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Let's Bet on Sediments! Deep East 2001 Exploration Let’s Bet on Sediments! FOCUS Part II: (per group of 2-4) Sediments of Hudson Canyon 3 large jars with lids (e.g. Snapple bottles) 1/2 cup of each of the 3 various sediments (peb- GRADE LEVEL bles, sand, silt) 9 - 12 Water - enough to fill the 3 large jars 1 Sediment Analysis Worksheet FOCUS QUESTION 1 Stop watch How is sediment size related to the amount of time 1 Magnifying glass the sediment is suspended in water? 1 plastic spoon LEARNING OBJECTIVES Part III Demonstration Extension: Students will be able to investigate and analyze the pat- 1-10 gallon aquarium terns of sedimentation in the Hudson Canyon. 1/2 cup of each of the 3 various sediments used Students will observe how heavier particles sink in Activity One faster than finer particles. Water - enough to fill the aquarium 1 hair dryer Students will learn that submarine landslides (trench 1 aquarium filter slope failure) are avalanches of sediment in deep ocean canyons. AUDIO/VISUAL EQUIPMENT Overhead Projector for Part I Students will infer that the passive side of a conti- nental margin is not as geologically quiet as previ- TEACHING TIME ously thought. One 45-minute period ADAPTATIONS FOR DEAF STUDENTS SEATING ARRANGEMENT Teaching Time: Cooperative groups of two to four • Two 45-minute periods MAXIMUM NUMBER OF STUDENTS MATERIALS 30 Part I: Exploring Ocean Frontiers: Hudson Canyon over- KEY WORDS head. Turbidites Sedimentation Sediments 1 Deep East 2001 – Grades 9-12 Deep East 2001 – Grades 9-12 Focus: Sediments of Hudson Canyon oceanexplorer.noaa.gov oceanexplorer.noaa.gov Focus: Sediments of Hudson Canyon North American Plate are trapped within these three zones (R. Maddock, Suspension 2000). These three zones are the thickest and most Deep sea fans continuous along passive continental margins. Active continental margin Passive continental margin The Hudson Canyon, located on the passive mar- Topography gin (Atlantic Coast) of the North American Plate, Turbid is a deep steep-sided valley, called a submarine. Turbidity currents Submarine canyons along the Atlantic coast usually Shelf break have V-shaped profiles, steep walls, rock outcrops, Continental shelf flat floors, strong currents, and deep-sea fans. Most Continental slope are located on the upper, steeper part of the slope. Continental rise The canyons, which run perpendicular to the shelf, Submarine canyon cross the continental shelf and continental slope; Graded bedding some even cross the continental rise! Some, but not Avalanche all, submarine canyons are located off the mouths of major rivers. As these submarine canyons cut BACKGROUND INFORMATION through soft surface sediments and the harder lay- The two most notable topographic features of the ers beneath, they expose a range of rock types and oceans are the continental margin and the deep sea. ages. Continental margins are described as either active or passive. Active margins are found along plate During the Pleistocene era, when sea levels were low, boundaries where earthquakes and/or volcanoes the Hudson River extended across the exposed area are common. Passive margins are not associated of what is now the continental shelf. Over time, the with plate boundaries and experience little volcanism Hudson River eroded the land to form the Hudson and few earthquakes. They are found around the Canyon. When sea level rose, the canyon was cov- area of the Atlantic Ocean. The profile of the pas- ered with water. Instead of emptying directly into sive continental margin includes the continental shelf, the ocean at the edge of the continental shelf, the continental slope, and continental rise. Hudson River then emptied into the Hudson Canyon. Today, the landward margin of the Hudson Canyon The continental shelf is a broad, gently slopping has been filled with sediments, but the rest of it con- platform that extends from the shoreline to the edge tinues to be eroded by ocean currents. The Hudson of the continental slope. Here, on the shelf, there Canyon extends 240 km out to sea and then contin- are thick accumulations of coarse and fine-grained ues for another 240 km across the continental rise (R. sediments. In comparison, the continental slope is a Maddock, 2000). shelf break with an abrupt drop. Sediments on the steep continental slope are mostly soft mud, which When sediments such as sand, dirt, silt, and other is finer than sediments found on the shelf. When fine particles become suspended in water by cur- the continental slope begins to flatten it is called the rents, the water becomes murky, or turbid. Turbidity continental rise. currents, down-slope movements of sediment- laden water (Tarbuck & Lutgens, 1999), continu- The continental rise is composed of thick accu- ously erode many submarine canyons such as the mulations of sediment which have fallen from Hudson Canyon. These currents are set into motion the continental shelf. The sediments delivered by when sand and mud on the continental shelf are turbidity currents form deep-sea fans at the base loosened, perhaps by melting of gas hydrates, an of the slope. Some 78% of the world’s sediments over-steepened slope, or an earthquake. They then 2 3 Deep East 2001 – Grades 9-12 Deep East 2001 – Grades 9-12 Focus: Sediments of Hudson Canyon oceanexplorer.noaa.gov oceanexplorer.noaa.gov Focus: Sediments of Hudson Canyon are mixed with the water to form a dense suspen- Analysis worksheet and predict what would hap- sion. As this sediment-laden suspension acts like pen if you put all three sediments together in one an avalanche and flows down-slope, it erodes jar. and accumulates more sediment. This erosion 6. Add 2 spoonfuls of each sediment sample to one process is thought to be the major force in growth of the jars. of submarine canyons. As the turbidity currents 7. Put a lid on the jar. lose momentum, they deposit sediment as deep- 8. Shake the jar to create a sediment-laden suspen- sea fans at the bases of the submarine canyons. sion. These deposits, called turbidites, are characterized 9. Observe the action of all three sediments together by a decrease in sediment size from bottom to top and record the observations on Sediment known as graded bedding. As sediments settle to Analysis Worksheet. the bottom, coarser, heavier particles settle out first and are followed by finer sand and then finer clay. Part III Demonstration Extension: Since fine particles remain suspended in the water 1. Set up a 10-gallon aquarium in front of class. column longer periods of time than larger, denser 2. Fill the10-gallon aquarium with water. particles, the finer particles are carried out far- 3. TEACHER ONLY!! Turn a hair dryer on and use ther, often to the edge of the shelf, before they are it to produce surface currents in the aquarium, deposited. and/or turn the filter on to produce turbidity cur- rents in the aquarium. SAFETY PRECAUTION: LEARNING PROCEDURE DO NOT DROP HAIR DRYER INTO AQUARIUM, Part I Discussion: A PERSON COULD GET ELECTROCUTED! Using the “Exploring Ocean Frontiers: Hudson 4. While the class is watching, pour all three sedi- Canyon” overhead, explain the features of a passive ment samples into the aquarium. continental margin. Introduce submarine canyons 5. Observe how the water currents affect the differ- and the location of Hudson Canyon. ent type(s) of sediment. 6. Discuss with the class why the Hudson Canyon Part II Activity: has fine sediment deposits on and around it and 1. Have student groups gather the following materi- not coarse sediments. Use this demonstration as als: evidence. a. 3 large jars filled with water per group 7. Discuss what turbidity currents are and how they b. 3 - 1/2 cup samples of sediments per group form deep-sea fans. c. 1 magnifying glass per group d. 1 Sediment Analysis Worksheet per student THE BRIDGE CONNECTION e. 1 plastic spoon per group www.hudsonvoice.com 2. Have students observe and analyze the three dif- bromide.ocean.washington.edu/oc540/lec01-16/ ferent sediment types using the Sediment Analysis www.abdn.ac.uk/geology/profiles/turbidites/homepage/ Worksheet. 3. Have students predict which of the sediment types CONNECTION TO OTHER SUBJECTS would reach the bottom the fastest and the slow- Mathematics, English/Language Arts est on the Sediment Analysis Worksheet. 4. Using a stopwatch, record on the Sediment EVALUATIONS Analysis Worksheet the time it takes a plastic Students will write a paragraph summarizing what spoon full of each sediment sample to fall to the they learned about turbidity currents and the sedi- bottom of each large jar. mentation in the Hudson Canyon. 5. Have students record observations on Sediment 2 3 Deep East 2001 – Grades 9-12 Deep East – Grades 9-12 Focus: Sediments of Hudson Canyon oceanexplorer.noaa.gov oceanexplorer.noaa.gov Focus: Sediments of Hudson Canyon The teacher will review each student’s Sediment Physical Science - Content Standard B: Student Handout Analysis Worksheet. • Motions and forces EXTENSIONS Earth and Space Science – Content Standard D: • Ask students to write a short essay comparing the • Structure of the Earth system Grand Canyon to the Hudson Canyon. • Earth’s History • Ask students to research slumping and underwa- ter avalanches. Science in Personal & Social Perspectives - Content Standard F: • Ask students to write a short paper comparing the • Natural Hazards three types of sediments found on the sea floor: physical, biological, and chemical. History and Nature of Science – Content Standard G: • Ask students to investigate the various sources of • Nature of science sedimentation caused by human activity. • History of science • Examine sediment samples from various places around the world. FOR MORE INFORMATION • Ask students to identify all of the deep-sea can- Paula Keener-Chavis, National Education yons found along the Atlantic Coast.
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