case studies volcanoes Flashcards
1
Q
what is the basic structure of the earth
A
core
mantel
crust
2
Q
what is the mantle- crust boundary separated by and how far underground
A
moho
2900km
3
Q
what is the asthenosphere
A
extends 100km to 300km underground
although solid flows under pressure
4
Q
what is the lithosphere
A
under the asthenosphere, varies with thickness. between asthenosphere and crust.
5
Q
who had a theory for continental drift
A
Alfred Wegner
6
Q
Was was Wegners theory
A
250 million years ago a single large continent existed, Pangea.
7
Q
how did paleomagnetism show continental drift
A
echo sounders used to locate submarines showed the existence of the mid Atlantic ridge.
- pattern of magnetism was discovered in basaltic rocks making up the ocean floor, showing repeated stripes moving away from mid Atlantic ridge,
-due to igneous rock cooling , iron minerals cooled into iron fillings.
8
Q
why did the iron striped indicate continental drift even more
A
reflected the fact earths polarity is not constant and changed every 400,000- 500,000 years
9
Q
how was sea floor spreading indicated
A
symmetrical pattern of geomagnetic reversals on either side of mid-ocean ridges- as fresh molters rock from aethenisphere reached the ocean bed, older rock was pushed away.
eventually this sea floor spreading reaches an ocean trench and rock becomes semi-molten
10
Q
biological evidence for continental drift
A
similar fossil brachiopods found in Australian and Indian limestone
similar fossils especially marsupials found in South America and Australia.
11
Q
What are the things called that the lithosphere and crust were broken up into
A
Tectonic plates
12
Q
A
13
Q
What are the three types of plate boundary
A
Divergent, convergent, conservative
14
Q
What happens at a divergent plate boundary and an example and what are mid ocean ridges
A
Plates are moving apart
- magma rises through the asthenosphere and forcing its way to the surface.
- plumes of lava, especially noticeable at mid ocean ridge
mid ocean ridges: consist of long chains of mountains, in places rising 3000m above the sea bed.
- not continuous in some areas broken into segments by transform faults.
- volcanic activity absent as it Is conservative but as they slip energy is released in earthquakes.
15
Q
What are pillow lavas
A
Magma erupting directly on to the sea bed is cooled rapidly, forming rounded mounds called pillow lavas.
16
Q
How are rift valleys formed from divergent plate boundary’s
A
As magma rises towards the surface the pressure reduces and it liquifies.
Overlying rocks are forced upwards as the lithosphere is placed under stress and eventually fractures.
W.g North Atlantic, has created Iceland.
17
Q
What are black smokers and how are they formed
A
At mid ocean ridges- sea water seeps into rifts and is superheated. As it rises towards the surface it causes chemical changes in basaltic rocks. Superheated jets of water sometime re emerge on the ocean floor known as black smokers.
18
Q
What is an example of the rift zone on land.
A
The continental crust must thin considerably.
- Red Sea northwards to turkey.
Forming sunken valley known as graben.
Eventually sunk below sea level forming the Red Sea
19
Q
What are the types of convergent plate boundaries
A
Oceanic- continental
Oceanic- oceanic
Continental- continental
20
Q
What happens at a convergent oceanic- continental plate margin
A
Oceanic plate as it is denser is forced under the continental plate by subduction.
Causes deepening of ocean forming ocean trench
Usually asymmetrical
Marks subduction where oceanic plates subduction into the aethensphere causing slab pull
21
Q
What is the Benioff zone
A
The angle at which the oceanic plate is subducted between 30 to 70 degrees. 45 degrees produced energy in the form of earthquakes.
22
Q
What happens to the water at convergent plate oceanic- continental boundaries
A
- Substantial amounts of water are contained in oceanic plates.
- As subduction takes place and pressure and temperature increase, dehydration takes place, triggering processes that partially melt the overlying plate.
- Milton magma material rises towards the surface as plutons of magma.
- instructions of magma cause further uplift of gold mountains, where magma reaches the surface it forms volcanoes.
23
Q
Oceanic- oceanic plate boundaries
A
slightly older and denser one will subduct under the other creating a trench
- as it descends dehydration takes place causing partial melting of the mantle wedge in the plate above.
- magma rises to the surface forming chains of volcanic islands known as island arcs.
Example is the Antilles due to the North America plate subducted under the Caribbean plate.
24
Q
Continental to continental convergent plate boundaries
A
Little if any subduction takes place, African Eurasian plates 40 million years ago created the alps
25
What happens at conservative plate boundaries
At some places neither divergence or convergence takes place but rather the plates slip past each other.
-frictional resilience causes build up of pressure leading to eathaukes
- not associated with particular landforms.
Possible to identify through giant tears.
- example would be the conservative plate boundary in California where the North America and pacific are moving in the same direction at different rates
26
how are explosive eruptions characterised
- convergent plate boundaries
- rhyolite (more acid), andesite (less acid)
- lava has more acid- higher silica content, high viscosity, lower temperature at eruption.
- more violent eruption bursting of gas bubbles when magma reaches surface, vent and top of cone often shattered.
- materials erupted: gas, dust, ash, lava bombs, tephra.
- long periods with no activity
- shape- steep sided Strat-volcano, caldera.
27
How are effusive eruptions characterised
- divergent plate boundary
- basalt lava
- is basic so low silica content, low viscosity, higher temp at eruption.
- gas bubbles expand freely, limited explosive force.
- materials erupted are gas and lava flows.
- more frequent eruptions, can continue for many months.
- shape of volcano is gently sloped sides, Shield volcanos, lava plateaux when eruption has many fissures.
28
how are volcanos categorised
type of eruption: explosive and effusive.
- the viscosity of lava
29
what are the features of strato volcano, or composite cone volcano
sills and dykes
30
what are calderas
volcanic craters, usually more than 2km in diameters.
- develop when an explosive eruption destroys ,such of the cone and the underlying magma chamber is largely emptied. Without the support of the underground magma, the sides of the eruption collapse to form a caldera.
Krakatoa 1883
31
what are other products of explosive eruptions except calderas
convergent plate boundaries give rise to chains of strata-volcanos. e.g Indonesia has 120 active volcanoes along its archipelago.
32
what are the products of effusive eruptions
lava plateaus
-basic magma erupts from multiple fissures
-vast areas covered in free flowing lava.
- known as flood basalts
e.g Deccan Plateau in central India 500,000 km 2 plateau also known as LIP.
widespread denudation has caused varied relief
Shield volcanoes
- usually the effusive eruptions are found at divergent plate boundaries.
-these boundaries coincide with mid-ocean ridges,
- most of these eruptions happen underwater.
-happens in Iceland
-eruptions cause developing sloping sides
e.g SKjaldbreidur on Iceland
33
what is the common name for intra plate volcanoes and example
hot spots, Hawaiian chain of islands, located in the centre of the pacific plate boundary
34
definition of a hot spot
A fixed area of intense volcanic activity where magma from a rising magma plume reaches the surface.
35
how have the Hawaiian island formed
pacific plate has moved over the hot spot 10cm/year. vast amounts of basalt has accumulated on the sea floor.
36
what are the names of the volcanic peaks in Hawaii
Mauna Loa and Mauna Kea and rise 9000 m over the ocean floor
37
why duo these volcanoes bec one extinct
as the plates move over the volcanoes loose their source, magma chamber.
38
what os happening to Loihi
rising, lies directly above a hot spot
39
Example of a strato volcano formed from a hot spot
El Teide on Tenerife, erupted most recently in 1909.
40
what is a super volcano and an example
when a volcano erupts more than 1000km squared of material in a single eruption, giant calderas.
Yellowstone Wyoming, caldera measuring 75km in diameter
41
what are the key factors used to asses and measure volcanic activity
magnitude
intensity
42
what is the most widely used measure of an eruption
volcanic explosively index
43
what does the VEI do
combines magnitude and intensity into a single number on a scale from 0 to 8, each increase represents a nearly 10 fold increase in explosively
44
what is taken into consideration when assessing the explosively
volume of material ejected
the height ejected material reaches
the duration in hours and various qualitative descriptions
not useful for effusive eruptions
45
what are LIP's
large igneous provinces.
46
how are mid ocean ridge basalts formed
when adjacent plates with divergent motions, are pulled apart.
47
where are LIPs formed
not only at boundaries but also hot spots, basalts and giant oceanic plateaus, massive effusive outpours, commonly erupting over long periods.
e.g Siberian traps, volume of 3 million km cubed
-earth shattering, correlation with earths climate, would cause ocean acidification and long term global warming, cause of 4 major extinctions
2 million years, Yellowstone caldera
48
what happened at the latest eruption of yet Yellowstone caldera
ash was spread over much of western half of North America
VEI of 8
49
what ate the hazards produced by volcanic activity
lava flows:
-impacts dependent on type.
Basic (basaltic), is free flowing, Hawaii 2015, lava extended 20km.
Acidic lavas such as cryolite are thick, cause destruction to infrastructure.
(silica content)
- pyroclastic flows, combination of very hot gases (500 degrees plus), ash and rock fragments travelling at 100km/hr. inhalation causes instant death. Pompeii, Mount Vesuvius AD 79.
gas forms almost liquid layer.
- Tephra, any material ejected out into the air. ranges from fine ash to lave bombs. Destroys crops. eruption enters stratosphere due t high temperature, Eyjafjallajokull in 2010- 10,000 flights cancelled.
- toxic gas CO, CO2 and SO2, acid rain.
-Lahars, mud flow with consistency of wet concrete. Snow and ice on top of volcanos, mix with rock fragments ash . travel at 50km/hr. Nevada del Ruiz Columbia, 23,000 deaths
-floods, volcanic eruptions below ice fields or glaciers cause rapid melting, Iceland.
Tsunami, cause massive displacement of water traveling at 600km/hr, 1 metre height , approaching shore they will increase in height rapidly Krakatoa 1883, 36,000 people drowned.
50
case study- lake nyos
Cameroon deep lake o. a crater. 2kim wide and 200m deep
1986 1700 people died, and animal life was asphyxiated. leak of CO2.
-gas but up at bottom of the lake, after being emitted from the magma chamber. CO2 is dense so flowed down the volcano sloped as a 50m thick layer travelling at 70km/hr.
could have been strong winds stirring up the water.
51
what is an earthquake
release of stress that has built up within the Earths crust caused by tension, compression or the shearing of rocks.
- a series of seismic shock waves originates from the earthquake focus
52
what is an earthquakes focus
the location where the stress is suddenly released, above this point is the epicentre.
53
where are earthquake activity concentrated in
mid ocean ridges- tension forces associated with spreading processes, faulting and rifting.
ocean trenches and island arcs- compressive forces associated with subduction of one plate below another.
collision zones- compressive forces associated with the grinding together of pates carrying continental crust.
conservative plate margins- shearing forces with the intermittent movement of one plate past another
can occur anyway tho.
54
what are the three types of seismic waves
primary waves- fast travelling, low frequency compressional eaves. vibrate in the direction in which they travel. travel through solids and liquids.
secondary waves- half the speed pf p waves, high frequency . vibrate at right angles to the direction. Cannot pass through liquids
Surface (L) waves- rolling movement. moves the surface vertically. travel through the outer crust only
55
what is the difference between a shallow and deep focus
shallow- down to 70km. occur in cold, brittle rocks, resulting from the fracturing of rock due to stress, releasing low levels of energy.
deep focus- 70 to 700km, high levels of temperature and pressure, mineral change type and volume, releasing energy., less frquent but powerful, due to dehydration.
56
what are the ways in which earthquakes are measured
Richter scale- 1935, uses amplitude of seismic waves to determine earthquake magnitude. Logarithmic scale, increase by tenfold, 30 fold increase in release of energy. largest is 9 Took in Japan 2011. Does not assess damage.
Modified Mercalli scale: measures earthquake intensity and impact. relates ground movement to impacts felt , qualitative, based on description and observation.
Moment Magnitude scale. Measures energy released more acucrately than Richter, amount of energy is related to rock rigidity, area of fault surface and amount of movement.
Logarithmic scale, most accurate measurement, uses amount of physical movement. Not used for small earthquakes. 2MW or less cALLED MICRO earthquakes.
57
what are the effects of earthquakes on landforms and landscape
on large areas, earthquakes are associated with the formation of entire mountain changes. Himalaya in Asia. Northward drift of Indian into Eurasia and the continental collision into has led to a complex folding pattern.
Rift valleys- along mid ocean ridges in East African and Iceland, are associated with Earthquakes on Earth's surface. The inwards, fault snaps or escarpments of rift valleys make the location of faults caused by tension and compressuib within the crust. Rift valleys are altered by weathering and erosion. Over time fault scars are worn away, disappearing under accumulated sediment.
58
what are the hazards associated with Earthquakes
ground shaking d ground displacement- severity depends on the magnitude distance from the epicentre and local geology.
e.g Mexico citu 1995, close to epicentre, high magnitude and surface layers unconsolidated and high water content. Tokoku earthquake was 5 mins.
ground movements can rip pipelines and structures like railway trcaks.
Liquefaction- earthquake striking an area with fine graded sands, alluvium and landfill with high water content, vibrations cause these materials to act like liquids. Materials lose strength, causing structures to tilt and foundations to give way. Christchurch 2011, 52 billion in damages. 400,000 tonnes of sludge
Landslides and avalanches.
- slope failures common in mountainous regions like Himalayas, increased by deforestation and heavy monsoon rains. Nepal earthquake 2015 triggered landslides. Cause blockages causing floods, displace water.
Tsunamis, Underwater Earthquakes, can cause sea beds to rise vertically producing powerful waves. Wave increases as it hits the shores. Drawdown- water is pulled out to sea Japan 2011 9.0Mw , Honshu. Wall of water can exceed 25m in height 200km long. depending on relief of the coast the water can spread variable distances.
Underwater landslides can also cause tsunamis, papa New Guinea 2200 villagers killed
59
what is seismic lensing
It is a phenomenon where seismic waves caused by earthquakes are bent/refracted as they travel through different layers of earths interior. This occurs due to seismic waves moving at different speeds through materials that vary in density and elasticity.
60
definition for an active volcano
one which has erupted since the last glacial period, 10,000 years
61
impacts of living with volcano case study Japan
-has 110 active volcanos, 70% of land is mountainous, including Mount Fuji
- located on a tectonically active zone, widespread subduction, four plates, philipean, pacific, North American and Eurasian. more than 1 eruption every 2 years.
- Intake, strato volcano, 200km west of Tokyo rises 3000m, had a sequence of eruptions in 1979-1980.
2014, erupted violently killed 63 people, ash fall, pyroclastic flow, volcanic bombs and lahars, unpredictable even to Japan. military rescue
62
case study impacts of living with volcanos, Indonesia
Southeast Asia, Mindanao trench, Java trench, records 80 eruptions.
3/4 of habitants lige 100km from volcano, that has erupted in 10,000 years.
Indonesia record 114 eruptions causing fatalities.
subduction zone along 3,00km length of archipelago. Much of Indonesia is an island arc.
Volcanos have high explosively, Krakatoa 1883, formed by Australian beneath and Eurasian plate, caused a tsunami in 1883.
caldera, toba- filled by lake toba
- mount megapixel, stratovolcano, 3000m highly active, eruptions from , pyroclastic flows, 3-4 VEI in 2010. lahars triggered due to monsoon season, 4km lava bombs.
367 people died, 130million m cubed of material ejected. destroyed crops and infrastructure.
63
what were the impacts people experienced as a result of the Great East Japan Earthquake in 2011
social, economic and political impacts
9 MW between the pacific and birth America plate, epicentre of 70km offshore of Honshu
-lasted 6 mins
-undersea megathrust
- Honshu moved 2.4cm
- focus of 30km
-tsunami 40.5 metres in height.
social:
claimed 16,000 lives, 90% due to drowning
- mass graves
- save the children reported 100,000 affected
-destruction to infrastructure
economic:
cost $200 billion, 45,700 buildings destroyed, 140,000 damaged
10% of japans fishing ports damaged
-4.4mil households lost electricity.
-Daichi, Fukushima, cooling system damaged, released radioactive, 30km evacuation zone
-train station was damaged, 23 train stations closed.
-farmland contaminated
political
Japan injected billions of yen into the economy, large amounts of debt, and large movement against nuclear power.
-inadequacy of defences.
64
Social, political and economical impacts of Haiti living with Earthquaked
poorest country in America's,
2010, squill fault
7.0MW,
epicentre 25km southeast of capital city
focus 12km.
shaking lasted 12-14 seconds
social impact:
- government and state institution were weak, 21 of 22 government buildings destroyed.
- 316,000 supposed deaths
-300,000 houses destroyed, 1.5 million people displaced.
-landslides
before only 50% of Haitians had access to freshwater and healthcare.
large amounts of deforestation for fuelwood increasing landslides
cholera outbreak- 2010 800,000 cases.
economic and political impact:
- part of slave revolution, forced to pay 21 billion so low gap and very poor and underdeveloped.
- supported dictatorships from USA, subsidised farmers so high bankruptcy,
since earthquake economy has barely recovered, aid recovery has been used for tourism
65
case study on the ability to manage volcanic activity in Indonesia
has the centre for volcanology and geological hazard mitigation established in 1920, seismograph of mount merapi, however low priority due to political instability
-has been able to upgrade instruments, now monitors 60 volcanoes, measures gas emissions and earthquake activity.
-gov established a national emergency for disaster management- works with unis, lahar sensors.
= mitigations strategies include community preparedness, relocation, safe zones, financial assistance in some cases.
modification of loss- ppl are developing strong relationship with villages, stops them form moving.
- LIDC so resources are limited, however, have a lot of trained and equpotment for emergencies
-established shelters in safe zones
-authorities clear river channels go volcanic matter, reduces flooding and contains lahars
- some material being used to build houses.
66
case study on the ability to manage volcanic activity in Italy
has mount Etna in Sicily, one of most active volcanoes.
-local scale success with diverting lava flow, using earth boundaries and channels
moderating vulnerability: Volcanic Risk service: evacuation orders, they have long term analysis of patterns, international comparison with similar eruptions
-seismographs and monitor gas emissions, closure of airports and airspaces, identify types of housing most at risk, provide emergence services/ alert.
modifying loss:
- well practiced rehearsals from frequent eruptions of mount Etna
- HiC so has financial resources, however lost of buildings and services have been destroyed due to recent eruptions.
- compare to mount Vesuvius, where 600,000 versuvians lived in red zones
-they monitor mount Vesuvius, confidence of predicting eruption however is low
67
living with earthquakes management strategies Japan
-has a highly developed education system, and political stability.
-high levels of preparedness.
mitigation strategies:
- research and monitoring. JMA- Japan meteorological agency- info and warnings on impeding earthquakes and tsunamis.
-planning includes the military transport, power supplies and telecommunication companies.
Buildings:
-have aseismic design
-steel frame and brances0 move without collapsing
-rubber shock absorbers in foundation, as well as deep foundations with car parks, for the pancaking effect
- counter weights on the riff
-suspension bridges capable of moving in Earrhquakes- flexible joints.
-fire proofing wooden buildings
-land use zoning- a lot of open spaces
-tsunami warning systems- refugee sites with aid
management of loss:
is an AD so has vast financial resources, well rehearsed recovery and reconstruction plans. Kobe quake in 1995 and other recent quakes, has allowed for reappraised plans.
short term impacts larger than long term
68
management of living with earthquakes case study -Haiti
modifying vulnerability:
-2010 they had no warning systems, due to it being very long ago in which they had previous earthquakes 1989.
-high amount of poverty, and hurricane vulnerability.
-USAID an USGS- invest into awareness and monitoring of earthquakes.
15 seismic stations, however they are not earthquake resistant themselves.
- do earthquake mapping- softer sediment is recognised as vulnerable to solifluction
-no education system like Japan.
-high amounts of concrete infrastructure to withstand hurricane, however it is weak in earthquakes.
-only 0.04% of national budget spent on earthquake surveillance.
- no effective government, roles of NGOs has been crucial
- 5.3 billion US pledge agreed to work on givernment, however NGOs set prioritise.
only 1% of the donor fund was offered to the government.
-Red Cross raised 480 million, only built 6 houses. USAID planned to build 15,000 homes, only 900 built.
130 miles from port instead of 9 miles proposed.
no houses were built originally to sustain earthquakes, so 21 mullion was spent to fix structural problems.
2/3 of money remains with NGO's bank accounts
