Volcanoes: Types, Parts, Eruptions, and Classification
Everything You Need to Know About Volcanoes: Volcanoes are the source of some of nature’s most powerful eruptions. They can reshape the land, create new mountains, and wipe out entire cultures. But what are volcanoes? Where do they come from? And why are there so many different types of volcanoes? We’re here to answer all your questions!
When you think of volcanoes, what do you envision? The fiery hot lava that spews from the crater? The ash and toxic gasses in the air? Here, we will discuss everything you need to know about volcanoes. From their formation to eruption patterns, this article has all your volcanic needs covered!
Table of Contents
- 1 What are Volcanoes?
- 2 What Are the Characteristics of Volcanoes?
- 3 What Are the Main Parts of a Volcano?
- 4 How Does a Volcano Form?
- 5 What Are the Different Types of Volcanoes?
- 6 What is Volcanic Eruption?
- 7 How Are Volcanoes Classified?
- 8 What are the Different Types of Volcanic Eruptions?
- 9 Conclusion
What are Volcanoes?
Volcanoes are openings in the planet’s crust that allow molten rocks (magma) and gasses trapped beneath to escape. The forceful ejection of lava and gasses often result in a relief on the planet’s surface, which appears in the form of a hill or mountain. The resulting structure is what we call a volcano.
Note: The thick blazing hot liquid made up of molten rocks beneath the surface is called magma. When magma reaches the surface, it is called lava.
What Are the Characteristics of Volcanoes?
- Volcanoes are elevated structures formed due to the magma moving to the surface.
- Volcanoes can vary in shape but generally consist of a conical structure formed due to the accumulation of erupted material.
- When magma reaches the surface, it’s called lava. Lava cools down over time and solidifies into rocks.
- Depending upon the activity, volcanoes can be active, dormant, or extinct.
- Volcanoes are formed where there is a fracture in Earth’s crust. These fractures allow magma to rise to the ground, pushing rocks and forming volcanoes.
What Are the Main Parts of a Volcano?
A volcano may seem like a single structure rising above the ground from the outside. However, it consists of several parts, from the top of the opening to the magma chamber inside. Let’s learn about different parts of the volcano in detail.
Different parts of a volcano are;
- Magma Chamber
- Rock Layers
- Conduit Pipe
- Branch Pipe
- Side Vent
- Volcanic Cone
- Lava Flow
- Volcanic Ash Cloud
- Layers of Lava and Ashes
A hollow space deep within the volcano where magma accumulates over time is called a magma chamber.
During an eruption, the material and gasses accumulated in the magma chamber come out violently to the surface and cause the explosion.
Rock Layers form the base of the volcano. These are the parts of the upper crust of the planet that floats on the mantle. It’s the fractures in the layers of the rock that give way to magma to rise to the surface.
Conduit Pipe or Volcanic Chimney
Conduit is simply the pathway that connects the magma chamber to the opening at the surface.
During an eruption, the magma in the magma chamber rises through the conduit or volcanic chimney to the surface.
Due to the enormous pressure of the rising magma, rocks along the conduit sometimes break off and erupt violently with the magma.
There could be some sideways cracks beside the main conduit pipe inside the volcano.
Rising magma from the magma chamber may move through these cracks branching the path further. It leads to the formation of branch pipes.
Magma sometimes moving through the branch pipes intrudes into the rocks layer forming horizontal sheets of solidified magma.
Vents, fissures, or crevices are the opening on the surface of the planet’s crust from which magma and gasses escape.
These raptures are formed due to the intense pressure exerted by the rising magma and gasses. Volcanoes can have more than one vent, but each of them contains a main central vent.
When magma reaches the surface moving through the branch pipe, instead of the main conduit pipe, it creates a second opening.
The secondary opening through which magma reaches the surface is called a side vent.
Bowl-shaped depressions at the top of vents of volcanoes are known as a crater. Craters are generally round in shape; however, different types of volcanic craters are unique in shape and size.
Interestingly, a volcano can have more than one crater. It’s the case with secondary cone volcanoes, and the second crater is usually called a lateral crater.
The cone-shaped structure formed due to the accumulation of lava and other materials from the volcano over several eruptions is known as a volcanic cone.
The thickness of a volcanic cone varies depending upon the number of eruptions a volcano has undergone.
The throat is the upper part of the conduit pipe. It’s the pathway just below the vent from which lava and volcanic gasses come out to the surface.
The lava flow is the stream of lava that flows through the sides of the volcano called the lava flow.
Depending upon the viscosity of the lava it can move freely to several kilometers or sluggishly to a few meters only before solidifying.
Volcanic Ash Cloud
When a volcano erupts violently, it sends up the skies huge quantities of materials, including lava, rocks, gasses, and ashes. The upwards moving material – dust, gasses, and ash form a cloud generally termed as ash cloud.
Layers of Lava and Ashes
The erupting material coming out of the volcano falls to the ground and settles down. Similarly, lava coming out of the volcano cools down and solidifies. Over several eruptions spanning over many years, the volcanic debris forms layers of lava and ash.
How Does a Volcano Form?
Volcano formation is linked with the functioning of tectonic plates. Earth’s crust is not uniform throughout its length – it consists of layers.
The topmost layer is where we live, and beneath it is the mantle. Mantle comprises very hot molten rocks known as magma. The top layer, also known as the tectonic plates, floats over the mantle.
These tectonic plates could move towards each other or away from each other. Volcanoes form at the boundaries of these tectonic plates where there are fractures in the Earth’s crust, allowing the magma to escape to the surface.
The resultant movement of tectonic plates gave rise to two types of plate boundaries;
- Convergent Plate Boundaries
- Divergent Plate Boundaries
Convergent Plate Boundaries
When two tectonic plates collide with each other, they create convergent plate boundaries. During the collision, the denser plate’s edge is often pushed beneath the less dense plate in a process known as subduction.
The edges of the downward-moving plate heat up due to enormous friction, which causes the rocks to melt, forming magma. Pressure build-up forces the magma to move towards the surface and results in an eruption forming a volcano.
The Ring of Fire in the Pacific lies in the subduction zone and hosts around 425 volcanoes or more.
Divergent Plate Boundaries
When two plates move away from each other, they form divergent plate boundaries.
Moving plates often result in vents or fissures that give way to magma and allow it to move upward, forming volcanoes.
Example: Mount Kilimanjaro in Kenya and Mount Nyiragongo in Congo are located at divergent plate boundaries.
What Are the Different Types of Volcanoes?
While lava and ashes are the typical characteristics of almost every volcano, they differ in their formation and eruption.
Depending upon their shape and formation, volcanoes can be of six types;
- Fissure Volcano
- Shield Volcano
- Dome Volcano
- Ash-Cinder Volcano
- Composite Volcano
- Caldera Volcano
Fissure Volcanoes or linear volcanoes are usually found along the oceanic ridges and, in rare cases, on land.
- They differ from other volcanoes due to their lack of central structure that forms around a crater.
- Instead, these volcanoes consist of a series of fractures that run deep underground.
- Lava escaping these volcanoes is of low viscosity; therefore, lateral development of fissure volcanoes is more profound than vertical development.
Examples of Fissure Volcanoes: Eastern African Rift, Cordón Caulle, Holuhraun.
The main characteristic of a shield volcano is its shape of an inverted shield.
- The height of a shield volcano is much less than its width. Therefore, these volcanoes have low slopes.
- The lava flow is effusive that is slow-moving due to less viscosity (low in silica).
- Being less viscous, lava flows to a greater distance before cooling. Accumulation of such a type of lava flow over a long period gives rise to a shield volcano.
Examples of Shield Volcano: Mauna Kea, Mauna Loa, Kohala volcano, Killauea, Tamu Massif.
Very thick lava that could not move too far beyond the crater gave rise to the dome volcano.
- The escaping lava moves sluggishly, cools down and piles around the vent giving the characteristic dome shape to the volcano.
- Lava domes are typically low in height. Similar to composite volcanoes, they can cause violent eruptions.
Examples of Dome Volcanoes: Mount Merapi, del Caribe volcano, Soufrière Hills and Chaitén lava dome,
Cinder cone volcanoes typically rise 300m to 500m and form by the fragmented and erupted ash that falls near the chimney or vent.
- Cinder cone volcanoes lack horizontal layers, unlike stratovolcanoes. Instead, they form a rather steep conical hill of tephra or pyroclast (volcanic debris).
- The loose volcanic debris escapes from the vent and collects around it, giving rise to ash-cinder cone volcanoes.
Examples of cinder-cone volcanoes: Mono-Inyo Craters, California, Paricutín in Mexico
Composite volcanoes are also known as stratovolcanoes due to their peculiar characteristics of layers of solidified material.
- They form from consecutive eruptions and lava flow over thousands of years.
- Composite Volcanoes often have a steep side and very pronounced volcanic cones.
- Lava coming out of composite volcanoes is usually viscous and sticky due to the greater quantity of silica. It flows slowly and forms a towering structure.
Example of Composite Volcano: Pico del Teide, Arenal volcano, Krakatoa, Monte Helena, Monte Vesubio
Caldera is a cauldron-like structure formed when a volcano erupts and creates a depression.
- When the magma chamber empties following an eruption, the support due to magma vanishes, and the chamber collapses inward, forming calderas.
- There are resurgent calderas too that form due to refilling of the magma chamber. The refilling magma pushes the caldera floor upward, hence the name, resurgent or ‘rise again.’
- Caldera often forms a lake as the depression formed fills with water.
Examples of Calderas: Oregon crater lake, Mt Mazama, Kilauea.
What is Volcanic Eruption?
The forceful and violent ejection of lava, gasses, and rocks from a volcano is known as a volcanic eruption.
The eruptions result from the pressure build-up due to magma moving from the mantle to the magma chamber inside the volcano.
How Are Volcanoes Classified?
Volcanoes are classified depending upon their activity. By this definition, volcanoes can be;
Active volcanoes are those volcanoes that can erupt at any time. Most active volcanoes have erupted in the recent past and have a very high chance of erupting again.
Examples of active volcanoes: Mount Etna, Kīlauea, Mount Stromboli.
These types of volcanoes have not erupted in the recent past.
But they show some signs of activity like hot springs or fumaroles (holes on Earth’s surface oozing steam and Volcanic gasses).
Although dormant volcanoes haven’t erupted for quite a long time, they can explode in the future.
Examples of dormant volcanoes: Mount Fuji, Japan, and Mount Kilimanjaro, Tanzania.
Extinct Volcanoes have minimal chance of eruption in the future. A volcano is considered extinct if there has been no eruption for thousands of years.
However, there is no guarantee that an extinct volcano may not wake up and become active someday. Examples of extinct volcanoes: Mount Thielsen, Oregon, US, and Mount Slemish, Antrim.
What are the Different Types of Volcanic Eruptions?
Volcanoes can also be characterized by the kind of eruption that occurs from them. Based on eruptions, volcanoes can be divided into six types;
- Hawaiian Eruptions
- Strombolian Eruptions
- Vulcan-type Eruptions
- Vesuvian Eruptions
- Plinian Eruptions
- Ultra Plinian Eruptions
- Hawaiian eruptions are characterized by quiet outpourings of lava without strong shocks or explosions.
- Lava coming out of Hawaiian eruptions is very fluid and could travel kilometers.
- Gasses trapped in lava are released smoothly; therefore, the lava forms a smooth surface.
- Volcanoes with Strombolian eruptions are characterized by effusive eruptions forming lava fountains.
- The Strombolian-type eruptions are regularly and moderately explosive.
- Lava effusions form layers of solidified material and give rise to stratovolcanoes.
- Vulcun-type eruptions are marked by violent explosions often destroying the cone they came from.
- The explosion involves, emission of volcanic bombs, gas clouds, and large quantities of ash.
- The emissions consist of very viscous lava, rich in silica and large quantities of gas.
- Vesuvian eruptions are similar to Vulcan-type eruptions; however, they are characterized by a very heavy initial explosion that empties the magma chamber completely.
- The eruptive material can reach 20-25 km in height
- The name Plinian eruption is derived from the Pelée volcano in Martinique, which erupted very violently in 1902.
- The eruption occurs under a “plug” formed by solidification in the volcanic duct. The magma is very acidic and, therefore, extremely viscous.
- The eruption is quite explosive, forming a river of expelled materials.
Ultra Plinian Eruptions
- The explosion in Ultra Plinian Eruption exceeds even Plinian eruptions in intensity.
- The eruption is so explosive it disintegrates the entire volcanic structure.
- The volume of expelled material is staggering. The escaping gasses could even impact the global climate.
Volcanoes are one of the most majestic yet violent structures on a planet. On Earth, different types of volcanoes constantly shape the planet’s surface and depth of the ocean, destroying the old and giving rise to new structures. A gateway connecting the blazing depth of Earth’s mantle to the surface, volcanoes bring essential minerals to the surface, making it possible for life to thrive.