Tungnaáröræfi is the name of an area between the river Tungnaá and the glacier Tungnafellsjökull. It was forged in fire, and the most extensive lava flows that have occurred in modern times originated there. Among them is the great Þjórsá lava flow ("Þjórsárhraun hið mikla"), which took place about 9000 years ago. The most likely area where it flowed onto the surface is in or by the pass Heljargjá. It is a great fault trough that extends north-east from Landmannalaugar to Vatnajökull in the direction of the volcano Hamarinn. The best view of the pass is from a path that lies to the north-east from the explosion crater called Máni. This area has many old lava formations and craters.