Bláhnúkur is the mountain closest to Landmannalaugar, 943 m high and of rhyolite. “It is thought that the mountain formed from eruptions under the glacier. It is made up of a lot of black columnar basalt with green and gray obsidian.” Bláhnúkur is the most popular mountain to climb in Landmannalaugar. The side is steep but a well-trodden and clear path ascends to the top where there is an azimuth scale view finder. The glacier during the ice age had been about 400 m thick when Bláhnúkur was built up. Instead of becoming a table mountain with a flat top, the lava that poured out at the end of the ice age ran down into ice tunnels at the top of the volcano.