Part of Hall of Planet Earth.
AMNH/R.Mickens
This sample illustrates how pillow basalts grow. First, a pillow structure forms, then increasing magmatic pressure fractures part of the surface. Lava is squeezed through the jagged fracture like toothpaste, forming a striated pillow tube.
Provided by Prof. Charles Langmuir, Lamont-Doherty Earth Observatory, Columbia University, New York, New York