Hazards 1- Geophysical systems

Question 1

Explain continental drift

Answer 1

-The Earth’s crust is made of a number of large and smaller plates.

-These plates are in constant motion, a process called continental drift.

-The plates move at very slow speeds (2-5cm a yr).

-Over millions of years the Earth’s continents come together & separate.

-There are 3 key factors that drive plate movement.

Question 2

What are the three key factors that drive plate movement?

Answer 2

-Internal heating and convection currents

-Subduction and rifting at plate margins

-Mantle plumes and hot spots

Question 3

What is the inner core of the Earth made of?

Answer 3

Iron and nickel

Question 4

What is the temperature in the inner core?

Answer 4

It ranges from 5,000-7,000 °C

Question 5

How has the heat from the inner core been generated?

Answer 5

-The heat from the inner core has been generated from the great frictional forced that occurred through the Earth’s formation, as well as through radio-active decay of elements.

-It generates 44 trillion watts of heat which flows away from the core to the mantle.

Question 6

Explain convection currents

Answer 6

-In the mantle is behaves like a viscous liquid ( it has phases of liquid & solid consistency under pressure).

-When the convection cells make contact with the base of the crust, they cause friction & drag the crust along in the general direction of the convection.

Question 7

Diagram of internal heating and convection currents

Answer 7

Question 8

Explain ridge push

Answer 8

-At rift zones ( constructive/divergent boundaries) the crust is moving apart under tensional stresses.

-This reduces pressure on the asthenosphere ( lower part of mantle), allowing magma to rise into the lithosphere ( crust & upper mantle- tectonic plates) creating new oceanic crust.

-As it moves away from the ridge it cools, solidifies and sinks creating a slope, enabling further movement.

Question 9

Explain subduction and slab pull

Answer 9

-At destructive plate boundaries, denser oceanic plate is subducted under the less dense continental plate e.g. at deep ocean trenches, volcanic activity 100km from the plate boundary on the continental side, and earthquake focal points as deep as 700km along the Benioff zone.

-As a slab of oceanic plate descends, it pulls ( perhaps with some suction) the rest of the plate with it.

Question 10

Diagram of ridge push and slab pull

Answer 10

Question 11

How many massive mantle plumes are there in the Earth’s mantle?

Answer 11

Two

Question 12

What are the two massive mantle plumes in the Earth’s mantle layer

Answer 12

One is centred under the Pacific plate and the other under the African plate.

Question 13

Explain how hot spots are created

Answer 13

-Molten viscous silicate material rises from the outer core/mantle boundary to about 700km beneath the lithosphere ( crust).

-From these mantle plumes, small hot spots are created where magma rises through the asthenosphere and sometimes breaks through the crust.

-Isolated hotspots occur where there is an upselling of molten material directly from the outer core/mantle boundary to the surface e.g. Hawaiian islands.

Question 14

What is a flood basalt?

Answer 14

The result of a giant volcanic eruption or a series of eruptions which covers large stretches of land or ocean floor with basalt lava.

Question 15

Diagram of a hot spot and flood basalts

Answer 15

Question 16

Explain what evidence of mantle dynamics has revealed about how plates move

Answer 16

-Evidence of mantle dynamics from sources such as seismic tomography have allowed us to develop our understanding of the mechanisms that move plates.

-It seems, rather than being carried passively like rafts on huge convections cells in the mantle, that the plates themselves appear to be the main cause of the convection system in our plantet.

-Mantle convection not only includes the plates, but is primarily driven by them.

Question 17

Explain how plates move by ridge push and slab pull

Answer 17

-The loss of heat from the lithosphere over time causes it to eventually become cold and dense enough to have negative bouyancy.

-This allows it to sink into the warmer and more ductile asthenosphere.

-This drags the surface plates by slab pull, which appears to be the main force responsible for plate movement.

-This, in turn, creates tension forces elsewhere on the plate (e.g. the Mid-Atlantic Ridge), thinning it and causing passive convection upwelling of the hotter mantle rock in response to the movement of the plates above (the convection seems to be an induced upwelling).

-This forms the ridge that slides away laterally as it cools, pushing the plates apart by ridge push and contributing to the process of slab pull to move the plates.

-This solid but ductile rock of the atmosphere does flow, but the movements there seem to be mostly induced by the movements of the plates (like how a paddle pushes water around as it moves through the water).

Question 18

Diagram explaining slab pull and ridge push

Answer 18

Question 19

Diagram explaining mantle dynamics

Answer 19

Question 20

Diagram of how islands move

Answer 20

Question 21

How many different types of plate margins are there?

Answer 21

Four

Question 22

What are the four types of plate margins?

Answer 22

-Constructive

-Conservative

-Destructive

-Collision

Question 23

Explain how constructive (divergent) plate margin works

Answer 23

-At adivergent plate boundary- also known as a constructive plate boundary, the plates move apart from one another.

-When this happens, the magma from the mantle rises up to make (or construct) new crust.

-The movement of the plates over the mantle can cause earthquakes.

-Rising magma can also create shield volcanoes.

-Landforms at a divergent plate boundary includeocean ridges,rift valleys, and shield volcanoes.

Question 24

What landforms form at a constructive plate boundary?

Answer 24

-Ocean ridges

-Rift valleys

-Shield volcanoes

Question 25

Give examples of constructive plate margins

Answer 25

-Ocean ridges, eg the Mid-Atlantic ridge (where the Eurasian plate and the North Atlantic plate are moving apart from each other under the Atlantic Ocean) -Rift valleys eg the East African Rift Valley

Question 26

Explain how conservative boundaries work

Answer 26

-At conservative plate margins, fault lines will be formed. -These are plate boundaries where two plates are either slipping past each other in opposite directions or at different rates in the same direction. -The plates do not move past each other smoothly. -There will often be a build-up of friction or energy that is ultimately released as an earthquake.

Question 27

Give an example of a conservative plate margin

Answer 27

The San Andreas Fault, where the Pacific and the North American plates are sliding past each other.

Question 28

Explain how destructive plate margins work

Answer 28

-As the plates collide, the oceanic plate is forced beneath the continental plate. -This is known as subduction and results in the formation of an ocean trench. -This happens because the oceanic plate is denser (heavier) than the continental plate. -When the plate sinks into the mantle it melts to form magma. -The pressure of the magma builds up beneath the Earth's surface. -The magma escapes through weaknesses in the rock and rises up through a composite volcano, also known as a stratovolcano. -The volcanic eruptions are often violent, with lots of steam, gas, and ash.

Question 29

Explain how collision boundaries work

Answer 29

-Collision zones form when two continental plates move towards each other and collide. -The land between the plates is forced upwards to form fold mountains, eg The Alps and Himalayas.

Question 30

Give examples of collision boundaries

Answer 30

The Alps and Himalayas

Question 31

Diagram of a constructive plate margin

Answer 31

Question 32

Diagram of a conservative plate margin

Answer 32

Question 33

Diagram of the San Andreas Fault

Answer 33

Question 34

Diagram of a destructive plate margin

Answer 34

Question 35

Diagram of a collision plate margin

Answer 35

Question 36

What are the different types of volcanoes?

Answer 36

-Composite -Shield -Cinder cone

Question 37

Where do volcanoes form?

Answer 37

-Destructive and constructive plate margins -Above hot spots

Question 38

Where are composite volcanoes found

Answer 38

On destructive plate margins, where the oceanic crust sinks beneath the continental crust.

Question 39

Explain how composite volcanoes form

Answer 39

-At destructive plate margins, the oceanic crust sinks beneath the continental crust. -Magma rising from the deep boundary has plenty of time to pick up silica-rich components.

Question 40

What are the characteristics of composite volcanoes?

Answer 40

-Acidic lava, which is very viscous (sticky). -Steep sides as the lava doesn't flow very far before it solidifies. -Alternate layers of ash and lava. For this reason, they're also known as stratovolcanoes. Strato means layers. -Violent eruptions. -Longer periods between eruptions.

Question 41

Diagram of a composite volcano

Answer 41

Question 42

Where are shield volcanoes found?

Answer 42

-On constructive plate margins, where two plates move away from one another. -They also often form in oceans, where the oceanic crust is thinner.

Question 43

Explain how shield volcanoes form

Answer 43

-On constructive plate margins, two plates move away from one another. -They also often form in oceans, where the oceanic crust is thinner. -The magma thus doesn’t have far to travel and has less time to change its composition to become silica-rich.

Question 44

What are the characteristics of shield volcanoes?

Answer 44

-Basic lava, which is non-acidic and very runny -Gentle sides as the lava flows for long distances before it solidifies -No layers, as the volcano just consists of lava -Less violent eruptions -Shorter periods between eruptions

Question 45

Diagram of a shield volcano

Answer 45

Question 46

What type of volcano is Mauna Loa (Hawaii) and where was it formed?

Answer 46

It is a shield volcano, but was formed over a hot spot, rather than at a constructive plate margin, like other volcanoes.

Question 47

Explain how cinder cone volcanoes form

Answer 47

-They form when runny, low silica magma contains a lot of dissolved gas. -The gassy eruptions explode and sputter like soda spraying from a can. -They issue loose volcanic fragments called cinders which settle and pile in conical shapes.

Question 48

Diagram of a cinder cone volcano

Answer 48

Question 49

Diagram of the three types of volcanoes

Answer 49

Question 50

What are the different types of volcanic eruptions?

Answer 50

-Effusive -Explosive

Question 51

What does the explosivity of an eruption depend on?

Answer 51

Two main factors: -How much silica (SiO2) and how many bubbles of gas there are in the magma.

Question 52

What is the effect of silica on the viscosity of magma?

Answer 52

It increases the viscosity (makes it less runny), trapping bubbles of gas in the magma, which increases pressure and leads to a more explosive eruption.

Question 53

Explain how effusive eruptions occur

Answer 53

-These occur when magma has a low silica content and therefore low viscosity. -They usually cause few hazards the gas emissions from larger eruptions can affect climate (?) -Effusive eruptions form shield volcanoes, which are typically large, round, and low-lying structures. -Effusive volcanoes do not produce ash, so the volcano is just made of lava. -These eruptions take place at divergent plate boundaries and in the middle of plates.

Question 54

Where do effusive eruptions occur?

Answer 54

At constructive plate boundaries and in the middle of plates.

Question 55

What do effusive eruptions form?

Answer 55

Shield volcanoes

Question 56

Explain how explosive eruptions occur

Answer 56

-Volcanoes with a high silica and gas content are explosive. -They are very hazardous, producing ash (small fragments of broken rock), pyroclastic density currents (hot clouds of gas and rocks that flow down the sides of the volcano), and lahars (cement-like mixtures of water and hot ash. -Explosive eruptions create composite volcanoes, build up of repeated layers of ash and lava over multiple eruptions. -These eruptions take place at convergent plate boundaries.

Question 57

Where do explosive eruptions occur?

Answer 57

At destructive plate boundaries.

Question 58

What do explosive eruptions create?

Answer 58

Composite volcanoes.

Question 59

Table comparing the type of plate margin (constructive vs. destructive) to the nature of the activity

Answer 59

Question 60

What is a secondary hazard?

Answer 60

The indirect effects that result from the main (primary) impact of a hazard.

Question 61

Give examples of secondary hazards

Answer 61

-Lahars -Flooding

Question 62

What are lahars?

Answer 62

Fast mud flows that occur when the rain mobilises deposits of volcanic ash.

Question 63

What is tephra?

Answer 63

-Fragmented magma produced during a volcanic eruption. -It includes ash, cinders, and volcanic bombs

Question 64

How do lahars form and why are they dangerous?

Answer 64

-When tephra mixes with water (either as it melts snow that might be on top of a volcano or as it mixes with rain water), it produces deadly mudflows called lahars. -These flow very fast and can have temperatures close to boiling. -They can also travel 1os of km away from a volcano. -Their consistency is like wet cement and they can bury infrastructure. -There can be a risk of secondary lahars months and years after an eruption has occurred, as deposited tephra may mix with subsequent rainfalls, triggering mudflows.

Question 65

Why are gases from a volcano dangerous?

Answer 65

-If volcanic gases build up to dangerous levels, they can be a risk to people if they are suddenly released in what is called a limnic eruption. -There are fears of such as release from Lake Kivu beside Nyiragongo should an earthquake stir up the lake waters.

Question 66

Explain how lava flows form

Answer 66

-The more viscous lava of composite volcanoes tends not to flow too far or too fast, so it is typically confined to within 5km of the volcano. -This means that few lives are lost from lava at these volcanoes. -However, where lava is less viscous at shield or fissure eruptions, it can travel many kilometers from its source. -Although people generally have time to evacuate, any immovable infrastructure will be destroyed and perhaps buried under the lava flows.

Question 67

Explain how pyroclastic flows occur and why it's dangerous

Answer 67

-If the tephra is denser than air, it will flow downhill as a pyroclastic density current, forming a hot (hundreds of degrees), fast flow of volcanic ashes. -When it hits buildings, it can destroy them due to its heat and force. -People and animals caught within it can be severely burned and even killed. -As PDCs flow downhill, they send to follow river valleys and are therefore more directional in their impacts. -However, less dense PDCs can overtop topographical barriers. -They are typically contained within 5-10 km of the volcano, but this can reach some of the villages that may be on the lower slopes of volcanoes.

Question 68

Explain how ash plumes form (check)

Answer 68

-An ash column may rise many kilometers into the atmosphere due to its force and buoyancy. -Ash can then spread far (10s to 100s of km, following the prevailing wind direction). -At height, it can disrupt air travel as ash is very dangerous to aircraft engines. -As the ash cools, it can fall to the cround.

Question 69

What are the negative impacts of ash falling to the ground as it cools?

Answer 69

-It covers infrastructure and can cause buildings to collapse (especially if rain follows, increasing its weight). -Vegetation and crops get destroyed. -Water supplies can be contaminated. -Breathing difficulties for locals (e.g. those with asthma). -Major challenges with clean-up post-eruption.

Question 70

What are the types of lava?

Answer 70

-Pahoehoe- smooth, billowy, has a low viscosity, and travels slowly. -A’A lava – rougher in appearance, has a higher viscosity, and carries lava blocks called clinkers.

Question 71

Why do risks from hazards vary?

Answer 71

-Location – hotspots are localized, so the risk is over a smaller area, whereas at plate margins the risks are over a larger area. Destructive – violent & explosive, whereas constructive basaltic & runny. -Secondary hazards – tsunami, lahar. -Rural or urban location -Magnitude & frequency – active or dormant.

Question 72

Describe the earthquakes at constructive margins

Answer 72

-Small earthquakes -Shallow -Not much friction or strain as plate diverge

Question 73

Describe the earthquakes at conservative (transform) margins

Answer 73

Have a large amount of friction and when the strain is released the shockwaves can be strong.

Question 74

Describe the earthquakes at destructive margins

Answer 74

-Create largest amount of friction and strain, with earthquake focal points following the Benioff zone to considerable depths. -Low frequency.

Question 75

Explain how earthquakes occur

Answer 75

-Earth’s crust is mobile, a build-up of stress within the rocks can take place. -When this stress is suddenly released ( where the strain overcomes the elasticity of the rock), parts of the surface experience an earthquake. -Much of the energy is transferred vertically to the surface and then moves outwards from the epicentre as seismic waves. -At the moment of fracture, rocks may regain their original shape but in a new position.

Question 76

What are the types of seismic waves?

Answer 76

-P waves (primary) -S waves (secondary) -L waves (love)

Question 77

Describe P (primary) seismic waves

Answer 77

-Fastest, though they cause the least damage. -Pushes & pulls in the direction of travel ( compresses). -Can move through solid rock & liquids.

Question 78

Describe S (secondary) seismic waves

Answer 78

-Shakes the ground violently. -Up and down movement. -Only moves through solid rock.

Question 79

Describe L (love) seismic waves

Answer 79

-Travel only across the surface -Have a large amplitude and cause significant damage, including fracturing the ground. -Moves from side to side ( horizontal) as moves forward.

Question 80

Diagram of the different types of seismic waves (seismogram)

Answer 80

Question 81

What are the different types of stress and fault? (earthquakes)

Answer 81

-Tensional stress -Compressional stress -Shear stress

Question 82

Where does tensional stress occur?

Answer 82

At constructive plate boundaries

Question 83

Where does compressional stress occur?

Answer 83

At destructive plate boundaries

Question 84

Where does shear stress occur?

Answer 84

At conservative plate boundaries

Question 85

Diagram of the types of faulting

Answer 85

Question 86

What is an earthquake?

Answer 86

An intense ground-shaking motion that lasts for a few seconds.

Question 87

What is the epicenter?

Answer 87

The point on the Earth's surface directly above the focus of an earthquake

Question 88

What is the focus?

Answer 88

The point below the Earth's surface where an earthquake occurs.

Question 89

What is the depth of focus for shallow and deep earthquakes?

Answer 89

-Shallow earthquakes (0-70km) (75% of all energy released) cause the most damage. -Deep ( 70-300km) and very deep ( 300-700km) earthquakes have much less effect.

Question 90

The human causes of earthquakes tend to cause ___ earthquakes

Answer 90

Low-magnitude

Question 91

What are the human causes of earthquakes?

Answer 91

-Mining activities -Fracking -Dam-building

Question 92

How can mining activities cause earthquakes?

Answer 92

They disturb the rock structure and the use of dynamite and heavy machinery can cause earthquakes.

Question 93

How can fracking cause earthquakes?

Answer 93

Fracking involves the removal of gas from shale rock and injection of fluids that loads stress into faults.

Question 94

How can dam-building cause earthquakes?

Answer 94

This adds significant weight and load to faults.

Question 95

What is the difference between primary and secondary hazards (earthquakes)?

Answer 95

A primary hazard is directly linked to seismic wave energy; a secondary hazard is a consequence of the ground shaking.

Question 96

What are the primary hazards associated with earthquakes?

Answer 96

-Crustal fracturing -Ground shaking

Question 97

Explain how crustal fracking is a primary hazard associated with earthquakes

Answer 97

-Shockwaves travel fast through solid rock and can increase stress in it, especially if rock types of different. -Stress causes strain until rock fractures. -Faults can rupture the surface & cause subsidence or uplift.

Question 98

Explain how the ground shaking is a primary hazard associated with earthquakes

Answer 98

-3 types of waves. -Can happen in less than 60 seconds. -Buildings may only be able to survive some types of shaking & will be damaged.

Question 99

What are the secondary hazards associated with earthquakes?

Answer 99

-Landslides -Liquefaction

Question 100

Explain how landslides are a secondary hazard associated with earthquakes

Answer 100

-This happens especially in mountainous areas e.g. Nepal. -It loosens rock and causes it to move down a slope. -It can hit settlements and block transport.

Question 101

Explain how liquefaction is a secondary hazard associated with earthquakes

Answer 101

-This is where the ground consists of loose sediments of silts and sands and gravels which are waterlogged. -Earthquakes compact the sediments and force the water to the surface, undermining buildings & roads.

Question 102

Diagram of soil liquefaction

Answer 102

Question 103

Diagram of a tsunami in the deep ocean and approaching shore

Answer 103

Question 104

How are most tsunamis generated?

Answer 104

By submarine earthquakes at subduction zones.

Question 105

Explain how tsunamis form and what their key features are

Answer 105

-The sea bed is displaced vertically – this motion displaces a large volume of water in the ocean column, which then moves outwards from the point of displacement. -They have a long wavelength when they are out at sea ( over 100km) -They are short in amplitude at sea, 1m in height, and barely noticeable. -Travel quickly at 700kph -When they reach land – rapidly increase in height +25m -Often preceded by a localized drop in sea level (drawback), as water is drawn back and then up. -Hit the coastline as a series of waves – more like a flood.

Question 106

What is mass movement?

Answer 106

The downwards movement of material down a slope.

Question 107

What is unconsolidated material?

Answer 107

Rock fall, avalanche.

Question 108

What is consolidated material?

Answer 108

Rotational slumps/landslides

Question 109

What factors affect the stability of a slope? (check this)

Answer 109

-Gravity – the steepness of the slope -Shear structure – structure & stability of the slope, preventing movement. -Shear stress – forces acting to reduce slope stability & lead to movement. -If shear stress is greater than shear structure & gravity & the angle of the slope is sufficient = mass movement.

Question 110

When does mass movement happen?

Answer 110

If shear stress is greater than shear structure & gravity & the angle of the slope is sufficient.

Question 111

Diagram of how mass movement happens

Answer 111

Question 112

What physical factors affect the speed of mass movement?

Answer 112

-The gradient/slope -Prolonged rainfall

Question 113

How does the gradient/slope affect the speed of mass movement?

Answer 113

It influences the effect of gravity & how fast the material moves.

Question 114

How does prolonged rainfall affect the speed of mass movement?

Answer 114

-This will saturate the soil and accelerate soil movement on a slope. -Water acts as a lubricant, causing greater instability. -Water enters the pores between the particles, forcing them apart, and preventing them from binding.

Question 115

Diagram of dry, moist, and saturated soil

Answer 115

Question 116

How can human activity impact shear stress? (check whether increase or decrease)

Answer 116

-E.g. deforestation, house & road construction -Tree roots bind the soil together and increase shear strength -They also reduce pore water pressure through infiltration. -Infrastructure can add weight to a slope, causing shear stress. -Water infiltration may also be disturbed.

Question 117

Annotated pictures of the effect of human activity on shear strength

Answer 117

Question 118

Table showing what factors contribute to shear strength

Answer 118

Question 119

Triangle diagram of the types of mass movement (check(

Answer 119

Question 120

Diagram showing how mass movements differ with wetness and speed

Answer 120

Question 121

Explain how fast mass movement occurs

Answer 121

-A rock fall begins as a rock becomes separated from the bedrock. -As it falls, it can set in motion an unconsolidated movement, as one rock knocks into another. -Topples occur where the strata of the rock are unstable in their alignment to the angle of slope.

Question 122

Diagram showing falls and topples in mass movement

Answer 122

Question 123

Diagram showing flows in mass movement

Answer 123

Question 124

Diagram showing slides in mass movement

Answer 124

Question 125

Explain what debris flows are

Answer 125

-A geological phenomenon in which water-laden masses of soil and fragmented rock rush down mountainsides, funnel into stream channels, entrain objects in their paths, and form thick, muddy deposits on valley floors. -They generally have bulk densities comparable to those of rock avalanches and other types of landslides (roughly 2,000 kilograms per cubic meter), but due to widespread sediment liquefaction caused by high pore-fluid pressures, they can flow almost as fluidly as water.

Question 126

Explain what slides are (mass movement)

Answer 126

-These are a very common form of mass movement and can be divided into rotational and transnational slides, which can be subdivided further depending on the structure of the soil and rock and whether it is consolidated or not. -Rotational slumps occur when a slump block, composed generally of loosely consolidated sediments, slides along a slip plane. -Translational slumps follow a more linear axis of slip. -Rotational slumps have several characteristic features. -The slip plane is concave in its shape.