"pillow lava." YourDictionary, n.d. Web. 06 December 2018. <https://www.yourdictionary.com/pillow-lava>.
pillow lava. (n.d.). Retrieved December 06th, 2018, from https://www.yourdictionary.com/pillow-lava
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.