Geological Work of Seas and Oceans
ENGINEERING GEOLOGY
Seas and Oceans •
Sea
•
Ocean
•
Seashore
•
Oceanography
•
Marine Geology
2
Seas and Oceans •
Sea
•
Ocean
•
Seashore
•
Oceanography
•
Marine Geology
2
Oceanic Relief •
Continental Shelf
•
Continental Slope
•
Abyssal Plane
•
Submarine Canyons
3
4
The Global Continental Shelf (cyan)
5
The Sea waves and currents •
•
Waves –
Oscillatory (deep water) waves
–
Translatory (shallow water) waves
Currents –
Littoral/Longshore Currents
–
Rip Currents
6
Thompson & Turk
Wave movement and breaking
7
8
9
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
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
11
Features of Marine Erosion •
Headlands and bays
•
Sea cliffs
•
Wave-cut terraces
•
Sea caves
12
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
Headlands and bay
14
Headlands and bay
15
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
Sea cliff Formation
Thompson & Turk
17
Waves crashing on a sea cliff
18
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
•
Formation of wavecut terrace
http://en.wikipedia.org
20
http://en.wikipedia.org
Wave-cut platform
21
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
22
Basalt sea cave at Akun Island, Alaska, U.S.A
23
Marine Deposition •
•
Shallow water (Neritic) deposits –
Beaches
–
Spits and bars
–
Tombolo
Deep water deposits –
Coral Reefs
24
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
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
Beach Formation
27 Thompson & Turk
1985
Evolution of Barrier beach at Chatham, Massachusetts
1986
28
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
Spits and Bars
Thompson & Turk
30
c. Tombolo •
Refers to a bar connecting a headland to an island, or one connecting two islands
31
golearngeo.wordpress.com
Marine depositional features
32
Tombolo
33
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
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
Anatomy of a coral polyp
http://en.wikipedia.org 36
Coral Diversity
37
Coral Reef Locations
20 C Isotherms °
38
39
The Great Barrier Reef
40
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 41
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
Fringing reef off the coast of Eilat, Israel.
43
Barrier Reef
44
Atafu atoll, the Pacific
45
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
46
Atoll formation
47
