Geological oceanography

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Geological Oceanography
Geology (geo:- “earth" and logy: - "study of”) is an earth science concerned with the solid Earth, the rocks
of which it is composed, and the processes by which they change over time. Geology can also refer to the
study of the solid features of any terrestrial planet or natural satellite, (such as Mars or the Moon).
Geomorphology is the scientific study of the origin and evolution of topographic and bathymetric features
created by physical, biological or chemical processes operating at or near the earth’s surface.
Geomorphologists work within disciplines such as physical geography, geology, geodesy, engineering
geology, archaeology and geotechnical engineering.
Earth science is a branch of science that deals with the study of any part of the Earth, including its
environments, climates, and composition. There are severalgeneraltypes of earth science that are roughly
grouped according to the broader fields into which they fall and which correspond to four area that divide
the Earth and its immediate environment:
1. The atmosphere
2. The lithosphere or geosphere
3. The biosphere, and
4. The hydrosphere are the domains into which all types of Earth science fall.
Geological oceanography: Marine geology or geological oceanography is the study of the history and
structure of the ocean floor. It involves geophysical, geochemical, sedimentological and paleontological
investigations of the ocean floor and coastalzone.
Geologic time scale
The geologic time scale (GTS) is a system of chronological dating that relates geological strata
(stratigraphy) to time. It is used by geologists, paleontologists, and other Earth scientists to describe the
timing and relationships of events that have occurred during Earth's history.
Physiography: it is the subfield of geography that studies physical pattern and processes of the earth. it
aims to understand the forces that produce and change rocks, oceans, weather,and global flora and fauna
patterns.
Physiography of bay of Bengal
The bay of Bengal is a triangle-shaped water body, which is an extension of the INDIAN OCEAN to the
north. It is stretched over an area of 5.7 million square mi (14.7 million square km) with an average depth
of approximately 8,530 ft (2,600 m). Countries that surround the bay are srilanka, India, Bangladesh,
Myanmar, Thailand , and Malaysia. The base of the basin is a gently sloping southward plain dissected
by sub-aqua valleys, trenches,and ridges. The bottom topography is prominently marked by the Java
trench, Ganga trough, Ninety East Ridge, Eighty Five Ridge and Bengal Deep Sea Fan. The Bay of
Bengal is dotted with numerous islands, including Andaman and Nicobar, Union Territory of India.
Continental Shelf the width of the continental shelf off the coast of Bangladesh varies considerably. It is
less than 100 km off the south coast between Hiron Point and the swatch of no ground and more than 250
km off the coast of cox's bazar.
Brief history of marine geology

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3: hypsometry? Draw and briefly explain it.
A hypsometric curve is a histogram or cumulative distribution function of elevations in a geographical
area.
A hypsometric curve is plotted on a graph on which the x-axis represents surface area and the y-axis
represents elevation above or below a datum (normally sea level). The curve shows how much area lies
above and below marked elevation intervals.
Inner structure of earth
Internal structure is divided into three parts

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1) Crust 2) Mantle 3) Core
) The Crust: - It is the upper most part of Earth; it is solidified and hard which composes of different
rocks. The Earth crust is divided into two part
i) Continental Crust ii) Oceanic Crust
i) Continental Crust: - Continental Crust is the continental shelf or part of earth and under the mountains.
Continental Crust is lesser denser and mostly light rocks are formed. Continental Crust is rich in Si and Al
and termed as SIAL Crust. Continental Crust thickness ranges from 30 to 100km. Specific gravity of
Continental Crust is 2.7 to 2.9.
ii) Oceanic Crust:- Oceanic Crust is too much denser then Continental Crust. Oceanic Crust is dark in
color. Oceanic Crust is composed of Si and Mg it is term as SIMA. Specific gravity of Oceanic Crust is
3.5 to 4.1. Dark and heavy minerals are found in Oceanic Crust.
The line or separation between Crust and Mantle is known as Mohorovicich Discontinuity.
2) Mantle:- It is semi-molten form, all the rocks are in molten form. 84% of Earth’s volume is made
up of mantle. 2,886(1,793 mil) average thickness of mantle.
Geologist always go for a easy way to understand the Geology so for that purpose Mantle is divided into
further more part
i) Upper mantle ii) Lower mantle
i) Upper mantle: - Upper mantle is semi-molten material; Upper mantle is composed of Si and Mg
minerals.
ii) Lower Mantle: - Lower Mantle has hot molten material; Lower Mantle is Si and Mg rich minerals.
The Lower Mantle has too much temperature then upper mantle.
After the Lower mantle Gutenberg Discontinuity starts which separates mantle from core.
3) The Core: - Core is the most inner part of Earth, The Core is thicker then crust and Mantle. The
Core show realcomposition of Earth. The Core is mostly rich in Fe and Ni, same as a meteorites tells us
that all the solar system is derived from one and same body.
To understand the mystery of core Geologist had divided the Core into two parts
i) Outer Core ii) Inner Core
i) Outer Core: - Outer Core is totally in molten form, Outer Core is composed of SIMA as well as little
bit S, Ni and Fe in small content. Due to high pressure this portion behaves like solid but it is in melt
form.
ii) Inner Core : - Inner Core is also in molten , Inner Core the portion where too much heat and pressure.
Due to high pressure it totally behaves like solid material. Ni and Fe are the main of which Inner Core is
compose of.

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The lithosphere is a layer that includes the crust and the upper most portion of the mantle (Figure 10h-2).
This layer is about 100 kilometers thick and has the ability to glide over the rest of the upper mantle.
Because of increasing temperature and pressure,deeper portions of the lithosphere are capable of plastic
flow over geologic time. The lithosphere is also the zone of earthquakes,mountain building, volcanoes,
and continental drift.
The asthenosphere is the highly viscous, mechanically weak and ductilely deforming region of the upper
mantle of the Earth. It lies below the lithosphere, at depths between approximately 80 and 200 km (50 and
120 miles) below the surface. The Lithosphere-Asthenosphere boundary is usually referred to as LAB.
The asthenosphere is almost solid, although some of its regions could be molten (e.g.,below mid-ocean
ridges)
One interesting property of the continental and oceanic crust is that these tectonic plates have the ability
to rise and sink. This phenomenon, known as isostacy, occurs because the crust floats on top of the mantle
like ice cubes in water. When the Earth's crust gains weight due to mountain building or glaciation, it
deforms and sinks deeper into the mantle .If the weight is removed, the crust becomes more buoyant and
floats higher in the mantle.This process explains recent changes in the height of sea-level in coastalareas.
The continental margin is the zone of the ocean floor that separates the thin oceanic crust from thick
continental crust. Together, the continental shelf, continental slope, and continental rise are called the
continental margin.

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There are two types of continental margins: active and passive margins
1: Active continental margins are those that are tectonically active, such as along much of the Pacific
coast. Active margins are marked by earthquakes,volcanoes, and mountain belts.
2: A passive margin is the transition between oceanic and continental lithosphere that is not an active
plate margin. A passive margin forms by sedimentation above an ancient rift, now marked by transitional
lithosphere.
Continental shelf : A continental shelf is the edge of a continent that lies under the ocean.A continental
shelf extends from the coastline of a continent to a drop-off point called the shelf break.every nation has a
continental shelf extending no more than 200 nautical miles from the nation's coastline. The width of
continental shelves worldwide varies from a 30 meters to 1500 kilometers.
From the break, the shelf descends toward the deep ocean floor in what is called the continental slope.
seafloor spreading:
abyssal plain : An abyssal plain is an underwater plain on the deep ocean floor, usually found at depths
between 3,000 metres and 6,000 metres .Lying generally between the foot of a continental rise and a mid-
ocean ridge, abyssal plains cover more than 50% of the Earth's surface.
Oceanic ridge
A mid-ocean ridge (MOR) is an underwater mountain system formed by plate tectonics. It consists of
various mountains linked in chains, typically having a valley known as a rift running along its spine. This
type of oceanic mountain ridge is characteristic of what is known as an 'oceanic spreading center',which
is responsible for seafloor spreading.
The oceanic ridge system is a continuous underwater mountain range with parts found in every ocean of
the world. The ridge system is created when magma rising between diverging plates of the lithosphere
cools and forms a new layer of crust.

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An oceanic trench is a narrow trough parallel to the coastline that can reach a depth of 10 kilometers (6
miles) or more and a slope of 15 degrees.
4: plate
A tectonic plate (also called lithospheric plate) is a massive, irregularly shaped slab of solid rock, generally
composed of both continental and oceanic lithosphere. Plate size can vary greatly, from a few hundred to
thousands of kilometers across; the Pacific and Antarctic Plates are among the largest. Plate thickness also
varies greatly, ranging from less than 15 km for young oceanic lithosphere to about 200 km
Crust is the outermost layer of a planet. The crust of the Earth is composed of a great variety of igneous,
metamorphic, and sedimentary rocks
Plate tectonics is a scientific theory which explains the origin, history and movement of rigid tectonic
plates of earth’s lithosphere. The theory builds on the concepts of continental drift, developed during the
first decades of the 20th century, and accepted by the majority of the geoscientific community when the
concepts of seafloor spreading were developed in the late 1950s and early 1960s.
Theory of continental drift
The theory of plate tectonics states that the crust of the earth is broken up into large pieces, or plates, that
move around by floating on top of the liquid layer of the earth known as the mantle. This process is
driven by convection currents within the mantle. Convection currents are formed by hot magma near the
core rising towards the surface,while cooler magma near the crust sinks, setting up a current that causes
the plates to move. These currents are the primary driving force behind plate movement.
All land was joined into 1 supercontinent called “Pangaea :Over Time: Continents drifted apart creating
Gondwanaland and Laurasia, then Laurasia broke apart into North America, Europe and Asia. Then
Gondwanaland broke into Africa, South America, Antarctica and Australia. Then India collided with

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Eurasia. Continents continue to drift apart due to the convection currents in the Earth to where the
continents are today.
Future: The plates will continue to move based on if they are divergent (away),convergent (towards) or
transform (slide) boundaries until the all come back together with an inland sea in the middle creating
Pangaea Altima.
Plate tectonic boundaries are regions where lithospheric plates meet. There are three types of plate
tectonic boundaries: divergent, convergent, and transform.
1.divergent: Divergent boundaries occur where two plates move apart from each other. This happens at
the mid-ocean ridges, where seafloor spreading and volcanic activity continuously add new oceanic crust
to the oceanic plates on both sides. Examples are the Mid-Atlantic Ridge and East Pacific Rise.
2: Convergent. Convergent boundaries occur where two plates slide towards each other to form either a
subduction zone (if one plate, normally an oceanic plate moves underneath the other) or a continental
collision. Subduction zones include the boundaries of the Pacific plate (e.g. Western South America)
where the dense oceanic lithosphere sinks beneath the less dense continental plates. The type of
convergence depends on the types of plates involved: namely, (1) oceanic–oceanic convergence; (2)
oceanic–continental convergence; (3) continental–continental convergence
3: transform: Transform boundaries are places where plates slide sideways past each other. At transform
boundaries lithosphere is neither created nor destroyed. Many transform boundaries are found on the sea
floor, where they connect segments of diverging mid-ocean ridges. California's San Andreas Fault is a
transform boundary.

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Different types of plate on earth
1: Major plate: major plate is any plate with an area greater than 20 million km2
. Pacific Plate –
103,300,000 km2 , North American Plate – 75,900,000 km2, Eurasian Plate African Plate – 61,300,000
km2 , Antarctic Plate , Indo-Australian Plate – 58,900,000 km2 often considered two plates: Australian
Plate – 47,000,000 km2, Indian Plate – 11,900,000 km2 and South American Plate
2: Minor plate: a minor plate is any plate with an area less than 20 million km2
but greater than 1 million
km2
. Example. Somali Plate – 16,700,000 km2
Philippine Plate – 5,500,000 km2
.
, Arabian Plate – 5,000,000 km2
, Caribbean Plate
3: Microplate: a Microplate is any plate with an area less than 1 million km2
. Such as Sunda Plate,
Greenland Plate , Madagascar Plate etc.
Isostacy in the light of Archimedes principle
Archimedes principle states that the buoyant force on an object submerged in a fluid is equal to the weight
of the fluid that is displaced by that object. the earth’s crust can move up and down a result of the
interaction of the downward force of the crust and the upward force of the mantle . The balance between
these two forces is called Isostacy.
Isostasy is a fundamental concept in the Geology. It is the idea that the lighter crust must be floating on
the denser underlying mantle. Isostasy describes vertical movement of land to maintain a balanced crust.
Greenland is an example of isostasy in action. The Greenland land mass is mostly below sea level because
of the weight of the ice cap that covers the island. If the ice cap melted, the water would run off and raise
sea level. The land mass would also begin to rise, with its load removed, but it would rise more slowly
than the sea level. Long after the ice melted, the land would eventually rise to a level where its surface is
well above sea level; the isostatic balance would be reached again.

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Volcanism in the light of plate tectonics
Volcanism is the phenomenon of eruption of molten rock (magma) onto the surface of the Earth, where
lava, pyroclastics and volcanic gases erupt through a break in the surface called a vent. It includes all
phenomena resulting from and causing magma within the crust or mantle of the body, to rise through the
crust and form volcanic rocks on the surface. Magma is formed at three main plate-tectonic settings:
divergent boundaries (decompression melting), convergent boundaries (flux melting), and mantle plumes
(decompression melting)
The plate-tectonic settings of common types of volcanism. Composite volcanoes form at subduction
zones, either on ocean-ocean convergent boundaries (left) or ocean-continent convergent boundaries
(right).
Both shield volcanoes and cinder cones form in areas of continental rifting. Shield volcanoes form above
mantle plumes, but can also form at other tectonic settings.

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Sea-floor volcanism can take place at divergent boundaries, mantle plumes and ocean-ocean-convergent
boundaries.
What evidence can you cite to support the theory of plate tectonics?
The evidence for plate tectonics includes the distribution and age of mid-ocean ridges, hot spots, and
trenches; the configuration and location of atolls and guyots; the age of sediments; the presence of
terranes at the edges of continental masses; fossils; and, of course,paleomagnetic data.
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Sediment is a naturally occurring material that is - broken down by processes of weathering and erosion,
and is subsequently transported by the action of wind, water,or ice, and/or by the force of gravity acting
on the particles and deposited in any other places
Sediments are classified according to their size. In order to define them from the smallest size to the
largest size: clay, silt, sand, pebble, cobble, and boulder.
Marine sediment, any deposit of insoluble material, primarily rock and soil particles, transported from
land areas to the ocean by wind, ice, and rivers, as well as the remains of marine organisms, products of
submarine volcanism, chemical precipitates from seawater,and materials from outer space (e.g.,
meteorites) that accumulate on the seafloor
Based on the sources, sediments (marine sediments) are of four kinds-
1. lithogenous: Lithogenous are from the land, they form through the weathering process and are composed
of small particles from weathered rock and volcanic activity. And within Lithogenous sediments there are
two sub categories:
Terrigenous and red clay. Terrigenous sediments are produced when the weathering process occurs above
water. Wind and other natural sources then carry these particles to the ocean where they sink.
Red clay, also known as abyssal clay however, is mostly located in the ocean and is formed from a
combination of Terrigenous material and volcanic ash.
2. Biogenous: Biogenous sediments are formed from the remnantsof organisms that refusedto be dissolved.
Good examples of these organisms include shellfish, clams, anything that has a shell. Other things that
could avoid being dissolved include bones and teeth and other appendages. In deeper waters, shells of
plankton and other microscopic organisms form these kinds of sediments.
3. Hydrogenous: Hydrogenous sediments are sediments solidified out of ocean water. As such, chemical
reactions create these kinds of sediments. The precipitation of dissolved chemicals from seawater. These
kinds of sediments are found commonly near hydrothermal vents.
4. Cosmogenous: Cosmogenous sediments are probably the most interesting of all four kinds of sediment
because they are alien in nature. These kinds of sediments are carried to earth on meteorites or asteroids.
What sediments accumulate most rapidly? Least rapidly?
Accumulation rate depends on the availability of the sediment in question. The rate of sediment deposition
on continental shelves is variable, but it is almost always greater than the rate of sediment deposition in the
deep ocean. Near the mouths of large rivers, 1 meter (about 3 feet) of terrigenous sediment may accumulate

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every 1,000 years. In the deep ocean, mudslides rushing down the continental slope deposit turbidites—
layers of coarse-grained terrigenous sediments interleaved with finer sediments typical of the deep-sea
floor. Turbidite accumulation may be quite rapid adjacent to continental shelves shaken by earthquakes and
subject to much erosional runoff from land.
The sediments slowest to accumulate are hydrogenous sediments. Accumulation rates on manganese
nodules are typically the thickness of a dime every thousand years. (The rate of accumulation of
cosmogenous sediment is so slow that they never accumulate as distinct layers. They occur as isolated
grains in other sediments, rarely constituting more than 1 percent of any layer.)
. Can marine sediments tell us about the history of the ocean from the time of its origin? Why?
The distribution, depth, and composition of sediment layers tell of conditions in the comparatively recent
past. In the Pacific, for example, sediments get older with increasing distance from the East Pacific Rise
spreading center, but the maximum age is roughly early Cretaceous or late Jurassic (around 145 million
years old). The "memory" of the sediments is not ancient and in fact is continually being erased by ocean
floor subduction. We can’t see farther back than about 180 million years because the oceanic conveyor belt
of plate tectonic processes destroys the evidence.
Still, marine sediments in the modern basins can shed light on unexpected details of the last 180 million
yearsof Earth's history. One of the oddest details is the unexplained extinction of up to 52 percentof known
marine animal species (and the dinosaurs) at the end of the Cretaceous Period 65 million years ago.
Researchers have proposed hypotheses such as a sudden and violent increase in worldwide volcanism or
the impact of one or more very large meteors or comets to explain this catastrophe. The clouds of dust and
ash thrown into the atmosphere by any of these events would have drastically reduced incident sunlight and
greatly affected the lives of organisms and the photosynthetic base of ecosystems. Oceanographers are
presently searching for evidence of the cause of the Cretaceous extinctions in layers of deep sediments.
How is crust different from lithosphere?
Lithosphere includes crust (oceanic and continental) and rigid upper mantle down to
the asthenosphere. The velocity of seismic waves in the crust is much different from that in
the mantle. This suggests differences in chemical composition, or crystal structure, or both.
The lithosphere and asthenosphere have different physical characteristics: the lithosphere is
generally rigid, but the asthenosphere is capable of slow plastic movement. Asthenosphere
and lithosphere also transmit seismic waves at different speeds
Factor affecting the rate and quantity of sediment transport in the sea.
CCD: Carbonate compensation depth: the depth at which the rate of carbonate dissolution on the seafloor
exactly balances the rate of carbonate supply from the overlying surface waters.

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6:
Coast: A strip of land of indefinite length and width (may be tens of Km) that extends from the seashore
inland to the first major change in terrain features. The coast extends inland from the shore as far as
ocean-related coast land that is affected by storm waves. The width of the coast may vary from less than 1
kilometer (0.6 mile) to many tens of kilometers.
A. Coasts can be classified based on geology as either active or passive.
1.Active coasts are those located near a plate boundary, and thus in close proximity to tectonic activity
(e.g.,earthquakes).
2.Passive coasts are located farther from plate boundaries and thus are not associated with the tectonic
activity of active coasts.
B. Coasts can also be classified based on the way that they are formed
1. Primary coasts are formed by more land-driven rather than ocean-driven processes like plate tectonics,
land erosion and sedimentation. .Primary coasts include land-deposition coasts,formed when rivers flow
into the ocean and sediment accumulates along a wide shelf. An example is the Nile River Delta.
Volcanic coasts,like the Hawaiian Island hot spot, are also primary coasts.
2. Secondary coasts are formed by more ocean driven processes like wave erosion or growth of a coral
reef. Secondary coasts include marine-deposition coasts where sea movement causes accumulation of
ocean sediments in a single place. Examples include barrier islands, mud flats and coral reef ecosystems.
Coasts are dynamic, constantly changing. Coasts are constantly being shaped by physical processes
including erosion of sediment from the movement of wind and waves. Many human societies are located
along coasts and their activities also change this environment.
Coastal area of Bangladesh
Pramanik (1983) has divided the Bangladesh coastal zone into three regions namely eastern, central and
western coastal region.
1.Eastern coastal zone: the eastern coastal zone starts from Bodormokam, the southern tip of mainland
Teknaf to the Feni river estuary. This zone is very narrow. A series of small hills are run parallel to this

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zone. Karnafully, Sangu and Matamuhury River fall into the Bay of Bengal in this area. The Naf river falls
to the Bay of Bengal dividing Bangladesh from Myanmar. Soil characteristics of the eastern coastal zone
are dominated by submerged sands and mudflats (Islam, 2001). Two of the country’s most important sandy
beaches from tourists’ perspective, namely Patenga and Cox’s Bazar are located in this coastal zone.
Fish farming, fishing in the bay, salt production and tourism are main economic activities of the zone.
2. Central coastal zone Central coastal zone extends from Feni river estuary to the eastern corner of the
Sundarbans, covering Noakhali, Barisal, and Bhola and Patuakhali districts. The zone receives a large
volume of discharge from the Ganges-Bhrahmputra-Meghna river system, forming high volume of silty
deposition. More than 70 % of the sediment load of the region is silt; with an additional 10 % sand
(Coleman, 1969; cited in Allison et al., 2003).Because of the sediment discharge and strong current, the
morphology of the zone is very dynamic and thus erosion and accretion rates in the area are very high
(Coleman, 1969; cited in Allison et al., 2003). Numerous islands are located in the area including the
country’s only island district Bhola.Kuakata, an attractive sandy beach is located at the zone under
Khepupara upazilla of Patuakhali district.
3.The western coastal zone is covered by the Sundarbans mangrove forest, covering greater Khulna and
part of Patuakhali district. Because of presence of mangrove forest, the zone is relatively stable in terms of
soil erosion. The area lies at 0.9 to 2.1 metre above mean sea level (Iftekhar and Islam, 2004). Soil
characteristics of the western coastal zone are silty loams or alluvium. Islam (2003).Most of the people are
depended on agricultural land, livestock, fisheries,forestry, waterways,salt production, seaport facilities,
sites of archeological importance and tourism.
Delta: A large or small subaqueous and subaerial accumulation of river-derived sediments forming a low
lying plain found at the mouth of a river.
Deltas form wherever sediment at a river mouth is being supply faster than it can be removed by marine
processes.They are dynamic areas that change rapidly due to continual recreation of land or the erosion of
unstable island and land during storm and flood events. Great examples can be found at the Ganges delta
in Bangladesh, the Nile Delta in Egypt.
Delta types
Deltas are typically classified into three basis on shape
1: Bird’s foot- where delta formation is river- dominated and less subject to tidal or wave action, a delta
may take on a bird’s foot shape. The Mississippi delta is an example of a bird’s foot delta. The shape of
the delta is like a claw.
2: Arcuate delta- has a rounded, convex outer margin. A good example is the Nile delta which is
dominated a little more by tidal and wave action. The land around the river mouth arches out into the sea.
The river splits many times on the way to the sea,creating a fan effect.
3: Cuspate delta- where the material brought down by a river is spread out evenly on either side of its
channel. It is like a cup and is shaped by gentle, regular, but opposing, sea currents or longshore drift. An
example of a cuspate delta is the Tiber.
Deltas are typically classified according to the main control on deposition

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1: Wave-dominated deltas: - wave-driven sediment transport controls the shape of the delta, and much of
the sediment emanating from the river mouth is deflected along the coast line. With a high wave energy
near shore and a steeper slope offshore, waves will make river deltas smoother. Waves can also be
responsible for carrying sediments away from the river delta, causing the delta to retreat.
2: Tide-dominated deltas:- A tide-dominated delta is one that forms where tidal currents are stronger than
river outflows. Tide-dominated deltas usually form in areas with a large tidal range, or area between high
tide and low tide.The massive Ganges-Bramhaputra delta
3: Gilbert deltas: - A Gilbert delta (named after Grove Karl Gilbert) is a specific type of delta formed
from coarse sediments, as opposed to gently-sloping muddy deltas such as that of the Mississippi.
4: Tidal freshwater deltas:- A tidal freshwater delta is a sedimentary deposit formed at the boundary
between an upland stream and an estuary.
formation and progradation
The process of formation is as follows;
1. As rivers near the sea they contain high sediment loads and the rivers start to spread out laterally.
Ocean water entering these streams can reduce velocities as well.
2. This lateral movement of water reduces hydraulic radius and increases wetted perimeter.
3. This causes sediment to be deposited, as does flocculation where clay sediments join together, gain
in mass and sink.
4. This sedimentation builds up over time and can create small islands which split the channel, similar
to braided streams.
5. This can happen again and again until the river consists of a number of smaller streams separated by
islands.
6. If sediment is coarse grained arcuate deltas form. If it is fine grained then birds foot deltas can be
created (e.g. Mississippi).
7. Sediment is often deposited on the sea ward side, which builds the delta outwards into the sea. These
areas are called fore beds, and are highly unstable. They often collapse and cause mass movements
within the sea and clouds of sediment known as turbidity currents.

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Progradation refers to the growth of a river delta farther out into the sea over time. This occurs when the
mass balance of sediment into the delta is such that the volume of incoming sediment is greater than the
volume of the delta that is lost through subsidence, sea-level rise, and/or erosion.
Progradation can be caused by:
1. Periods of sea-level fall which result in marine regression. This can occur during major continental
glaciations within ice ages, be caused by changes in the rates of seafloor spreading that affects the volume
of the ocean basins, or tectonic effects on the regional mantle density structure that can change the geoid
elevation.
2. Extremely high sediment input.
Estuary: An estuary is a partially enclosed coastal body of brackish water with one or more rivers or
streams flowing into it, and with a free connection to the open sea.Estuaries form a transition zone
between river environments and maritime environments.
Shore and shore profile
The shore is a zone that lies between the lowest tide level (low tide) and the highest elevation on land that
is affected by storm waves. The width of the shore varies between a few meters and hundreds of meters.
Shoreline: The demarcation line between water and land is called shoreline. . The line delineating the
shoreline on Nautical Charts (Sea Maps) approximates this Mean High Water Line. The shoreline is not
easy to identify in the nature in contrast to the coastline, which is based on a clear morphological shift
between the shore and the coast.
Shore profile :

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Classification of coastal landforms
Probably the most comprehensive, and therefore, the most widely used classification was
given by marine geologist Francis P. Shepard (1937), which he modified and further advanced in
later years .
He divided coasts into primary coast and secondary coast, and divided each into several categories.

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Primary coasts are the coasts that were created by general geological but non-marine processes.
These coasts are generally young and are shaped by terrestrial processes including erosion,
rivers/stream deposition, glaciers, volcanism, and tectonic movements. Above is an outline of the
classification of primary coasts.
Secondary coasts are shaped mainly by marine processes including marine erosion and deposition
due to wave action, sediment transport by currents, or building activities of certain organisms.
These coasts are generally older, they are old enough that their non-marine character has been
removed (or out-weighed) by marine physical or biological processes.

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Coastline: Technically the line that forms the boundary between the COAST and the SHORE. The
coastline marks the boundary between the shore and the coast. It is the landward limit of the effect of the
highest storm waves on the shore
Coastal area:Coastal areas are commonly defined as the interface or transition areas between land and
sea,including large inland lakes. Coastal areas are diverse in function and form, dynamic and do not lend
themselves well to definition by strict spatial boundaries. Unlike watersheds,there are no exact natural
boundaries that unambiguously delineate coastalareas
Coastalzone: Coastalzone means the coastalwaters (including the land therein and thereunder) and the
adjacent shorelands (including the waters therein and thereunder), strongly influenced by each and in
proximity to the shorelines of the severalcoastal states,and includes islands, transitional and intertidal
areas,salt marshes,wetlands and beaches.
The beach is an accumulation of Unconsolidated sediments(sand, shingle, cobbles ,pebbles, cobblestones,
shell etc.) extending from the mean low tide line to some physio-graphic change such as a sea cliff or
dune field or to point where permanent vegetation is established. A shore of unconsolidated material is
usually called a beach. The area of the beach above the shoreline is often called recreational beach.
shore profile

19. 19
A beach is a landform along the shoreline of an ocean, sea,lake, or river. It usually consists of loose
particles, which are often composed of rock, such as sand, gravel, shingle, pebbles, or cobblestones.
Beaches typically occur in areas along the coast where wave or current action deposits and reworks
sediments.
Types of beach
1. Wave dominated beach
2. Tide dominated beach
3. Tide modified beach
Wave-dominated beaches occur predominately along the higher wave energy coast where the spring tide
range is predominately less than 1.5 m. and average waves range between 0.5 and 3 m.
1. Dissipative beach: Dissipative beaches only occur on parts of the high energy southern coast
where waves regularly exceed 2.5 m and where the beaches are composed of fine sand.
2. Longshore bar and trough: Longshore bar and trough beaches are characterized by waves
averaging 1.5-2 m, which break over a near continuous longshore bar located between 100-150 m
seaward of the beach, with a 50-100 m wide, 2-3 m deep longshore trough separating it from the
beach.
3. Rhythmic bar: They usually consist of relatively fine-medium (0.3 mm) sand and exposure to
waves averaging more than 1.5 m. They are characterized by an outer bar which is separated from
the beach by a deep trough.
4. Transverse bar and rip (TBR): They occur primarily on beaches composed of fine to medium
sand (0.3 mm) and exposed to waves averaging 1.5 m.
5. Low tide terrace:Low tide terrace beaches tend to occur when waves average about 1 m and sand
is fine to medium. They are characterised by a moderately steep beach face,which is joined at the
low tide level to an attached bar or terrace,hence the name - low tide terrace. The bar usually
extends between 20-50 m seaward and continues alongshore, attached to the beach.
6. Reflective sandy beaches lie at the lower energy end of the wave-dominated beach spectrum.
They are characterised by relatively steep,narrow beaches usually composed of coarser sand (0.4
mm).

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The beach profile extends from the offshore zone to the backshore zone. The beach itself forms from the
nearshore to the backshore within the tidal range.
Optimum conditions and theory of coral reef
1. Sunlight: Corals need to grow in shallow water where sunlight can reach them. Corals depend on
the zooxanthellae (algae) that grow inside of them for oxygen and other things, and since these
algae needs sunlight to survive, corals also need sunlight to survive. Corals rarely develop in
water deeper than 165 feet (50 meters).
2. Clear water: Corals need clear water that lets sunlight through; they don’t thrive well when the
water is opaque. Sediment and plankton can cloud water,which decreases the amount of sunlight
that reaches the zooxanthellae.
3. Warm water temperature:Reef-building corals require warm water conditions to survive.
Different corals living in different regions can withstand various temperature fluctuations.
However,corals generally live in water temperatures of 68–90° F or 20–32° C.
4. Clean water:Corals are sensitive to pollution and sediments. Sediment can create cloudy water
and be deposited on corals, blocking out the sun and harming the polyps. Wastewater discharged
into the ocean near the reef can contain too many nutrients that cause seaweeds to overgrow the
reef.
5. Saltwater: Corals need saltwater to survive and require a certain balance in the ratio of salt to
water. This is why corals don’t live in areas where rivers drain fresh water into the ocean
Types of Coral Reef Formations
Scientists generally divide coral reefs into four classes: fringing reefs,barrier reefs,atolls, and patch reefs.
1. Fringing reefs grow near the coastline around islands and continents. They are separated from the
shore by narrow, shallow lagoons. Fringing reefs are the most common type of reef that we see.

21. 21
2. Barrier reefs also parallel the coastline but are separated by deeper, wider lagoons. At their
shallowest point, they can reach the water’s surface forming a “barrier” to navigation. The Great
Barrier Reef in Australia is the largest and most famous barrier reef in the world.
3. Atolls are rings of coral that create protected lagoons and are usually located in the middle of the
sea. Atolls usually form when islands surrounded by fringing reefs sink into the sea or the sea
level rises around them (these islands are often the tops of underwater volcanoes). The fringing
reefs continue to grow and eventually form circles with lagoons inside.
4. Patch reefs are small, isolated reefs that grow up from the open bottom of the island platform or
continental shelf. They usually occur between fringing reefs and barrier reefs. They vary greatly
in size, and they rarely reach the surface of the water.
Coral reef and coral reef formation
Coral reefs are most diverse underwater structures made from calcium carbonates secreted by corals.
Coralllium rubrum, produces coral reef Reefs grow best in warm, shallow, clear, sunny & agitated waters.
Factors for coral reef formation
1: temperature
2: salinity
3: light
4: current
5: water depth
6. water clarity
1: Darwin’s or subsidence hypothesis
Darwin’s theory starts with a volcanic island which becomes extinct
• Asthe island and ocean floor subside, coralgrowth builds a fringing reef,often including a shallow lagoon
between the land and the main reef.
• As the subsidence continues, the fringing reef becomes a larger barrier reef further from the shore
With a bigger and deeper lagoon inside.
• Ultimately, the island sinks below the sea,and the barrier reef becomes an atoll enclosing an open lagoon.

22. 22
2: Daly glacial hypothesis: Daly’s Glacial Control Theory:
Daly, while studying the coral reefs of Hawaii, was greatly impressed by two things. He observed that the
reefs were very narrow and there were marks of glaciations. It appeared to him that there should be a close
relationship between the growth of reefs and temperature.
According to Daly’s hypothesis, in the last glacial period, an ice sheet had developed due to the fall in
temperature. This caused a withdrawal of water, equal to the weight of the ice sheet. This withdrawal
lowered the sea level by 125-150 m.
The corals which existed prior to the ice age had to face this fall in temperature dining this age and they
were also exposed to air when the sea level fell. As a result, the corals were killed and the coral reefs and
atolls were planed down by sea erosion to the falling level of sea in that period.
When the ice age ended, the temperature started rising and the ice sheet melted. The water returned to the
sea,which started rising. Due to the rise in temperature and sea level, corals again started growing over the
platforms which were lowered due to marine erosion.
As the sea level rose, the coral colonies also rose. The coralcolonies developed more on the circumference
of the platforms because food and other facilities were better available there than anywhere else.
Hence, the shape of coral reefs took the form of the edges of submerged platforms, A long coral reef
developed on the continental shelf situated on the coast of eastern Australia. Coral reefs and atolls
developed on submerged plateau tops. After the ice age, the surface of platforms was not affected by any
endogenetic forces and the crust of the earth remained stationary.
Estuary : Anestuary is a partially enclosed coastalbody of brackish waterwith one or more rivers or streams
flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river
environments and maritime environments

23. 23
Dune: a mound or ridge of sand or other loose sediment formed by the wind, especially on the sea coast or
in a desert.
7. Difference between
Geology and physiography
Geology Physiography
1 Geology is a science that is interested in how the
land got into the shape it did.
Physiography is the description including
form, substance,arrangement and changes of
especially, natural features.
2 structure and formation of earth physical characteristics of the earth such as;
bodies of water,climate, soils, natural
vegetation and animal life
3 There are many sub-divisions to Geology which
includes Mineralogy, structural geology,
palaeontology, geomorphology, engineering
geology
Subfield of geography
4
5
Plate and crust
Crust Plate
1 crust is the outer shell of the earth A plate is a section of crust
2 Plates can be made up of both oceanic crust,
which is thinner and denser, and continental
crust, which is thicker and less dense
3 crust is the solid lithified surface of earth plate is broken part of that crust
4
5
Crust and lithosphere
Crust Lithosphere
1 The crust is the thin layer of distinctive
chemical composition overlying the
ultramafic upper mantle
The lithosphere is the rigid outer layer of the
Earth. The lithosphere includes the crust
(whether continental or oceanic) and the
uppermost part of the upper mantle.
2 typically 6 - 7 km thick It thins to a few kilometres at ocean
spreading centres,thickens to about 100 -
150 km under the older parts of ocean basins,
and is up to 250 - 300 km thick under
continental shield areas
3 Crust consists of the things that are
necessary for life.
Lithosphere is broken into giant plates
4 The crust is the topmost layer out of the
three layers called the core, mantle and
crust
The region below thelithosphere is made up
of asthenosphere

24. 24
5 Crust is studied having the chemical
composition of the earth
studied having the mechanical properties of
the earth
6 Crust can be divided as oceanic crust and
continental crust
Lithosphere also can be divided as oceanic
lithosphere and continental lithosphere.
Note :
Bengal fan
The Bengal Fan is the largest submarine fan in the world, with a length of about 3000 km, a width of
about 1000 km and a maximum thickness of 16.5 km. It has been formed as a direct result of the India–
Asia collision and uplift of the Himalayas and the Tibetan Plateau. It is currently supplied mainly by the
confluent Ganges and Brahmaputra Rivers, with smaller contributions of sediment from severalother
large rivers in Bangladesh and India. The fan completely covers the floor of the Bay of Bengal. It is
bordered to the west by the continental slope of eastern India, to the north by the continental slope of
Bangladesh and to east by the northern part of Sunda Trench off Myanmar and the Andaman Islands and
continues along the west side of the Ninety East Ridge. The Nicobar Fan.
Statistics of the shape and size of the earth and it’s ocean
Ocean Avg. depth Area ×106
km2
% of ocean surface area % of earth’s surface
Pacific 4028 m 179.7 50.1 35.5
Atlantic 3332 m 93.7 25.9 18.4
Indian 3897 m 73.6 20.4 14.4
arctic 1117 m 14.1 3.9 2.8
All oceans 3795 m 361.1 100 70.8
Statistics of Earth
Feature Measurement
Mass 5.9723 ×1024
kg
The radius of Earth at
the equator
6,378 kilometers
At polar 6356.752 km
Mean density (kg/m3) 5514
Bathymetry of Bay of Bengal
Geophysical map
Volcanic Island
Geological time scale is a scale to divide all the time since the earth first came into being about 4.5 billion
years ago. The main purpose of a time scale is to determine the age of rocks, fossil and express their age

25. 25
using a standard unit of time. It is also useful for expressing the timing of an event that took place in
earth’s geologic history.
Earth science/ geoscience: It is the branch of science dealing with the physical constitution of the earth and
its atmosphere. The four basic areas of Earth science study are: geology, meteorology, oceanography, and
astronomy. Geology deals with the composition of Earth materials, Earth structures, and Earth processes.
Meteorology is the study of the atmosphere and how processesin the atmosphere determine Earth'sweather
and climate. Oceanography is the study of Earth's oceans - their composition, movement, organisms and
processes.
1: continental drift : Continental drift, large-scale horizontal movements of continents relative to one
another and to the ocean basins during one or more episodes of geologic time.
Features created by plate tectonics
a: ocean ridge
b: ocean trench
c: volcanic island and archipelago
description :
a: aseismic ridge
b: abyssal plain
c: seamount
2: birth of ocean / seafloor spreading
Seafloor spreading is a process that occurs at mid-ocean ridges, where new oceanic crust is formed
through volcanic activity and then gradually moves away from the ridge. When oceanic plates diverge,
tensional stress causes fractures to occur in the lithosphere. At a spreading center basaltic magma rises up
the fractures and cools on the ocean floor to form new seabed. As new seafloor forms and spreads apart
from the mid-ocean ridge it. Hydrothermal vents are common at spreading centers.
Rates vary from about 0.1 cm (0.04 inch) per
year to 17 cm (6.7 inches) per year. Seafloor-
spreading rates are much more rapid in the
Pacific Ocean than in the Atlantic and Indian
oceans.
1.2 What types of sediment found on
seafloor

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1.3 Plates names in Indian ocean and bay of Bengal, Bangladesh?
The bengal basin occupied mostly by Bangladesh, is the result of plate collision between the
Indian plate and the Asian plate. The collision took place in stages, beginning in the Eocene time
(50 to 55 million years before present). Underneath the Bay of Bengal, which is part of the great
Indo-Australian Plate and is slowly moving north east. This plate meets the Burma Microplate at
the Sunda Trench. The Nicobar Islands, and the Andaman Islands are part of the Burma
Microplate. The India Plate subducts beneath the Burma Plate at the Sunda Trench or Java
Trench. Here,the pressure of the two plates on each other increase pressure and temperature
resulting in the formation of volcanoes such as the volcanoes in Myanmar, and a volcanic arc
called the Sunda Arc.
Bangladesh and the Ganges Brahmaputra Delta lies at the junction of three plates: the Indian
Plate, the Eurasian Plate and the Burma Plate.
how many plates are there in earth ?
1.4
3: whey volcano lies near subduction zone?
Subduction is a geological process that takes place at convergent boundaries of tectonic plates where one
plate moves under another and is forced or sinks due to gravity into the mantle. Regions where this process
occursare known assubduction zones. Ratesofsubduction are typically in centimetersper year. Subduction
zones are sites that usually have a high rate of volcanism and earthquakes. A subduction zone forms when
continental crust and oceanic crust collide. The continental crust is thicker and more buoyant than the
oceanic crust so the oceanic crust subducts beneath the continental crust. As the plate sinks deeper, it can
reach depths of 50 to 100 miles (80-160 kilometers) were it is so hot that the crust releases fluids trapped
inside. The fluid melts some of the silica-rich minerals in the overlying material producing dark, silica-poor
basaltic magma. The basaltic melt migrates upwards and becomes more silica-rich it melts its way toward
the surface. Sticky, silica-rich magma erupts explosively with high pressure at the surface forming steep-
sided volcanoes. Examples Mount St. Helens National Volcanic Monument, WA.
4: evidence of plate tectonics
1. Matching geologic structures(coastlines,ore deposit,same rocks ofsame age,mountain
chains):
The similarity of coastlines for different continents suggests that they may once have been
connected. they were separated by sometimes thousands of miles suggested continental drift.
Such as south America and Africa .

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2. Matching fossils found in different continents
Paleontologists have found bones of the exact same
species of organisms on continents that are separated
by vast oceans. It is extremely unlikely that the same
species evolved twice in two different places.
3. Magnetic orientation :Iron-rich magnetic minerals such as magnetite are present in basaltic lava
flows. this magnetic minerals within the igneous rocks that form from cooling magma are
oriented pointing straight at magnetic north. For 14,000 years all of the rocks formed at the
spreading center will be pointing North. In the next band, the minerals will be orienting towards
the south because that is where magnetic north is.
4. Earthquake and volcanoes happen more frequently
at plate boundaries:
Earthquakes don’t occur randomly across the world, but
happen across limited belts which also contain most of the
world’s volcanoes. These belts mark the location of plate
boundaries. These areas are so active because the stress of 2
plates against each other and eventually gives in the form of
a volcano or earthquake. The largest belt of activity is the “Ring of Fire” surrounding the Pacific
Ocean which is home to 90% of all quakes.
5. Heat flow and age: heat flow measures the amount of heat leaving rocks in the crust. Rocks at
spreading centers are recently formed from magma rising to earth's surface. Radiometric dating
shows that the rocks at mid-ocean ridges are the youngest.
5: causes of Plate tectonics

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1. Thermal convection
mechanism of plate motion (‘mantle convection theory’)
Mantle convection is the slow creeping motion
of Earth's solid silicate mantle caused by
convection currents carrying heat from the
interior to the planet's surface. a number of
plates that are continuously being created and
consumed at plate boundaries. Accretion occurs
as mantle is added to the growing edges of a
plate, associated with seafloor spreading. This
hot added material cools down by conduction
and convection of heat. At the consumption
edges of the plate, the material has thermally
contracted to become dense, and it sinks under
its own weight in the process of subduction
usually at an ocean trench.
6: early configuration of continents (figure)