Flash Card

LAKSHYA-75 [Day-16] Static Flash Cards for IAS Prelims 2020

Physical weathering; Force for Drifting; Ring of Fire; Metamorphic Rocks; Diastrophism; Erosional landforms by Groundwater; Distribution of Temperature; Extra Tropical Cyclones & Tropical cyclones; Clouds; Horizontal and Vertical Distribution of Temperature
By IASToppers
March 22, 2020

 

 

This boundary region, from where there is a rapid decrease of temperature, is called?

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Answer:

This boundary region, from where there is a rapid decrease of temperature, is called the thermocline.

Enrich Your Learning:

Horizontal and Vertical Distribution of Temperature

  • The temperature-depth profile for the ocean water shows how the temperature decreases with the increasing depth.
  • The profile shows a boundary region between the surface waters of the ocean and the deeper layers.
  • The boundary usually begins around 100 – 400 m below the sea surface and extends several hundred of metres downward.
  • This boundary region, from where there is a rapid decrease of temperature, is called the thermocline.
  • About 90 per cent of the total volume of water is found below the thermocline in the deep ocean. In this zone, temperatures approach 0°C.
  • The temperature structure of oceans over middle and low latitudes can be described as a three-layer system from surface to the bottom.
  • The first layer represents the top layer of warm oceanic water and it is about 500m thick with temperatures ranging between 20° and 25° C.
  • This layer, within the tropical region, is present throughout the year but in mid latitudes it develops only during summer.
  • The second layer called the thermocline layer lies below the first layer and is characterised by rapid decrease in temperature with increasing depth. The thermocline is 500 -1,000 m thick.
  • The third layer is very cold and extends up to the deep ocean floor.
  • In the Arctic and Antartic circles, the surface water temperatures are close to 0°C and so the temperature change with the depth is very slight.
  • Here, only one layer of cold water exists, which extends from surface to deep ocean floor.
  • The average temperature of surface water of the oceans is about 27°C and it gradually decreases from the equator towards the poles.
  • The rate of decrease of temperature with increasing latitude is generally 0.5°C per latitude.
  • The average temperature is around 22°C at 20° latitudes, 14° C at 40° latitudes and 0° C near poles.
  • The oceans in the northern hemisphere record relatively higher temperature than in the southern hemisphere.
  • The highest temperature is not recorded at the equator but slightly towards north of it.
  • The average annual temperatures for the northern and southern hemisphere are around 19° C and 16° C respectively due to the unequal distribution of land and water in the northern and southern hemispheres.
  • The maximum temperature of the oceans is always at their surfaces because they directly receive the heat from the sun and the heat is transmitted to the lower sections of the oceans through the process of convection.
  • It results into decrease of temperature with the increasing depth, but the rate of decrease is not uniform throughout.
  • The temperature falls very rapidly up to the depth of 200 m and thereafter, the rate of decrease of temperature is slowed down.

 

 

They are generally formed at a height of 4,000 – 7,000 m. They exist in patches and can be seen scattered here and there. They have a flat base. Identify this clouds.

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Answer:

  • Cumulus clouds

Enrich Your Learning:

Clouds

  • Cloud is a mass of minute water droplets or tiny crystals of ice formed by the condensation of the water vapour in free air at considerable elevations.
  • As the clouds are formed at some height over the surface of the earth, they take various shapes.
  • According to their height, expanse, density and transparency or opaqueness clouds are grouped under four types: cirrus; cumulus; stratus; nimbus.

Cirrus

  • Cirrus clouds are formed at high altitudes (8,000 – 12,000m).
  • They are thin and detatched clouds having a feathery appearance. They are always white in colour.

Stratus

  • As their name implies, these are layered clouds covering large portions of the sky.
  • These clouds are generally formed either due to loss of heat or the mixing of air masses with different temperatures.

Nimbus

  • Nimbus clouds are black or dark gray. They form at middle levels or very near to the surface of the earth.
  • These are extremely dense and opaque to the rays of the sun.
  • Sometimes, the clouds are so low that they seem to touch the ground.
  • Nimbus clouds are shapeless masses of thick vapour.

A combination of these four basic types can give rise to the following types of clouds:

  • High clouds – cirrus, cirrostratus, cirrocumulus
  • Middle clouds – altostratus and altocumulus
  • Low clouds – stratocumulus and nimbostratus and clouds with extensive vertical development – cumulus and cumulonimbus.

 

 

How does the extra tropical cyclone differ from the tropical cyclone?

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Answer:

The extra tropical cyclone differs from the tropical cyclone in number of ways.

  • The extra tropical cyclones have a clear frontal system which is not present in the tropical cyclones.
  • They cover a larger area and can originate over the land and sea. Whereas the tropical cyclones originate only over the seas and on reaching the land they dissipate.
  • The extra tropical cyclone affects a much larger area as compared to the tropical cyclone.
  • The wind velocity in a tropical cyclone is much higher and it is more destructive.
  • The extra tropical cyclones move from west to east but tropical cyclones, move from east to west.

Enrich Your Learning:

Extra Tropical Cyclones

  • The systems developing in the mid and high latitude, beyond the tropics are called the middle latitude or extra tropical cyclones.
  • The passage of front causes abrupt changes in the weather conditions over the area in the middle and high latitudes.
  • Extra tropical cyclones form along the polar front.
  • Initially, the front is stationary. When the pressure drops along the front, the warm air moves northwards and the cold air move towards, south setting in motion an anticlockwise cyclonic circulation.
  • The cyclonic circulation leads to a well-developed extra tropical cyclone, with a warm front and a cold front.
  • There are pockets of warm air or warm sector wedged between the forward and the rear cold air or cold sector. The warm air glides over the cold air and a sequence of clouds appear over the sky ahead of the warm front and cause precipitation.
  • The cold front approaches the warm air from behind and pushes the warm air up. As a result, cumulus clouds develop along the cold front.
  • The cold front moves faster than the warm front ultimately overtaking the warm front. The warm air is completely lifted up and the front is occluded and the cyclone dissipates.
  • The processes of wind circulation both at the surface and aloft are closely interlinked.

Tropical cyclones

  • Tropical cyclones are violent storms that originate over oceans in tropical areas and move over to the coastal areas bringing about large scale destruction caused by violent winds, very heavy rainfall and storm surges.
  • They are known as Cyclones in the Indian Ocean, Hurricanes in the Atlantic, Typhoons in the Western Pacific and South China Sea, and Willy-willies in the Western Australia.
  • Tropical cyclones originate and intensify over warm tropical oceans.
  • The conditions favorable for the formation and intensification of tropical storms are:
    • Large sea surface with temperature higher than 27° C
    • Presence of the Coriolis force
    • Small variations in the vertical wind speed
    • A pre-existing weak low-pressure area or low-level-cyclonic circulation
    • Upper divergence above the sea level system
  • The energy that intensifies the storm, comes from the condensation process in the towering cumulonimbus clouds, surrounding the center of the storm.
  • With continuous supply of moisture from the sea, the storm is further strengthened.
  • On reaching the land the moisture supply is cut off and the storm dissipates.
  • The place where a tropical cyclone crosses the coast is called the landfall of the cyclone.
  • The cyclones, which cross 20oN latitude generally, recurve and they are more destructive.
  • A mature tropical cyclone is characterized by the strong spirally circulating wind around the centre, called the eye. The diameter of the circulating system can vary between 150 and 250 km.

 

 

Isotherms are lines joining places having equal a) temperature OR b) Pressure OR c) latitude OR d) Longitude

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Answer:

Isotherms are lines joining places having equal temperature.

Enrich Your Learning:

Distribution of Temperature

  • The temperature distribution is generally shown on the map with the help of isotherms. The Isotherms are lines joining places having equal temperature.
  • In general, the effect of the latitude on temperature is well pronounced as the isotherms are generally parallel to the latitude.
  • The deviation from this general trend is more pronounced in January than in July, especially in the northern hemisphere.
  • In the northern hemisphere the land surface area is much larger than in the southern hemisphere. Hence, the effects of land mass and the ocean currents are well pronounced.
  • In January the isotherms deviate to the north over the ocean and to the south over the continent. This can be seen on the North Atlantic Ocean.
  • The presence of warm ocean currents, Gulf Stream and North Atlantic drift, make the Northern Atlantic Ocean warmer and the isotherms bend towards the north.
  • Over the land the temperature decreases sharply and the isotherms bend towards south in Europe. It is much pronounced in the Siberian plain.
  • The mean January temperature along 60° E longitude is minus 20° C both at 80° N and 50° N latitudes.
  • The mean monthly temperature for January is over 27° C, in equatorial oceans over 24° C in the tropics and 2° C – 0° C in the middle latitudes and –18° C to –48° C in the Eurasian continental interior.
  • The effect of the ocean is well pronounced in the southern hemisphere. Here the isotherms are more or less parallel to the latitudes and the variation in temperature is more gradual than in the northern hemisphere.
  • The isotherm of 20° C, 10° C, and 0° C runs parallel to 35° S, 45° S and 60° S latitudes respectively.
  • In July the isotherms generally run parallel to the latitude. The equatorial oceans record warmer temperature, more than 27°C. Over the land more than 30°C is noticed in the subtropical continental region of Asia, along the 30° N latitude.
  • Along the 40° N runs the isotherm of 10° C and along the 40° S the temperature is 10° C.
  • The highest range of temperature is more than 60°C overs the north-eastern part of Eurasian continent. This is due to continentality. The least range of temperature, 3°C, is found between 20° S and 15° N.

 

 

Lapies and Stalagmites are the landforms created by a) Water OR b) Wind?

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Answer:

Water

Enrich Your Learning:

Erosional landforms by Groundwater

Pools, Sinkholes, Lapies and Limestone Pavements

  • Small to medium sized round to sub-rounded shallow depressions called swallow holes form on the surface of limestones through solution.
  • Sinkholes are very common in limestone/karst areas. A sinkhole is an opening more or less circular at the top and funnel-shaped towards the bottom.
  • Some of these 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. The term doline is sometimes used to refer the collapse sinks.
  • When sink holes and dolines join together because of slumping of materials along their margins, a long, narrow to wide trenches called valley sinks or Uvalas
  • Gradually, most of the surface of the limestone is eaten away by pits and trenches, leaving it extremely irregular with a maze of points, grooves and ridges or lapies.
  • The lapie field may eventually turn into somewhat smooth limestone pavements.

Caves

  • In areas where there are alternating beds of rocks 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.
  • There can be a maze of caves at different elevations depending upon the limestone beds and intervening rocks.
  • Caves normally have an opening through which cave streams are discharged. Caves having openings at both the ends are called tunnels.

Depositional landforms by Groundwater

  • 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. Stalactites 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.

 

 

What are the Difference between Epeirogeny and orogeny?

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Solution & Enrich Your Learning:

Diastrophism  

  • Diastrophism is an endogenic geomorphic processes.
  • All processes that move, elevate or build up portions of the earth’s crust come under diastrophism.
  • They include:
  • Organic processes involving mountain building through severe folding and affecting long and narrow belts of the earth’s crust;
  • Epeirogenic processes involving uplift or warping of large parts of the earth’s crust;
  • Earthquakes involving local relatively minor movements;
  • Plate tectonics involving horizontal movements of crustal plates.
  • In the process of orogeny, the crust is severely deformed into folds.
  • Due to epeirogeny, there may be simple deformation.
  • Orogeny is a mountain building process whereas epeirogeny is continental building process.
  • Through the processes of orogeny, epeirogeny, earthquakes and plate tectonics, there can be faulting and fracturing of the crust.
  • All these processes cause pressure, volume and temperature (PVT) changes which in turn induce metamorphism of rocks.

Difference between Epeirogeny and orogeny:

Orogeny

Epeirogeny

In this process plate tectonics or volcanic activities form mountains.

In this process tectonics deformations of the earth’s crust forms continents and ocean basins

Due to orogeny, the crust is severely deformed into folds.

Due to epeirogeny, simple deformation occurs in the crust.

Formation of highly elevated mountains accumulate ice, which increase earth’s albedo.

Due to this process, sea levels rises and fall as new plate materials modify the shape of ocean basis.

 

 

 

How does salt weathering occurs?

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Answer:

Salts in rocks expand due to thermal action, hydration and crystallisation. Many salts have a tendency to expand. Expansion of these salts depends on temperature and their thermal properties. High temperature ranges between 30 and 50oC of surface temperatures in deserts favour such salt expansion. Salt crystals in near-surface pores cause splitting of individual grains within rocks, which eventually fall off, resulting in granular disintegration or granular foliation.

Enrich Your Learning:

Physical Weathering Processes

What is weathering?

  • Weathering is defined as mechanical disintegration and chemical decomposition of rocks through the actions of various elements of weather and climate.
  • Weathering processes are conditioned by many complex geological, climatic, topographic and vegetative factors. Climate is of particular importance.
  • There are three major groups of weathering processes :
  • Chemical;
  • Physical or mechanical;
  • Biological weathering processes.

Physical Weathering Processes:

  • Physical or mechanical weathering processes depend on some applied forces.
  • The applied forces could be:
  • Gravitational forces such as overburden pressure, load and shearing stress;
  • Expansion forces due to temperature changes, crystal growth or animal activity;
  • Water pressures controlled by wetting and drying cycles.
  • Many of these forces are applied both at the surface and within different earth materials leading to rock fracture.
  • Most of the physical weathering processes are caused by thermal expansion and pressure release.
  • These processes are small and slow but can cause great damage to the rocks because of continued fatigue the rocks suffer due to repetition of contraction and expansion.

Unloading and Expansion

  • Removal of overlying rock load because of continued erosion causes vertical pressure release with the result that the upper layers of the rock expand producing disintegration of rock masses. Fractures will develop roughly parallel to the ground surface.
  • In areas of curved ground surface, arched fractures tend to produce massive sheets or exfoliation slabs of rock. Exfoliation sheets resulting from expansion due to unloading and pressure release may measure hundreds or even thousands of metres in horizontal extent. Large, smooth rounded domes called exfoliation domes result due to this process.

Temperature Changes and Expansion

  • Various minerals in rocks possess their own limits of expansion and contraction. With rise in temperature, every mineral expands and pushes against its neighbour and as temperature falls, a corresponding contraction takes place. Because of diurnal changes in the temperatures, this internal movement among the mineral grains of the superficial layers of rocks takes place regularly. This process is most effective in dry climates and high elevations where diurnal temperature changes are drastic.
  • The surface layers of the rocks tend to expand more than the rock at depth and this leads to the formation of stress within the rock resulting in heaving and fracturing parallel to the surface. Due to differential heating and resulting expansion and contraction of surface layers and their subsequent exfoliation from the surface results in smooth rounded surfaces in rocks. In rocks like granites, smooth surfaced and rounded small to big boulders called tors form due to such exfoliation.

Freezing, Thawing and Frost

  • Wedging Frost weathering occurs due to growth of ice within pores and cracks of rocks during repeated cycles of freezing and melting. This process is most effective at high elevations in mid-latitudes where freezing and melting is often repeated. Glacial areas are subject to frost wedging daily. In this process, the rate of freezing is important.
  • Rapid freezing of water causes its sudden expansion and high pressure. The resulting expansion affects joints, cracks and small inter granular fractures to become wider and wider till the rock breaks apart

Salt Weathering

  • Salts in rocks expand due to thermal action, hydration and crystallisation. Many salts like calcium, sodium, magnesium, potassium and barium have a tendency to expand. Expansion of these salts depends on temperature and their thermal properties. High temperature ranges between 30 and 50oC of surface temperatures in deserts favour such salt expansion. Salt crystals in near-surface pores cause splitting of individual grains within rocks, which eventually fall off. This process of falling off of individual grains may result in granular disintegration or granular foliation.

Salt crystallisation is most effective of all salt-weathering processes. In areas with alternating wetting and drying conditions salt crystal growth is favoured and the neighbouring grains are pushed aside. Sodium chloride and gypsum crystals in desert areas heave up overlying layers of materials and with the result polygonal cracks develop all over the heaved surface. With salt crystal growth, chalk breaks down most readily, followed by limestone, sandstone, shale, gneiss and granite etc.

 

 

How does the Metamorphic Rocks from?

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Answer:

  • Metamorphism occurs when rocks are forced down to lower levels by tectonic processes 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 by overlying rocks.

Enrich Your Learning:

Metamorphic Rocks

  • The word metamorphic means ‘change of form’.
  • These rocks form under the action of pressure, volume and temperature (PVT)
  • Metamorphism occurs when rocks are forced down to lower levels by tectonic processes 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 by overlying rocks.
  • Metamorphism is a process by which already consolidated rocks undergo recrystallization and reorganization of materials within original rocks.
  • Mechanical disruption and reorganization of the original minerals within rocks due to breaking and crushing without any 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 – contact metamorphism and regional metamorphism.
  • In contact metamorphism the rocks come in contact with hot intruding magma and lava and the rock materials recrystallise under high temperatures. Quite often new materials form out of magma or lava are added to the rocks.
  • In regional metamorphism, rocks undergo recrystallization due to deformation caused by tectonic shearing together with high temperature or pressure or both.
  • In the process of metamorphism in some rocks grains or minerals get arranged in layers or lines. Such an arrangement of minerals or grains in metamorphic rocks is called foliation or
  • Types of metamorphic rocks depend upon original rocks that were subjected to metamorphism.
  • Metamorphic rocks are classified into two major groupsfoliated rocks and non-foliated
  • Gneissoid, granite, syenite, slate, schist, marble, quartzite are some examples of metamorphic rocks.

 

 

Mariana Trench, the deepest ocean trench, is located on Pacific Ring of Fire. True OR False.

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Answer:

True

Enrich Your Learning:

Ring of Fire:

  • The Ring of Fire is a horseshoe-shaped region surrounding the Pacific Ocean. Around 25,000 miles long, this region contains 75 % of the world’s volcanoes, and 90% of the world’s earthquakes hit the countries that border this region.
  • The ring of fire lies on Pacific tectonic plate, which joins with several other plates. These areas therefore are also prone to volcanic and seismic activity.

Key facts about the Ring of Fire:

  • The countries that border the Ring of Fire include the Western Coast of the United States, Japan, Indonesia, and many Pacific islands.
  • The Ring of Fire is home to the deepest ocean trench, called the Mariana Trench.
  • Mount Tambora of Indonesia is on Ring of fire which erupted in 1815 and became the largest volcanic eruption in recorded history.
  • 22 of the 25 largest volcanic eruptions in the last 11,700 years occurred in the ‘Ring of Fire’.
  • Most of the active volcanoes in the ring are situated underwater.
  • Mount Ruapehu in New Zealand is the most active volcano in the ring, with yearly minor eruptions and major eruptions every 50 years.

What causes Ring of Fire?

 

  • Most of the Earth’s volcanoes are located around the Pacific Ring of Fire because that the location of most of the Earth’s subduction zones.
  • A subduction zone is a place where one plate of oceanic lithosphere (= the crust + uppermost mantle) is shoved under another plate.
  • The down going plate is always the oceanic one. The oceanic plate collected water-saturated sediments and its uppermost few hundred meters got water saturated also.
  • As it is shoved into the hotter mantle the plate heats up and all this water and other volatiles boil off and migrate upwards through the overlying plate. The addition of volatiles such as water to the hot overlying mantle causes partial melting and the production of magma.
  • This magma rises up through the over-lying plate to erupt at the surface. If the overlying plate is a continent, formation of chain of volcanoes such as the Andes or Cascades occurs. If the overlying plate is ocean, a chain of volcanic islands such as the Marianas or Aleutians occurs.
  • This is also where the Earth’s deep ocean trenches are and where the Earth’s deep earthquakes are. The trenches form because the down going plate is bent downward as it sub ducts. The earthquakes form as the two plates scrape against each other (earthquakes down to about 150 km) and then as the down going plate bends (earthquakes down to about 700 km).
  • The earthquakes do a very good job of tracing the position of the down going plate. These zones of earthquakes are called Wadati-Benioff zones, after the two seismologists who first recognized them.

 

 

According to Wegener, the movement responsible for the drifting of the continents is due to convention currents generated due to radioactive elements. True OR False?

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Answer:  

False

Correct Answer:

  • Wegener suggested that the movement responsible for the drifting of the continents was caused by pole-fleeing force and tidal force.
  • Arthur Holmes in 1930s discussed the possibility of convection currents operating in the mantle portion. These currents are generated due to radioactive elements causing thermal differences in the mantle portion.

Enrich Your Learning:

Force for Drifting

  • Wegener suggested that the movement responsible for the drifting of the continents was caused by pole-fleeing force and tidal force.
  • The polar-fleeing force relates to the rotation of the earth.
  • The earth is not a perfect sphere. It has a bulge at the equator. This bulge is due to the rotation of the earth.
  • The second force that was suggested by Wegener- the tidal force– is due to the attraction of the moon and the sun that develops tides in oceanic waters.

Post-drift Studies

  • For continental drift, most of the evidence was collected from the continental areas in the form of distribution of flora and fauna or deposits, like
  • A number of discoveries during the post–World War II period added new information to geological literature.
  • The information collected from the ocean floor mapping provided new dimensions for the study of distribution of oceans and continents.

Convectional Current Theory:

  • Arthur Holmes in 1930s discussed the possibility of convection currents operating in the mantle portion.
  • These currents are generated due to radioactive elements causing thermal differences in the mantle portion.
  • Holmes argued that there exists a system of such currents in the entire mantle portion.
  • This was an attempt to provide an explanation to the issue of force, on the basis of which contemporary scientists discarded the continental drift theory.

Mapping of the Ocean Floor:

  • Detailed research of the ocean configuration revealed that the ocean floor is not just a vast plain but it is full of relief.
  • Expeditions to map the oceanic floor in the post–World War II period provided a detailed picture of the ocean relief and indicated the existence of submerged mountain ranges as well as deep trenches, mostly located closer to the continent margins.
  • The mid-oceanic ridges were found to be most active in terms of volcanic eruptions.
  • The dating of the rocks from the oceanic crust revealed the fact that they are much younger than the continental areas.

Rocks on either side of the crest of oceanic ridges and having equi-distant locations from the crest were found to have remarkable similarities both in terms of their constituents and their age.

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Daily Current Flash Cards 2020 Prelims 2020
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