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!
Astrid, #wavewatching supporter from Day 1, sent me these pictures for a #friendlywaves post. Today, I want to start with a spoiler picture (or, rather, I did start with a spoiler picture already — see above) that shows you the setting at low tide to help us explain the wave pattern that we then observe at high(er) tide.
Note the headland in the picture above? Below shows what it looks like when it is covered in water:
Astrid, as a real #wavewatching pro, also sent me a video, so I can show you the super cool interference happening here.
Wave crests from far offshore (probably caused by a storm somewhere far away) arrive in shallower water and get broken up into parts on either side of the (now submerged) headland. But on either side, the wave crests also change their shape, being refracted towards the headland. And some of the wave crests make it over the headland, now at an angle to each other, meeting waves from the other side. And where they meet, they steepen up and even break occasionally. Doesn’t it look super cool to watch waves run towards each other in such a way, creating these interference pattern?
This wave pattern always reminds me of one that I saw years ago — coincidentally with Astrid! — when we were in Iceland in 2013, the day after my dad’s heart surgery. And while watching those waves then was beautiful and calming, seeing this pattern still always reminds me of a pretty traumatic time. So I am happy that this new wave pattern will now at least partially overwrite some of those memories with a very happy day: Herzlichen Glückwunsch und alles alles Gute, liebe Simone* & family!
*That is Astrid’s friend Simone, not my own sister Simone, although of course alles Gute to her, too :-)
I love #friendlywaves! Victor sent me the picture above. He took it in 2017 in Tampa, Florida, and I think it’s so fascinating! There is so much going on, let’s try to make sense of it!
First, the most obvious thing making waves here: The two boats. Clearly they are making waves, and they might explain a lot of what we see here. But on the other hand, they might not.
Below, you see the part of the wave field that is 100% due to these two ships: Their V-shaped wakes (in red) and the turbulent wake behind one of the ships (in yellow).
The very prominent wave pattern (marked in red in the image below) might be due to these two ships as was suggested to me, but if it is, then those ships changed course quite drastically before they created the waves I marked in the previous picture (and I can see no evidence of such a change of course, usually a turn would leave a trace similar to this one).
If the boats, as I assume they did, came out from underneath the bridge and sailed in a more or less straight line (and that seems to be the case judging from their wakes as indicated in the picture above), there is no way they could have made waves that travel in front of their V-shaped wake. Similarly to how you can’t hear the supersonic aircraft before the supersonic boom (because the sound can’t travel faster than the speed of sound and the pressure signal thus gets formed into the Mach cone), waves can’t outrun their wake (which is like their 2D Mach cone). So I don’t believe that those waves were made by those two ships. Rather, I believe that they were made by a ship that is no longer visible in the area we are able to see.
So remember, this is the wave pattern we are trying to explain (Marked is only one wave crest, but you see that there are several parallel to the marked one):
We do nicely see how the wave is reflected by the straight sea walls. But what direction is it traveling in? And what caused it? Let’s speculate!
First: let’s consider the very weird shape of the body of water shown in the picture. Quick search for Tampa on Google Maps lets me believe is that the picture was taken more or less from the position of the white star and the view is the area between the two red lines. Looking at that map, we see that the water we see opens up into four different water ways: One to the north, one to the east, one to the south east, and one to the south west. The two to the south eventually open up into Tampa Bay.
The wave field that we are trying to explain would look somewhat similar to what I drew in below (green):
My best explanation of that green wave field above is this: A boat that went on the course that I drew in in yellow:
So far, so good. Wanna know why I believe this is what happened? Then this is the picture for you!
Assuming the boat followed along the yellow track, the other lines are the wake it would have produced:
green: Those are two parts of the wave field that I marked above that I am fairly confident of: The wake propagated across the body of water, got reflected and came then over towards the photographer. Note how not all waves reach the shoreline close to the photographer yet? That’s because they are the “newer” waves that haven’t traveled for long enough to reach that spot
light blue: The “newest” waves that aren’t very long yet and are traveling in an area where we can’t clearly make out the presence or absence, let alone direction, of waves. They are fanning away from the “green waves” because the ship is turning (similar to here).
dark blue: Those is a part from the wake that originated on the other side of the ship, got reflected, and now traveled across the body of water to reach the point where the picture was taken from. They do so at an angle that looks like they might be reflections of the incoming green waves (which is another possibility which I can’t rule out with 100% certainty). Newer wakes from that side, once they’ve been reflected on the shore, will lead to waves almost parallel to the green part of the wake and would be indistinguishable from those in the picture.
orange: Those are “old” wakes that must have happened when the ship came out of that inlet, but that would not interfere with our picture because their reflection stays caught within the inlet itself.
This is the best explanation of what must have happened that I can come up with, and I have thought about this quite some time (more on that at the end of this post) :-)
But then there are tons of shorter wave length waves that we have to explain, too: See those marked in red, yellow and green below.
I am confident that the ones I marked in red are wind-driven waves coming across the open area. Their direction also agrees quite well with the wind directions the flags indicate (marked with a white arrow above). I believe that the ones I marked in yellow and in green are two separate wave fields at a slight angle, but that might be an optical illusion, I am not quite sure.
If we go back to the map, I believe the wave fields I marked above would look pretty similar to the ones I drew in below (I changed the red waves above to magenta waves below, because red was already taken. Note the wind direction marked with a white arrow: it looks pretty much perpendicular to the now-magenta wave crests):
And looking at the angles in that depiction of the waves, I could imagine that the green wave field is a reflection of the magenta wave field where that one hits the shore on the side where the picture was taken from (see light blue wave crests). As for the yellow one: I still have no idea what caused that. But maybe there need to be some mysteries left to life? ;-)
To end on something that I am confident in: The half circles near the bottom of the picture are the result of something (two buoys? two small boats?) moored on that pier, bobbing up and down in the waves, thus radiating wave rings with shorter wavelengths and higher frequency than the wave that is exciting the movement.
But after all this hard work (more on that at the bottom of this post) — let’s take a minute and look at those beautiful interference pattern again where the wave fields cross each other and create a checkerboard pattern. How amazing is this?
Phew! I love #friendlywaves, but this was quite a challenge! How did I do, Victor? :-)
If you or anyone else have any comments or suggestions — I would love to chat about alternative explanations!
P.S.: Just to give you an idea of what my process was like: It involved late night scribbles on a tea bag (because that was the best “paper” I had available on my bedside table in the hotel in Manchester) and I needed to play scenarios through in my head…
…and some sketches on my phone while I was on a train…
Inspired by the absolutely brilliant job that Kati is doing for my project GEO-Tag der Natur, I have recently started experimenting with “Insta stories” on the topic of wave watching.
Insta stories, for those who aren’t familiar with them, are a special type of post on Instagram that only stays visible for 24 hours (unless you save them as highlight, in which case they can be watched until you decide to delete them). They are usually used to give quick glimpses into what’s going on that day, and can be anything from random snap- or screen shots to elaborate stories. The latter is what Kati has been doing for GEO-Tag der Natur — she tells cute and engaging short stories about different topics, using photos and video clips, which she combines with fun gifs to make them even cuter (if you have an Instagram account you can watch them in the highlights of our account).
So that’s what I have been trying to do, too.
My first attempt is posted below — except that what I post below doesn’t contain the links and gifs and stuff, because it turns out that while you can export stories from Instagram, I couldn’t convert them into a format that my blog or vimeo would accept and still keep the gimmicks (original version here). But I still like the format of telling a story. What do you think?
The feedback I got on that story was super positive, so I decided to do it again.
Since my second Insta story contained so many cute gimmicks, I didn’t even attempt to export it, but wrote a separate blog post using the same videos and pictures (But you can watch the story — including the cute gimmicks! — here).
(And then, when writing this blog post, I realized that if I did a screencast, I could that then convert into something my blog accepts. Duh! So below you can watch my story the way I see it when logged into my account — including how many people watched it and all the buttons that I could click to edit and exit etc.. In the future I should probably just do the screencast from a different account to give you a cleaner view…)
By this point, it started bugging me that I was putting effort into Insta stories but that I didn’t have a good way to use them on my own blog (remember, I hadn’t come up with the screencast idea yet). I like having full control over hosting the stuff I don’t want to disappear, and I don’t like telling the same story twice for different platforms (although I realize that customizing stories for each platform and thus audience is always good advice).
So the next story didn’t use fancy gimmicks (except on the last slide), and I could export the pictures and combine them into the .gif you see below.
Mmmmh, I like that!
Except now I am thinking I should still do an English gif for my blog and keep the German one to my Instagram. Which, again, feels like a lot of work for something that I want to do in random pockets of time like on my commute, not as a real task. So my next story was a language-free one:
So in the end it turns out that classical gifs work quite well for transporting my stories. Not nearly as cute as they could be, but maybe that’s ok?
What do you think? What style of Insta story would you like to see more of?
Option A: Give me cute little gimmicks like ducks on surfboards and ladies jumping into pools!
Option B: GIFs work well and I don’t need all the cutesy gimmicks
This is the story of a pilot ship, merrily sailing along on a beautiful day, making waves.
Since it’s windy and Kiel fjord is a little choppy, the waves break and both side of the V-shaped wake with the pilot ship at its tip are visible. See the foam of the breaking waves? And in the middle of both sides of the V, visible as a lighter-colored stripe, there is the turbulent wake where the ship’s propeller has set the water into chaotic motion.
Both constituents of the wake — the V-shaped feathery waves and the turbulent wake — stay visible for quite some time after the ship has passed!
Can you spot the one side of the V approaching the shore?
A little while later, the pilot ship returns. nice bow wave (where its bow is breaking the water apart) and all. Also note the wave field inshore of the floating wave breaker — it is a lot calmer than on the outside!