Why do volcanoes erupt?
Context
This article explains how magma forms beneath the Earth’s surface, how volcanic eruptions occur, and discusses recent findings about Bolivia’s dormant Uturuncu volcano.
Formation of Magma: High temperature and pressure deep within the Earth melt parts of the mantle and crust to form magma, a molten rock.
- Magma is less dense than surrounding solid rock, so it rises upward and collects in subterranean reservoirs.
Gas Pressure and Magma Movement
- Magma contains volatile compounds like water vapour, CO₂, SO₂, which remain dissolved under high pressure.
- As magma ascends, the pressure drops, allowing gases to form bubbles — similar to a fizzy drink when opened.
- These bubbles increase internal pressure, contributing to the explosive nature of volcanic eruptions. Eruption Mechanism
- Eruptions often occur at tectonic plate boundaries or over mantle plumes where crustal fractures or faults
- Magma and gas surge through weak zones, and the rapid drop in pressure accelerates gas expansion, causing an eruption of lava, ash, and gases.
- If magma movement is suddenly blocked, the resulting reverberations create low-frequency seismic waves, an indicator of volcanic activity.
Types of Volcanoes
- A volcano is considered active if it is erupting now or is expected to erupt
- “Zombie volcanoes”, such as Uturuncu in Bolivia, have not erupted in a long time (2.5 lakh years in this case) but still emit gases and trigger earthquakes, indicating ongoing subterranean activity.
Recent Scientific Findings
- Scientists have used new techniques to detect that gases are accumulating in the magma chambers beneath Uturuncu’s crater.
- However, data suggest that an eruption is unlikely in the near future, though the volcano remains under observation due to potential risks.
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