Hraunfossar (Borgarfjörður, western Iceland) is a series of waterfalls formed by rivulets streaming over a distance of about 900 metres out of the Hallmundarhraun, a lava field which flowed from an eruption of one of the volcanoes lying under the glacier Langjökull. The waterfalls pour into the Hvítá river from ledges of less porous rock in the lava.