How are pillow lavas different from sheet flows?

In the context of oceanic crust geology, pillow lavas and sheet flows represent two distinct forms of basaltic lava eruptions that occur at spreading centers. They differ primarily in their physical structure, formation process, and coverage:1

• Pillow Lavas: These are characterized by ovoid, pillow-shaped masses typically about 1 meter in cross-section and several meters long. They form when highly fluid lava is rapidly chilled upon contact with water, creating budlike projections with tough, elastic crusts that enlarge as more lava is fed into them. These structures often accumulate to form small hills tens of meters high.123
• Sheet Flows: These appear as thin, wrinkled layers resembling bed sheets, typically measuring only about 10 cm in thickness. Unlike pillow lavas, sheet flows cover broader areas of the seafloor and are believed to be erupted at higher temperatures.1

While both are fundamental components of the topmost layer of the oceanic crust, their distinct morphologies reflect different eruption dynamics and cooling conditions on the seafloor.1