Fjallabak mountains, Iceland. Aerial photograph of moutains in the Fjallabak region of southern Iceland. The Jokulgil gorge cuts through the mountains (top left to bottom right) and a stream runs through the gorge. The mountains are formed from prehistoric volcanoes. During the last ice age, glacial erosion carved out the gorge. Sediment at the bottom of the gorge mixes with water from the stream to create quicksand.