How Do Volcanoes Create Towering Columns in Rock?

The glaciated tops of columns in the Devil's Postpile of California. Photo by Erik Klemetti. Last week, Commander Chris Hadfield (of International Space Station fame) tweeted this image, asking what could have caused such strange columns to form in rocks. I read a lot of the replies to the Commander's question and while many got at the key processes, it seems like there is some confusion about how columns can form in rock. In most cases, it is thanks to magma! Under the right conditions, magma can cool in such a way as to form polygonal shapes that can be straight or bend and twist - we call these phenomena columnar joints. They can be spectacular, created with what looks like the precision of a master sculptor, but really it all boils down to the physics of cooling.