UNIT-I

PART A

1. WHAT IS AN AQUIFER AND MENTION ITS TYPES?(MAY/ JUNE 2011)

• Aquifer is defined as the water-bearing formation which is porous and permeable enough to supply adequate
quantity of water to wells.

TYPES OF AQUIFER

• Unconfined aquifer
• Confined aquifer
• Semi-confined or Leaky aquifer
• Perched aquifer

2. WHAT ARE THE METHODS OF WIND EROSION?(NOV/DEC 2013)

• Deflation
• Abrasion
• Attrition

3. WRITE THE TYPES OF WAVES AND CURRENTS? (NOV/DEC 2013) Types of waves

• Oscillatory waves
• Translatory waves

Types of currents

• Littoral currents
• Rip currents
• Long shore currents

4. NAME A FEW SECONDARY TECTONIC PLATES.(NOV/DEC 2014) Secondary tectonic

plates

• The Arabian plate

• The Nazca plate

5. WHAT IS MEANT BY SEISMIC ZONE? (MAY/ JUNE 2016)

• In is an area which refers to the frequency , type and size of earthquakes experienced over a period of time is
to be named as an Seismic Zone
6. WHAT ARE BARCHANS AND SAND DUNES? (NOV/DEC 2014)
• The barchans are crescent or half moon shaped dunes of variable size. Their ‘horns’ point in the downward
direction. Their height may vary from 15-200 mts. And width from a few to 1000s meter. They have a gentle
windward slope and steeper leeward slope.

• Sand dunes are whenever the velocity of wind is arrested due to the presence of a barrier along its path, the
sand particles carried by the wind will be deposited there, forming sand dunes.

7. WHAT IS MEAN BY WATER TABLE? (NOV/DEC 2014)

• The depth to upper surface of zone of saturation in free ground water is called water table. In other words, a
static level of water in wells penetrating the zone of saturation is called water table
8. EXPLAIN THE TERM EXFOLIATION? (NOV/DEC 2014)- REG 2013
• Exfoliation is the process of physical weathering in which the rock mass, undergoing weathering will be
peeling off into concentric shells and split up into layers, due to the influence of temperature variations in
association with chemical weathering.
• The phenomenon of peeling off layer from the rocks under the influence of thermal is called as the term
Exfoliation
9. DEFINE WEATHERING.(MAY/JUNE 2011)

Weathering, is a natural process of in-situ mechanical disintegration and/or chemical

decomposition of the rocks of the crust of the Earth by certain physical and chemical

agencies of the atmosphere.

10. WHAT IS THE COMPOSITION AND NATURE OF THE INNER AND OUTER CORE OF THE
EARTH (NOV/DEC 2012)

It is the third and the innermost structural shell of the earth as conclusively proved by the seismic evidence. It
starts at a depth of 2900 km below the surface and extends

right up to the center of the earth, at a depth of 6370 km. The liquid like core extending from a depth of 2900
km to about 4800 km is often termed as outer core. The inner core - starting from 4800 km and extending up to
6370 km is of unknown nature but definitely of solid character and with properties resembling to a metallic
body. According to a widely favored view, the core may be made up of iron and nickel, alloyed in some yet
unknown manner.

11. DESCRIBE BRIEFLY , THE LAYERS OF THE INTERIOR OF THE EARTH.(MAY/JUNE 2012)

The layers of the interior of the Earth is

• The Crust
• The Mantle
• The Core

12. WHAT IS SPHEROIDAL WEATHERING?(MAY/JUNE2013)

It is a complex type of weathering observed in jointed rocks and characterized with the breaking of original rock
mass into spheroidal blocks.

13. THE
••••

HOW ARE ROCKS CLASSIFIED ACCORDING TO SCALE OF WEATHERING?(NOV/DEC2015)

Highly weathered – Very intensive weathering rocks Fractured Rocks – High weathering
Jointed Rocks – Low to moderate weathering Massive Bed rocks – No weathering

14. MENTION THE THICKNESS OF EARTH’S CRUST. (NOV/DEC2015)

(a) Under the oceans 5 - 6 km

(b) Under the continents 30 - 35 km (c) Under the mountains : 60 - 70 km

PARTB
1. Explain in detail about branches of geology. (Nov/Dec 2015) Reg 2013

Main and Allied branches of geology:

Main Branches

• Physical geology
• Mineralogy
• Petrology
• Structural geology
• Stratigraphy
• Paleontology
• Economic geology

PHYSICAL GEOLOGY:

It deals with:

i) Different physical features of the earth, such as mountains, plateaus, valleys, rivers.lakes glaciers and
volcanoes in terms of their origin and development.
ii) The different changes occurring on the earth surface like marine transgression, marine regression, formation
or disappearance of rivers, springs and lakes.
iii) Geological work of wind, glaciers, rivers, oceans, and groundwater ands their role in constantly moulding
the earth surface features
iv) Natural phenomena like landslides, earthquakes and weathering.

MINERALOGY:

This deals with the study of minerals. Minerals are basic units with different rocks and ores of the earth are
made up of. Details of mode of formation, composition, occurrence, types, association, properties uses etc. of
minerals form the subject matter of mineralogy. For example: sometimes quartzite and marble resemble one
another in shine, colour and appearance while marble disintegrates and decomposes in a shorter period because
of its mineral composition and properties. PETROLOGY:
Petrology deals with the study of rocks. The earths crust also called lithosphere is made up of different types of
rocks. Hence petrology deals with the mode of formation, structure, texture, composition, occurrence, and types
of rocks. This is the most important branch of geology from the civil engineering point of view.
STRUCTURAL GEOLOGY:
The rocks, which from the earth’s crust, undergo various deformations, dislocations and disturbances under the
influence of tectonic forces. The result is the occurrence of different geological structures like folds, fault, joints
and unconformities in rocks. The details of mode of formation, causes, types, classification, importance etc of
these geological structures from the subject matter of structural geology. STRATIGRAPHY:
The climatic and geological changes including tectonic events in the geological past can also be known from
these investigations. This kind of study of the earth’s history through the sedimentary rock is called historical
geology. It is also called stratigraphy (Strata = a set of sedimementary rocks, graphy description). ECONOMIC
GEOLOGY:
Minerals can be grouped as general rock forming minerals and economic minerals. Some of the economic
minerals like talc, graphite, mica, asbestos, gypsum, magnesite, diamond and gems. The details of their mode of
formation, occurrence, classification. Association, varieties, concenteration, properties, uses from the subject
matter of economic geology. Further based on application of geological knowledge in other fields there is many
other allied branches collectively called earth science.

2. Describe the interior Structure of the earth with neat sketch. (May/Jun 2014)reg 2008
THE CRUST
It is the uppermost solid shell of the earth which has varying thickness in different areas as follows

(a) Under the oceans 5 - 6 km

(b) Under the continents 30 - 35 km (c) Under the mountains : 60 - 70 km

It is obvious that when compared with the radius of the Earth (6730 km. on an average), the crust makes just an
insignificant part in the structure of the earth.
The chemical composition of the crust
(i) Silica - Si0 is the most dominant component; its value lies above 50% by volume in the oceanic crust and
above 62% in the continental crust;

(ii) Alumina-A is the next dominant component, its value varying between 13-16 percent;
(iii) Iron Oxide (Fe Lime (CaO)-6%; Sodium Oxide-4%, Magnesium Oxide-4%, Potassium Oxide and Titanium
oxide- 2% are the other components making the crust of the Earth. The solid aggregate that makes the crust of
the earth is named as a rock, stone. The entire crust is made up of different types of rocks.

(B) THE MANTLE

Materials making the earth become quite different in properties at the base of the crust. This depth below the
surface of the Earth at which a striking change in the properties of the materials is observed has been named as
Mohorovicic discontinuity.In geological literature, it is often referred as M-discontinuity or simply as Moho.
The material below Moho forms a nearly homogeneous zone till a depth of 2900 km is reached.

• At that depth, another striking change is observed in the quality of the material on the basis of the seismic
waves reaching there.
• Hence, mantle is that zone within the Earth that starts from M-discontinuity and continues up to a depth of
2900 km. Mantle is made up of extremely basic material called aptly ultra basic, that is very rich in iron and
magnesium but quite poor in silica

• This zone is characterized with a high density that increases with depth.
• The material of the mantle is believed to be variably viscous in nature so much so that the overlying
crusted blocks can virtually float over it, of course at a very slow rate and in a broader sense of the
term.
(C) THE CORE

• It is the third and the innermost structural shell of the earth as conclusively proved by the seismic evidence. It
starts at a depth of 2900 km below the surface and extends right up to the center of the earth, at a depth of 6370
km.
• The core remains a mystery in many ways. Within the core, the physical nature and composition of the
material is not uniform throughout its depth. Further, it has a very high density at mantle-core boundary, above
lOg/cc.
• But despite such a high density, the outer core behaves like a liquid towards the seismic waves.
• The liquid like core extending from a depth of 2900 km to about 4800 km isoften termed as outer core.
• The inner core - starting from 4800 km and extending up to 6370 km is of unknown nature but definitely of
solid character and with properties resembling to a metallic body.

• According to a widely favored view, the core may be made up of iron and nickel, alloyed in some yet
unknown manner.

2. Briefly explain the process of weathering of rocks and its relevance to engineering geology.(April/May
2015)Reg 2008
Weathering, is a natural process of in-situ mechanical disintegration and/or chemical decomposition of the rocks
of the crust of the Earth by certain physical and chemical agencies of the atmosphere.

DISINTEGRATION:

It may be defined as the process of breaking up of rocks into small pieces by the mechanical agencies of
physical agents.
DECOMPOSITION:
It may be defined as the process of breaking up of mineral constituents to form new components by the chemical
actions of the physical agents.

DENUDATION:

It is a general term used when the surface of the earth is worn away by the chemical as well as mechanical
actions of physical agents and the lower layers are exposed. The process of weathering depends upon the
following three factors:

1. i) Nature of rocks
2. ii) Length of time
3. iii) Climate

Two Chief types of weathering are commonly distinguished on the basis of type of agency involved in the
process and nature of the end product. They are:

1. i) Physical or mechanical weathering

2. ii) Chemical weathering
MECHANICAL (PHYSICAL) WEATHERING

• It is a natural process of in-situ disintegration of rocks into smaller fragments and particles through essentially
physical processes without a change in their composition.
• A single rock block on a hill slope or a plain, for instance, may be disintegrated gradually into numerous small
irregular fragments through frost action that in turn may break up naturally into fragments and particles of still
smaller dimensions.

• These loose fragments and particles may rest temporarily on the surface if it is a plain.
• On slopes, however, the end product fragments and particles may roll down under the influence of gravity and
get accumulated at the base as heaps of unsorted debris.

• All these fragments and particles, however, have the same chemical composition as the parent rock.
• Mechanical weathering is one of the very common geological processes of slow natural rock disintegration in
all parts of the world.

• Temperature variations and organic activity are two important factors that bring about this change under
specific conditions.
(A) FROST ACTION
• As is known, water on freezing undergoes an increase in its volume by about ten per cent. This expansion is
accompanied by exertion of pressure at the rate of 140 kg/cm (2000 lbs/in on the walls of the vessel containing
the freezing water.

• In areas of intensive cold and humid climates, temperatures often fall below the freezing point of water
repeatedly during winter months.
• In such areas freezing of water in pots and pools, water pipes and taps and in cavities and cracks in concreted
roads causing their bursting and disintegration in many cases is a matter of common observation.

• This process of freezing of water when happening within the pores, cracks, fractures and cavities of rocks
affects them considerably.

• The original openings are widened at the first stage of attack and thereby accommodate more and more water
to come and freeze in subsequent cycles.
(B) THERMAL EFFECTS (INSOLATION)
• In arid, desert and semi-arid regions where summer and winter temperatures differ considerably, rocks
undergo physical disintegration by another phenomenon related to temperature.

• As we know, rocks, like many other solids, expand on heating and contract on cooling. They (rocks) are, of
course classed as bad conductors of heat but even then prolonged exposure to direct heating by the Sun does
induce appreciable volumetric changes in them.
• Such repeated variations in temperature experienced by a body of rock gradually break it into smaller pieces,
especially in the top layers, by development of tensile stresses developing from alternate expansion and
contraction. EXFOLIATION

• In a thick rock body or where the rock is layered, these are the upper layers that get affected most due to the
temperature variations.
• As a result, the upper layers may virtually peal off from the underlying rock mass. In many cases such a
change is also accompanied by chemical weathering, especially at margins and boundaries of the separated
layers, developing curved surfaces.

• This phenomenon of pealing off of curved shells from rocks under the influence of thermal effects in
association with chemical weathering is often termed as exfoliation.
(C) UNLOADING

• This is another process of mechanical weathering where large-scale development of fracturing in confined
rock masses is attributed to removal of the overlying rock cover due to prolonged erosional work of other
agencies.
• These rock masses remain confined from sides but due to relief of pressure from above, they expand upwards;
consequently joints develop in them parallel to the uncovered surface dividing them into sheets.

• This rupturing or jointing in itself is a mechanical breakdown of rocks and makes them available for further
weathering or decay along the joint planes. CHEMICAL WEATHERING
• It is a process of alteration of rocks of the crust by chemical decomposition brought about by atmospheric
gases and moisture.

• The chemical change in the nature of the rock takes place in the presence of moisture containing many active
gases from the atmosphere such as carbon dioxide, nitrogen, hydrogen and oxygen.
• As we know, rocks are made up of minerals all of which are not in chemical equilibrium with the atmosphere
around them.

• Chemical weathering is, essentially a process of chemical reactions between the surfaces of rocks and the
atmospheric gases in the direction of establishing a chemical equilibrium.
• The end product of chemical weathering has a different chemical composition and poorer physical constitution
as compared to the parent rock.

• Chemical weathering eats up the rocks in a number of ways depending upon theirb mineralogical composition
and the nature of chemical environment surrounding
them.

(A) SOLUTION

• Some rocks contain one or more minerals that are soluble in water to some extent.
Rock salt, gypsum and calcite are few common examples.
• It is also well known that though pure water is not a good solvent of minerals in most cases, but when it (the
water) is carbonated, its solvent action for many common minerals is enhanced.

• Thus, limestone is not easily soluble in pure water but carbonated water dissolves the rock effectively.
Limestone gets pitted and porous due to chemical weathering.

(B) HYDRATION AND HYDROLYSIS

• These two processes indicate the direct attack of atmospheric moisture on the individual minerals of a rock that
ultimately affect its structural make up.
• It is believed that though the interior of many minerals is in electric equilibrium, the surfaces of many crystals
are not; they may have partially unsatisfied valences.
• When polarized water molecules come in contact with such crystals, it may cause any one of the following two
reactions:
• The ions tend to hold the polarized side of the water molecule and form a hydrate.

• This process of addition of the water molecule is termed as hydration. Examples are provided by hydration of
iron oxides and calcium sulphate crystals. In some minerals with ferrous iron, the Fe++ ion holds the water
molecule and forms water-iron complex or a hydroxide.
Similarly, CaSO or anhydrite gets slowly converted to gypsum by hydration:

• Ions may be exchanged whereby some ions from water may enter into the crystal lattice of the mineral.

• This process of exchange of ions is called hydrolysis.

• It is a very common process of weathering of silicate minerals (which are quite abundant in rocks) and
is best explained with reference to weathering of mineral Orthoclase, a feispar.

(C) OXIDATION AND REDUCTION

• Iron is a chief constituent of many minerals and rocks.

• The iron bearing minerals (and hence rocks) are especially prone to chemical weathering
through the process of oxidation and reduction. Oxidation. Ferrous iron (Fe++) of the
minerals is oxidized to ferric iron (Fe+++) on exposure to air rich in moisture. Ferric iron is
not stable and is further oxidized to a stable ferric hydroxide:

Reduction. In specific types of environment, such as where soil is rich in decaying vegetation (swamps),
minerals and rocks containing iron oxide may undergo a reduction
of the oxides to elemental iron. In this case the decaying vegetation supplies the carbonaceous content causing
reduction.

(D) CARBONATION

• It is the process of weathering of rocks under the combined action of atmospheric carbor dioxide and moisture,
which on combination form a mildly reacting carbonic acid.
• The acic so formed exerts an especially corrosive action over a number of silicate bearing rocks.

• The silicates of potassium, sodium and calcium are particularly vulnerable to decay undez conditions of
carbonation.
• A typical example is that of feispar orthoclase, a very common and important constituent of many igneous,
sedimentary and metamorphic rocks, which decomposes according to following reaction:

(E) COLLOID FORMATION

• The processes of hydration, hydrolysis, oxidation and reduction operating on the rocks and minerals under
different atmospheric conditions may not always end in the formation of stable end products.
• Often they result in splitting of particles into smaller particles- the colloidscharacterized by atoms with only
partially satisfied electrical charges. Formation of colloidal particles is especially common in the weathering of
clay minerals, silica and iron oxides.

SPHEROIDAL WEATHERING
• It is a complex type of weathering observed in jointed rocks and characterized with the breaking of original
rock mass into spheroidal blocks.
• Both mechanical and chemical weathering is believed to actively cooperate in causing spheroidal weathering.

• The original solid rock mass is split into small blocks by development of

parallel joints due to thermal effects (insolation).

• Simultaneously, the chemical weathering processes corrode the borders and surfaces of the blocks causing
their shapes roughly into spheroidal contours. FACTORS AFFECTING WEATHERING
(I) NATURE OF THE ROCK

• Rocks vary in chemical composition and physical constitution.

• Some rocks are easily affected by weathering processes in a particular environment whereas others
may get only slightly affected and still others may remain totally unaffected under the same conditions.

• Thus of granite and sandstones exposed to atmosphere simultaneously in the same or adjoining areas having
hot and humid climate, the sandstone will resist weathering to a great extent because they are made up mainly of
quartz (Si0 which is highly weathering resistant mineral.
(II) CLIMATE
• The process of weathering is intimately related to the climatic conditions prevailing in an area.
• Same types of rocks exposed in three or more types of climates may show entirely different trends of
weathering.
• Thus cold and humid conditions favour both chemical and mechanical types of weathering, whereas in totally
dry and cold climates, neither chemical nor mechanical weathering may be quite conspicuous (due to absence of
moisture).
(III) PHYSICAL ENVIRONMENT
• The topography of the area where rocks are directly exposed to the atmosphere also affects the rate of
weathering to a good extent.

• Rock forming bare cliffs, mountain slopes devoid of vegetation and valley sides is more prone to weathering
than same rocks exposed in level lands in similar climates and/or under vegetable cover.

3. Describe in detail how earthquakes are caused. Add a note on the earthquake prone belts of India
(May/June 2016) Reg 2008
The physical forces the surfaces are rearranging rock materials by shifting magmas about altering the structures
of solid rocks. The adjustment beneath the surface however involve various crystal movements, some of which
because of suddenness and intensity produce tremors in the rocks and they are known as earthquake. The
science dealing with the study of earthquakes in all their aspects is called seismology.

FOCUS AND EPICENTER:

The exact spot underneath the earth surface at which an earthquake originates is known as its focus. These
waves first reach the point at the surface, which is immediately above the focus or origin of the earthquake. This
point is called epicenter. The point which is diametrically opposite to the epicenter is called anticenter.

INTENSITY AND MAGNITUDE:

Intensity of an earthquake may be defined as the ratio of an earthquake based on actual effects produced by the
quakes on the earth. Magnitude of a tectonic earthquake may be defined as the rating of an earthquake based on
the total amount of energy released when the over strained rocks suddenly rebound, causing the earthquake.

CAUSES OF EARTHQUAKE:

The earthquake may be caused due to various reasons, depending upon it intensity. Following causes of
earthquake are important:
1. EARTHQUAKES DUE TO SUPERFICIAL MOVEMENTS:
The feeble earthquakes are caused due to superficial movements.i.e, dynamic agencies, and operation upon
surface of the earth.
§ The dashing waves cause vibrations along the seashore.

§ Water descending along high water falls, impinges the valley floor and causes vibrations along the
neighbouring areas.
§ At high altitudes the snow falling down is an avalance.also causes vibrations along the neighbouring areas.

2. EARTHQUAKE DUE TO VOLCANIC ERUPTIONS:

Most of the volcanoes erupt quietly and as consequence, initiate no vibration on the adjoining area. But a few of
them when erupt, cause feeble tremors in the surface of the earth. But there may be still a volcanic eruption may
cause a severe vibration on the adjoining area and have really disastrous effects.

3. EARTHQUAKE DUE TO FOLDING OR FAULTING:

The earthquakes are also caused due to folding of the layers of the earth’s crust. if the earthquakes are caused
due to folding or faulting then such earthquakes are more disastrous and are known as tectonic earthquakes and
directly or indirectly change the structural features of the earth crust.

MAGNITUDE AND INTENSITY OF THE EARTHQUAKE.

Intensity of an earthquake may be defined as the ratio of an earthquake based on actual effects produced by the
quakes on the earth.
Magnitude (M) of a tectonic earthquake may be defined as the rating of an earthquake based on the total mount
of energy released when the over strained rocks suddenly rebound causing the earthquake.

CLASSIFICATION OF EARTHQUAKES:

Earthquakes are classified on a no. Of basis. Of these the depth of focus, the cause of origin and intensity are
important.
A) DEPTH OF FOCUS:
Three classes of earthquakes are recognized on this basis, shallow, intermediate and deep seated. In the shallow
earthquakes the depth of focus lies anywhere up to 50 km

below the surface.

The intermediate earthquakes originate between 50 and 300 km depth below the surface.

B) CAUSE OF ORIGIN:
i) Tectonic earthquakes are originated due to relative movements of crystal block on faulting, commonly,
earthquakes are of this type.

ii) Non tectonic earthquakes: that owes their origin to causes distinctly different from faulting, such as
earthquakes arising due to volcanic eruptions or landslides.
C) INTENSITY AS BASIS:
Initially a scale of earthquakes intensity with ten divisions was given by Rossi and ferel. Which was based on
the sensation of the people and the damage caused. However it was modified by Mercalli and later by wood and
Neumann. ENGINEERING CONSIDERATIONS:

The time and intensity of the earthquake can never be predicted. The only remedy that can be done at the best, it
is provide additional factors in the design of structure to minimize the losses due to shocks of an earthquake.
This can be done in the following way:

• To collect sufficient data, regarding the previous seismic activity in the area.
• To assess the losses, which are likely to take place in furniture due to earthquake shocks

• To provide factors of safety, to stop or minimize the loss due to sever earth shocks.
Following are the few precautions which make the building sufficiently earthquake proof.
• The foundation of a building should rest on a firm rock bed. Grillage foundations should preferably be
provided.
• Excavation of the foundation should be done up to the same level, throughout the building.

• The concrete should be laid in rich mortar and continuously

• Masonry should be done with cement mortar of not les than 1:4 max.
• Flat R.CC slab should be provided.

• All the parts of building should be tied firmly with each other.
• Building should be uniform height.
• Cantilivers, projections, parapets, domes etc, should be provided.
• Best materials should be used.

4. Describe in detail, the erosional and depositional landforms formed due to the work of
rivers.(November/December 2012)

Write an essay on the geological work of river. (November/December 2014)

Give a detailed account of the erosional and depositional landforms created by the action of a river.
(November/December 2014) Regulation 2013

INTRODUCTION

The upper surface of ground water is called water table, may sometimes, at some places, intersect the ground
surface, where a spring is originated. The spring water may also become an important source of river.
RIVER

River may be defined as a main stream into which a number of streamlets join. The term stream and river are
used synonymously. In the simplest form the geological work of river is to erode the valleys, transport the
material thus eroded and deposit the same in the lower reaches at favorable sites.

Types of River

Two types of rivers are distinguished:

¬Perennial River
¬Intermittent / Non-Perennial River PERENNIAL RIVER
The river never gets dry. Throughout the year some water will be flowing in the river. The volume of water may
be less in dry season and very high during rainy season.

INTERMITTENT / NON-PERENNIAL RIVER

Water flows only during monsoon period in this river and the river becomes dry in summer.
RIVER PROFILE

The longitudinal section of the river starting the place of its origin (mountainous region) to is final destination to
the sea is called the river profile. It has two parts.
¬The Head

¬The Mouth

The mountainous region or high land where from the river originates is called the Head region and the place
where river enters a sea is called the Mouth.

1. Stages in a River System 2. River Erosion

3. River Transportation
4. Deposition by River

1. STAGES IN A RIVER SYSTEM There are 3 stages in the river profile:

¬The young stage ¬Mature stage ¬Old stage

In the youth stage, the river flows along an undulating

and the gradient is very high. Because of this the river suffers heavy

topography

headword erosion and develops valleys.

During mature stage, valley widening begins by latter cutting. A

Complex branching system of the river develops and the flow is almost uniform. The reduction in gradient
reduces the velocity of the river, resulting in the decrease of erosive power.

In the old stage the river gradient is very gentle and velocity is also less. During this stage, the river loses its
erosive power. As a last stage
the river merges into the sea forming a delta.
2. RIVER EROSION
GEOLOGICAL WORK / PROCESSES ASSOCIATED WITH RIVER The Various processes associated
with the geological work of running water can be broadly classified into:
¬Hydraulic Action
¬ Abrasion
¬ Attrition
¬Solution and corrosion
¬ Transportation
¬ Deposition

1. HYDRAULIC ACTION:

Hydraulic action of a river is defined as the process of

the rock masses due to the continuous impact of water moving with appreciable velocity along the channel. It is
the dominating process of erosion along the upper part of the river course where the gradient is considerable.
2.ABRASION

The Large boulders and pebbles formed due to hydraulic action of the river roll down along the valley floor and
move downstream while the smaller fragments travel in suspension or siltation.

Eroded materials which are moved along with the river water may exert considerable rubbing on the bed rock
depending on the type of bed rock. Three situations may arise depending on the river bed and flowing rock
materials.

breaking down of

¬Abrasion of the bed rock is more pronounced, if the transported rock- material is hard and the river bed is soft.
¬Polishing of the river bed happens if both, river bed and transported rock material are hard.

¬On the contrary, if the river bed rock is hard and the moving rock fragments are soft, there will not be any
appreciable instead weathered rock waste is eroded away.

3. ATTRITION

The process of mechanical breaking down of the transported rock fragments, due to the impacts and mutual
collisions between themselves is described as Attrition.

Abrasion and Attrition always work together and produce fine rock particles, which are transported to greater
distance.
4. SOLUTION AND CORROSION

A River, during its travel, traverses through a variety of country rocks along its path of travel. The readily
soluble carbonate rocks (like lime stone) are attacked most conventionally by running water and are gradually
removed in solution.
5. TRANSPORTATION/ RIVER TRANSPORTATION

Amount of solid material transported by a river is referred to as load. River transport comprises of three ways:
¬DISSOLVED LOAD: It is the load acquired directly from soluble rocks which occur along the steams course.
It is also brought to the river by groundwater.

¬SUSPENDED LOAD: Major portion of the load carried by river is suspended load. Generally small-sized
particles such as clay and fine silt travel in suspension.
¬BED LOAD: Moving water with its forward force acts more directly on the larger grains at the bottom by
pushing, rolling and sliding them along the bed.

6. DEPOSITION/ DEPOSITION BY RIVER

Velocity of a river is a major factor which contribute for the flow of river during all stages starting from erosion
till deposition. Materials which are thus deposited by rivers are called alluvium or alluvial deposits.
Materials carried by rivers, while entering a lake, deposit all the coarse particles because of a sudden decrease in
velocity. Such coarse material deposits are called lake deposits. But the fine grained particles move to the
centre of the lake and settle when the water becomes quiet.

Alternate layers are formed with season, and such lake deposits are called lacustrine deposits.

Glacial soils transported by rivers from melting of glacial water create deposits of stratified glacial drift and are
referred to as glacio fluvial deposit or stratified drift.
DEPOSITS & FEATURES / LANDFORMS OF RIVER EROSION:
1. Alluvial fans and cones
2. Flood plains
i)Convex flood plains
ii)Flat Flood Plains

3. Natural levees
4. Deltas

i) The bottom set beds ii)The fore set beds iii)The top set beds

LANDFORMS / FEATURES OF STREAM EROSION:

1. Water Falls 2. Pot holes

3. River valley 4. Escarpment

i)Hogs back ii)Cuesta

iii)Mesa and Butte

5. River Meandering
6. Oxbow Lakes
ENGINEERING CONSIDERATIONS:
1. Deforestation should be stopped
2. Massive afforestation should be promoted.
3. Check dams should be constructed across streams.
4. Additional channels to be provided to the main channel of the river to divert some water.
5. Silt accumulation from river bed should be removed.
6. Future townships may be planned at places away from flood plains.

5. Write an essay on the erosional and depositional features of wind. (May/June 2013)
Describe the work of wind with sketch. (May/ June 2011) INTRODUCTION

Atmospheric gases are collectively known as Air. Moving air is called wind. The pressure difference created in
atmosphere makes the air to move from high pressure area to low pressure area in the form of winds.
The effect of wind erosion depends on wind volume, its velocity, duration of blow and nature of ground surface
over which if blows. Hence strong winds blowing over loose ground, dry soils or deserts may create many new
surface features.
Blowing wind generally causes erosion by 3 distinct processes known as

¬ Deflation ¬ Abrasion ¬ Attrition

DEFLATION

The process of lifting and removal of loose soil or rock particles during Strom, along the course of blowing
wind is known as Deflation. Wind deflation is the main process of erosion in desert areas.

FEATURES/LAND FORMS OF WIND EROSION:

Deflation creates the following surface features in deserts ¬Blow out and oasis
¬Desert pavement
¬ Hammada

¬ Dreikanter

1.BLOW OUT & OASIS:

Wind deflation creates big depressions by removal of sand in deserts.

Sometimes water table may intersect the base of such depressions. such depressions are variously called as
blowouts, When developed on a small scale with shallow water depth and as Oasis, when deeper.

Oasis may be defined as much deeper and extensive depressions intersected by water table and partially filled up
with water. often vegetation is found to occur around oasis.
2.DESERT PAVEMENT

Desert pavements are flat rock surfaces covered by rounded or sub rounded pebbles and are the typical features
of rock deserts.
3.HAMMADA

It is a bare rock surface (found in desert) from which thin cover of sand has been blown away by strong winds.
4.DREIKANTER

A Dreikanter is a type of ventifact that typically formed in desert or periglacial environments due to the abrasive
action of the blowing wind.

WIND ABRASION

The loose rock particles, which are lifted up and transported by the blowing wind, do always, have a tendency to
jump upon and collide with any rock exposures lying along their path of travel. The process of wear and tear of
the exposed country-rocks as described above is known as Abrasion. FEATURES OF WIND ABRASION

¬ Ventifacts ¬Pedestal rock ¬ Yardangs

1. VENTIFACTS

Due to wind abrasion, the exposed irregular surface of a rock mass is gradually converted into a plane, smooth
and polished surface. Such pebbles of rock or minerals with smooth, plane and polished surfaces developed due
to wind abrasion are called Ventifacts.

2.PEDESTAL ROCK/MUSHROOM ROCKS

It has been found that the heavier rock/sand particles travelling along with blowing wind are commonly more
concentrated at bottom level. More so the vertical columns of rock exposures are more readily worn out towards
their lower portions than at their top.

The so formed rock structures having wider tops supported on comparatively narrower bases are called Pedestal
rocks or mushroom rocks.

3.YARDANGS

Yardangs are formed in areas where rocks of alternate hard and soft nature occur one above the other with
gentle slope.

When such rock strata is attacked repeatedly by wind loaded with abrasive sand grains and blowing in the same
direction, the softer layers of the strata get abraded quickly, leaving behind harder layers in the form of
overhanging ridges, called Yardangs.

ATTRITION

The wind borne particles, travelling in suspension, do often have the chance of colliding with one another. Such
mutual collision amongst themselves causes a further grinding of the particles and this process of collision
between the particles themselves is described as attrition TRANSPORTATION OF ERODED SEDIMENTS

The wind eroded sediments generally include heavier& courser particles such as sand, pebbles, gravels etc. and
lighter and finer particles such as silt, clay and dust. These sediments are transported from one place to another
by two distinct processes namely

¬ SUSPENSION ¬ SALTATION

1.SUSPENSION

The finer particles such as silt, clay, dust etc. are conveniently lifted up in air to higher elevation (level) of wind
and they travel in suspension along with the blowing wind due to the turbulence of air currents. This process of
transportation of particles is called suspension.
2.SALTATION

In the case of heavier particles such as sand, gravels etc. transportation takes place due to a forward movement
of the grains in a series of jump sand the process is described as saltation.
WIND DEPOSITS

The wind borne particles are dropped down and deposited at places where the velocity of the wind is checked.
This wind made deposits may ultimately take the shape of landforms. These deposits, formed due to wind
erosion are described as Aeolian deposits.

There are two types of Aeolian deposits. ¬SAND DUNES

¬ LOESS

SAND DUNES

Whenever the velocity of wind is arrested due to the presence of a barrier along its path, the sand particles
carried by the wind will be deposited there, forming sand dunes.

Due to this deviation of wind, a wind shadow zone is formed behind the barrier and it is called Leeward side
where the velocity of wind is much reduced. Sand dunes are found to have a gentle slope along the wind-ward
side and a comparatively steep slope along the leeward side.

TYPES OF SAND DUNES 1.BARCHANS

Dunes which are more or less crescent shaped are commonly described as

barchans. Barchans are convex towards the windward side and the tapering horns of the crescent point towards
the direction of blow of wind.
2. FORE DUNES

Fore dunes are ridge like deposits of wind borne sand particles formed along the coasts of sea and lakes.

3. TRANSVERSE DUNES

Sometimes ridges of sand accumulate off from the shore line i.e.furher inland,off from the sea and orient
themselves across the direction of below of wind. They are known as Transverse dunes.

4. PARABOLIC DUNE

Dunes of parabolic shape are described as Parabolic dunes. These dunes have their horns pointing towards the
direction opposite to that of the blowing wind.

5. LONGITUDINAL DUNES

In deserts, elongated ridges of sand are sometimes found to occur parallel to the direction of blow of wind.
These are known as longitudinal dunes.

6. SIGMOIDAL DUNE
Sigmoidal dune is having a curved or S-shaped outline with absence of horns.

¬Simple dune : is a single dune of above types ¬Compound dune: two or more dunes of same type
¬Complex dune: group of dunes of different types.

LOESS

It is a wind borne deposit of silt and clay grade particles. It is unconsolidated, unstratified and porous in nature.
Particles are of 0.01- 0.05mm diameter.

ENGINEERING CONSIDERATIONS

As sand dunes tend to move and travel along the wind direction, they bury agricultural lands and forests.
Agricultural lands can be protected by taking the following remedial measures.
¬Growing belts of vegetation (coniferous trees) for checking the velocity of the wind.

¬Construction of wind breaks or walls around the area

¬Treating sands locally with crude oil to reduce their susceptibility of transport

Since loess is unconsolidated, it will settle down quickly and create foundation problems.

6. Explain in detail about working of sea with their engineering importance with neat
sketch.(November/December 2013)
Give a detailed account of the geological work of the sea. Add a note on importance of geology in coastal
engineering.(April/May2015) INTRODUCTION

The continuous and extensive bodies of water encircling the greater part of the earth’s surface, covering nearly
three fourths of the landmass are described as the oceans and seas.

GELOGICAL WORK OF OCEAN AND SEA/ (PROCESSES ASSOCIATED WITH SEA)

¬Hydraulic action
¬ Abrasion
¬ Attrition
¬ Solution
¬Transportation and Deposition

HYDRAULIC ACTION

The process of gradual breaking down of the rock masses, due to the hydraulic pressure of the impinging water
is known as hydraulic action. ABRASION

The process of wear and tear of the country rocks of the shore, due to the continuous impact of already broken
fragments travelling with the advancing waves is known as abrasion
ATTRITION

The process of mutual collision between the rock fragments themselves is known as attrition which brings about
further reduction in size of the individual rock fragments.
SOLUTION

The rocks having some soluble constituents attacked by waves, along the shore. This solvent action of sea water
is generally much less pronounced than hydraulic action and abrasion.
TRANSPORTATION AND DEPOSITION

The products of marine erosion are transported by the waves and currents and deposited suitably upon the ocean
floor.
¬Long shore currents always shift the rock debris parallel to the shore line ¬Marine sediments are generally
well sorted.

¬These sediments are collectively known as marine sediments.

FEATURES AND LANDFORMS DEVELOPED BY MARINE EROSION

¬Shore profile
¬Shore lines

¬Spits and bars ¬ Oozes

¬ Islands

¬ Tombolo

1.SHORE PROFILE

The erosional and depositional activities of waves and currents give rise to a characteristic shore profile, by
grading the shore zone.

The shore profile is made up of 4 erosional features.

 • Wave-cut cliff
• Beach
• Wave-cut Bench
• Wave Built Terrace

I) WAVE-CUT CLIFF

The dashing waves and breakers gradually erode the land masses forming the coast, going rise to a
vertical or steeply sloping strip of land features called Wave-cut cliff, showing seaward slope.
II) BEACH

With transgression of sea further inland, the cliff is worn out and the products of its decay are spread
upon the shore forming a beach.
III) WAVE-CUT BENCH

The shore line shifts further inland and the adjacent stretch of shallow marine water is found to move to
and fro upon a basement which is known as Wave- cut bench
IV) WAVE BUILT TERRACE

The Waves and currents move the rock debris and waste away from the beach and gradually drop them
down along the sea-ward side of the beach,

forming what is known as a wave built terrace.

2. SHORE LINES

The border line which separates the continental land mass from the sea or ocean is called a shore line.
¬Shore lines of emergence
¬Shore lines submergence

¬Compound or complex shore lines ¬Neutral shore lines

3. SPITS AND BARS

The rock debris are sometimes happened up in the form of a ridge, running parallel to the shore line. These
ridges visible above sea level in the long run are called spits. with more depositional activities, spits grow in
dimension and connect themselves with coastal tracts, giving rise to Bars which contain a portion of marine
water.

4. OOZES
The finest particles like silt and clay are transported by waves and under toe currents and dropped down at
greater distances away from the shore, say the deep sea basin. These sediments of deep sea basin are of organic
or inorganic origin and are called oozes.

O Oozes of organic origin O Radiolarian oozes

O Foraminiferal oozes
O Diatomaceous oozes
O Oozes of inorganic origin

5. ISLANDS

The isolated land masses, occurring within the extent of oceans and seas with their all sides surrounded by sea
water are described as islands ¬VOLCANIC ISLANDS
¬CONTINENTAL ISLANDS

¬CORAL ISLAND

VOLCANIC ISLANDS

They are formed due to accumulation of lava upon the ocean floors, due to eruption of volcanoes.

E.g The Hawaiian Isands in Pacific Ocean

CONTINENTAL ISLANDS

The land masses which were, once, parts of the continents and have been cut off from them, due to marine
erosion or crustal movements are called continental islands.

E.g Srilanka, Japanese and British Isands.

CORAL ISLAND

Coral islands are formed due to the accumulation of calcareous remains of marine organisms, known as Corals,
upon the submarine banks or around the existing islands.
There are 3 common types of coral islands or reefs.
¬FRINGING REEFS
¬BARRIER REEFS
¬ ATOLL
FRINGING REEFS

The reefs which occur in contact with the fringes of the existing islands and found totally encircling them are
known as Fringing reefs.
BARRIER REEFS

They encircle the islands, no doubt, but necessarily lie off from them, leaving a strip of marine water in between
the reef and the enclosed island. E.g Great Barrier Reef of Australia.
ATOLL

When a coral reef, occurring more or less in the form of a ring, encloses only a body of comparatively shallow
marine water, it is known as an atoll. E.g. Lakshadweep and Maldives in Arabian sea
6.TOMBOLO

Tombolo is a form of marine deposit that connects a head land and an island with another island.
ENGINEERING CONSIDERATIONS

India has longest coast line, extending over 7,000km.Erosion of coast line occurs in parts of Tamilnadu, Andhra
Pradesh, Karnataka, Maharashtra, West Bengal and more severely along Kerala coast.

Hence, coastal protection measures should be necessarily taken for the safety of our nation.
There are two types of coastal protection techniques available.
¬ STRUCTURAL

¬NON- STRUCTURAL

i) STRUCTURAL METHODS OF COASTAL PROTECTION

In this method of coastal protection, sea walls are constructed along the highly erodible sea coasts to reduce the
wave action.
ii) NON-STRUCTURAL METHODS OF COASTAL PROTECTION

1.Grass Dykes- It is designed and laid along the coast. This grass dykes with stand even 30 hours of wave
attack.
2.Beach Nourishment- This is the process of adding beach materials at the upper coast level.

3.Sand Dune Reconstruction – This is the process of storing sand in the dunes and re-bridging the dune ridge,
after the strom crosses over.

41

7. Describe the geology of ground water and its importance in civil Engineering. (November/December
2014) (16 mark)
Write short notes on Ground water mode of occurrence (November/December 2014) (8 mark)

Ground water is a very powerful agent like river for creating various geological features upon or below the
surface of the earth.

• Chemical work due to corrosion

• Mechanical work
• Molecular Replacement
• Deposition by Precipation
1. CHEMICAL WORK DUE TO CORROSION

When ground water comes into contact with lime stones, dolomites, gypsum, etc. during its
underground flow, it becomes carbonated.
 • Climate
• Geological structures
• Composition of rock and Ground water
• The porosity and Permeability of rocks
• Flow Velocity of ground water
• Temperature and Pressure
• Depth of Ground water contact.

LANDFORMS BY SOLVENT ACTION KARST TOPOGRAPHY

Karst Topography is an important land feature developed due to the solvent action of sub surface water
and was first studied in KARST region of YUGOSLAVIA.
2. MECHANICAL WORK

The ground water is subject to movement due to gravity and its hydrostatic head. But its velocity is
much less than that of surface water. Due to its movement, it mechanically lubricates the surface of
rocks, rendering them becoming weaker, leading to sliding and failure of slopes.

3. MOLECULAR REPLACEMENT

When ground water percolate through a wood fossil, the wood cells may be replaced by silica molecules carried
by ground water, converting the wood fossil into silicified wood
4. DEPOSITION BY PRECIPATION
• Calcite, Silica, Fluorite, Barite, etc are some of the mineral deposits formed by precipitation from ground
water.
• Stalactites and Stalagmites are the most common cave deposits, formed due to dripping of ground water in
lime stone caverns and hence they are called drip stones.

DRIP STONES

Thus the various land forms and features formed due to ground water action and its dripping are:
• KARST TOPOGRAPHY
O Domelins

O Solution Cavities
O Blind Valleys
• LAND SUBSIDENCE • SILICIFIED WOOD • STALACTITES
• STALAGMITES