Geological Work Of Oceans And Seas 644u67

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 uned 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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1985

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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golearngeo.wordpress.com

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

http://en.wikipedia.org 36

Coral Diversity

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http://en.wikipedia.org

Coral Reef Locations

20° C Isotherms

http://en.wikipedia.org

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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