Jökulhlaups are massive, volcanically induced flash floods that regularly burst out from under Vatnajökull, carrying untold tonnes of debris and water before them. One cause of these floods is Grímsvötn, a smouldering volcano buried 400m under the ice cap inland from Skeiðarársandur. The volcano’s last major eruption was in 2011, but the biggest event of recent times occurred in October 1996 after a 6km-long vent opened up under the ice. For ten days the volcano blew steam, ash and smoke 6km into the sky; then, at 8am on November 5, the melted ice suddenly drained out underneath Skeiðarárjökull, sending three billion litres of water spewing across Skeiðarársandur in a 5m-high wave, sweeping away 7km of road and – despite design precautions – demolishing several bridges. Fourteen hours later the flood rate was peaking at 45,000 cubic metres per second, and when the waters subsided a day later, the sandur was dotted with house-sized chunks of ice ripped off the front of Skeiðarárjökull. Aside from the barren scenery, there’s very little evidence for any of this today – the ice has long gone and the bridges are repaired – though look for the twisted remains of Skeiðarárbrú, one of the Ringroad bridges destroyed by the event, which are on display by the roadside west of Skaftafell.