Physical Geology( Unit 7)

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Course Title: Engineering Geology
Course Code: EG453CE
UNIT 7
Physical Geology
Dr. Suman Manandhar, Dr. Eng. & PostDoc
(Kyushu University)
Visiting Faculty,
School of Engineering, Department of Civil & Geomatic Engineering, Kathmandu University, NEPAL
Visiting Associate Professor
Institute of Lowland and Marine Research (ILMR), Saga University, JAPAN
Former Secretary General cum Treasurer
International Association of Lowland Technology (IALT), JAPAN
Chief Guest Editor & Associate Editor
Lowland Technology International Journal (LTI), JAPAN
Unit 7: Physical Geology
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Phases
Geological Agents and Geological
Cycle
Geomorphological Process:
Weathering and Erosion
Geological Agents: Landform
Produced By Glacier, River,
Groundwater, Wind and Sea-water
Suman Manandhar, Dr. Eng. (Geotechnical Engineering)

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Geological Agents
Suman Manandhar, Dr. Eng. (Geotechnical Engineering) 3
Suman Manandhar, Dr. Eng. (Geotechnical
Engineering)
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Engineering)
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Engineering)
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The Geological Cycle
• Internal geologic processes
– Generally build up the earth’s surface
• External geologic processes
– Generally wear down the earth’s surface
– Driven directly or indirectly by sun and gravity
• Weathering
– Physical, Chemical, and Biological
• Erosion
– Wind
– Flowing water
– Human activities
– Glaciers
Engineering)
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Source: Google Suman Manandhar, Dr. Eng. (Geotechnical
Engineering)
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The upper part of the crust are in close interaction with the process
of atmosphere, hydrosphere and biosphere. So mostly rocks are not
stable and resistant.
Source: Google

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Weathering
 Breakdown of earth materials due to
various factors.
 Disintegration or alteration of rock
in its natural or original position at or
near the Earth’s surface.
 Weathering refers to the combination
of processes that break up and
corrode solid rock, eventually
transforming it into sediment.
Denudation
• Weathering + Erosion +Transportation
• Exposed or uncovered the rocks.
• It is the process of breaking the earth’s surface by the help of external force,
converted into loose soil and transport to other places.
Source: Google
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Characteristics of weathering:
• disintegration of rocks
• chemical change in rocks
• change in the surface of land
• formation of soil
due to change in temperature and weather.
Source: Google
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Weathering processes
Micas  Vermiculite  Smectite  Kaolinite  Al,Fe-Oxides
Young, weakly weathered soils
= fine-grained mica, chlorite, vermiculite
(Entisol, Inceptisol)
Intermediate weathering
= vermiculite,smectite, kaolinite
(Mollisol,Alfisol, Ultisol)
Strong weathering
= kaolinite, hydrous oxides
(Ultisol--> Oxisol)
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 Physical or MechanicalWeathering
 ChemicalWeathering
 BiologicalWeathering
 PhysicalWeathering
 Processes that disintegration and decay of rocks via weather elements
without altering its composition.
 Takes place when rock is split or broken into smaller pieces of the same
material without changing its composition
• Abrasion or grinding
• Freeze and thaw
• Exfoliation (Sheet)
• Frost action
• Effect of Vegetation
FrostWeathering
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Source: Google

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Freeze andThawWeathering
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Source: Google
Exfoliation
• Weathering due to pressure
release.
• Outer layer of the rock
expand more than inner
layer and thin slabs of rock
form and detached.
Bed rock within the earth’s surface in under high pressure and temperature.
When uplift and erosion brings bed rock to the surface, its temperature drop slowly
while pressure drop immediately.The sudden drop cause the rock to rapidly
expand and crack, this is due to pressure expansion and is called sheeting or
exfoliation, the surface spalls off in layers.
Source: Google

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Effect of Vegetation
Source: Google
 ChemicalWeathering
 Processes that change the chemical composition of rocks
and minerals. It decomposes rocks through a chemical change in
its minerals.
• Dissolution
• Carbonation
• Oxidation
• Hydrolysis
• Hydration

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• Water reacts with rock and helps
in dissolving of minerals.
• Water leads in dissolve minerals in
the rock forming holes or voids.
• Weathering by water.
For instance, dissolving of sugar or
salt (halite).
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Dissolution
Engineering)
• Acidic water reacts with rock and
helps in dissolving of minerals.
• Acid react with water.
• Water containing acid from dissolved
carbon dioxide leads to dissolve
minerals in the rock leaving cavities.
(limestone caves).
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Carbonation
Source: Google

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• Iron combines with oxygen in
the presence of water in a
processes called oxidation.
• The product of oxidation is rust.
(rusting)
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Oxidation
Source: Google
• Water reacts with rock for a long time and the minerals dissolve forming clay
which is also called as leaching.
• Decomposition of rocks generally contains silicate minerals.
• Silicate minerals generally formed clay due to hydrolysis.
• Igneous rocks have much silica which readily combines with water.
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Hydrolysis
Source: Google

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Difference between Hydrolysis & Dissolution
• In this weathering the hydroxyl molecules are inserted into the
molecular structures of minerals and decomposed.
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Hydration
Source: Google

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 Biological Weathering
Biological weathering takes place when rocks are broken down by
living organisms.Trees and other plants can grow within the cracks
in a rock formation. As the roots grow bigger they push open
cracks in the rocks making them wider and deeper.
Tiny organisms like bacteria, algae and moss can grow on rocks
and produce chemicals which can break down the surface layer of
the rock. Burrowing animals such as rabbits can accelerate the
formation of cracks.
• Action of plants and animals
• Lichens (algae and fungi living as single unit) and mosses
grow on rocks.
• They wedge their tiny roots into spores and crevices.
• When the roots grow, the rock splits.
• Burrowing animals can increase weathering.
Source: Google
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• A part of rainfall always snips into the soil on the covered rocks
and looses the rock particle by dissolving it.
• Frost action also takes place in the pore spaces of rocks and
causes disintegration and splitting of rocks into fragments.
• Chemical reactions are also taking place in rocks internally and
causing rock loosening.
• Slow geological process of construction and destruction.
Factors ofWeathering
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1. Rock composition:
There are certain elements which are included in rock composition. Some rocks will
weather quickly and some slowly e.g. acidic rocks weather more quickly than basic
ones.
2. Climate:
It includes the meteorological elements effect on rocks such as moisture,
temperature, and wind and air pressure. Climate determines whether physical or
chemical weathering will be more active and speedy.
3.Topography
Topography directly effects weathering by exposing rocks to the temperature or sun
and wind. The elevated areas will be affected more and low level areas will be
affected less.
4.Vegetation (Floral effect)
Surface covered by the vegetation are protected from weathering but bare surfaces
are weathered to great extent. Thin root plants protects weathering. Thick root
plants accelerates weathering.
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• Weathering gradually weakens rocks, and eventually produces new
geological materials (rock fragments, sands, silts and clays) that are more
stable in the new environment.
• Weathering generally produces finer and less dense rock materials,
and weaker, more porous and permeable rock masses.
• In the tropics and subtropics, intense weathering in the hot and
humid conditions produces thick weathered profiles, which may be
up to 100 meters, or more, thick.
Weathering Products
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ꝿ Destabilization of natural slope.
ꝿ Removal of surface materials.
ꝿ Formation of soil or sediment.
ꝿ Chemical modification of soil.
Impact of Weathering
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Agents of Weathering
 Water
 Wind
 Glacial
 Waves (Sea waves)
 Under ground water

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Difference between
Weathering and Erosion
Weathering - processes at or near Earth’s surface
that cause rocks and minerals to break down
Erosion - process of removing Earth materials from
their original sites through weathering and transport
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Weathering Profile of Granitic Rock
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Source: Google

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Engineering Classification
of Weathering of Rocks
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Engineering)
Weathering classification suggested by
ISRM Working Party, 1981.
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Engineering)

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Different stages of
weathering of rocks and
formation of soil.
Suman Manandhar, Dr. Eng. (Geotechnical Engineering) 37
Source: Google
The 5 Factors of Formation
Soil is formed by…
• Parent Material: the original “Mom & Pop” soil transported
from elsewhere, usually by wind or water, at different speeds.
• Climate: the amount, intensity, timing, and kind of
precipitation that breaks down parts of ecosystem (i.e. rocks,
trees) into soil.
• Topography: Slope and Aspect affect the angle of the land and
position toward/away from the sun that soil will be exposed
to.
• Biological: Plants, animals, microscopic organisms, and
humans interact with soil in different ways.
• Time: the amount of time it takes for the four factors
(above) to interact with each other.
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Soil Profile
• A Soil Profile is a vertical cross-section of layers of soil found in a
given area. Below are two examples of soil profiles.
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Source: Google
Soil Horizon
• Soil horizons are the layers in a soil profile used to classify soil
types.
• Horizons based on color, texture, roots, structure, rock
fragments, and any unique characteristic worth noting.
• Master Soil Horizons are depicted by a capital letter in the order
(from top down): O, A, E, B, C, and R
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Engineering)

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O-Horizon
The “Organic Matter”
Horizon
• Surface-layer, at depths of 0-2 feet
• Dark in color, soft in texture
• Humus - rich organic material of
plant and animal origin in a stage of
decomposition
• Leaf litter – leaves, needles, twigs,
moss, lichens that are not
decomposing
• Several O-layers can occur in some
soils, consisting only of O-horizons
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Source: Google
A-Horizon
“Topsoil” or “Biomantle”
Horizon
• Topmost layer of mineral soil, at
depths of 2-10 feet
• Some humus present, darker in
color than layers below
• Biomantle - most biological
productive layer; earthworms,
fungi, and bacteria live this layer
• Smallest and finest soil particles
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Engineering)

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E-Horizon
The “Leaching Layer”
Horizon
• Small layer between A & B
horizons
• At depths of 10-15 feet
• Light in color, mainly sand & silt
• Poor mineral and clay content
due to leaching – the loss of
water-retaining plant nutrients
to the water table
• Soil particles larger than in A
horizon but smaller than in B
horizon
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Source: Google
B-Horizon
The “Subsoil” Horizon
• Rich in clay and minerals like
Fe & Al
• Some organic material may
reach here through leaching
• Plant roots can extend into
this layer
• Red/brown in color due to
oxides of Fe & clay
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Source: Google

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C-Horizon
The “Regolith” Horizon
• Made up of large rocks or
lumps of partially broken
bedrock
• Least affected by
weathering and have
changed the least since
their origin
• Devoid of organic matter
due to it being so far down
in the soil profile
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Engineering)
R-Horizon
The “Bedrock”
Horizon
• At depths of 48+ feet
• Deepest soil horizon in
the soil profile
• No rocks or boulders,
only a continuous mass of
bedrock
• Colors are those of the
original rock of the area
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Source: Google

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• Fast moving water has a lot of energy and can carry
larger pieces of rocks and sediments.
• Slow moving water has less energy and can only carry
tiny particles of sediment.
• When water loses energy, the sediments settle out.
• Water has the ability to move materials over long
distances.
Erosion by water, is carried out mainly by 2 factors:
• Rainwater (Rainfall)
• Running water (River)
Erosion by Water
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Source: Google

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Process of erosion due to rainfall
• Splash erosion
– Initial or the first stage of erosion.
– It mainly occurs when rain drops hit
the surface and uppermost layer wash
away.
– Transportation of loose material
comparatively very less.
• Sheet erosion
– Sheet erosion is transportation of
loose soil particles by overland flow.
– Removal of uniform/thin layer of soil
from the soil surface.
– It occurs in shallow depth.
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Suman Manandhar, Dr. Eng. (Geotechnical Engineering) Source: Google
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Source: Google

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Process of erosion due to rainfall
• Rill erosion
– Runoff water form small channels and that
channels wash away soil with them.
– Rills are shallow drainage lines less than 30
cm deep.
• Gully erosion
– Gullies are channels deeper than 30 cm.
– When rills become more deep and wide,
gully formed.
– Erosion that occurs when rills meets together,
widen and deepen.
– Gully erosion can be defined as detachment
and removal of soil in large mass comparative
to others.
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Source: Google
Development or Formation of Gullies
The gully development is recognized in four stages:
• Formation Stage: Scouring of top soil in the direction of
general slope occurs as the runoff water concentrates. It
normally proceeds slowly where the top soil is fairly resistant
to erosion.
• Development Stage: Causes upstream movement of the
gully head and enlargement of the gully in width and depth. The
parent materials are removed rapidly as water flows.
• Healing Stage:Vegetation starts growing in the gully.
• Stabilization Stage: Gully reaches a stable gradient, gully
walls attain a stable slope and sufficient vegetation cover
develops over the gully surface to anchor the soil and permit
development of new topsoil.
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Classification of Gullies
1. Based on size
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2. Based on Shape
U-Shaped: These are formed where both the topsoil and subsoil
have the same resistance against erosion. Because the subsoil is
eroded as easily as the topsoil, nearly vertical walls are developed on
each side of the gully.
V-Shaped: These gullies develop where the subsoil has more
resistance than topsoil against erosion. This is the most common
form of gully.
Trapezoidal:These gullies are
formed where the gully bottom is
made of more resistant
material than the topsoil. Below
the bottom of gully, the subsoil layer
has much more resistance to get
eroded and thus the development of
further depth of gully is restricted. 54
Source: Google

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Factors affecting Gully erosion
• Intense rainfall
• Topography
• Urbanization or improper land management
• Over grazing
• Construction of new road without planning
(Haphazardly)
• Mining activities
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Erosion due to running water
While talking about erosion due to running
water (rivers/streams), generally two types of
erosion can be observed:
• Bank erosion
• Base scouring
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Source: Google

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River Systems & the Work of Rivers
River system is a larger system of rivers and its tributaries. These
are the streams of water which is flowing through a particular channels.
Groups of these streams together called a river system. The lowest
level to which a river can erode its bed is called base level. Sea level
is the ultimate base level, but the floor of a lake or basin into
which a river flows may become local and temporary base
level.
There are 4 types of River Systems:
1. Braided Rivers
2. Meandering Rivers
3. Anastomosing Rivers
4. Straight Rivers
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1. Braided Rivers:
Braided streams typically get their start when a central sediment bar
begins to form in a channel due to reduced streamflow or an increase in
sediment load. These channels are constituting ripple crossed bedded
sands. These channels are active during flood stage and these can
produce the cross beds in larger scales. The sediments formed are
pebbly and sandy in nature.
Source: Google

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2. Meandering Rivers:
These are formed in coastal areas, lower gradient. Because of the
continuous flow, fine sediments were seen. In inner bends of meanders
cross laminated sands are constructed. Channels are seperated by levees
from flood plains that are comprised of finer grained muds and sands
deposited after breach of levees during flood stage, usually vegetated.
Flood stage can lead to cut off of meanders and break through of river.
Source: Google
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3.Anastomosing Rivers:
Anastomosed streams form when the downstream base level rises,
causing a rapid buildup of sediment. Since bank materials are not easily
erodible, the original single-thread stream breaks up into multiple
channels. Streams entering deltas in a lake or bay are often anastomosed.
Most often they seem to form under relatively low energetic conditions
near a base level. It appears to be impossible to define anastomosing
rivers unambiguously on the basis of channel planform only. It can be
defined as an anastomosing river is composed of two or more
interconnected channels that enclose flood basins.
Source: Google

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3. Straight Rivers:
Straight river is generally regarded as one of the typical river patterns in
conventional classifications in terms of their channel plain land forms.
However, very few straight patterns were found to be distributed in
wider spatial and temporal spans in the self adjusted fluvial rivers.
Source: Google
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After Miall (1977)
Source: Google

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The Work of Rivers
The erosional work of streams/rivers carves and shapes the landscape
through which they flow.
Functions of rivers:
a. Erosion
b. Transportation
c. Deposition
The work of a river depends on its energy.
Energy a function of:
a. Volume of water
b. Speed of water flow (dependent on gradient)
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Source: Google

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Source: Google
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Source: Google
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Youth stage = Upper course
Mature stage = Middle course
Old stage = Lower course
Source: Google

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Three stages of river:
A river rises from the highest level of the ground, called source.
When the river flows downwards through the slope, it is said to be
course.
Finally it reaches/meets the sea/ocean called mouth.
Three stages may occur in the path (course) of the river.
The upper part is called youthful stage, the middle is called mature
stage and the lower is called old age stage.
Source: Google
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Source: Google

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Process of erosion:
1. Hydraulic action
It is the work of turbulence in the water. In other words it is force of
moving water. Running water causes friction in the joints of rocks in a
stream channel.
It breaks fragments of the river bed and the banks of the river. These
fragments are carried along by the river which is called load.
Source: Google
2. Abrasion/corrosion
When a load is carried by the river, the load hits against its bed and the
sides (banks) of the river (i.e. bounced and dragged). As a result, bed
and bank materials started to pluck out and erodes rapidly. Abrasion is
the most powerful process of river erosion.
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Source: Google Suman Manandhar, Dr. Eng. (Geotechnical
Engineering)

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3.Attrition
When particles of the load themselves break into smaller pieces (worn
down), the process is said to be attrition. When thrown against the bed
and banks of the rivers, shapes of load turned into rounded and the
edges of the load changes to smooth.
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Source: Google
4. Solution/Corrosion
When chemicals in the water dissolves certain minerals in rocks, it is
said to be solution. For example, carbonic acid slowly dissolves
limestone.
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Source: Google

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112
Source: Google
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1.Traction
2. Saltation (Bounce)
3. Suspension
4.Solution
Transportation
Source: Google Suman Manandhar, Dr. Eng. (Geotechnical Engineering)

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1.Traction
Larger and heavier rocks/gravels are dragged or rolled along the bed.
2. Saltation (saltism: by leaps/jumps)
Smaller and lighter rock fragments and sand hop and bounce along the
river bed. At times, the distinction between traction and saltation may be
difficult to determine.
3. Suspension
Some of the load like silt and clay (fine-grained) will float along.
They may only be deposited when stream velocity reaches near 0.
Turbulence in the water is crucial in holding a load of sediments.
4. Solution
Some minerals are transported in dissolved form. Especially chemical
solution derived from minerals like limestone or dolomite.
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Deposition
When the river looses its ability to carry sediments/loads, it will
suddenly drops the materials on the bed and sides of the river. The
phenomenon is called deposition.

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River’s volume
decreases
• Presence of permeable
rocks
• Receding flood waters
River’s speed decreases
• It enters a lake
• It enters a calm sea
• It enters a gently sloping
plain
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Youth stage
• V-shaped
valleys
• Interlocking
Spurs
• Waterfalls
Mature stage
• Meanders
• Ox-bow
lakes
Old age stage
• Deltas
• Levees
• Flood Plains
Features of Stages of rivers

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Hjulstrom curve
Source: Google
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Source: Google

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Erosional Features of Rivers
Types of Erosional Features
 V-shaped RiverValley
 Gorge and Canyon
 River Meanders
 RiverTerraces
 Waterfall
 Pothole
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V-shaped RiverValley
The valleys sculptured by the rivers forming deep and narrow in a way to valley sides
meet each other at the valley floor. The valley formed in the youth stage of fluvial
erosion with steep valley side slope of convex element and developedV-shaped.
Source: Google

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Gorge and Canyon
It represents very deep and narrow valleys incorporating very steep valley side slope. It
is formed through a long period of time with frequent erosions.
Kaligandaki
gorge, Mustang
District (Source:
Google)
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River Meanders
River meander refers to the bends or longitudinal courses of the river, shape formed as
the movement of a snake. The shape is usually circular but sometimes it becomes semi-
circular. The concave slope is formed by the channel where river strikes and erosion
takes place resulting the formation of vertical cliffs. On the other hand, the convex
slope is characterized by gentle slope due to deposition of sands and gravels but
sometimes alluvium is deposited.
River Meander
(Source: Google)

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RiverTerraces
The narrow flat surface on either side of the valley floor are known as river terrace.
They are produced due to the dissection of fluvial sediments of flood plains deposited
along the valley floor. Layers of terraces are formed as stepped structures indicating
terraces of different time period along the valley floor.
RiverTerrace (Source: Google)
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Waterfall
A vertical drop of water with high energy occupying large volume of water from the
great height along the longer profile of the river.
Nyarchang
waterfall,
Myagdi (Source:
Google)

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Pothole
A kettle-like small depressions in the rock beds of the river valleys are termed as
“potholes” forming a cylindrical shape. It is formed in the upper course of a river
causing erosion due to high potential energy with increasing diameter and depth. It is
generally formed in coarse-grained rocks, for instance, sandstones and granite.
Pothole (Source: Google)
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Depositional Features of Rivers
Types of Depositional Features
Alluvial Fan and Alluvial Cone
Alluvial fand and alluvial cone are formed at the base of foothill where there is abrupt
drop in the channel gradient.Alluvial fan is gently sloped (averaged 5०) compared to
alluvial cone (averaged about 15०). Alluvial cones are characterized with the presence
of relatively coarse grained materials than the alluvial fans.
Source:
Google
Fan Cone

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Oxbow Lake
An oxbow lake forms when a meandering river erodes through the neck of one of its
meanders.This takes place because meanders tend to grow and become more curved
over time.The river then follows a shorter course that bypasses the meander.
Oxbow Lake (Source: Google)
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Natural Levees
The narrow belt of ridges of low height parallel to the channel built by the deposition
of the sediments are termed as natural levees, and it limits the lateral spread of the
river water.
Natural Levee (Source:Google)

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Flood Plain
An area of flat land near the river often subjected to flooding. It is an area of low-lying
surface ground adjacent to the river constituted mainly the river sediments.
Floodplain (Source:Google)
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Delta
The triangular shaped depositional feature at the mouth of a river debouncing in a lake
and/or sea is delta. It constitutes medium-sized sediments.
Delta (Source: Google)

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Erosional Features of Glaciers
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 Striations
 U-ShapedValley
 HangingValley
 Cirques &Tarns
 Horn
 Fjords
 Aretes
• Ice moves and carries rocks, grinding the rocks beneath it.
• Plucking happens when materials are picked up by the moving ice and pushed
along by the glacier.
• During abrasion, smaller rocks act like large pieces of sand paper and cause
grooves to be carved into the land.
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Striations
(Source: Google)
Erosion resulted surface material is washed out by glacial activity and rock fragments
are carried out by abrasion formed scratches and polished on underlying bedrock
pavement, called glacial striations.

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U-ShapedValleys
(Source: Google)
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Horns
Horns (Source: Google)

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Cirques &Tarns
Cirques &Tarns (Source: Google)
Depositional Features of Glaciers
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 Till
 Moraine
 Outwash Plains
 Kettleholes
 Drumlins
 Kame
Source: Google

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Till
Source: Google
• Till is a form of glacial drift, which is rock material transported by a glacier
and deposited directly from the ice or from running water emerging
from the ice. It is distinguished from other forms of drift in that it is deposited
directly by glaciers without being reworked by meltwater.
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Moraine
Source: Google
• A moraine is material left behind by a moving glacier. This material is usually soil and
rock. Just as rivers carry along all sorts of debris and silt that eventually builds up to
form deltas, glaciers transport all sorts of dirt and boulders that build up to form
moraines.There are four types of moraines.
Types of Moraines:
 Lateral Moraines
 Medial Moraines
 Terminal Moraines
 Supraglacial Moraines
 Ground Moraines

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Source: Google
Types of Moraines:
 Lateral Moraines: Unsorted glacial deposits along the sides of a glacier which are
formed parrallel to the ridges are termed as lateral moraines.
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Source: Google
Types of Moraines:
 Medial Moraines: Medial moraines form where two tributary glaciers come
together. They are generally surficial features on the ice and often consist of rock
that has fallen from a rockwall where the glaciers converge. Because they are thin,
surficial features, medial moraines are rarely preserved after the ice retreats..

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105
Source: Google
Types of Moraines:
 Terminal Moraines: A terminal moraine, also called end moraine, is a type of
moraine that forms at the terminal (edge) of a glacier, marking its
maximum advance.
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Source: Google
Types of Moraines:
 Supraglacial Moraines: A supraglacial moraine is enunciated of when the surface
of a glacier is covered with debris and/or boulders. A supraglacial moraine can
cover a glacier completely or only partially in the area of the glacier tongue. The
photos below show different variants.

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Source: Google
Types of Moraines:
 Ground Moraines: Ground moraines are till-covered areas with irregular
topography and no ridges, often forming gently rolling hills or plains, with
relief of less than 10 meters (33 ft). Ground moraine is accumulated at the base
of the ice.
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Outwash Plains
Source: Google
• An outwash plain, also called a sandur (plural: sandurs), sandr or sandar, is
a plain formed of glaciofluvial deposits due to meltwater outwash at
the terminus of a glacier.

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Kettle holes
Source: Google
• A kettle (also known as a kettle lake, kettle pond, kettle hole, or pothole)
is a depression or hole in an outwash plain formed by
retreating glaciers or draining floodwaters. The kettles are formed as a
result of blocks of dead ice left behind by retreating glaciers, which become
surrounded by sediment deposited by meltwater streams as there is
increased friction
110
Drumlins
Source: Google
• A drumlin, from the Irish word droimnín ("little ridge"), first recorded in 1833,
in the classical sense is an elongated hill in the shape of an inverted spoon
or half-buried egg formed by glacial ice acting on underlying
unconsolidated till or ground moraine.

56
111
Kame
Source: Google
• A kame, or knob, is a glacial landform, an irregularly
shaped hill or mound composed of sand, gravel and till that accumulates in a
depression on a retreating glacier, and is then deposited on the land surface with
further melting of the glacier. Kames are often associated with kettles, and this is
referred to as kame and kettle or knob and kettle topography.
Erosional Features of Groundwater
112
 Sinkhole
 Cavern
 Karst topography
 Solution valley
 Stylolite
Source: Google

57
113
Sinkhole
(Source: Google)
A sinkhole is a depression or hole in
the ground caused by some form of
collapse of the surface layer.The term is
sometimes used to refer to doline.
Most sinkholes are caused by karst
processes – the chemical dissolution
of carbonate rocks, collapse or
suffusion processes.
(Sinkhole in Nadipur,Pokhara, Source: Kathmandu Post)
114
Cavern
(Gupteshwor Mahadev Cave, Pokhara, Source: Google)
A cave or cavern is a
natural void in
the ground, specifically a
space large enough for a
human to enter. Caves often
form by the weathering of
rock and often extend deep
underground. Caves are
often ornamented with
calcium carbonate
formations produced
through slow
precipitation.These include
flowstones, stalactites,
stalagmites, helictites, soda
straws and columns.

58
115
KarstTopography
(Source: Google)
Karst is a topography formed from the dissolution of soluble rocks such
as limestone, dolomite, and gypsum. It is characterized by underground drainage
systems with sinkholes and caves.
116
Solution valley
(Source: Google)
The collapse of a cavern over a large area can create a feature referred to
as a solution valley or basin, sometimes referred to as a karst gulf, which from the
air resembles a huge sinkhole.These depressions may reach hundreds of meters across
and may contain numerous smaller, local sinkholes.

59
117
Stylolite
(Source: Google)
Stylolite, secondary (chemical) sedimentary structure consisting of a series of
relatively small, alternating, interlocked, toothlike columns of stone; it is
common in limestone, marble, and similar rock.
Depositional Features of Groundwater
118
 Stalactites & Stalagmites
 Replacement deposit
 Dripstone column

60
119
Stalactites & Stalagmites
(Source: Google)
Stalactite and stalagmite, elongated forms of various minerals deposited from
solution by slowly dripping water. A stalactite hangs like an icicle from the
ceiling or sides of a cavern. A stalagmite appears like an inverted stalactite,
rising from the floor of a cavern.
Stalactite
Stalagmites
120
Replacement deposit
(Source: Google)
Rocks are dissolved due to groundwater activities leaving behind a new
mineral deposit as a replacement is termed as replacement deposit.

61
121
Dripstone columns
(Source: Google)
These structures form when limestone dissolves a little in water. As that water
flows through cracks in the rock, it leaves behind traces of what's dissolved in it –
slowly building up on the ceiling and the floor. Eventually, a stalactite and stalagmite
will grow together into a single column (connects in a single column).
Erosional Features of Wind/Aeolin
122
Types of Erosional
Features
 Ventifacts
 Yardangs
 Deflation Hollows
 Pedestal Rock
• Erosion by abrasion may occur as particles come in contact with solid objects.
• Small sediments can be carried in the air by the wind.
• Larger sediments can be rolled along the ground.

62
123
Ventifacts
(Source: Google)
Ventifacts are rocks that have been sculpted by wind-borne particles (Bridges et al.
1999) and worn, faceted, cut, or polished by the abrasive action of windblown sand,
usually under arid conditions, in areas subject to frequent, high-velocity, sand-laden
winds.
124
Yardangs
(Source: Google)
A yardang is a streamlined bump carved from bedrock or any consolidated
or semi-consolidated material by the dual action of wind abrasion by dust and
sand and deflation (the removal of loose material by wind turbulence).

63
125
Deflation Hollows
(Source: Google)
Dune deflation hollows are where
wind has removed sand down to
a level where a layer of particles
too heavy for the wind to move
(an armored surface) stabilizes the
sand and prevents the surface
being lowered further.
126
Pedestal Rock
(Source: Google)
A mushroom rock, also called rock pedestal, or a pedestal rock, is a naturally
occurring rock whose shape, as its name implies, resembles a mushroom. The rocks
are deformed in a number of different ways: by erosion and weathering, glacial
action, or from a sudden disturbance. Mushroom rocks are related to, but different
from, yardang.

64
Depositional Features of Wind/Aeolin
127
 Sand Dunes
 Loess
 Sand Sheets
128
Sand Dunes
(Source: Google)
A dune is a mound of sand this is formed by the wind, usually along the beach or in a
desert. Dunes form when wind blows sand into a sheltered area behind an
obstacle. Barchans, Transverse, Parabolic and Longitudinal Dunes are the
types of sand dunes.

65
129
Sand Dunes
(Source: Google)
Barchans
Dune: A
barchan or
barkhan dune is
a crescent-
shaped dune.
Transverse Dunes: Abundant
barchan dunes may merge
into barchanoid ridges, which
then grade into linear (or
slightly sinuous) transverse dunes,
so called because they lie
transverse, or across, the wind
direction, with the wind blowing
perpendicular to the ridge
crest.
130
Sand Dunes
(Source: Google)
Parabolic Dune: U-shaped
mounds of sand with convex
noses trailed by elongated arms
are parabolic dunes. These dunes
are formed from blowout dunes
where the erosion of vegetated
sand leads to a U-shaped
depression.
Longitudinal Dunes: Seif dunes
are linear (or slightly sinuous)
dunes with two slip faces. The
two slip faces make them
sharp-crested. They are called
seif dunes after the Arabic word
for "sword". They may be more
than 160 kilometres (100 miles)
long

66
131
Loess
(Source: Google)
Loess (from German: Löss ) is a clastic, predominantly silt-
sized sediment that is formed by the accumulation of wind-
blown dust. 10% of Earth's land area is covered by loess or similar deposits .
132
Sand Sheets
(Source: Google)
Sand sheets are flat, gently undulating plots of sand surfaced by grains that
may be too large for saltation. They form approximately 40%
of aeolian depositional surfaces.

67
Erosional Features of Coast/Sea Water
133
 Cliffs &Wave Cut Bench
 Headlands & Bays
134
Cliffs &Wave Cut Bench
(Source: Google)
When the sea moves against
the base of the cliff
(headlands) using corrasion
and hydraulic action (for e.g.,
limestone or chalk), it
undercuts the cliff and forms a
wave-cut notch. Above this
notch, an overhang will form; it
will fall into the sea as a result
of the pressure of its own
weight and the pull of gravity.
This phenomena will continue
and form another notch with
retreating the cliff and form
higher and steep cliff rock.
Hence formed remains of the
cliff rock, now below the sea
at high tide, form a rocky cliff.

68
135
Headlands & Bays
(Source: Google)
The bands of soft rock, such as sand and clay, erode more quickly than those
of more resistant rock, such as chalk. This leaves a section of land jutting out
into the sea called a headland. The areas where the soft rock has eroded away,
next to the headland, are called bays.
136
Caves,Arch, Stack & Stump
(Source: Google)
When a wave-cut notch collapses in
time due to gravity, it leaves behind a
column of rock not attached to the
cliff, known as stack.
The continuous erosion & weathering
will lead to the formation of stump,
visible only at low tide.

69
137
Caves,Arch, Stack & Stump
(Source: Google)
Caves occur when waves force their
way into cracks in the cliff face. The
water contains sand and other
materials that grind away at the rock
until the cracks become a cave (e.g.,
hydraulic action).
If the cave is formed in a headland, it
may eventually break through to the
other side forming an arch.
Depositional Features of
Coast/Sea Water
138
 Beach
 Spits
 Sand Bars
 Abyssal Plain
 Coral Reefs
 Atoll
(Source: Google)
Assignment
27 march, 2023

70
• Downward movement of rock and sediment
down a slope due to the pull of gravity
• The process is quite slow and almost
impossible to see until the land mass is no longer
able to support itself and falls or slides down
a slope.
Erosion by Gravity
139
140

71
Thank you for
your kind attention !!!

Physical Geology( Unit 7)

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