plate tectonics and volcanoes Flashcards
1
Q
what is the earth divided into?
A
- crust
- mantle
- inner core
- outer core
2
Q
what is the crust?
A
- this is the outer layer of the earth which is mostly made of oxygen and silicon and is 0-100km thick
- it is split into a thin layer of dense basalt that is found under the oceans and a thicker layer of less dense granite rock that makes up the continents
3
Q
what is the core and what is it split into?
A
- the core is made up of dense rocks containing iron and nickel alloys and is a solid because of pressure
- it is subdivided into a solid inner core and a very hot molten ( liquid ) outer core with a temperature of over 5000 degrees
4
Q
what is the mantle?
A
- the thickest layer made of molten and semi-molten rock that is rich in iron and magnesium
- has a depth of 2900km and around 1000-3500 degrees
- the part of the mantle nearest the core is quite rigid and the very top is rigid
5
Q
what is the asthenosphere?
A
- this is a semi-molten mantle that lies below the lithosphere, at depths between 100 and 700 km
- it acts plastically, meaning it can move and deform very slowly
6
Q
what is the lithosphere?
A
the rigid uppermost part of the mantle and the crust together
7
Q
what are the two types of crust?
A
- continental crust
- oceanic crust
8
Q
what are the features of a continental crust?
A
- this is the thicker crust ( 30-70km )
- older ( 1500 millions years )
- lighter ( 2.6 g/cm3 )
- mainly made up of granite, silicon, aluminium and oxygen
9
Q
what are the features of an oceanic crust?
A
- thinner crust ( 6-10 km )
- younger ( less than 200 million years old )
- heavier ( 3 g/cm3 )
- mainly made of basalt, silicon, magnesium and oxygen
10
Q
what is the theory of continental drift?
A
this theory was introduced by Alfred Wegener and stated that at one point in time, all of the continents were joined together as one large mass of land, then spread apart and drifted apart into their current positions
11
Q
what evidence did Alfred Wegener have for continental drift?
A
- the distribution of ancient fossils, rocks and mountain ranges matched across different continents e.g. South Africa and North America
- he used the location of ancient climate zones, such as glaciation, as he found grooves that when matched with different continents, fit perfectly e.g. South America, Antarctica and India
12
Q
why wasn’t Alfred Wegener initially believed?
A
as Wegener couldn’t provide evidence for the physical processes of the continents, moving through the oceanic crust and mantle, as he stated they ‘could move’ but not how
13
Q
define a tectonic plate
A
one of a series of rigid sections of the earths crust that float on the upper mantle and move relative to one another
14
Q
what is plate tectonic theory and what evidence supports it?
A
- the theory that states that the earths crust is made up of several rigid plates moving relative to one another
- the mid-Atlantic ridge provides evidence for plate tectonics as the polarity of the rock either side of the ridge was alternated in a striped pattern- that was mirrored on each side of the ridge
15
Q
what is paleomagnetism?
A
- paleomagnetism happens approximately every 100,000 years and the rock containing iron particles is made of liquid, this allowing the iron to orientate itself from north to south
- on the mid-oceanic ridge volcanoes will form providing lava
- as tectonic plates diverge, the magma rises which then cools and condenses to form new crust
- overtime the new crust is dragged apart and even more new crust forms between it pushing older crust further away from the mid-Atlantic ridge
16
Q
what is sea floor spreading?
A
- this is when more crust is being created due to new volcanoes
- this means that the distance between continents is increasing at a rate of a few centimetres per year
17
Q
what are the 3 main causes of plate movement?
A
- convection currents
- slab pull
- ridge push
18
Q
what are convection currents?
A
- these are circular movements of semi-molten rock and occur when:
- the earths mantle is hottest close to the core, so lower parts of the asthenosphere heat up and become less dense and slowly rise
- as they move towards the top of the asthenosphere they cool down and become more dense and slowly sink
- these circular convection currents create drag on the base of the tectonic plates, causing them to move
19
Q
what is slab pull?
A
- slab pull happens at destructive plate boundaries when the colder, denser oceanic plate sinks into the mantle
- gravity then pulls the whole plate into the mantle and this force that the sinking edge exerts is slab pull
20
Q
what is ridge push?
A
- ridge push happens at the constructive plate margins when magma rises to the surface and forms new crust which is very hot, and heats the surrounding rocks which expands and rises above the surface
- the new crust cools and becomes denser
- gravity acts on this older, denser lithosphere causing it to slide away from the ridge, down the sloping, semi-molten asthenosphere below
- the occurrence of shallow earthquakes from the tearing apart of the newly formed crust, indicates that there is some frictional resistance to this force
21
Q
what are the three main types of plate margins?
A
- constructive plate ( divergent )
- destructive plate ( convergent )
- conservative plate
22
Q
what happens to the plates at a constructive margin?
A
at this margin the two plates move apart from each other ( diverging )
23
Q
how are volcanoes formed at a constructive plate margin?
A
- the mantle is under pressure from the plates above, when they move apart the pressure is released at the margin
- the release of pressure causes the mantle to melt producing magma
- the magma is less dense than the plate above so it rises and can erupt to form a volcanoe
24
Q
how are earthquakes formed at a constructive plate margin?
A
- the plates don’t move apart in a uniform way - some parts move faster than others
- this causes pressure to build up and when the pressure becomes too much the plate cracks making a fault line, causing an earthquake
25
what 2 landforms are created at the constructive plate margin?
- ocean ridge
- rift valley
26
how is an ocean ridge formed?
- at constructive plate margins, plates are moving away from one another and the lithosphere is created
- under the oceans, this has produced an extensive ocean ridge system comprising of underwater volcanoes that stretch for nearly 65,000 km and most of them lie at an average depth of 2,500 metres
- some examples are the mid Atlantic ridge and the east pacific rise
27
how is a ridge valley formed?
- where plates diverge beneath land, rising magma causes the continental crust to bulge and fracture, forming fault lines
- as the plates keep moving apart, the crust between parallel faults drop down to form a rift valley e.g. east African rift system that stretches from Mozambique to the red sea
- volcanoes are found around rift valleys e.g. mount Kilimanjaro and mount Kenya are volcanoes in the east African rift system
28
what happens to the plates at a destructive plate margin?
at this margin the two plates move towards each other ( converging )
29
what three plate movements happen at the destructive plate margin?
- oceanic continental
- oceanic oceanic
- continental continental
30
what landforms are created at the oceanic-continental?
- deep sea trench
- fold mountains
- volcanoes
- earthquakes
31
how are deep sea trenches formed?
- this is where the continental crust and oceanic crust converge, the more dense oceanic crust is forces under the less dense continental crust e.g. Mariana trench
32
how are fold mountains formed at the destructive plate margin?
- formed when the plates meet
- they're made up of sediments that have accumulated on the continental crust, which are folded upwards along the edge of the continental crust
33
how are volcanoes formed at the destructive plate margin?
- the oceanic crust is heated by friction and contact with the upper mantle, which melts into magma
- the magma is less dense than the continental crust and will rise back to the surface to form volcanoes
34
how are earthquakes formed at the destructive plate margin?
- as one plate moves under the other they can get stuck
- this causes pressure to build up
- when the pressure becomes too much the pates jerk past each other, causing an earthquake
35
what happens at the oceanic oceanic crust?
- two plates of oceanic crust are moving towards each other, the denser of the two will be subducted forming a deep sea trench and triggering earthquakes and volcanic eruptions
- volcanic eruptions that take place underwater create island arcs, which are clusters of islands that sit in a curved line
36
what happens at the continental continental crust?
- where two plates of continental crust move towards each other, neither is subducted so there are not any volcanoes but the pressure build up between them can cause earthquakes
- fold mountains form when continental crusts converge e.g. the Himalayas
37
what happens to the plates at the conservative plate margin?
- at this margin the two plates move past each other
- the two plates get locked in place and pressure builds up, releasing the energy as an earthquake
- e.g. the pacific plate is moving past the north American plate causing many earthquakes along it's fault line e.g. the San Andreas fault in California
38
what is a magma plume / hot spot?
a vertical column of extra-hot heat that rises up from the mantle, the magma is less dense than the surrounding rock, where volcanoes form above the magma plumes
39
what happens to hot spots as tectonic plates move?
as hot spots are caused by mantle plumes that exist below the tectonic plates, as the plates move the hot spots do not, which is why overtime volcanoes become dormant
40
do volcanoes become dormant straight after the plate moves?
- no, as some magma that is stored below the plates can still rise and cause the volcano to erupt
41
how is intense volcanic activity created by a magma plume?
- volcanoes form above the magma plumes
- the magma plume remains stationary overtime, but the crust moves above it
- volcanic activity in the part of the crust that was above the magma plume decreases as it moves away
- new volcanoes form in the part of the crust that is now above the magma plume
- as the crust continues to move, a chain of volcanoes is formed
- the chain of islands that makes up Hawaii, a chain of volcanoes is formed by a magma plume
42
what does viscosity mean?
a measurement of how thick or syrupy lava is
43
what makes lava have a low or high viscosity?
- having a low or high amount of silicon
44
where are most volcanoes located?
most volcanoes are located near constructive and destructive plate margins
45
what type of lava is formed at constructive plate margins?
- basaltic lava is formed here, it is very hot and has a low viscosity ( runny ) so it flows easily and quickly
- eruptions of basaltic lava are frequent and go on for a long time, but they're not very violent
46
what is the difference if the margin is underwater or on land?
underwater- the magma rises to fill the space left by plates moving apart, forming ocean ridges
on land- as plates pull apart, forming rift valleys, they become thinner and magma is able to break through the surface
47
what type of lava is found at destructive plate margins?
- andesitic and rhyolitic lavas are found here, they are cooler and more viscous ( less runny ) so they flow less easily
- these lavas usually erupt intimately ( every once in a while ) and the eruptions are short-lived
48
what happens at the subduction zone of a destructive plate margin?
- the oceanic plate is subducted and melting of the continental plate forms magma
- this magma rises to the surface as volcanoes
- as the lava is viscous it forms blockages in the volcanic vents, causing pressure to build and form violent eruptions
49
why is there magma at destructive plate margins?
- as when the oceanic plate is subducted it creates high friction and pressure
- this build up creates heat also know as plutons that rise and create magma chambers underneath volcanoes on the surface
50
explain why the volcanoes at destructive plate margins are highly explosive?
- as the lava at high explosive volcanoes is very viscus and thick, meaning it is more difficult for gases to escape
- these gases build-up and cause an explosion
51
what is the VEI?
- volcanic explosivity index
52
what does the VEI measure?
- the volume of tephra, which can comprise of lava, ash, volcanic bombs etc
53
how do we work out VEI e.g. how many times larger is a VEI 7 from a VEI 4?
7 - 4 = 3 so add 3 zeros onto 1
= x1000 bigger
54
what is the longitude?
- a geographic coordinate that specifies the east-west position on the surface of the earth
- if it is to the east it is a positive coordinate and if it is to the west is it a negative coordinate
55
what is the latitude?
- how far north or south a place is from the equator
- if it is north it is positive and if it is south it is negative
56
what is a primary effect of a hazard?
this is a direct result of the eruption e.g. people can be killed by falling tephra
57
what is a secondary effect of a hazard?
this occurs as a result of the primary effect e.g. pyroclastic flows can melt glaciers and cause flooding
58
what are some primary effects of a volcanic eruption?
- tephra
- pyroclastic flows
- lava flows
- volcanic ash
-volcanic gases
59
what is tephra?
- solid material of varying grain size ranging from volcanic bombs to ash, all ejected into the atmosphere, generally larger pieces fall closer to their source
- these larger rocks ( volcanic bombs ) can hit people and ash can cause breathing issues
60
what is a pyroclastic flow?
- very hot ( over 800 degrees ), gas-charged, high velocity flows ( 10-15km ) made up of a mixture of gas and tephra
- these usually hug the ground and flow down the sides of a volcano with speeds of up to 700km per hour, which can cause widespread deaths and destruction
- an example of this is the roman city of Pompeii
61
what are lava flows?
- this is when lava can flow from a volcanic vent down the side of the volcano
- it is a low-velocity and viscosity ( 10km/h ) flow of lava which is often unstoppable due to their high temperatures
- most flows are relatively slow, so people have time to evacuate areas that will be affected
62
what are volcanic gases?
- lava contains gases such as carbon dioxide and sulphur dioxide, which are released into the atmosphere when a volcano erupts
- some of these gases can be harmful and cause breathing problems as well as contributing to global warming
63
what is volcanic ash?
- a type of tephra which is a very fine particle which can cause respiratory distress if inhaled
- it can have far reaching consequences as wind blows it around earth and reduces solar radiation
64
what are some secondary effects of volcanic eruptions?
- tsunami
- acid rain
- climate change
- lahars
- volcanic landslides
- flooding
65
what is a tsunami?
- sea waves generated by violent volcanic eruptions, displacing sea water
66
what is acid rain?
- volcanic gases can react with water vapour in the atmosphere, which then falls as acid rain
- this can damage ecosystems, and can also cause stone and metal to deteriorate, damaging buildings, bridges, statues etc
67
what is climate change in terms of volcanic eruptions?
- the ejection of huge amounts of volcanic debris into the atmosphere can reduce global temperatures and is believed to have been an agent in past climatic change such as the 'year without summer' following Tambora eruption of 1815
68
what are lahars?
- these are also known as volcanic mudflows
- it is unconsolidated ash from a recent eruption combined with water that can be swept down river valleys in the form of hot, dense, fast-moving mudflow
- the water can come from heavy rain e.g. mount Pinatubo, Philippines in 1991, or from melting snow and ice e.g. Nevada del Ruiz, Columbia in 1985
- lahars can lead to sides of volcanoes collapsing into the sea, causing potential tsunamis
69
what is a volcanic landslide?
- these are great momentum and high velocity landslides that range in size from less than 1km cubed to more than 100km cubed
- the momentum of the landslides allows them to cross between valleys and run up slopes several hundred metres high
70
how is flooding caused by volcanic eruptions?
- caused when an eruption melts glaciers and ice caps, which result in major floods
71
how can volcanic eruptions have a social effect on a country?
- people are killed, and buildings and infrastructure are destroyed by pyroclastic flows and fallout
- pyroclastic flows and lava can start fires that damage buildings
- mudflows and flooding from ice melt can cause further damage and deaths
72
how can volcanic eruptions have an economic effect on a country?
- eruptions can destroy businesses and ash clouds can prevent aircrafts flying and damage crops
- damage to buildings and infrastructure can be very expensive to repair
- eruptions and the scenery they form can attract tourists, boosting the economy
73
how can volcanic eruptions have an environmental impact?
- ecosystems can be damaged or destroyed by lava flows
- acid rain can cause acidification of aquatic ecosystems, killing some plants and animals
- it also damages the leaves of trees and removes nutrients from the soil, damaging forests
- clouds of ash and debris can reduce the amount of sunlight reaching the earth, decreasing temperatures
- volcanic gases contribute to the enhanced greenhouse effect and can add to global warming
74
how can volcanic eruptions cause political impacts?
- damage to agricultural land can cause food shortages, leading to conflict and political unrest
- governments may have to spend money on repairing damage to buildings and roads, rather than e.g. hospitals and schools, so countries may not develop as rapid
75
what is mitigation?
- anything that is done to reduce the severity or impacts of a hazard
- this can be done through short-term or long-term responses
76
what is a short-term response?
- a response that normally occurs immediately before, during or immediately after the hazard begins e.g. evacuating people from areas at risk from eruption
77
what is a long-term response?
- designed to reduce the impacts of future eruptions by managing the risks and they fall into 3 main categories:
- prevention
- preparedness
- adaptation
78
how do we prevent a volcano?
- it is not possible to prevent a volcano however it is possible to prevent eruptions by posing a risk to people e.g. authorities can prevent the land around volcanoes from being developed
79
how do we prepare for a volcanic eruption?
- authorities can install monitoring systems to predict when an eruption might occur, and make plans to evacuate people if there is an eruption
- if an eruption is imminent, authorities can stop people from entering the area around the volcano or making an emergency kit containing essentials
- communities can set up search and rescue teams or fire response units to tackle the impacts of an eruption
80
what is adaptation?
- how people change their behaviour or surroundings to minimise the risks and maximise the benefits of living near a volcano
81
how do we adapt to a volcanic eruption?
- buildings can be strengthened to reduce the chance of collapsing if a layer of ash lands on them
- people can capitalise on the opportunities of living near a volcano e.g. by farming as volcanic ash makes soil very fertile, or by working in the tourist industry
82
why is early prediction important?
- as authorities can mitigate the areas and pose any evacuations of hazardous areas, they can also prevent any further people from entering the area
- can also strengthen buildings
83
why is it helpful for scientists to have monitored an individual volcano and to understand it's volcanic history?
- as there can be specific patterns in each eruption or a specific direction the lahars moved, meaning governments can pre-plan
- could also be a pattern in frequency and magnitude which can be helpful in pre planning
84
explain why risk communication is important?
- risk communication is important as people within the exclusion zone can evacuate before the hazard occurs and people within other areas can prepare and decide whether or not they want to stay
85
what are the main facts about mount mayon?
- mount mayon is a composite volcano located in the Philippines as the most active volcano with records of eruptions dating back to 1616
- it is surrounded by the city of Legaspi and 8 others
- it covers an area of 250km squared and is around 2463 m above sea level
- the most recent eruption took place on the 13th of January 2018
86
what are the physical causes of mount mayon?
- mount mayon is caused by the Philippine plate ( oceanic ) being subducted under the Eurasian plate ( continental ) as the oceanic plate is denser
- partial melting of the continental crust occurs, creating a rise of magma
87
how does the relief and climate of the philippines impact volcanic hazard risk?
- the climate is very wet and hot which increases the frequency of lahars as there is an increase in water that creates faster paced flows
- the relief of the land ( the steepness, height and shape ) is quite steep which also provides a greater slope for the lahars to scale down
88
how do the Philippines prepare and mitigate against mount mayon?
- mount mayon is actively monitored by PHIVOLCS, a philippine government department dedicated to providing information on the activities of volcanoes
- the government raised the alert level of mount mayon and approximately 40,000 residents were evacuated from a 6km radius
89
what was the brief timeline of the 2018 eruption and what were the immediate reaction?
13th January 2018- a high-pressure steam driven eruption began that blasted ash and steam approximately 2500m into the air
- the government raised the alert level from 1-2 and 40,000 people were evacuated from a 6km radius
16th January 2018- lava flows reached limits of the 6km evacuation zone
- the province of Albay declared a state of calamity ( a condition defined as involving mass casualty and/or major damage to property
22/23rd January 2018- 3km ash column developed and 300-500 metre lava flows and fountains developed
- schools and colleges were shut and the danger zone was expanded to 9km
- further evacuations took place totalling up to 74,000 people
early February/march 2018- eruption slowly subsides
- some schools and colleges reopened and the alert levels dropped
90
what were some impacts of the mount mayon eruption?
- 0 deaths due to effective mitigation methods, such as the evacuation of 74,000 people, and well organised emergency procedures
- by the 5th of February 86,052 people were affected of which 64,895 stayed in 58 designated evacuation centres
- a total of US $3.4 million worth of damage to agriculture, affected more than 10,000 farmers
- some roads were made impassable by landslides and ash falls
- some, but not all, flights were cancelled in and out of Legaspi
91
what were the local and national responses to the eruption?
- the Filipino government committed US $1 million for a 'Cash to work' programme as well as providing hygiene packages for 50,000 families for 10 days
- they also provided food packs to evacuees for 100 days
- the army was called in for help- to enforce evacuation and to be present if there was any civil disturbance
- the Philippine red cross set up first-aid stations and welfare desks to provide psychological support to affected individuals, as well as the national council of churches providing immediate relief assistance to 3446 families
92
what were the international responses to the eruption?
- following the declaration of a level 3 alert for the volcano, the US government advised it's nationals against travelling to mayon
- the US government committed over $100,000 which was used to distribute vouchers for families to buy essential items and hygiene kits to help reduce illness in evacuation centres
- they also constructed latrines, bathing cubicles and handwashing stations and promotes safe water and hygiene practices through educational materials
93
what factors could have affected the vulnerability in the Philippines?
mobility- 5.4 million units in the Philippines meaning many have a way of evacuating
wealth- GNI of $3900 per capita and a GDP of $4130 per capita meaning they would have struggled feeding money to help with aid and damage
education- compulsory for all children and free public education is provided for primary and high school, they also have a literacy rate of 99.27% meaning many can read warnings and better education can lead to an increase in doctors
94
what is the hazard management cycle?
- a framework used in disaster risk management including:
- preparation e.g. communications and alerts
- mitigation e.g. in the 1980's when the Philippines built lahar dikes to constrain mudflows
- recovery e.g. rebuilding areas back up, economic recovery and getting people back into work
- response e.g. evacuation, search and rescue and medical aid
95
what is the Park model?
- the park model shows the relationship between the event and it's impact on a country
- it is easy to understand and clearly demonstrates what has happened and is easily compared to countries of significant different incomes
- shows duality of life against time
- but is less specific to features including how the country has actually recovered
