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pillow lava

noun Geology.
  1. lava in the form of an agglomeration of rounded, pillow-shaped masses, the result of subaqueous or subglacial volcanic eruption.
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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
  1. lava that has solidified under water, having a characteristic structure comprising a series of close-fitting pillow-shaped masses
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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

[pĭlō]
  1. 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.
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The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.