Why in News?
Mount Semeru, one of the most active stratovolcanoes of Indonesia, erupted, spewing hot ash clouds, debris, and tephra. It is part of Indonesia’s 120 active volcanoes, located along the Pacific Ring of Fire.
Description:
About Mount Semeru:
- Location: East Java, Indonesia.
- Type: Stratovolcano (Composite Volcano) → high viscosity, highly explosive.
- Tectonic Setting: Convergent Plate Boundary — Indo-Australian Plate subducting under the Sunda Plate.
Why Volcanoes Erupt:
- Extremely high temperatures inside Earth melt rocks → magma forms.
- Being less dense, magma rises and accumulates in magma chambers.
- Pressure builds → eruptions release lava, gases, ash, and pyroclasts.
Why Some Eruptions Are More Explosive:
Eruptive power depends mainly on the viscosity of magma and gas content.
Low-viscosity magma: Runny / fluid. Gases escape easily → gentle, effusive eruptions. Found in shield volcanoes (Hawaii)
High-viscosity magma:
- Thick, sticky
- Traps gases → pressure buildup → violent, explosive eruptions
- Produces pyroclastic flows, tephra, and large ash clouds
- Seen in stratovolcanoes (like Semeru)
Products of Volcanic Eruptions:
· Solids: Pyroclastic debris, Tephra (ash → lapilli → bombs → blocks).
· Liquids: Lava (magma reaching the surface)
· Gases: Water vapour (H₂O) – largest share, CO₂, Sulphur compounds (SO₂, H₂S), Nitrogen compounds (NO, NO₂), Chlorine compounds.
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