Mount Etna Eruption

Volcanoes

About Volcanoes

• A volcano is a vent in the Earth's crust through which molten rock (lava), gases, ash, and steam are expelled.
• Volcanic activity is part of endogenic processes and is linked to plate tectonics.
• Eruptions can form different landforms:
• • Explosive eruptions ? volcanic mountains.
  • Gentle eruptions ? lava plateaus.
  • Intrusive landforms ? batholiths, laccoliths, etc.

Magma vs Lava

• Magma: Molten rock beneath the Earth's surface; originates in the asthenosphere.
• Lava: Magma that has erupted onto the Earth’s surface.
• Tools and Methods to Predict Volcanic Eruptions
• Seismic Monitoring: Detects tremors indicating magma movement.
• Ground Deformation Tools: GPS, tiltmeters to detect swelling.
• Gas Emissions Monitoring: Tracks increase in sulfur dioxide (SO?), carbon dioxide (CO?).
• Gravity and Magnetic Surveys: Identify subsurface changes before eruption.

Types of Volcanoes (Based on Frequency)

• Active Volcanoes:
  • Erupt frequently; mostly found in the Pacific Ring of Fire.
  • Example: Kilauea (Hawaii), Santa Maria (Guatemala).
• Dormant Volcanoes:
  • Have not erupted recently but may in future.
  • Example: Mount Kilimanjaro (Tanzania).
• Extinct Volcanoes:
  • Show no signs of future activity.
  • Example: Dhinodhar Hill (Gujarat).

Types of Volcanoes (Based on Nature of Eruption)

• Shield Volcanoes:
• • Broad, gentle slopes; low-viscosity basaltic lava.
  • Less explosive unless water is involved.
  • Example: Hawaiian volcanoes.
• Composite (Strato) Volcanoes:
  • Formed by alternating lava and pyroclastic layers.
  • Cooler, more viscous lava ? explosive.
  • Examples: Mount Fuji (Japan), Mayon (Philippines).
• Caldera Volcanoes:
  • Extremely explosive; collapse forms a depression.
• Flood Basalt Provinces:
  • Large-scale lava flows covering vast areas.
• Mid-Ocean Ridge Volcanoes:
  • Found along diverging oceanic plates; frequent eruptions.
  • Example: Mid-Atlantic Ridge.

Global Distribution of Volcanoes

• Circum-Pacific Belt (Pacific Ring of Fire):
  • Most active; surrounds the Pacific Ocean.   
• Mid-World Mountain Belt:
  • Extends from the Mediterranean to the Himalayas.
• African Rift Valley Belt:
  • Features rift volcanoes due to diverging African plates.

PYQ:

Mains

1. Mention the global Occurrence of volcanic eruptions in 2021 and their impact on the regional environment     (2021)
2. Discuss the formation of hot spots and their role in the distribution of volcanoes over the Earth’s surface.   (2015)

Prelims

1. Consider the following:    (2024)

1. Pyroclastic debris
2. Ash and dust
3. Nitrogen compounds
4. Sulphur compounds

How many of the above are products of volcanic eruptions?

1. Only one
2. Only two
3. Only three
4. All four

2. Which of the following phenomena might have influenced the evolution of organisms?   (2011)

1. Continental drift
2. Glaciations
3. Volcanic eruptions

Select the correct answer using the codes given below:

1. 1 only
2. 1 and 2 only
3. 2 and 3 only
4. 1, 2 and 3