There has been a wave of articles over the last few weeks out on the geoblogosphere on columnar jointing in lavas – with many, many great images of columns seen around the world. I thought I’d jump in the fray, but as usual, basalt seems to have gotten the center stage when it comes to looking at columnar jointing in volcanic deposits – but columns aren’t just for basalt!
First a bit of a review:
Columnar jointing is a product of differential cooling in a volcanic deposit. Remember, they are hot and when they are deposited as lava flows or tephra deposits, they encounter the Earth’s surface that, comparatively speaking, is cold. The tops and bottoms of the deposits are especially exposed to the cold surface of the Earth. When most lavas or tephra cool, they tend to contract. When they contract, they respond to the change in volume by ...
