In Iceland's Vatnajökull National Park, the waters of the mighty Dettifoss are ever-crashing.
The waters of the falls comes from the nearby Vatnajökull glacier, whose sediment-rich runoff colors the water a greyish white. The superlative of "most powerful" comes from its water flow coupled with its height. The falls, fed by the wide River Jökulsá, fall a total of about 150 feet, causing a massive, crashing spray.
This can make getting close to the falls difficult. The pathways surrounding are frequently slippery, and authorities warn visitors to maintain a safe distance due to frequent accidents on the paths. This doesn't stop visitors though. Dettifoss is the Niagara of Iceland (although more powerful) and draws thousands of sightseers.