Composite Volcano: Structure, Formation, Life Cycle, Location of Volcanoes

Composite volcanoes or stratovolcanoes are one of the most common categories of volcanoes. Multiple eruptions spanning hundreds of thousands of years create a composite volcano. The eruptions gradually build up the composite volcano, layer by layer, until it reaches tens of thousands of meters in height. Some strata may be made of lava, while others may be made of ash, rock, or pyroclastic flows. Large amounts of thick magma can build up inside a composite volcano, causing it to detonate in a volcanic explosion. 

---

Location of Composite Volcanoes

Composite volcanoes are usually found in groups, each one a few kilometers apart. In the Pacific Ocean, stratovolcanoes make up the "Ring of Fire." Mount Fuji, Mount Rainier, and Mount St. Helens in Washington State, and Mayon Volcano in the Philippines are all instances of composite volcanoes. Mount Vesuvius erupted in 79, destroying Pompeii and Herculaneum, while Mount Pinatubo erupted in 1991, ranking as one of the twentieth century's largest eruptions.

Fig. Ring of Fire

---

Composition of Composite Volcanoes

The composition of composite volcanoes, also known as stratovolcanoes, gives them their name. Layers of pyroclastic material, such as lava, pumice, volcanic ash, and tephra, are used to construct these volcanoes. With each eruption, the layers build up on top of one another. Because the lava is viscous, the volcanoes produce steep cones rather than circular shapes.

The silicate-rich minerals rhyolite, andesite, and dacite are found in composite volcanic magma, making it felsic. Low-viscosity lava pours from fissures and spreads from a shield volcano, such as that found in Hawaii. A stratovolcano's lava, boulders, and ash either flow a short distance from the cone or eject explosively into the air before returning to the source.

Also Read: 

A composite volcano can reach heights of up to 8,000 feet above its base. The majority of composite volcanoes have a summit crater with a central vent or a clustered collection of vents. Lava is discharged from the composite volcano through cracks in the crater wall or fractures on the cone's flanks. The ribs formed by the solidified lava within the fissures considerably strengthen the cone.

One of the most important characteristics of composite volcanoes is their conduit system (The volcanic conduit is the pipe that takes magma from the magma chamber up through the crust and into the volcano itself until it reaches the surface.) . Magma from the Earth's chamber's deep reservoir rises to the surface via a composite volcano's conduit system. The buildup of material spewed through the conduit builds composite volcanoes, which grow in size when lava, ash, and other materials are added to the slope.

Fig. Structure of Composite Volcano

---

Formation of Composite Volcanoes

At subduction zones, where one plate at a tectonic boundary is pushed below another, stratovolcanoes occur. This can occur when the oceanic crust slides beneath an oceanic plate (for example, near or beneath Japan and the Aleutian Islands) or when the oceanic crust is dragged beneath the continental crust (underneath the Andes and Cascades mountain ranges).

The porous basalt and minerals trap water. Temperature and pressure rise as the plate goes deeper, resulting in a process known as "dewatering." The melting point of rock in the mantle is lowered as water from hydrates is released. 

Because melted rock is less dense than solid rock, it rises and becomes lava. As the magma rises, the pressure decreases, allowing volatile chemicals to escape the solution. Pressure is exerted by water, carbon dioxide, sulphur dioxide, and chlorine gas. Finally, the stony plug that has been covering the vent bursts open, resulting in a tremendous explosion.

Fig. Composite volcanoes or Stratovolcanoes

The following sections go through the steps involved in the development of composite volcanoes:

• Magma's Ascension

Magma rises from the Earth's chamber below to build a volcanic cone, which explodes at the surface via the conduit system. Lava pours and spreads throughout the area.

• Volcanic Activity is Active

Volcanic activity in a composite volcano can last for hundreds of years, until a large cone forms and lava flows construct a vast plateau around its base.

• Cone Eroding

The cone begins to erode as volcanic activity ceases. The cone is scraped away to reveal the hardened "volcanic plug" in the conduit after thousands of years of volcanic activity. Streams widen their canyons and sever the lava plateau during this time of inactivity.

• Final Activities 

All remnants of the cone are being eroded away by soil erosion. Only the protruding plug, the volcano's ruins, and the lava plateau that surrounds it are left.

Also Read:

---

Consequences of Eruptions

Composite volcanoes cause more than just death and property harm. They affect weather and climate because they discharge particles and gasses into the stratosphere. Composite volcanoes generate particles that cause vibrant sunrises and sunsets. Even though no car accidents have been attributed to volcanic eruptions, explosive debris from composite volcanoes poses a threat to aviation traffic.

Magma from a composite volcano isn't fluid enough to flow around obstructions and emerge as a lava river. A stratovolcano eruption, on the other hand, is sudden and destructive. Toxic fumes, ash, and hot debris are ejected with force, and often without warning.  Another hazard is lava bombs. 

These molten rock chunks can range in size from small stones to the size of a bus. Although most of these "bombs" do not explode, their mass and velocity produce damage similar to that caused by an explosion. Lahars are also created by composite volcanoes. A lahar is a mudslide that combines water and volcanic debris. Lahars are volcanic landslides that fall down a steep slope at such a fast rate that they are difficult to avoid. Since 1600, volcanoes have killed over a third of a million people. The majority of the deaths have been linked to stratovolcanic eruptions.

Sulfuric acid can be produced when sulphur dioxide is discharged into the environment. Acid rain can be produced by sulfuric acid clouds, which can obscure sunshine and lower temperatures. Stratovolcanic eruptions may have played a role in the world's largest extinction event, at least in part. Beginning 300,000 years before the end-Permian mass extinction and lasting half a million years after the disaster, a complex of volcanoes known as the Siberian Traps emitted vast volumes of greenhouse gasses and ash. 

Also Read:

---

Things to Remember

• Composite volcanoes, also known as stratovolcanoes, are cone-shaped volcanoes composed of many layers of lava, pumice, ash, and tephra.
• Composite volcanoes tend to generate tall peaks rather than rounded cones because they are made up of layers of viscous material instead of fluid lava. A caldera is formed when the peak crater collapses.
• The most catastrophic eruptions in history have occurred due to composite volcanoes.
• When big composite volcanoes erupt, they can leave behind a caldera, which is a collapsed area. The volcano's position was indicated by deep, steep-walled depressions. And it is in this area that a new composite volcano will erupt.
• Apart from Earth, stratovolcanoes have only been discovered on Mars.

Also Read: 

---