This is Hraunfossar, a very unusual waterfall. I have never seen anything like it. It is about one kilometer long and it is coming out from the middle of the cliffs. The water is flowing between two lava flows and it coming from Langjökull, a nearby glacier.

On the subject of wide angle lenses. I have a 16-35 zoom, but that is not nearly wide enough for this subject, so I took several panoramic scans (by hand) in the hope of getting something useful. Well, it came out OK, but there is so much detail you can't see in this image which is downsized to 800 pixels for pbase. The original is 11,400x3400 pixels (from four exposures stitched together.)