8/11/2019 5 Unit-I Sea

http://slidepdf.com/reader/full/5-unit-i-sea 1/27

GENERAL GEOLOGY

Unit - I

External agencies

•Weathering

•

Wind•River

•Sea

•Landslide

Internal agencies

• Earthquakes

•

Plate tectonics• Groundwater

Scope of Geology in engineering

Geological Agencies

8/11/2019 5 Unit-I Sea

http://slidepdf.com/reader/full/5-unit-i-sea 2/27

8/11/2019 5 Unit-I Sea

http://slidepdf.com/reader/full/5-unit-i-sea 3/27

Introduction

• More than 70% of earth is covered with

water in forms of river, sea and ocean

• A sea is an extensively developed continuous

body of salt water having numerous inland

extensions

8/11/2019 5 Unit-I Sea

http://slidepdf.com/reader/full/5-unit-i-sea 4/27

• There is generally a sequences of slopes from shore

to the sea floor

 – Continental shelf 

 – Continental slope

 – Abyssal plain

8/11/2019 5 Unit-I Sea

http://slidepdf.com/reader/full/5-unit-i-sea 5/27

Geological work of SeaThe Sea waves and Currents

•Waves – (a) Oscillatory Waves (surf zone)

 – (b) Translatory Waves (shallower depth)

• Currents

 –

(a) Littoral Currents (parallel to the shore) – (b) Rip Currents (moving backwards)

8/11/2019 5 Unit-I Sea

http://slidepdf.com/reader/full/5-unit-i-sea 6/27

Marine Erosion

8/11/2019 5 Unit-I Sea

http://slidepdf.com/reader/full/5-unit-i-sea 7/27

 Attrition

Hydraulic action

 Abrasion

Corrosion

Processes of erosion

Processes of erosion

8/11/2019 5 Unit-I Sea

http://slidepdf.com/reader/full/5-unit-i-sea 8/27

Features of Marine Erosion

• Modification of the original shoreline

• Depending on number of factors

 – The strength of the sea waves and currents, their magnitude, velocity

and duration of operation

 – The lithology of the shore, that is, the type of rocks, their texture,

structure and chemical composition

 – The seaward slope of shore line – whether gentle or steep

 – The height of the shore-line

 –

The depth and chemical composition of water and – The original profile of the shore-line

8/11/2019 5 Unit-I Sea

http://slidepdf.com/reader/full/5-unit-i-sea 9/27

EROSIONALLANDFORMS

8/11/2019 5 Unit-I Sea

http://slidepdf.com/reader/full/5-unit-i-sea 10/27

Landforms of Coastal Erosion

Headlands

Bays

Sea Cliffs

Wavecut Terraces

Sea Caves

Sea ArchStack

Stump

8/11/2019 5 Unit-I Sea

http://slidepdf.com/reader/full/5-unit-i-sea 11/27

Headlands and Bays

•

Sloping shore line materials of unequal harness, thesofter rocks get eroded easily and quickly.

8/11/2019 5 Unit-I Sea

http://slidepdf.com/reader/full/5-unit-i-sea 12/27

Headlands

Bays

8/11/2019 5 Unit-I Sea

http://slidepdf.com/reader/full/5-unit-i-sea 13/27

Sea Cliffs• Seaward facing steep front of a moderately high shore-line

and is the first stage of the work of waves on the shore rocks.• They are outstanding rock projections having been smoothed

and plucked, pitted at one place and polished at another spot

by a combined action of waves and currents

8/11/2019 5 Unit-I Sea

http://slidepdf.com/reader/full/5-unit-i-sea 14/27

Wave-Cut Terraces

• A wave-cut terrace is a shallow water-shelf 

carved out of the shore rocks by advancing

waves.

• The waves first cut a notch where they strike

against the cliff rock.

8/11/2019 5 Unit-I Sea

http://slidepdf.com/reader/full/5-unit-i-sea 15/27

How are cliffs and wave-cut platforms formed?

8/11/2019 5 Unit-I Sea

http://slidepdf.com/reader/full/5-unit-i-sea 16/27

8/11/2019 5 Unit-I Sea

http://slidepdf.com/reader/full/5-unit-i-sea 17/27

DEPOSIONALLANDFORMS

8/11/2019 5 Unit-I Sea

http://slidepdf.com/reader/full/5-unit-i-sea 18/27

Landforms of coastal deposition

Shallow Water

(Neritic Deposition)

•Beaches

• Spits

• Tombolos and Bars

Deep Water Deposits

• Coral Reefs

 – Fringing reefs

 – Barrier refs

 – Atolls

8/11/2019 5 Unit-I Sea

http://slidepdf.com/reader/full/5-unit-i-sea 19/27

8/11/2019 5 Unit-I Sea

http://slidepdf.com/reader/full/5-unit-i-sea 20/27

Tombolo

Beach

8/11/2019 5 Unit-I Sea

http://slidepdf.com/reader/full/5-unit-i-sea 21/27

CORAL REEFSPeculiar types of ridge-like marine deposits which have been formed

due to accumulation of dead parts of certain types of sea-organisms -

corals (calcium secreting organisms)

Tabular sheets

Islands

Sinking of Islands

Flat topped ridges

Fully Submerged

Forms Lagoons

8/11/2019 5 Unit-I Sea

http://slidepdf.com/reader/full/5-unit-i-sea 22/27

Shore Control Problems

• Two main aspects of shore-control

problems are :

 –

Rehabilitation and stabilization of thebeach areas that have acquired immense

importance in the developmental

programmes.

 – Safety of Offshore structures

8/11/2019 5 Unit-I Sea

http://slidepdf.com/reader/full/5-unit-i-sea 23/27

People and Coastlines

• Sea Walls –

Sea walls are concrete walls with a curvedtop on them which helps to deflect the waves back outto sea.

• Boulders –

Large rocks are placed at the base of cliffsor in front of sand dunes. It prevents erosion byreducing the power of the waves.

•

Groynes –

Groynes are low walls built of wood. Theyare built at right angles to the shore to help preventsand being moved along the beach by Longshore Drift.

8/11/2019 5 Unit-I Sea

http://slidepdf.com/reader/full/5-unit-i-sea 24/27

Protecting the Coastline using Groynes

Groynes help to trap sand as it is being moved bylongshore drif 

8/11/2019 5 Unit-I Sea

http://slidepdf.com/reader/full/5-unit-i-sea 25/27

Protecting the Coastline using Boulders

To protect sand dunes from erosion

8/11/2019 5 Unit-I Sea

http://slidepdf.com/reader/full/5-unit-i-sea 26/27

How are spits formed?

8/11/2019 5 Unit-I Sea

http://slidepdf.com/reader/full/5-unit-i-sea 27/27

How are spits formed?