and last for several days, months, or even years. The size of the magma body beneath a volcano has a strong influence on the magnitude of eruptions, since the availability of magma can severely limit its size. Small magma bodies simply cannot produce large eruptions because there is not enough material.
Furthermore, in the various mechanisms of volcanic eruptions, there are 3:
- Magmatic eruption: it results from the release of the gas contained in the magma due to a decompression effect. This causes the density to decrease, allowing the magma to rise to the top. These are the most well-observed type of eruption.
- Phreatic eruption: it occurs when the water that comes in contact with the magma evaporates. In other words, they are driven by the superheating of steam due to the proximity of magma. The evaporation ejects the surrounding materials and particles. This type exhibits no magmatic release, instead causing the granulation of existing rock.
- Phreatomagmatic eruption: it occurs when the magma cools on contact with water. In this case, the magma rises explosively to the surface and breaks apart, unlike phreatic eruptions where no fresh magma reaches the surface.
Within these broad eruptive types, there are several subtypes. Some are named after specific volcanoes where the type of eruption is common. Others refer to the shape of the eruption products or the location where the eruptions occur. Here are some of the most common types of eruptions subtypes listed in order of increasing degree of explosiveness:
- Icelandic: characterized by outpourings of molten basaltic lava flowing from long, parallel fissures. Such eruptions often form lava plateaus.
- Hawaiian: the lavas of this type of volcano are ejected through the crater or through the cracks on the flanks of the volcano. These lavas are of the basaltic type and have a low gas content.
- Strombolian: in this type of volcano, the explosions are interspersed in time between quiet phases that can change their extension.
- Vulcanian: it is a volcano in which there are violent eruptions in which the water interacts with the magma and causes a small fragmentation in the magma. These interactions between magma and water produce large amounts of ash, bombs, blocks, and steam.
- Pelean: is associated with explosive eruptions that produce pyroclastic flows, dense mixtures of hot volcanic fragments and gas described in the Lava, Gas, and Other Hazards section.
- Plinian: it is characterized by a gas explosion that successively ejects a large amount of pumice at a high altitude, about 20 km above the crater.
If you want to learn more about volcanoes, do not miss the video we leave you below, in which we list the most dangerous active volcanoes of the present.
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