pillowlava

Pillowlava, commonly written as pillow lava, is a form of igneous rock produced when molten lava erupts underwater. The rapid cooling by seawater forms rounded, pillow-like masses that are usually bounded by a thin, glassy rind. The interior remains hotter and may be vesicular, yielding a contrast between a brittle exterior and a more plastic interior. Pillows often occur in clustered stacks as successive lava bursts accumulate on the seafloor, and the spaces between individual pillows may be filled by fragmented glass and crystals, a texture known as hyaloclastite.

Composition and texture: Pillows are typically basaltic or andesitic in composition, reflecting their oceanic crustal setting. The characteristic pillow shape and glassy rind are diagnostic features; the interior can be vesicular from gas bubbles. Pillow lavas form at mid-ocean ridges, volcanic islands, seamounts, and other submarine eruptive settings; they can also develop when eruptions interact with ice in subglacial environments, or when lava flows enter lakes or seawater.

Geological significance and distribution: Pillow lavas are a hallmark of submarine volcanism and are widespread on the ocean floor, especially at mid-ocean ridges and submarine volcanoes. They can also be found in ophiolites that expose ancient oceanic crust. The thin glassy rind and vesicular interior record rapid cooling and volatile loss during eruption, while the interiors preserve evidence of magma composition and crystallization. As a result, pillow lavas help scientists interpret eruption conditions, magma supply, and the creation of the oceanic crust.