Unit 8_Lab_BeachSediment

Name ____ Date ____ Class Day/Time ___________________ Lab 8: A Tale of Two Beach Faces – Florida Beach Sediment Comparison Lab As a student living in the state of Florida, you have likely experienced a sandy beach before. However, you may not have recognized that there are some significant differences between the beaches of the west coast, along the Gulf of Mexico and the East Coast, facing the Atlantic Ocean. The sands of each of the beaches have different grain sizes, textures, and colors – why? The laboratory exercise objective today is to recognize the major differences between provided lab samples of sand from the west coast and east coast of Florida. Through this, you will also relate these differences to wave action and the angle of the beach face at each of the respective locations. Beach Sand and the Wentworth Scale Sand is a reference to a specific size of sediment, ranging between 1/16 and 2 millimeters in diameter. Most beach sand, as much as 90%, is derived from sediment-carrying rivers that deposit materials near the coast. As the heavier materials, such as gravel, are usually deposited upstream, much of the smaller materials are prevalent closer to the coast. The finest material, such as silt or clay, is usually suspended in the water and carried out to the open ocean. Once deposited, sand on beaches are distributed by wave action and a process called “longshore drift,” where sand is carried up shorelines since waves refract when approaching the shallow depths adjacent to shorelines. Quartz makes up a vast majority of beach surfaces, especially along the west coast of Florida as it is a widely abundant material that is fairly resistant to weathering. Along the east coast, however, the beaches contain a significant amount of carbonate materials, causing the sand to look tanner in color, than the white sand of the west. Carbonates along the east coast are mostly made up of broken pieces of shells that have been continuously broken down and rounded off by waves. To adequately measure grain size, a scale is used called the Wentworth Scale of Grain Size. Familiarize yourself with this scale below: Sieving In order to measure the distribution of grain sizes from a beach sample, we will undergo a process called, “sieving” (s-iv-ing). A sieve (siv) is a container with a mesh base that has specific sized openings. Sieves are stacked on top of one another, with the largest opening mesh sieve stacked at the top and the smallest at the bottom. Sediment is poured into the top of the stack and shaken, to allow for the sediment to settle and be sorted by grain size. Once complete, the sieve set is separated, and each pan is compared to the total sample size to determine the percentage of sediment across each size in the scale. Data Display A histogram is created to graph the frequency distribution of the sediment sample. In this lab, you will create histograms to represent each of the sample – west coast and east

coast. The Beach Face – Angles The slope of the beach, which is related to wave action, is referred to as the beach face. This angle, which is measured from the horizontal, gives us clues about the sediment grain size and the amount of wave action that occurs in the area. Beaches with a very shallow slope, typically contains much finer sediment. This is because a lack of intense wave action means that the finer sediment has not been carried away from the beach. Conversely, where beaches have courser sediment, much of the finer materials have already been eroded away due to a significant amount of wave action in the area. Laboratory Procedures • Record the sample name (west coast or east coast). Measure out exactly 100g of your sample using the laboratory balance. • Examine your sieve set - make sure they are free from loose sediment and that they are stacked in order from largest opening size to smallest. • Pour the sediment sample into the top of the set and shake it (back and forth, not up and down) to allow the sediment to be properly sorted for approximately 15 minutes. • Carefully separate your sieve set and measure the mass of each of the sieves separately. Record your measurements in the table. • Follow steps 1-4 for the other sample. Lab Part 1: West Coast Sample Starting Sample Mass (g): ____100.6_____________ A B C D Sediment Sample Grain Size Mass (grams) Mass (g) / Total Sample Mass (g) Column C x 100 (Percent of Total) Gravel >2mm 0.3 0.0029 0.29 Very Coarse Sand 1-2mm 0.5 0.0049 0.49 Coarse Sand 500 µm – 1mm 1.5 0.0149 1.49 Medium Sand 250 µm – 500 µm 25.8 0.2564 25.64 Fine Sand 125 µm – 250 µm 67.7 0.6729 67.29 Very Fine Sand <125 µm 4 0.0397 3.97 Note: 1 millimeter = 1000 micrometers Calculate the sum of the masses in Column B: ___99.8____________ Calculate your percent error (100g (Original Mass) - Sum of Masses in Column B / 100g (Starting Sample Mass) x 100 = _99.9901______________

clay and silt very fine sand fine sand medium sand coarse sand very coarse sand gravel Histogram – East Coast Sample Grain Distribution clay and silt very fine sand fine sand medium sand coarse sand very coarse sand gravel Analysis Questions Compare and contrast the grain size distributions presented in your histograms for the two beach samples.

Based on grain size distribution and the pre-reading, describe the expected differences in wave energy of both beaches.