Jointed pillow lava from a basalt flow near the former Copco Lake, California
Detailed Description
Pillow lavas like these form when a lava flow erupts under a significant body of water (including oceans, lakes, and rivers). Lobes of lava crystallize immediately in the water, forming crusts over molten interiors which continue to inflate. New breakouts of lava repeat the process and stack onto each other. These pillow basalts were found near the former Copco Lake in northern California. USGS photo by A. Pivarunas.
Sources/Usage
Public Domain.