A busy day again today. Started at Dettifoss waterfall on the Jokulsa River, claimed to be the most powerful in Europe. A short way to the north, at the recommendation of our driver, we visited Hljodakletter vent along an extended rift parallel to the river. There we observed spectacular convoluted columnar jointing speculating on the origin of what we saw. At the same location we observed landforms that result from massive glacial outburst floods (jökulhlaup). We then examined the only area on Iceland where sedimentary rocks outcrop. The day ened with a warm soak in the Myvatn Nature Baths.