Absolutely Stunning Illusion of an Underwater Waterfall in Mauritius

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On the southwestern point of Mauritius is a crazy-looking phenomenon.  When viewed from the air (either in real life or in Google Earth) it appears to be an underwater waterfall!

Mauritius is an island just off the coast of Africa, close to Madagascar and Mozambique. With its stunning beaches, jewel-toned lagoons and spot of multi-colored earth, we rightly declared it one of the most beautiful islands in the Indian Ocean. The island is home to some of the rarest plant and animal specimens in the world.

But now we know that Mauritius has something even more rare — an optical illusion that makes it look like there’s really an underwater waterfall WITHIN THE OCEAN!


Okay, now that you’ve seen the illusion, what’s really going on here? Obviously, water is water, and even though we can do some very clever things by manipulating fluid flow, even very cold water wouldn’t sink like this picture suggests.

Instead, there’s some really amazing and fun geology behind it!

Image credit: Ker & Downey diving, via http://kerdowney.com/.

Like many ocean islands, there are fabulous reefs off the coast of Mauritius, living ecosystems that are fascinating in their own right. But unlike many of them, Mauritius, and indeed the entire land-and-seascape around it, is very, very new on geological timescales.

Image credit: NOAA's National Geophysical Data Center, via http://www.ngdc.noaa.gov/mgg/image/2minrelief.html.

Mauritius is located at the southern edge of the Mascarene Plateau, the prominent (mostly underwater) shelf located at the 11 o’ clock position in the image above. There are a few islandsthere, including Mauritius, which is visible (along with Réunion Island) from the International Space Station in the image below!

Image credit: NASA / International Space Station, via Astronaut Karen Nyberg (@AstroKarenN).

This oceanic shelf didn’t exist a few million years ago; sea-floor spreading created this plateau fairly recently. And there’s a huge drop-off when you leave the plateau! While most of the ocean waters around these islands is at depths ranging from 8-to-150 meters, there’s a huge plunge off that shelf into the ocean, where the depth drops to many thousands of meters!

Image credit: © 1984 by Tasa Graphic Arts, Inc.

What you’re witnessing, that looks like an underwater waterfall, is actually sand from the shores of Mauritius being driven via ocean currents off of that high, coastal shelf, and down into the darker ocean depths off the southern tip of the island.

Image credit: © 2008 Seafarer Cruising & Sailing Holidays.

It’s a beautiful sight that I’d love to take in with my own eyes, someday, but what’s actually going on is in many ways far more beautiful than a (physically impossible) waterfall under the ocean. It’s the natural world simply doing what it does, and we’re fortunate enough to get to not only enjoy it, but to understand it!