Weekend Diversion: An Underwater Waterfall?

Note: This post has been updated and improved as of 2014 here, at the new Starts With A Bang blog. What follows, below, is the original version that was first published here.

“I love the sounds and the power of pounding water, whether it is the waves or a waterfall.” -Mike May

The world’s oceans have always been special to me, and bodies of water in general. The air smells different, the wind blows cool, and you’re reminded of the power of the salty seas every time you step in. It’s one of the reasons that the old sea shanties have always fascinated me. This week, have a listen to an updated take on that genre, as The Real McKenzies sing a cover of the more recent classic,

Barrett’s Privateers.

But there’s one ocean sight I had never seen before until earlier this week: an underwater waterfall!

Image credit: St. Regis Mauritius Resort, Mauritius.

Image credit: St. Regis Mauritius Resort, Mauritius.

Yes, off the island of Mauritius in the Indian Ocean, for all of its beauty, has what appears to be one of the most unexpected feasts for human eyes. It’s especially prominent from the air.

Image credit: Photographer Unknown (via KULfoto.com), via http://twistedsifter.com/.

Image credit: Michael Friedel of http://www.foto-friedel.com/www_de//library.lib/img/MAURITIUS/INSEL+MAURITIUS/MORNE+BRABANT/.

Even Google Maps gets in on the action!

Image credit: Satellite Photograph by DigitalGlobe via Google Maps.

Image credit: Satellite Photograph by DigitalGlobe via Google Maps.

Okay, now that you’ve seen the illusion (brought to my attention courtesy of Twisted Sifter), 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/.

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.

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 islands there, 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).

Image credit: NASA / International Space Station, via 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.

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.

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. And that’s your diversion for this weekend!

Comments

  1. #1 Michael
    September 22, 2013

    Technically, an underwater “waterfall” is possible if the density of the water flowing over a drop is sufficiently different from the surrounding ocean with minimal mixing. I’ve heard the flow of hypersaline water off the Antarctic continental shelf in places referred to as an underwater waterfall.

  2. #2 Mark McAndrew
    September 22, 2013

    Underwater freezing mini-waterfalls, aka ‘brinicles of death’, filmed by the BBC: http://www.bbc.co.uk/nature/15835017

  3. #3 MandoZink
    Louisville, KY
    September 22, 2013

    The “sandfall” was interesting, but The Real McKenzies’ version of Barrett’s Privateers was a true delight. I hadn’t heard that shanty before. I was more surprised when I looked up the band and found there was a musical genre called Celtic Punk. I immediately cranked it up the song, to the puzzlement of my wife. It reminded me of driving home one day in a rare depressed mood when Tom Waits’ pirate song “Singapore” came on the radio and cheered me right up.

    That NASA Space Station image also caught the glow of Pleiades – The Seven Sisters. I’m surprised that info tidbit wasn’t mentioned. After purchasing my only pair of good binoculars in the early 90′s (Nikon 10×50), I spent nearly every night for months lying on my driveway (with pillows) and scanning the stars, with the assistance of Skyglobe. I remember seeing Pleiades on my first night.

  4. #4 Robin Kirby
    Ontario, Canada
    September 23, 2013

    Thoroughly enjoyed this blog. I find most of your blogs to be very interesting and stimulating. I too was delighted that you had the reference to Barrett’s Privateers, a wonderful ditty written and first performed by the great Stan Rogers who did several other “sea shanties”. I find Stan’s version to be more pleasing but then that is the one I’m accustomed to. Worth a listen as are most of his other works.

  5. #5 Jan Vones
    NYC
    September 24, 2013

    Why haven’t you won the Pulitzer yet, Ethan?

    Yet another incredible blog entry!

  6. #6 zxx
    September 25, 2013

    ? If the sand is flowing the water is also, no?

  7. #7 Artor
    September 25, 2013

    I don’t expect that there’s an overwhelming current there, but there must be some steady flow to shape the sand that way, right? I suspect evaporation in the shallower waters around the island increases the salinity of the water, and therefore the density. It would be interesting if there were enough flow to install a turbine and supply all the island’s power needs, but I suspect it is too slow for that.

  8. [...] Weekend Diversion: An Underwater Waterfall? [...]

  9. #9 Sovereignty
    https://vimeo.com/19691370
    September 25, 2013

    yes the beauty of our oceans is amazing…. the potential power that can be developed from these kinetic energies is equally impressive. To see what a sustainable tidal power bridge project looks like to: https://vimeo.com/19691370

  10. [...] Weekend Diversion: An Underwater Waterfall? — This is pretty wild. (Via threeoutside.) [...]

  11. #11 Jon H
    September 28, 2013

    “? If the sand is flowing the water is also, no?”

    The water could be flowing mostly horizontally, not downward. The sand’s weight would provide its downward motion.

  12. […] We don’t really get how it works, but if you’re super curious check out Ethan Segal’s blog: Starts With a Bang. […]

  13. #13 Robert Wicklund
    Virginia
    October 13, 2013

    Undersea waterfalls are not rare. In my new book “Eyes In The Sea” I describe two undersea waterfall events in the Bahamas.
    One off the coast of Andros Island when we were close to the deep dropoff in a small research submarine during the winter and were caught in a waterfall of cold high density water flowing over the dropoff during an outgoing tide. A few years later I experienced frequent undersea waterfalls off the coast of the Exumas during the summer. In this case, it was an outgoing tide of warm high salinity/high density water from the vast shallow Great Bahamian Bank. The Bank water was obviously dense from evaporation. We could and often rode the current down to about 140 feet depth with SCUBA where the density found its own level due to deeper, colder water.

  14. #14 magali d
    texas
    October 27, 2013

    Wow learn something new today :)

  15. #15 jemma
    melbourne sunshine
    November 20, 2013

    awesome pics (:

  16. […] An Underwater Waterfall of Mauritius ? Read the story here. […]

  17. #17 Wandercy
    Belo Horizonte
    November 27, 2013

    God blues.

  18. #18 Hugo
    December 10, 2013

    As mentioned in previous comments, it is possible
    http://www.oceanfootage.com/stockfootage/Underwater_Waterfall/owner%3Dnwu

  19. […]  Photo via ScienceBlogs […]

  20. […] Fonti: Google Earth Blog | Sience Blog […]

  21. […] Photo Source: Science Blogs […]

  22. […] Pour des informations plus approfondies sur les processus géologiques à l’origine de cette illusion fascinante, lisez l’explication détaillée sur le site ScienceBlog.com. […]

  23. #24 abby normal
    sunny san diego
    May 16, 2014

    this is simply magnificent i love how nature never ceases to amaze me with its beauty and power.

  24. #25 Pradeep gokhool
    Mauritius
    May 28, 2014

    Your photo are very beautiful especially the under sea waterfall I really like it

  25. #26 Zain Patel
    Mauritius
    June 7, 2014

    I live on that island! :’)

  26. #27 anna
    August 18, 2014

    would you get sucked in because what i was thinking if in a normal waterfall there s presure and its trying to push you down would that under waterfall pull you in to the in side or is there no presure so it can pull you in.