Geological Work of Seas and Oceans ENGINEERING GEOLOGY Seas and Oceans • Sea • Ocean • Seashore • Oceanography • Mar
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Geological Work of Seas and Oceans
ENGINEERING GEOLOGY
Seas and Oceans • Sea • Ocean • Seashore • Oceanography
• Marine Geology
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Oceanic Relief • Continental Shelf
• Continental Slope • Abyssal Plane
• Submarine Canyons
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claseshistoria.com
The Global Continental Shelf (cyan)
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http://en.wikipedia.org
The Sea waves and currents • Waves – Oscillatory (deep water) waves – Translatory (shallow water) waves • Currents – Littoral/Longshore Currents – Rip Currents
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Thompson & Turk
Wave movement and breaking
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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
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Factors influencing Marine Erosion • 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
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Features of Marine Erosion • Headlands and bays
• Sea cliffs • Wave-cut terraces
• Sea caves
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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
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Headlands and bay
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Headlands and bay
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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
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Sea cliff Formation
Thompson & Turk
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Waves crashing on a sea cliff
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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
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• Formation of wavecut terrace
http://en.wikipedia.org
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http://en.wikipedia.org
Wave-cut platform
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d. Sea Caves • 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
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Basalt sea cave at Akun Island, Alaska, U.S.A
http://en.wikipedia.org
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Marine Deposition • Shallow water (Neritic) deposits – Beaches – Spits and bars – Tombolo • Deep water deposits – Coral Reefs
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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
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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
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Beach Formation
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Evolution of Barrier beach at Chatham, Massachusetts
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1995
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http://www.whoi.edu
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
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Spits and Bars
Thompson & Turk
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c. Tombolo • Refers to a bar connecting a headland to an island, or one connecting two islands
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Marine depositional features
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Tombolo
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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
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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
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Anatomy of a coral polyp
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Coral Diversity
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http://en.wikipedia.org
Coral Reef Locations
20° C Isotherms
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The Great Barrier Reef
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Visible Earth – NASA
The Fringing Reefs Thin, tabular sheets of coral accumulations along the border of mainland, or along the rim of an island
The Barrier Reefs They occur at a distance from the shore/island A lagoon separates the reef from the shore/island
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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
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Fringing reef off the coast of Eilat, Israel.
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http://en.wikipedia.org
Barrier Reef
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http://www.macminde.info
Atafu atoll, the Pacific
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http://en.wikipedia.org
http://en.wikipedia.org
Formation of Coral Reefs: Darwin’s Theory 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
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Atoll formation
http://en.wikipedia.org
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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