Cracking up

Site: Devils Postpile

Where: Devils Postpile National Monument, Mammoth Lakes, Calif.

Wild forces: “Devils Postpile was created by a lava flow 100,000 years ago. You need thick lava to get this kind of formation. This was originally up to 400 meters [1,333 feet] thick. The spectacular feature of the Postpile is its columnar joints, the big columns that extend the distance of the pile. They are basically a cooling feature. The lava cools from top to bottom. As it goes from liquid lava to solid basalt, it shrinks, causing the fractures and the polygonal shapes. It’s a geometrically easy thing for nature to do. Another process that’s occurring is frost action. Water gets into the cracks and, when it freezes, it gets bigger and separates the fractures more over time until gravity takes over. The exposure we see today is due to the last Ice Age, which scraped off one side, so we can look into the flow.”

-- Craig Scott

Volcanologist,

Cal State Northridge