Unit 2: Geomorphology Flashcards
(265 cards)
1
Q
The sources which provide knowledge about interior of Earth can be divided into
A
- Direct Sources: Volcanic eruptions, mines, drilling projects
- Indirect sources: temperature, pressure density, gravitation, magnetic field and seismic activity
2
Q
What are the three layers earth is divided into
A
Crust
Mantel
Core
3
Q
Sates of the following
- Crust
- Asthenosphere
- Mantle
- Outer Core
- Inner Core
A
- Solid
- Plastic
- Solid State
- Liquid State
- Solid
4
Q
Inside the earth, _______ and ______ increases with depth
A
Temperature and pressure
5
Q
Which crust is thicker?
A
Continental crust
6
Q
Which crust is thinner?
A
Oceanic crust
7
Q
The mean density of material in continental crust is
A
2.7g per cm Qube
8
Q
Continental crust is constituted of
A
Silica and Aluminium
9
Q
Oceanic crust is made of
A
Silica and Magnesium
10
Q
The Oceanic crust has a density of
A
3g/cm cube
11
Q
The kind of rock seem in the oceanic crust is
A
Basalt
12
Q
The ________________ separates Crust from the Mantle
A
Moho Discontinuity
13
Q
The Mantel extends from
A
Moho’s discontinuity to a depth of 2,900km
14
Q
The mean density of mantle is
A
4.6 g,/ centimetre cube.
15
Q
Mantle is made of
A
Made of Mafic (a word from “ma,” for magnesium-bearing, and “fix, “from ferric, or iron-bearing, and “fic, “from ferric, or iron-bearing) silicate minerals
16
Q
Which is the upper portion of the mantel
A
Asthenosphere
17
Q
The word “astheno” means
A
Weak
18
Q
The asthenosphere extends up to
A
400km
19
Q
Asthenosphere has a density of
A
3.4g/cm qube
20
Q
_______________ is the chief source of magma that finds its way to the surface during volcanic eruptions
A
Asthenosphere
21
Q
The upper and lower mantle is separated by a layer is known as __________________ which is basically is around a depth of ________kms
A
Repti Discontinuity
700kms
22
Q
Temperature of Upper mantle and lower mantle
A
1800˚C
2800˚C
23
Q
The crust and the uppermost part of the mantle are called the
A
Lithosphere ( with thickness of about 20 to 100 km)
24
Q
Mantel is the most voluminous portion of the earth’s interior occupying ___ of the Earth;s volume and around ___ of the ______ of the earth
A
83%
68%
Total mass
25
What is responsible for the movement of plates over a long period of time
The plasticity in the upper portion of the mantle is mainly responsible for the movement of plates over a long period of time.
26
It is believed by many geologists and geographers that the phenomena driving the movement of the material inside the mantle is the
Convective currents
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Conventional movements inside the mantle are believed to be the driving force behind the __________ movements and is also a reason for the __________________ volcanism
Tectonic
Hotspot
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The core is made up of heavier metals which sunk to the bottom at the very beginning when the earth was still in a molten state. That region is generally reffered to as the
Barysphere
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The density of the core is ______as that of the mantel
twice
30
The core-mantle boundary is located at a depth of
2900km
31
The Earth's core is about _____ km in radius and is very hot- somewhere between __________ and ___________.
3500km
3000degree C
5000 degree C
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The density of material at the mantle-core boundary is around ______ which increases to around ______ at the centre of the earth at _______
5g/cm^3
13g/cm^3
6300km
33
The core is made up of very heavy material mostly constituted by ______ and _____. Hence it is also called the __________
Nickel
Iron
"NiFe" layer
34
The liquid iron core creates a ________ as the fluid flows around the solid core and interacts with the Earth's existing magnetic field. This process in turn generates a dynamic energy condition that maintains the
magnetic field
Earth's perpetual magnetic field (Geomagnetism)
35
Discontinuities in the Earth's interior
1. Conrad Discontinuity: Lies between the upper and the lower crust
2. Mohorovicic discontinuity: Lies beteween the lower crust and the upper mantle
3. Repti Discontinuity: Between upper and lower Mantle
4. Gutenberg Discontinuity: Lies between lower Mantle and Upper core
5. Lehman Discontinuity: Lies betwen the Outer and the inner core
36
Continental drift theory was proposed by
Alfred Wegener
37
Post drift theories:
1. Convection current theory
2. Paleo-magnetism
3. Seafloor spreading
4. Plate tectonics theory
38
According to Wegener, there was the presence of a supercontinent called_______ in the _______ period (250 million years ago). By the end of __________, supercontinent started to break into 2 parts: _______________ and ________________.
Pangea
Triassic period
Triassic period
Laurasia(north)
Gondwanaland(south)
39
Wegener presented a set of evidencfes in support of his theory
1. Shape of continents: The coastlines of South America and Africa fronting each other have a remarkable and unique match. In 1964, Bullard crated a map using a computer program to find the right fit of the Atlantic margin and it proved to be quiet fit.
2. Rocks of the same age across the oceans: The radiometeric dating methods have helped in correleating the formation of rocks present in different continents across the ocean. The ancient rocks belts in the coast of Brazil match with those found in Western Africa. The old marine deposits found on the coasts of South America and Africa belong to the Jurassic Age. This implies that the Atlantic ocean never existed ther before that time.
3. Fossil Evidence: Wegener used already documented fossil evidence of Mesozoic life forms. For example, the fossils of Mesosaurus, a small reptile, was found only in two places: South Africa and Brazil. Continental Drift seems to be only logical explanation to this finding.
4. Placer Deposits: The presence of abundant placer deposits of gold along the Ghana coast and the complete lack of its source rocks in the area is a phenomenal fact. The gold-bearing veins ar epresent in Brazil and it is evident that the gold deposits of Ghana in Africa are obtained from the Brazil plateau from the time when the two continents were beside each other.
5. Paleo-climatic evidence: Tilite is a sedimentary rock made from glacier deposits. the Gondwana system of sediments from India is recognised as having its counterparts of this series are found in Madagascar, Africa, Antarctica, Falkland Island, and Australia not to mention India. At the base, the system has thick tillite significantly widespread and sustained glaciation. Generally, the similarity of the Gondwana type sediments evidently shows that these landmasses had exceptionally similar origins. The glacial tillite givers clear evidence for paleoclimates and the drifting of continents
40
What was the need for post drift studies?
Wegner suggested that polar-fleeing force due to Earth's rotation and Tidal force due to gravitational pull of sun and moon are respoinsbile for drifting of continents northward. But later studies suggested that both these forces are too weak to account for continental drift and even if accounted for they would have rather stopped continents from drifting. These shortcoming paved the way for other studies
41
Convention Current Theory
Arthur Holmes
He postulated that through convection currents mechanism, heat distribution takes place in the mantle. The convection currents occupy entire mantle and when rising limbs of these currents meet they put a frictional drag on the base of lithospheric plates and divergence of lithospheric plates occur and falling limbs result in convergence of plates
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Paleo-magnetism
refers to the study of ancient geo-magnetism
43
What is the concept of Paleo-magnetism
Paleo-magnetism refers to the study of ancient geo-magnetism that wa recorded in the rocks formed during that period. Several rocks such as basalt contain magnetic minerals and these magnetic minerals align themselves in the direction of earth's magnetic field present at the time of rock formation/solidification. Thus rocks acquire geo-magnetic properties associated with their formation period and thus act as natural record of earth's geomagnetic properties including magnetic field of earth. Paleo-magnetic studies have proved that orientation of earth's magnetic field has frequently altered over time.
Paleo-magnetism provided strong evidence in support of sea floor spreading and plate tectonics. The regions along MID OCEANIC RIDGES (MOR) hold a unique record fo earth's magnetic field. Paleo-magnetic studies revealed that along mid oceanic ridge, rocks with alternate patters of magnetic properties are found on both sides of ridge. MOR is a region of diverging plate boundaries. As result when the plates move apart magma from below rises through fissures and solidify along the narrow band of rocks on either side of the vent and also while cooling the rocks acquire the earth's magnetic field present during that period. As the convention currents pull the oceanic plates apart the solidified band of rocks move away fromt eh vent and new magma rises and solidifies along narrow band of rocks next to MOR. This process continues for million of years and during which magnetic field of earth reverses thus adjacent rock bands have opposite polarities. This process repeats over and over again giving parallel bands of on either side of MOR and alternate pattern of magnetic striping on seafloor.
44
Sea Floor Spreading
Harry Hess propounded the hypothesis known as the "sea floor spreading" in the 1960s based on ocean floor and paleomagnetic studies. According to him MORs are regions on earth's surface located directly above rising limbs of convection currents flowing in the mantle. Convection currents put a frictional drag on the base of oceanic crust and force them to spread laterally in the opposite direction i.e. divergence of plates. This leads to volcanism along MOR and causes formation/creation of oceanic crust. MORs are the areas of creation whereas trenches are the areas of destruction of oceanic crust.
Trenches are regions where subsiding limbs of convection, current drag oceanic crust into mantle. This process continues and new oceanic crust forms at MORs as old one gets destroyed at trenches. The fact that the Oceanic crust is very much younger than continental crust adds validity to this theory.
45
Plate Tectonic Theory
In 1967, McKenzie and Parker and also Morgan, independently collected the available ideas and came out with another concept termed Plate Tectonics. Plato Tectonic is nothing but movement of lithospheric plates due to internal forces emanating from the earth's interior.
Lithosphere consisting o fcrust and top mantle is broken into a network of distinct plates referred to as lithospheric plates. A lithospheric plate is a massive, irregularly shaped slab of solid rock as lithospheric plates. A lithospheric plate is a massive irregularly shped slab of solid rock generally composed of both continental and oceanic lithospheres. Plates move (float) over the asthenosphere as rigid units and interact with each other leading to tectonic activity. Most of the tectonic activity like earthquakes, volcanism is seen along plate boundaries. According to Plate tectonic theory Earth's lithosphere is divided into seven major and some minor plates.
46
Major tectonic plates include
1. Antarctic and surrounding oceanic plate
2. North American plate
3. South American plate
4. Pacific Plate
5. India-Australia-New Zealand plate
6. African with eastern Atlantic floor plate
7. Eurasian and adjacent oceanic plate
47
Minor tectonic plates
1. Cocos plate: between Central America and Pacific plate
2. Nazca plate: between South America and Pacific plate
3. Arabian plate: Saudi Arabian landmass
4. Phillippine plate: between Asiatic and Pacific plate
5. Caroline plate: between Philippine and Indian plate
6. Fuji plate: North-east of Australia
7. Caribbean plate
8. Juan de Fuca plate: between North American plate and Pacific plate
48
Plate boundaries
Plate boundaries are the regions where plates interact with each other. Geographical features and phenomenon such as Mountains, Trenches, Mid Oceanic Ridges, Volcanism, Earthquakes are direct consequeces on interactions between various plates. There are three types of plate boundaries
49
Divergent Plate Boundaries
Plates move away from each other resulting in formation of faulting and gaps. Magma moves upwards to fill the gap leadin to volcanism and formation of new crust. Divergent plate boundaries are also known as constructive boundaries as new xrust is formed at this boundary. Earthquakes and Volcanic activity are very common along divergent boundaries. Mid Atlantic Ridges are found at divergent boundaries.
50
What are the three types of plate boundaries
Divergent Plate Boundaries
Convergent plate boundaries
Transform Plate Boundaries
51
What are the three types of convergence
1. Ocean-Ocean convergence
2. Ocean-Continent Convergence
3. Continent-Continent Convergence
52
Convergent Plate Boundaries
They are also known ass destructive plate boundaries. Here plates move towards each other causing collision and subduction of the denser plate under the lighter plate
53
Which plate subducts more
oceanic
54
Ocean-Ocean convergence
When two oceanic plates converge, the heavier and denser oceanic plate subducts under less dense oceanic plate forming trenches along the boundary. The subsiding plate material can melt and become magma, which tends to rise. This upward moving magma creates volcanic landforms along the boundary. Island Arcs are a chain of volcanic islands formed at the boundary. Japan, Phillippines, Indonesian islands are examples of volcanic landforms formed due to ocean-ocean convergence
55
Ocean-Continent convergence
When an oceanic and continental plate converge, denser oceanic plate subducts under lighter continental plate forming a trench along the boundary (trenches here as not as deep as in O-O convergence). Continent-Ocean Convergence in similar to ocean-ocean convergence except that in continent-ocean convergence mountains are formed instead of islands
Eg: Andes and Rockies are mountain ranges formed due to Ocean-Continent convergence.
56
Continent-Continent convergence
In most cases of Continent-Continent plate convergence, neither plate subducts and even if one of the plates subducts, the subduction zone will not go deeper than 40-50km. Convergence leads to collision and deformation of plates along boundaries leading to formation of fold mountains
Eg: Himalayas formed due to the collision of Eurasian and Indian Plates
57
What is Transform Plate Boundaries
Lithosphere plates slide past one another without separating or converging. The two plates are in contact along a vertical fracture, called a transform fault.
Here plates slide horizontally to each other I.e. they move parallel to each other without causing any construction or destruction but only deformation of existing land form. San Andreas Fault along eastern coast of Pacific Ocean is the best example of a transform fault.
Plate tectonics theory forms the core of the modern geological paradigm that helps explain many seemingly unrelated geological phenomena. It geographical studies by providing a uniform context for understanding mountain-building processes, volcanoes, and earthquakes as well as the evolution of Earth’s surface and reconstructing its past continents and oceans. Formation of most of the major landforms can also be satisfactorily explained using PTT.
58
Earthquake is a manifestation of the power of ____________________. It is the result of energy caused due to a ______________________________________ of the rocks at or beneath the surface of Earth.
Tectonic forces (endogenetic)
Transient disturbance of the elastic or gravitational equilibrium
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The point inside the earth where the energy is released is called the _________________ of an earthquake
Focus or hypocentre
60
Earthquake: The point on the Earth’s surface, nearest to the focus, is called the
Epicentre
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______________ is the study of Earthquakes
Seismology
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About 68% of all earthquakes observed in the vast regions of the Pacific Ocean as a ____________ and is closely linked with _______ _________ and _________ __________
Ring of fire
Crustal dislocation
Volcanic phenomena
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What are the types of earthquake waves
Earth’s interior (body waves)
Earth’s surface (surface waves)
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____________ type of seismic waves are generated due to the release of energy at the focus
Body waves
65
____________ waves move in all directions traveling inside the body of the Earth
body waves
66
What are the type of Body Waves
Primary wave
Secondary Wave
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__________ waves are fastest among seismic and are the first to arrive at the surface.
P-waves
68
______________ are similar to sound waves
P-waves
69
____________ can travel though gaseous, liquid and solid materials
P-waves
70
P-wave is also called
Compressional wave
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How does P-wave travel
P wave, or compressional wave, vibrate parallel to the direction in which wave is traveling. This exerts pressure on the material in the direction of the propagation. Hence, it creates density differences in the material leading to stretching and squeezing of the material.
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S wave is also called
Secondary wave
Shear wave
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How does secondary wave move?
It is a seismic body wave that shakes the ground back and forth perpendicular to the direction of the wave is moving.
S-waves vibrate perpendicular to the direction of the wave in the vertical plane, creating troughs and crests in the material through which they pass
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Which waves comes first to the surface: S waves or P waves
P-waves
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__________ waves travel only through solid medium
S-waves
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An instrument called _____________ located at far off locations records the seismic/earthquake waves
Seismograph
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Earthquake waves travel towards the focus or away from the focus?
Away from the focus
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What is a shadow zone?
There exists some specific areas where seismic/earthquake waves are not recorded on a seismograph. Such zone is called ‘Shadow Zone’
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It is a well established fact from various observations that seismograph located at any distance within _________ from ________, records arrival of both P and S-waves
105˚ from epicenter
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The seismographs located _____________ from epicenter, record the arrival of P-waves, but not that of S-waves
Beyond 145˚
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Which is the shadow zone of both types of waves?
103˚ to 145˚ from epicentre
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The entire zone beyond ______ does not receive S-wave
103˚
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How are surface waves generated?
The body waves interact with the surface rocks and generate a new set of waves called surface waves.
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________________ waves are the last to log on a seismograph
Surface waves
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______________ are considered to the the most destructive waves
Surface waves
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What are the types of surface waves?
1. Rayleigh Wave
2. Love Wave
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Rayleigh wave is a seismic surface wave causing the ground to shake in an ______________, with no _________ or _____________
Elliptical motion
Transverse
Perpendicular
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What waves are also called ‘Rolling waves’
Rayleigh wave
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Love wave is a surface wave having a _________________ that is ___________ or ___________ to the direction in which the wave is traveling
Horizontal motion
Transverse
Perpendicular
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The amplitude of ground vibration caused by a Love wave _______ by depth
Decreases
//as the name itself suggests its a surface wave
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Mercalli Scale
The intensity scale is named after Mercalli, and Italian seismologist. It takes into account the visible damage caused by the event. The range of intensity scale is from 1-12
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________ range of intensity scale is from 1-12?
Mercalli scale
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Richter scale
The magnitude scale is known as the Richter scale. The magnitude relates tot eh energy released during the quake. The magnitude is express in absolute number, 0-10
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Which scale that measures earthquake, has the magnitude expressed in absolute numbers?
Richter Scale
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In Richter scale the magnitude is expressed in
Absolute numbers, 0-10
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What are the types of earthquakes?
1. Tectonic earthquakes
2. Volcanic earthquakes
3. Collapse earthquakes
4. Explosion earthquakes
5. Reservoir-induced earthquakes
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The most common types of earthquakes are
Tectonic earthquakes
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_____________________ are generated along a fault plane due to the sliding of rocks.
Tectonic earthquakes
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Volcanic earthquakes
These are generated due to violent volcanic eruptions. However, these are confined to areas of active volcanoes
100
Sometimes the roofs of the underground mines collapse causing minor tremors. These are called
Collapse earthquakes
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Earthquakes associated with volcanic activity often occur in
Swarms
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What is Earthquake swarm?
An earthquake swarm is a sequence of seismic events occurring in an area without a major earthquake within a relatively short period of time. The period used to define the swarm can vary but generally is of the order of days, months or even years.
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Volcanoes are located on or near
plate boundaries
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Definition of Volcano
A volcano is a vent or fissure in the crest through which hot gases, molten ale, mud-flows, some rock fragments, and ask erupts outward from the interior of the Earth
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_________ zones around the _________________ have significant volcanic activity and that's why it is aptly named as the __________________
Subduction zone
Pacific Rim
Pacific Ring of Fire
106
____________ and certain hotspots also generate volcanic activity
Mid-oceanic Ridges ( divergent plates)
107
Underground molten mineral is called
Magma
108
When magma cools and solidifies below the Earth's surface in the gaps, its creates intrusive topographic features like
Batholith's
Laccoliths
Phacoliths
Lopoliths
Silly
Dykes
109
When is Magma called LAVA
When it reaches the surface of Earth
110
the lave cools and hardens, building the extrusive volcanic landforms like
Cones,Craters, Domes and even lava plains
111
Volcanic material
1. Vapour and Gases
2. Magma and LAVA
a. Felsic Lava
b. Mafic Lava(basalt)
i. Acidic
II. Basic
3. Pyroclastic material, or tephra
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How much percentage of vapours and stream are a part of the gases erupted from the volcano
60 to 90%
113
What all gases are erupted from the volcano
Carbon di oxide
Nitrogen dioxide
Sulphur dioxide
sulpharated hydrogen
Hydrochloric acid
114
Which type of LAVA has very high viscosity
Felsic lava
115
Felsic lava features:
1. Usually, very thick with high viscosity
2. Lava does not usually flow very far from the volcano's vent and builds up steep slopes.
3. Ejected pyroclastic material or tephra from volcano, fall on the area surrounding the crater, creating a cone shape
4. Associated rocks are rhyolite and andesite
5. The most common type of volcano associated with felsic magma is the stratovolcano, sometimes called a composite volcano
116
Mafic lava (basalt)
1. in contrast to felsic lava, it is not very viscous and holds little gas
2. Eruptions are usually quiet
3. The lava can travel long distances and spread out in thin layers.
4. Large basaltic volcanoes typically have rounded domes and gentle slopes
5. The most common type of volcano associated with magic lave is the shield volcano.
117
Acidic Magma/Lava
Higher percentage of Silica
118
Basic Magma/Lava
Lower percentage of silica
119
Ejected particles of different sizes, known collectively as
Pyroclastic material or tephra
120
What is Pyroclastic material or tephra
Ejected particles of different sizes, known collectively as pyroclastic material or tephra
Volcanoes can be classified on the basis of nature of eruption (explosiveness) and the form (shape, size) developed at the surface. This, in turn, depends on the type or nature of magma involved which is generally felsic (rich in Iron and aluminium) or mafic (rich in magnesium and iron)
121
What are the major type of volcanoes
1. Shield Volcanoes
2. Cinder Cones
3. Composite volcanoes
4. Caldera
5. Flood basalt Provinces
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Shield Volcanos
1. A shield volcano is a type of volcano usually build of very fluid lava flows
2. Slopes are not steep
3. Shield volcanoes are build by effusive eruptions, which flow out in all directions
4. Characterised by no or low -explosivity with basic lava simply flowing out. They can become explosive if somehow water gets into the vent
5. Barring the basalt flows, the shield volcanoes are the largest of all the volcanoes on the earth. The Hawaiian volcanoes are the most famous examples
6. the upcoming lava moves in the form of a fountain and throws out the cone at the top of the vent and develops into cinder cones.
7. Eg: Mauna Loa shield in Hawaiian volcanoes
123
Cinder cones
1. Cinder cones are small volcanoes. There are rarely more than a few hundred metes high height.
2. These form when frothy (blobs) magma is ejected under high pressure from a narrow vent, producing tephra
3. The tephra accumulates around the vent to form a roughly circular hill with a central crater
4. Example is Wizard Island, oregon
124
What is composite volcano also called
Stratovolcano Volcano
125
Composite Volcanoes
1. Sometimes called a Stratovolcano volcano
2. Characterised by eruptions of cooler and more viscous lavas than that of basalt
3. Volcanic eruption are explosive as felsic magma can contain gases under high pressure
4. Stratovolcanoes are tall, steep cones built of layers of felsic lava and volcanic ash
5. In eruptions along with lava, large quantities of pyroclastic material and ashes find their way to the ground
6. These erupted materials accumulates in the vicinity the vent openings leading formation of layers, and the makes the mounts appear as composite volcanoes
7. Eg many active stratovolcanoes lie within the circus-Pacific mountain belt, volcanic are of Sumatra and JAVA
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Which volcano is the most expensive of all volcanoes
Caldera
127
Caldera
1. Most explosive among all volcanoes. These are so explosive that when they erupt they tend to collapse on themselves rather than building any tall structure. The collapsed depression are called calderas
2. The magma chamber supplying the lava is huge and in close vicinity
128
Flood basalt Provinces
1. Form due to eruptions from a volcanic hotspot pouring enormous volumes of basalt lava that emerge from numerous vents and fissures and accumulate layer upon layer
2. These basalt layers, called blood basalts, can become thousands of meters thick and covered thousands of square kilometres
3. Eg The Deccan Traps in india
129
Volcanoes can be classified based on periodicity of eruptions into categories:
Active: recently erupted and a possibility of erupting soon
eg: Mount St Heles, US. Barren Island in India
Dormant
extinct
130
Which is the only Active volcano in India
Barren Island
131
Dormant volcano
Not erupted in a long time, but there is possibility of erupting in the future
eg:Vesuvius in Naples, italy
132
Extinct volcano
An extinct volcano is one which has erupted thousands of years ago and there's no possibility of eruption
Eg: Mount Thielsen in Oregon
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External forces are known as __________ while internal forces are called __________
Exogenic
Endogenous
134
The actions of exogenic forces results in
Wearing down(degradation) of relief/elevations and filling up (aggravation) of basins/depressions, on the earth’s surface.
135
The phenomenon of wearing down of relief variations of the surface of the earth through erosion is known as
Gradation
136
________________ continuously elevate or build up parts of the earth’s surface and hence the exogenic process are mainly ____________
Endogenous forces
Land wearing forces
137
_______________ are building forces
________________ are land wearing forces
Endogenic forces
Exogenic forces
138
Geomorphic Process
the endogenic and exogenic forces causing physical stress and chemical action on earth materials and bringing about changes in the configuration of the surface of the earth are known as geomorphic process.
Diastrophism and catastrophism (volcanism and earthquakes) are endogenic geomorphic process. Weathering, mass wasting, erosion and deposition are exogenic geomorphic process.
139
Geomorphic agents
Any exogenic element of nature capable of acquiring and transporting earth materials can be called a geomorphic agent. These elements of nature become mobile due to gradients in fact all the movements either within the earth or on the surface of the Earth occur due to gradients-from higher levels to lower levels, from high pressure to low pressure areas etc
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The forces emanating within the Earth are called
Endogenetic forces
141
Endogenic forces is mostly generated by
Radioactivity within the interior of Earth, rotational and tidal friction and primordial heat from the origin of the earth. This energy due to Gerry thermal gradients and heat flow from within induces endogenetic forces causing contraction and expansion of rocks which isn turn leads to horizontal and vertical movements.
142
Endogenetic forces are divided into
1. Sudden movements (Catastrophism)
A. Volcanic Eruptions
B. Earthquakes
2. Diastrophic forces
A. Epirogenetic
I. Upward (Emergence)
II. Downward (Submergence)
B. Orogenetic
I. Tensional
A. Cracking
B. Faulting
II. Compressional
A. Wrapping
1. Upwraping
2. Down wrapping
B. Folding
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Mountains occupy ______ of the worlds land surface
27%
144
Which is the smallest mountain and where is it?
Mahul in Thane district of Maharashtra with height around 852m
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What is a mountain?
A mountain is nay natural elevation, rising considerably higher (above 600m) than the surrounding area. Where as a hill is a land surface that rises higher than the surrounding area but not more than 600 meters. Mountains generally have a small summit and a broad base. They vary in their heights, like they can be as high as Mt.Everest which has an elevation of 8848m and as low as Mahul in Thane district of Maharashtra with height around 852m
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What are the four main types of mountains?
1. Fold Mountains
2. Block Mountains
3. Volcanic Mountains
4. Residual or Relict mountains
147
Fold mountains are created by _______
Intense compressional(or convergent) endogenetic forces that cause crustal wrapping or folding
148
The upward rise of the crustal art due to compress (convergent) forces is called ___________ and while bending of crustal part downwards forming a basin or depression is called __________
Upwrappping
Downwrapping
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Folding effectively shortens Earth’s crust creating waves like bends called as ________. The upfolds are called __________________ and the downfolds are ____________
Folds
Anticline
Syncline
150
_______________________ are by far the most widespread mountains and many of the world’s biggest mountain belts, such as the Himalayas, rockies, Andes, Alps etc are examples of fold mountains
Fold Mountains
151
Fold Mountains are also called
Mountains of elevation
152
Sharp break in the crustal rocks is called a
Fault
153
Faults are caused due to the cracks developed in the Earth’s crust mostly due to_________________. The plane along which rocks blocks gets displaced is called a ___________
Tensional Force
Fault plane
154
How are block mountains created?
Block mountains are created when large ares are broken and displaced vertically along a fault. The uplifted blocks are termed as horses and the lowered blocks are called GRABEN
155
Examples of Block Mountains
The Rhine valley
The Great African Right Valley (valley floor is graben)
the Vosges mountain in Europe
156
In Block mountain the blocks that go up are called_________ and down are called_________
Horst
Graben
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Volcanic mountains are also called
Mountain of Accumulations
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What are Volcanic Mountains?
Volcanic mountains are the accumulations of large amounts of volcanic lavas and pyroclastic material around the volcanic vent, such as seamounts and stratovolcanoes.
They are also called “Mountains of accumulations”
They can be different shapes and sizes like cinder, shield, composite etc.
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_____________ mountains are formed by due erosion by various geomorphic agents
Residual or Relict mountains
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What are the examples of Residual Mountains
Monadnock USA
Palkonda, Parasnath, Rajmahal , Grinar hills
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What are residual or relict mountains
1. These are formed due erosion by various geomorphic agents
2. Some rocks/areas may remain resistant to erosion when the general level of land is lowered by the agents of denudation, forming residual or relict mountains Eg. Monadnock USA
3. These can also form when a river cut through a plateau like that in the Highland of Scotland and Scandinavia
4. Palkonda, Parasnath and Rajmahal, Grindr hills are examples
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All the exogenic geomorphic process are covered under a general term
Denudation
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What does the word Denu mean
Strip off or uncover.
164
Denudation process
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What are the types of Weathering
1. Chemical Weathering: Carbonation, Hydration, Oxidation, Reduction
2. Physical Weathering Process: Unloading and expansion, Temperature changes and expansion, Salt Weathering, water pressure, Expansion forces, Gravitational forces
3. Biological Weathering
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What is weathering
Weathering is defined as mechanical disintegration and chemical decomposition of rocks through the actions of various elements of weather and climate. As very little or no motion of materials takes place in weathering, it is an in-situ or on-site process. Weathering process are affected by many complex geological, climate, topographic and vegetative factors.
There are three major groups of weathering process: (1) Chemical (2) Physical or Mechanical (3) biological weathering processes
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What are Mass Movements?
These movements transfer the mass of rock debris down the sloped under the direct influence of gravity. The movements of mass may range from slow to rapid, affecting shallow to deep columns of materials and include creep, flow, slide and fall.
Gravity exerts its force on all matter, both bedrocks and the products of weathering. So, weathering is not a prerequisite for mass movement though it aids mass movements.
Mass movements do not come under erosion through there is a shift (aided by gravity) of materials from one place to another. Materials over the slopes. Have their own resistance to disturbing forces and will yield only when force is greater than the shearing resistance of the materials. Weak unconsolidated materials, thinly bedded rocks, faults, steeply dipping beds, vertical cliffs or steep slopes, abundant precipitation and torrential rains and scarcity of vegetation etc,. Favour mass movements.
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What are the types of mass movements?
1. Slow movements
2. Rapid movements
3. Landslides
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_____________ and ___________ are the most common minerals found in rocks
Feldspar
Quartz
170
Where are weak rocks and where are strong rocks
Valley
Hills, ridges, uplands
171
Types of rocks and their classifications
1. Igneous Rocks (igneous is a Latin word meaning fire)
2. Sedimentary Rocks (Latin word sedimentum)
3. Metamorphic Rocks (Greek word metamorphose meaning change of form)
Porous rocks
Non-porous rocks
Permeability
Texture
Fossils
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Igneous rocks are made from
LAVA
173
Igneous rocks made from lava is called
Extrusive Igneous rocks
174
______________ are known as primary rocks or parent rocks
Igneous Rocks
175
Examples of Igneous rocks
Granite, Gabbro, Pegmatite, basalt, Volcanic breccia
176
Igneous rocks are classified based on Texture and how does the texture differ
1. If molten material id cooled slowly at great depths, mineral grains may be very large
2. Sudden cooling (at the surface) results in small and smooth grains
3. Intermediate conditions of cooling would result in intermediate sizes of grains making up igneous rocks
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____________ formed rocks are fine-grained. Examples of it
Extrusive igneous rocks
Basalt, Tuff, Pumice
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Based on the rate and place of cooling Igneous rocks are divided into two types
1. Extrusive igneous rocks: The rocks cool quickly and as a result, these rocks are fine-grained. they are formed on the surface of the Earth. Here magma has less time to from granules/crystals. Basalt, tuff, pumice are examples of extrusive igneous rocks
2. Intrusive igneous rocks: These rocks are formed when magma cools slowly inside the Earth. These rocks are coarse-grained as they have enough time to form granules or crystal. Diorite, Granite, Pegmatite are examples of intrusive igneous rocks
179
Examples of Intrusive Igneous rocks
Diorite, Granite, Pegmatite
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What are the types of igneous rocks based on their Textures
1. Aphanitic: fine-grained, less than 1mm, grains not seen with the unaided eye (invisible)
2. Phaneritic: “coarse-grained”; visible crystals; 1 to 10mm
3. Pegmatitc: “very coarse-grained”> 1cm
4. Porphyritic: composed of both large and fine-grained crystals, and the large crystals are called phenocrysts, and the background is the matrix
5. Vesicular: rocks that have vesicles, resembling a sponge (e.g. scoria and pumice)
6. Pyroclastic: fragmented, angular grains ejected during the eruption (e.g volcanic breccia)
7. Glassy: when lava cools quickly, there is not enough time for large mineral crystals to form (e.g obsidian)
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Based on Silica content, igneous rocks are divided into two types
Acidic: They have high silica content (60-80%). They constitute the ‘sial’ part of the earth’s crust. This means it contains Aluminium. They lack iron and magnesium. They are hard rocks and hence less prone to erosion. Examples: Granite (sial)
Basic: They have low silica content (45-60%). These rocks are dark in colour as they contain more iron and magnesium. It can be easily eroded. Eg: Basalt
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Characteristics of Igneous Rocks
1. The igneous form of rocks does not include any fossil deposit
2. Most of the igneous forms include more than one mineral deposit
3. They can be either glassy or coarse in appearance
4. These usually do not react with acids
5. They do not have strata (layers) like sedimentary rocks
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What is Lithification?
Fragments are transported by different exogenous agencies and deposited. With time, more layers pile up and presses down the lower layers. These layers through compaction turn into rocks.
184
Examples of sedimentary rocks
Limestone, chalk, clay, sandstone, shale
185
______________ also include rocks made from newly formed organic matter, both plant biomass and invertebrates
Sedimentary rocks
186
___________ % of the surface area of Earth is covered by sedimentary rocks
75
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Cross-bedded
the sedimentary structures known as cross-bedding are the (near) horizontal units that are internally composed of inclined layers
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Characteristic of Sedimentary Rocks
1. It is believed that around 75% of the surface area of Earth is covered by sedimentary rocks.
2. In several sedimentary rocks, the layers of deposits maintain their characteristics even after lithification.
3. They have layered structure and are also called stratified rocks.
4. The rocks may be coarse or fine-grained, soft or hard.
5. Cross-bedded: the sedimentary structures known as cross-bedding are the (near) horizontal units that are internally composed of inclined layers
6. They have high porosity and permeability
7. They are relatively poor in metallic minerals
8. They often contain fossil fuels.
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What are the types of sedimentary rocks
1. Clastic
2. Chemically precipitated
3. Organic
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Mechanically formed sedimentary rocks are called
Clastic sedimentary rocks
191
Examples of Clastic rocks
Sandstone, Conglomerate, Limestone, Shale, Loess
192
Examples of Clastic rocks
Sandstone, Conglomerate, Limestone, Shale, Loess
193
Examples of Organically formed sedimentary rocks
Porous Sandstone
Geyserite, Chalk, Limestone, Coal, etc
194
Chemically formed sedimentary stones eg:
These rocks are precipitated chemically from solutions of one kind or another. For example they are formed when inorganic mineral compounds precipitate from a salt water solution from sea or salty inland lakes.
195
Eg of Chemically formed sedimentary rock
Chert, Limestone, halite, Gypsum, Potash, Nitrates
196
The word Metamorphic means
Change of form
197
What is Metamorphism
It is a process by which rocks undergo recrystallisation and reorganisation of material within original rock
198
What are the examples of metamorphic rocks
Extreme head and pressure transform shale into slate or schist,
Sandstone into Quartzite
Limestone into Marble
Igneous rocks or clastic sediments into gneiss
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Formation of metamorphic rocks
1. These rocks form under the action of pressure, volume and temperature changes
2. During metamorphism, rocks(sedimentary, igneous, metamorphic) are forced down to lower levels by tectonic process or when molten magma rising through the crust comes in contact with the crustal rocks or the underlying rocks are subjected to great amounts of pressure from overlying rocks
3. Metamorphism is a process by which rocks undergo recrystallisation and reorganisation of materials within original rocks
4. For example, extreme heat and pressure transform shale into slate or schist, sandstone into quartzite, limestone into marble, and igneous rocks are clastic sediments into gneiss
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What are the Types of Metamorphism
**1. Dynamic Metamorphism**
it is mechanical disruption and reorganisation of the original minerals within rocks due to breaking and crushing without any appreciable chemical changes
**2. Thermal Metamorphism**
The Materials of rocks chemically alter and recrystallise due to thermal metamorphism.
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What are the two types of thermal Metamorphism
**Contact Metamorphism**
When the rocks come in contact with hot intruding magma and lava and then rock materials recrystallise under high temperatures.
**Regional Metamorphism**
The rocks experience recrystallisation due to deformation caused by tectonic shearing together with high temperature or pressure or both
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Characteristics of Metamorphic rocks
1. **Foliation or Lineation**: During metamorphism in some rocks grains or minerals get arranged in layers or lines. Such an arrangement of minerals or grains in metamorphic rocks is known as Foliation or Lineation
2. **Banding**: when minerals or materials of different groups are arranged into alternating thin to thick layers appearing in light and dark shades. Such a structure in metamorphic rocks is known as banding and rocks displaying banding are called banded rocks.
3. Metamorphic rocks tend to the more resistant to weathering than their parent rocks because the heat and pressure welds their mineral grains together and may transform their minerals into stronger forms.
4. metamorphic rocks may be pervious or impervious.
5. Metamorphic rocks are classified into two major groups —foliated rocks eg. Slates, gneiss, schists etc. and non foliated rocks eg: Quartzites, marbles, serpentines etc
6. During metamorphism, fossils are destroyed and hence they do not contain fossil fuels
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_____________ is a science that studies landforms on the Eath’s surface and involves interpretive description of landforms, their origins, development and processes associated with them
Geomorphology
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Rills develop over time to form
Gully
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The characteristics of each of the stages of landscape developing in running water regimes may be summarised as follows
**Youth**
1. Few streams with poor integration and glow over original slopes
2. Shallow V-shaped valleys with no floodplains or with very narrow floodplains along trunk streams
3. Streams divides are broad and flat with marshes, swamp and lakes.
4. Meanders are usually not there and if present develop over these broad upland surfaces. These meanders may eventually entrench themselves into the uplands.
5. Waterfalls and rapids may exist where local hard rock bodies are exposed
**Mature**
1. Streams are plenty with good integration
2. The valleys are still V-shaped but deep
3. The flat and broad inter stream areas and swamps and marshes of youth disappear and the stream divides turn sharp
4. Waterfalls and rapids disappear.
**Old**
1. Smaller tributaries during old age are few with gentle gradients
2. Streams meander freely over vast floodplains showing natural levees, oxbow, lakes etc
3. Divides are broad and flat with lakes, swamps and marshes.
4. Most of the landscape is at or slightly above sea level.
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What are the different types of valleys?
V-shaped valley, gorge, Canyon etc
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Valleys depend upon the _______ and __________ of the rocks in which they form
Type
Structure
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Gorge VS Canyon
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Plunge Pools
1. Once a depression (or pothole) forms, it receives pebbles and boulders which were rotated by flowing water continuously and consequently the depressions grow in dimensions. These depressions may join to become larger depression and the valley gets deepened.
2. At the foot of waterfalls also, large, deep and wide potholes from because of the sheer impact of water and rotation of boulders. Such large and deep holes at the base of waterfalls are called plunge pools.
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Incised or Entrenched Meanders
1. Lateral erosion is more fervent on gentle slopes. Due to the lateral erosion, streams develop sinuous or meandering courses. This is why we find meandering courses over floodplains and delta plains where stream gradients are very gentle.
2. But very deep and wide meanders can also be found cut in hard rocks. Such meanders are called incised or entrenched meanders.
3. Where rapid uplift causes meandering rivers to cut deeply into bedrock, entrenched meanders are formed.
4. We don’t find meanders in streams that flow rapidly over steep gradients as normally erosion in concentrated on the bottom of the stream channel. Also steep gradient streams do more vertical erosion than lateral erosion
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River Terrance
1. River terraces are basically products of erosion as they result due to vertical erosion by the stream into its own depositional floodplain.
2. As a river lowers its bed, it can leave behind parts of its floodplains at a higher level as a series of alluvial terrances. They may be formed/found as with time the level of water might have decreased or sedimentation or upliftment of a rock mass. This is why they mark old valley floors or floodplain levels.
3. There can be a number of such terraces at different heights indicating former river bed levels.
4. **Paired terrances**: The river terraces on either side of the rivers occur at the same elevation they are called paired terraces.
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Types of Erosional Landforms
1. Valleys
2. Potholes and Plunge Pools
3. Incised or Entrenched Meanders
4. River Terraces
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The River terraces on either side of the rivers occur at the same elevation they are called
Paired Terraces
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Depositional Landforms
1. Alluvial Fans
2. Deltas
3. Floodplains
4. Natural Levees
5. Point Bars
6. Meanders
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Alluvial Fans
1. Alluvial fans are formed when streams flowing from higher levels break into foot slope plains of low gradient.
2. When streams flow over mountain slopes, they do more vertical erosion and hence carry very coarse load. this load is too heavy for the streams to carry over gentler gradients and gets dumped and spread as a broad low to high cone-shaped deposit called alluvial fan.
3. The streams flowing on these fans may distribute forming many channels called distributaries.
4. Alluvial fans in humid areas show normally low cones with gentle slopes from head to toe and they appear as high cones with steep slopes in arid and semi-arid climates
5. A pediment is a gently sloping erosion surface or plain of low relief formed by running water in arid or seminaries region at the base of a receding mountain front
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Deltas
1. When the river reaches its old stage ie, it is about to enter a later or sea or ocean, its load carrying capacity decreases.
2. The load carried by it is dumped and spread near the sea. If this load is not carried away far into the sea or distributed along the coast, it spreads and accumulates as a low cone.
3. This is why Deltas are often like alluvial fans but develop at a different location. But unlike alluvial fans, the deposits making up deltas are very well sorted with clear stratification.
4. The coarsest (heavy) materials settle out first and the finer (light) fractions like silts and clays are carried out into the sea
5. As the delta grows, the river distributaries continue to increase in length and delta continues to build up into the sea.
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Floodplains
1. Floodplain is a major landform of river deposition
2. Large sized materials are deposited first when the stream channel breaks into a gentle slope. Thus, normally, fine sized materials like sand, silt and clay are carried by relatively slow moving waters in gentler channels usually found in the plains and deposited over the bed and when the waters spill over the banks during flooding above the bed
3. A river bed made of river deposits is the active floodplain. The floodplain above the bank is an inactive floodplain
4. Inactive floodplain above the banks basically contain two types of deposits - flood deposits and channel deposits
5. In plains, channels shift laterally and change their courses occasionally leaving cut-off courses which get filled up gradually. Such areas over flood plains build up by abandoned or cut-off channels contain coarse deposits.
6. The flood deposits of spilled waters carry relatively finer materials like silt and clay. The floodplains in a delta are called delta plains.
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Natural Levees
1. Natural levees and point bars are some of the important landforms found associated with floodplains.
2. Natural levees are found along the banks of large rivers when the velocity of the water flowing away from the bank and across the floodplain decrease, the sediment begins to settle out. Sand and silt accumulate first, building up natural levees along the channel.
3. Levees are low, linear and parallel ridges of coarse deposits along the banks of rivers, quite often cut into individual mounds.
4. Farther away, fine sediment settles out of the nearly stagnant water, accumulating between the levees and the bluffs that bound the floodplain- an area known as the back swamp.
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Point Bars
1. Point bars are also known as meander bars
2. Theta re found on the concave side of meanders of large rivers and are sediments deposited in a linear fashion by flowing waters along the bank
3. They are almost uniform in profile and in width and contain mixed sizes of sediments.
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Meanders
1. Meander is not a landform but is only a type of channel pattern.
2. In large flood and delta plains, rivers, rarely flow in straight courses. Loop-like channel patterns called meanders develop over flood and delta plains
3. This happens because of various reasons.
(I) Propensity of water flowing over very gentle gradients to work laterally on the banks
(II) Unconsolidated nature of alluvial deposits making up the banks with many irregularities which can be used by water exerting pressure laterally
(III)Coriolis force acting on the fluid water deflecting it like it deflects the wind.
4. When the gradient of the channel becomes extremely low, water flows leisurely and starts working laterally. Slight irregularities along the banks slowly get transformed into a small curvature in the banks; the curvature deepens due to deposition on the inside of the curve and erosion along the bank on the outside.
5. If there is no deposition and no erosion or undercutting, the tendency to meander is reduced
6. Normally, in meanders of large rivers, there is active deposition along the concave bank and undercutting along the convex bank. The concave bank is known as cut-off bank which shows up as a steep scarp and the convex bank presents a long, gentle profile.
7. As meanders grow into deep loops, the same may get cut-off due to erosion at the inflection points and are left as ox-bow lakes.
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Karst Topography
The two process of solution and precipitation are active in limestone or dolomites regions, occurring either exclusively or inter bedded with other rocks. Any limestone or dolomite region showing typical landforms produced by the action of groundwater through the process of solution and deposition is called **Karst topography**, named after the typical topography developed in limestone rocks of Karst region in the **Balkans adjacent to Adriatic Sea**. The karst topography is also characterised by Erosional and depositional landforms.
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Small to medium sized round to sub-rounded shallow depression called ______________ form on the surface of limestones through solution
Swallow Holes
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Sinkholes
are very common in limestone/karst areas. It is an opening more or less circular at the top and funnel-shaped towards the bottom with sizes varying in areas from a few Sq.m to a hectare and with depth from a less than half a metre to thirty meters or more.
Some sinkholes form solely through solution action (solution sinks) and others might start as solution forms first and if the bottom of a sinkhole forms the roof of a void or cave underground, it might collapse leaving a large hole opening into a cave or a void below (collapse sinks).
Quite often, sinkholes are covered up with soil mantle and appear as shallow water pools. Anybody stepping over such pools would go down like it happens in quicksands in deserts.
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The term ___________is sometimes used to refer the collapse sinks. ___________ sinks are more common than collapse sinks.
Doline
Solution
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Quite often the surface runoff simply goes down swallow and sink holes and glow as underground streams and reemerge at a distance downstream through a cave opening. When sink holes and dolines join together because of slumping of materials along their margins or due to roof collapse of caves, long, narrow to wide trenches called _______________
Valley sinks or Uvalas form
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Caves
In areas where there are alternating beds of rocks (shales, sandstone, quartzites) with limestones or dolomites in between or in areas where limestones are dense, massive and occurring as thick beds, cave formation is prominent.
Water percolates down either through the materials or through cracks and joints and moves horizontally along bedding planes. It is along these bedding planes that the limestone dissolves and long and narrow to wide gaps called caves result.
Caves normally have an opening through which cave streams are discharged. Caves having openings at both the ends are called **Tunnels**
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Many depositional form develop within the
Limestone caves.
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The chief chemical in limestone is _________ which is easily soluble in ________
Calcium carbonate
Carbonated water (carbon dioxide absorbed in rainwater)
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Stalactites, Stalagmites and Pillars
Stalactites hang as icicles of different diameters. Normally they are broad at their bases and taper towards the free ends showing up in a variety of forms.
Stalagmites rise up from the floor of the caves. In fact, stalagmites form due to dripping water from the surface or through the thin pipe, of the stalactite, immediately below it. Stalagmites may take the shape of a column, a disc, with either a smooth, rounded bulging end or a miniature crater like depression.
The stalagmite and stalactites eventually fuse to give rise to columns and pillars of different diameters.
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Depositional Landforms
Many depositional forms develop within the limestone caves. The chief chemical in limestone is calcium carbonate which is easily soluble in carbonated water (carbon dioxide absorbed rainwater). This Calcium carbonate is deposited when the water carrying it in solution evaporates or loses its carbon dioxide as it trickles over rough rock surfaces
**Stalactites, Stalagmites and Pillars**
Stalactites hang as icicles of different diameters. Normally they are broad at their bases and taper towards the free ends showing up in a variety of forms.
Stalagmites rise up from the floor of the caves. In fact, stalagmites form due to dripping water from the surface or through the thin pipe, of the stalactite, immediately below it. Stalagmites may take the shape of a column, a disc, with either a smooth, rounded bulging end or a miniature crater like depression.
The stalagmite and stalactites eventually fuse to give rise to columns and pillars of different diameters.
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Glaciers
Masses of ice moving as sheet over the land (continental glacier or piedmont glacier if a vast sheet of ice is spread over the plains at the foot of mountains) or as linear flows down the slopes of mountains in broad trough-like valleys (mountain and valley glaciers) are called glaciers.
1. The movement of glaciers is slow unlike water flow. The movement could be a few centimetres to a few meters a day or even less or more. Glaciers move basically because of the force of gravity.
2. Erosion by glaciers is tremendous because of friction caused by sheer weight of the ice. The material plucked from the land by glaciers (usually large-sized angular blocks and fragments) get dragged along the floors or sides of the valleys and cause great damage through abrasion and plucking/
3. Glaciers can cause significant damage to even unweathered rocks and can reduce high mountains into low hills and plains. As glaciers continue to move, debris gets removed, divides get lowered and eventually the slope is reduced to such an extent that glaciers will stop moving leaving only a mass of low hills and vast outwash plains along with other depositional features.
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Types of Erosional Landforms
1. Cirque
2. Horns and Serrated Ridges
3. Glacial Valleys/Troughs
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Cirque
1. Cirques are the most common of landforms in glaciated mountains
2. The cirques quiet often are found at the heads of glacial valleys.
3. The accumulated ice cuts these cirques while moving down the mountain tops.
4. Cirque are deep, long and wide troughs or basins with very steep concave to vertically dropping high walls at its head as well as sides.
5. A like of water can be seen quite often within the cirques after the glacier disappears. Such lakes are called **cirque or tarn lakes**
6. There can be two or more cirques one leading into another down below in a stepped sequence.
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Horns and Serrated Ridges
1. Horns form through head-ward erosion of the cirque walls.
2. If three or more radiating glaciers cut headward until their cirques meet, high, sharp pointed and steep sided peaks called horns form.
3. The divides between cirque sidewalls or head walls get narrow because of progressive erosion and turn into serrated or saw-toothed ridges sometimes referred to as *aretes* with very sharp crest and a zig-zag outline.
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Glacial Valleys/Troughs
1. Glaciated valleys are trough-like and U-shaped with broad floors and relatively smooth, and steep sides.
2. The valleys may contain littered debris or debris shaped as moraines with swampy appearance. There may be lakes gouged out of rocky floor or formed by debris within the valleys.
3. There can be hanging valleys at an elevation on one or both sides of the main glacial valley. The faces of divides or spurs of such hanging valleys opening into main glacial valleys are quite often truncated to give them an appearance like triangular facets.
4. Very deep glacial trough filled with sea water and making up shorelines (in high latitudes) are called **fjords/fiords**.
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Types of depositional landforms
1. Moraines
2. Eskers
3. Outwash Plains
4. Drumlins
237
The unassisted coarse and fine debris dropped by the melting glaciers is called
Glacial till
238
Outwash deposits
Streams form by melting ice at the bottom, sides or lower ends of glaciers. Some amount of rock debris small enough to be carried by such meltwater streams is washed down and deposited. Such glacial-fluvial deposits are called outwash deposits
239
Depositional Landforms
1. The unassisted coarse and fine debris dropped by the melting glaciers is called **glacial till**. Most of the rock fragments in till are angular to sub-angular in form.
2. Streams form by melting ice at the bottom, sides or lower ends of glaciers. Some amount of rock debris small enough to be carried by such meltwater streams is washed down and deposited. Such glacial-fluvial deposits are called outwash deposits.
3. Unlike till deposits, the outwash deposits are roughly stratified and assorted. The rock fragments in outwash deposits are somewhat rounded at their edges.
240
Moraines
1. They are long ridges of deposits of glacial till
2. **Teminal moraines** are long ridges of debris deposited at the end (toe) of the glacier.
3. **Lateral moraines** form along the sides parallel to the glacial valleys.
4. The lateral moraines may join a terminal moraine forming a horse-shoe shaped ridge.
5. There can be many lateral moraines on either side in a glacial valley. These moraines partly or fully owe their origin to glacio-fluvial waters pushing up materials to the sides of glaciers.
6. Many valley glaciers retreating rapidly leave an irregular sheet of till over their valley floors. Such deposits varying greatly in thickness and in surface topography are called ground moraines.
7. The moraine in the centre of the glacial valley flanked by lateral moraines is called medial moraine. They are imperfectly formed as compared to lateral moraines. Sometimes medial moraines are indistinguishable from ground moraines.
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Eskers
When glacier smelt in summer, the water flows on the surface of the ice or seeps down along the margins or even moves through holes in the ice. These waters accumulate beneath the glacier and flow like streams in a channel beneath the ice.
Such streams flow over the ground (not in a valley cut in the ground) with ice forming its banks. Very coarse materials like boulders and blocks along with some minor fractions of rock debris carried into this stream settle in the valley of ice beneath the glacier and after the ice melts can be found as a sinuous ridge called esker.
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Outwash Plains
The plains at the foot of the glacial mountains or beyond the limits of continental ice sheets are covered with glaciers-fluvial deposits in the form of broad flat alluvial fans which may join to form outwash plains of gravel, silt, sand and clay
243
Drumlins
1. Drumlins are smooth oval shaped ridge-like features composed mainly of glacial till with some masses of gravel and sand
2. The long axes of drumlins are parallel to the direction of ice movement. Drumlins give an indication of direction of glacier movement.
3. They may measure up to 1 km in length and 30m or so in height.
4. One end of the drumlins facing the glacier called the stops end is blunter and steeper then the other end called tail.
5. The drumlins form due to dumping of rock debris beneath heavily loaded ice through fissures in the glacier.
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Landforms created by Waves and Currents
Some of the changes along the coasts take place very fast. At one place, there can be erosion in one season and deposition in another. Most of the changes along the coasts are accomplished by waves. Constant impact of breaking waves drastically affects the coasts. Storm waves and tsunami waves can cause far-reaching changes in a short period of time than normal breaking waves. As the wave environmental changes, the intensity of the force of breaking waves changes.
Other than the action of waves, the coastal landforms depend upon
A. The configuration of land and sea floor
B. Whether the cost is advancing (emerging) seaward or retreating (submerging) landward.
Assuming sea level to be constant, two types of coasts are considered to explain the concept of evolution of coastal landforms:
A. High, rocky coasts (submerged coasts)
B. Low smooth and gentle sloping sedimentary coasts (emerged coasts)
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High Rocky Coast
Along the high rocky coasts, rivers appear to have been drowned with highly irregular coastline. The hillsides drop off sharply into the water. Shores do not show any depositional landforms initially. Erosion features dominate.
246
Cliffs
Along high rocky coast, waves break with great force against the land shaping the hill sides into cliffs
247
Wave-cut terrace
With constant pounding by waves, the cliffs recede leaving a wave-cut platform in front of the sea cliff. Waves gradually minimise the irregularities along the shore. The material which fall off, and removed from the sea cliffs, gradually break into smaller fragments and roll to roundness, will get deposited offshore. After as considerable period of cliff development and retreat when coastline turns somewhat smooth, with the addition of some more material to this, a wave-built terrace would develop in front of wave-cut terrace.
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Bars and barrier bars
As the erosion along the coast takes place a good supply material becomes available to long shore currents and waves to deposit them as beaches along the shore and as bars (long ridges of sand and / or shingle parallel to the coast) in the nearshore zone. Bars are submerged features and when bars show up above water, they are called barrier bars. Barrier bar which get keyed up to the headland of a bay is called a spit.
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Lagoon
When barrier bars and spits form at the mouth of a bay and block it, a lagoon forms. The lagoons would gradually get filled up by sediments from the land giving rise to a coastal plain.
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Low sedimentary coasts
1. Along low sedimentary coasts the rivers appear to extend their length by building coastal plains and deltas. The coastline appears smooth with occasional incursions of water in the form of lagoons and tidal creeks. The land slopes gently into the water.
2. Marshes and swamps may abound along the coast.
3. Depositional features dominate. When waves break over a gently sloping sedimentary cost, the bottom sediments get churned and move readily building bars, barrier bars, spits and lagoons. lagoons would eventually turn into a swamp which would subsequently turn into a coastal plain.
4. The maintenance of these depositional features depends upon the steady supply of materials. Storm and tsunami waves cause drastic changes irrespective of supply of sediments.
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Erosional Landforms
1. Cliffs, Terraces, Caves and Stacks
2. Wave-cut cliffs and terrace are two forums usually found where erosion is the dominant shore process.
3. Almost all sea cliffs are steep and may range from a few m to 30m or even more.
4. At the foot of such cliffs there may, be a flat or gently sloping platform covered by rock debris derived from the sea cliff behind. Such platforms occurring at elevations above the average height of waves is called a wave cut Terrance.
5. The lashing of waves against the base of the cliff and the rocks debris that gets smashed against the cliff along with lashing waves create hollows and these hollows get widened and deepened to form sea caves. The roofs of caves collapse and the sea cliffs recede further in land.
6. Retreat of the cliff Amy leave some remnants of rock standing isolated as small islands just off the shore. such resistant masses of rock, originally parts of a cliff or hill are called sea stacks.
7. Like all other features, sea stacks are also temporary and eventually coastal hills and cliffs will disappear because of wave erosion giving rise to narrow coastal plains, and with onrush of deposits from over the land behind may get covered up by alluvium or may get covered by by shingle or sand to form a wide beach.
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Landforms Created by Waves and Currents: Depositional Landforms
1. Beaches
2. Dunes
3. Bars
4. Barriers
5. Spits
6. Lagoons
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Beaches
1. These are characteristic of shorelines that are dominated by deposition, but may occur as patches along even the rugged shores.
2. Most of the beaches are made up of sand sized materials and these sand sized materials making up the beaches comes from land carried by the streams and rivers or from wave erosion.
3. Beaches are temporary features
4. **Shingle beaches** : Beaches which contain excessively small pebbles and cobbles.
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Dunes
Just behind the beach, the sands lifted and winnowed from over the beach surfaces will be deposited as sand dunes. Sand dunes forming long ridges parallel to the coastline are very common along low sedimentary coasts.
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Bars
A ridge of sand and shingle formed in the sea in the off-shore zone (from the position of low tide waterline to seaward) lying approximately parallel to the coast is called an off-shore bar.
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Barriers
An off-shore bar which is exposed due to further addition of sand is termed a barrier bar. The off-shore bars and barriers commonly form across the mouth of a river or at the entrance of a bay
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Spits
Sometimes such barriers bars get keyed up to one end of the bay when they are called spits. Spits may also develop attached to headlands/hills
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Lagoons
The barriers, bars and spits at the mouth of the bay gradually extend leaving only a small opening of the bay into the sea and the bay will eventually develop into a lagoon. The lagoons get filled up gradually by sediment coming front he land or from the beach itself (aided by wind) and a broad and wide coasted plain may develop replacing a lagoon.
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Erosional Landforms
1. Pediments and Pediplains
2. Playas
3. Deflation Hollows and Caves
4. Mushroom, Table and Pedestal Rocks
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Pediments and Pediplains
1. Landscape evolution in deserts is primarily concerned with the formation and extension of pediments.
2. Gently inclined rocky floor close to the mountains at their foot with or without a thin cover of debris, are called pediments.
3. Such rocky floors form through the erosion of mountain front through a combination of lateral erosion by streams and sheet flooding. Erosion starts along the steep margins of the landmass or the steep sides of th tectonically controlled steep incision features over the landmass.
4. Once, pediments are formed with a steep wash slope followed by a cliff or free face above it, the steep wash slope and free face retreat backwards. This method of erosion is termed as parallel retreat of slopes through backwasting.
5. So, through parallel retreat of slopes, the pediments extend backwards at the expense of mountain front, and gradually, the mountain gets reduced leaving an inset erg which is a remnant of the mountain. That’s how the high relief in desert areas is reduced to low featureless plains called *pediplains*.
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Playas
1. Plains are by far the most prominent landforms in the desert. In deserts, the drainage is towards the centre of the basin and due to gradual deposition of sediment from the basin margins, a nearly level plain forms at the centre of the basin.
2. In times of sufficient water, this plain is covered up by a shallow water body. Such types of shallow lakes are called playas where water is retained only for short duration due to evaporation and quite often the playas contain good deposition of salts. The playa plain covered up by salts is called alkali flats.
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Deflation Hollows and Caves
1. Deflation hollows are shallow depressions created by weathered mantle from over the rocks or bare soil, gets blown out by persistent wind movement in one direction.
2. Deflation also creates numerous small pits or cavities over rock surfaces. The rock faces suffer impact and abrasion of wind-borne sand and first shallow depressions called **blow outs** are created, and some of the blow outs become deeper and wider fit to be called **caves**.
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Mushroom, Table and Pedestal Rocks
Many rock-outcrops in deserts easily susceptible to wind deflation and abrasion are worn out quickly leaving some remnants of resistant rocks polished beautifully in the shape of mushroom with a slender stalk and a broad and rounded pear shaped cap above. Sometimes, the top surface is broad like a table top and quite often, the remnants stand out like pedestals.
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Sand Dunes
Dry hot deserts are good places for sand dune formation. Obstacles to initiate dune formation are equally important.
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Varieties of dunes
1. Crescent shaped dunes called **barchans** with the points or wings directed away from wind direction I.e downwind, form where the wind direction is constant and moderate and where the original surface over which sand is moving is almost uniform.
2. **Parabolic dunes** form when sandy surfaces are partially covered with vegetation. That means parabolic dunes are reversed barchans with wind direction being the same.
3. **Seif** is similar to barchans with a small difference. Seif has only one wing or point. This happens when there is shift in wind conditions. The lone wings of serifs can grow very long and high.
4. **Longitudinal dunes** form when supply of sand is poor and wind direction is constant. They appear as long ridges of considerable length but low in height
5. **Transverse dunes** are aligned perpendicular to wind direction. These dunes form when the wind direction is constant and the source of sand is an elongated feature at right angles to the wind direction. Thy may be very long and low in height.
6. When sand is plenty, quite often, the regular shaped dunes coalesce and lose their individual characteristics. Most of the dunes in the deserts shift and a few of them will get stabilised especially near human habitations.
