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Mud volcanoes are non-igneous “sedimentary volcanoes” formed in young oil-field regions, where methane and hydrocarbons under compactional stress force mud and gases to the surface.

A recent eruption of a mud volcano in Diglipur, Andaman Islands, has drawn attention to this rare geological phenomenon. Mud volcanoes differ fundamentally from magmatic volcanoes as they do not involve molten lava but are driven by sedimentary and hydrocarbon processes.

What is a Mud Volcano?

Mud volcanoes, also called sedimentary volcanoes or gas-oil volcanoes are surface expressions of subsurface pressure systems associated with hydrocarbon-rich sedimentary basins.

Key Characteristics

• Non-igneous in origin (no magma involved).
• Occur mainly in young oil-field regions with soft, unconsolidated sediments.
• Erupt mud, water, methane and other gases instead of lava.
• Often form cone-shaped structures.
• Can release flames if methane ignites.
• May emit hot mud and steam due to deep compactional heat.

Though different in origin, their eruptive behaviour can resemble magmatic volcanoes in intensity.

Formation Mechanism

Mud volcanoes develop due to:

• Compactional Stress
  • Deep sediment layers experience pressure over time.
  • Methane and hydrocarbons accumulate in porous formations.
• Gas Build-up and Upward Migration
  • Trapped gases mix with mud and water.
  • The pressurized mixture forces its way upward through fractures.
• Surface Eruption
  • Mud and gases erupt, forming a cone.
  • Repeated eruptions may enlarge the structure.

Due to the depth of origin, expelled mud is sometimes warm and accompanied by steam clouds.

Global Distribution

• Around 1,000 mud volcanoes have been identified globally on land and in shallow waters.
• Prominent concentrations occur in:
  • Azerbaijan (Caspian region)
  • Indonesia
  • Mediterranean region
• Many also occur on the ocean floor, forming islands, banks, and altering coastal geomorphology.

Mud Volcanoes in India

In India, mud volcanoes are confined to the Andaman and Nicobar Islands.

Major Locations

• Baratang Island – Known site of India’s mud volcano.
• Diglipur – Recent eruption reported after several years of dormancy.

These eruptions are linked to the tectonically active Andaman subduction zone, where sediment compression and hydrocarbon accumulation occur.

Geological Significance

• Indicator of hydrocarbon-rich sedimentary basins.
• Provide insights into subsurface gas migration and petroleum systems.
• Important for understanding:
  • Methane emissions (climate relevance)
  • Coastal geomorphology changes
  • Seismic and tectonic processes in subduction zones

Differences: Mud Volcano vs Magmatic Volcano