Hazardous Earth Flashcards
(126 cards)
1
Q
moho
A
- boundary between crust and mantle
- 35km beneath continents and 10-15km beneath ocean floor
- short for Mohorovici discontinuary
2
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tectonic plate
A
A large slab of the Earth’s lithosphere and crust
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Pangea
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A ‘super continent’ in the Carboniferous period, in which all of the Earth’s land mass were connected
4
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continental drift
A
- continents mobile and have moved across the Earth’s surface through geological time
5
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palaeomagnetism
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Traces of changes in the Earth’s magnetic field in the alignment of magnetic of magnetic materials in sedimentary and igneous rock
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sea-floor spreading
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- lateral movement of new oceanic crust away from mid-ocean ridges (constrictive plate boundary)
- key process in continental drift
7
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seismic
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An elastic wave generated by an impulse e.g. earthquake, that can travel along or near the Earth’s surface or through its interior
8
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mid ocean ridges
A
- 2.5km beneath ocean surface
- consist of long chains of mountains, which can rise up to 3000m above sea bed
- can be broken into segments by transform faults; which can cause earthquakes
- vary in shape depending on rate of spreading and amount of magma brought to surface by convection currents
9
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hot spots
A
volcanoes that occur not at plate boundaries
10
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pillow lavas
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Rounded mounds of lava erupted along mid-ocean ridges, which cool rapidly on contact with sea water
11
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graben
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The down faulted section of a rift valley
12
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transform faults
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large-scale faults in the crust at right angles to a mid ocean ridge, which range from 10-100skm, earthquakes common as they slip
13
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subduction
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the tectonic process found at convergent plate margins where an oceanic plate descends into the Earth’s mantle and is destroyed
14
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trench
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- narrow, deep depression on the ocean floor, adjacent to a subduction zone
15
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ocean trench
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long, narrow depressions, 6,000-11,000m deep, with steepest side towards continent
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Benioff zones
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boundary between a subducting ocean plate and the overriding continental plate at a destructive boundary
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island arcs
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chain of volcanic islands formed along a subduction zone
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fault
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A fracture between two blocks of rock. Allow the blocs to move more relative to each other, and can cause an earthquake
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convection currents
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movement of heat from core to asthenosphere, which causes movement of tectonic plates
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viscosity
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An indication of how well a substance flow’s. Acid lavas have a high viscosity as they are sticky and don’t flow far from a vent
21
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explosive
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A violent eruption, owing to the build-up of pressure within a volcano, due to the viscous magma preventing escape of gases (especially steam)
22
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effusive
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gentle, free flowing, basic eruption of lava
23
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mantle
A
- lies between core and crust
- most solid part of Earth’s interior
- 2,900km thick
- density 3.3 at Moho and 5.6 at core
- mineral composition rich in magnesium and iron
- separated from core by sharp boundary
24
Q
strato-volcano
A
steep-sided volcano made up of layers of lava and ash emitted during explosive eruptions (also known as composite cone)
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sills
minor, approximately horizontal, intrusion of magma into surrounding older rock
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dykes
vertical or near vertical minor intrusion of magma through surrounding older rocks
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calderas
large-scale volcanic crater formed as a result of an explosive eruption which emptied the magma chamber causing the volcano sides to subside
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Volcanic Explosivity Index (VEI)
Combines magnitude and intensity of an eruption on a logarithmic scale: 0=least explosive, 8=most
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pyroclastic flow
dense, fast-moving flow of solidified lava pieces, volcanic ash and hot gases, occurring as part of certain volcanic eruptions
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tephra
fragmental material produced by a volcanic eruption
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lahars
hot or cold mixture of water and rock fragment that flows down the slopes of a volcano and typically enter a river valley
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tsunami
series of waves caused by an earthquake or undersea volcanic eruption. As they travel inland, the waves build up higher as the depth of the ocean decreases. Their speed depends on death rather than distance from the source wave
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focus
point inside the crust where pressure is released, below the epicentre
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epicentre
point at the surface directly above an earthquake focus
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Richter scale
system measuring magnitude of an earthquake by using energy released when overstrained rocks suddenly fracture
- uses a logarithmic scale, with just over 9.0 being the largest quake scale to date
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mercalli scale
measures amount of damage caused by an earthquake, by measuring intensity, and changes according to which area you are measuring (damage near the epicentre would usually be greater than further away)
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Moment Magnitude Scale (Mw)
measure of earthquake strength using the amount of physical movement caused by a quake
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rift valley
valley formed by downfaulting between parallel faults e.g. mid ocean rides, East African Rift Valley
39
liquefaction
sediment and soils lose their mechanical strength from a sudden loss of cohesion
- material is temporarily transformed into a fluid as the result of being violently shaken during an earthquake
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resilience
degree to which an area can recover from the impacts of a hazard. The level of vulnerability affects a community's resilience
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primary effect
immediate and predicable events
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risk
frequency/ capacity to cope and adapt
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secondary effects
subsequent, less predicable or indirect events
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crust
- outermost shell of Earth,divided into older, continental crust and younger oceanic crust
- geology managed by plate tectonics
- 70km deep,
- 5-10km deep at ocean
- mineral composition, mainly granitic silicon and aluminium
- at ocean mainly basaltic, silicon and magnesium
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upper mantle
- had 2 layers: asthenosphere and lithosphere, which make up the oceanic and continental plates
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mantle-crust boundary
- marked by Moho discontinuity
- 35km deep below continents, 10-15km below ocean
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lithosphere
- above rigid layer in mantle between crust and asthenosphere
- divided into a series of tectonic plates
- varies in thickness and boundary with asthenosphere difficult to define as melts into semi-molten rock and becomes incorporated into asthenosphere
48
asthenosphere
- layer in Earth's mantle below lithosphere
- high temps cause rocks to soften and become viscous, so easily deform
- 100km-300km deep, semi-molten and flows slowly
- convection currents caused by vast amount of heat generated in mantle
- as a result, carries solid lithosphere and crust
- boundary with lithosphere difficult to define as melts and becomes incorporated into it
49
Wegener continental drift theory
- in Carboniferous period, large single continent, Pangaea, existed
- slowly broke down
- movement continued as continents separate & spread
- although scientists recognised value of this, failed to explain movement of continents. thus, until mid 20th century, his ideas existed as little more than footnotes
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Wegener continental drift theory: geographical evidence
- fit of continents e.g. South America and Africa on either side of the Atlantic
- effects of glaciation in Southern Africa, India, South America and Antarctica suggests these were connected
- mountain chains and some rock sequences on either side of oceans similar e.g. northeast Canada, and northern Scotland
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Wegener continental drift theory: biological evidence
- similar fossils/ marine shellfish found in Australian and Indian limestone e.g.
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palaeomagnetism
- technology designed to track submarines measured very small variations in Earth's magnetic field, which showed up as a striped pattern across the ocean floor
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palaeomagnetism: sea-floor spreading
- indigenous rocks, contain iron particles
- as lava erupts, cools and magnetic orientation of iron locked into the rock, depending on Earth's polarity
- every 400,000-500,000 years, polarity changes orientation, recorded in rocks on ocean floor
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palaeomagnetism: sea-floor spreading
- width of each strip of ocean bed with the same magnetic orientation corresponded with time scale
- as fresh molten rock reached ocean bed, older rock 'pushed' away from ridge
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palaeomagnetism: sea-floor spreading
- sea-floor spreading moves material across ocean floor as 'conveyor belt', on each side of mid-ocean ridge
- eventually, sea floor reaches an ocean trench where material subducted into asthenosphere and becomes semi-molten
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sea-floor spreading
- ideas of sea-flooring spreading and movement of continents linked in the mid 1960s
- with increased knowledge about shape and size of crustal plates and their boundaries, became clear plates were moved by sea-flooring spreading from the mid-ocean subduction at ocean trenches
- continents carried by plates, which supported Wegener's ideas
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age of sea-floor rocks
- during 1906s, ocean drilling programme investigated ocean sediments on ocean floor
- recovered cores in water up to 7000m deep, revealing spatial pattern of sediments (sea-floor spreading)
- thickest/ oldest sediments found nearest to continents
- however, cores also showed rock no older than 200 million years, confirming ocean crust constantly recycled over this period
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global patterns of plate boundaries
- from mid 1960s, nuclear tests released vast amounts of energy picked up on seismometers
- showed most earthquakes spatially concentrated in narrow bands
- in between, large areas generating fewer earthquakes
- suggested crust broken into tectonic plates
- today, patterns of 7 major plates and other minor ones are well known, although details still subject of research
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convergent (destructive) plate boundaries
where 2 plates collide
- layer of crust 'lost'
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convergent: oceanic-continental
- subduction: denser oceanic plate forced under continental plate
- creates ocean trench: marks subduction where oceanic crust ascends into asthenosphere, which is asymmetrical with steepest side towards continent
- e.g. Andes, South America
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convergent: oceanic-continental hazards
- faulting and fracturing occur in Benioff zone, causing earthquakes
- causes oceanic plate to melt, which rises to surface and uplift fold mountains - causing volcanoes
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convergent: oceanic-oceanic
- where they meet, the denser one subducts under the other
- forms trenches
- forms island arches: as descending plate melts magma rises to the surface and forms chains of volcanic islands
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convergent: oceanic-oceanic case studies
- in central Atlantic, North American subducted beneath Caribbean plate, forming Antilles
- in Pacific 'Rim of Fire' contains island arcs e.g. Aleutian Islands, extending west from Alaska
- Mariana Trench: 11,000 m below ocean surface where Pacific subducted underneath Philippine plate
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convergent: continental-continental
- when converge, little subduction takes place - as have similar densities
- e.g. collision of African and Eurasian plates in Europe over past 40 million years created the Alps
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divergent (constructive) plate boundaries
where 2 plates move apart
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divergent: continental-continental
- continental crust can thin and cause rifting
- as it widens, magma erupts at the surface, eventually sinking below sea level
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divergent: continental-continental case studies
- rifting formed Red Sea (its rift stretches to Turkey), its crust also stretched and caused graben. if crust continues to thin, magma will well up and form a new spreading boundary between Africa and Arabian Peninsula
- in Israel, rift dips below sea level, forming Dead Sea at -400m
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divergent: oceanic-oceanic
- plates move apart and magma rises through asthenosphere and forces it's way to the surface
- mid-ocean ridges can fault, creating earthquakes when they slip
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divergent: oceanic-oceanic
- formation of mid ocean ridges
- eruption of lava causes pillow lavas
- underwater rift valley's created when magma rises to surface and is forced into a dome, putting lithosphere under stress
- black smokers: at mid ocean-ridges sea water water seeps into rifts and rises towards the surface, causing chemical changes in basaltic rocks, resulting in superheated jets of water re-emerging on the ocean floor containing metal sulphides
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conservative: continental-continental
- 2 continental plates try to slide past each other side by side, but will only move after a long time after pressure has built up, which is released in a sudden movement
- possible to see where plates have shifted
- cause earthquakes
- e.g. San Andreas Fault on west coast of USA
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conservative plate boundaries
where plates slide horizontally past each other
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divergent: oceanic-oceanic case study
- North Atlantic: extrusion of magma so great it created Iceland, the world's largest volcanic island, with a central rift valley
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explosive eruptions
- on convergent plate boundaries
- lava acidic, high viscosity, low temp at eruption
- eruption violent: bursting of gas bubbles when magma reaches surface, top of cone often shattered
- long periods with no activity
- steep-sided strato-volcanoes
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effusive eruption
- on divergent plate boundaries
- lava basic, low viscosity, high temp at eruption
- gas bubbles expand freely; limited explosive force
- eruption more frequent can continue for many months
- volcano gently sloping sided, shielded
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Icelandic lava eruption
- characterised by persistent fissure eruption
- large quantities of basaltic lava build up vast horizontal planes
- formed Deccan and Columbian Plateau
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vulicanian eruption
- violent gas explosions bursts out sticky cooled lava
- fragments build up into cones of ash and pumice
- occur when there is very viscous lava which solidifies rapidly after an explosion
- often clears a blocked vent and spews large quantites of volcanic ash into atmosphere
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Hawaiian eruptions
- more noticeable activity
- runny, basaltic lava travels down sides of volcano in lava flows
- gases escape easily
- occasional pyroclastic activity occurs but less important than lava eruption
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Strombolian eruptions
- frequent gas explosions which blast fragments of runny lava into the air to form cones
- very eruptions with large quantities of pyroclastic rock thrown out
- eruptions commonly marked by a white cloud of stem emitted from crater
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plinian eruption
- gas rushes up through sticky lava and blasts gas and fragments into the sky in a huge explosion
- create immense gas clouds and volcanic debris several km thick
- gas clouds and lava rush down slopes
- part of volcano may be blasted away
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vesuvian eruptions
- very powerful blasts of gas pushing ash clouds high into the sky
- lava flows
- ash falls to cover surrounding areas
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strato volcanoes (explosive eruptions)
- made of layers of ash and acid lava
- complex internal networks of lava flows
- acid magma doesn't flow easily, vents often fill with mass of solidified magma
- this prevents magma from rising freely from depth
- enormous pressures can build up inside a volcano until it erupts
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calderas (explosive eruptions)
volcanic craters
- distance 2km+
- develop when explosive eruption destroys cone and underlying magma chamber largely empties
- without support of underground magma, sides of the volcano collapse to form a caldera
- e.g. Krakatoa eruption 1883 left caldera 7km wide
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lava plateaux (effusive eruptions)
- magma erupts from multiple fixtures, vast areas can be covered by free-flowing lava
- when first formed, have uniform slope about 1 degree
- however, millions of years of denudation have created more varied relief
- no large-scale flood basalt events have occurred in the past 50 million years
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shield volcanoes (effusive eruptions)
- divergent plate boundaries coincide with mid-ocean ridges, most effusive eruptions occur on sea floor
- eruptions of basic lava cause volcanoes with gently sloping sides
- if successive flows accumulate for long enough cause huge volcanoes e.g. Skjaldbreidur in Iceland
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shield volcanoes (effusive eruptions)
- however, Iceland an exception: owes its formation to effusive volcanic activity and is one of the most active volcanic regions in the world
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hot spot
fixed area of intense volcanic activity where magma from a rising mental plume reaches the earths surface
- however, not all volcanism leads to shield volcanoes e.g. El Teide in Tenerife a strato-volcano which has erupted on several occasions since 1700, most recently in 1909
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eruptions at hot spots - Hawaiian chain
- lies at centre of Pacific plate, 1000s km from nearest plate boundary
- as plate moved northwest over Hawaiian hot spot (1cm/yr), vast amounts of basalt accumulated on ocean floor
- volcanic peaks of Mauna Loa over 4000m above sea level and rise more than 9000km from the ocean floor
- older islands in chain, e.g. Kauai no longer active
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eruptions at hot spots - Hawaiian chain
- on older volcanoes, weathering and erosion broke down volcanic rocks into deep/fertile soils and valleys carved by rivers
- in northwest, volcanic islands have sunk below surface forming underwater mountains
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eruptions at hot spots - Hawaiian chain
- 30km southeast, next volcano in chain, Loihi, slowly rising up, currently 970m below sea level
- its position above hot spot means it will continue to grow, and eventually will emerge
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super volcanoes
- a volcano that erupts more than 1000 km(3) of material in a single eruption
- giant calderas
- e.g. Yellowstone has 75km wide caldera
- most recent eruption 27,000 years ago at Taupo, New Zealand: depth of ash layers had impacts on plants, insects and animals
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hazards produced by volcanic activity
- usually short term
- can have long term impacts if emit large quantities of ash into atmosphere, as can reduce global temps and blocks sunlight (e.g. so2 with water = sulphur acid)
- e.g. super volcano eruptions like Toba, Indonesia
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hazards produced by volcanic activity: lava flows
- depend on the type of lava
- basic (basaltic) free flowing so can run distances e.g. 20km in Hawaii July-August 2015
- acidic flows thick so dont flow as easily, and everything in their path destroyed or buried
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hazards produced by volcanic activity: pyroclastic flows
- combination of hot gases (500+), ash and rocks travelling at a high speed (100km/h)
- follow contours of ground and destroy everything
- inhalation causes almost death
- e.g. Pomeii in 79 from mount Vesuvius
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hazards produced by volcanic activity: tephra
- any material ejected from a volcano into the air
- ranges from fine ash to volcanic noms (>6cm across)
- buries farmland and crops, buildings collapse, difficulty breathing and transport disrupted
- e.g. an eruption in Iceland in 2010 led to the cancellation of 100,000 flights
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hazards produced by volcanic activity: eruptions
- emit toxic gases, which can be deadly
- when so2 combines with atmospheric water acid rain produced, enhancing weathering, damaging crops and polluting surface water and soils
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hazards produced by volcanic activity: lahars
- type of mud flow with consistency of wet concrete
- can move up to 50km/h
- rocks, soil and ash mix, and destroy all in its path
- e.g. eruption left 23,000 dead in Armero, Columbia
- in places like Southeast Asia, ash covered slops continue to produce lahars after heavy rain
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hazards produced by volcanic activity: tsunami
- caused my displacement of ocean water
- waves can travel 600 km/h
- about 1km high and 200km wavelength in deep water, but increase in height as near the shore and transfer vast amount of energy when they break
- e.g. Boxing Day tsunami 2004 killed 230,000 people
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advantages of living in a volcanic area
- geothermal energy: magma is close to the surface, groundwater turns to steam with drives turbines
- tourism and recreation
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living on a plate margin
pyroclastic flows e.g. hot mixtures of gas, destroying everything in its path
- lahars (volcanic mud flows) that bury settlements and cause flooding
- earthquakes and tsunamis
- heavy ash fall: crop failure, illness, disrupts transport
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why people live on plate margins
- unaware of dangers
- overpopulation
- history
- in denial (haven't experienced eruption e.g.)
- weighed up risks
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utilising volcanic resources on plate margins: agriculture
- crops grow well on volcanic soil as have large pores allowing root development and drainage
- soils young: high in nutrients
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utilising volcanic resources on plate margins: tourism
- improvements in travel e.g. cruises
- climbing easier e.g. access to routs, aware of dangers
- marketing: packages combine visits and skiing e.g.
- landscapes created by volcanoes
- hot springs e.g. blue lagoon, Iceland
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earthquakes
- represents release of stress that has been built up within earths crust caused by tension or compression
- seismic waves originate from earthquake focus, just below epicentre
- can be predicted by fore-shocks
- after-shocks afterwards
- concentrated at: mid-ocean ridges, ocean trenches and island arcs, collision zones and conservative plate margins
- despite happening close to tectonic plate margins, stress within crust widespread; so can occur anywhere
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seismic waves: primary (P)
- move through solids and liquids in earths interior
- fast, low frequency, vibrate in direction they travel
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seismic waves: secondary (S)
- pass through liquids so cannot travel through outer core
- slow, high frequency, vibrate at right angle to direction they travel
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seismic waves: surface (L)
- move through outer crust
- slowest, some roll surface vertically, others move ground at right angle to direction of movement
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depth of focus: shallow
- surface down to about 70km, common
- occur in cold, brittle rocks due to stress within crust
- many release low levels of energy, although high energy ones can have severe impacts
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depth of focus: deep
- 70-700km, poorly understood
- with increasing depth, pressure and temp increase
- minerals change type and volume, contributing to release of energy
- water also may play a role in energy release
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The Ritcher scale
- uses amplitude of seismic waves to determine mag
- logarithmic: each whole number increase in mag represents 10 fold increase in mag of seismic waves
- has no upper limit: highest recorded 9 (Sendai quake off Pacific Ocean near Japan in 2011)
- not used to express damage
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The Modified Mercalli Scale
- measures quake intensity and impact
- qualitative: relates ground movement to impacts that can be felt and seen by anyone in affected location
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The Moment Magnitude scale (MW)
- measures energy released by quake more accurately than richter, as uses physical movement caused
- energy released related to geological properties e.g. movement of fault, rock rigidity
- however, not used for small earthquakes
- e.g. 5.0= atomic bomb - Nagasaki, Japan in 1945
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human causes of earthquakes
- collapse of mine works
- extraction of oil/ gas
- nuclear testing
- creation of geothermal electricity (water to lithosphere then pumping back up)
- artificial lakes e.g. Koynanagar quake, India, linked to this and caused 177 deaths and 2000 injured
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effects of earthquakes on landforms and landscapes
- can form entire mountain ranges e.g. Himalayas, due to the complex pattern of folding and faulting of rocks
- rift valleys shown inward facing fault scarps caused by tension and compression
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hazards produced by earthquakes: ground shaking and displacement
- depends on magnitude, distance from epicentre, geology
- locations close to epicentre of high magnitude quake where surface unconsolidated and have high water content experience extreme ground shaking e.g. Japan
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hazards produced by earthquakes: ground shaking and displacement
- buildings can withstand vertical movements better horizontal, as affects stability
- displacement of rocks can rip sewers, train tracks e.g.
- can disrupt natural drainage, diverting movement of ground water and impact water supplies
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hazards produced by earthquakes: liquefaction
- when quake strikes an area with surface materials of fine-sand with high water content, vibrations can cause these materials to act like liquids
- loose strength e.g. mass movement, land slides
- e.g. Kobe quake, port built on reclaimed land, affecting worldwide trade
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hazards produced by earthquakes: landslides and avalanches
- liquefaction causes slop failure; steep slopes more vulnerable e.g. Himalayas, increased by deforestation, heavy moonsoon rain - triggered 2015 Nepalese quake
-landslides block transport, especially mountain regions
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hazards produced by earthquakes: landslides and avalanches
- movement of soil and rock blocks rivers, creating natural dams and sometimes floods e.g. Kashmir 2005
- upland sites favours reservoirs e.g. Italy, 1963 collapse of hillside near Vaiont reservoir caused 100m wave which drowned 3000 people
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earthquake benefits
- create faults that trap oil and gas reserves
- water tables elevated water can be trapped
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hazards produced by earthquakes: tsunamis
- underwater quakes cause sea bed to rise vertically, displacing water above and producing powerful waves that spread out at high velocity from epicentre
- low height (<1m) and long wavelength (200km), can travel under ships unnoticed
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hazards produced by earthquakes: tsunamis
- heigh increases as get to shore and shallow water
- drawdown: before wave breaks, water in front pulled back to sea
- tsunami wave rushes as wall of water, exceeding 25m
- e.g. Boxing Day, 2004 tsunami delivered 1000t water per metre of shoreline
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hazards produced by earthquakes: tsunamis
- can be caused by underwater landslides; rock shaken and slides downslope, water dragged behind and collides in the centre
- doesn't always have enough power to cross oceans, but in Papua New Guinea, 1998 2200 people killed by this
- local, so warning signs short
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active, dormant and extinct volcanoes
- described as these on basis of eruption history; can be difficult to do this
- however, extinct seen as one that wont erupt again
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active volcanoes
- some only see active if erupted in historic times; but can be difficult due to records available
- others only see as active if evidence of unusual quake activity or gas emissions
- widely accepted active if erupted since last glacial period or within past 10,000 years
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dormant volcanoes
- Smithsonian institute: hasn't erupted over past 10,000 yrs but expected to erupt in future
- Mount St Helens considered dormant until 1980 eruption, but Yellowstone caldera not erupted for 70,000 yrs but seen as active e.g. quakes, ground infiltration, geothermal features
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