pillow lava

noun Geology.

lava in the form of an agglomeration of rounded, pillow-shaped masses, the result of subaqueous or subglacial volcanic eruption.

Origin of pillow lava

First recorded in 1900–05

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

British Dictionary definitions for pillow lava

pillow lava

noun

lava that has solidified under water, having a characteristic structure comprising a series of close-fitting pillow-shaped masses

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

pillow lava in Science

pillow lava

[pĭl′ō]

Lava that forms from an underwater eruption and is characterized by pillow-shaped masses. Pillow lava forms when hot lava is suddenly exposed to cold water, forming a sacklike membrane that is filled with additional cooling and solidifying lava. The outer membrane is usually finer grained than the inner lava.