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.

noun

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

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.