ERTH 160L Lab 9
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Long Beach City College *
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Dec 6, 2023
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ERTH 160L
Name: Lorelai Burke
Lab 9: Coasts around the World
______________________________________________________________________
PURPOSE
Explore different types of coastlines, their importance, key features and why some are threatened by global sea level rise.
INTRODUCTION
California has a diversity of coastlines—but two main types: sandy beaches and cliffs. Beach processes were explored in the waves lab. This lab is set up as a GoogleEarth Tour of some of the different coastal features around the world. At each stop there are pictures and videos. There are also questions. Answer the questions on this worksheet. Not all stops have questions to answer but there is a lot to explore.
https://earth.google.com/web/@21.93685805,-
159.38371299,129.50442464a,152076.96858204d,35y,359.99999921h,0t,0r/data=MicKJQojCiE
xV3FIbGZreV9fb0hCTVMtelI3Rm9neGRHUUtsbWhNN1c
Stop 1: Dauphin Islands-- Gulf Coast region of the United States
We start our tour in the Gulf of Mexico. The coasts of Texas, Louisiana, Mississippi, Alabama and Florida are very different from those in California. A broad flat shelf and no tectonics (e.g. faults and subduction zones) results in sand piling up and the formation of long, narrow, sandy islands. Our first stop, Dauphin Island, is a typical example of all of these islands. Make sure you study the GoogleEarth image and look at all the pictures in the inset before answering the questions.
1. Based on lectures and your book (you can also reference the pdf sheet on BeachTerminology), what is the name of this type of island?
Low Profile Barrier Island
2. How can you tell in the first photo and the GoogleEarth picture which side of the island faces the ocean and which side faces land? What clues are you using?
In the first photo on GoogleEarth, you can tell that the left side of the island (directionally
North side) is facing land. I am using the clue of what seems to be shallower water on that side, signaling that there is a wider continental shelf, and that is it not a wide-open ocean with a steep drop off, but rather a shallower lagoon.
3. During storms, ocean waves can wash over the entire island and leave strips of sand
in the vegetation. Make sure you can see these. What is the name given to these features?
Hummocky Discontinuous Dunes
Stop 2: Big Sur Coast, California
The iconic Highway 1 hugs much of the rugged coast of Central California. Here, the steep rocky coast has small sandy beaches and some of the classic features found in text books such as the sea arch in the first picture in the inset. 4. What is the name of the feature in the yellow circle?
Sea Stack
5. A similar feature is connected to the beach by a strip of sand. This combined feature
is called a . . .?
Tombolo
6. The largest landslide in modern times occurred along the Big Sur Coast in 2017. It cut-off coastal communities that rely on Highway 1. Watch the short video. How tall is the landslide?
Four stories high
Stop 3: Point Arena, California—northern California Coast
The coastline of northern California has very steep cliffs. Look at all three of the points on Stop 3 and then answer the questions.
7. In the close up pictures of the cliffs and in the picture of the lighthouse, you can see that the cliffs have vertical stripes. These stripes are different layers of rock that were laid down flat. But subduction and faulting have tilted them to rest on their sides. Do you think the cliffs are easier or more difficult to erode if the rock layers are tilted or if they are flat? Why?
Easier to erode, because gravity pulls eroded particles downward to follow the tilt.
8. The home (let’s call it Cliffhouse) beneath the yellow dot is for sell for $960,000 dollars. It has beautiful ocean views. Your friends and their 4 year old daughter want to
buy the house. Is this a good investment? What do you recommend? Let’s do some quick calculations. I would recommend NOT investing in that home. Due to the quicker rates of erosion found in cliffs with these parallel stripes of rock extending into the ocean, the edge of that cliff is very likely to be eroded to be closer and closer to the home, putting it at risk of falling victim to a landslide.
The home was finished in 2003 with a projected 75-year lifespan. Based on the State of California requirements, the home was put a minimum of 30 feet from the edge of the cliff. The home to the north and the concrete patio in front of Cliffhouse provide us observable stations from which to measure active cliff erosion. Using GoogleEarth Pro, we can measure the original distances and modern distances of the homes to the cliff
edge. The googleearth pictures are below as is a table of the measurements. (Note how much better the satellite imagery is today than in 2005).
Date
Edge of concrete patio to cliff
SW corner of house to cliff
August 2005
27.2 feet (1.4 avg, 1.1 and 1.7)
40 feet
August 2011
14 feet
28 feet
August 2013
11.8 feet
25.2 feet (1.4 avg, .83 and 2)
August 2017
5 feet
23 feet
8a. Based on the patio, what is the average rate (distance/year) of the cliff erosion based on the patio measurements? [hint: you will make two calculations and then average them.]
1.4 ft/yr 14-11.8/2 = 2.2/2 = 1.1 11.8-5/4 = 6.8/4 = 1.7 1.1 * 1.7 / 2 = 1.4
8b. Based on the SW corner of the house, what is the average rate of cliff erosion?
1.4 ft/yr
40-28/6 = 12/6 = 2 28-23/6 = 5/6 = 0.83 2 * 0.83 = 1.416 = 1.4
8c. Why do you think the two numbers are different? They’re not different; in fact, they are very similar, the difference the numbers used to create the average.
8d. The geologic engineer calculated a rate of cliff loss of 0.31ft/yr. Is this what you calculated? If not, what might be the reason for the difference?
He may be calculating his measurements from a different location or in a different line of
direction.
8d. Based on your calculations in 8a, how many years before the patio starts falling into
the ocean? [Hint: The edge of the patio is 5 feet from the cliff edge now. With the average rate of erosion, how long will it take to erode 5 feet?]
Approximately 3 ½ years
5/1.4 = 3.57
8e. Based on your calculations in 8a, how many years before the house is 10 feet from the edge and too dangerous to live in? [The closest corner is 23 feet from the edge today, so how many years to erode 13 feet of cliff?]
Approximately 9.3 years
13/1.4 = 9.29
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8f. Remember that the numbers are averages: the erosion could be slower or faster. Do you think this is a good investment for your friends and their young daughter?
No, I do not think it is a good investment because the rate of erosion is so uncertain. It could be 10 years or it could be 2, which is not worth spending money on.
Notes: Blue dot is Bowling Ball Beach near the house. Red line is the fault trace ~ 3 miles away.
August 2005
August 2011
August 2017: red circle near concrete pad clearly shows cliff loss.
Cliffhouse and the area of Point Arena are not the only places where rising sea level and larger storms are eroding coastal cliffs and homes are being lost. Watch the video to find out how the same thing is impacting Puerto Rico.
Stop 4: Bay of Fundy
9. The Bay of Fundy in Canada has one of the largest tide ranges in the world. At Hopewell rocks (the first inset picture), the difference between high tide and low tide is 14 meters. How many feet is that?
Approximately 46 feet
Stops 6, 7, 9: England, France, Vietnam
10. Discussion question.
Three coasts have limestone rocks (Dover, the calanques, and Ha Long bay). What do you notice about these three coasts? Why do you think they have small or NO beaches
at all? We know that limestone dissolves in acid. What role might the acidity of ocean water have in the formation of these coasts? [We will revisit this idea in our last lab.]
These coasts have calcite in them, making them much harder to erode. The reason for little to no beaches on these coasts is because they have been eroded away and all that
is left is the hard-to-erode limestone or chalk.
Stop 11- Great Barrier Reef
11. The Great Barrier Reef is largely underwater and made of coral. Coral is an animal
with a limestone exterior. If limestone dissolves in acid, what role might increasing ocean acidity play in the health of this coast?
Increasing ocean acidity in these areas of this coast would put underwater life forms and habitats, like the Great Barrier Reef, in grave danger for being killed and disappearing, seeing as the only way limestone can dissolve is with high acidity.
Stop 12—Hawaii No questions here. Sometimes it’s just nice to look around and listen to Israel Kamakawiwo’ole.
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