Dettifoss

Where it sits. Dettifoss drops out of the treeless basalt desert of north-east Iceland into the canyon of Jökulsárgljúfur, about thirty kilometres inland from Route 1 and roughly an hour's drive from either Lake Mývatn or the whale-watching harbour of Húsavík. The river is the Jökulsá á Fjöllum, Iceland's second-longest, which begins under the northern margin of the Vatnajökull ice cap and gathers meltwater across a vast, uninhabited interior before it reaches this step in the plateau. The falls are 100 metres wide with a drop of 44 metres, and they carry an average of about 193 cubic metres of water per second — the second-largest discharge of any Icelandic waterfall, behind Urriðafoss, and enough force that Dettifoss is routinely described as the most powerful fall in Europe after the Rhine Falls. The whole site lies inside the northern territory of Vatnajökull National Park.

What the water is doing. The Jökulsá is not clear. It carries so much glacial rock flour that it runs a flat, opaque grey-white, and where it goes over the lip it turns the colour of wet cement rather than the transparent green of a spring-fed river. That sediment load is also the reason the canyon exists: Jökulsárgljúfur was cut, in part very rapidly, by catastrophic glacial outburst floods that repeatedly tore down this valley after subglacial eruptions, stripping columnar basalt away in blocks. Standing at the rim you are looking at a river actively removing its own bed. The spray is heavy and constant, drifts a long way in the wind, and coats the surrounding rock with a film that freezes into black ice from autumn onward. A kilometre upstream, Selfoss spreads across the full width of the canyon in a low horseshoe; downstream, Hafragilsfoss falls into a deeper, redder section of the gorge.

On screen. Dettifoss opens Prometheus (2012). In the film's first sequence, a hooded Engineer stands above a vast waterfall on a primordial, unpopulated Earth, drinks a black liquid, and comes apart at the cellular level as his body falls into the water — the strands of his DNA seeding life in the river below. Ridley Scott's unit shot the location plates here on the western bank, with the hovering craft, the alien figure and the surrounding terrain extended digitally around the real fall. It is an unusually pure piece of location casting: the sequence needed a landscape that carried no trace of any human century, and the grey water, black rock and complete absence of vegetation at Dettifoss delivered that without set dressing. The waterfall also lent its name much earlier to an orchestral work by the Icelandic composer Jón Leifs, whose "Dettifoss" tries to reproduce the sound of the fall in a full orchestra and chorus.

Which bank to choose. The two sides are genuinely different experiences and are not connected by any bridge near the falls; picking the wrong one costs about two hours of driving. The western bank is served by Route 862, paved in 2011, and offers a maintained gravel path, a viewing platform slightly back from the edge, and a pit toilet — the safer, tidier, more accessible side, and the one most tour buses use. The eastern bank is reached by Route 864, an older gravel road that is normally passable only in summer; the payoff is a rougher path that lets you stand almost level with the lip of the fall, close enough to be soaked, with an information panel and toilet maintained by park staff. Photographers generally prefer the east for the sense of scale and the west for the head-on view and reliable footing.

Safety and surface. There are no railings along much of the rim on either side. The rock is smooth, wet and often slick with algae or ice, and the drop is unforgiving. Park rangers reroute paths and close sections when conditions demand it, and those closures are not decorative. Sensible footwear, a waterproof shell and a firm rule about not stepping past the marked edge cover most of the risk; a camera on a strap rather than in a hand covers the rest.

Getting there and timing. Dettifoss sits on the tourist circuit marketed as the Diamond Circle, alongside Ásbyrgi canyon, the lava formations of Hljóðaklettar, Lake Mývatn and Húsavík, and it is comfortably done as a half-day from Reykjahlíð or Húsavík. Flow is highest in June and July when the ice cap is melting hardest, and the falls are correspondingly loudest and mistiest then. Late August and September bring thinner crowds and better light on the canyon walls. In winter the approach roads close or become genuinely serious driving, and the falls, encrusted in ice, are usually reached only on organised super-jeep trips. Whatever the season, fuel and food come from Mývatn or Húsavík — there is nothing at the site itself.