It doesn’t feel like it, but today marks the 7-year-anniversary of my first blog post on my “Adventures in Oceanography and Teaching”! To celebrate, I sent out this call to action (and please feel free to respond, no matter when you are reading this):
Below, I am sharing the pictures that people sent me plus my thoughts on them, newest on top. Pictures that reached me after August 28th 2020 will be posted in follow-up posts! (Keep them coming, I love it!)
Oooh, I love the internal waves on the interface between the milky part of the coffee and the not-yet-milky part! Looking at them moving very slowly always feels like being caught in slow motion, when of course the phase speed has to be very slow because of reduced gravity
21:55 — Phil (San Francisco)
Ooooh, this is awesome! Phil writes “photo of an awesome phenomenon that I took just before landing at SFO. San Mateo Bridge, San Francisco Bay on an evidently quickly rising tide!” and I am love the vortex streets! Count 4 pylons up from the bottom — that’s such a nice and clear von Kármán vortex street, absolutely beautiful! And then the bottom one does seem to show som shear instability. Now. In some spots vortex streets develop, while in others they don’t. But why?
Clark wrote an entire thread explaining this awesome observation in the Bay of Fundy. You should totally check out the whole thread & explanations on Twitter, but I had to share this video so you can see what an exciting situation it is!
20:51 — Elin (Bergen)
Oh, nice one! Lots of tiny air bubbles in a vase or jug filled with water. Now. Is the line crossing through the water level? It kinda looks like it at first glance, because it seems to show a meniscus. On the other hand, there are bubbles sitting above that line, and they don’t look qualitatively different from the ones “under water”, so that seems unlikely. But then light seems to be refracted substantially differently above and below that line, so maybe we are looking at the water surface at some weird angle? Intuitively I would say that we are looking in from underneath the water level, but see the water line on the opposite side of the vessel. But that doesn’t seem to make sense with the (most likely level) table top? I will have to think about this some more!
18:14 — Simone (Hamburg)
How beautiful — in this drop we see the tip of the leaf it is hanging on pointing uo from the lower end of the drop! Nice example of how drops act as lenses and show us the world upside-down!
Oh! Nice long waves coming in from far offshore. From the shape of the wave profiles I would guess that this was taken close to shore in shallow-ish water. This seems to be confirmed by the waves changing direction from further away coming towards us, which would indicate that the depth is changing over that distance
Unfortunately I could only screenshot that gif, check it out in the original tweet! What I find fascinating here is how there are two waves breaking offshore running towards us, but then there are several wave crests even closer to us that are still distinct and pointy (so the waves clearly didn’t loose all their energy breaking), but not breaking. I think there must be a shallow area where those two breaking waves are, making them break, and then deeper water again so that they are only temporarily tripping up and breaking, but then propagating further towards the shore without too much of an interruption
15:18 — Nena (Bodensee)
Oh, waves and a piece of driftwood! I wonder if it’s floating, it looks like it’s grounded. Otherwise I’d expect it to move with the waves, creating a dipole pattern when the ends take turns coming further out and then sinking deeper into the water.
And now a larger wave, breaking as it reaches the shore and also washing over the driftwood. I love how the water that came washing over the driftwood “in one piece” then disintegrates into drops when it falls down the other side!
Wow, this video is super tricky! Please check it out — volume up!
At first, I thought that the periodicity was set by eddies shedding periodically after water had washed over the obstacle. But after about the 50th time I looked at the video, the obstacle (is it driftwood?) seemed to start moving. If it is actually moving, the periodicity makes sense: The wood is trapped in place (you see that on the far side of the river) but it can move a little. It’s bopping on the water, floating at whatever height the waterlevel is at, but at the same time acting as a dam and trapping water on its upstream side, thus influencing the waterlevel. So this is basically a recharge-discharge oscillator. Maybe. Or maybe not. Any ideas, anyone? This is really tricky!
12:38pm — Gabriela (Lüneburg)
I would be so jealous of those kids playing with the locks and weirs and water channels if they weren’t my adorable nieces. Now I just can’t wait to go visit & play with this really cool toy!
11:49am — Gabriela (Lüneburg)
Somehow raindrop photography seems to be the topic of the day today? Here we see really well how a drop shows us an upside-down image of the world. See the sky at the bottom and the shed at the top, with the wine branches in the middle?
11:39am — Gabriela (Lüneburg)
Oh, a rain barrel! I think someone touched the side (possibly kicked it) so we get waves radiating from the outside in. Could also be that someone moved the ropes, but I would expect shorter wavelength waves then
This would be sooo difficult to interpret if I didn’t have inside knowlege: There are rocks hanging at the end of those strings to keep them in the center of the barrel, to guide the rain water in. What happened here is that someone pulled one of the strings to the side and let go of it. We see that the rock that was lifted when the rope was pulled out, is pulling the rope down again. That’s why the rope still has this weird bow shape, and that’s why we get kinda a wake where the rope moved from the outside of the barrel towards the center. All the other smaller ring waves are either drops that fell from the wet rope, or the ones that are centered around the other rope are caused by that rope vibrating because it’s attached to the first rope somewhere up on top
Here, my niece is demonstrating how to make wakes by swinging weighted ropes through water
Same as above, but we nicely see the capillary waves that radiate away
11:20am — Katharina (Hamburg)
I guess I said I liked a challenge… Screenshots with comments below! And check out the sound in the movie! Volume up!
At first I thought this was going to be a movie with pretty rainbows and reflections — water can create awesome prism effects!
But no! She dropped a fizzy tablet in! Here we see the first gas bubbles bubbling up to the surface. The bubbles get bigger the closer they get to the surface, because the pressure decreases and they can therefore expand
Already a lot of bubbling and fizzing going on! On the right side of the glass we can see that the gas bubbles are released in bursts. We also hear that when listening to the sound in the movie. Also funny to see how the bubbles raise in the middle of the glass and the flow is really turbulent there. Only at the rim can bubbles persist without bursting for a little while
The tablet has almost completely dissolved now, and what little is left has floated up to the surface (upper right). Btw, that fizzing sound is not really made by the water itself, it’s all the tiny bubbles bursting. Since sound are pressure waves and bursting bubbles radiate pressure, as the gas inside of the bubble is at higher pressure than the surrounding air and expands until the bubble bursts and then the pressure equilibrates. That’s what we hear!
10:46am — Astrid (Hamburg)
Astrid has a great taste! Both in her choice of reading materials (my blog!) and in her taste of coffee, with the beautiful swirls of milk in it. Here we see that molecular diffusion is slow when it has to physically swap whole molecules around — the swirls of milk are still distinguishable in the coffee (she clearly didn’t stir). But I would be prepared to bet that the milk has the same temperature as the coffee, because molecular diffusion of heat is fast (and also because she likes her coffee hot, the milk most likely went in hot)!
10:38am — Sara (Klein Waabs)
Phew, this is a difficult one! The first structures that jump at me (besides the wind surfers, of course) are the shadow of the sail (from the board to the left) and the reflection of the sail (from the board towards us), which are kind of distracting from the waves. And the waves are kind of messy, there is no clear direction visible. There is some wind causing the waves. Not very much, but enough to make it difficult to distinguish wind waves from others caused e.g. by the surf board.
Now we have some wind! We see waves breaking at the stones offshore (and looking at how high the foam is flying, those waves were not too shabby!), but we don’t actually see a lot of those waves because everything from the wave breakers towards us is in the lee and thus sheltered. But we see some long waves that have propagated into this bay that break on the beach
10:37am — Florian (all over the world!)
Cabo da Roca in Portugal; westernmost point of the continent. This is beautiful! Waves from far offshore arrive at the beach. As they reach the shallower water, all of their properties except their frequency change: Their wavelength gets shorter, their height larger, their steepness larger. When one part of a crest is in shallower water than the rest, the crest bends towards the shallower areas. The breaking waves create a lot of foam, indicating that there was some biological activity creating a surface film
Falesia Beach, Algarve. Oh how beautiful! Breaking waves on the other side of those rocks, and only the longer waves make it into the calm, sheltered space this side of the rocks. Interesting example of a filter that only lets long wavelength come through!
Algarve-Coast. What strikes me here are the beautiful colors! Near the beach, we can look into the water and see the sandy sea floor as well as some larger rocks, that seem to be partly overgrown. The further we look offshore, the bluer the sea gets, because at shallower angles the reflection from the sky increases, until at a critical angle, we only see reflections and can’t look into the water any more.The different shades of blue in those areas show where breezes rough up the water, darker areas are those where there is currently more wind and the surface roughness is higher. Another thing I am noticing are the waves that the person in the water makes — circles around them.
Timmendorfer Strand, Baltic Sea coast. On a windy day! We can see that from the whay the waves are breaking, not only right at the beach and in areas where the water is shallower, but also in smaller, more random bursts. Also waves don’t have the same regular shape as they would have had this wave field traveled to the beach from far away, it seems to be somewhat regional. Also love how far the waves run up the beach (as you see from the large area covered in foam). This must have been a fun day to play at the beach!
Maschsee Hanover — I love how you see different things in this picture: First, how stuff floating in the water dampens out the waves (see how there are a lot more waves behind the plants floating in the water than on this side). And then the wakes that this cute family of swans is making as they are swimming towards us!
9:09am — Gabriela (Lüneburg)
Honestly, what jumps at me most is my ADORABLE niece who’s saying Kaffefoto (“coffee pic”). But then there is also the puzzle of why the coffe coming out of the machine looks so much lighter than when it’s in the mug (underneath the foam)? Well, the foam is the clue here! When there are a lot of airbubbles in the coffee still, they reflect light differently (i.e. from all different directions, making it look white, rather than directional, showing either the color of the coffee or a reflection) than when the coffee has settled down and the air bubbles have gone away.
9:01am — Kristin (hiking somewhere near Bergen)
Did you ever wonder why waterfalls (or really turbulent rivers) always look white, while a lake or the ocean can look all kinds of different colors depending on what is dissolved in the water and what they are reflecting on the surface? The answer is that in waterfalls (or the really turbulent, “white water” rivers), there are tons of tiny air bubbles trapped in the water. All the surfaces of those air bubbles and also the turbulent flow itself make the water surface very irregular. Since the surface is so irregular, it reflects light from all different directions, rather than just one. As we receive all that different-colored light, our eye interprets it as white. Fun exception: Sometimes we see rainbows in water falls. Then the sun as light source is so dominant that we see the sunlight reflected in the falling water drops and a rainbow appears!
Oh I love this! I think that what Sid doesn’t show us on the very right is a narrow connection to a second body of water, on which waves are generated by wind. (Alternatively, there might be something there at the very right just outside the frame that is making waves, such as a bird or a fountain, but I don’t think that’s the case. Birds usually don’t move this regularly for long enough to generate this wave field even before you started filming and then throughout the whole movie. Fountains usually generate concentric waves (unless there are several fountains, in which case this would be a trick question ;-))) So let’s assume that wind-generated waves from a second body of water pass through a narrow inlet onto this pond. As they pass the narrowest part, they start spreading to all directions, forming concentric waves that grow over time. Well, almost concentric, because the narrowest part isn’t a perfect point source. Therefore we don’t see diffraction at a slit, but rather at a wider opening.
8:58am — Torge (Kiel)
Not a picture, but even better: He managed to fix the problem we had been having with the co-rotating video of our rotating tank. Super excited! If I wasn’t so busy today (slightly underestimated how many pics my dear friends would send me!) I would go try it out right away!
8:51am — Sam (Manchester)
Raindrops on the window! I love how, especially with the ones in the upper part of the window, you can see the world upside down: the bright sky at the bottom of the drops, the darker trees at the top. In the drops further down the window you see the sky at the bottom, then the darker bushes and trees, and then the brighter gravel & car! So cool!
8:28am — Ronja (Nordsee)
On this beautiful picture you clearly see wave crests meeting up at an angle, even though further offshore they all seem to be coming in parallel to the beach. Why? Because there is this groyne going out perpendicular to the shore. You see some of the stones at the bottom of the picture, but from the wave field we see that it reaches further offshore and is just submerged there. Where it is submerged, the water depth suddenly decreases. Waves running close to and on top of it therefore change their speed, and with changing speed, the wave crests bend towards the obstacle (as they are being slowed down more on the obstacle side than on the deeper side). Since this happens on both sides of the groyne, we get this cool checkerboard pattern!
Same explanation as above, but another beautiful picture! :-)
8:13am — Elsa (Bergen)
Ha! Knowing where this picture was likely taken, the fist thing I notice is the reflection of the masts of the sailing ship Statsraat Lehmkuhl! And how pretty the light is looking in between the hulls of the catamaran. And how there are waves radiating away from where other waves bumped against the bottom of those tyres
Bergen is so beautiful! I love how we see the reflection of the colorful houses of Bryggen, then the dark mountain of Fløyen behind it, and then a blue sky with pink clouds! And how the structures of waves are clearest where there are strong contrasts in brightness of the reflected light, for example at the pink/blue boundaries!
More beautiful Bergen. The dark mountain’s reflection does not have a sharp edge, because the water surface isn’t flat. So depending on the angle of the surface, some spots still show mountain while others already show the sky
Same as above, PLUS isn’t it cute how the floaty bits in the foreground have their own little wave rings around them???
What jumps at me here is the turbulent (white) water, most likely caused by a speedboat
Here I love how the surface appears smooth even though there are very clearly waves on it. That means that the waves we see haven’t been caused locally by wind, otherwise there would have to be smaller wavelength stuff on them. Instead, they were generated further offshore and traveled here
7:26am — Kati (Schönbrunn, Wien)
First thing I notice here: How pretty this looks with the reflection! And beautiful weather! Hardly any waves, but there are some structures in the lower right that look like there are possibly plants growing in the water, just breaking the surface
7:07am — Marisa (Hamburg)
Looks like it’s raining in Hamburg! What I always find super cool about rain drops is how they act as tiny lenses and show us an upside-down picture of the world
6:26am — Désirée (Möhnestausee)
This is a picture taken at the Möhne reservoir — a river that has been dammed to create this lake. The water level is regulated, which you see in the horizontal stripes on the opposite side of the lake, each representing what the water level was like at some point in the past..
What an awesome pic! But wait — aren’t water drops (or anything, really) supposed to fly in a straight line, unless there is a force acting on them? There is obviously gravity acting, but why the curve? This riddle is solved by looking at the flying droplets, which are individual droplets. And even though they look as if they are following a curved path one behind each other, this is just our eye being tricked into that. Each drop is flying on a parabola (thanks, gravity) away from the spot where it detached from the end of the flying wet hair. But the drops are not following each other, they just happen to have detached from the hair along a path.
I’m posting a couple of screenshots from that video to make it easier to discuss…
First, doesn’t this lake look absolutely beautiful? The calm surface is an almost perfect mirror of the sky because we are looking at the water at a shallow angle, thus we only see reflections and can’t look into the water
Then, we look down. See the plants in the water in the top left of the picture? They indicate quite a strong flow from top left to bottom right of the picture. But wait, there is an obstacle in the way! That stone introduces turbulence. There are waves that are created as water washes past, and there are also eddies shed because the current shear between the flowing water and the more stagnant water in the shelter of the stone is so strong. See that one water plant thingy right below the train of eddies? It seems to be moving in the turbulent flow, too!
And we reach the next obstacle! At the top left, water is still flowing slow(ish), thus the surface is flat and we can clearly recognize the tree reflected in the water. But then we reach the threshold, and all of a sudden the flow goes from laminar to turbulent. See how the whole right side of the picture seems to be full of tiny bumps? That’s where the water is influenced by the structure of the bottom underneath
I absolutely LOVE that my blog and twitter have helped me meet and connect with so many wonderful people all over the world! Here we see Khajoo Bridge in Isfahan, Iran. So beautiful! As for wave watching: In the left side of the picture we see what was the right side of the picture above, the very fast, turbulent flow down the slope. And then at the bridge, there is a jump in surface height: As the water is deeper there, the flow slows down to subcritical speed and a hydraulic jump develops
Last screenshot: The hydraulic jump shown in the last picture, only more prominently pictured. Also visible: The influence of that stone edge on the flow. See all the waves that radiate from it as it is restricting the flow? Super awesome!
What I notice first is the tiny white sliver of light, close to where the spoon breaks the coffee’s surface. That’s showing us that the surface isn’t perfectly straight, but that it is deformed where the metal of the spoon and the coffee meet. The effect — cohesion between molecules — makes the coffee rise up a little at the edgs of the cup and also where the spoon breaks the surface. You might know this from the meniscus that shows up in test tubes and makes it difficult for the untrained eye to estimate how full a test tube really is
A week’s worth of #WaveWatching pictures for you. Enjoy!
Starting off strong: I love living in Kiel!
Totally different vibe the next morning, looking very winter-y somehow.
And then another early morning on my way to the beach. Below you see the locks on Kiel canal from the bridge that crosses the channel. I really love this view but I have to admit — if the ferry ran this early in the morning already, I’d totally take it to cross the channel rather than cycling that bridge!
But arriving at the beach always makes it worth it!
Taking the ferry back home… Love this picture! A turbulent wake, a feathery wake, those clouds… What more could anyone want?
….and we are back on the next day! Waves breaking pretty much right on the beach because the beach profile has a step shape right at the water line. Looks surreal to have those long smooth waves, than a tiny bit of breaking, then nothing but sand…
All those bubbles in the white water of the breaking waves!
I actually took the picture below because of the birds’ wakes in the center. Weird how it turned out!
And here is one just because it’s pretty!
Always surprising how many fossils there are on the beach, even though this is the 5th day in 8 days of me collecting on the really short stretch from there to the lighthouse! How many more are hiding underneath our feet and we’ll never know?
Took a very similar picture as on the day before, but I love all the different parts of the wake, the clouds, the reflections. So beautiful and calming.
Running, seal watching, swimming in Kiel fjord, now my well-deserved coffee. Have a nice Sunday everybody!
On Monday, a colleague from GEO visited me to do an interview on wave watching. Amazing day!
Taking the ferry & admiring the wakes. Isn’t it fascinating for how long turbulence persists & wipes out any waves / prevents formation of new waves? Love the different surface textures!
Also fascinating how differently wakes look depending on weather conditions!
Love how dramatic this looks!
…and how turbulent patches are so smooth and reflect the building so well. And then a sharp boundary and we are back to the normal surface roughness of wind waves!
I can’t get over how fascinating this is!
Also love the pictures for their beauty. Below: After we had arrived at a stop, the ferry has just started sailing again (see where the wake changes between smooth and turbulent and then those large eddies of the propeller rotating for propulsion?)
Very nice pattern in the waves this morning, showing constructive interference (where the crests are high and the troughs are low) and destructive interference in between where the surface is completely flat. So fun to watch!
And that’s it! Hope you enjoyed and hope it inspires you to do some wave watching yourself! :-)
My perfect Saturdays start like this: Early morning walk along the water, followed by coffee while blogging about waves. Today’s focus: The cool waves that birds make!
First, let’s look at the weird way in which seagulls take off from water. They make a big splash which develops into ring-shaped waves. So far, so good. But…
…that’s usually not all that happens: They usually hit the water a couple more times before they fully take flight, thus leaving a trail of circular waves radiating from each of the points where they hit the water.
This morning, there was a seagull sitting very close to the sea wall (which you see in the lower right corner of the picture), probably eating or washing its feathers; in any case radiating off waves. When I looked down, it flew up, hit the water once, landed again, and then began to swim away.
And you can see all of this in the waves!
The green cross below marks the spot where the seagull sat before I interrupted it. It must have been sitting there for a bit judging from the radius of the circular waves marked in green that radiate from that exact spot.
But then when the seagull saw me, it took off, dipped once into the water (green cross and corresponding wave circle), and then landed again (red cross) and swam away from there (following the red arrow on which the centers of the red circles fall).
How cool is this?
Once it was just swimming and not dipping in and out of the water, it begand to develop a regular, v-shaped wake (red V) that consists of individual “feathers” or wakelets (yellow).
It continued swimming away, albeit taking a little turn…
You still see the green waves from where it was sitting originally, and then the red waves from where it landed and swam away on the path marked by the red arrow.
This kind of stuff makes me so happy! :-)
From the waves in the picture below, can you tell me what that seagull did before the picture was taken?
The year started off in the very best company — watching ships and waves and flowers with Astrid!
But of course there is also actual wave watching happening: Here we see a ship’s wake arriving. I find it fascinating how there are the stripes where you can look into the water and then those where you can’t! Total reflection in action. When I learned about that in physics class I never thought that was a phenomenon I would ever see in real life!
When the waves from the picture above meet the curved sea wall, they get reflected into this pretty pattern.
Another day, foggy and very windy! That day, my focus was on how there are no waves in the lee obstacles. Only after sufficiently long fetch do waves start to grow.
See how the surface roughness changes with distance from the obstacle?
Oh, and then there was a sunny day! The Oslo ferry is leaving in the distance. See the stripes in different blue tones? In the foreground you can see how the colors are related to surface roughness. Areas that are more exposed to wind are rougher with more waves and different wavelengths, and look darker. More sheltered areas in the lee of structures have fewer waves and appear in a lighter blue.
Oh, and then I had a great day with my nephew in the port of Hamburg with harbour boat trips, walks on the beach, and tons of wave watching. He was very impressed by my skill to know how far each wave would run up the beach, especially since we saw lots of people who either ran away screaming or got wet feet :-D
Another picture from the same day with my nephew: Here is a wave train from a ship’s wake arriving at the beach. I love watching this kind of stuff!
And then one day, I went#WakeWatching! On all three pictures below, you see waves made by the same little ferry. On the right is the turbulent wake where the ship just moved through the water, and on the left some of the feathers that form the V.
Here the ship is turning so we see water that is disturbed by the ship moving through, but doesn’t have the „boiling“ like where the propeller stirred up everything.
Now we see how the wind waves seem to be bunching up at the boundary between the wake and the area that wasn’t affected by the ship moving through.
Then, for #SciCommSunday, I posted a picture of a book that I think is a brilliant introduction to the science of communicating science that I also wrote a blogpost on.
And surprise: Bonus pic for my dear readers that I didn’t post on Instagram but that I think is cool (will definitely experiment with this kind of pictures more! Except panorama mode does weird things to waves, so on second thought maybe not…)
What we are looking at in the picture above is a really low-water day in Kiel. Which leads to interesting wave watching opportunities!
See how waves that arrive with straight crests somewhere offshore get bent as they reach the shallow water? That’s because the velocity of a wave depends on water depth. The deeper the water, the faster the wave can move. The shallower the water, the more the wave is slowed down. Therefore, waves get slowed down first in regions where the water is shallower, and the parts of the wave crest that are still in deeper water wrap around the shallower part. Kinda like when you are slipping on an icy road, you fall in the direction of the foot that didn’t slip because your body spins in that direction.
When there is really low water in Kiel fjord, we can observe the influence of topography on waves much better than we usually can! For example here we see how on one part of the “beach”, there are several wave crests behind each other, all breaking, whereas on the other part on the other side of the headland there is only one wave crest at the water’s edge. Why is that?
Wave crests get steeper and start to break when the water is shallow enough for the wave to “feel” the bottom. On the left side of the picture, depth is increasing faster towards the open ocean: The wave only feels the bottom right before it has reached the water’s edge. On the right side of the picture, on the other hand, the depth changes very gradually. Therefore waves feel the bottom already much earlier and many wave crests are steepening, preparing to break and finally breaking at the same time.
And then I just thought this picture was fun :-)
And a rainy day at work!
I actually don’t mind all the rain: It makes the flow in all the storm drains so much more interesting! Here we see how water shoots out of a pipe into a little lake. Note that I’m saying the water is shooting rather than flowing: That means that it is moving so fast that any disturbance is washed away with the water.
As the water shoots into the much slower flowing lake, it pulls water from the sides with it. This water obviously needs to be replaced from further away, so a recirculation is set up.
Here is an annotated version of the picture to see the recirculation going on:
On the GEOF105 student cruise that I was lucky enough to join like I did last year, I happened to observe what you see in the picture above: Standing waves in a bucket! And this isn’t a staged photo, this is me taking a picture of a student at work.
We are looking at the bucket the students use to take surface water samples which they measure on deck. The bucket happens to stand just above the engine room. Which leads to vibrations. Which, in turn, leads to waves. Many different kinds of waves! In addition to what you see above, we find, for example, plain circular waves. They might look like they do in the picture below:
And here is a short movie of the waves, first in real time, then in slow motion.
Sometimes the circular waves also have other wave lengths.
The next pattern that develops from a monopole (like the one you see above) is my favourite: A monopole with higher order stuff developing at the edge of the bucket.
Watch the movie below to see it in motion (first at real speed, then in slow motion).
The next step, then, is water that almost looks as if it was boiling. Like so:
Here is a movie of the bucket with the “boiling” wave pattern, again in real time first and then in slow motion.
The movie below shows a close-up of some of the waves in the “boiling” state, when there was enough energy in the system to throw drops up in the air. The movie goes from real time to slow motion. Careful when you play it, I left the sound in in order to show how the frequency of the waves is the same as the frequency of the engine. (And because of the annoying sound, it doesn’t start up automatically, so you have to click to play)
Here is a movie that shows the bucket in different positions, shot continuously to show how quickly the wave pattern develop and also how close together the different spots with the different pattern are located. Thanks for playing along, Kjersti!
So clearly the location has an influence on what wave pattern develops. But what are other important factors? We tested material, shape and size of the container.
A small plastic bucket which is almost cylindrical, for example. Guess what happens?
We can get the same wave pattern as in the large bucket! The movie below shows three different wave pattern. When the frequency suddenly changes that’s because the movie is in parts played in slow motion.
As to material: It seems to be important that it’s flexible. Iron cast pans don’t work (yes, there is water in it!), neither do metal lunch boxes…
And round shapes make nicer waves. But the rectangular vanes of the surface drifters (aka paint roller trays) also make pretty pattern! But now the waves are, unsurprisingly, only parallel to the edges of the tray.
Yep, this is the kind of stuff that makes me really happy! :-)
Even though I’ve been looking at waves for years now, wave watching is still full of surprises. Yesterday I showed you capillary waves that a jellyfish made, and today I’m showing you a helpful seagull.
What I found most fascinating walking through this marina were the long straight wave crests that form in parallel to the step in the foreground as waves leap up on the step and then the water flows back. I can watch this kind of thing for a very long time!
But I was also pointing out the ring waves around the bollards to my friend, which are a lot more difficult to spot. But, as if it had just been waiting for the opportunity to help out, the seagull on one of the bollards dropped something and created ring waves for us! Can you spot it?
We saw Piel Island with a very cool castle ruin across the bay when visiting the South Walney Nature Reserve the other day, and were intrigued by it. Depending on the tides, you can drive over by car, walk, or take a ferry, which is what we did.
Arriving at the spot where the ferry was supposed to leave, we were greeted with this beautiful sight: A pier going down into the water, creating beautiful wave pattern in the strong incoming tide! We see a hydraulic jump similar to the one we saw on Walney Island, except that this one is even cooler: It happens in the area where the pier is just below the water surface, but a strong current goes underneath the pier on the land side as soon as it is above water level.
Above, you see the current going left-to-right, creating a lot of turbulence where water comes out from underneath the pier (see those eddies where the water looks as if it was boiling?). You also see the waves hitting the pier on the left side, and then standing waves towards the right of the pier, locked in place because they are propagating upstream with the current’s exact velocity, thus staying in place (aka “standing”).
This is super fascinating! To me, anyway ;-)
Once on Piel Island, there is a lot of really cool wave watching to be done, too.
Below, you see waves reaching the island and “wrapping around it” — i.e. being refracted towards regions of lower velocities, which means that they will be bent towards the shore, no matter which direction they originally came from.
You can observe this for quite a big part of the island as you walk around it! The original wave direction is the one seen in the bottom left, all the rest of the wave field has been refracted by the change in water depth!
But obviously there is a limit to how long you can play this game. Below, you still see waves wrapping around the island, but they aren’t reaching the shore more or less parallel to it.
But even just watching all these crests break, one after the other, along the shore looks pretty cool!
But, obviously, if waves get wrapped around an island, but not completely, there must be areas where wave fields going around either side of the island meet up at an angle to each other. Like here:
And once again, this time moving:
And another very good spot to see this kind of pattern is a little headland like below:
Can you spot the distinct checkerboard pattern of the waves, and see how they break where a crest meets another crest?
I can watch these kind of things forever without getting tired of it!
And once more, as a short movie, because waves are even more awesome when they are moving:
Or waves more generally, especially breaking waves.
How beautiful is this?
I can really watch waves for hours without getting tired of it.
But anyway, walking further around the island, here is a spot with fewer waves: Here we are in the lee of the island, the area that is sheltered from the wind by the island itself.
Oh, and this is the ferry that got us over to the island. As you might notice below, the current has turned and is now going out — unfortunately I didn’t take another video or even good picture! But you see the edge of the jetty in the lower right, and the current downstream of the obstacle with a very different surface texture than the surrounding water. And then there is always next time… ;-)
On our way back home, we stopped for scones and coffee (sorry, no tea) and had the amazing views you see below. These channels don’t look dangerous by themselves when they are empty, but thinking back to how quickly the tide comes in around here they don’t seem as harmless any more, do they?
Arnside is a beautiful little town on the banks of the river Kent, and Astrid and I went on a nice hike along the shores of the estuary a little while ago.
The difference between high water and low water is quite impressive here, and we started our hike right after high tide to make sure we wouldn’t be cut off by an incoming tide. Which was definitely the safest thing to do, but also made for pretty muddy shoes…
There is a ton of amazing wave watching to be done in the Kent river bed. For example the waves being diffracted around these rocks.
Or this diffraction at a “slit” between the rocks.
And the whole landscape is just gorgeous!
Very intriguing to me: A foam stripe that seems to be coming out of nowhere. Or, better, that we can’t see the cause of just yet. It’s coming from somewhere downstream (to the left).
But where is it coming from? From somewhere behind that headland. Let’s go inquire!
A little further down the coast line, we see that the foam stripe ends on a sandbank.
And coming closer still, we see that the foam is created by waves breaking on that sandbank and a second one a little further offshore. It gets collected where the bank brakes the water surface, and is then just driven downwind, but stays together, forming the stripe.
This is a closer look of the waves breaking on the sand banks.
And speaking of sand banks: There is some cool wave action in between the sand banks, too! Waves are driven in by the wind through the channel from the left. This is a clearly visible wave field with larger wavelengths and heights than the rest of the small basin, where waves are only created locally once the wind reaches the water surface. See how on the left edge of the basin the water is sheltered from the wind by the higher edge of the sand bank?
Again, what a pretty landscape!
I really like the contrast of the lush green grassy areas and then the sandy muddy tidal river in the background.
Walking a little further, we now see a large muddy area. When we were walking here, a local told us that when he was a kid, all this area was also grass land and it only became sandy and muddy a couple of decades ago. Fascinating how the landscape changes!
But even on timescales of hours the landscape changes, and all the sandbanks and channels move with each incoming and outgoing tide.
It’s so beautiful here!
Our walk took us away from the water and up a little hill, but that gave us the opportunity to look at the channels from a different perspective.
And even the whole estuary. Do you see the rail bridge below? That’s the one we saw in the very first picture of this post.
Back in Arnside, we are approaching low tide. Which means that we have lots of freshly exposed mud with new ripples in it, as well as still water running off it. Below you see a really cool turbidity current coming out of the channel with the seagull, going into the larger reservoir. See how it carries mud with it and how the channel is meandering and clearly changing right in that moment?
Another picture, just moments later, and already has the shape of the channel changed!
Or the edges of this little basin that get exposed little by little as the tide goes out.
And then there is of course more wave watching to be done. See how this wave changes direction as it runs around the little headland?
And thanks to two kids playing in the water, we get even more waves where they threw a ball into the little basin.
And those waves spread over time…
Checking in with the seagull and the turbidity current again. See how much dissolved mud is being washed out all the time?
And as you might have guessed in a tidal river like river Kent — there is even more to see. Which is why we came back a couple of days later to see what all the warning signs were about…
For me, it is not the cute little hide which is a perfect spot for seal and bird watching, for me it is — obviously! — what is going on with the waves! So much so that I spent the better part of an hour looking at the opposite direction of where all the seals were frolicking in the waves (except for one that came and played in the most fun part of the sea — more about that later).
Looking at the picture below, do you notice how different the different areas of water surface look? To the left of the wave breaker and going offshore from there, the surface is quite rough, with many waves of different wavelengths. But then going directly offshore from the wave breaker, the surface is smooth(er)! Followed by a rougher stripe, before it becomes smooth again, and a couple of well-defined wave crests reach the shore.
Zooming in on that area right off the wave breaker, you see that there are actually waves breaking towards the smoother area, away from the beach. Any idea what’s going on here, what might be causing those waves? (Hint: Even though there is a boat in the background, it is not some ship’s wake!)
What we can observe here is actually a pretty cool phenomenon, called a hydraulic jump. Due to the tide going out, there is a current developing around the tip of Walney Island, going from left to right in the picture above. This current goes over the still-submerged part of the wave breaker. Since the cross section through which the water has to squeeze is all of a sudden a lot smaller than before and after, the water has to accelerate. And it accelerates so much that waves traveling on it are just flushed downstream and the surface looks smooth(er). Only when the cross section is wider and the water has slowed down, waves become visible again.
The spot where waves are exactly as fast as the current, but running against it, is called “hydraulic jump”. You can spot it right where the waves are breaking: They are trying to go back upstream but don’t manage to, so they stay locked in one place (see here for an analogy of people running up and down escalators to explain this phenomenon). You do see hydraulic jumps “in the wild” quite often, for example in rapids in rivers (and even more so in regulated rivers, very nice example here!). In case of the hydraulic jump right here, there was a seal playing in the current, clearly enjoying the wave action (and quite possibly also feeding on poor fish that suddenly get swept away with the current).
And indeed, 20 minutes later, the same spot looks like this: the surface roughness is a lot higher towards the right of the wave breaker, but all in all there are much fewer, and much smaller waves.
And another 20 minutes later, the formerly submerged wave breaker is revealed!
I find it always so cool when you see a wave field and just from what that wave field looks like, you can deduce what the ground underneath has to be like! In this case from seeing the hydraulic jump, you know that the wave breaker has to continue on offshore.
Wanna see the whole thing in action? Then here is a movie for you!
And the coolest thing is that this spectacle will repeat with every outgoing tide, so pretty much twice a day! And I am fairly confident that it will also happen halfway between, again, when the tide comes in and the current goes in the opposite direction. I would love to go back and check!