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Geography class 7 > changes of face of earth > Flashcards

changes of face of earth Flashcards

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1
Q

when was the theory of plate tectonics introduced

A

1960s

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2
Q

what did the theory of plate tectonics state

A

lithosphere broken into pieces called lithospheric or tectonic plates

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3
Q

define folding

A

when two tectonic plates converge the land is pushed up into folds

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4
Q

define faulting

A

when rocks are compressed beyond a point they develop cracks or fractures called faults

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5
Q

give examples for fold mountains

A

Himalayas, Andes (South America), Alps (Europe), Appalachians (North America)

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6
Q

example for block mountains and rift valleys

A

black forest mountains narmada and tapti

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7
Q

define earthquakes

A

earthquakes are vibrations caused by disturbances that originate inside the earth that move through earth and its surface

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8
Q

define seismic focus and epicentre

A

the point where disturbance originates is called the seismic focus and the epicentre is the point that lies perpendicular to the seismic focus on the surface of the earth. The earthquake is strongest at the epicentre

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9
Q

define seismograph

A

seismograph is an instrument that detects and records the intensity of a earthquake

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10
Q

how we refer to the ritcher scale

A

below 4 is mild tremor. above 4 and below six is considered a moderate tremor buildings shake and things fall down above 6 is severe tremor an can be disastrous

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11
Q

how are tsunamis caused

A

earthquakes under water

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12
Q

what is a volcano

A

a volcano is a vent in earth’s crust through which molten rocks and gases erupt

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13
Q

what is magma

A

magma is molten rock from the mantle that pushes it’s way through cracks towards the surface

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14
Q

what is a magma chamber

A

a magma chamber is a pool of magma located deep inside earth

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15
Q

what is a crater

A

a crater is opening at the top of a volconic mountain

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16
Q

what is a volcanic mountain

A

a volcanic mountain is a cone formed by the lava around the vent. alternating layers of ash and lava

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17
Q

what is the ritcher scale

A

scale of numbers used to indicate severity of the earthquake

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18
Q

what is a caldera

A

a lake formed in the crater of a extinct volcano

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19
Q

gradation definition

A

change in the level of earth’s surface

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20
Q

degradation or erosion definition

A

activity that reduces the level of the earth’s surface

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21
Q

aggradation

A

build up of land

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22
Q

meander

A

loop made by river in its lower course

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23
Q

levee

A

raised bank of river flowing through flood plain caused by alluvial deposition

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24
Q

mesa

A

area of resistant rock left after wind erosion of surrounding softer rock

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25
Q

active volcano definition and example

A

volcanoes that have erupted recently. mt etna mt stromboli of the mediterranean sea

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26
Q

dormant volcanoes definition and explanation

A

quiet for long time but could erupt soon. Mt vesusius in 79 ce with destrucion of pompeii and herculanean

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27
Q

what is a common feature of dormant volcanoes

A

their vent is often blocked with a plug of solidifies lava resulting in a violent eruption

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28
Q

extinct volcanoes definition and example

A

shows no indication of future eruption. Mt Kilimanjaro in Tanzania. no volcano can be called extinct with absolute certainty

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29
Q

weathering definition

A

breaking up of rock material o the surface of the Earth due to exposure to the atmosphere

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30
Q

erosion definition

A

further disintegration and and removal of weathered material by agents of gradation is called erosion

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31
Q

in what ways do rivers function as agents of gradation

A

they erode material, they carry eroded material, they deposit eroded material

32
Q

what are the stages in a rivers life

A

start flow from mountains (the source), flow through plains (the course) and flow into sea (the mouth) hence upper course(youth) middle course (maturity) lower course (youth)

33
Q

features of upper course of river

A

starts as stream from source
flows fast down steep slopes
mainly erosional
forms narrow gouges or v shaped salleys

34
Q

middle course features

A

river joined by tributaries
activities are largely balanced
transports large amounts of eroded materials

35
Q

features of lower course

A

flows slowly
meanders over flat plains near sea
deposits its load of eroded materials as it does not have the energy to carry great loads

36
Q

what is alluvium

A

alluvium is finely grained deposit from rivers

37
Q

what are the two ways rivers break up bedrock they flow over?

A

mechanical erosion and chemical erosion

38
Q

what are the kinds of valleys formed by rivers and how are they formed?

A

I-shaped valleys or canyons are formed when a river cuts out a narrow valley with steep walls
V-shaped valleys are formed when the river is young and the flow is rapid. The erosion is mainly vertical but there is still a certain amount of horizontal erosion which gives it it’s v shape
In the middle course the slope gets less steep resulting in more lateral erosion leadinf to formation of wide flat bottomed valleys

39
Q

what are waterfalls

A

when there is a steep drop in the course of a river and the water rushes down with great force it forms a river

40
Q

what causes an overhang

A

alternating layers of soft and hard rock cause the soft rock to be eroded first leaving a band of hard rocks hanging creating a steep fall over which the river falls

41
Q

what can be other causes of formation of river

A

earthquake

42
Q

what is a plunge pool

A

when water falls on a surface with great force it erodes rock material causing a depression called a plunge pool

43
Q

highest and widest waterfalls in the world

A

angel falls in venezuela is the highest waterfall with fall of almost 1km and victoria falls is the broadest

44
Q

what features are caused by river erosion

A

valleys and waterfalls

45
Q

what features are cause by river deposition

A

meanders and oxbow lakes
flood plains
deltas

46
Q

how are meanders formed?

A

river swings side to side as it flows over a level tract forming winding loops. continuous erosion on the concave side and deposition on the convex side can cut a loop of the main body and form a oxbow lake

47
Q

what is a flood plain

A

a flood plain is an almost flat plain that is formed as a result of a river flooding it’s banks

48
Q

how is a flood plain formed

A

as the river in it’s lower course can no longer carry the entire load of sediments it deposits some onto the river bed raising it. this raises the level of water so it almost reaches the river banks. during heavy rain it overflows and floods it’s banks. the river deposits alluvium making the flood plain very rich and fertile

49
Q

what is a delta

A

a delta is a triangular alluvial tract formed by sediment deposited by distributaries as the river enters the sea

50
Q

what is a distributary

A

as a river approaches the mouth (the place where it meets the sea) it deposits the sediments in the form of sandbars. To flow through these sandbars the river forms channels called distributaries

51
Q

features of delta

A

fertile ideal for agricultutre

delta plains are thickly populated

52
Q

examples of deltas

A

ganga bramhaputra delta is the largest and one of the richest in the world. nile is also known for its fertility

53
Q

alternate name for sea erosion

A

marine erosion

54
Q

how does marine erosion happen

A

happens when waves hitting coastal rocks and cliffs cause rocks to shatter. small pebbles and rocks flung by waves also cause erosion. tumbling motion of waves causes further erosion

55
Q

marine deposition result

A

takes thousands of years to form as it is very slow. most sediments are deposited at the bottom of the ocean and form sedimentary rocks. beaches are also depsitional

56
Q

what landforms are created by waves

A

sea caves, sea arches, wave-cut platforms, cliffs and beaches

57
Q

how are sea caves formed?

A

strong waves break and erode material they form hollow caves along the coast

58
Q

how are sea arches formed

A

over time as waves continue to strike rocks the cave walls diappears till only the 2 supporting pillars and roof are left called sea arches

59
Q

what are sea stacks

A

roof of sea arches erodes pillar is left

60
Q

what are sea cliffs

A

vertical and steep rock faces along the shore

61
Q

what are wave-cut platforms

A

eroded sea cliffs collapse and move backward leading to formation of gentle sloping surfaces

62
Q

where is the gradational activity of winds most visible and why

A

it is most visible in deserts as there is an abundance of loose sand particles

63
Q

features caused by wind erosion

A

mesas and mushroom rocks

64
Q

how is a mushroom rock created?

A

when winds blow in deserts they pick up sand particles and when these winds blow against rocks, the dust particles, suspended in the lower layers of the air blow with great force eroding the rock, resulting in a mushroom rock with a broad top and a narrow bottom

65
Q

features caused by wind deposition

A

sand dunes, barchans and loess plains

66
Q

how are sand dunes created?

A

during sandstorms the wind picks up large amounts of sand grains. as the winds loses energy it drops the sand grains in hills called sand dunes

67
Q

what are barchans?

A

barchans are dunes with long gentle slope on the windward side and a steep slope on the leeward sign forming a crescent shape

68
Q

what are loess plains

A

when fine sand particles are deposited over very large areas they are called loess plains

69
Q

what are glaciers

A

glaciers are slow moving rivers of ice that consist of large masses of ice blocks spread over several kilometres they move at such a slow pace their movements are hardly noticeable

70
Q

what are the two kinds of glaciers

A

mountain and continental glaciers

71
Q

how does a glacier play it’s part as an agent of gradation

A

the rocks picked up by the glacier erode the floors and walls of valley and as the glacier melts it leaves it’s load of sediments to form various depositional features.

72
Q

what are the 2 major landforms formed by glaciers

A

moraines and cirques

73
Q

what is a cirque

A

a cirque is an armchair like depression caused by the erosive action of a glacier. as the ice accumulated in the hollows alternate freezing and thawing the rocks below it expand and contract till it breaks down. the ice deepens the hollow till the weathered rock itself is now an agent of erosion

74
Q

what is a tarn

A

a tarn is a cirque in which the ice has melted

75
Q

what are moraines

A

moraines are deposits of the eroded rock debris that glaciers carry with them that look like a and wall on a now covered mountain

Geography class 7 (6 decks)

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