|lava that has solidified under water, having a characteristic structure comprising a series of close-fitting pillow-shaped masses|
|pillow lava (pĭl'ō) Pronunciation Key
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.