trying to get unit 5 in my brain

Question 1

what makes plates move

Answer 1

Convection currents takes place in the mantle
heat form the core heats the mantle which therefore rises
this current cools down as it comes closer to the surface of the earth
as a result it moves in a horizontal direction along the bottom of the crust
when the current cools down more the convection current descends and goes towards the core

Question 1

divergent boundaries

Answer 1

at a divergent plate boundary 2 plates move apart from each other
it can be 2 oceanic plates or 2 continental plates
as the plates move apart, faults are formed into ehich rising magma enters
it cools and creates new crust
under oceans this is sea floor spreading and creates mid ocean ridges
ridges are elevated mountain ranges on the ocean floor that consist of rock that is hotter and less dense than the older colder plate
as the plates separate rising hot magma comes to fill the gap and rises to create a ridge
spreading rates are not the same throughout the worlds mid ocean ridge system
slow spreading ridges are fed by small, discontinuous magma chambers
fast spreading ridges are fed by large continuous magma chambers

Question 2

how people found sea floor spreading

Answer 2

the earths magnetic field has different polarity in the different periods of time
lava cooling on the sea floor acquires the polarity of the earths magnetic field at the time of cooling

Question 3

convergent plate boundaries

Answer 3

a convergent boundary is formed where one plate moves underneath the other one
this could be an oceanic plate sub-ducting under a continental plate as it is more dense or an oceanic plate which is older and denser sub-ducting under another oceanic plate which is younger

Question 4

subduction zones

Answer 4

the area where one plates moves underneath another
the denser plate is pushed underneath
the oceanic crust remains cooler and therefore denser than the surrounding mantle for millions of years so subduction continuues and the crust is destroyed
as the earth has not grown, the amount of subduction balances against the new crust created at divergent boundaries
the plate subducting tends to dip at an angle between 30 and 70 degrees
the older the crust the steeper it dips

Question 5

oceanic trenches

Answer 5

ocean trenches are formed at subduction zones
they are long narrow depressions in the ocean floor
most in the pacific
trenches are usually symmetrical with the steepest side towards a landass

Question 6

benioff zones

Answer 6

a narrow zone of deep earthquake foci at a subduction zone
the zone extends from the surface of the ocean trench down
the deeper earthquakes occur further from the subduction zone

Question 7

island arcs

Answer 7

chains of volcanic islands on the continental side of an ocean trench
associated with subduction zones
normally formed when oceanic crust subducts below ocean crust

Question 8

formation of island arcs

Answer 8

the descending plate starts to heat up ans at a depth the rocks are leted to form magma and rise toward the surface
eventually this magma makes its way up into the overrising plate where they add material to the crust and build volcanoes above it
if the upper plate is oceanic the volcanoes pile up until they poke through the surface of the ocean and form an arc

Question 9

types of weathering

Answer 9

mechanical: the action of the physical environemnt which breaks down rock into smaller pieces
chemical: the action of a chemical found in nature that breaks down rock or changes its substance

Question 10

freeze-thaw weathering

Answer 10

all rocks have cracks and joints in them which water gets into
the water will freeze and expand when it turns to ice
it exerts a pressre
this exceeds most rocks resistance and the rocks cracks expand and pieces of the rock around it rack
when the water melts these pieces are broken off the rock
this process repeats again and occurs in environemnts where temperatures fluctatuations are common

Question 11

exfoliation

Answer 11

found in hot desert with a large diurnal range
rocks heat up during the day and the outer layers epxand
rocks then cool and contract at night
that causes the peeling or exfoliation of the rock to occur

Question 12

salt crystallisation

Answer 12

occurs when a saline solution gets into the joints of rocks
when the water evaporates salt crystals are left behind and as temperatures rise the salt expands and exerts a pressure on the rock
this causes the joints to expand and disintegrate
the more porous a rock, the more susceptible to salt crystallisation

Question 13

pressure release

Answer 13

pressure release occurs when overlying rocks are removed by erosion
the underlying rocks then expand as the pressure above them is released
this causes cracking and fractures parallel to the surface
with increasing depth the cracks become smaller

Question 14

carbonation

Answer 14

occurs only on rocks with calcium carbonate in them
rainfall that falls to earth is always slightly acidic as the water has combined with carbon dioxide to make a weak carbonic acid
the mineral calcium carbonate in the rock reacts with the carbonic acid in the water to form calcium bicarbonate
calcium bicarbonate is soluble and is therefore removed by the peroclating rain water which breaks down the rock

Question 15

hydrolysis

Answer 15

occurs only on rocks with the mineral feldspar in them
acidic water reacts with the feldspar to form kaolin, silicic acid and potassium hydroxyl
the acid and hydroxly are removed by the water solution leaving kaolin behind as an end product

Question 16

hydration

Answer 16

the clay minerals in shales and mudstones absorb water
these minerals expand as they absorb water
the volume of the shales and mudstones can then increase
this causes cracking and breaking down of the rock

Question 17

oxidation

Answer 17

occurs only on rocks containing iron minerals
dissolved oxygen in both the soil and the air react with the iron minerals in rocks to oxidise and become iron oxide
this iron oxide remains in soils or rocks as a reddish brown coating or in waterlogged areas can be removed in solution

Question 18

factors affecting the rate and type of weathering

Answer 18

climate
rock type
rock structure

Question 19

how climate affects weathering

Answer 19

the wetter and more humid the climate, the deeper and more intense the weathering becomes

Question 20

how rock type affects weathering

Answer 20

minerals are the chemicals that form the rocks
some minerals are more resistant to weathering than others

Question 21

grain size

Answer 21

the bigger the grains or crystals that make up the rock, the faster the rate of weathering
this is because they have a large void space and therefore high permeability so water can enter them more easily

Question 22

lines of weakness

Answer 22

natural cracks in rocks are lines of weakness
they allow water to penetrate the rocks and increase the effects of weathering
these joint patterns create differential resistance within the same rock type

Question 23

porosity and permeability

Answer 23

porosity is a measure of how much of a rocks volume is open space
this can be between grains or within cracks or cavities of the rock
permeability is a measure of the ease with which water can move through a porous rock
the more permeable the rock, the more it can be weathered

Question 24

slope

Answer 24

refers to an inclined surface or hill slope
it is the area between a watershed and the base of the slope
slope form is the shape of the slope in cross section
slope evolution is the development of slopes over time
slope processes are the activities acting on the slopes

Question 25

the slope system

Answer 25

slopes are open systems
inputs are energy from the sun and mass
outputs are energy and mass
regolith is the unconsolidated material on top of the rock
some factors occur on the outside (exogenetic) or inside (endogenetic)

Question 26

climate slope control

Answer 26

humid areas-slopes are rounder due to chemical weathering
arid areas–slopes are more jagged due to more mechanical weathering

Question 27

geological structure and rock type slope control

Answer 27

faults create lines of weakness and therefore instability in a slope and can create steep valley sides
rock type can affect a slopes vulnerability to weathering
vulcanicity can cause igneous intrusions which when exposed create steep slopes

Question 28

regolith and soil slope control

Answer 28

deep regolith can mean slope instability
regolith with high percentage of sand can cause slope failures

Question 29

aspect slope control

Answer 29

aspect is the direction a slope faces
south slopes were often in shade
north slopes faced south and therefore had cycles of freeze thaw increasing weathering and altering slope

Question 30

vegetation slope control

Answer 30

vegetation can decrease overland runoff and reduce erosion of a slope
vegetation can increase landslips as build up of soil between trees deepens regolith and therefore increase potential for failure of the slope

Question 31

mass movements

Answer 31

large-scale movements of the earths surface that are not accompanied by a moving agent such as a river glacier or ocean wave
mass movements occur because of slope failure when gravity acts to move the material downwards and the resistance of the slope is not strong enough

Question 32

falls

Answer 32

movements of rocks/debris under the effect of gravity

Question 33

flows

Answer 33

movements of a mass of soil or rock that contain a significant amount of water

Question 34

heaves

Answer 34

slow movements of material up to the surface of a slope and down slopes

Question 35

slides

Answer 35

an entire mass of material moving along a slip plane

Question 36

classification by speed and water content

Answer 36

wettest fastest movement is a mudflow
slowest driest movement is a soil creep

Question 37

soil heave/creep

Answer 37

very slow and small scale process
occurs mainly in winter
individual soil particles are pushed to the surface by wetting, heating or freezing of water

Question 38

talus creep

Answer 38

slow movements of fragments on a scree slope

Question 39

rock falls

Answer 39

falls occur on steep slopes
on bare rock faces where joints are exposed they are more common
normally causing by weathering and once the rocks are detached they fall under the influence of gravity
if the fall is short it produces straight scree
if it is long it forms a concave slope

Question 40

slides

Answer 40

occurs when an entire mass of material moves along a slip plane
they occur where there is a combination of weak rocks and steep slope and undercutting
as the slide moves along the slip plane it tends to retain its shape and structure until it hits the bottom of the slope
slip planes occur at fault lines along a bedding plane and at the junction of 2 layers
rock slides are when a huge volume of rock moves together
landslides include rock, stones and soil

Question 41

slumps and flows

Answer 41

slumps occur on weaker rocks
this is often rotational along a curved slip plane
clay absorbs water and becomes saturated and exceeds its liquid limit
it then flows along a slip plane
this can be due to the undercutting at the base of a cliff
flows are more continuous and less jerky

Question 42

avalanches

Answer 42

rapid movements of snow down a slope
they are common in mountainous areas
new snow can fall over older snow
or partially melted snow moves
they occur on slopes over 20 degrees
they also occur on north facing slopes where the lack of snow limits snow stability

Question 43

causes of mass movements

Answer 43

likelihood is its safety factor
this is the relative strength/resistance of the slope compared with the force that is trying to move it
for slope failure to occur there needs to be a reduction in shear strength or an increase in shea stress

Question 44

factors increasing shear stress

Answer 44

removal of lateral support
removal of underlying support
loading of a slope
transient stresses
lateral pressure

Question 45

factors reducing shear strength

Answer 45

changes of rock structure
weathering
changes in porewater level
removal of vegetation which previously bound the soil
borrowing of animals, decay of plant roots

Question 46

the human impact

Answer 46

quarrying
mining
pollution
acid rain
dumping of material

Question 47

terracing

Answer 47

cuts steps into the profile of a slope
can also stabilise an entire hillside
the steep slopes between the steps can become less stable

Question 48

buidling a dam

Answer 48

can destabilise the slopes surrounding the reservoir as they are cut to create it
it changes their shape
loading the valley with water can also destabilise slopes

Question 49

road cutting

Answer 49

create an artificial valley with steep slopes on either side
these can be unstable

Question 50

deforestation

Answer 50

can cause soil erosion and less binding of soil leading to slides or flows
can increase CO2 levels in the atmosphere increasing the carbonation of limestone

Question 51

adding lighting

Answer 51

encourages the growth of plants and can increase biological weathering

Question 52

soil erosion

Answer 52

soil is eroded away changing the shape of the slope and the area is destabilised leading to slides and flows

Question 53

foundations

Answer 53

material is removed to make a flat area to put solid concrete
changes slope form

Question 54

mining

Answer 54

surface mining leads to the removal of overburden to reveal the mineral below
this changes the height of a slope
underground mining can lead to small depressions appearing on the surface of the land
this can lead to instability and collapse

Question 55

quarrying

Answer 55

excavating large areas to use the rock creates dips in the landscape devoid of soil and vegetation
slopes either side of quarries can have landlsides

Question 56

urban areas

Answer 56

increased temperatures in urban areas have led to increased chemical weathering rates

Question 57

heaps of material

Answer 57

after material is removed during mining and quarrying it is often piled into a heap
these can be very unstable as they are unconsolidated masses

Question 58

global warming

Answer 58

CO2 additions have increased temperatures leading to increase rates of chemical weathering
carbonation relies on CO2 and so this will increase also

Question 59

release of gasses

Answer 59

high rates of acid rain and cry acid deposition increase corrosion of buildings and structures