Dettifoss

The river starts under a huge sheet of ice.

Long ago, giant floods burst out from under the ice. The rushing water ripped away rock and made a deep canyon. Now the river tumbles into it.

The river Jökulsá á Fjöllum starts from beneath the Vatnajökull ice cap and flows to the sea in Öxarfjörður Bay. Where the land drops at the edge of the highlands, the river plunges into a canyon in a series of waterfalls.

The national park says huge floods from under the ice are believed to have carved the canyon, most recently about 2,000 years ago. These glacial outburst floods, called jökulhlaups in Icelandic, happen when water stored in lakes under or beside a glacier suddenly bursts out. The floods swept away broken-up lava rock and left the canyon behind.

Jökulsá á Fjöllum emerges from beneath Vatnajökull and flows to the sea in Öxarfjörður Bay; its drainage basin is the largest in Iceland. The canyon lies on the Northern Volcanic Zone, crossed by the Krafla, Fremrinámar and Askja fissure swarms, at least two of which erupted after the Ice Age.

The park describes massive glacial outburst floods from under Vatnajökull, most recently around 2,000 years ago, as among the greatest on Earth since the Ice Age; aided by weathering, they carried off the basaltic lava and carved Jökulsárgljúfur. The Icelandic Meteorological Office defines jökulhlaups as floods released from ice-dammed marginal or subglacial lakes, which subglacial eruptions can also cause, and UNESCO says recurring jökulhlaups have led to the park's rapidly evolving canyons.

Dettifoss is moving, very slowly.

The water wears away the rock edge, bit by bit. So the waterfall creeps back up the river, a little every year.

Waterfalls do not stay in one place forever. Bit by bit, the water of Dettifoss breaks away the edge it falls over, so the waterfall moves further south, up the river, by about half a meter a year.

Just north of the falls, the canyon is at its narrowest, about 100 meters wide, for a stretch 500 meters long. Dettifoss made that narrow stretch itself, wearing it out day after day since the great floods ended. The park explains that waterfalls in Iceland change slowly over time and can even disappear completely, a natural part of a waterfall's life.

The park describes Iceland as young in a geological sense, with many waterfalls that have not yet worn down the ledges in their path. Dettifoss is retreating southward, upstream, about half a meter a year as it erodes the lip of the fall.

The narrowest part of Jökulsárgljúfur, about 100 m wide and 500 m long, lies just north of Dettifoss; the park attributes it to the waterfall's daily erosion since the end of the outburst floods, while the larger gorges were shaped by those floods and the glacial river over recent millennia. Plans to harness the river's power were dropped because the lava is too porous to hold water in a reservoir.

Near Dettifoss the land is bare and rocky.

Further down the canyon there are wet meadows and forests. Many kinds of birds live there.

The land around Dettifoss is bare: the park describes a barren but magnificent landscape of gravel plains. As you follow the canyon north toward Ásbyrgi, the land changes. In the middle there are fields of a soil called loess, and wetlands, and in the north there are forests.

Because there are so many different habitats, the park says the birdlife of Jökulsárgljúfur is very diverse. Hikers on the long canyon trail pass deep gorges, quiet ponds, clear springs and forests.

Jökulsárgljúfur runs from Dettifoss in the south to Ásbyrgi in the north. The park describes its habitats in bands: gravelly plains furthest south, loess soil fields and wetlands in the middle, and forest in the north, which together support very diverse birdlife.

The 32 km Canyon Trail from Ásbyrgi to Dettifoss crosses this whole range, from the luxuriant Ásbyrgi to the barren surroundings of Dettifoss, past gorges, ponds, springs and gravel plains. The park notes that the river's drainage basin remains almost untouched by human activity, which makes it a place to study how glacial rivers shape land and life.

People walk on paths to see the falls.

The rocks can be wet and slippery. Stay on the path, hold a grown-up's hand, and keep back from the edge.

Dettifoss can be reached from both the west and the east side of the river, and both sides have marked paths. On the west side, a paved road leads to a car park, and the viewpoint is about a kilometer's walk away. The road on the east side is gravel and closes when snow begins to fall in autumn.

The park asks visitors to take care on whichever route they choose. Conditions can change quickly: in June 2024 the west side was closed for a while after a storm left a lot of snow that melted fast, with slush on the paths and hollow spaces under the snow.

Per Vatnajökull National Park: Dettifoss is reached on the west by paved Road 862 between Mývatnsöræfi and Kelduhverfi, which has limited winter service, and on the east by gravel Road 864, which closes when snow begins to fall in autumn and reopens in spring once the mud has dried. Both sides have marked trails, and the viewpoint is about 1 km from the western car park.

The park urges care on either route and advises checking conditions before visiting, since they can change rapidly outside summer. In June 2024 it temporarily closed the west side after storm snow melted quickly, leaving slush on the footpaths and hollow cavities under the snow.