Question.3569 - MAJOR OCEAN-FLOOR FEATURES LAB Objectives: for you to recognize important ocean-floor features, and where appropriate, to relate them to plate tectonics theory. You need to have Google Earth Pro on your desktop or device (see resources below) Terms passive continental margin - continental crust is welded to oceanic crust; not a plate boundary. Earthquakes are rare, and volcanic activity is nonexistent. Typically, a passive margin is greater that 200 miles away from the nearest plate boundary. Continental shelves along passive margins tend to be broad, often from 50 to 300 miles across. active continental margin - where a plate boundary is near a continents shoreline; typically less than 200 miles from edge of continent. Volcanism is common, especially where subduction occurs just off shore, and earthquake activity is prevalent, promoting mass wasting of continental shelf edges, keeping shelves from growing as wide as their passive margin equivalents. Most active-margin shelves are less than 50 miles across. submarine fan - large wedge of sediment formed where currents flowing from a submarine canyon deposit sediment at the base of a continental slope. Sediment which composes a submarine fan is derived from the weathering and erosion of inland mountains. Streams/rivers then deliver the sediment into the ocean where it is eventually carried down into deeper water. Major rivers (Nile, Ganges, Mississippi) are associated with the largest submarine fans. Continental Shelves 1) In your own words, what is a continental shelf? gently sloping area extending from the shoreline to the continental slope, typically ranging from 0 to 350 kilometers (217 miles) in width, and also it can characterized in shallow depth and is primarily composed of sediment eroded from the continent. left587375002) On your copy of the Physiographic Chart of the Sea Floor (below), use a green pencil to indicate the positions of shelves at all passive continental margins, and a blue pencil to indicate the positions of shelves along the active continental margins. (if you do not have a printer, color it using on Microsoft Words, PowerPoint, or edit it using y our cellphone (let me know if you struggle with this part) https://www.deepseanews.com/2015/07/its-time-to-geek-out-over-a-new-global-bathymetric-data-set/ 3) Use Google Earth (GE) to measure the widths of the following shelves, perpendicular to the shoreline out to the shelf edge. Follow the links (or google resources) to learn how to measure distances using Google Earth (in kilometers) http://earth.google.com/intl/ar/userguide/v4/index.htmhttps://www.businessinsider.com/how-to-measure-distance-on-google-earthhttps://support.google.com/earth/answer/9010337?co=GENIE.Platform%3DAndroid&hl=enhttps://www.youtube.com/watch?v=ysMo6cZQtHkFor each, indicate if it is at an active or a passive margin based on the distance from shoreline to the nearest plate boundary. Indian Ocean a) shelf at southern tip of South Africa 200 kilometers 124 miles passive b) western shelf of Madagascar 200 kilometers 124 miles passive c) shelf west of Bombay 300 kilometers 186 miles passive d) shelf south of Java Island 50 kilometers 31miles active Pacific Ocean a) shelf west of Lima 50 kilometers 31 miles active b) shelf west of Los Angeles 200 kilometers 124 miles passive c) shelf east of Kamchatka Peninsula 100 kilometers 62 miles active d) shelf between Australia and Great Barrier Reef 250 kilometers 155 passive Atlantic Ocean a) shelf east of Valdes Peninsula 50 kilometers 31 miles active b) shelf east of New York 200 kilometers 124 miles passive c) shelf west of Lisbon 300 kilometers 186 miles passive d) shelf north of Puerto Rico 100 kilometers 62 miles active 4) Calculate the average width of passive continental margin shelves for all of the ocean, from the above calculations. 200 kilometers 124 miles 5) Calculate the average width of active continental margin shelves for all of the ocean, from the above calculations. 50 kilometers 31 miles 6) Provide a hypothesis to explain why the average widths of active and passive shelves are so different (think of plate tectonics). Since passive margins are wider (because they are formed by gradual settlement of sediment) when compared to active margins (formed due to tectonic activities like subduction or transformation faults, which itself acted as a limitation to sediments). Continental Rises 1) In your own words, what is a continental rise? Sloping area at the base of continental margin that leads to abyssal plain 2) On your Physiographic Chart of the Sea Floor (see the map above), use a red pencil to indicate the locations of major submarine fans (must have four). To find them, think of the largest rives in the world and see if they have submarine fans. Label each fan according to the names on the World Maps above. Bengal Fan, Indus Fan, Amazon Fan, Niger Fan. 3) What is the source of the sediment comprising the Indus and Ganges fans (where does the sediment come from; think of a geographic location)?_____________________________ How does that sediment reach the Indian Ocean? Ganges and Brahmaputra rivers which transports Himalayas and Tibetan Plateau 4) Calculate the approximate areal size of the Ganges Fan (area = length x width) 1 million square kilometers 386,100 square miles 5) How is the Amazon River related to the Amazon Fan? As it is largest submarine fan in the world, Amazon river is the source Abyssal Plains 1) In your own words, what is an abyssal plain? A deep-sea floor area that is flat. 2) Why are abyssal plains so flat and featureless? Due to the accumulation of sediment for several years, filling up irregularities. 3) Calculate the approximate surface area of the largest abyssal plain on the Atlantic Ocean floor. Around 100 million square kilometers 38,610,000 square miles Hawaiian-Emperor chain of islands and seamounts 1) Locate this chain of islands/seamounts on your Pacific Ocean World Map. The Big Island, Hawaii, is volcanically active today. The cluster of seamounts at longitude 174 degrees east and latitude 35 degrees north are also volcanic in origin, but are approximately 40 million years old. At the north end of the Emperor Seamount Chain of volcanoes, the Detroit Tablemount is roughly 65 million years old. All the volcanoes mentioned above were formed at the same hotspot, now beneath the Big Island. a) What was the rate and direction of motion of the Pacific Plate from 65 to 40 million years ago? rate = distance/time rate = 5 cm/year direction = Northwest b) What was the rate and direction of motion of the Pacific Plate from 40 million years ago to the present? rate = 5 cm/year direction = Northwest 2) Speculate as to why the rate and direction of Pacific Plate movement changed 40 million years ago. (Hint: What causes the plates to move?)-can be found from the last lab video. Due to the changes in the position of mantle plume that created Hawaiian-Emperor chain
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