North of the crater Eldborg at Trölladyngja is an oval hyaloclastite mount named Lambafell. At its southern end are active high-temperature steam vents. Along the entire mount is a groove or a ledge which leads to a a narrow and deep open fissure named Lambafellsgjá. The fissure is only a few metres across but about 50 metres deep. It is possible to hick along the entire fissure.
The best route is to descend into it from the south, down a steep and rather loose slope. At the northern end it opens at the same level as the surroundings. In the walls of the fissure are excellent outcrops of subglacially formed basaltic pillows.
This fissure is definitely formed during the Holocene but the pillows are probably older than the last glacial period, being from the previous one or possibly even older.
Haukur Jóhannesson, 2010