Pumice is similar to the liquid foam generated when a bottle of pressurized soda is opened – the opening depressurizes the soda and enables dissolved carbon dioxide gas to escape or erupt through the opening. During an explosive eruption, volcanic gases dissolved in the liquid portion of magma also expand rapidly to create a foam or froth; in the case of pumice, the liquid part of the froth quickly solidifies to glass around the glass bubbles.
Related category GEOLOGY AND PLANETARY SCIENCE
Source: U.S. Geological Survey
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