Geological Work of Oceans and Seas

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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4claseshistoria.com

5http://en.wikipedia.org

The Global Continental Shelf (cyan)

The Sea waves and currents

• Waves

– Oscillatory (deep water) waves

– Translatory (shallow water) waves

• Currents

– Littoral/Longshore Currents

– Rip Currents

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Wave movement and breaking

Thompson & Turk

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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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• 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

shoreline11

Factors influencing Marine Erosion

• Headlands and bays

• Sea cliffs

• Wave-cut terraces

• Sea caves

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Features of Marine Erosion

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

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

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 wave-cut terrace

20http://en.wikipedia.org

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Wave-cut platformhttp://en.wikipedia.org

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• 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

d. Sea Caves

23http://en.wikipedia.org

Basalt sea cave at Akun Island, Alaska, U.S.A

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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27Thompson & Turk

Beach Formation

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http://www.whoi.edu

Evolution of Barrier beach at Chatham, Massachusetts

1985

1986

1995

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

c. Tombolo

• Refers to a bar connecting a headland to

an island, or one connecting two islands

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32Marine depositional features

golearngeo.wordpress.com

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Tombolo

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

37http://en.wikipedia.org

Coral Diversity

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Coral Reef Locations

http://en.wikipedia.org

20° C Isotherms

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40The Great Barrier Reef

Visible Earth – NASA

Thin, tabular sheets of coral

accumulations along the border of

mainland, or along the rim of an island

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The Fringing Reefs

The Barrier Reefs

They occur at a distance from the

shore/island

A lagoon separates the reef from the

shore/island

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.

http://en.wikipedia.org

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Barrier Reef

http://www.macminde.info

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Atafu atoll, the Pacific

http://en.wikipedia.org

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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

Atoll formation

47http://en.wikipedia.org

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