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Chapter 8 - Waves — Transcript

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0:00Hello, I'm Dr. Jeff Ashley and welcome
0:02to chapter 8. Chapter 8 deals with
0:04waves. Let's get started. So, if you
0:07open up your e textbook, you'll notice
0:08that one of the images, the first part
0:10of this chapter is this surfer riding
0:13this seemingly gigantic wave. That wave
0:16is actually one of the waves that are
0:18produced seasonally in Nazare, Portugal.
0:21Let's take a look at this video. Name is
0:24McNamera from Hawaii. Like to surf big
0:27waves.
0:31In Nazareth, you really never know what
0:33you're going to get. It's so bizarre.
0:35And it's like you take Jaws, you take
0:37corduroy, escandido, and you take
0:40Yorbre and then put them on steroids all
0:43together. And we got
0:45Nazareth. I knew it was going to be the
0:47biggest wave I've ever rode and I knew
0:48what I was getting myself into. I've
0:50been preparing for it for years. Just
0:53the bait wand of the world. When it
0:55comes to big waves, it's I found the
0:57Holy Grail. Sometimes I look at it and
0:59go, "Not that big at all." And then
1:01other times I look at it and go,
1:03"Wow." When you're in the water looking
1:05at this wave, it's a lot bigger than it
1:08has been
1:09photographed. The main part of the wave
1:12where it was really big, you can't even
1:14see it. This picture that went around
1:16the world, that was the end of the wave
1:18when it's peeking out is half as big as
1:20what it was in the beginning. really
1:22weird because it like took off and kind
1:24of was trying to find where it was going
1:26to break and it broke right at the top,
1:29but then this wave went for like
1:32forever and then it kind of backed off
1:35and then it it went into the inside and
1:38started to break again and that's where
1:40I kicked out. When I'm in the ocean, I
1:43really am totally comfortable. And when
1:46you're riding waves or in any situation
1:49in life, if you're in the moment, then
1:51you're really connected to what's going
1:53on. And I I usually just deal with the
1:55situation they come. I actually really
1:57enjoy the situations, whether it's
1:59getting sucked over by an 80 foot wave
2:01or or uh you know, going in to pick up
2:04my friend in a really dangerous spot. Um
2:07just deal with it.
2:09People have to come see for
2:23themselves. You're interested in
2:25watching this. This is actually coming
2:27from a miniseries called the 100 foot
2:29wave. And although it's still elusive
2:31going to 100 ft, you saw here they're
2:33getting pretty close to it. Just
2:34amazing. So, let's start off with the
2:37question. What are waves? Waves are
2:40progressive waves. And what are
2:42progressive waves? Well, they form based
2:45on three constituents here. There's the
2:47longitudinal wave motion back and forth
2:50where particles move back and forth in
2:52the direction of an energy transmission.
2:55These waves transmit energy through all
2:57states of matter, but we're looking at
2:59water. Then you also have a second type
3:01of wave that is a transverse wave.
3:03Particles move back and forth at right
3:06angles to the direction of the energy
3:08transmission. These waves transmit
3:10energy only through
3:12solids. Orbital wave and these become
3:15what we see in the open sea orbital
3:17waves. Or orbital waves are particles.
3:20Imagine little particles of water that
3:22move in an orbital path. And these waves
3:24transmit energy along an interface
3:26between two fluids of different
3:28densities. Sometimes liquids or gases.
3:31But in the open ocean, we're talking
3:32about uh wave energy in the form of an
3:35orbital wave in the liquid phase only.
3:38So let's look at the nomenclature or
3:41characteristics of a wave. And this goes
3:44back to any wave description that you've
3:45seen maybe in physics class that if you
3:48have a wave form here and it's kind of
3:50sinosoidal as shown here. Uh the top is
3:52called the crest and the bottom of that
3:54wave is called a trough. We have the
3:57wave length which is the crest to crest
4:00or trough to trough distance or it can
4:03be anywhere from here to equally here.
4:05It's the whole waveform one waveform and
4:08that's called the wavelength. We also
4:10have pictured here is a still water
4:12line. That's an absence of waves. But
4:15you can measure height as the distance
4:18from the crest to the trough. So that's
4:20defined as height. Here we have some
4:23other characteristics or nomenclature of
4:26waves and you can look at wave height uh
4:29we just saw that that's the height given
4:32by h wavelength as we saw up here wave
4:35length is given by l wave period what is
4:39that given by t it's the time it takes
4:41for two successive waves to pass a
4:43particular point or the time it takes
4:45for that full waveform to pass a
4:48particular for um point. So if you're
4:51standing there with a stopwatch, you
4:53calculate the amount of time for that
4:55one waveform to pass by. Wave frequency,
4:59you're taking that time and putting it
5:01one over time. It's the number of waves
5:02that pass a particular point in a given
5:05period of
5:06time. And amplitude, the amplitude is
5:09equal to 1/2 of the wave height. So it's
5:12the still water line to the crest. As I
5:15said, there were three types of waves
5:17possible. But this circular motion, this
5:20orbitalike description is actually what
5:23happens to waves in the ocean. So wave
5:26particles move in a circle, the wave
5:28form travels forward and wave energy is
5:31advanced in that. So this circular
5:33motion, the diameter orbital motion
5:35decreases with depth. So, we can see
5:38that if you have a waveform here and
5:39maybe your little rubber ducky going up
5:41and down and up and down, beneath that,
5:44you have a series of orbitals moving,
5:46not your rubber ducky, but moving
5:48particles of water. As you go down and
5:51down and down, they get smaller and
5:53smaller until they're this point where
5:55there's no apparent movement in that
5:57circular
5:58pattern. This is called the wave base,
6:01and it's depth where the orbital
6:03movement of particles stops. and it's
6:06usually given by the wavelength L
6:08divided by two. There are three types of
6:12ocean waves. There's a deep water wave
6:14and scientists say that these do not
6:17feel the bottom of the ocean. The
6:19circular patterns diminish as we go
6:21down, but you see they become
6:23non-apparent here. So no movement of
6:26water particles, but that's above the
6:29depth of the ocean here. So these are
6:31deep water waves. They are in deep water
6:33where you have tremendous depth. The
6:36little orbital patterns here although
6:38they diminish as you go down do not fuel
6:40the bottom of the basin of the ocean. On
6:43the other hand, you can have shallow
6:44water waves happens in shallow water.
6:47Water depth D is less than uh L divided
6:51by 20 usually. And the water actually
6:54feels the seafloor. So in these circular
6:56patterns which we saw before, they don't
6:58dissipate entirely before you reach a
7:01depth. They actually are feeling the
7:03bottom of the ocean or the basin or the
7:07shoreline. Most likely wind generated
7:10waves in shallow areas near the seashore
7:14actually generate these shallow water
7:15waves. Other things are responsible for
7:18too and we'll talk about that towards
7:19the end of the chapter. But things like
7:21tsunamis, um tides, which we'll discuss
7:23in the next chapter. So here we have the
7:26two categories we spoke of. We started
7:27with the deep water waves. When do you
7:29have that? When wavelength is less than
7:32two or the depth is greater than the
7:34wavelength divided by two. So open water
7:36here as the name denotes shallow water
7:38waves. They're feeling the bottom. When
7:40is that? When your depth is less than
7:44your wavelength over 20 as I said. And
7:46then in the middle you have this sort of
7:48gray zone where you can have um these
7:50things called transitional waves.
7:52They're beginning to fill the bottom of
7:54the ocean basin or seashore. So this is
7:57an idealized uh plot that plots wave
8:01speed. These things are moving. They're
8:04um being propagated through the medium,
8:06the water medium and water depth. And
8:09here you have the three distinct and
8:11this is idealized three distinct forms.
8:14You have the shallow water waves in
8:16shallow areas, right? And then you have
8:19these transitional waves appearing not
8:21as shallow water waves and not quite as
8:23fully developed as deep sea waves. So
8:25they're transitional and then in deeper
8:28water and again depends on the wave
8:29speed you can have your deep water waves
8:32here in green. This is an idealized
8:35pattern. How are waves formed? They are
8:38generated by wind. So that chapter on
8:41atmospheric conditions and wind
8:43generation is really important. It comes
8:45into play here. They can be generated by
8:48earthquakes, either terrestrial
8:50earthquakes or often enough those
8:52earthquakes that are happening at plate
8:55boundaries. They can generate be
8:57generated by storms, changes in pressure
8:59like a hurricane or a low pressure
9:01system. And as we'll see in the next
9:03chapter, waves can be formed by the sun
9:06and the moon and these are called tide
9:08waves. So Stumble provided a model for
9:11deep water creation of waves here in the
9:14open ocean and he said it starts off
9:16with the wind blowing over the surface
9:18and that creates these small orbital
9:20patterns here and it generates what we
9:22call capillary or capillary waves on the
9:24surface. They're small and these are
9:26akin to the example of blowing on your
9:28coffee and you see these small little
9:30waves. So as I said capillary waves that
9:32restoring force is gravity but it's also
9:35surface tension of water. The restoring
9:38force here of these waves if you shut
9:40off the wind is totally gravity not
9:42surface tension. There are three
9:44important
9:46factors to increase the amount of energy
9:49transferred to the waves. So waves take
9:52energy in the form of uh wind. Three
9:56factors here though it is the wind speed
9:59um the direction of the wind and the
10:04fetch. So fetch is the distance over
10:07which the wind blows. So here we have a
10:09storm here and it's very windy. This
10:11would be the fetch. That distance over
10:13which the wind is
10:15blowing. We have the wind speed here.
10:19And we also have the
10:22direction. Remember that plot I just
10:24showed you? Wave height versus uh uh
10:27sorry, this is a different plot. This is
10:29wave height versus wind speed. So it's
10:32not all truly about just the speed of
10:34the wind. It has something to do with
10:36fetch and the directionality of it as
10:38well. So you can see real data here. It
10:40doesn't fit a nice straight line. As you
10:42increase wind, you increase wave. It
10:44depends on some other things. We looked
10:47at scales, scales for hurricanes, scales
10:50for grain size. Here is another scale.
10:52It is the Bowfort wind scale. And I love
10:56this one because it shows you of the sea
10:58surface here and what that looks like.
10:59So development of waves it it's based on
11:02your wind speed. It creates a number
11:05here for the bow for number and it also
11:08has a description here and an
11:09appearance. We'll skip down here uh to
11:12the highest number which is a 10 which
11:14is a storm. We've got the wind speeds
11:16and you have very high waves with
11:18overhanging rests. Foam is blowing. So
11:21it's a fully developed sea as we call
11:25it. So what is the maximum wave height
11:28denoted? Uh well, the US Ram Mo
11:32Remopo in 1933 uh it was 152 meters long
11:37ship that was caught in a Pacific
11:39typhoon. The waves were estimated to be
11:42over that 100 ft mark. Um like the
11:45surfing video we just saw was around 90
11:48mid 90s. Um but this is seems to be the
11:51highest recorded wave height at 34 m or
11:54112 ft high. Uh previously it was
11:56thought that waves could not exceed
11:58around 50 feet. So back in the uh 30s it
12:02was seen that that's not true that they
12:04can develop to sort of super heights
12:09here. The cause damage um the Ram mopo
12:13was not damaged but other uh carriers
12:18like the Bennington were were and here's
12:20the damage here. though either ships can
12:22be damaged by this um waves hitting them
12:25or in actual fact if we go back to this
12:28if their ship is long enough and it is
12:31suspended from the crest to the crest so
12:34there would be no sea below they can
12:37actually break in part and that was
12:38thought to be what happened to the
12:40Edmund Fitzgerald on Lake Superior it
12:42was carrying iron ore very heavy long
12:45ship loaded up with iron ore and there
12:48was a huge storm you think lakes don't
12:50develop huge waves. They do in a very
12:53long wavelength and the ship was almost
12:56suspended between the crest to crest.
12:58So, not coming down like here, but it
13:01was actually held in midair and that was
13:04enough to cause a fracture in that ship.
13:06Um, we see that wave height can be
13:08determined and this sort of looks like a
13:10temperature plot, but it's not. It's
13:12actually looking at uh wave height and
13:16wave direction. So these little vectors
13:18are showing you the direction of the
13:20waves and also the wave height. We'll
13:22come back to this as we look at possibly
13:25using waves for energy generation. And
13:27where's the best spot to do that? Again,
13:30satellite image of wave height. Um you
13:33see that in the very stormy southern o.
13:35We talked about that in chapter 1 when
13:37Shackleton was trying to escape the ice
13:40pack and venture to the whailing station
13:42that he had to transverse part of the uh
13:46swirling area below here um all in red
13:50extremely high waves here. So he must
13:52have endured a lot of that as he
13:54traveled to off the coast of South
13:57America right over here. So fetch the
14:00distance at which the wind actually
14:02blows over and the duration how long the
14:05wind is actually blowing is used to
14:09describe this thing called a fully
14:10developed sea and we call it as an
14:12equilibrium condition where waves cannot
14:15grow any higher. It's that point where
14:19waves grow to their maximum before they
14:21start to spill over or create what we
14:24see often in storms like white caps. So
14:26it's the fully developed waveform right
14:29before it becomes uh energy expendable
14:33in the form of spilling or
14:36uh plunging over. We also have to keep
14:38in mind that the open ocean is very
14:40complicated that you can have waveforms
14:42that come together in phase or out of
14:44phase. So I remind you of just some
14:47waveform uh characteristics here. Uh
14:50imagine that you have a waveform here
14:53and one that is in phase with that. So
14:56it's totally uh the same that if these
14:58wave fronts come together they will
15:01heighten their amplitude. So it's
15:02additive and we call that constructive
15:05wave interference. We have destructive
15:08where they're totally out of phase. They
15:10actually can negate. So you see here the
15:12crest and the trough and it's completely
15:15out of phase here. It's reversed and
15:18that will nullify the effects. You'll
15:20get a still water sea surface as they
15:23call. But most often you have waves
15:26interfering with different waveforms to
15:28create something that we call is a mixed
15:31interference. This is what usually
15:33happens in the open
15:34ocean. As we can see here, imagine the
15:37open ocean, right? And we have these
15:39different waveforms coming in either
15:41inphase, out of phase. But it can get
15:43really complicated. It's not about just
15:45two phases coming together. It's uh a
15:48whole bunch of phases here depending
15:49upon the wind and the duration of the
15:52wind and the fetch. So here you can have
15:55a zone of destructive in uh constructive
15:59or more often than not mixed
16:02interferences. So you get something like
16:04wave height. If you're situated here,
16:06you get very variable wave height.
16:09Because of that, in certain areas, you
16:11might have a constructive
16:13interference that enables these waves to
16:16get super high. Super high waves, sort
16:19of out of the ordinary, uh, not so
16:22prevalent, but they do happen, are
16:23called rogue waves. If you ever watch
16:25the movie The Perfect Storm, you got to
16:28watch it because that actually depicts
16:30the true story of a fishing vessel that
16:33gets caught in a storm and actually sees
16:36one of these rogue waves. I won't give
16:38it away, but it's incredible footage. If
16:40you can just Google that, you can watch
16:41that two-minute video of them
16:43interacting with the rogue wave. So,
16:46what happens in the open ocean? Well, we
16:48saw a little bit of that. We can have
16:50waveforms that are just as we imagine
16:53these syosoidal waves or interference
16:56areas where you can have mixed
16:57constructive or destructive interference
16:59or you could even have a rogue wave.
17:02That's open ocean. But what happens as
17:04these waveforms, these transition
17:06propagation of energy
17:10forms hit the seashore? So, we're going
17:13to find out. So, let's head towards not
17:16the open ocean, but let's head towards
17:18the shore. The surf zone first of all is
17:20that zone of breaking waves near the
17:22shore. We have what's termed sholing
17:24water. Water becoming gradually more
17:27shallow. Okay? So when deep water waves
17:30encounter sholing water less than about
17:33a half of their wavelength, they become
17:35transitional waves. And then as they
17:37progress to the surf zone, they get to
17:40be shallow water waves. As a deep water
17:43wave becomes a shallow water wave, that
17:45means deep water not feeling the bottom
17:48to a waveform that now starts to
17:50interact with that bottom. Here's what
17:52it does. Those little orbitals are now
17:56feeling the bottle bottom, but they
17:58actually slow the wave speed down. So
18:02every time a deep water becomes a
18:04shallow water, your wind speed
18:06decreases. Your wavelength decreases as
18:09well. Your wave height increases. And
18:12this is a no-brainer. You can look
18:14offshore and you see these rolling waves
18:17that are maybe a couple meters, but when
18:19they start to fill the shoreline, that
18:21shallow water, they increase in height.
18:24And if you're swimming out there, they
18:25can become quite big. So wave height
18:27increases. Wave steepness, which is
18:30height divided by wavelength, also
18:32increases. And this leads to the
18:34eventual propagation of this wave energy
18:37into a spilling or plunging situation
18:40where the wave cannot now remain in its
18:43wave form. It just spills over and it
18:46releases that energy. That's when the
18:48wave actually totally fuels the bottom
18:51and can no longer exist as a wave form.
18:54The money shot here. If you're trying to
18:56explain how waves interact with the
18:58shoreline, here we go. So waves uh
19:01longer wavelength. they're not feeling
19:02the bottom. As they start to feel the
19:04bottom, that frictional force slows down
19:07that waveform, right? But that energy is
19:10the same and it propagates into lowering
19:14or decreasing the wavelength. So, the
19:15waves are getting closer and closer
19:17together, but their height is
19:19increasing. Here's where they no longer
19:22can sustain that waveform energy, and
19:25they spill over. They're releasing that
19:27energy in the form within the surf zone
19:30of waves breaking forward. So when that
19:33release happens, we call these breakers.
19:35So where are the breakers in the surf
19:37zone? That's when the energy is being
19:39released and you see a lot of white foam
19:42or white water, right? So surf as swell
19:45in distance uh distant storms. Waves
19:48break close to the shore as we saw and
19:50we often see these uniform lines of
19:52where they're breaking and these are
19:53uniform breakers. The surf is generated
19:56by local winds. Usually choppy, high
19:58energy, unstable water is most commonly
20:01what you actually see as the visible
20:03form of these waves dissipating their
20:06energy. These are shallow water
20:08waves. There's three types of breakers.
20:11Spilling, plunging, and surging. And
20:14they have mostly something to do with
20:17the depth and the broadness of the
20:21break. So I'll explain that in a minute.
20:23So if you have a gently sloping
20:25seafloor, gently sloping, and we all
20:27have been there to the shore, you walk
20:29out and it just slopes really, really
20:31gently, right? There's no drop off or
20:34decrease in that slope at a large angle.
20:37You have energy that is uh expended or
20:40dissipated over a longer distance. Water
20:43just slides down the front slope of
20:46that. It doesn't curl. It just slides
20:48down the front. Plunging breakers are
20:50those that surfers really like because
20:52you can see how we go from just spilling
20:55to now curling. This happens when you
20:58have moderately steep seafloor. So if
21:00you're waiting out like this, you might
21:02go down like that. The angle is more
21:04impressive than in spilling breakers.
21:08Wave energy is expended over a shorter
21:10distance. As I said, best for surfers.
21:13We get a curling wave crest. And the
21:15last one is you have the steepest
21:17seafloor. So, you've all been there,
21:20right? Walk into the water and it really
21:22I call this the drop off. It's a steep
21:25inclination here or a complete drop off.
21:28Energy is spread over a really short
21:31distance. Great for body surfing. Here,
21:33waves break ultimately uh close to the
21:36shore or even right at the shoreline. We
21:39have to talk about how waves are
21:41refracted and this comes from physics.
21:43We can look at the refraction of wave
21:45light uh energy but we can also see it
21:48in uh wave as a sea surface phenomenon
21:52as well. Waves rarely appro approach the
21:56shore at perfect 90° angles. As they
21:58approach shore they bend. So the wave
22:00crests are nearly parallel to the shore.
22:02Wave speed is proportional to the depth
22:04of water. Shallow water waves are
22:06slowing down. You generate uh different
22:09segments of the wave crest that travel
22:12at different speeds. Let's see what
22:13happens. So here we have waves not
22:15coming in parallel to the shore which
22:17happens most of the time. But you can
22:19see that the waves
22:21here which are deep sea waves begin to
22:24feel the bottom of the the uh uh sea
22:28within the surf zone. They slow down. So
22:31these waves begin to slow down. These
22:33are still moving at the same speed. At
22:35that point the waves are feeling the
22:37bottom. The wave speed, as we said
22:39before, slows down and you get this sort
22:42of a refraction happening here based on
22:45the shoreline. That was a straight
22:47shoreline. If you have features like
22:49this, we have a peninsula or um an
22:53outcropping here of land, we get again
22:56the same thing happening, but we get the
22:58waveform bending and maybe building up a
23:01lot more energy here. So, the vectors
23:03are all heading towards that little cape
23:05here where the lighthouse is. That's
23:07going to be a high energy zone and
23:09probably erode that at a faster rate.
23:12Here we have the waveforms because
23:14they're not coming in totally parallel.
23:16They're slowing down. They're probably
23:18going to build up the beach more here.
23:20There's less energy. So waves depending
23:22upon how they refract can eat away or
23:25erode at the coastline or they can
23:27dissipate that energy nicely and maybe
23:30even build up beaches. So here we
23:32actually see that gradual erosion of the
23:35headland or this cape here. And in areas
23:39where that energy is dissipated. So the
23:41buildup of energy here, you can see
23:42these waves. You'd get a lot of erosion
23:45on this side and you'd get a lot more
23:48energy dissipation and sediment and sand
23:51being deposited here. An accumulation.
23:54Waves can be refracted and they can be
23:56reflected. So when they hit a barrier,
23:58they can actually bounce back. reflected
24:01waves can interfere with the next
24:02incoming wave. Surfers love this. Uh so
24:05here we have a man-made or humanmade
24:08structure here called a jetty and that
24:10is reflecting the waves. So they come in
24:14and it's reflecting it. So here's the
24:16new wavefront but you have the usual
24:18waves coming in. So this is an area of
24:21convergence and that's a buildup of one
24:24waveform with a reflected wave and it's
24:26going to build up the amplitude or
24:28height. So in this area, this is called
24:31the wedge. It's from California here.
24:33But this happens along the east coast as
24:35well that have uh many jetties or
24:37obstructions as well. And this is
24:39reflection. So waves can be reflected.
24:40It's kind of like a constructive
24:42interference here. So here we just have
24:44a pictorial of that. Waves can even be
24:47reflected and refracted into quiescent
24:50zones. So you think this would be a nice
24:52harbor and it is. Harbors are great
24:54because they dissipate that wave energy
24:57and create smaller waves or quiescent or
24:59quiet zones. So we have to talk about
25:02tsunamis which I just find fascinating.
25:05They are seismic sea waves. They
25:07originate from a sudden seafloor
25:09topography change. So imagine um I think
25:13we saw this video that we have
25:15converging plates and then we have a
25:18slippage that uh it goes beneath really
25:21quickly that will allow the sea surface
25:24to sort of bend down towards it to mimic
25:28what's happening on the seafloor. So if
25:30your seafloor is giving away and giving
25:32out, your sea surface will equally do
25:35that. And look what I formed. I formed a
25:37really long wavelength wave. So,
25:40earthquakes are one and the most common
25:42ways to do this. Underwater landslides
25:44can do it. Uh, volcanoes being
25:46collapsed. Underwater volcanic eruption
25:50can do this as well. And a last one, a
25:52meteoric or a meteor impact can create a
25:56wave. Tsunamis are extremely long wave.
26:00Look at this. 200 uh or 125 200
26:03kilometers or 125 miles greater than
26:06that. So off the coast if you have this
26:09seismic earthquake happening here that
26:11is giving way the seafloor is giving way
26:14and then the water surface will actually
26:17because of gravity give way as well or
26:19bend a little. They're extremely long
26:21wavelengths. They
26:22encompass the entire water column
26:25regardless of the ocean depth and can
26:27pass undetected. If you're sitting on a
26:29boat, you're not going to actually feel
26:32yourself going down with that collapse
26:34of the sea floor. You won't even feel
26:36anything. These are really, really small
26:39heights
26:40here. Speed proportional to the water
26:43depth. So, they're very fast in the open
26:44ocean. Here's where it gets messy when
26:47they approach land. So here we have the
26:50seafloor being fractured and triggering
26:52this energy and the sea surface
26:55responding to that generating a very
26:57long way range wave called the tsunami
27:00and that starts to travel and it travels
27:02quite quickly. As that long
27:06wavelength waveform of the tsunami
27:09approaches a shallow area we know what
27:12happens right the speed decreases but
27:15the height increases. So our wavelength
27:18also will decrease here. But more
27:21importantly is our wave height increases
27:24substantially. So out here if you're
27:26sitting on a boat this is
27:27overexaggerated not to scale. You won't
27:29even feel that up and down motion of
27:31this large waveform that was generated
27:33by the tsunami. But once it reaches or
27:35interacts with a shallow area it
27:37certainly will. Sea level can rise up to
27:40a staggering 40 m. That's 131 ft when a
27:44tsunami reaches shore. Here you have
27:46images of the so-called Boxing Day
27:49tsunami. It happened in 2004 on December
27:5326. And there's some horrific video out
27:56there uh that you can watch. There's
27:58actually a wonderful movie um that was
28:01very well done about a family surviving
28:04this. Tsunamis mostly occur in the
28:06Pacific Ocean and more often than not
28:08they're generated by undersea
28:10earthquakes and sometimes volcanic
28:12eruptions extremely to damaging to
28:15coastal systems and loss of human lives.
28:18Here we have in 1946 Hilo Hawaii where
28:21there's $25 million damage at the time
28:23and 159 deaths. A lot of other
28:26historical tsunamis. Crackkrakatoa was
28:28volcanic eruption created in 1883. We
28:32have the Indian Ocean. This is Sumatra
28:34again, the Boxing Day tsunami in 2004.
28:38And more recently in Japan, we can all
28:39remember this perhaps. In 2011,
28:42magnitude 9.0 earthquake induced a
28:45tsunami that created damages of 235
28:48billion, the most expensial expensive
28:51natural disaster in world history. And
28:54we can also remember too that it damaged
28:56a nuclear reactor and emitted nuclear
28:59radioactive waste and tracers into the
29:02sea.
29:03These are historical large tsunami areas
29:06and again they're often around the map
29:08that we saw before this ring of fire
29:10volcanic activity convergent plate areas
29:14where things are coming together and
29:16those have the ability to generate large
29:18undersea earthquakes which then will
29:20generate on the sea surface these super
29:22long wavelength waves called tsunamis.
29:25The Boxing Day tsunami in 2004 as I
29:28mentioned it was magnitude 9.2 2 off the
29:30coast of Sumatra 1,200 km seafloor
29:34displaced between two tectonic plates
29:36there. This was the deadliest tsunami in
29:39history. Coastal v villages were
29:41completely wiped out and as I said you
29:43can watch some pretty uh dramatic video
29:47of that. Uh this was detected by a
29:50satellite imagery called Jason 1
29:52traveled more than 5,000 kilometers from
29:54its point of origin to these coastal
29:57areas. The wavelength out at sea was 500
30:00kilometers long. Incredible. But as it
30:03reaches the shallow area, these
30:05wavelengths really compress really
30:07quickly. Uh estimated that around
30:10300,000 people in 11 countries were
30:12killed and there was a lack of a warning
30:14system
30:15here. More and more we are developing
30:18warning systems here, certainly in
30:20Hawaii, uh at Alaska, um just to name a
30:23few in the United States. Here's some
30:26satellite imagery detecting the Indian
30:28Ocean
30:30uh
30:31tsunami. Uh as I said in 2011 uh
30:35magnitude 9.0 earthquake induced this
30:37one. Uh we mentioned this before the
30:40expense and the initial surge was at 15
30:43meters and again this is the Fukushama
30:46nuclear plant that we was exploded and
30:49um the radionuclides were released.
30:52So, it's great to have a warning system
30:54in place and there are several. There's
30:56a Pacific Tsunami Warning Center in
30:59Honolulu and deep ocean assessment and
31:02reporting of tsunamis is by this thing
31:04called Dart. It's a system of buoys that
31:06can detect small changes in the height
31:08or amplitude. So, here we have this buoy
31:11system that can use satellite imagery to
31:14be very responsive to these tsunamis. I
31:17just had to add this one here. We saw
31:19this before when low pressure systems
31:21like storms or hurricanes are on the sea
31:24surface they act as like vacuum to the
31:26sea surface increasing the sea height
31:30and then when that comes on shore it
31:32acts to propagate this wave. So these
31:34are called storm surges another type of
31:37wave. We've talked much about surface
31:40waves almost entirely in this chapter.
31:42Uh but there are internal waves here and
31:45these are happening because of lower
31:47density water sitting on high density
31:48water. We saw this two-layer system that
31:51compartmentalizes these two regions.
31:54Well, there's things called internal
31:56waves. They are extremely long
31:58wavelength waves that are actually
32:00moving water up and down and
32:02horizontally as well. Can we generate
32:06any energy from these waves? They are
32:08high energy
32:09systems and the answer is yes. In
32:12highwave energy areas, we can use
32:16floating turbines like this. So the wave
32:18action will rotate a turbine and that
32:20will generate electricity. Uh the bummer
32:23here is that you need then to get that
32:24generated electricity by some means back
32:27to shore where it's usable to humans. Um
32:30here's a wave plant called the limpant.
32:33Um it's small, but it's the world's
32:35first commercial wave power plant. If
32:37you're really into this, there's other
32:38examples of how you generate um energy
32:42from waves. And here you have a
32:44schematic. If you're really into it, you
32:46can look at it. But once again, the
32:48ability of water to drive the movement
32:50of this turbine and then generate
32:52electricity is really the quintessential
32:56um feature of any thing that generates
33:00electricity. So we'll see see that with
33:02maybe wind energy, a turbine being
33:04turned, hydroelectric, again turbine,
33:07and here wave energy. The Portuguese
33:09have done this really well because a lot
33:11of the wave energy, the height of the
33:13waves are concentrated around their
33:16country. We saw it in Nazare, right?
33:18Birthplace of the largest waves on
33:20Earth. So uh several decades ago,
33:23Portugal began to implement this system
33:25of a farming of wave energy. So these
33:29are long buoys. So this one is segmented
33:32here. We can see in one, two, three
33:34little portions. They have the ability,
33:36I'll just be two segments here. Have the
33:38ability to go up and down like that. So
33:41any way that you can generate some up
33:43and down movement or movement at all,
33:45that energy can then be transferred into
33:48electrical energy. And again, you have
33:50to then take that energy that's being
33:52displaced here regionally offshore and
33:55wire it to a
33:57system. So, global wave energy, where
34:00would we do it? So, uh Portugal right up
34:02here. Uh you can see why they're doing
34:04it right here. Uh there's Spain and
34:07there's Portugal right here. So, a high
34:09energy system. Other places exist too.
34:12South Africa, the tip of South America,
34:15um Australia. You also have to have
34:17proximity to an urban source. So you may
34:21be able to generate wave energy in
34:23southern Australia, but a lot of the
34:25cities are not around there. So by being
34:29close to an urban center, you can then
34:31capitalize on that generation of
34:32electricity and then the minimal
34:34transport of that to an area where you
34:37would use it. If you're transporting at
34:39long distances, it just doesn't work.
34:41There we have it. That was the chapter
34:43again. I got to use the word whirlwind
34:46tour of wave energy. In the next
34:48chapter, we look at tides and touch upon
34:51actually tidal energy.

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