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vdocuments.mx_geological-work-of-oceans-and-seas.pptx
- 1. Geological Work of Seas and Oceans ENGINEERING GEOLOGY
- 2. Seas and Oceans • Sea • Ocean • Seashore • Oceanography • Marine Geology 2
- 3. Oceanic Relief • Continental Shelf • Continental Slope • Abyssal Plane • Submarine Canyons 3
- 5. 5 http://en.wikipedia.org The Global Continental Shelf (cyan)
- 6. The Sea waves and currents • Waves – Oscillatory (deep water) waves – Translatory (shallow water) waves • Currents – Littoral/Longshore Currents – Rip Currents 6
- 7. 7 Wave movement and breaking Thompson & Turk
- 8. 8
- 9. 9
- 10. Marine Erosion Erosion is done through: o Hydraulic action – breaking, loosening and plucking out of rocks by waves and currents o Marine abrasion – rubbing and grinding action o Corrosion – solvent action of seawater 10
- 11. • Strength and velocities of waves and currents • The lithology of the rocks • The seaward slope of the shoreline • The depth and chemical composition of water • The height and original profile of the shoreline 11 Factors influencing Marine Erosion
- 12. • Headlands and bays • Sea cliffs • Wave-cut terraces • Sea caves 12 Features of Marine Erosion
- 13. a. Headlands and bays • Soft rocks along a coastline gets eroded faster than harder ones • Seawater enters the eroded portions, forming bays • The stronger rocks, which resist erosion, project outwards, and are called headlands 13
- 16. b. Sea Cliffs • A seaward facing steep front is called a sea cliff • They represent the first stage of work of waves on the shore rocks • The base of sea cliffs are prone to undercutting by wave action 16
- 17. 17 Sea cliff Formation Thompson & Turk
- 18. 18 Waves crashing on a sea cliff
- 19. c. Wave-cut terraces • They are shallow, shelf like structures, carved out from the shore rocks by sea waves • Terraces are formed when the wave-cut notches extend backwards such that the sea cliff above is unsupported and falls down 19
- 20. • Formation of wave- cut terrace 20 http://en.wikipedia.org
- 22. • The erosive action of waves along the fissures in the sea cliffs initiate the process of sea cave formation • The waves eventually widen the fissures through hydraulic action and abrasion, resulting in cave formation 22 d. Sea Caves
- 23. 23 http://en.wikipedia.org Basalt sea cave at Akun Island, Alaska, U.S.A
- 24. Marine Deposition • Shallow water (Neritic) deposits – Beaches – Spits and bars – Tombolo • Deep water deposits – Coral Reefs 24
- 25. Shallow water (Neritic) deposits • Neritic zone extends from the lowest tide limit to the continental shelf • These deposits are derived from the adjacent land and shore rock • Marine benthos also contribute source material for shallow water marine deposits – mollusks, seaweeds 25
- 26. a. Beaches • Loose deposits made by the sea near the shore, from materials eroded from nearby regions • The lower and upper margins of the beach are beneath and above the still water level • A part of the stream deposits from near shore are brought back to the shore by the waves and is deposited due to a check in their velocity • Barrier beaches are formed away from and parallel to the shore 26
- 27. 27 Thompson & Turk Beach Formation
- 28. 28 http://www.whoi.edu Evolution of Barrier beach at Chatham, Massachusetts 1985 1986 1995
- 29. b. Spits and Bars • Ridge shaped deposits of sand and shingle, extending across the embayment's • An embayment is a recess in the coastline, forming a bay • A spit that completely closes the mouth of an embayment is called a bar 29
- 30. 30 Spits and Bars Thompson & Turk
- 31. c. Tombolo • Refers to a bar connecting a headland to an island, or one connecting two islands 31
- 33. 33 Tombolo
- 34. Deep water (Pelagic) deposits • They are mostly comprised of mud and oozes • Oozes are derived from planktons • Over time, such accumulations take the shape of extensive ridges, partly or totally submerged under seawater, and are called reefs 34
- 35. Coral Reefs • Ridge like marine deposits formed due to the accumulation of dead organisms, predominantly, corals, hence the name coral reef • They provide habitat for more than 25% of the marine species • Charles Darwin identified three types: – Fringing reefs – Barrier reefs – Atolls 35
- 36. 36 Anatomy of a coral polyp http://en.wikipedia.org
- 38. 38 Coral Reef Locations http://en.wikipedia.org 20° C Isotherms
- 39. 39
- 40. 40 The Great Barrier Reef Visible Earth – NASA
- 41. Thin, tabular sheets of coral accumulations along the border of mainland, or along the rim of an island 41 The Fringing Reefs The Barrier Reefs They occur at a distance from the shore/island A lagoon separates the reef from the shore/island
- 42. The Atolls • An annular, circular, or semi-circular reef surrounding a central body of water (lagoon) • The top of atolls are flat, pavement like, in appearance 42
- 43. 43 Fringing reef off the coast of Eilat, Israel. http://en.wikipedia.org
- 45. 45 Atafu atoll, the Pacific http://en.wikipedia.org
- 46. 46 Formation of Coral Reefs: Darwin’s Theory http://en.wikipedia.org 1.A volcanic island becomes extinct 2.As the island and ocean floor subside, coral growth builds a fringing reef 3.As the subsidence continues, the fringing reef becomes a barrier reef, with a lagoon separating it from the island 4.Ultimately, the island sinks below the sea, and the barrier reef becomes an atoll enclosing an open lagoon
- 48. Reference • Singh, P, Engineering and General Geology, S K Kataria & Sons • Garg, S K, Physical and Engineering Geology, Khanna Publishers • Thompson, G R and J Turk, Introduction to Physical Geology, Thomson Brooks/Cole • chl.erdc.usace.army.mil/, Coastal and Hydraulics Laboratory, U.S. Army Corps of Engineers