Why do some volcanic eruptions produce pumice that can float?
Quick Answer
Pumice forms when gas-rich lava cools so quickly that it traps bubbles inside. Those air-filled pores can make the rock less dense than water.
The Full Story
Pumice is a volcanic rock with so many trapped gas bubbles that its density can be very low. During explosive eruptions, frothy lava can cool rapidly before the bubbles escape, leaving a lightweight, vesicular rock. If the pores are plentiful enough, a fresh piece may float on water until it gradually becomes waterlogged. Pumice rafts have been observed after eruptions such as the 2012 Havre submarine eruption near New Zealand. This makes pumice one of the most unusual rocks in nature.
Key Facts
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