East Pacific Rise pillow basalt main content.

East Pacific Rise pillow basalt

Part of Hall of Planet Earth.

East Pacific Rise Pillow Basalt AMNH/R.Mickens

This sample illustrates the hollow nature of many pillow basalts. The pillow inflates from the magma’s pressure, but when the eruption cases, some magma drains back, creating an interior cavity. The pillow cools and contracts, forming fractures that radiate from the interior.

Loaned by the Scripps Institute of Oceanography