Many of Iceland’s glaciers conceal fiery secrets below and such is the case with Myrdalsjokull glacier in South Iceland which covers the highly active and overdue Katla volcano. The caldera of the volcano has a diameter of 10 km (6 mi) and the volcano usually erupts every 40–80 years.

During an eruption, the glacier above the volcanic vent melts and the melted water collects under the ice-cap until it makes its way out from under the edge in a violent flood. These are called "Jokulhlaup". Huge amounts of ice, rocks, silt and sand are carried along by the floodwater. Most of the Myrdalssandur sand plain has been formed by deposits in past floods.

Myrdalsjokull is to the north of Vik i Myrdal and to the east of the smaller ice cap Eyjafjallajokull. The popular Fimmvorduhals hiking trail lies between the two glaciers. The ice cap is the fourth largest on the island covering nearly 600 km2. Its highest peak reaches around 1500 meters and offers adventure opportunities like ice climbing, glacier walking and snowmobiling. Travellers on the glacier have to be extremely careful about crevasses and inexperienced travellers should not go there alone. Weather conditions shift very rapidly and high winds and snowstorms can appear in a flash all year round.