Which mechanism amplifies volcanic explosivity when magma ascending through a subduction zone encounters groundwater near the surface?

💡 Explanation

When magma encounters groundwater, steam flashing causes rapid vaporization because heat transfer flash-boils the water, creating a rapidly expanding vapor that fragments the surrounding rock and magma, resulting in explosive eruption. Therefore the intensity increases, rather than purely decompression melting, lithostatic pressures, or viscosity, effects which would produce more effusive eruptions.

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