What Is a Volcano? Types, Eruptions & Formation Explained

Editor: Arshita Tiwari on Apr 15,2025

 

What Is a Volcano? Understanding Types, Eruptions, and Formation. Volcanoes are among the most powerful and fascinating natural phenomena on Earth. They are both destructive and life-giving, shaping the planet’s surface while enriching the soil and influencing climate patterns. But what is a volcano exactly? How do they form, and why do some erupt more violently than others? This article dives deep into the world of volcanoes, covering everything from their formation to the different types of volcanoes and eruptions.

What Is a Volcano? 

A volcano is an opening in Earth's crust, which allows the escape of magma, gases, and ash from below the surface to the earth atmosphere. This measure is what can be said in a more common sense to release some internal pressure called the volcanic eruption. If this process is repeated many times, these eruptions generally build a mountain or an island that consists of hardened lava and volcanic ash. Volcanoes generally occur at or near the different boundaries of tectonic plates of Earth, at which time one plate will be subducted beneath the other, or where the plates are pulling apart. Some volcanoes also form in areas known as 'hot spots,' where the Pacific Plate is moved slowly across the Hawaiian hotspot fixed in the mantle and mantle plume rises through the crust; for example, Hawaii.

What Causes the Formation of Volcanoes?

volcano eruption

Volcano formation requires a delving into the inner workings of the Earth, which is made up of many layers: a core, surrounded by the mantle and then by the crust. The crust is broken into tectonic plates that float on the semi-molten upper part of the mantle.

Generally, volcanoes occur under these geological conditions:

1. Convergent Boundaries (Subduction Zones)

Subduction is the process whereby the oceanic plate, being denser, is forced underneath the lighter continental plate. The subduction of the plate creates melting, which generates magma that rises to the surface to form volcanoes.

2. Divergent Boundaries (Mid-Oceanic Ridge)

Divergent boundary processes involve tectonic plates moving apart from one another and magma rising to fill the gap. Hence, mid-ocean ridges and some volcanic islands are formed. 

3. Hot Spots

These are spots in the mantle where heat rises as a thermal plume from deep within the Earth; magma breaking through to create volcanoes. Hawaii is a textbook example of hot spot volcanism.

Different Types of Volcanoes

Volcanoes can take on different shapes, erupt differently, and be geologically unique. In fact, they can be classified into types based on shape and formation process.

1. Shield Volcanoes

  • Shape: Broad with gently sloping sides
  • Eruption Style: Non-explosive lava flows
  • Example: Mauna Loa, Hawaii
  • Details: Formed by successive lava outpouring over large areas, so the wide, low-viscosity basaltic lava flows easily and creates a shield form. 

2. Stratovolcanoes (Composite Volcanoes)

  • Shape: Tall and conical with steep slopes.
  • Eruption Style: Explosive and hazardous. 
  • Example: Mount Fuji, Japan, Mount St. Helens, USA. 
  • Details: Often alternate layers of lava flow, ash, and volcanic rocks. Found mostly at subduction zones, stratovolcanoes have some of the worst eruptions in human history.  

3. Cinder Cone Volcanoes

  • Shape: Small, steep-sided cones.
  • Eruption Style: Moderate eruptions throwing lava fragments. 
  • Example: Paricutin, Mexico. 
  • Details: Formed quickly by eruptions that throw lava fragments skywards, which then fall back around the vent and build a cone. 

4. Lava Domes

  • Shape: Rounded and dome-like. 
  • Eruption Style: Slow extrusion of viscous lava. 
  • Example: Mount St. Helens Lava Dome.
  • Details: Lava is thick and viscous, which piles up next to the vent rather than flowing away. Collapse of a lava dome may generate pyroclastic flows.

5. Caldera Volcanoes

  • Shape: Large sunken crater.
  • Eruption Style: Extremely explosive.
  • Example: Yellowstone Caldera.
  • Details: Formed when a large eruption results in the summit collapsing inward leaving behind a large crater.

Types of Volcanic Eruptions

Different kinds of volcanic eruptions depend mainly on the composition of magma and gas pressure inside the volcano; also, it may even involve how the volcano is erected. Here are mentioned the principal types: 

1. Hawaiian Eruption 

  • Characteristics: Calm; effusive; the lava flows out on its own.
  • Most commonly associated with: Shield volcanoes.
  • Resulting in: The building of wide, flat landforms.  

2. Strombolian Eruption 

  • Characteristics: Moderate sputtering of lava and gas.
  • Most commonly associated with: Cinder cone volcanoes.
  • Resulting in: The building of steep-sided cones.

3. Vulcanian Eruption 

  • Characteristics: Short, violent explosions of vapor and ash. 
  • Most commonly associated with: Stratovolcanoes. 
  • Resulting in: Clouds of ash, pyroclastic flow.

4. Plinian Eruption 

  • Characteristics: Highly explosive, propelling ash many miles into the skies.
  • Most common in: Composite and caldera volcanoes. 
  • Result: Devastation over a wide area with much longer-term impact on climate. 

5. Pelean Eruption 

  • Characteristics: Collapse of domes leads to pyroclastic flows.
  • Most common in: Lava dome volcanoes. 
  • Result in: Fast-moving, deadly pyroclastic surges. 

Must Read: Understanding Volcanic Earthquakes and Their Hazards

Types of Volcanic Activity

Volcanic activity types can be grouped based either on eruption frequency or ongoing activity status. They can be classified into three: 

1. Active Volcano: A volcano is called active when its last eruption was recently followed by signs of activity which indicate the possibility of its further eruption. These signs include gas emission and seismic activity. Example: Mount Etna, Italy.

2. Dormant Volcano: Dormant volcanoes have not erupted within the history of man, meaning they have been "sleeping", but they can and will erupt again. Example: Mount Kilimanjaro, Tanzania.

3. Extinct Volcano: Volcanic landforms that are not expected to erupt again because the magma supply has ceased are called extinct. Example: Shiprock, New Mexico, USA.

What Is a Volcanic Eruption?

In basic volcanic eruptions, the intense pressure from gases inside the magma forces the magma upwards toward the surface, breaking through the Earth's crust in the process. This may either end in a violent eruption characterized by explosion, ash, and gases, or in a gentle and slow flow of lava downhill. 

The eruptions can exert tremendous force and have devastating effects on their surroundings and on human life. They can cause landslides, river damming, and tsunamis (if undersea), disruption of air traffic, the release of ash, and sulfur dioxide into the atmosphere, which can lead to climatic changes.

Final Thoughts

So, what is a volcano? It's more than just a mountain that erupts—it’s a complex and dynamic geological structure formed by powerful forces within the Earth. From the different types of volcanoes and types of volcanic eruptions to the processes behind their formation, volcanoes offer a glimpse into the raw power of nature.

Whether active, dormant, or extinct, volcanoes continue to shape our planet in profound ways. By understanding what causes the formation of volcanoes and how they behave, scientists can better predict eruptions and minimize their impacts on human life.

Next time you see footage of a volcano or read about an eruption, you’ll know that it’s not just a random event—it’s the result of deep, intricate processes that have been at work for millions of years.


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