Physical Geography Flashcards
Inaugurator of geography/coining of term
Eratosthenes
Shape of earth
Geoid- spherical but flattened at poles
Geographical Information system (GIS)
Collects and manipulates data to create maps
Global Navigation Satellite System (GNSS)
To find out the exact location of something on the earth. Also called GPS (USA), GLONASS (Russia), IRNSS (India) etc.
Theories of the origin of planets/ earth
Nebular hypothesis by Laplace and Immanuel Kant- from cloud of rotating material
Chamberlain and Moulton considered that a wandering star approached the sun. As a result, a cigar-shaped extension of material was separated from the solar surface. As the passing star moved away, the material separated from the solar surface continued to revolve around the sun and it slowly condensed into planets
Accretion theory- Schmidt and Weizascar- nebula of hydrogen helium spun and collapsed on itself due to gravity, forming disc shaped cloud and clumps and bunching- heavier stuff stuck together (rocky planets), lighter flew away (gas giants).
Origin of the universe theory
Big Bang theory/expanding universe hypothesis by Lemaitre and Hubble- 13.75 billion years ago rapid expansion in a millisecond from a single atom of small volume, infinite temperature and infinite density, it exploded, some energy converted to matter, Within 300,000 years from the Big Bang, temperature dropped to 4,500 K (Kelvin) and gave rise to atomic matter. The universe became transparent.
Hoyle’s concept of steady state. It considered the universe to be roughly always the same.
Formation of stars
Nebula (cloud of matter) develops localised clumps of gas. These clumps continue to grow into even denser gaseous bodies, giving rise to formation of stars.
Earth age
4.6 billion years
Evolution of lithosphere of the earth
Separation of material into different layers depending upon density. Heavy sank to centre, lighter floated upwards. With time, cooling, solidification and condensation into crust. Moon collision further shook things up before settling again. Differentiation.
Evolution of Atmosphere of the earth
The first stage is marked by the loss of the primordial atmosphere of hydrogen and helium due to solar winds. In the second stage, the interior of the earth released gases (nitrogen, carbon dioxide, methane, ammonia and very little free oxygen) The process through which the gases were outpoured from the interior is called degassing and water vapour condensed contributed to the evolution of the atmosphere. Finally, the composition of the atmosphere was modified by the living world through the process of photosynthesis.
Evolution of Hydrosphere of the earth
Degassing (through volcanic eruptions) contributed water vapour and gases to the atmosphere. As the earth cooled, the water vapour released started getting condensed. The carbon dioxide in the atmosphere got dissolved in rainwater and the temperature further decreased causing more condensation and more rains. The rainwater falling onto the surface got collected in the depressions to give rise to oceans. The earth’s oceans were formed within 500 million years from the formation of the earth. Sometime around 3.8 billion years ago, life began to evolve. However, around 2.5 billion years before the present, the process of photosynthesis evolved. Oceans began to have the contribution of oxygen through the process of photosynthesis. Eventually, oceans were saturated with oxygen, and 2 billion years ago, oxygen began to flood the atmosphere.
Inner and outer planets
mercury, venus, earth and mars are called as the inner planets as they lie between the sun and the belt of asteroids the other four planets are called the outer planets.
Jovian planets
The outer four are called Jovian or Gas Giant planets. Jovian means jupiter -like.
Difference between terrestrial and jovian planets
(i) The terrestrial planets were formed in the close vicinity of the parent star where it was too warm for gases to condense to solid particles. Jovian planets were formed at quite a distant location.
(ii) The solar wind was most intense nearer the sun; so, it blew off lots of gas and dust from the terrestrial planets. The solar winds were not all that intense to cause similar removal of gases from the Jovian planets.
(iii) The terrestrial planets are smaller and their lower gravity could not hold the escaping gases.
Moon formation
Sir George Darwin suggested that initially, the earth and the moon formed a single rapidly rotating dumbbell shaped body, and it broke off. Now believed that outcome of ‘giant impact’ or “the big splat”. A body of the size of one to three times that of mars collided into the earth, blasted a large part into space which eventually formed into the present moon about 4.44 billion years ago.
Evolution of life on earth
Modern scientists refer to the origin of life as a kind of chemical reaction, which first generated complex organic molecules and assembled them. This assemblage was such that they could duplicate themselves converting inanimate matter into living substance sometime 3,800 million years ago.
Formation of planets
Nebula becomes star by bunching and clumping. The gas cloud starts getting condensed and the matter around the core develops into small- rounded objects by the process of cohesion and collision develop into planetesimals. Large number of small planetesimals accrete to form a fewer large bodies in the form of planets.
Phases of the moon
Full Moon- Poornima- once a month, entire visible
New Moon- Amavasya- completely disappeared
Each occur a fortnight apart
Celestial bodies
Objects shining in the night sky
Stars
Made up of gasses, emit their own heat and light. Sun, and nearest to it is Proxima Centauri
Constellations
Patterns formed by stars
Pole Star
Aka north star, fixed position and indicates north
Planets
Celestial bodies that do not emit own heat and light
Planets in solar system number and name
8- Mercury venus earth mars jupiter saturn uranus neptune
Which planets have debris/ rings
jupiter saturn uranus
Light travel speed
300,000 km per second
Composition of solar system
Sun, 8 planets, asteroids and meteoroids
Discuss the sun
Hydrogen (70%), Helium (27%), remaining gasses (3%). Provides gravity that keeps solar system together.
Six main regions- Interior- 1.core where nuclear fusion (combo) occurs 2.radiative zone energy transported by photons i.e electromagnetic waves 3.convective zone- energy movement via fluids like gasses. Exterior- 4.photosphere- visible surface 5.chromosphere- giving reddish hue 6.corona-hotter than sun surface, transitions into solar wind
Discuss Mercury
Smallest, no satellite, second hottest
Discuss Venus
Earth’s twin, hottest planet, aka morning/evening star
Discuss Earth
1 orbit- 365 days, 1 rotation on axis- 1 day. Sunlight takes 8.2 minutes to reach
Discuss Mars
Similar landmass, reddish due to iron oxide, 2 moons
Discuss Jupiter
Largest gas giant, ring system, 79 moons
Discuss Saturn
Avg density less than water, rings, 82 moons
Discuss Uranus
Frigid, rings, 27 moons
Discuss Neptune
Coldest and windiest, 13 moons
Dwarf planets
Small celestial bodies that revolve around the sun. Pluto was demoted because it could not clear orbit of other debris. Other eg- Ceres
Satellite
Celestial bodies that revolve around planets, can be artificial also
Discuss Our Moon
27 days to rotate and revolve, thus only one face shows
Asteroids
Bodies that move around the sun, are found in the belt between mars and jupiter, aka minor planets.
Comets
Objects made of ice particles and gasses that move around the sun, have a distinctive tail. Found in Kuiper Belt- between Neptune to 50 AU from sun.
Meteoroids
Asteroids that have been removed from the belt, which sometimes enter earth atmosphere and burn
Axis
Imaginary line passing through the poles on which the earth spins
Equator
Imaginary line divind the earth into two parts- northern and southern hemisphere
Parallels of latitudes
All circles parallel to the equator upto the poles, measured in degrees
Important Parallels of latitudes
0 degree equator
North pole 90 degree N
South pole 90 degree S
Tropic of cancer 23 ½ degree N
Tropic of capricorn 23 ½ degree S
Arctic circle 66 ½ degree N
Antarctic circle 66 ½ degree S
Heat zones of the earth
Torrid- between Tropic of cancer 23 ½ degree N and Tropic of capricorn 23 ½ degree S
Temperate between-Tropic of cancer 23 ½ degree N-Arctic circle 66 ½ degree N and Tropic of capricorn 23 ½ degree S and Antarctic circle 66 ½ degree S
Frigid- North pole 90 degree N- Arctic circle 66 ½ degree N and South pole 90 degree S- Antarctic circle 66 ½ degree S
Longitudes
Imaginary perpendicular lines, measured in degrees minutes seconds-1 degree= 6 minutes. Prime meridian that divides earth into eastern and western hemispheres is at Greenwich observatory i.e. 0 degrees and the 180 degree longitudes E and W overlap and is the International date line.
IST
5:30 more than greenwich, longitude of 82 ½ degree N
Rotation
Spinning of earth on axis, determine day-night, tides, coriolis force, geoid bulge. Axis is tilted 66 ½ degrees from orbital plane and 23 ½ degrees perpendicular plane. 23 hours 56 minutes (earth day)
Revolution and orbit distances from sun
Movement of earth around sun in elliptical path- causes seasons, variations in day-night lengths, and variations in solar energy distribution. Avg 150 million km from sun which becomes Aphelion 152 mkm and Perihelion 147 mkm. 365 days 6 hours.
Summer solstice
21st June Sun directly overhead the tropic of cancer, max heat, and N pole 6 months of continuous daylight. Longest day and shortest night for N. Opposite in S hemisphere.
Winter Solstice
22nd December- Sun directly overhead the tropic of capricorn, max heat, and S pole 6 months of continuous daylight. Longest day and shortest night for S. Opposite in N hemisphere.
Equinox
Neither poles tilted towards sun, so whole earth experiences equal days and nights. 21st March Vernal, 23rd September Autumnal- rays of sun fall directly on equator.
What influences landscape development?
Endogenic processes happening inside the earth as well as exogenic processes happening outside.
Sources for the interior of the earth
Direct sources- mining, volcanic eruptions. Indirect sources- studying properties of matter, meteors, gravity, magnetic fields, seismic activity.
Discuss the gravitational force on earth
The gravitation force (g) is not the same at different latitudes on the surface. It is greater near the poles and less at the equator. This is because of the distance from the centre at the equator being greater than that at the poles. The gravity values also differ according to the mass of material. These readings differ from the expected values. Such a difference is called gravity anomaly. Gravity anomalies give us information about the distribution of mass of the material in the crust of the earth.
Earthquake
An earthquake is the shaking of the earth due to release of energy, which generates waves that travel in all directions.
Cause of earthquake
The release of energy occurs along a fault. A fault is a sharp break in the crustal rocks. Rocks along a fault tend to move in opposite directions. As the overlying rock strata press them, the friction locks them together. However, their tendency to move apart at some point of time overcomes the friction. As a result, the blocks get deformed and eventually, they slide past one another abruptly. This causes a release of energy, and the energy waves travel in all directions.
what is a fault?
sharp break in crustal rocks
Hypocentre/focus and epicentre of an earthquake
The point where the energy is released is called the focus of an earthquake, alternatively, it is called the hypocentre. The energy waves travelling in different directions reach the surface. The point on the surface, nearest to the focus, is called epicentre. It is the first one to experience the waves. It is a point directly above the focus.
Where do earthquakes take place?
All natural earthquakes take place in the lithosphere, the portion of depth up to 200 km from the surface of the earth.
What device measures earthquakes and what exactly does it do?
An instrument called ‘seismograph’ records the waves reaching the surface.
Types of earthquake waves
body waves and surface waves. Body waves are generated due to the release of energy at the focus and move in all directions travelling through the body of the earth. They are called P and S-waves. P-waves move faster and are the first to arrive at the surface. These are also called ‘primary waves’. The P-waves are similar to sound waves. They travel through gaseous, liquid and solid materials. S-waves arrive at the surface with some time lag. These are called secondary waves and can travel only through solid materials.
The body waves interact with the surface rocks and generate new set of waves called surface waves. These waves move along the surface. The surface waves are the last to report on a seismograph. These waves are more destructive.
Different names for P S and L waves
P- longitudinal
S- transverse
L- surface waves
Propagation of Earthquake Waves
The velocity of waves changes as they travel through materials with different densities. The denser the material, the higher is the velocity. P-waves vibrate parallel to the direction of the wave. This exerts pressure on the material in the direction of the propagation. As a result, it creates density differences in the material leading to stretching and squeezing of the material. Other three waves vibrate perpendicular to the direction of propagation. The direction of vibrations of S-waves is perpendicular to the wave direction in the vertical plane. Hence, they create troughs and crests in the material through which they pass.
Shadow Zone
Areas where earthquakes are not recorded on seismographs due to refraction and reflection as they pass through the Earth’s layers.. Such a zone is called the ‘shadow zone’. For S waves, anything beyond 105 degree from epicentre, while for P waves between 105 and 145 degrees from epicentre. Thus, S wave shadow zone larger (40% of earth’s surface)
Types of earthquakes
(i) tectonic earthquakes. These are generated due to sliding of rocks along a fault plane.
(ii) A special class of tectonic earthquake- volcanic earthquake. However, these are confined to areas of active volcanoes.
(iii) In the areas of intense mining activity, sometimes the roofs of underground mines collapse causing minor tremors. These are called collapse earthquakes.
(iv) Ground shaking may also occur due to the explosion of chemical or nuclear devices. Such tremors are called explosion earthquakes.
(v) The earthquakes that occur in the areas of large reservoirs are referred to as reservoir induced earthquakes.
Measuring earthquakes scales
The earthquake events are scaled either according to the magnitude or intensity of the shock. The magnitude scale is known as the Richter scale. The magnitude relates to the energy released during the quake. The magnitude is expressed in numbers, 0-10. The intensity scale is named after Mercalli, an Italian seismologist. The intensity scale takes into account the visible damage caused by the event. The range of intensity scale is from 1-12.
layers of the earth
Crust, mantle, core
Discuss the crust
It is the outermost solid part of the earth. It is brittle in nature. The thickness of the crust varies-oceanic crust is 5 km, continental 30 km, mountain systems 70 km.This type of rock found in the oceanic crust is basalt. The mean density of material in oceanic crust is 2.7 g/cm3. Continental made up of heavier rocks having density of 3 g/cm3.
What is the lithosphere?
The crust and the uppermost part of the mantle are called lithosphere. Its thickness ranges from 10-200 km.
Discuss the mantle
Between crust and core. The mantle extends from Moho’s discontinuity to a depth of 2,900 km. 1.The upper portion of the mantle is called asthenosphere. The word astheno means weak. It is considered to be extending upto 400 km. It is the main source of magma. Density- 3.4 g/cm3.
2.The lower mantle extends beyond the asthenosphere. It is in solid state.
Discuss the core
The outer core is in liquid state while the inner core is in solid state. The density of material at the mantle core boundary is around 5 g/cm3 and at the centre of the earth at 6,300 km, the density value is around 13g/cm3. The core is made up of very heavy material mostly composed of nickel and iron. It is sometimes referred to as the nife layer.
What is a volcano?
A volcano is a place where gases, ashes and/or molten rock material – lava – escape to the ground.
Magma lava difference and constituents
The material in the upper mantle portion is called magma. Once it starts moving towards the crust or it reaches the surface, it is referred to as lava. The material that reaches the ground includes lava flows, pyroclastic debris, volcanic bombs, ash and dust and gases such as nitrogen, sulphur compounds and minor amounts of chlorene, hydrogen and argon. N SHAC
Types of volcanoes
1.Shield Volcanoes- are the largest of all the volcanoes on the earth, are made up of basalt, a type of lava that is very fluid when erupted. For this reason, these volcanoes are not steep, but since comes out in a fountain fashion, formation of cinder cone. Usually low explosivity, but explosive when water gets into the vent. Eg. Hawaii
2.Composite Volcanoes- These volcanoes are characterised by eruptions of cooler and more viscous lavas than basalt. These volcanoes often result in explosive eruptions. Along with lava, large quantities of pyroclastic material and ashes find their way to the ground. This material accumulates in the vicinity of the vent openings leading to formation of layers, and this makes the mounts appear as composite volcanoes.
3.Caldera-most explosive of the earth’s volcanoes so much that when they erupt they tend to collapse on themselves rather than building any tall structure. The collapsed depressions are called calderas. Their explosiveness indicates that the magma chamber supplying the lava is not only huge but is also in close vicinity.
4.Flood Basalt Provinces- outpour highly fluid lava that flows for long distances. Eg The Deccan Traps from India, presently covering most of the Maharashtra plateau.
5.Mid-Ocean Ridge Volcanoes- These volcanoes occur in the oceanic areas, and experience frequent eruptions in the central region. There is a system of mid-ocean ridges more than 70,000 km long that stretches through all the ocean basins.
Volcanic landforms types
Lava cools into igneous rocks which are classified as volcanic rocks (cooling at the surface) and plutonic rocks (cooling in the crust, assumes intrusive forms).
Batholiths
Are the cooled portion of magma chambers, form granite domes.
Lacoliths
Domes with base level with a pipe-like structure. Resemble composite volcanoes, only are inside the crust. Eg Karnataka plateau.
Dykes
Lava solidifying perpendicular to ground, forming wall-like structure. Eg. Maharashtra
Lapolith
Lava flowing horizontally and assuming saucer or concave shapes.
Sills, sheets
Lava solidifying near perfectly horizontally. Thin called sheets, thick called sills.
Phacoliths
Lava assuming wavy shapes at the base of synclines or top of anticlines, with a source beneath (magma chamber)
Land-ocean ration on surface
29-71%
Contributors to continental drift theory
Abraham Ortelius, a Dutch map maker, who first proposed such a possibility. Antonio Pellegrini drew a map showing the three continents together. However, it was Alfred Wegener—a German meteorologist who put forth a comprehensive argument
Formation of present day continents theory
CONTINENTAL DRIFT- Alfred Wegener- all the continents formed a single continental mass and mega ocean surrounded the same. The super continent was named PANGAEA, which meant all earth. The mega-ocean was called PANTHALASSA, meaning all water. He argued that, around 200 million years ago Pangaea, began to split first into two large continental masses as Laurasia and Gondwanaland forming the northern and southern components respectively which continued to break into various smaller continents that exist today.
Evidence in favour of continental drift
1.jigsaw fit eg. Africa and South America
2.rocks of same age eg. Brazil rocks 2 billion years old match Africa. Marine deposits in both from jurassic age.
3.tillite- sedimentary rock formed via glaciers. Gondwana system of sediments found in africa, australia, madagascar, antarctica, falkland islands.
4.placer deposits-ghana gold deposits do not have source rocks but remarkably similar to Brazilian veins
5.fossil distribution- lemurs in India, Madagascar, Africa. Mesosaurus reptile in Southern Cape province of South Africa and Iraver formations of Brazil.
Forces causing continental drift
Wegner attributed the shift to tidal and pole-fleeing force due to rotation of earth, but contemporary scientists reject these forces. Arthur Holmes discussed the possibility of convection currents operating in the mantle portion.
Ocean floor configuration
the ocean floor may be segmented into three major divisions based on the depth as well as the forms of relief. These divisions are continental margins, deep-sea basins and mid-ocean ridges.
Continental Margins
These form the transition between continental shores and deep-sea basins. They include continental shelf, continental slope, continental rise and deep-oceanic trenches.
Abyssal Plains
These are extensive plains that lie between the continental margins and mid-oceanic ridges. They are the areas where the continental sediments that move beyond the margins get deposited.
Mid-Oceanic Ridges
This forms an interconnected chain of mountain system within the ocean. It is the longest mountain-chain on the surface of the earth. It is characterised by a central rift system at the crest, a fractionated plateau and flank zone all along its length. The rift system at the crest is the zone of intense volcanic activity.
Distribution of Earthquakes and Volcanoes around the globe
In general, the foci of the earthquake in the areas of mid-oceanic ridges are at shallow depths whereas along the Alpine-Himalayan belt as well as the rim of the Pacific, the earthquakes are deep-seated ones. The map of volcanoes also shows a similar pattern. The rim of the Pacific is also called rim of fire due to the existence of active volcanoes in this area.
Sea floor spreading
Hess’ hypothesis. Hess argued that constant eruptions at the crest of oceanic ridges cause the rupture of the oceanic crust and the new lava wedges into it, pushing the oceanic crust on either side. The ocean floor, thus spreads. 1.spreading of one ocean does not cause the shrinking of the other 2.ocean floor that gets pushed due to volcanic eruptions at the crest, sinks down at the oceanic trenches and gets consumed.
Evidence for seafloor spreading
1.along the mid- oceanic ridges, volcanic eruptions are common and they bring huge amounts of lava to the surface in this area.
2.The rocks equidistant on either sides of the crest of mid-oceanic ridges show remarkable similarities in terms of period of formation, chemical compositions and magnetic properties.
3.The ocean crust rocks are much younger than the continental rocks. 200 million v/s 3200 million
4. sediments on the ocean floor are unexpectedly very thin.
5.deep trenches have deep-seated earthquake occurrences while in the mid- oceanic ridge areas, the quake foci have shallow depths.
Plate tectonics
McKenzie, Parker, Morgan-Lithosphere composed of several tectonic plates (continental/oceanic depending on location) which move horizontally. Thus, plates move, not continents.
Major minor plates
7 major and several minor plates- I Antarctica and the surrounding oceanic plate
II North American (with western Atlantic floor separated from the South American plate along the Caribbean islands) plate
III South American (with western Atlantic floor separated from the North American plate along the Caribbean islands) plate
IV Pacific plate
V India-Australia-New Zealand plate
VI Africa with the eastern Atlantic floor plate
VII Eurasia and the adjacent oceanic plate.
Minor-
Some important minor plates are listed below: (i) Cocos plate : Between Central America and Pacific plate
(ii) Nazca plate : Between South America and Pacific plate
(iii) Arabian plate : Mostly the Saudi Arabian landmass
(iv) Philippine plate : Between the Asiatic and Pacific plate
(v) Caroline plate : Between the Philippine and Indian plate (North of New Guinea) Fuji plate : North-east of Australia.
Types of plate boundaries
Where two/more plates meet. 1.Divergent Boundary-Where new crust is generated as the plates pull away from each other. The sites where the plates move away from each other are called spreading sites. The best-known example of divergent boundaries is the Mid-Atlantic Ridge. At this, the American Plate(s) is/are separated from the Eurasian and African Plates. 2.Convergent Boundaries-Where the crust is destroyed as one plate dives under another. The location where sinking of a plate occurs is called a subduction zone. 3.Transform Boundaries
Where the crust is neither produced nor destroyed as the plates slide horizontally past each other. Eg. San Andreas fault california shows this wrt American and Pacific plates.
Rates of Plate Movement
rates vary considerably. The Arctic Ridge has the slowest rate (less than 2.5 cm/yr), and the East Pacific Rise near Easter Island, in the South Pacific about 3,400 km west of Chile, has the fastest rate (more than 15 cm/yr).
Force for the Plate Movement
Arthur Holmes- earth not smooth solid motionless, but operation of convective currents due to core heat (radioactive decay and residual heat). Thus heated material rises to surface, cools, sinks, generating movement.
Movement of Indian plate
Eastern boundary- Rakinyoma Mountains of Myanmar towards the island arc along the Java Trench-spreading site with Pacific. Western boundary- Kirthat mountain Pakistan, spreading site. Southern boundary with the Antarctic also spreading site. The Tethys Sea separated Indian plate and Eurasian plate. But northern boundary convergence, due to northward movement 60 million ya, pouring of Deccan traps near equator. Himalayas formed 40 million ya.
What is the earth composed of at its fundamental level?
Elements. 98% of crust Old Indian Sailors Always Cautiously Seek Precious Metals - oxygen, silicon, aluminium, iron, calcium, sodium, potassium and magnesium and 2% crust- Nice Horses Prefer Mango Smoothies To Carrot- Nickel Hydrogen Phosphorous Manganese Sulphur Titanium Carbon. However elements rarely free standing, found in combinations as minerals.
What is a mineral?
Thus, a mineral is a naturally occurring organic and inorganic substance, having an orderly atomic structure and a definite chemical composition and physical properties. A mineral is composed of two or more elements. But, also sometimes single element minerals found.
Sources of minerals
The basic source of all minerals is the hot magma in the interior of the earth. When magma cools, crystals of minerals appear.
Classification of minerals
Metallic and non metallic
Metallic Minerals
These minerals contain metal content and can be sub-divided into three types:
(i) Precious metals : gold, silver, platinum etc.
(ii) Ferrous Metals:iron and other metals often mixed with iron to form various kinds of steel.
(iii) Non-ferrous metals : include metals like copper, lead, zinc, tin, aluminium etc.
Non-Metallic Minerals
These minerals do not contain metal content. Sulphur, phosphates and nitrates are egs.
Rocks
A rock is an aggregate of one or more minerals.
Petrology
Petrology is science of rocks.
Types of rocks
three families on the basis of their mode of formation (i) Igneous Rocks — solidified from magma and lava; (ii) Sedimentary Rocks — the result of deposition of fragments of rocks by exogenous processes; (iii) Metamorphic Rocks — formed out of existing rocks undergoing recrystallisation.
Igneous Rocks
form out of magma and lava from the interior of the earth. If molten material is cooled slowly at great depths, mineral grains may be very large. Sudden cooling (at the surface) results in small and smooth grains. Egs. Granite, gabbro, pegmatite, basalt, volcanic breccia and tuff.
Sedimentary rocks
Rocks (igneous, sedimentary and metamorphic) of the earth’s surface are exposed to denudational agents, and are broken up into fragments which are transported by different exogenous agencies and deposited. These deposits through compaction turn into rocks. This process is called lithification. In many cases, the layers of deposits retain their characteristics even after lithification.
Depending upon the mode of formation, sedimentary rocks are classified into three major groups: (i) mechanically formed — sandstone, conglomerate, limestone, shale, loess etc. are examples; (ii) organically formed — geyserite, chalk, limestone, coal etc. are some examples; (iii) chemically formed — chert, limestone, halite, potash etc. are some examples.
Metamorphic Rocks
These rocks form under the action of pressure, volume and temperature (PVT) changes. Metamorphism is a process by which already consolidated rocks undergo recrystallisation and reorganisation of materials within original rocks.
In metamorphism some rocks, grains or minerals get arranged in layers or lines which is called foliation or lineation. When they get arranged in alternating thin to thick layers appearing in light and dark shades, it is called banding
Metamorphic rocks are classified into two major groups — foliated rocks and non-foliated rocks. Gneissoid, granite, syenite, slate, schist, marble, quartzite etc. egs
Mechanical reorganisation without appreciable chemical changes is called dynamic metamorphism. The materials of rocks chemically alter and recrystallise due to thermal metamorphism. There are two types of thermal metamorphism. In contact metamorphism the rocks come in contact with hot intruding magma and lava and the rock materials recrystallise under high temperatures. In regional metamorphism, rocks undergo recrystallisation due to deformation caused by tectonic shearing together with high temperature or pressure or both.
Rock cycle
is a continuous process through which old rocks are transformed into new ones. Igneous (primary) → metamorphic → sedimentary → subduction making them magma → igneous.
What are endogenic forces and exogenic forces? Name them exactly
The external forces are known as exogenic forces (Weathering, mass wasting, erosion and deposition) and the . The energy emanating from within the earth is the main force behind endogenic geomorphic processes. This energy is mostly generated by radioactivity, rotational and tidal friction and primordial heat from the origin of the earth. This energy induces diastrophism and volcanism.
The actions of exogenic forces result in?
wearing down (degradation) of relief/elevations and filling up (aggradation) of basins/ depressions, on the earth’s surface.
What is gradation?
The phenomenon of wearing down of relief through erosion is known as gradation.
Geomorphic processes means
Those relating to changing the configuration of the crust/ surface of the earth
geomorphic agents means
exogenic elements (like water, ice, wind, etc.,) capable of acquiring and transporting earth materials can be called a geomorphic agent. Gravity also important.
Diastrophism, Volcanism means
Diastrophism covers movement of solid (plastic) crust material, as opposed to movement of molten material which is covered by volcanism. Diastrophism includes Orogeny- a mountain building process epeirogeny- continental building process, earthquakes involving local relatively minor movements, plate tectonics involving horizontal movements of crustal plates.
Sources for exogenic geomorphic processes
The exogenic processes derive their energy from the atmosphere determined by the ultimate energy from the sun, the gradients created by tectonic factors, stress (force per unit area) due to gravity.
What is denudation?
All the exogenic geomorphic processes are covered under a general term, denudation. The word ‘denude’ means to strip off or to uncover. Weathering, mass wasting/movements, erosion and transportation.
Weathering
When weather and climate act over earth materials, causing mechanical disintegration or chemical decomposition. Very little/ no motion of materials, thus in situ process. Driving force includes gravity, molecular stress, and chemical actions. There are three major groups of weathering processes (mostly happen in conjunction) : (i) chemical; (ii) physical or mechanical; (iii) biological weathering processes.
Chemical weathering processes
When chemical reactions occur on rocks- solution, carbonation, hydration, oxidation and reduction through oxygen, acid, carbon etc.
Physical Weathering Processes
When weathering happens due to forces like (i) gravitational forces such as overburden pressure, load and shearing stress; (ii) expansion forces due to temperature changes, crystal growth or animal activity; (iii) water pressures controlled by wetting and drying cycles.
Biological weathering processes
Biological weathering is the contribution to or removal of minerals and ions from the weathering environment and physical changes due to growth or movement of organisms. Burrowing and wedging by organisms, Human beings disturbance, decaying animal and plant matter, plant roots pressure exertion.
Exfoliation means
when the surface layers of rock peel away due to weathering.
Enrichment means
In an economic sense when non-useful substances are removed to reveal a more concentrated version of a favourable substance.
Importance of weathering
1.aids other exogenic forces- mass wasting, erosion, deposition that helps determine landscape
2.helps in enrichment of minerals for economy
3.formation of soil
Mass movements
These movements transfer the mass of rock debris down the slopes under the direct influence of gravity alone. No aid by running water, glaciers, wind, waves and currents. Debris may carry with it air, water or ice rather than vice versa. Weathering is not a prerequisite. Heave (heaving up of soils due to frost growth and other causes), flow and slide are the three forms of movements.
Landslides
Rapid and perceptible movements. The materials involved are relatively dry. Several types based on material and movement. 1.Slump is slipping of one or several units of rock debris with a backward rotation with respect to the slope over which the movement takes place 2.debris slide does not involve backward rotation 3.debris fall- free fall of earth debris from a vertical or overhanging face 4.rock slide-Sliding of individual rock masses 5.rock fall-free falling of rock blocks over any steep slope keeping itself away from the slope.
Erosion and deposition
Erosion involves acquisition and transportation of rock debris. When these settle, it is called deposition. Powered through kinetic energy. The erosion and transportation of earth materials is brought about by wind, running water, glaciers (climatic) and waves and ground water.
Soil
is the loose material that covers the earth’s surface and is made up of solids, liquids, and gases. It is a dynamic medium.
Soil formation name and process
Pedogenesis. Soil forms through weathering, where bacteria, mosses, and lichens colonize weathered material, leading to humus buildup. Plants, starting with grasses and ferns and progressing to bushes and trees, further develop the soil. Roots and burrowing animals create a porous, water-retentive structure, resulting in mature soil with a mix of minerals and organic matter.
Soil-forming Factors
(i) parent material; (ii) topography; (iii) climate-moisture, temperature (iv) biological activity; (v) time.
Soil of tropical climates
In climates like wet equatorial rainy areas with high rainfall, not only calcium, sodium, magnesium, potassium etc. but also a major part of silica is removed from the soil. Removal of silica from the soil is known as desilication.
Soil of dry climates
evaporation exceeds precipitation, leaving behind salts in the soil. Such salts form into a crust in the soil known as hardpans. In tropical climates and in areas with intermediate precipitation conditions, calcium carbonate nodules (kanker) are formed.
what is a landform?
Small to medium tracts or parcels of the earth’s surface are called landforms.
What are landscapes?
Aggregation of several landforms.
Geomorphic agents
Water, wind, glaciers, groundwater, waves.
Components of running water
One is overland flow on the general land surface as a sheet. Another is linear flow as streams and rivers in valleys.
Monadnocks
a lowland of faint relief with some low resistant remnants
Peneplain
An almost plain
Running water in youth stage features
1.Streams are few 2. poor integration 3.shallow V-shaped valleys 4. no floodplains or with very narrow floodplains along trunk streams 5.Streams divides are broad and flat with marshes, swamp and lakes 6.Meanders if present develop over these broad upland surfaces 7.Waterfalls and rapids may exist where local hard rock bodies are exposed.
Running water in mature stage features
1.plenty of streams 2.good integration 3.deep V shaped valleys 4.wider floodpains 5.swamps marshes disappear 6.meanders present 7.waterfalls rapids disappear
Running water in old stage features
1.fewer tributaries 2.vast floodplains 3.meanders, oxbow lakes, swamps, marshes
Valleys
rills<gullies<valleys. V shaped, gorge-equal at width at top and bottom (hard rocks), canyon wide at top and narrow at bottom (sedimentary rocks).
Potholes and Plunge Pools
On the rocky beds of hill-streams circular depressions called potholes form because of stream erosion. Plunge pools are large potholes at the base of waterfalls.
Erosional landforms of running water
Valleys, potholes and plunge pools, incised/entrenched meanders, river terraces.
Incised or entrenched meanders
Sinuous/meandering courses cut in hard rocks.
River Terraces and paired terraces
marking old valley floor or floodplain levels. The river terraces may occur at the same elevation on either side of the rivers in which case they are called paired terraces.
Depositional landforms of running water
Alluvial Fans, Deltas, Floodplains, Natural Levees and Point Bars, Meanders
Alluvial Fans
When a river carrying considerable coarse load flows from a high to low gradient, deposit it at slope base in a cone shaped formation. Such rivers usually keep changing course across fan forming channels called distributaries.
Deltas
Similar to alluvial fans, differ in location. Coarse load dumped near sea. Unlike in alluvial fans, the deposits making up deltas are very well sorted with clear stratification. The coarsest materials settle out first and the finer fractions like silts and clays are carried out into the sea.
Floodplains, delta plains
Plains created by river deposits of sand, silt, clay etc. River bed constitutes the active floodplain while the one above bank is inactive that consists of flood and channel deposits. The flood plains in a delta are called delta plains.
Natural levees
They are low, linear and parallel ridges/mounds of coarse deposits along the banks of rivers
Point bars/meander bars
Concave side of meanders, and are sediments deposited in a linear fashion
Meanders
Sinuous, looping, bending courses of rivers created by sediment obstruction, coriolis force, gradient etc.
Ox bow lake
When a deep meander of a river gets cut off
Karst topography
a landscape that’s characterised by caves, sinkholes, springs, and other features. It’s formed when groundwater dissolves soluble rocks like limestone, marble, and gypsum. Chemical processes of solution and precipitation deposition are important as physical processes often insignificant.
Erosional landforms formed by groundwater
Pools, Sinkholes, Lapies, Uvalas Limestone Pavements, Caves
Sinkholes
A sinkhole is an opening more or less circular at the top and funnel-shaped towards the bottom
Dolines/collapse sinks
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
Uvalas
When sink holes and dolines join together long, narrow to wide trenches called valley sinks or Uvalas form.
Lapies
maze of points, grooves and ridges
Limestone Pavements
The lapie field may eventually turn into somewhat smooth limestone pavements.
Caves
In areas where there are alternating beds of rocks, softer rocks dissolve, creating cavernous features called caves. Caves having openings at both the ends are called tunnels.
Depositional landforms formed by groundwater
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. Stalactites, Stalagmites and Pillars.
Stalactites, Stalagmites and Pillars.
Stalactites hang as icicles, 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 and form due to dripping water from the surface. The stalagmite and stalactites eventually fuse to give rise to columns and pillars.
Glaciers
Vast moving sheets of ice, over plains or through trough like valleys due to gravity. Erosion by glaciers is tremendous because of friction caused by sheer weight of the ice.
Erosional landforms formed by glaciers
Cirque, Horns and Serrated Ridges, Glacial Valleys/Troughs, fjords
Cirque
a bowl-shaped depression or amphitheater-like basin that glaciers carve into mountains and valley sides. cirque or tarn lakes often form.
Horns
These are sharp, steep-sided peaks that form when multiple glaciers erode a mountain from different sides. Eg The highest peak in the Alps, Matterhorn and the highest peak in the Himalayas, Everest are in fact horns formed through headward erosion of radiating cirques.
Serrated Ridges
Also known as arêtes, these are jagged, steep ridges that form between cirques.
Glacial Valleys/Troughs
Glaciated valleys are trough-like and U - shaped with broad floors and relatively smooth, and steep sides.
Fjords
Very deep glacial troughs filled with sea water and making up shorelines (in high latitudes) are called fjords/fiords.
Depositional landforms formed by glaciers
Eskers, Moraines, Outwash Plains, Drumlins EMOD
Moraines
a pile of debris or rock left behind by a glacier
Eskers
long, winding ridges of sand and gravel that are formed by glacial meltwater
Outwash Plains
The plains at the foot of the glacial mountains covered with glacio-fluvial deposit
Drumlins
are smooth oval shaped ridge-like features composed mainly of glacial till, gravel and sand. One end of the drumlins facing the glacier called the stoss end is blunter and steeper than the other end called tail. Drumlins give an indication of direction of glacier movement.
Types of coast
HIGH ROCKY COASTS eg Indian west coast and LOW SEDIMENTARY COASTS eg indian east coast
Erosional landforms by currents and waves
Cliffs, Terraces, Caves and Stacks
Cliffs, Terraces, Caves and Stacks
Steep faces of rock upto 30m. At foot of cliffs, platform with debris from cliffs called terraces. Hollows created in cliff to create caves. The roofs of caves collapse and the sea cliffs recede further inland. Retreat of the cliff may 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.
Depositional landforms by currents and waves
Beaches and Dunes, Bars, Barriers and Spits, lagoons
Beaches and Dunes
Most of the sediment making up the beaches comes from land carried by the streams and rivers or from wave erosion. 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.
Bars, Barriers and Spits
A ridge of sand and shingle formed in the sea that is off-shore, approximately parallel to the coast is called an off-shore bar. An off-shore bar which is exposed due to further addition of sand is termed a barrier bar. Sometimes such barrier bars get keyed up to one end of the bay when they are called spits
Lagoon
Shallow body of water that’s separated from a larger body of water by a barrier
Erosional landforms by winds
Pediments and Pediplains, Playas, Deflation Hollows and Caves, Mushroom, Table and Pedestal Rocks
Pediments and Pediplains
Gently inclined rocky floors close to the mountains at their foot with or without a thin cover of debris, are called pediments. That’s how the high relief in desert areas is reduced to low featureless plains called pediplains.
Playas and alkakli flats
a flat, dry, and vegetation-free area in a desert basin that can periodically fill with water. The playa plain covered up by salts is called alkali flats.
Deflation Hollows and Caves
Depressions in rock or soil due to wind called deflation hollows, and hollow cavities called caves
Mushroom, Table and Pedestal Rocks
Many rock-outcrops in the deserts easily susceptible to wind deflation and abrasion are worn out quickly in these shapes.
Depositional landforms by winds
Wind is a good sorting agent. Sand Dunes
Sand Dunes
1.Crescent shaped dunes called barchans with the points or wings directed away from wind direction. 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 barchan with a small difference. Seif has only one wing or point. 4.Longitudinal dunes form when supply of sand is poor and wind direction is constant 5.Transverse dunes are aligned perpendicular to wind direction.
