Current events: Water that moves

Take a look at the photo on this page, and tell me: If you had to give it a one-word label, what would that be?

Non-divers might think something like 'pastels.' To a diver that photo screams current! That's 'current' as in moving water. [You can click on the photo for a larger view.]

Pastel soft corals in the Red SeaNot only are the soft corals in the photo bending like wheat in a windswept field, but all the little fishies are facing in the same direction. That's what little fishies do in a current -- they point their little noses into the current and wiggle their tails for all they are worth, just to stay in place.

Good divers recognize and understand currents in the ocean, and know how to deal with them. The two most common factors relating to the kinds of currents that divers are likely to encounter are wind and tides.

Currents relatively close to the surface can be caused by wind blowing across the water. When wind blows across the surface it pushes a certain amount of water ahead of it. The stronger the wind, and the more open and unsheltered the surface, the stronger the surface current. Most wind-driven surface currents in coastal areas are only a meter or so deep -- a good thing to know. For instance, if there's a wind-driven surface current, a diver will probably have an easier time swimming back to a boat or a shoreline exit point by swimming a couple of meters beneath the surface instead of on the surface.

Some currents are caused by changing tides. The water mass flows toward shore during an incoming tide (called flood flow), and sucks back out to sea during an outgoing tide (called ebb flow).

Currents can be enhanced by underwater topography and the shape of a coastline. Think of the way water in a river or creek flows around rocks and other obstructions. The same thing happens underwater. If there is some relatively large feature in the path of the water mass during a tidal shift, for example, the water will flow around it and the current usually will be stronger and more turbulent closest to the obstruction. The same thing happens where there is a bottleneck -- a place where the flow of water gets squished between two large obstructions.

Currents encountered by divers most often move horizontally, but there are places and times where vertical currents are encountered. Upwellings occur when deeper water rises toward the surface. Downwellings occur in some places, too, but a more common type of downward current a diver may encounter happens where there is a dropoff of some sort. For example, a tidal ebb flow may literally spill over an underwater dropoff, just like a waterfall spills over a cliff on land.

Some currents are gentle, while others rip along with incredible force. Next time I'll tell you about some very interesting experiences we've had dealing with currents while diving.

11 comments:

  1. What are rip currents? Or did one of your explanations cover that and I missed it?

    The only thing I know about rip currents is that they're considered dangerous to swimmers/beach goers.

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  2. Hi Mikster -

    Rip currents are a type of current generated along areas of shoreline that have breaking surf. (Rule of thumb: No surf = no rip current.) They flow away from shore, toward the open sea, and they can be quite strong. Swimmers who get caught in a rip current will get pulled out to sea, away from the shore.

    A good thing to know about rip currents is that they fizzle out pretty quickly -- they won't take you to the other side of the ocean, but they can take you 50 or 100 feet offshore in a hurry.

    Since most rip currents are not very wide, usually you can get out of a rip by swimming parallel to the shore -- that is, perpendicular to the direction of the current, NOT against it. Worst case, just float or tread water to ride along with the current until the thing fizzles out, and then arc back to shore a little farther down the coast where the current isn't!

    Divers don't encounter true rip currents very often, because we don't enter the water where there is surf (in most cases). It's a bear passing through surf wearing a gazillion pounds of dive gear, believe me! :-b

    Bobbie

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  3. Thanks for visiting my wordless wednesday post!
    I am not a diver, but I love to snorkel (though i am a whimpy - shallow water snorkeler...) The last time i was able to go snorkeling, I saw sea turtles, an octopus and an eel. I was just completely blown away, and quite satisfied with that experience. So often it is just about the "pretty fish." But that experience was much more personal and intimate, for me.

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  4. Hi Flying Mum -

    I know exactly what you mean. Experiences like the one you describe are what prompt all of us to keep putting our faces back into the water again and again.

    Bobbie

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  5. Bobbie, I awarded you. And rightfuly so! Come see: http://nodirecton.blogspot.com/2007/10/community-blogger-award.html

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  6. Jos, thank you so much for the recognition. We really appreciate your support.

    Bobbie

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  7. Ocean in Motion..Oops thats three, but it doesn't matter, because I can give you one word to describe your image and that's...Beautiful.

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  8. Aw thanks, Bernie. (Actually 'Ocean in Motion' suits that image quite well.)

    Bobbie

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  9. Hi Bobbie. I am not a swimmer nor a diver. I even get a little scared when I'm out there in the open sea sometimes. But I love to snorkel though (but not in too deep waters! :D)

    Anyway, I'm glad I learned something today -about currents. Thanks for the insight.

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  10. We think about the all the wind currents up on land and how they affect us - it seems like it is the same thing under the water. I wonder though - are they as damaging as the land ones? I seems like the water would slow down the force, where on land there is nothing to slow the forces.

    Very, very interesting - I do love your blog!

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  11. ZAM - Welcome to The Right Blue. I'm glad you learned something new from your visit here.

    Kathy - The 'normal' kinds of currents in the ocean are not particularly damaging, but storm surge can just pummel reefs. Hurricanes are some of the worst, but even ordinary winter storms in our waters, for instance, can break coral,uproot whole coral heads, overturn rocks, and just generally rearrange things underwater.

    We've also seen damage from the kinds of currents produced by torrential rains on land that create lots of runoff that enters the ocean. Runoff from land carries with it mud, debris, and even chemicals (from fertilizers and pesticides on lawns, for example). Those kinds of currents deposit silt and debris on reefs. The reef critters are very affected by that: Their homes are disrupted and their feeding grounds are altered, at least temporarily. Silt on a coral reef is a very sad sight.

    Bobbie

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We welcome your comments and invite your questions. Dialogue is a good thing!

Bobbie & Jerry