EQ1 tectonics

Question 1

what are convergent plate boundaries and what occurs here?
- example

Answer 1

oceanic plate is subducted beneath less dense continental plate. The plate is destroyed as plate dives under other at the subduction zone.
rocks that catch against each other are not smooth- build up of friction and potential for earthquakes in the Benioff zone.
Eruptions; magma created from meeting oceanic plate oil pushed through the faults in the continental plate which meets the surface and causes explosive eruptions.
Destructive plate margins are the most seismically active areas of a hazard.
e.g the 2004 Indian Ocean tsunami was causes by 2 oceanic plate (Indian sunk beneath the Burma, part of Eurasian plate).

Question 2

what are divergent plate boundaries and what occurs here?
- example

Answer 2

occurs when two plate boundaries diverge to form a new crust (move apart from each other).
The divergence of oceans causes mid=atlatnic ridges e.g in iceland
convection currents push apart and create a gap between plates and magma rises to fill the gap created.
Shallow focus earthquakes produced, little risk, occur underwater.
volcanic eruptions create submarine volcanoes, these can grow above sea level.
e.g- Iceland is on Midatlatnic ridge (North American and Eurasian, mNTLE PLUMES APPEARED).

Question 3

collision plate boundaries

Answer 3

continental meetsb continental
plates have the same density, less dense than the asthenosphere beauty and hence neither is subducted.
As they collide, sediments beneath crumpleqnand forced up, this creates fold mountain such as the Himalayas (Indian and Eurasian plate) and the Andes.
There can be some subduction causes when compressed/denser sediment results in subduction beneath- e.g the Nepal eq.
no volcanic activity and earthquakes have a shallow focus (severe damage).

Question 4

conservative plate margins

Answer 4

two plates slide past eachother
major fault in the crust- larger scale= transform fault
rough rocks create friction, pressure builds up, overcomes elasticity of rocks and threshold is reached- crust fractures and seismic energy is released as earthquakes.
no volcanic activity, however tectonically active and hence powerful earthquakes.
The plates sometime stick and pressure builds, resulting in shallow focus earthquakes.
e.g the San Andreas fault , California, a conservative palate margin which has generated significant earthquakes.

Question 5

properties of oceanic crust

Answer 5

high density materials, made up of basaltic rock, only 7-10km thick, can subduct, make up the ocean floor.

Question 6

properties of continental crust

Answer 6

lower density than oceanic, thicker (25-75km), made of granite rock, does not subduct, makes up the earth’s land masses.

Question 7

What’s the history of plate tectonics?

Answer 7

1900s- Wegner noticed continents looked like they fit together, continental drift (Pangea_.
The lithosphere divided into continents, move 1-2 inches per year
1950s and 60s- heated magma rising through dykes (cracks)- observe location of els and ves on plate boundaries.
subduction zones (e.g ring of fire), convergent boundaries, composite volcanoes

Question 8

hotspots

Answer 8

mantle plume rises in the mantle, local mantle stream is directed upwards, this burns through the lithosphere and crust and forms Shield volcanoes and hotspots if no plate boundaries are nearby.
Eruptions are usually effusive
as the plates move along the plume like a conveyer belt, islands are formed e.g Hawaii through the pacific plate.
the oldest island is the smallest, hence being eroded the most e.g the canary islands

Question 9

what is the theory of mantle convection?

Answer 9

Holmes theory (1930s)
- old idea, less accepted now
mantle movement- heat produced by the decay of radioactive elements in the core, driving convection currents which move in the asthenosphere and causes plates to move.

Question 10

what is the theory of slab pull?

Answer 10

now seen as a major driving force of plate movement.
- newly formed oceanic crust at midatlatnic ridges becomes denser and thicker as it cools
this causes it to sink into the mantle under its own weight and pulls the rest of the plate with it (high downward gravitational force), beneath the adjoining continental crust.
- occurs at convergent plate boundaries
It was first theorised by Dan McKenzie​

Question 11

what is the theory of sea floor spreading?

Answer 11

in the middle of many oceans, there are midatlatnic ridges, which are formed when hot magma (molten rock) is forced up from the asthenosphere and hardens, forming new oceanic crust.
the new crust pushes the tectonic plates apart in the process of sea floor spreading.
In the 1950s, paleomagnetism confirmed sea floor was spreading (magnetic stripes in the ocean floor seabed).
every 400k years, earth’s magnetic fields change direction and causes the north/soth poles to swap.

Question 12

tectonic trends since the 1960s

Answer 12

Tectonics Trends since 1960
▪ The total number of ​recorded hazards​ has ​increased.
▪ The number of ​fatalities​ has ​decreased,​ but there are some spikes during ​mega
disasters​.
▪ The ​total number​ of people being ​affected​ by tectonic hazards is ​increasing​, due to
population growth.
▪ The ​economic costs​ associated with hazards and disasters has ​increased​ significantly.
This is partly due to increases in development as infrastructure in more developed countries costs more to repair. Also, increasing number of ​insurance policies​, especially in developed countries, heightens the costs.

Question 13

what’s new known as the primary mechanism for plate movement

Answer 13

It is important to note that tectonic movement isn’t fully understood. Previously, ​convection currents​ were thought to be the primary cause of plate movement. However, researchers now believe that ​Slab Pull​ is the ​primary mechanism​ for plate movement; convection currents seem too weak to move massively dense plates.

Question 14

p waves

Answer 14

Primary
-Travels through solids
-Compressional
-Vibrates in the direction of travel
- Travels at 4-8 km/s

Question 15

L waves

Answer 15

Love
-Near to ground surface
-Rolling motion producing vertical ground movement
-Travels at 2-6 km/hr

Question 16

S waves

Answer 16

Secondary
-Vibrate at right angles to direction of travel -Travels only through solid rocks
-Travels at 2.5 - 4 km/hr

Question 17

R waves

Answer 17

Rayleigh
-Vertical and horizontal displacement -Travels at 1-5 km/hr -Compressional

Question 18

what are the most destructive waves and why?

Answer 18

Secondary and Love waves are the most destructive as they have ​large amplitudes​. Due to their different speeds, these different waves will hit a location at different times. The aftershocks​ that survivors feel are these different types of waves arriving after each other.

Question 19

why does decrease g intensity of waves further from the epicentre not mean vulnerability is guaranteed to reduce?

Answer 19

Intensity​ of waves will ​decrease further from the epicentre​, as waves lose energy as they travel. However, this does not mean that impacts felt or damage caused will always decrease further from the epicentre as other factors affect a location’s ​vulnerability: geology, geographical location (whether the earthquake occurs near the sea or intraplate), education of locals, durability of buildings, mitigation.

Question 20

how are intra-plate volcanoes formed?
- how are intra-plate els triggered?

Answer 20

these are volcanoes that happen at hotspots.
isolated plumes of convecting heat rise towards the surface, generating basaltic volcanoes.
The plume remains stationary and the tectonic plate moves slowly over it.
the continuation of plate movement over time produces a chain of volcanic islands. The extinct ones are furthest away from the current plume location.
stresses reactivate ancient fault lines (cause of intra-plate earthquakes).

Question 21

describe the earths Internal structure

Answer 21

segments of the earth; core, mantle (lithosphere and asthenosphere), outer core and inner core.

Question 22

properties of the earths core

Answer 22

centre of the earth, made from inner and outer core.
inner core is solid, outer crew is liquid.
both made from iron and nickel.
the core is a source of radioactive heat

Question 23

properties of the mantle

Answer 23

semi-molten body of rock between the earth’s crust and its core.
The asthenosphere is semi-molte and is the lower mantle
lithosphere- above asthenosphere, floats on top
lithosphere is the crust and upper mantle- forms tectonic plates

Question 24

how thick is oceanic crust

Answer 24

6-10km, denser

Question 25

how thick is conteintnal crust

Answer 25

thicker, 30-40km, less dense

Question 26

how many km is the outer core

Answer 26

2900km

Question 27

how many km is the inner core

Answer 27

5100km

Question 28

primary volcanic hazards- lava flows

Answer 28

streams of lava, reaching 1170 degrees c , can take years to cool completely. move slow, hence nit a huge threat, however destroys everything in its path. e.g Kilauea volcano in hawaii- destroyed farmland and set horse on fire- November 2014

Question 29

primary volcanic hazards- pyroclastic flows

Answer 29

very dangerous, a mixture of hot rock, lava, ash and gases ejected from volcanoes. move very quickly and destroy everything they touch up to 700 degrees c, 100km per hour - cannot outrun! e.g mount sinabug, sumatra, indonesia, July 2015 mount Vesuvius, pompei, 79AD

Question 30

primary volcanic hazards- tephra and ash falls

Answer 30

tephra are pieces of volcanic rock and ash, blast into air during eruptions larger pieces fall near volcanoes, can cause injury- death/damage smaller pieces (ash) can travel thousands of km ash falls are very disruptive- poor visibility and slippery roads, roofs collapse under weight, engines clog up and stop working, delays flights internationally as redirection routes have to take place (e.g E15 ash cloud, Iceland).

Question 31

primary volcanic hazards- gas eruptions

Answer 31

magma contains dissolved gases, released into the atmosphere during eruption. water vapour- 80% co2 sulfur dioxide gases can travel for thousands of km

Question 32

secondary volcanic hazards- lahars

Answer 32

masses of rock, mud and water - travel quickly down the sides of volcano , speeds vary some are too fast to outrun caused when an eruption quickly melts snow/ice heavy rainfall after eruption- erodes loose rock/soil and this surges downslope e.g- Nevado del Rurz, destruye town of Armero, colombia november 1985

Question 33

secondary volcanic hazards- jokullhaups

Answer 33

heat of volcanic eruption can melt snow/ice in a glacier causes heavy and sudden floods (jokullhaups) dangerous, release sudden amounts of water rock, gravel and ice, catch people unaware, flood damages land and structures. e.g- 1996 Iceland, followed eruption on vatnajokull ice sheet.

Question 34

define earthquake

Answer 34

a sudden or violent movement within the earth's crust, followed by a series of shocks. Happens when the earth's plates move and cause the ground to shake, releasing energy as seismic waves.

Question 35

what are earthquakes caused by?

Answer 35

caused by a relief of build up of stress plates on crust are always moving- tensions build between the rocks. stress can suddenly be released when the strain overcomes the elasticity of the rock the release of stress can cause parts of the surface to experience an intense shaking motion that lasts for a few seconds.

Question 36

define focus

Answer 36

the location where the pressure is released underground and where the energy radiates out from. This is the place with the strongest waves that cause the most damage

Question 37

define epicentre

Answer 37

the point directly above the centre of the earthquake (focus) ON THE EARTH'S SURFACE

Question 38

define seismic waves

Answer 38

when energy is released from the focus in shock waves. The most damage will occur at places where the shock waves are the strongest (e.g closest to the epicentre).

Question 39

how is energy transferred in earthquakes

Answer 39

large amounts of energy released in seismic waves much of the energy is transferred vertically to the surface and moves outwards from the epicentre as seismic waves after the moment of fracture, rocks may regain their original shape, but in a new position

Question 40

shallow focus eqs

Answer 40

0-70km deep, more damaging than deep focus and shock waves have less distance to travel and hence there is more shaking at the surface

Question 41

deep focus eqs

Answer 41

70-700km focus caused by previously subjected crust moving towards the core, heating up or decomposing. these are less damaging than shallow eqs as the shock waves have to travel further, less shaking at surface.

Question 42

underwater earthquakes

Answer 42

move the seabed, causes the water to get displaced if another water is displaced, a tsunami can occur can be shallow/deep focus the deer the focus, the bigger the tsunami waves travel fast in deep water- tsunamis can strike shores with little warning- can catch people off guard and cause many deaths e.g 2004 Indian Ocean./Boxing Day tsunami

Question 43

how is a tsunami formed (5 steps)?

Answer 43

1) tectonic upthrust causes vast quantities of water to be displaced, this generates a lot of energy. 2) energy from the quake/impulse causes a train of simple, progressive, oscillating waves to propagate over the ocean surface, as fast as 500mph 3) the wavelength continues to grow with the waves period. 4) as waves approach the coastline, slowed dramatically by friction. But as the velocity lessens, the wavelengths become shortened and the amplitude (height) increases. 5) wavelength compressed and heightened to large levels. Giant waves collide with shore causing damage, outflow of waves- destruction/deaths/injury.

Question 44

how does a volcanic eruption occur (6 steps)?

Answer 44

1) pressure builds up in the magma chamber 2) magma forces its way up the vent 3) gas and steam escape into the atmosphere 4) magma erupts out of the crater 5) lava flows down the side of the volcano 6) ash and bombs fall on surrounding area

Question 45

how many people worldwide are at risk from volcanic hazards?

Answer 45

500 million

Question 46

over the cause of 300 years, how many people have died as a result of an eruption?

Answer 46

260k

Question 47

the volcanic explosively index what is it ? what factors are used to assign a number?

Answer 47

describes and used to compare size/magnitude of volcanic eruptions uses scale from 0-8 (extremely explosive) logarithmic scale, each number increases by a factor of 10x. factors: - amount and height of volcanic material ejected (tephra, ash fall etc). - how long the eruption lasts for (duration) - qualitative descriptive terms (e.g effusive, gentle etc.)

Question 48

how many volcanos are currently active?

Answer 48

1900

Question 49

how does a volcano become explosive?

Answer 49

most explosive volcanos are found on convergent plate margins, high silica lava most effusige/gentle are found on divergent plate margins (low silica lava) however this is not the rule for all volcanoes, as some effusive shield volcanoes in Icelands have high silica lava and are gentle.

Question 50

what is the caldera in New Zealand?

Answer 50

The Rotorua Caldera is a large rhyolitic caldera that is filled by Lake Rotorua. It was formed by an eruption 240,000 years ago that produced extensive pyroclastic deposits. Smaller eruptions have occurred in the caldera since, the most recent less than 25,000 years ago. super volcano, every 50-100k years there's a large scale eruption. highest on volcanic explosively index

Question 51

cone volcanos- New Zealand

Answer 51

Cone volcanoes (also called composite cones or stratovolcanoes) are characterised by a succession of small-moderate eruptions from one location. The products from the successive eruptions over thousands of years build the cones. New Zealand cone volcanoes include volcanoes like Ruapehu, Taranaki/Egmont and Ngauruhoe. They are the most frequently active type.

Question 52

caldera volcanoes- New Zealand

Answer 52

Caldera volcanoes have a history of infrequent but moderate-to-large eruptions. Caldera-forming eruptions create super craters 10-25 km in diameter and deposit cubic kilometres of ash and pumice. Resurgent caldera activity is usually smaller than the caldera forming eruptions. There are 8 caldera volcanoes in the central portion of the Taupo Volcanic Zone, between Rotorua and Taupo. This area is known as Te Ahi Tupua.

Question 53

volcanic fields- New Zealand

Answer 53

In volcanic fields, small eruptions occur over a wide geographic area and are spaced over long periods of time (i.e. thousands of years). Each eruption builds a single new volcano, which does not erupt again. Mounts Eden and Wellington are examples from the Auckland Volcanic Field.

Question 54

how many types of volcanos are there in New Zealand what are they called?

Answer 54

3: volcanic fields, caldera volcanos and cone volcanos

Question 55

describe the features of an eq with a shallow focus

Answer 55

They are commonly associated with conservative, collision and divergent plate boundaries. They also occur in convergent boundaries as the denser plate starts to initially subduct. SHALLOW FOCUS earthquakes are commonly occurring "crustal" earthquakes, caused by faults and movements of the continental plates. These are earthquakes with their focus nearer the surface of the earth. Shallow focus earthquakes are usually of large spread, causing greater damage at the surface or the earth's crust. However, being of smaller magnitudes they are very often not even felt.

Question 56

describe the features of an eq with a deep focus

Answer 56

Deep-focus earthquakes are caused by the crust that is subducting beneath a lighter plate at a convergent plate boundary. They have a focus between 300km and 700km below the Earth's surface. DEEP FOCUS earthquakes, occur within the sub-ducting oceanic plates as they move beneath the continental plates. Appearing along fault lines, these are earthquakes with focus much deeper within the earth. These are typical of the subduction zone of the earth which are seismically active zones, often existing in patterns as in Wadati-Benioff zones. They happen as huge quakes with larger magnitudes, as a great deal of energy is released with the forceful collision of the plates.

Question 57

Explain why earthquake magnitude varies between convergent and divergent plate boundaries? (4)

Answer 57

Earthquakes occur as a result of plates either colliding or moving past each other and getting stuck. Pressure builds up. When the pressure is released, that is an earthquake - often in a series of slips or judders which release large amounts of pent-up energy. On divergent plate margins, although there are transform faults, most of the movement of plates is away from each other. This means that not as much pressure builds-up.

Question 58

What is an Earthquake's magnitude?

Answer 58

Earthquake magnitude measures the amount of energy released at the epicentre whereas earthquake intensity considers the earthquake's effect on people, structures and the natural environment.

Question 59

How is magnitude measured?

Answer 59

Magnitude can be measured using the Richter scale or the Moment Magnitude Scale whereas intensity can be measured using the Modified Mercalli Intensity Scale.

Question 60

Define Tectonic Hazard

Answer 60

A natural event caused by internal earth processes e.g plate movement that have the potential to cause loss of life or damage to property e.g primary and secondary hazards.

Question 61

What are volcanoes?

Answer 61

Extrusive features found on the earth's surface where molten rock (magma) reaches the surface and cools.

Question 62

What are Rhyolite Caldera Complexes?

Answer 62

These are rhyolite volcanoes which have erupted and blown the top of the volcano off which then goes into the mantle (they collapse in on themselves). e.g- New Zealand

Question 63

What are the characteristics of basalt lava?

Answer 63

Temperate = High (1000-1200 degrees) Main Minerals = Low silica (50%) Gas Content = Low Formation = Melting of the mantle materials Flow Characteristics = Low (thin and runny, gases escape) Eruption = Gentle, effusive Location = Hot spots, mid-ocean ridges, divergent plate boundary.

Question 64

What are the characteristics of rhyolitic lava?

Answer 64

Temperate = Coolest (650-800 degrees) Main Minerals = Highest silica (70%) Gas Content = High Formation = Melting of the lithosphere mantle materials Flow Characteristics = High (traps gases) Eruption = Very violent, cataclysmic Location = Super-volcanoes e.g composite, cone volcanoes

Question 65

What are the characteristics of andesitic lava?

Answer 65

Temperate = Intermediate (800-1000 degrees) Main Minerals = Intermediate silica (60%) Gas Content = Intermediate Formation = Subducted oceanic plates Flow Characteristics = Intermediate (viscosity traps gases) Eruption = Violent, moderately explosive Location = Subduction zones

Question 66

What is the benioff zone? what does it explain?

Answer 66

-A dripping flat zone of earthquakes that is produced by the interaction of a down-going oceanic plate with a continental place. -Subduction creates an area of seismicity producing intermediate and deep focused earthquakes. -The benioff zone explains why we get earthquakes at different depths and of varying distances from the surface plate boundary.

Question 67

The distribution of earthquakes around the world

Answer 67

On or near plate boundaries in land or sea Earthquakes can occur in mountain ranges e.g the Alps Anomalies - centre of the Antarctic plate and Pacific plate (intra-plate earthquakes)

Question 68

What is crustal fracturing?

Answer 68

Primary effect of earthquakes: When pressure in the rock causes the rock to break and shear due to an earthquake creating a fault in the rock. The faults can happen suddenly and leave sections of the crust sinking down or raising up.

Question 69

ground shaking- primary effect of earthquakes

Answer 69

Primary effect of earthquakes: As seismic waves travel through the crust they result in shaking. Vibration of the ground in an earthquake is due to seismic waves. Ground shaking can trigger liquefaction and land slides. Most earthquake damage is the result of ground shaking.

Question 70

What is liquefaction?

Answer 70

Secondary effect of earthquakes: Due to applied stress on the soil e.g because of an earthquake, saturated or unconsolidated soil loses its strength and behaves like a liquid. This was seen after the Japan earthquake in 2011.

Question 71

What are landslides?

Answer 71

Secondary effect of earthquakes: The shockwaves sent out by earthquakes can cause land that is weak or on a slope to fall or slip. Earthquakes destabilise cliffs and slopes due to stresses. This was seen after the El Salvador earthquake in 2001.

Question 72

What are body waves?

Answer 72

There are two types - primary and secondary waves and they travel through the interior of a body e.g earth's inner layers (P waves can also travel through the molten core):

Question 73

What are surface waves?

Answer 73

There are two types - love waves and reyleigh waves. They travel on the surface and arrive after body waves, they cause the most surface destruction

Question 74

What are reyleigh waves?

Answer 74

They are surface waves which travel through the crust in a rolling motion, they cause the ground to move up and down/side to side, they have a retrograde particle motion confined to the vertical plate of motion.

Question 75

What factors determine the impact of a tsunami?

Answer 75

ength of the tsunami in time e.g longer it lasts the more damage it makes. The size of the wave e.g bigger wave = more destruction as more water has been displaced, the further its travelled the smaller the wave. The gradient of the wave e.g the lower the gradient = the more dangerous as waves go further inland, shallower water makes bigger waves. Coral reefs and mangrove forests act as natural protection, absorbing wave energy. Time of day e.g night is more dangerous as it's harder to get to safety, there's a lack of visibility. Coastal developments near the sea increase vulnerability as more live near the coast. The quality of early warning systems. e.g DART systems

Question 76

Volcanic Eruption - Eyjafjallaljokull, Iceland 2010

Answer 76

Constructive plate margin along the Mid-Atlantic Ridge, 110 million cubic metres of tephra and a gas cloud. Disrupted European air travel, 17,000 flights cancelled, 800 evacuated due to jokulhaups. Insurance helped with financial loss, quick government response and UK sent nay boats and citizens sailed over to pick up stranded tourists. High community spirit, wealthy country, good emergency procedures, predictions and services.

Question 77

Volcanic Eruption - Monserrat, Carribean, 1995

Answer 77

Destructive plate boundary. Warning signs made e.g small earthquakes, eruptions of ash, create pyroclastic flows and lahars. 2/3 of island covered in ash, 17 dead, farmland destroyed, Plymouth (capital) abandoned, 50% were evacuated North to makeshift shelters. Educated children, warning signs allowed for evacuation, government initiatives e.g exclusion zone, services in North. Good emergency procedures, warning systems, services. Small population.