Volcanoes are the planet’s geologic builders and designers. They are responsible for the formation of more than 80 percent of the surface of our planet, thereby creating the groundwork that has fostered the growth of life. Craters and mountains are both formed by the explosive force of their attacks.

A desolate landscape was brought about by the expansion of lava rivers. However, as time passes, the elements wear away at these volcanic rocks, freeing the nutrients that were imprisoned within their stony prisons and resulting in the creation of exceptionally rich soils that have enabled the growth of civilizations.

Every continent, including Antarctica, is home to at least one active volcano. Today, there are over 1,500 volcanoes that are thought to possibly still be active somewhere in the world; of those, 161—or more than 10 percent—are located within the borders of the United States.

But each volcano is distinct. The eruption of Mount Pinatubo in 1991 was an example of an explosive eruption, while the activity of Hawaii’s Kilauea volcano in 2018 was an example of an effusive eruption. Some volcanoes come to life in the form of explosive eruptions, while others burp rivers of lava in what is known as an effusive eruption.

All of these changes can be attributed to the chemistry that is driving the activity of the molten state. When the magma is less viscous, also known as runny, effusive eruptions are more likely to occur. This is because it is easier for gas to escape and for the magma to flow down the slopes of the volcano. Explosive eruptions, on the other hand, take place when gasses are entrapped by viscous molten rock, which builds pressure until the gas suddenly bursts violently free.

The majority of the world’s volcanoes are thought to have originated near the edges of the Earth’s tectonic plates. These plates are enormous regions of our planet’s lithosphere that are constantly moving and crashing into one another. When two tectonic plates clash, the result is frequently a zone known as a subduction zone, in which one plate dives deeply below the other.

As the continent continues to sink deeper into the Earth, temperatures and pressures continue to rise, which causes water to be released from the rocks. The water slightly lowers the melting temperature of the rock that is located above it, which results in the formation of magma that is capable of making its way to the surface. This magma is the spark of life that can reawaken a dormant volcano.

However, subduction is not always a factor in the formation of volcanoes. Hotspot volcanism is a different type of formation that can lead to the formation of volcanoes. Near such a scenario, a region of magmatic activity, often known as a “hotspot,” in the center of a tectonic plate has the potential to break through the crust and give rise to a volcano.

The tectonic plates continue their sluggish march, constructing a line of volcanoes or islands on the surface as they go. This is despite the fact that the hotspot itself is assumed to be relatively immobile. It is believed that this mechanism is responsible for the volcanic chain that includes Hawaii.


When magma erupts at the surface as lava, many kinds of volcanoes can be formed depending on the following factors:

the thickness of the magma, also known as its stickiness.
the amount of gas that is contained within the magma.
the components that make up the magma.
the process by which the magma rose to the surface of the earth.
However, there are many distinct volcanic features that can arise from erupted magma (such as cinder cones or lava domes), and there are also mechanisms that shape volcanoes. Strictly speaking, there are two basic types of volcanoes: a stratovolcano and a shield volcano. In this lesson, you will learn the distinctions between lava domes and calderas, as well as the differences between stratovolcanoes and shield volcanoes.

Volcanology places a significant emphasis on viscosity. The eruption of highly viscous (very sticky) magma typically results in the formation of steep-sided volcanoes with slopes that are approximately 30–35 degrees. This is due to the fact that the viscous volcanic material doesn’t flow very far from the location where it is erupted, and as a result, it piles up in layers to form a cone-shaped volcano known as a stratovolcano. On the other hand, shield volcanoes have mild slopes that are less than 10 degrees and erupt basalt, which is a more fluid type of lava than other types. When a shield volcano erupts, the molten basalt can travel great distances away from the vent, creating slopes that are broad and gentle.


When a volcano erupts and produces lava with a low viscosity and a high flow rate, the lava spreads out in all directions and eventually creates a volcano with gentle slopes. This type of volcano is called a shield volcano. The majority of shield volcanoes are generated from basaltic lava flows that are fluid. Both Mauna Kea and Mauna Loa are types of volcanoes known as shield volcanoes. Around the perimeter of the island of Hawaii are a group of active volcanoes that reach heights of more than 9 kilometers above the ocean floor.

Stratovolcanoes are distinguished from shield volcanoes by their more conical shape and generally steeper slopes. They originate from thick, sticky lava that moves more slowly than other types of lava. As a result, a volcano with steep sides is formed around the vent by the lava that piles up around it. As a result of the accumulation of gas in the viscous magma, stratovolcanoes have a greater potential for producing explosive eruptions.

Andesite, which gets its name from the Andes Mountains, is the type of rock that is most frequently erupted by stratovolcanoes. However, stratovolcanoes can also erupt a broad variety of other rocks, depending on the tectonic environment in which they are located.

The Soufrière Hills volcano is located on the island of Montserrat in the Caribbean. This volcano is famous for the lava dome complex that sits on its peak, which has gone through periods of expansion and contraction over the course of its history. When viscous lava is extruded from a vent, it does not have the ability to quickly flow away from the vent since it is not very fluid. Instead, it gathers on top of the vent in the shape of a big dome and builds up there.

A magma chamber is located beneath a volcano and is used to store magma. When a very huge and explosive eruption takes place, which empties the magma chamber, the ceiling of the magma chamber may collapse, forming a depression or bowl with very steep sides on the surface. This can happen when the magma chamber is emptied. These are known as calderas, and their diameters can reach tens of kilometers.

The summit of a single stratovolcano can be removed during an eruption, which can potentially result in the formation of a caldera. Eruptions that generate calderas have the potential to remove significant parts of a single stratovolcano. It is possible to completely remove the top.

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