Three glaciers and a river-built valley
Official South Iceland descriptions place Thórsmörk between Mýrdalsjökull to the east, Krossá to the south, and the rivers Markarfljót and Þröngá to the north. That geography explains the mood you feel on site: cliffs, ravines, scrubby birch growth, and sudden pockets of shelter instead of one open plateau. The valley reads dramatic, but it also feels unexpectedly intimate.
1918: reserve status after Katla
A key turning point came after the 1918 eruption of Katla, when Thórsmörk was designated a natural mountain reserve. That protection helps explain why the area is remembered not only for big scenery, but also for unusual rock forms, fragile vegetation, and the sense that this valley is something to look after, not rush through.
2010 changed the wider valley story
The first 2010 eruption phase near Fimmvörðuháls began on 21 March 2010, and the broader Eyjafjallajökull sequence pushed Thórsmörk back into global travel attention. Even years later, names around you, Gígjökull, Magni, Móði, and the raw volcanic context, remain part of the landscape memory you are walking through.
Why the base areas matter
Húsadalur, Langidalur, and Básar are not interchangeable labels. They shape how the valley feels. Húsadalur is the softer service base, Langidalur carries strong hut-and-trail energy, and Básar sits closer to the serious hiking logic around Fimmvörðuháls. Knowing your base changes the whole rhythm of the day.