hazardous earth Flashcards
what is the earth’s core made of?
dense rock eg iron + nickel
inner core solid, outer core molten
what is the temperature of the core and how is it heated?
> 5000 degrees celcius
heated from primordial and radioactive (eg from plutonium) heat
what is the mantle made of?
molten/semi-molten, mainly silicon + oxygen
g
what is the continental crust composed of?
granite, silicon, aluminium and oxygen
what is the thickness of continental crust?
30-70km
what is the age of continental crust?
1,500 milllion+ years
what is the density of continental crust?
2.7g/cm3
what is the thickness of oceanic crust?
6-10km
what is the age of oceanic crust?
up to 200 million years old
what is the density of oceanic crust?
3.3g/cm3
b
what is oceanic crust composed of?
basalt, silicon, magnesium, oxygen etc
what was Alfred Wegener’s theory?
1912, Theory of Plate Tectonics, suggested Supercontinent called Pangaea, suggested continents moved via continental drift
what was the geological evidence for Wegener’s theory?
fit of the continents
glacial deposits 290 million years ago in South America, Antarctica and India
same rock sequences found in Scotland and Canada
biological evidence for Wegener’s theory?
similar fossils found in India and Australia
Mesosaurus fossils in S. America and S. Africa
same plant fossil in India and Antarctica
what is sea floor spreading? (+ paleomagnetic evidence)
mid Atlantic ridge, scientists found crust on either side of the ridge that suggested that sea-floor spreading was occurring
molten material comes from mantle and pushes up between the two plates and forming new material in the middle. this pushes the plates on either side apart
magnetic field of the earth switches at 400,000 year intervals from north to south, iron particles in crust will align themselves to the polarity of the Earth. Alternating bands with differing polarity of iron particles shows oceanic crust has been spreading over time
what are the thermal currents in the mantle called?
convection currents
what is slab pull?
slab pull is a force that drives the movement of tectonic plates. It is caused by the sinking of the cold, dense lithosphere into the mantle at a destructive margin. the weight of the subducted slab may drag the rest of the plate toward the trench.
how is an ocean ridge formed?
at a constructive plate boundary, lava rises to form a ridge. this can lead to submarine volcanoes
how is a Rift Valley formed?
plates moving apart on continents at a constructive plate boundary, fault moves downwards (see a diagram i can’t attach one)
a horst refers to a raised elongated block of the earth’s crust lying between two faults
eg East African Rift Valley, this might end up forming a new ocean
how is a deep sea trench formed?
destructive boundaries, oceanic and continental boundary. oceanic plate subducted.
eg Mariana Trench
can get Island Arcs when oceanic crust melts again at Benioff Zone, rises up and cools to form new land
how are Young Fold Mountains formed?
destructive plate boundary
continental-continental convergence
forms mountain range eg Himalayas, Mt Everest etc, formed with Indian and Eurasian plate
what is the asthenosphere?
the layer in the Earth’s mantle below the lithosphere. The high temperatures cause the rocks to soften and become viscous meaning that they can easily deform
what is the lithosphere?
layer in the earth’s mantle above the asthenosphere together with the crust which is divided into a series of tectonic plates
is rigid and is moved by the flows of semi-molten rock in the asthenosphere
what was pangaea?
wegener proposed that in the Carboniferous period 250 million years ago, a large single continent existed called Pangaea
how do the age of sea floor rocks evidence sea floor spreading?
the prediction was that oceanic rocks would get older the further one was from the mid-ocean ridge. the cores also showed that nowhere in the oceans was rock older than 200 million years. this confirmed that the ocean crust was constantly recycled over this period
what are the three types of plate boundary?
divergent (constructive), convergent (destructive) and conservative
what are transform faults?
large scale faults in the crust at right angles to a mid ocean ridge, which range from a few tens of km to several hundred. earthquakes occur along their lengths as they slip
what type of landforms are a result of fast spreading?
broad and smooth mountain chains; no central rift valleys
eg East Pacific Rise (Pacific and Nazca plates)
what type of landforms are a result of medium spreading?
poorly defined central rift valleys; relatively smooth mountain chains
eg Galapagos Ridge (just south of the Nazca and Cocos plate boundary)
what type of landforms are a result of slow spreading?
steep slopes to mountain chains; clearly defined central rift valleys
what are pillow lavas?
the eruption of magma along divergent boundaries occurs mostly underwater. Magma erupting directly on to the sea bed is cooled rapidly, forming rounded mounds called pillow lavas
how are underwater rift valleys found along mid ocean ridges formed?
as magma rises towards the surface, the pressure reduces and it liquefies. The overlying rocks are forced upwards as the lithosphere is placed under stress and eventually fractures. This produces the underwater rift valleys..
In the North Atlantic, the extrusion of magma has been so great it has created the world’s largest volcanic island – Iceland.
how are black smokers formed?
at mid ocean ridges, sea water seeps into rifts and is superheated.
As it rises towards the surface it causes chemical changes in the basaltic rocks.
Superheated jets of water sometimes re emerge on the ocean floor containing metal sulphides.
These features are commonly known as black smokers and support unique and highly specialised organisms and ecosystems
how was the Red Sea formed?
rift zones are not confined to the ocean floor; they also occur on land in part explain how continents can break up. the continental crust must thin considerably for rifting to occur
one of the best examples is the rift stretching from the Red Sea northwards to Turkey. Here, the crust has been uplifted and stretched, causing faulting and forming a sunken valley known as a GRABEN. as the rift widened, magma erupted at the surface. eventually, the rift valley sank below sea level, forming the present day Red Sea.
If the crust continues to thin here, magma will well up to form a new spreading boundary between Africa and the Arabian Peninsula. Further north in Israel, the rift dips below sea level, forming the Dead Sea.
what is subduction?
when oceanic and continental plates converge, the denser oceanic plate is forced under the continental plate.
how are mountain chains such as the Andes formed?
layers of sediment and sedimentary rock develops on oceanic plates adjacent to continents. As an oceanic plate converges on a continental plate, these sediments and rocks crumple, fold and are uplifted along the leading edge of the continental plate. In addition, the continental crust is buckled and uplifted, and significant amounts of molten material are injected into it.
what is the Benioff zone?
boundary between a subducting ocean plate and the over-riding continental plate at a destructive boundary
what angle is the oceanic plate subducted?
between 30 and 70 degrees
faulting and fracturing occur in the Benioff zone, where the descending plate is at an angle close to 45 degrees. This process releases considerable amounts of energy in the form of earthquakes
what happens at oceanic-oceanic plate margins? (convergent)
when two oceanic plates meet, the slightly older and therefore denser one will subduct under the other, creating a trench.
as the plate descends, dehydration takes place causing partial melting of the mantle wedge in the plate above. this magma rises to the surface and forms chains of volcanic islands known as island arcs.
what happens when two continental plates converge?
little, if any, subduction takes place. This is because the two plates have similar densities.
In Europe, the collision of the African and Eurasian plates over the last 40 million years has created the Alps
what are conservative plate margins?
where plates slide past each other
volcanic activity absent bc no subduction takes place
frictional resistance to movement along the plate boundaries often causes the build up of pressure. from time to time these pressures cause rocks to fracture, releasing enormous amounts of energy as the pressure is released, causing earthquakes
example of a conservative plate boundary?
in California, where the NA and Pacific plates, although moving in the same direction, are doing so at different rates
where are explosive eruptions found?
convergent plate boundaries
where are effusive eruptions found?
divergent plate boundaries
what type of lava comes from explosive eruptions?
rhyolite (more acid)
andesite (less acid)
what type of lava comes from effusive eruptions?
basalt
lava characteristics of explosive eruptions?
acid (high % silica), high viscosity, lower temp at eruption
lava characteristics of effusive eruptions?
basic (low % silica), low viscosity, higher temperature at eruption
style of eruption in explosive eruptions?
violent bursting of gas bubbles when magma reaches surface
highly explosive
vent and top of cone often shattered
style of eruption in effusive eruptions?
gas bubbles expand freely
limited explosive force
materials erupted in explosive eruptions?
gas, dust, ash, lava bombs, tephra
materials erupted in effusive eruptions?
gas, lava flows
frequency of eruption in explosive eruptions?
tend to have long periods with no activity
frequency of eruption in effusive eruptions?
tend to be more frequent
an eruption can continue for many months
shape of volcano from explosive eruptions?
steep sided strato-volcanoes; caldera
shape of volcano from effusive eruptions?
gently sloping sides, shield volcanoes
lava plateaux when eruption from multiple fissures
what are icelandic lava eruptions?
characterised by persistent fissure eruption. Large quantities of basaltic lava build up horizontal plains
what are hawaiian eruptions?
involve more noticeable central activity than the Icelandic type.
runny, basaltic lava travels down the sides of the volcano in lava flows
gases escape easily
occasional pyroclastic activity occurs
what are strombolian eruptions?
characterised by frequent gas explosions which blast fragments of runny lava into the air to form cones
they are very large explosive eruptions with large quantities of pyroclastics thrown out
what are vulcanian eruptions?
violent gas explosions blast out plugs of sticky or cooled lava.
fragments build up into cones of ash and pumice
vulcanian eruptions occur when there is very viscous lava which solidifies rapidly
often the eruption clears a blocked vent and spews large quantities of volcanic ash into the atmosphere
what are vesuvian eruptions?
characterised by very powerful blasts of gas creating ash clouds high into the sky
they are more violent than vulcanian eruptions
lava flows also occur
what is a plinian eruption?
gas rushes up through sticky lava and blasts ash and fragments into the sky in a huge explosion
the violent eruptions create large clouds of gas and pyroclastics
along with the lava these clouds can rush down the slopes
part of the volcano may be blasted away during the eruption
what are the reasons behind the variety of landforms formed by volcanic eruptions?
this diversity is related to where the eruption occurs, the type of lava, the variety of materials (such as ash, pumice and gases) produced, and how the eruption takes place
for example, differences in the chemistry of the magma influences the type of eruption and the shape of the volcano
once magma is ejected at the surface, its behaviour is affected by its viscosity, which in turn is determined by its chemical composition and temperature, and the changes that take place to magma within the magma chamber
what are strato-volcanoes like?
sometimes known as composite cone volcanoes
are made up of layers of ash and acid lava
have concave symmetrical profiles
most contain complex internal networks of lava flows which form minor igneous features such as sills and dykes
because acid magma does not flow easily, the vents are often filled with a mass of solidified magma, which prevents magma from rising freely from depth. as a result, enormous pressures can build up inside a volcano until it eventually erupts explosively, sometimes literally blowing its top off
what is a sill?
a minor, approximately horizontal, intrusion of magma into surrounding older rocks
what is a dyke?
a vertical or near vertical minor intrusion of magma through surrounding older rocks
what are calderas?
volcanic craters, usually more than 2km in diameter
they develop when an explosive eruption destroys much of the cone and the underlying magma chamber is largely emptied
without the support of the underground magma, the sides of the volcano collapse to form a caldera
the 1883 eruption of Krakatoa in Indonesia left a caldera 7km wide
examples of stratovolcanoes?
convergent plate boundaries and explosive eruptions often give rise to chains of stratovolcanoes
Indonesia, for example, has 130 active stratovolcanoes along its archipelago, while in the Andes, 66 stratovolcanoes have erupted in recorded history
what is important to recognise about the classification of volcanoes?
that volcanoes are unpredictable and resist easy classification
for example, Icelandic volcanoes include stratovolcanoes, shield volcanoes and fissures
(give example and say what an LIP is)
what is a lava plateaux like?
when basic magma erupts from multiple fissures, vast areas can be covered by free-flowing lava. these events are known as flood basalts
examples include the Deccan Plateau in central India, which covers more than 500,000km2, known as an LIP (large igneous province), while the Columbia Plateau in NW USA covers 130,000km2
however, millions of years of denundation have created more varied relief. no large scale flood basalt events have taken place in the past 50 million years. When they do occur they have a devestating impact on the atmosphere and hydrosphere, and consequentially the biosphere
what are shield volcanoes? (give example)
effusive eruptions are usually found at divergent plate boundaries. Because these boundaries coincide with mid-ocean ridges, most effusive eruptions occur unseen on the ocean floor
Iceland is an exception. It owes its formation to effusive volcanic activity and is one of the most active volcanic regions in the world
eruptions of basic lava result in volcanoes with gently sloping sides
if successive flows accumulate for long enough, huge volcanoes, extending horizontally for tens of kilometres, such as Skjaldbreidur on Iceland, can develop
what is a hot spot?
a fixed area of intense volcanic activity where magma from a rising mantle plume reaches the Earth’s surface
how have the hawaiian islands been formed?
as the pacific plate has moved northwest over the Hawaiian hot spot (at an average rate of 10cm/year), vast amounts of basalt have accumulated on the ocean floor to produce the Hawaiian islands
why is volcanism on the older islands in the Hawaiian chain, such as Kauai, no longer active?
over millions of years, as the pacific plate move northwest and over the hotspot, the volcanoes lose their source of magma and become extinct
thus, on the older islands in the Hawaiian chain, such as Kauai, volcanism is no longer active. there, weathering and erosion have broken down the volcanic rocks into deep and fertile soils. further along the chain to the NW, the volcanic islands have sunk below the surface of the Pacific to form underwater mountains or seamounts
what are super volcanos?
a volcano that erupts more than 1000km3 of material in a single eruption event is known as a super volcano.
the evidence of past and perhaps future super volcanic activity is the existence of giant calderas.
eg The Yellowstone supervolcano in Wyoming has a caldera measuring 75km in diameter
the most recent supervolcanic eruption occured 27,000 years ago at Taupo, New Zealand.
The impact of these very high magnitude events is deduced from the extent and depth of ash layers and their impact on plant, insect and animal species
what are the two key factors that need to be considered when comparing eruptions?
magnitude (the amount of material erupted)
intensity (the speed at which material is erupted)
what is the most widely used measure of eruption?
the Volcanic Explosivity Index (VEI)
it combines magnitude and intensity into a single number on a scale from 0, the least explosive, to 8, the most explosive
what are the factors taken into account when assessing the explosivity of an eruption?
the volume of erupted material
the height ejected material reaches
the duration in hours
various qualitative descriptions
what is the VEI useful and not useful for?
The VEI is not that useful for effusive eruptions such as those on Hawaii. However, it is valuable in suggesting the relative impacts volcanoes might have at different geographical scales
what are continental flood basalts and giant oceanic plateaus?(+ example of one of the largest)
these are massive effusive outpourings of basalt that commonly erupt intermittently over very long periods of time and typically cover areas between 2000-2500km across.
one of the largest of them, the Siberian Traps, has a total volume of 3 million km3 which would be enough to bury the whole of western Europe under a 1km thick sheet of basalt
what is the current favourite theory as to how continental flood basalts and giant oceanic plateaus are formed?
is that they are formed by mantle plumes of very hot but solid material that rises from the junction between the mantle and the liquid outer core; the same process that creates convection currents in the mantle
the material making up the plume is mafic but changes chemically by the time that it reaches the surface depending on whether the last leg of the plume’s route to the surface is through the oceanic crust or continental
what are the impacts of large igneous provinces (LIPs)?
LIP events are devastating. Millions of cubic km of magma ponds up below the lithosphere before periodically breaking through the lithosphere and crust, erupting over several million years
the amount of material produced might create global cooling initially, as other eruptions have historic time, but given that CO2 is the most significant gas emitted by most effusive eruptions, the long term impact is global warming and ocean acidification
LIP events have been identified as possible causes for at least four major extinctions, including the Permian extinction. Each of these were brought about by significant peaks in atmospheric CO2
how are supervolcanoes and hotspots linked to LIPs?
some Earth scientists propose that supervolcanoes and hot spots are the final remnants of past LIP events
about 15 million years ago, a LIP created the Columbia River flood-basalts in what is now the NW of USA. That corresponds to where the Yellowstone caldera would have been located at the time. In its current hot spot position, volcanic activity began about 2 million years ago when a giant caldera formed. Two further huge eruptions took place 1.3 million years and 640,000 years ago. In addition to these, dozens of smaller eruptions occured
bc the evidence of earlier eruptions may have been either buried or destroyed by later ones, it is not known exactly how often the volcano has erupted, nor the volume of material extruded. during the largest eruptions, ash was spread over much of the western half of NA, while gases and tiny particulates were carried around the globe in the upper atmosphere
what are lava flows and their impacts?
the impacts are dependent on type of lava. Basic (basaltic) lava is free-flowing and can run for considerable distances
on hawaii in july 2015, a lava flow extended from 20km before stopping and in August the same year a flow was reported to have covered about 800m in a day
acidic lavas such as rhyolite are thick and pasty so do not flow easily.
everything in the path of lava will be either burned, bulldozed or buried. Although they destroy infrastructure, property and crops, lava flows rarely cause injuries or fatalities
what are pyroclastic flows?
a combination of very hot gases, ash and rock fragments travelling at high speed.
they follow the contours of the ground and destroy everything in their path
the inhalation of such hot and poisonous gas and ash causes almost instant death
Pompeii was overwhelmed by a pyroclastic flow from Vesuvius in AD 79
what is tephra?
this describes any material ejected from a volcano into the air
ranges in size from very fine ash to large volcanic bombs
also includes lighter debris such as pumice
potentially very hazardous, burying farmland in layers of ash and destroying crops
eruption columns can carry material into the stratosphere largely bc the temp of ejected material is always much hotter than the surrounding air, so it rises very fast, in addition to the propulsion of the explosion itself
buildings can collapse due to the weight of accumulated ash and people with respiratory diseases may have difficulty breathing
how can the gases released from volcanoes be dangerous?
eruptions emit a wide range of toxic gases, including CO, CO2 and SO2. these can pose a deadly threat to humans
when SO2 combines with atmospheric water, acid rain is produced. this can damage crops and pollute surface water and soils
what are lahars?
these are a type of mud flow with the consistency of wet concrete
snow and ice on a volcano summit melt during an eruption and flow rapidly down the cone
rock fragments large and small, as well as ash and soil, are mixed together
can travel at speeds up to about 50km/h. everything in their path is either destroyed or buried under thick layers of debris
in places such as southeast asia, ash-covered slopes of volcanoes continue to generate lahar hazards after periods of heavy rain
how do volcanoes cause floods?
volcanic eruptions beneath an ice field or glacier cause rapid melting
in iceland, several active volcanoes lie under the Vatnajokull ice field. during an eruption, vast quantities of water accumulate until they find an exit from under the ice. the resulting torrent of water is known locally as a JOKULHLAUP
how can volcanoes cause tsunamis?
the violent eruption of some island volcanoes can cause massive displacement of ocean water and tsunami waves capable of travelling at speeds of up to 600km/h
approaching the shore, tsunami waves increase rapidly in height and when they break transfer vast amounts of energy and water along the shore and inland
the tsunamis created by the eruption of Krakatoa in 1883 are believed to have drowned 36,000 people
how can volcanoes impact longer-term climatic change?
past eruptions of super-volcanoes such as Toba, Indonesia led to reductions in global temperatures as ash blocked sunlight from reaching the Earth’s surface, and has been linked with a dramatic fall in the global human population at the time
what is lake nyos?
lake nyos is one of a number of deep lakes that occupy volcanic craters in Cameroon in West Africa
it is 2km wide and 200m deep
in August 1986, 1700 people and all animal life in the area around the volcano were asphyxiated. the cause was a leak of CO2 from a volcanic crater lake. the gas had built up at the bottom of the lake after being emitted from the underlying magma chamber
when the CO2 escaped it flowed down the volcano slopes as a 50m thick ground hugging layer travelling at about 70km/h
it is not known for certain what caused the CO2 to escape the lake. possible explanations are a deep movement of magma, an earthquake, a change in water temp in the lake, or strong winds stirring up the lake waters, much like shaking a fizzy drink
what is an earthquake?
earthquakes represent the release of stress that has built up within the Earth’s crust caused by tension, compression or the shearing of rocks
what is the epicentre?
point at the surface directly above an earthquake focus
example of a pyroclastic flow?
Pompeii was overwhelmed by a pyroclastic flow from Mount Vesuvius in AD 79
example of tephra impacts?
the eruption of Iceland’s Eyjafjallajokull volcano in April 2010 led to the cancellation of 100,000 flights
example of a lahar?
in 1984, following the eruption of Nevado del Ruiz, the Colombian town of Armero was overwhelmed by lahars, resulting in the deaths of 23,000 people
where does earthquake activity tend to be concentrated to?
mid ocean ridges: tensional forces associated with spreading processes and subsequent faulting and rifting
ocean trenches and island arcs: compressive forces associated with the subduction of one plate below another
collision zones: compressive forces associated with the grinding together of plates carrying continental crust
conservative plate margins: shearing forces associated with the intermittent movement of one plate past another
what are the three types of seismic waves?
P WAVES– fast travelling, low frequency compressional waves. They vibrate in the direction in which they travel
S WAVES– half the speed of P waves, high frequency waves. they vibrate at right angles to the direction in which they travel
L WAVES– slowest of the three types, low frequency waves. some L waves have a rolling movement that moves the surface vertically, while others move the ground at right angles to the direction of the movement
where do the types of seismic waves travel?
L waves travel through the outer crust only
S waves cannot pass through liquids (and so cannot travel through the outer core)
P waves travel through the Earth’s interior (through both solids and liquids)
what are shallow focus earthquakes?
surface down to about 70km
occur in cold brittle rocks, resulting from the fracturing of rock due to stress within the crust
very common, with many releasing only low levels of energy, although other high energy shallow quakes are capable of causing severe impacts
what are deep focus earthquakes?
70-700km.
are poorly understood
with increasing depth, pressure and temperatures increase to very high levels. minerals change type and volume, which may contribute to a release of energy. it is likely that dehydration of water in subducting plates plays a significant role in these events but scientists continue to evolve their ideas about these less frequent but often powerful quakes
what is the richter scale?
uses the amplitude of seismic waves to determine earthquake magnitude.
logarithmic scale
has no upper limit, though the largest earthquakes record a magnitude of around 9 (eg Tohoku, Japan 2011)
is not used to express damage. an earthquake’s damage is determined partly by magnitude but also by other factors such as population density and levels of preparedness
what is the modified mercalli scale?
measures earthquake intensity and its impact
relates ground movement to impacts that can be felt and seen by anyone in the affected location
is a qualitative assessment based upon observation and description
what is the Moment Magnitude Scale?
measures the energy released by the earthquake more accurately than the Richter scale
the amount of energy released is related to the geological properties such as the rock rigidity, area of the fault surface and amount of movement on the fault
also logarithmic
provides the most accurate measurement of large earthquakes as it uses the amount of physical movement caused by an earthquake, which is a direct function of energy
not used for small earthquakes
example of where earthquakes are associated with entire mountain chains?
on geological timescales and across areas covering many thousands of squarek km, earthquakes are associated with the formation of entire mountain chains such as the Himalaya-Karakoram Range in Asia.
The northward drift of India into Eurasia and the subsequent continental collision led to a complex pattern of folding and faulting of rocks
what is the tibetan plateau?
to the north of the Himalaya-Karakoram Range lies the Tibetan Plateau.
averaging 4500m above sea level it covers an area of 2.5 million km2
major fault systems are evident in the rocks and these indicate considerable movement
the entire region is tectonically active, as the 2008 and 2013 earthquakes in Sichuan province and 2015 event in Nepal demonstrated
what is an escarpment?
a tilt block forming an extensive upland area, with a short, steep (scarp) slope and a long, gentle (dip) slope
what is a fault scarp?
a cliff or escarpment formed directly by rocks being displaced either side of a fault
how do rift valleys get altered?
rift valleys on the continents are altered by weathering and erosion. over time fault scarps are worn away, blending into the landscape. they can even disappear under accumulated sediments
what is ground shaking and ground displacement?
(and what affects it)
this is the vertical and horizontal movement of the ground. the severity of ground shaking depends on:
- earthquake magnitude
- distance from the epicentre
- local geology
locations that are close to the epicentre of a high magnitude quake and where the surface layers are relatively unconsolidated and have a high water content will experience extreme ground shaking. these conditions existed in parts of Mexico City and the Japanese port of Kobe hit by devastating earthquakes in 1985 and 1995 respectively
what are the impacts of ground shaking and ground displacement?
in general, most buildings can withstand vertical movements better than horizontal ones: it is the swaying of structures that is so dangerous to their stability.
ground movements that cause displacement of rocks along fault lines can rip apart pipelines and sewers, sever rigid structures such as railway tracks and roads, and cause buildings to collapse
the displacement of the surface can also disrupt natural drainage, diverting streams and rivers and affecting the movement of groundwater in aquifers. this can have serious implications for public water supplies and irrigation for agriculture
what is liquefaction?
when an earthquake strikes an area with surface materials of fine-grained sands, alluvium and landfill with a high water content, the vibrations can cause these materials to behave like liquids. as a result, these materials lose their strength and structures tilt and sink as their foundations give way
example and impacts of liquefaction?
liquefaction was a major issue during the Kobe earthquake as much of the port had been built on reclaimed land in Osaka Bay. Just under 200 berths in the port were destroyed, affecting not just the Japanese economy but trade throughout the world
examples of places where landslides occur?
steep slopes in mountainous regions like the Himalaya-Karakoram range are notoriously unstable and vulnerable to landslides.
their vulnerability is increased by deforestation and heavy monsoon rains, so that even small tremors can trigger landslides
the nepalese earthquake of 2015 triggered large numbers of landslides and avalanches caused by ground shaking
impacts of landslides?
block transport routes in mountainous regions where accessibility is already difficult
movement of soil and rock on slopes can also block rivers. these natural dams create temporary lakes, which can threaten areas downstream with catastrophic floods. this was the case in several locations in Kashmir in 2005 and Sichuan in 2008
should an earthquake creates a landslide on slopes above a reservoir, the displacement of waters and the waves generated could weaken and overtop the dam eg an earthquake did this in italy in 1963. it led to the collapse of a hillside above the vaiont reservoir, generating a 100m wave which swept over the dam and down the valley of the Piave river, drowning nearly 3000 people
how are tsunamis created?
underwater earthquakes can cause the sea bed to rise vertically
this displaces the water above, producing powerful waves at the surface which spread out at high velocity from the epicentre. because of their low height and very long wave length, tsunami waves can pass underneath a ship out at sea unnoticed. However, wave height increases greatly as they approach the shore and enter shallow water
before the wave breaks, water in front of the wave is pulled back out to sea, a process known as drawdown, finally, the tsunami wave rushes in as a wall of water that can exceed 25m in height
how much water did the Boxing Day Tsunami deliver?
estimated to have delivered about 1000 tonnes of water per metre of shoreline
how can underwater landslides create tsunamis?
they displace water and create tsunami waves
when a large volume of rock is shaken and slides downslope, water is dragged in behind it from all sides and collides in the centre. this can generate a tsunami wave which radiates outwards
while the resulting wave may not have enough power to cross oceans, the local effects can be devastating. for example in 1998, 2200 villagers living in coastal communities in Papua New Guinea were killed by a local tsunami generated from an underwater landslide triggered by an earthquake, because such events are local, warning times are short, making them particularly hazardous
what is japan’s tectonic setting?
movements along plate boundaries lying just offshore of the japanese mainland create an ever-present risk of tsunamis
the pacific coastal zone is especially vulnerable, being densely populated and containing three huge conurbations: Tokyo, Osaka and Nagoya
when was the japan earthquake?
11 March 2011
magnitude of the japan earthquake?
9.0 MW
where did the japan earthquake occur?
occurred along the boundary between the Pacific and North American plates
its epicentre was 70km offshore of northeast Honshu Island
was an undersea megathrust earthquake
how long did the japan earthquake last for?
6 minutes
geophysical impacts of the japanese earthquake?
Honshu island moved 2.4m east
the Earth shifted on its axis by 10-25cm
a 400km stretch of coastline dropped vertically by 0.6m
sea bed rose by about 7m and moved westwards by 40-50m
social impacts of the japan tsunami?
claimed nearly 16,000 lives and injured another 6000 people
mass mortality and destruction of crematoria, morgues and the power infrastructure created problems of how to dispose of the dead bodies. traditional funeral traditions were waived– the authorities felt they had no choice but to bury bodies in mass graves as quickly as possible to reduce the chances of diseases being spread
Save the Children reported that 100,000 children were affected. The problem was made worse as most children were at school when the earthquake struck
the destruction of infrastructure (eg housing, schools and health centres) was on such a scale that reconstruction was still taking place ten years after the disaster. Some communities have even been relocated from their original settlement site
economic impacts of the japan earthquake: cost?
cost of the earthquake, including reconstruction, has been estimated at anything between US$200 billion and nearly five times that amount
economic impacts of the japan earthquake: buildings?
Japan’s National Police Agency issued an official figure of 45,700 buildings destroyed, with a further 143,300 damaged.
economic impacts of the japan earthquake: ports?
15 ports were directly affected, with four destroyed in the NE of Japan, including Sendia.
10% of Japan’s fishing ports were damaged, although most had reopened a year after the earthquake
economic impacts of the japan tsunami: electricity/fukushima?
4.4 million households and thousands of businesses lost electricity. The major cause of this disruption was the immediate shutdown of 11 nuclear reactors
at the Fukushima Daiichi nuclear power plant, all six of its reactors were so severely damaged by the tsunami that the plant was decommissioned. the plant’s cooling systems were disabled by sea water flooding, which led to a meltdown of reactor cores and the release of radioactivity
a 30km evacuation zone was established around the plant, and soils in the surrounding countryside were contaminated by radiation. even today radioactivity continues to seep into the Pacific Ocean, affecting the fishing industry and incurring further costs
Japan experienced several weeks of power cuts (lasting 3-4 hours at a time), which added to the economic cost of the earthquake.
Two oil refineries were set on fire during the earthquake, one fire taking ten days to put out
economic impacts of the japan earthquake: transport infrastructure?
transport infrastructure was badly hit
many road bridges were damaged or destroyed and in the north east train services were badly disrupted
twenty-three train stations were swept away, while others suffered severe damage, such as collapsed roofs
environmental impacts of the japan earthquake?
some 25 million tonnes of debris was created by the earthquake, requiring a costly clean up operation
over large areas, farmland flooded by sea water has been contaminated by salt and made uncultivable
how did the japan earthquake impact japan’s stock markets?
japan’s stock markets fell as the implications for businesses such as Sony, Toyota and Panasonic were realised. their production was hit by the shortage of electricity.
overseas operations were also affected, as supplies of parts exported from Japan were interrupted
political impacts of the japan tsunami?
a large popular movement against nuclear power developed after the Tohoku earthquake. Concerns over safety standards and regulation of the nuclear industry became a political issue
it emerged that warnings about the inadequacy of the defences against tsunami hazards had been made several years before the disaster
political fallout from the Fukushima nuclear accident spread around the world. for example, in Western Europe, the anti-nuclear lobby in Germany used the incident to support their arguments against nuclear power
what was the Haiti earthquake in 2010 like?
12 January 2010
7.0MW
A slip along a 40km section of the Enriquillo fault
Epicentre 25km southwest of Port-au-Prince, the capital city
Focus = 12km
Shaking lasted 12-14 seconds with significant aftershocks within 20 minutes of 6.0 MW and 5.7 NW, and then another of 5.9 MW on 20 January
Total of 51 aftershocks >4.5 MW in the year after the initial 12 January event
Haiti had no seismic network to record the earthquake
social impacts of the haiti earthquake?
official figures place deaths at 316,000 but other estimates based on survey data suggest a much lower figure between 46,000 and 84,000
over 300,000 houses and 30,000 commercial buildings were either damaged or destroyed, displacing as many as 1.5 million people, many of whom were forced to live in camps
many of the destroyed and damaged houses were in the poorest areas of the city, built on steep slopes prone to landslides. By 2020, ten years after the earthquake, over 30,000 people still lived in those camps
social impact of the haiti earthquake: cholera outbreak?
as a secondary effect of the earthquake, a cholera epidemic broke out in October 2010; the first case was detected close to the UN base for Nepalese troops bought in to help with the reconstruction effort. Since the first case over 800,000 cases of cholera have been recorded
the official number of deaths was, in 2020, put at just under 10,000. Once again, this figure is disputed; one epidemiologist puts it at 8 times that number
economic impacts of the haiti earthquake?
since the earthquake, the economy ha barely recovered
aid money has not, by and large, been directed at an economic recovery, with schemes such as the establishment of tourism and a more diverse economy less reliant on US companies that have not delivered very much
the Haitian economy has hardly grown since the earthquake. Its largest income sources are remittances: money sent to the country by expatriate Haitians working abroad, providing 25% of its GDP, followed by foreign aid, which provides 20% of its annual budget.
A weak and corrupt government still struggles to collect tax income
what is the disaster risk equation?
risk = (frequency or magnitude of hazard x Level of vulnerability) / capacity of population to cope and adapt
what does the scale of physical exposure to earthquake and volcanic hazards depend on?
frequency of earthquakes and volcanic activity
magnitude of earthquakes and volcanic activity
types of hazards generated by earthquakes and volcanoes in a particular location
number of people living in an earthquake-prone and/or an eruption-prone area
what is vulnerability concerned with?
vulnerability is concerned with the ability of a person or community to withstand exposure to, and risks from, a hazard such as an earthquake or volcanic eruption.
people are most vulnerable when relatively small physical changes have major socio-economic implications
what is resilience?
resilience is an indication of the rate of recovery from a hazardous event that has put an individual and/or community under stress
it is about how well an individual and society are able to function at an acceptable level when a destabilising force has affected them
what are some strategies for managing tectonic hazards involving modifying the event?
not possible for the vast majority of volcanic eruptions. however, the following have been tried with some success:
- lava diversion channels
- spraying lava to cool it so it solidifies
- slowing lava flows by dropping concrete blocks
Nothing can be done to modify an earthquake event.
what are some strategies for managing tectonic hazards that modify people’s vulnerability?
EDUCATION: recognise the signs of possible eruption; what to do when an eruption occurs; drills to practise what to do when a tectonic event strikes
COMMUNITY PREPAREDNESS: eg building of tsunami shelters and walls; strengthening of public buildings
PREDICTION AND WARNING: increasing use of technology to monitor particularly active locations eg individual volcanoes
HAZARD-RESISTANT BUILDING DESIGN: eg cross-bracing of buildings to support them during an earthquake; steep sloping rooves to prevent ash building up
HAZARD MAPPING, eg predicted lahar routes; ground likely to liquify in an earthquake
LAND USE ZONING to avoid building in locations identified by hazard mapping
what are some strategies for managing tectonic hazards that modify people’s loss?
emergency aid, eg bottled water, medical supplies, tents, food packs
disaster-response teams and equipment, eg helicopters and heavy lifting machinery
search and rescue strategies
insurance for buildings and businesses
resources for rebuilding public services, eg schools and hospitals, and help for individuals to rebuild homes and businesses
what is one widely accepted definition as to what is considered an active volcano?
an active volcano is one that has erupted since the last glacial period or within the past 10,000 years
how does the Smithsonian Institute define dormant volcanoes?
one that has not erupted during the past 10,000 years but is expected to erupt some time in the future
how does the Smithsonian Institute define extinct volcanoes?
one that is not expected to erupt again
what is mount Ontake?
Mount Ontake is a classic strato-volcano situated 200km west of Tokyo on Japan’s largest island, Honshu
had been dormant for many centuries until a sequence of eruptions between October 1979 and April 1980. Further eruptions followed in 1991 and 2007
the area was popular with climbers and trekkers and was a noted tourist destination , with various facilities including a lodge close to the summit. It was also a place of spiritual pilgrimage for many Japanese people
what was the 2014 Mount Ontake eruption?
On 27 September 2014, just before midday, Mount Ontake erupted violently and without warning.
at the time the volcano was not under any alerts or warnings, although some increase in earthquake activity has been observed.
the eruption killed 63 people and large areas surrounding the volcano were affected by ash fall, pyroclastic flows, volcanic bombs and lahars
most casualties were climbers and hikers on the slopes of the volcano. More than 200 survivors made it down the mountain and search and rescue teams were deployed to recover those seriously injured
what was one important message from the Mount Ontake eruption?
even in Japan, with one of the most sophisticated monitoring and warning systems anywhere in the world, the country can be taken by surprise by the unpredictability of tectonic hazards
what is indonesia’s tectonic setting?
complex, with widespread subduction along the entire 3000km length of the Indonesian archipelago
much of indonesia is an island arc formed by subduction of the Indo-Australian plate beneath the Eurasian plate.
a feature of volcanism in Indonesia is the large number of volcanoes that are highly explosive. This was exemplified by the cataclysmic eruption of Krakatau in 1883, which also generated a devastating tsunami. In the north of Sumatra, Lake Toba fills the caldera caused by the devastating eruption of the super-volcano 70,000 years ago
what is merapi?
merapi is a stratovolcano which reaches nearly 3000m in altitude.
it is highly active, with eruption events in 1994, 1997, 2001 and 2006. On each occasion, a dome developed in the crater, which eventually collapsed, producing pyroclastic flows. The force of these eruptions was 3-4 VEI.
what was merapi’s 2010 eruption like?
the VEI 4 eruption between 26 October and 12 November 2010 affected people living around the volcano
pyroclastic flows extended 4km to the north, 11.5km to the west, 7km to the east and 15km to the south
lava bombs were thrown 4km from the summit in all directions.
the eruption happened at the start of the rainy season, triggering lahars fed by ash from the eruption and from earlier eruptions
impacts of merapi: airport?
ash falls forced the closure of Yogyakarta airport for over a fortnight
impacts of merapi: acid rain?
emissions of sulphur dioxide caused acid to fall over a large portion of the region
impacts of merapi: people killed and injured and refugees
367 people were killed
277 injured
410,000 in the vicinity became refugees
impacts of merapi: agriculture and infrastructure
large numbers of livestock killed
ash fall and pyroclastic flows amounting to 130 million m3 of material destroyed crops and infrastructure such as buildings, power lines and bridges
why do people choose to live in tectonically active locations? (fertile soils)
the slopes of volcanoes often attract settlement
weathered lava produces fertile soils especially in wet tropical regions. intensive farming therefore supports very high population densities.
Japan’s agricultural sector uses just 13 per cent of the country’s land area but does so very intensively. In part this is possible due to the high fertility of volcanic soils
in both Indonesia and Japan, the steep-sided slopes of the strato-volcanoes have been terraced to allow farming to be practised.
HOWEVER, colder climates like icelands mean there are no agricultural benefits of living close to volcanoes. The basalt lava flows remain largely unweathered and is a hostile environment for plants
why do people choose to live in tectonically active locations: geothermal?(+issue)
iceland has developed geothermal energy from ‘hot rocks’ to help it become 100% renewable in its production of electricity
japan also has had geothermal power stations since the 1960s but these were small scale
interest and research into geothermal energy were also given a major boost in the aftermath of the 2011 earthquake in Japan
One issue Japan faces in exploiting its geothermal energy resources is that nearly 80% of the hot rock locations are in national parks or protected hot spring locations
geothermal power in indonesia (in relation to why people live in tectonically active locations)
indonesia also has a vast geothermal energy potential and is beginning to exploit this
currently, only about 3% of Indonesia’s total electricity comes from geothermal but there are plans to increase this
Sarulla power plant has the potential to be the world’s largest such plant
how does having a stepped profile reduce a building’s vulnerability?
multi storey buildings can sway, especially towards their tops. a stepped profile gives considerable stability against lateral forces
what is a key factor in modifying vulnerability through aseismic design?
how rigorously building codes and laws are applied
in most locations, many buildings were built before the rules became law
retro-fitting measures are very expensive and may not always be possible even in ACs
what is the history of Indonesia’s CVGHM?
established in 1920
its key division is the Volcano Observation Section, which over the years has constructed permanent observatories on several active volcanoes.
first seismograph was set up on Mount Merapi in 1924, but as with monitoring elsewhere, the capability of the technology at the time was limited
Indonesia was a Dutch colony until the end of the Second World War. Its emergence into independence was accompanied by political tension and violence among competing groups. Managing volcanoes was therefore given a low priority
what is Indonesia’s Centre for Volcanology and Geological Hazard Mitigation (CVGHM) like today? (modifying vulnerability)
today more than 60 volcanoes are monitored.
Sophisticated equipment measures gas emissions, inflation as magma rises and earthquake activity in some, but not all of Indonesia’s volcanoes
what is Indonesia’s National Agency for Disaster Management? (modifying vulnerability)
in association with university-based researchers, both Indonesian and foreign, lahar sensors and closed-circuit television have been installed to monitor locations and greatest risk
how are the CVGHM and local governments linked?
the CVGHM works closely with local governments, advising them on mitigation strategies such as community preparedness
additionally, on Mount Merapi for example, permanent settlement is forbidden on the highest slopes around the crater. Villagers on the southern slopes (at greatest risk) have been encouraged to relocate to safe zones, in some cases receiving financial assistance and a small plot of lands as incentives to move
what is an enduring problem with people in Indonesia and their village sites (regarding volcano management)?
an enduring problem is that people have a strong bond with their village site and their family fields. They often return, rebuild and accept the risks
how does indonesia modify loss after volcanic events?
indonesia is a lower-middle-income country, so the resources it can deploy once an eruption is underway are limited. many of the farming communities affected also have limited resources.
That said, Indonesia has some well-trained and well-equipped emergency services, including the military, experienced in search and rescue.
Temporary shelters in safe zones are available in case of evacuation and sometimes these are upgraded into permanent residential areas
the authorities have also cleared river channels of volcanic material and other debris in order to reduce the risk of flooding and to contain lahars. Some of this material has a commercial value (eg road building) and people living along the river valleys have used it for rebuilding houses and communities facilities.
how does italy modify the event for mount etna?
italy has had some local scale success with slowing and diverting lava flows from Etna
Earth barriers, large concrete blocks dropped into the lava flow and channels dug to divert flowing lava away from settlement have been used
how does italy modify the vulnerability for volcanoes
monitoring plays a significant role in mitigating eruption hazards, providing accurate information to the Volcano Risk Service (CFCRV), which is the basis of decision-making such as evacuation orders. The CFCRV includes:
- long term analysis of the eruption patterns of individual volcanoes
- international comparison with similar eruptions elsewhere
- constant monitoring, eg seismometers, tilt meters, analysis of gas emissions, aerial and satellite survey eg infrared to detect heat. daily and weekly bulletins are issued
- a well established alert-level sequence understood by emergency services, all levels of government and local communities
- close of airports and air space when threatened by ash in the atmosphere
- much work carried out to identify the types of housing most at risk and to offer affordable solutions, eg adding a pitched roof to an existing flat roof, which will then shed ash fall
how does italy modify the loss for mount etna
with frequent eruptions from etna, italy is well practiced in dealing with volcanic hazards.
the italian government has the resources to compensate individuals and businesses and restore infrastructure
casualties have been minimal thanks to timely evacuation based on accurate data and well trained public services such as the fire service, the police and the military
how are earthquakes monitored in haiti (as part of modifying the vulnerability)
prior to the 2010 earthquake there was no monitoring system in Haiti.
following the earthquake, the USGS has helped with earthquake awareness and monitoring in the country, with continued support from the US Agency for International Development (USAID).
a total of 15 seismic stations are now operating in haiti. unfortunately, the monitoring facilities are not earthquake resistant and there is not enough money to staff a 24 hour team
what are hazard maps, disaster risk management plans and education like in haiti, with regards to modifying the vulnerability?
progress has been made with hazard maps developed where none existed before, showing areas especially at risk, such as areas with softer sediments liable to liquefaction
however, there is no national disaster risk management plan; there is no ‘Japanese’ style education programme so that children know what to do in the next earthquake
what is the issue about earthquake-resistant building design in Haiti (modifying vulnerability)
the inability of the state to enforce earthquake-resistant building design
there is no government approved building code and given that the country has had four presidents and seven prime ministers since 2010, stability and long-term planning are not evident
for example, the Bureau of Mines and Energy, which oversees earthquake surveillance among many other responsibilities, has an annual budget of just $US 600,000, which is 0.04% per cent of the national budget
how does haiti modify the loss from earthquakes?
with no effective government of its own, the role of NGOs in Haiti has been critical but has been controversial from the start
At the International Donors Conference ‘Towards a New Future for Haiti’ (March 2010), donors pledged over $US5.3 billion to be spent over two years.
However, as international donations flooded in (45% of US households donated to Haitian charities), the dream of a constructive did not, for the most part, happen
critics argue that from the very start, NGOs followed their own agendas and set their own priorities, largely excluding the Haitian government and its people. in the first rush of aid after the earthquake, just 1% of all donor funds available for emergency assistance was offered to the Haitian government
almost two-thirds of the money raised for the charitable NGOs (in the billions) remains in the bank accounts of the aid money managers that were there before the earthquake
there have been a series of scandals surrounding the work of NGOs in Haiti, including the behaviour of some of their senior officials
how does japan modify vulnerability: research and monitoring
the Japan Meteorological Agency (JMA) lies at the heart of Japan’s mitigation strategies for natural disasters, including earthquakes and tsunamis and extreme weather events such as typhoons
it is responsible for providing information and warnings of impending earthquakes and tsunamis.
detailed disaster planning involves a wide range of organisations, eg governments, medical services, fire, military etc
how does japan modify the vulnerability: buildings with aseismic design
steel frames and braces capable of moving without collapsing
rubber shock absorbers in foundations
very deep foundations in solid rock
flexible joints in underground utility pipes, eg gas and water
how does japan modify vulnerability: fire proofing
fire proofing older wooden buildings, which are common in historic districts of Japanese cities
how does japan modify vulnerability: land use zoning
land use zoning that provides for open spaces where people can assemble after an earthquake
what other strategies does japan use to modify vulnerability (not land use zoning, fire proofing, aseismic design or monitoring)
controlling building in locations susceptible to excessive ground shaking or liquefaction
tsunami warning systems off the coast
refuge sites on permanent stand-by equipped with tents, bottled water, blankets
community preparedness– ongoing education and training for all ages
how does japan modify loss from earthquakes?
being one of the most advanced countries in the world, Japan has vast resources to manage losses caused by earthquakes. Well-rehearsed recovery and reconstruction plans, at national, regional and local levels, can be actioned immediately following an earthquake
the aim is to rebuild physically, economically and socially as quickly as possible
Describe the Park Model (disaster response curve)
Stage 1: normality
Stage 2: hazardous event, rapid detioration follows
Stage 3: search, rescue and care
Stage 4: Relief and rehabilitation period, may include outside help. Quality of life etc gradually improves
Stage 5: Nature of recovery related to the need to reduce vulnerability and the need to restore normality as soon as possible.
Could end in either improvement or return to normality
