Environmental Geology Lab Week 4 Coastal Processes

next thing we're going to talk about in lamp is to deal with coastal processes coastlines and coastal processes and the course since a lot of new jersey and spends their summers at the beach this is an important thing to you okay so you went next time you go to the beach rather than playing frisbee checking out the ladies and men on the beach you can be looking at all the processes that are taking place okay so this will give you something to do anyway what we're gonna talk about first then is a couple of the processes of how the water comes to the beach okay how does the water come in and then the next thing we'll do is we'll look at some of the features that you actually have on the beach and what you're going to do today then it's all out of chapter 15 of the lab manual and just gonna go through the questions in there so we'll do a little bit of the introductory stuff and mostly it's going to be working through all the book questions first thing off is how does water come to the beach basically you have this huge body of water called the ocean okay and it's got a lot of water in the ocean well what happens is we have two factors that come in there are tides and there are waves the tide as you know comes up twice a day so you get I tide low tide high tide low tide through a day and that's the tidal effect so the water levels will go up the water levels will go down and this is all related to where the position of the Moon and also the Sun is relative to the earth so as the Earth turns underneath the Moon the moon draws the water up and gives you giving you higher tides or pulls it down giving you low tides that's one factor the big factor we're gonna talk about however are waves and waves basically are travel just like sinusoidal waves that you would deal with in physics across the ocean now why are there waves waves come because you have wind blowing over the surface of the ocean as wind blows over the surface it creates some friction on the ocean and it pushes the water now water can't really be pushed up too high it always wants to go low so you have a driving of the waves towards the beaches in reality nothing moves very far instead the water just makes a rotation so as the wave passes the point rather than you thinking the water is all getting pushed up onto the beach notice it comes back again so though as a wave passes through you get this rotation of the water in an orbital fashion alright and that's how waves move now waves then can move along through the water at a certain speed as it approaches the coast okay and so that's why you see waves coming in and breaking at the shore now as they come in they will these orbitals the movement of water will penetrate to a certain depth and the distance between the wave crests were troughs divide that by half and that is the depth to which these waves will penetrate okay and that's where the what we call wave base okay so wait base is how deep the water movement is penetrating into this ocean and that penetration will move along as the wave moves along okay now that wavelength how far from one class to the next then also how fast the wave goes depends on how long it takes for you to get from one wave to the next and that is called the period of the wave usually a capital T the period is how long does it take from one wave to the next wave to get to you divide the wave length by this by the period you get the speed of the waves so you can calculate the speed by that move by the period of how long it takes to go across okay and so those are all factors in determining waves coming in then with several other equations you can figure out when waves will break okay and so in your lab manual you will see that there's a series of equations mostly of the things that I just talked about but also several others so what you will do is you will take the equations that I just give you out of your lab manual and you're going to do a little bit of a calculation on wave motion how fast does it come in where does it break when it breaks what happens and now those are some of the things you'll see what you do the lab today when you go to the beach they'll see there are different parts to the beach there are things that come in call the Breakers with the waves themselves drag on the base of the ocean and fall over so a breaking wave is actually a falling over wave and you get what is called then the breaker zone and then where the water slides up onto the beach that's the swash zone and the beach face and then on top there's the flat area where everybody's laying out sunbathing called the berm and back behind that is the dunes okay and so all of those are different parts of the beach and they're all covered with sand which sits along the edge of the beach now in addition to having this sand though beaches don't stay still even though you sitting there they look like they stay still beaches are constantly moving in fact there is a movie out on that that used to be show called beaches river of sand that's basically what they are if you can imagine with time all the sand on the beach is constantly moving down so if you went over the period of years and years sand moves a long way along beaches and it's being pushed by the waves now if the waves come in head-on so that the crest crests are flat to the beach then you wind up with most of the sand staying pretty well still however in most cases they come in at an angle so there's an angle between the beach and the wave crests and in fact the case you can usually tell because the waves will break with time so you ever known as you stand on the beach and the wave is breaking in front of you and then it breaks all the way down the beach as you look down that's because they're coming in at an angle when they come in at an angle it shoves the water sideways and you get what is called a longshore current now longshore current means you're going to get water moving sideways along the beach water carries sand so it in turn brings sand with it and that movement of sand is what is called littoral drift so you get this littoral drift dragging the sand sideways along the beach well that's that we're moving our sand down the beach to different areas now in addition to that if this coastline is not flat then the water kind of will come in and Bend the bending of way is what we call wave refraction and wave refraction can cause water to build up in places and then escape very fast and those are what are called when you when you get rip currents or rip tides is when you're dragging water out at high speeds to great depth and that's because you're getting refracting waves because of an uneven coastline and that's how we start out by developing these now in New Jersey what we have is the beaches are typically on islands okay and even notice you go to an island most of the places they're sitting on islands and these are called barrier islands they have the beach on one side they have a bay or a lagoon on the other and they have all of the features in between and these islands can move with time the reason we have them is because we had an ice age not too long ago and the water has been rising ever since and so it spills back behind most of our rivers are flooded because of this and we get what are called estuaries as a result of this spilling in you can also get terraces wave-cut terraces depending on if the land is rising or sinking with the changing water if the beach sits at a certain height for a while and the land rises up all of a sudden the beaches are there different for height you will get these stepped terraces on the coast you've probably seen a lot of those in California where you have these these Beach terraces and that's another common feature of beaches looking at the waves the way the way water moves along the beach and we can tell by the way the sand is dragged off as to which way the current has moved okay so this longshore current will be shown by Spitz and things like that on the edges of beaches that will tell us which way the water moves and so by analyzing pictures of these things we can see how the beach and how the coastline has changed with time by looking at progressive photographs and in this lab today that's what you're going to look at is a bunch of photographs a bunch of maps showing you changes from one picture to the next showing you how the coastal processes work so today what you're going to do is look a bunch of different coastal processes in a bunch of areas mostly in the United States but also around the world and you're gonna analyze what has been happening with regard to changing coastlines a couple of different kind of coastlines you can get a submerged in coastline is one in which things are submerging in other words you're getting rising sea level and some of the features you get in there are things like estuaries which is a drowned River Valley a headland which is a projection of land into the ocean a wave cut cliff these are sea cliffs and these are produced by wave erosion and then you have beaches which are generally narrow and a lot of marshes and tidal areas as opposed to an emergent coastline where you have a falling sea level in these cases you will get marine terraces wave-cut platforms and the beaches which will generally wide width broad marshes and tidal flats and so these terraces tell you emerging coastline as opposed to drown features estuaries which tell you submerged in coastline in addition you can get other features on coastlines things like spits which is a sandbar which will extend from the beach into a bay a delta which is a piece of land that sticks out from a river we also have human modifications to shorelines things like sea walls or break waters or groins that these are things to try to prevent sea erosion and if you look on these pictures you can see clearly that what they will do is involve a buildup of sand in different spots and also erosion of sand in different spots relative to what nature would have them do and so therefore these are things that can modify the coast sometimes for good and sometimes not for good hey what you're going to do in lab today then is the first part you're gonna answer a little bit of mechanic's questions just simple math to figure out how waves come in and how what their damage is done and what kind of things you got to be careful of with waves after all certain times your wave can be pretty dangerous especially if you live by the coast the next thing we're going to do is there are a bunch of questions in the back that are all based on maps and pictures of coastal situations and what you're going to do basically is look at the situation understand the processes that we just went over and describe what happened tell me how fast islands are moving how fast deltas are building out what is happening with regard to things and that's what you're going to do so you're going to look at certain situations by understanding the processes that we just went over then you can answer the questions and so those last part of the chapter you should look ahead and look at the pictures you're going to answer several questions about each one of these maps figures diagrams

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