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Engineering Geology
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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
3
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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• 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
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
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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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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
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
