World Distribution of Volcanoes: Class 11 Geography Notes

Volcanoes are fascinating natural phenomena that play a significant role in shaping our planet’s surface. They occur in various settings, from ocean floors to mountain ranges, and even in unexpected places like the middle of tectonic plates.

Let us discuss in detail the world distribution of Volcanoes!

World Distribution of Volcanoes: Class 11 Geography Notes

Distribution of Volcanoes Around the Globe

Here’s a simplified table showing the distribution of volcanoes around the globe:

Region	Number of Volcanoes
Pacific Ring of Fire	Most volcanically active region includes the coasts of North and South America, Asia, and islands in the Pacific Ocean.
Mid-Atlantic Ridge	Underwater volcanic mountain range running down the center of the Atlantic Ocean.
Africa	Includes volcanic activity in the East African Rift and areas like the Canary Islands.
Europe	Primarily volcanic activity in Italy (e.g., Mount Etna) and Iceland.
Indonesia	Contains numerous active volcanoes, part of the Pacific Ring of Fire.
Japan	Located along the Pacific Ring of Fire, has several active volcanoes.
Philippines	Archipelago with a significant number of active volcanoes.
New Zealand	Located on the Pacific Ring of Fire, has both active and dormant volcanoes.
Alaska	Contains several active volcanoes, part of the Pacific Ring of Fire.
Central America	Region with active volcanoes, part of the Pacific Ring of Fire.

Reasons Behind the Distribution of Volcanoes

The distribution of volcanoes around the globe is primarily influenced by tectonic plate boundaries and mantle hotspots. Here are the main reasons behind their distribution:

1. Plate Boundaries: The majority of volcanoes occur along tectonic plate boundaries, where the Earth’s lithosphere (outer shell) is either being pulled apart (divergent boundaries), pushed together (convergent boundaries), or sliding past each other (transform boundaries). These interactions result in the formation of volcanic activity.
2. Subduction Zones: Volcanoes are particularly common at convergent plate boundaries where one tectonic plate is forced beneath another in a process called subduction. The subducted plate melts as it descends into the Earth’s mantle, generating magma that rises to the surface, leading to volcanic eruptions. The Pacific Ring of Fire is a prime example of this, where many volcanoes are located around the perimeter of the Pacific Ocean due to subduction zones.
3. Mid-Ocean Ridges: Divergent plate boundaries, such as mid-ocean ridges, also feature volcanic activity. Here, new oceanic crust is formed as tectonic plates move apart, and magma rises from the mantle to fill the gap, creating underwater volcanic activity.
4. Mantle Hotspots: Some volcanoes are not directly associated with plate boundaries but instead occur above mantle hotspots, where plumes of hot magma rise from deep within the Earth’s mantle. These hotspots can create chains of volcanic islands or individual volcanic peaks. Examples include the Hawaiian Islands, formed by the movement of the Pacific Plate over a hotspot beneath the Earth’s crust.
5. Rift Zones: Rift zones, such as the East African Rift, occur where tectonic plates are pulling apart, causing the Earth’s crust to thin and crack. Magma rises to fill these fissures, leading to volcanic activity along the rift.

World Distribution of Subduction Zones

Volcanic activity is closely linked to plate tectonics, with the majority of volcanic eruptions occurring along subduction zones and rift zones. Around 80% of volcanic activity takes place along subduction zones, where one tectonic plate is forced beneath another. Another 15% of volcanic activity occurs at mid-ocean spreading centers and continental rifts, where tectonic plates are moving apart.

The Circum-Pacific Ring of Fire, encircling the Pacific Ocean, is home to most of the world’s high volcanic cones and mountains, with active subduction zones involving the Pacific, Nazca, Cocos, and Juan de Fuca plates. Examples like Sumatra and Java illustrate this, lying above the subduction zone between the Australian and Eurasian plates.

The Mid-Atlantic belt features basaltic volcanoes along the mid-oceanic ridge, where seafloor spreading occurs. In the Mid-Continental belt, volcanoes in the alpine mountain chains, the Mediterranean Sea, and Eastern Africa’s fault zone are prevalent. These areas are influenced by the collision of plates, such as the African, Eurasian, and Indian plates.

Intraplate volcanoes, found within plates, away from plate boundaries, are also known as hot spot volcanoes. They occur at centers of plate boundaries, where magma escapes through surface cracks. The Hawaiian Islands serve as an example of hot spot volcanoes.

Five Countries Having Greatest Numbers of Volcanoes

Country	Number of Volcanoes	Number of Active Volcanoes
United States	165	42
Japan	122	44
Indonesia	118	58
Russia	117	33
Chile	91	19

Volcanoes in the Mid-Atlantic belt

The Mid-Atlantic Ridge is an underwater mountain range that runs along the floor of the Atlantic Ocean. It is a divergent plate boundary, where two tectonic plates (the North American and Eurasian plates) are slowly moving apart.

As these plates separate, magma (molten rock) from the Earth’s mantle rises to fill the gap. This magma cools and solidifies, forming a new oceanic crust and volcanic mountains on the seafloor.

The volcanoes found along the Mid-Atlantic Ridge are mainly:

1. Seamounts: These are underwater mountains formed by volcanic activity along the ridge. They can grow tall enough to become islands if they breach the water’s surface.

2. Hydrothermal Vents: These are cracks or openings in the seafloor where hot, mineral-rich fluids are expelled from the Earth’s interior. They are often associated with volcanic activity along the ridge.

3. Rift Valleys: These are deep, trenched valleys that run along the centre of the Mid-Atlantic Ridge, formed by the spreading of the tectonic plates and the upwelling of magma.

The volcanoes along the Mid-Atlantic Ridge are generally not explosive like volcanoes on land. Instead, they are characterized by more gentle effusive eruptions that release fluid basaltic lava.

The volcanic activity along this underwater mountain range is a continuous process, constantly creating new oceanic crust and shaping the seafloor as the tectonic plates slowly drift apart.

Circum Pacific Ring of Fire

The Circum-Pacific Ring of Fire is a horseshoe-shaped belt that runs around the Pacific Ocean. It is a region with a high concentration of volcanoes and earthquakes.

– It traces the boundaries of the Pacific tectonic plate, where it meets and interacts with other major plates like the North American, Eurasian, and Australian plates.

– It extends for about 40,000 km (25,000 miles), passing through the western coasts of North and South America, across the Aleutian Islands, and down through Japan, the Philippines, New Zealand, and Antarctica.

– This region accounts for about 75% of the world’s volcanoes and 90% of its earthquakes.

– The intense volcanic and seismic activity is caused by the movements and collisions of tectonic plates along the Ring of Fire.

– At some points, plates are converging (moving together), leading to subduction zones where one plate is pushed under the other, causing earthquakes and volcanic eruptions.

– At other points, plates are spreading apart at divergent boundaries, allowing magma to rise and create underwater volcanic mountains.

– Major volcanic belts and chains like the Andes Mountains, the Cascade Range, and the Kuril-Kamchatka Arc are part of the Ring of Fire.

– Devastating earthquakes and eruptions have occurred frequently in this region, such as the 2011 Tōhoku earthquake and tsunami in Japan.

The Ring of Fire is a stark reminder of the powerful geological forces constantly reshaping the Earth’s surface through the movement of tectonic plates.

Intraplate volcanoes

– Intraplate volcanoes are like surprise volcanoes! They pop up in the middle of big tectonic plates, not near the edges where we usually expect volcanoes.

– Think of them like hot bubbles in a pot. Deep inside the Earth, there are spots hotter than others (called hot spots). These hot spots can make the ground bubble up and form a volcano, even if it’s far from the edge of a plate.

– Hawaii: Picture the beautiful Hawaiian Islands. They were formed by intraplate volcanoes over a hot spot in the middle of the Pacific Ocean.

– They often look like wide, flat shields because their lava flows spread out a lot.

– They usually don’t explode as much as volcanoes near plate edges, so they’re often less scary.

Volcanoes in India

The Himalayan region and the Indian peninsula do not have any volcanoes. During the 1990s, Barren Island, which is India’s only active volcano located in the Andaman and Nicobar Islands, became active. Following eruptions of lava and ash in 2017, it is now classified as an active volcano. Narcondam, situated approximately 150 kilometers northeast of Barren Island, is the only other volcanic island within Indian territory; however, it is believed to be extinct as its crater wall has been destroyed.

Conclusion

Understanding the different types of volcanoes and their locations, such as the Mid-Atlantic Ridge, Circum-Pacific Ring of Fire, and intraplate regions like Hawaii, helps us grasp the dynamic and ever-changing nature of Earth’s geology. While some volcanoes result from plate boundaries, others emerge as surprises in the heart of our planet’s plates, showcasing the Earth’s intricate and powerful processes.

World Distribution of Volcanoes- FAQs

What causes the Mid-Atlantic Ridge volcanoes?

The Mid-Atlantic Ridge’s volcanoes are caused by magma rising from the mantle to fill the gap between separating tectonic plates, forming new oceanic crust and underwater mountains.

Why is the Circum-Pacific Ring of Fire significant?

The Ring of Fire is significant due to its high concentration of volcanoes and earthquakes, accounting for about 75% of the world’s volcanoes and 90% of its earthquakes.

How do intraplate volcanoes differ from other volcanoes?

Intraplate volcanoes form in the middle of tectonic plates, often due to hot spots, and are generally less explosive compared to those at plate boundaries. An example is the Hawaiian Islands, formed by intraplate volcanic activity over a hot spot.