The rock wall in the background is either the edge of the Eurasian or the North American tectonic plate. I don't remember which direction I was looking. The companion plate is right up next to it, and there is a walking path between the two. These tectonic plates slice right through Iceland as can be seen in this map: https://www.thoughtco.com/map-of-tectonic-plates-and-their-boundaries-1441098
