Ask me to envision the tallest waterfall in the world, and I see water cascading off a cliff, transforming into mist and crashing down with a thunderous sound. That image accurately depicts Angel Falls in Venezuela, but it completely misses the mark for the Denmark Strait.
Situated between Greenland and Iceland, frigid water from the Nordic Seas flows over a submerged ridge and sinks beneath the warmer waters of the Atlantic. The National Oceanic and Atmospheric Administration identifies this phenomenon as the world’s largest waterfall, measuring approximately 11,500 feet, equivalent to 3.51 kilometers.
This height exceeds the typical measurement attributed to Angel Falls by more than three and a half times. However, this comparison requires a crucial distinction: the cataract in the Denmark Strait is an oceanographic overflow, not a river plummeting through the air. Therefore, Angel Falls retains its status as the traditional record holder for waterfalls on dry land.
How water can descend through water
The process begins with density. Water becomes denser as it cools, and the salt content also influences how much mass a certain volume holds. In the northern reaches of the Atlantic, extremely cold water flows toward the Denmark Strait from the Nordic Seas. South of the underwater ridge, it encounters warmer water from the Irminger Sea.
The colder, denser water slips below the lighter water and spills across a sill situated about 600 meters beneath the surface. Gravity subsequently draws it down the continental slope of Greenland.
No gap needs to be created in the ocean. Two water masses can exist in different layers for a similar reason that oil floats atop water in a glass. Here, however, both layers consist of water, with temperature and salinity generating the density difference.
The term “fall” can also be misleading. This is not a vacant shaft through which water falls freely. Instead, it is a dense, bottom-hugging current flowing downslope beneath the lighter water above.
What the 11,500-foot measurement signifies
NOAA’s infographic attributes a height of roughly 11,500 feet to this cataract. On the same page, the agency describes a series of cataracts starting about 2,000 feet beneath the surface and descending toward depths near 10,000 feet to the south of the strait. These descriptions summarize a vast, uneven underwater landscape rather than measurements of a singular clean vertical drop.
The overflow spans a wide current, traces the seafloor, and mixes with surrounding water as it advances. Consequently, oceanographers employ terms like “overflow,” “plume,” and “cataract.” The popular term “underwater waterfall” is convenient, but it simplifies a complex three-dimensional flow into a more familiar concept.
For the terrestrial record, Guinness World Records acknowledges Angel Falls, also referred to as Kerepakupai Merú, at a total height of 3,212 feet. Its longest uninterrupted drop measures 2,648 feet. Guinness also notes ongoing discussions on how the total should be computed.
So is the Denmark Strait cataract genuinely the highest waterfall? Yes, in both oceanographic and popular-science contexts. According to the standard geographic definition of a waterfall exposed to air, Angel Falls maintains its standing. The apparent contradiction dissolves once the categories are clarified.
A flow quantified in sverdrups
The concealed cataract is not just tall. NOAA estimates its downward flow at over 123 million cubic feet or 3.5 million cubic meters every second. Oceanographers express this flow as approximately 3.5 sverdrups, where one sverdrup equals one million cubic meters per second.
A 2017 study published in the Journal of Geophysical Research: Oceans estimated the mean transport of Denmark Strait Overflow Water at 3.2 sverdrups from 1996 to 2016, with an uncertainty of about 0.5 sverdrups. A subsequent ship-based analysis reported an average total overflow transport of around 3.54 sverdrups.
These values are close, but their variances are significant. This is not a conduit with a stable output. The flow fluctuates, instruments capture only a portion, and researchers must determine which combinations of density and direction qualify as overflow water. Estimates also evolve as measurement techniques advance.
Even the lower figure is hard to visualize. At 3.2 million cubic meters per second, the cataract would displace a volume equivalent to an Olympic swimming pool numerous times before one could finish this sentence.
How scientists perceive a waterfall concealed in darkness
From a ship, there is no clear division marking the cataract below. The sea does not drop off over an edge. NOAA asserts that its turbulence remains undetectable without specialized instruments.
Researchers secure moorings to the seabed and equip them with current meters, temperature and salinity sensors, as well as Acoustic Doppler Current Profilers. The profilers deduce water velocity from the Doppler shift in reflected sound. As explained by the Woods Hole Oceanographic Institution, fixed moorings log the current as it flows, while instruments set at various depths record changes through the water column.
Extensive records are crucial as the overflow can fluctuate over both days and years.