Tag Archives: slope

Wave watching in an end moraine lake in Brodowin

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On our work trip to Brodowin to prepare the GEO-Tag der Natur (which will take place here only  a little more than a week from now! Crazy!), I had the chance to do some cool wave watching on different lakes.

Above, for example, you see wind waves coming in from the right, and their very distinct reflection on the left row boat.

Below, at the stern of the left row boat, you see a sudden gust of wind, causing lots of capillary waves, and thus high surface roughness.

And below, what would you guess is the secret to the ring waves radiating away from the end of the pier? It’s a surf board, bobbing up and down in the incoming wind waves!

I just love looking at water, it has such a calming effect on me, even in 35 degrees heat (which I am really not good with).

I love to see how the more lively wave field offshore gets calmed down as only longer wave lengths make it through the water lily frequency filter! And how the wave crests get bend as they reach the shallow shore.

Now, different lake. This one is 38 m deep! Would you have guessed that?

Here you see that we are standing on the downwind side of the lake: Smooth water on the other edge in the lee of the land, then, after sufficiently large fetch, waves that grow more and more the further they have progressed over the lake.

Same lake, same phenomenon, different view.

And the last bit of the lake just to give you an impression of the glacial landscape it is situated in, explaining the very steep slopes and the 38 m depth.

This would be such a lovely place to sit at and enjoy the view, if only there was a little shade…

I find it fascinating how the shape of the waves doesn’t change as they approach the shore. That’s because the shore is so steep that when, at last, the waves start feeling the bottom, they have already reached the edge of the lake and didn’t have time to change their shape.

Same phenomenon, different view.

Water is just so amazing :-)

Same beach, different waves. Why?

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Here is a puzzle for you.

Walking along a beach, first, the waves looked like this: One wave breaking at a time.

That’s the situation you also see in the foreground of the picture below, while in the background, a little further down the beach, something else starts happening.

If we look closely at that situation (shown in the picture below), there are several waves breaking at the same time, one behind the other.

And it isn’t just coincidence, it keeps happening throughout hundreds of pictures I took that windy Sunday. Why is that?

I think (and this theory would be easy enough to test if the water was warmer or if I wasn’t such a sissy) that the slope of the beach is just different on either side of this little jetty or whatever it is. The shallower the slope, the earlier waves of the same wavelength can “feel” the sea floor, or the shorter waves have to be to “feel” the sea floor at the same distance from the water line.

So I think the slope on the left of the jetty is shallower than on the right, making the incoming wave field that is the same on either side (I’m assuming, but give me a good reason for why it shouldn’t be?) behave differently.

Funnily enough, the only reason I ended up on that beach was that I wanted to go watch a cruise ship go through the locks and into the Kiel canal with a friend. And, funnily enough, the ship decided to not go through the Kiel canal, as it did the week before. So we decided that we should go to the beach. Very good decision! :-)

But here is a “before” pic from when I was still thinking I would be writing a blog post about the ship going through the locks. Isn’t the seagull hilarious, posing like that?

Waves on a slope

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Earlier this year at Forscherfreizeit Ratzeburg – the summer camp at which Conny, Siska, Martin, a bunch of teenagers and myself spent a week sailing, exploring and playing with water – I spent a good amount of time staring at waves hitting the wooden boards that form the slip in the port. They create a nice slope with a very interesting structure, especially at the joints where the angle of the slope isn’t exactly the same.

Watch what happens when the wave approaches the shore (and focus on the left part of the picture, where it is clearer):

At first, it arrives pretty much as an ordinary wave.

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As it is running up the slip, you start seeing the structure of the boards below.

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As the wave becomes steeper and steeper, the front one is being slowed down more than the second one, because it is in shallower water (and we all know that the phase velocity of shallow water waves depends on the water depth, right?).Screen shot 2015-09-26 at 4.41.34 PM

Eventually, they form one steep wave and break.
Screen shot 2015-09-26 at 4.41.54 PM

Watch the movie to see it happen:

For more waves on a slope, check out these posts (Norway, Hawaii).

Types of breaking waves depending on steepness of slope – small scale

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Video of different types of breakers – small scale.

In this recent post we talked about types of breakers depending on the steepness of the slope. But even on a single stretch of coast line you can easily observe several kinds of breakers. My friend E lend her cabin on an island just outside of Bergen to me and another friend E for the weekend, and just sitting on the rocks we could observe at least two types of breakers.

Different types of “breakers” depending on the slope of the beach. Also see video below where it might become more clear…

In the movie below, you see surging breakers on the first little headland – the water level just raises and falls and no breaking occurs – whereas in the small bay behind the headland and on the next headland the slope is much less steep and here spilling breakers develop. Spilling breakers can also be seen about halfway through the movie on the right hand side beach. Isn’t it awesome how you can see so many concepts on the smallest scales once you start looking for them?

Waves breaking depending on steepness of the slope

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Waves breaking on slopes of different steepnesses.

Depending on a slope’s steepness, waves can break in very different ways. On nearly horizontal beaches, spilling breakers develop. On steeper beaches, plunging breakers, the kind of breakers that form the tunnels that people surf in, form. And on very steep beaches, the breakers don’t actually break, but surge up and down.

Types of breakers developing on beaches depending on the beach’s slope.

This can be seen on  the large scale when different beaches are known for different kinds of breakers, and one impressive example are Oahu’s North Shore plunging breakers that my friend Tobi took me and a couple of friends to see in 2010.

Plunging breakers on Oahu’s North Shore in September 2010.

 

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Another plunging breaker on Oahu’s North Shore. See surfer for scale.

More awesome breakers were to be seen on the Big Island a couple of days later:

Plunging breakers on Big Island in September 2010.

And of course I have movies of those breakers for you, too, first Oahu and then Big Island: