Dettifoss is the Icelandic waterfall on the Jökulsá á Fjöllum river often called Europe's most powerful.
The waterfall is about 100 metres wide and drops roughly 44 metres through the rugged landscape of Vatnajökull National Park. Its estimated average flow is about 193 cubic metres per second, although discharge varies with seasonal meltwater and weather. The water carries sediment from the Vatnajökull ice cap, giving the river a striking gray appearance.
Dettifoss lies in northeast Iceland and is part of a chain of major waterfalls on the same river, including Selfoss upstream and Hafragilsfoss downstream. The surrounding canyon was shaped by powerful glacial outburst floods, which helped carve the stark basalt landscape.
The phrase “most powerful in Europe” is a convention based mainly on flow and drop together, not a universally fixed scientific ranking. Dettifoss is nevertheless the standard answer in travel and geographic references. It also appeared in the opening sequence of the 2012 science-fiction film Prometheus.