Salt Polygons Are Caused by Convection

[MojaveGeek]

There's some great columnar jointing at Devil's Postpile.    Giant's Causeway in Ireland is pretty famous.  Here is some pretty cool columnar jointing in adesite I came across on Mt. Rainier last summer.  Those joints are big - the sections are about a foot and a half to two feet across, and break off into chunks that are scattered around on the ground.  All moss covered - this is on the aptly named Emerald Ridge.