Pillow lava refers to a type of submarine lava flow morphology. As lava is extruded underwater it cools quickly and forms lobes. These lobes expand and branch out as fresh lava enters the system and breaks through the cooled crust.
Pillows are interesting because their size and shape tell us something about the environment in which they formed. Lava morphology is determined by a competition between flow (how quickly the lava spreads out) and cooling rate (how quickly the lava solidifies). Flow rate is thought to be the main control on morphology.
I did a small experimental project using PEG wax, where I varied water temperature, flow rate and 'lava' viscosity in order to recreate a variety of submarine lava flow morphologies in a tank of cold water.Simulating submarine lava flow emplacement in the lab by extruding PEG wax with a peristaltic pump. The temperature of PEG controls its viscosity.