changes of face of earth Flashcards
when was the theory of plate tectonics introduced
1960s
what did the theory of plate tectonics state
lithosphere broken into pieces called lithospheric or tectonic plates
define folding
when two tectonic plates converge the land is pushed up into folds
define faulting
when rocks are compressed beyond a point they develop cracks or fractures called faults
give examples for fold mountains
Himalayas, Andes (South America), Alps (Europe), Appalachians (North America)
example for block mountains and rift valleys
black forest mountains narmada and tapti
define earthquakes
earthquakes are vibrations caused by disturbances that originate inside the earth that move through earth and its surface
define seismic focus and epicentre
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
define seismograph
seismograph is an instrument that detects and records the intensity of a earthquake
how we refer to the ritcher scale
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
how are tsunamis caused
earthquakes under water
what is a volcano
a volcano is a vent in earth’s crust through which molten rocks and gases erupt
what is magma
magma is molten rock from the mantle that pushes it’s way through cracks towards the surface
what is a magma chamber
a magma chamber is a pool of magma located deep inside earth
what is a crater
a crater is opening at the top of a volconic mountain
what is a volcanic mountain
a volcanic mountain is a cone formed by the lava around the vent. alternating layers of ash and lava
what is the ritcher scale
scale of numbers used to indicate severity of the earthquake
what is a caldera
a lake formed in the crater of a extinct volcano
gradation definition
change in the level of earth’s surface
degradation or erosion definition
activity that reduces the level of the earth’s surface
aggradation
build up of land
meander
loop made by river in its lower course
levee
raised bank of river flowing through flood plain caused by alluvial deposition
mesa
area of resistant rock left after wind erosion of surrounding softer rock
active volcano definition and example
volcanoes that have erupted recently. mt etna mt stromboli of the mediterranean sea
dormant volcanoes definition and explanation
quiet for long time but could erupt soon. Mt vesusius in 79 ce with destrucion of pompeii and herculanean
what is a common feature of dormant volcanoes
their vent is often blocked with a plug of solidifies lava resulting in a violent eruption
extinct volcanoes definition and example
shows no indication of future eruption. Mt Kilimanjaro in Tanzania. no volcano can be called extinct with absolute certainty
weathering definition
breaking up of rock material o the surface of the Earth due to exposure to the atmosphere
erosion definition
further disintegration and and removal of weathered material by agents of gradation is called erosion
in what ways do rivers function as agents of gradation
they erode material, they carry eroded material, they deposit eroded material
what are the stages in a rivers life
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)
features of upper course of river
starts as stream from source
flows fast down steep slopes
mainly erosional
forms narrow gouges or v shaped salleys
middle course features
river joined by tributaries
activities are largely balanced
transports large amounts of eroded materials
features of lower course
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
what is alluvium
alluvium is finely grained deposit from rivers
what are the two ways rivers break up bedrock they flow over?
mechanical erosion and chemical erosion
what are the kinds of valleys formed by rivers and how are they formed?
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
what are waterfalls
when there is a steep drop in the course of a river and the water rushes down with great force it forms a river
what causes an overhang
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
what can be other causes of formation of river
earthquake
what is a plunge pool
when water falls on a surface with great force it erodes rock material causing a depression called a plunge pool
highest and widest waterfalls in the world
angel falls in venezuela is the highest waterfall with fall of almost 1km and victoria falls is the broadest
what features are caused by river erosion
valleys and waterfalls
what features are cause by river deposition
meanders and oxbow lakes
flood plains
deltas
how are meanders formed?
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
what is a flood plain
a flood plain is an almost flat plain that is formed as a result of a river flooding it’s banks
how is a flood plain formed
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
what is a delta
a delta is a triangular alluvial tract formed by sediment deposited by distributaries as the river enters the sea
what is a distributary
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
features of delta
fertile ideal for agricultutre
delta plains are thickly populated
examples of deltas
ganga bramhaputra delta is the largest and one of the richest in the world. nile is also known for its fertility
alternate name for sea erosion
marine erosion
how does marine erosion happen
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
marine deposition result
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
what landforms are created by waves
sea caves, sea arches, wave-cut platforms, cliffs and beaches
how are sea caves formed?
strong waves break and erode material they form hollow caves along the coast
how are sea arches formed
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
what are sea stacks
roof of sea arches erodes pillar is left
what are sea cliffs
vertical and steep rock faces along the shore
what are wave-cut platforms
eroded sea cliffs collapse and move backward leading to formation of gentle sloping surfaces
where is the gradational activity of winds most visible and why
it is most visible in deserts as there is an abundance of loose sand particles
features caused by wind erosion
mesas and mushroom rocks
how is a mushroom rock created?
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
features caused by wind deposition
sand dunes, barchans and loess plains
how are sand dunes created?
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
what are barchans?
barchans are dunes with long gentle slope on the windward side and a steep slope on the leeward sign forming a crescent shape
what are loess plains
when fine sand particles are deposited over very large areas they are called loess plains
what are glaciers
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
what are the two kinds of glaciers
mountain and continental glaciers
how does a glacier play it’s part as an agent of gradation
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.
what are the 2 major landforms formed by glaciers
moraines and cirques
what is a cirque
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
what is a tarn
a tarn is a cirque in which the ice has melted
what are moraines
moraines are deposits of the eroded rock debris that glaciers carry with them that look like a and wall on a now covered mountain
