Tectonics Flashcards
Example of a tsunami caused by a volcano? ancient/modern
Krakatoa 1883 largest and most disastrous volcanic tsunami in history up to 40m tall up to 36,000 people killed Recently 1997 Montserrat eruption generated minor tsunami
Tsunamis caused by submarine volcanic eruptions?
5% are caused in this way Resulting in the collapse of the caldera flank failure (side of volcano collapses) or pyroflastic flow discharge into the sea leading to a column of water pushed above sea level
Tsunamis caused by earthquakes?
80% in the Ring of Fite This happens as two plates converge due to convection currents leading to the subduction of the less dense plate Friction builds in the Benioff Zone Eventually released in a large snap movement causing an earthquake This tilts and vertically offsets or displaces the above large amounts of water varying of 1000km or more Displacing lqrg amounts of water disturbing ocean surface generating large destructive tsunami waves
Example of a tsunami caused by an earthquake?
2011 Japan Earyhquake 9.1 magnitude earthquake Subduction of pacific place Displacing column of water above Japan tench
Explain how tsunamis can be generated by landslides?
When an undersea landslides occurs a large mass of sand mud and gravel moves downslope and rapidly displaced large volumes of water
how do you predict volcanos
Monitoring warning signs using equipment 1) volcano bulges - the volcano magma chamber expands as magma rises within volcano. Deformation measured by tilt meters, field tilt diverting techniques and minute changes can b measured by tilt meters 2) Volcanoes predicted through shallow minor earthquakes measured by seismometers
Explain the formation of hotspot volcanoes
Where heat from the hotspot produced a constant source of magma partly due to melting of the overriding plate, in the form of magma plume The magma is less dense, rises through the mantle; texomtic movement and mounting pressure causes the thin crust to crack, forming a fissure at the surface forming a shield volcano
Example of a hotspot volcano
Reunion Indian Ocean
describe the hazard of shield volcanoes
Icelandic or Hawaiian less explosive (low gaseous content) volume of ejected materials is minimal basaltic lava flows are easy to avoid as they are slow moving and predictable eruptions are frequent removing the element of suprise from the hazard risk
describe the hazard of stratovolcanoes
Vary from Strombolian to Plinian Strombolian: short lived and explosive, viscous lava, ejected high in the air eg Mount Etna Plinian: most violent, large amounts of lava and pyroclastic flows, massive eruption columns (1 to 28 miles in the atmosphere) eg Mount St. helens eject large amounts of magma and other volcanic material high into the air explosively (due to a high gas content) nuee ardennes - turbulent rapid incandescent pyroclastic flows
EXAMPLE: Mount Vesuvius; Soufiere Hills, Montserrat
example of a stratovolcanic eruption
Mount Vesuvius 79 AD lead to 3m if ash suffocated 2,000 people or and lead to the destruction k of the city of pompeii
Definition of earthquake
A sudden violent movement on the earths dircsve causing the release of stress
definition of volcano
an opening in the earths crust where there is lava and ash and gas they can differ in their proportions
example of volcano response in LEDC
Niyragongo 2002 distributed and international aid totalled $15 million in providing food blankets healthcare clean water food
example of successful volcano prediction?
since 1980 18 of mount st. helens 22 eruptions have been predicted
Fact about tsunami generation in ring of fire?
80% are venerated there
Japan tsunami basic information
9.1 magnitude 2011 japan earthquake pacific plate subduction under the plate beneath northern honshu 10m high
tsunami generated by volcanic eruption example
1883 Krakatoa volcanic eruption waves up to 40m
Impact of Indian Ocean Tsunami
2004 Indonesia was hit within 15mins of the under sea earthquake massive damage to infrastructure drinking water supplies and farm fields contaminated for years by salt water from the ocean estimated up to 220,000 people died (Aceh) Kenya - one person died involved 14 countries
why do tsunami waves get bigger as they approach the coast?
when offshore in deep water the tsunamis have a small wave height and a long wavelength (up to 200km long) due to the shallower nature of the coast, the sea bed is up sloping, reducing the speed (below 80 km per hour) decreasing the wavelength and increasing the ave length
example of tsunami prevention
40% of japan’s coastline has sea walks of up to 10m high to withstand incoming tsunami walls
but had waves up to 40m in some places 50% of tsunami walls toppled
2016 Japanese authorities plan to build a £4.6bn 250 mile long sea barrier, 12.5m high
additional concrete breakwaters and floodgates protecting ports and costal areas
vs Indian ocean with no preperation infrastructure
response to Indian Ocean Tsunami
countries involved were unable to coordinate their own effective response due to lack of infrastructure World Food Program provides food aid to more than 1.3 million people heavy reliance on foreign aid
response to Japan Tsunami 2011
sending in specifically trained people such as the Japanese self defence forces - a domestic response rapidity of response - just 6 days after motorway was repaired and fully functional,
a month later 96% of electricity supply,
98% water supply,
100% of expressway
taiwan provides $253 million in concerts and events, red cross
tsunami prediction in the indian ocean
setting up the communications infrastructure to issue timely warnings is difficult in poorer less developed pars of the world BUT now UN dissaster mitigwtion committee set up to deal with tsunami threat
example of MEDC volcano preparedness
Mount Vesuvius Action Plan 2001 based off geological evidence from 1631 eruption three zones: red yellow blue eg red: highest, gas, pryor last jc flows and nuee ardennes 550,000 people live would be completed evacuated Twinnings system - people spread across the country with each district evacuated paired with an Italian province
impact of LEDC volcano eruption
Niyragongo 147 people killed 120,000 homeless
The Congo rainforest meant it was difficult to transport aid
MEDC volcanic eruption response was
Iceland’s 2010 volcanic eruption
100,00 flights grounded
coordinatde evacuation; fask masks distributed
less developed country earthquake case study impact
6.6 on richter scale Bam Iran 2003
26,000 deaths and 30,000 injuries
Many houses built of mud bricks didn’t not comply with regulation 1989
Built traditionally NOT earthquake proofed - collapsed 75% were completely destroyed
Date growing industry suffered due to loss of infrastructure
Electricity and water supplied cut industry suffered as irrigation infrastructure damaged
Earthquake occurred at night people crushed as they slept
more developed country earthquake impact
5.2 richter scale 2008, Lincolnshire no bridges collapsed, no one died houses shaken, falling on slopes historic structures (church steeples damaged) falling chimneys only serious injury
less developed country earthquake response
Bam, Iran 6.6 on richter scale
Short Term: aid and personnel sent in 44 countries - USA and China biggest (US initially declined accepted later) sent in rescue squadsand medical support
UN world food programme airlifted in 100,000 food rations tents, blankets, medical supplies, personnel, field hospitals set up (post traumatic stress)
“bitterly cold” at night harboured efforts
Long term: building codes with earthquake durable materials
government considered moving capital Tehran as it is on a similar fault line
iranian housing federation removed debris from 19,000 homes
funding from the humanitarian office of the eu to reconstruct city
more developed earthquake response
Lincolnshire 2008
emergency services eg ambulance and police insurance payouts worth £300 million structural repairs to buildings
earthquake preparedness (hard engineering)
Japanese government - following 1995 kobe earthquake, 64000 deaths
enforced further regulations on infrastructure in order to reduce the damage of tectonic events
new buildings are built further apart to prevent the domino effect
high rise buildings should be built with flexible steel frames rubber blocks put under bridges to absorb shock. EG. 54 storey Mori Tower in Tokyo finished in 2003 has fluid filled shock absorbers that slosh with thick oil in the opposite direction of swaying
seismic isolation: decoupling the main building from the basement so that the structures are not affected by ground tremors. EG. The 18 story Sendai building remained undamaged following the 9.1 2011 earthquake despite a horizontal displacement of 20cm
reduce earthquake impact by education
duck and cover scheme in south asia 800,000 school children involved in monthly drills fire deparpment - children earthquake stimulation machines familiarise the sensation raise awareness via media all tv and radio stations switch immediately to earthquake coverage
describe and explain the hazardous nature of materials from volcanoes
tephra (ash) - extends over large distances, can include lava bombs and vast ash clouds lava flows - invade settlements and destroy buildings and populations puroclasyic flows - high speed avalanches of rock ash and gases (up to 100km/h; 600-900 degrees) nuee ardennes landslides and lahars can be hazardous eg Nevada Del Ruiz killing 23,000 people
what is a volcano
an extension of magma from a magma chamber through a rupture in the crust allowing hot lava volcanic ash and gases to escape from the chamber below
what are the primary hazards of earthquakes
Ground shaking, caused by seismic waves.
This causes the collapse of buildings, dams (which may cause flooding and the spread of water borne disease) and major pieces of infrastructure such as elevated highways, the release of hazardous material e.g. the radiation from Fukushima as a result of March 2011 tsunami, fires caused by damage to gas pipelines and domestic appliances.
These waves are generated when P and S waves, emanating from the earthquake focus, reach the surface as waves.
liquefaction buildings sink into the ground risk in areas with un consolidated material (eg alluvium or lake deposits) with high water tables
what are the secondary hazards of earthquakes
fTsunamis are generated as an earthquake creates a vertical shockwave in the water column that is translated into a horizontal wave movement at the surface. The resultant waves can move at 700kph and inundate coastal areas – causing death by drowning and wide scale destruction through the sheer force of waves hitting buildings. Japan 2011.
rupturing of dams (washing away buildings and drowning)
Salt water inundating farmland and causing damage to crop by salinization. Experienced by Indian Ocean tsunami 2004.
fire broken gas or power lines shaking only on slopes suceptible to mass movement (already weakned)
landslides (11,000 following nortridge earthquake 1994) mudslides avalanches - They result from the shaking but only on slopes susceptible to mass movement where the material has already been weakened
how is ash fallout dangerous?
great distances it can travel distrusting air traffic large ash falls near volcano may lead to roof collapse and will affect agriculture livestock and humans via inhalation and ingestion
what are the methods of monitoring/forecASTING earthquakes?
seismographs
radon gas emission (pre-seismic stress or fracturing of the rock) - radioactive, easily monitored
electromagnetic anomolies - 2004 Parkfield earthquake found no evidence of precursory electromagnetic signals of any type; earthquakes with magnitudes under 5 do not produce
methods for predicting volcanoes
seismic tremors - in the weeks before Montserrat eruption in 1995 eruption major seismic events were detected, caused by the movement of magma in the chamber. However, small tremors are very common at plate boundaries, so they are not necessarily the best indicator of an eruption: Eldfell 1973 Iceland
ground bulging - satellites or eyesight (Mount St Helens visibly bulged 2m per day before erupting in 1980 ; in Iceland cameras monitor remote volcanos for activity)
electrical and magnetic fields indicating the ascent of magma 1975 China successful
gas emission from fumaroles - Iceland various monitors measure gases SO2 and CO2
groundwater change
heat increase at surface and subsurface: satellites provide infrared imaging (as the magma rises to the surface)
characteristics of a tsunami?
violent displacement of the sea (earthquakes, landslides, eruptions) powerful waves that increase in height as they approach the shore almost unnoticeable offshore but an upward sloping sea bed reduced their speed and wavelength it is transferred to save height waved up to 30m high destroy costal installations carry debris far in land this poses a threat of building collapse and drowning and secondarily disease soil degradation
how do volcanoes occur at divergent plate margains?
eg iceland magma rises to the surface as the plates move apart reduced presdure on the magma chamber basic lava tends to emerge from fissures producing mainly shield volcanoes which erupt more frequently but less violently
how do volcanoes occur at convergent plate boundaries?
the denser oceanic plate is subducted beneath continental crust.
The friction creates faults and cracks along the edge of the continental which provides pathways for magma to rise and reach the surface.
As the oceanic crust descends the heat will melt the edge of the plate creating a magma chamber at the base of the volcano.
The magma chamber will be volatile as it includes dissolved gases and parts of the former sea bed.
As pressure increases the magma will be forced through the central vent and andesitic lava will explode from the crater at the top of the volcano.
The vent may become blocked and powerful eruptions may occur through parasitic cones on the side of the main volcano. If the plate boundary occurs under the ocean, island arc volcanoes may be formed.
why are convergent volcanoes volatile?
this will be volatile as its magma includes dissolved silica and gas from the sea bed
explain how earthquakes can be monitored?
seismometers - measure vibrations in the earths crust radon gas, variations in groundwater levels, changes in animal behaviour tilt-meters and simple observation can recognise changes to the land surface (ground deformation) laser beams can be used to detect minute movements along plate boundaries satellite imagery
how can the products of volcanoes be protected against?
diverting them by digging channels ( amount Etna) cooling them with water (Iceland 2010 eruption) building design by roof strengthening in order to combat ash flows monitoring ash clouds for aviation
explain the causes of earthquakes
due to the friction engendered by the plate movement and the development of seismic waves intra plate earthquakes can occur and are thought to be caused by friction and movement along faults
describe the lava of a hotspot location
for continental plates it is acidic due to the incorporation of granitic crust material initially explosive but followed by outpourings of basaltic lava for ocean plate examples eg Hawaii the erupts are of basalt and less explosive lava is mobile
why are some volcanoes more hazardous than others
nature of eruption (location - densely populated or plate margains and hotspots) HOWEVER iceland isolates widespread effects due to effect on stratospheric dust type of erupted material - explosive or effusive eg hawaiian or plunian prediction preparation response
what are the physical reasons some earthquakes are more hazardous than others
strength distance from epicentre - only hazardous when they occur close to the earths surface nature of terrain - offshore may result in tsunami; mountains low population
what are the human reasons some earthquakes are more hazardous than others
poor building lack of regulation prediction precautions eg flexible gas pipes response
describe explosive volcanic eruptions
form in convergent plate margains often when an oceanic plate is subduction below a continental plate enormous ash clouds descend to form pyroclastic flows that pour down the flanks of the volcano with often side explosions at Mt St. helens eg strombolian - incandescent lava Plinain - nuees ardentes
how can political climate impact tsunami response
2004 indian ocean tsunami only 30% eligible received said allegations of local officials only giving aid to supporters many of whom were not victims
tsunami monitoring case study
japan deep ocean assessment and reporting of tsunami collects sea level info every 15 mins, less than 1mm changes in sea level, signal sent to Japan Meterologicsl agency unreliable: 75% are false alarms; Japan predicted as a 13m tsunami but was in fact up to 39m
case study of how can tsunamis be forecasted
JAPAN hazard maps : disaster risk, evacuation routes, tsunami drills and local awareness chloropleth map: purple section has risk of waves over 10m in height eg Sendai or INDIAN OCEAN tsunami warning system following UN conference in Kobe 2005
case study of tsunami monitoring
japan meterological agency issue warning in 3m predicted at a smaller scale 13m but was in reality 39m in some places
2013 in new system unveiled collects sea level info every 15mins of less than 1mm, monitors changes every 1m
unreliable: 75% of warnings are false alarms
japan’s monitoring of tsunamis
180 seismic stations, 80 water borne sensors that are monitored 24 hours a day
superimposed alerts on tv screens activate sirens and loudspeakers
how can political climate affect tsunami response
2004 indian ocean 30% those eligible received aid allegations of local officials only giving aid to supporters some of whom were not victims of the tsunami
example of accurate earthquake prediction
japan september 2004 7.1 magnitude earthquake predicted by changes in electromagnetic waves, unusal groundwater movements and animal behaviour
explain how earthquakes can cause liquefaction
occurs when the ground shaking caused by earthquakes turns soil ground into mud
buildings may then sink into the ground or tilt over, underground pipes may rise to the surface
when the shaking stops, the sediments settle and groundwater squeezes out of holes in the ground causing flooding
it takes place in unconsolidated sediment such as alluvium or lake deposits, where there is a high water table
nature of convergent volcanoes
explosive due to silica rich magma and gases
list the products of volcanic eruptions
pyroclastic flow (nuee ardennes) tephra or ash fallout lava flows lahars gases
describe why pyroclastic flows are hazardous
fast moving current of hot gas and fragmented volcanic matter speeds of up to 700 km/h temperatures of 1,000 degrees hurtle downhill spreading laterally under gravity
why are nuee ardentes particularly hazardous
turbulent and incandescent type of pyroclastic flow flowing close to the ground after violent ejection from a. volcano they are so dangerous as they ignite everything they pass are fast moving highly unpredictable
how are lava flows hazardous
very hot between 550-1400 degrees
can cause injuries slow moving so no deaths bigger
can destroy property eg 1980s Kalapana in Hawaii was destroyed by lava flows burnt and buried buildings homes vegetation
can melt snow and ice causing flooding
Lava flows fountained 50 to 150m high following the Eldfell eruption.
methods of stopping lava flows
breaching the sides of a lava channel diverting flow constructing barrier spraying it with water bombing the lava flow
why are lahars hazardous
mudflow composer of a mixture of pyroclastic material rocky debris and water
flow 10s if m per second up to 140m deep
destroys any structure in its path
solidifies quickly when it slows down
difficult to predict
eg nevada del ruiz 1985 melted killed 20,000 people and engulfed the town
how is ash hazardous
can affect communities and farmland across hundreds or thousnands of km damages: buildings transport water power supply communications equipment agriculture can cause damage to lungs
Montserrat LEDC Volcano response
RED ALERT enabled full evacuation
UN emergency rations: biscuits, maize, beans
$15 million on blankets and shelter - camps set up to house the displaced
Higher cost of rebuilding in Goma
Further economic downturn
Applications for British citizenship
CONTRAST TO NIYRAGONGO - IN CONGO RAINFOREST SO DIFFICULT TO TRANSPORT AID
how does human geography affect earthquake impact
Bam vs Northridge (6.6/6.7 on richter scale)
almost same strength
both very shallow (depths of 7-10km)
epicentres close to urban areas
conservative margain
BUT Bam had a lack of building regulation
California less dependent on unstable agirculture / middle class area, wide strees and low density
case study contrast of volcanic eruption prediction
MONTSERRAT: 1995/7
Montserrat: there were inital eruptions for 18 weeks over plymoth; detected as early as 1992
NIYRAGONGO: 2002
Niyragongo: one volcanologist with a basic volcanic observatory
All other methods of predction destroyed for resources during the civil war (1998-2003);
BUT if eruption occured now, volcano risk managment unit established from UN
why is the location of earthquakes harder to predict than volcanos
It is not fixed - although some areas may be more suceptible to earthquakes e.g. clay areas
By contrast, volcanoes have a fixed location so a volcano moinitoring station could be set up to check for warning igns
explain how landslides are a secondary impact of earthquakes
When an earthquake of greater than 4.0 on the richter scale is triggered, on areas of steep slopes (70 degrees or more) the movement on the ground causes the soil to slip under gravity
As the shear stress exceeds the sheer strength, a landslide results
E.g. following the 1994 North Ridge, California earthquake (6.7 on RS)
11,000 landslides were triggered
example of how ground shaking is a hazard of earthquakes
75% of houses in Bam, Iran completely destroyed following a 6.6 RS earthquake
Heavy rain and mud bricks made acted as exabarating factors
example of liquefaction
San Francisco earthquake 1989
$100,000 damage was caused by liquefaction
example of a citizen level response to an earthquake
in Japan all offices, schools and many homes have earthquake kits which include hard hats, gloves, drinking water, basic medical supplies and enough dry rations for a couple of days
what experiment proved how difficult earthquakes are to predict
Parkfield California
It found great inaccuracy in mistakenly predicting an earthquake in 1985 and 1993 which eventually happened 9 years later in 2004
what is tephra
fragments of rock and pyrcolastic material, produced when magma or rock is explosively ejected
Lapilli size material 6-64mm can be carried upward within a volcanic plume and downwind in a volcanic cloud
what causes pyroclastic flows
teh collapse of an eruption column from a plinian eruption where the material forcefully ejected from the vent
this heats the surrounding air and the turbulent mixture rises and then falls as convection currents arent strong enough to carry the plume upwards
this sends it flowing down the flank of the volcano
explain how ground shaking occurs following an earthquake, and its hazardous effects
caused by seismic waves
caused when sesmic waves become surface waves; travelling along the earths surface from the epicentre outwards
ground either moves side to side (love w.) or up and down (Rayleigh waves)
hazardous effects:
the collapse of buidlings and dams (causing flooding & so disease)
the realse of hazardous material e.g. radiation from Fukushima nuclear power plant on the coast of Japan
fires caused by damage to gas pipelines and domestic appliances e.g. cookers
describe the hazarous effects of tsunamis
inundate costal areas causing death by drowning
wide scale destruction due to the sheer force of the wave hitting buildings
salt water from the sea inundating farmland, salinizing crops
water draining back to sea when the wave recedes causes futher distruction
explain liquefaction
the ground behaves like a liquid when strongly shaken
causing the foundations of buildings to give way
if groundwater is squeezed upwards through the rock and soil further damage occurs
example of completely unexpected earthquakes
bam, iran (2003)
northridge, california (1994)
it was not known that the settlements were situated on an active fault zone
contrast building preperation in two earthquake areas
Japan: shock absorbers, steel frames, space between buildings
Iran: traditional structures of mudbricks
what gases do volcanos produce after an eruption
hydrogen sulphide
carbon dioxide
sulphur dioxide
chlorine
why do microearthquakes occur before a volcanic eruption
fissures fill with magma
causing tiny earthquakes
the foci of this moves upwards as an earthwuake approaches
what changes to gas emissions from volcanos happen before the eruption
water vapor
chlorine
sulphur
specific response to lava flows
In 1992 Mount Etna erupted
Italian and American airforce bombed and dropped concrete slabs into the flow
halting its advance
example of lava flows being prepared for
Italian army, assisted by Swedish engineers
attempted to divert lava flows away from the area of Rocca
using a specially excavated anal
Mount Etna
land planning sustainable managment of Volcano
1981 Mount Etna delcared a protected area
prevent further building
preserve the unique vegetation of the area
given national park status 6 years later
play host to toursits (income)
how can volcanos be used to provide opportunities for locals
opportunity of in expensive hot water and central heating
hot water bore holes feed an intricate pipe network
that then supplies households in Reykjavik
opportunity of toursim: land of fire and ice
spectacular waterfalls e.g. Gullfoss, geysirs and boiling mudpools
explain why gas emission from volcanos is hazardous
Poisonous gases of carbon dioxide led to widespread destruction in Lake Nyos, Cammeroon.
In 1986, a 50m cloud deprived people and animals of oxygen, asphyxiating them – 1,700 people were suffocated and 3,000 cattle died.
general prediction of VOLCANOS
hazard zoning:
Mount Vesuvius Action Plan, formed based on the 1631 eruption. It divides the eruption area into three zones: red, yellow and blue.
E.g. red has the highest risk with high temperature gas, pyroclastic flows and nuee ardentes - 550,000 people evacuated.
Twinning’s system – people are spread across the country, with each district evacuated paired with an Italian province.
specific forecasting of VOLCANOS
Effective monitoring techniques only possible with a large scientific base & sufficent funding.
Iceland:
Seismic stations installed in and around glaciers to detect and located subaerial eruptions under ice.
Ceilometers (cloud base analysers) and radars have been set up to analyse eruption clouds.
Various monitors measure gases such as SO2 and CO2.
Various cameras monitor remote volcanos for signs of activity e.g. bulging that can occur up to 2m a day.
However, small tremors are very common so the eruption of Eldfell in 1973 was completely unexpected
Montserrat experienced major seismic events in the weeks before
general preperation for VOLCANOS
Roof strengthening against ash fallout or given a smooth surface so ash falls off.
Walls can be constructed between poisonous gas volcanic vents, and local populations in order to divert the gas (Eldfell).
Advise from FEMA:
goggles and disposable breathing mask for each member of the family to a disaster supplies kit, and put in a spare air filter for each vehicle.
Assemble a 3-day disaster supplies kit with food, water, medical supplies, and NOAA Weather Radio All Hazards
make evacuation plans: main route and backup route.
short term response for VOLCANOs
1973 Eldfell, short term response - the Icelandic State Civil defence organisation evacuated the entire population of Heimaey.
Alerted the population by sounding fire engine sirens, pre-planned evacuation strategy to gather at the harbour.
Boats left an hour after the eruption; the elderly who could not leave by boat were airlifted out.
Two weeks later, the lava flow posed a serious threat to the village 1.5km away, and so the ISCDO sprayed the leading edge of the lava flow with sea water. This began to cool the flow advancing towards the town, slowing its movement dramatically and soon to a stop.
Instead of abandoning the fishing tradition in the local area, the new lava flow acted as a breakwater, improving the shelter afforded to the harbour.
long term response for VOLCANOs
Geothermal energy utilised from the gradually cooling lava flows. In 1979 four large plants were built to extract heat from the flows. Up to 40 MW of power could be generated by the plants, supplying hot water to nearly every house on the island.
A new runway was added to the island’s small airport, over the tephra that was produced by the eruptions. Also, a landfill was built on which 200 new homes were built.
human causes of minor earthquakes
Fracking of shale rocks for shale gas can trigger earthquakes – triggered two in Lancashire in 2011.
Underground nuclear testing triggered 30 minor earthquakes in Nevada following nuclear testing in 1968.
Increased crustal loading on previously stable surfaces can cause earthquakes – Colorado river dammed by the Hoover dam filled over 10 years causing 6,000 minor earthquakes.
intraplate earthquake cause
These earthquakes can occur and are thought to be caused by friction and movement along faults.
Regional compression caused by the motion of the Earth’s tectonic plates, which crack and bend as they float around on the mantle could cause earthquakes.
Linconshire, England 2008 5.2 on richter scale
explain the formation of earthquakes at conservative boundaries
e.g. San Andreas Fault where the Pacific plate moves northwest and the North American plate moves south west).
Two plates travel in the same direction at different speeds; or in opposite directions.
These rocks catch, causing a build-up of stress - when the stress exceeds the friction or the breaking strength of the rocks, the rocks break or jolt and in seconds the energy stored in the rock is released in the form of seismicity.
1994 Northridge Earthquake 6.7.
explain the formation of earthquakes at subduction boundaries
Powerful, megathrust earthquakes.
AT 40-70 degrees in the Benioff Zone the descending plate is bent during subduction.
When the two plates lock together, a large amount of friction and stress is built up.
The two plates overcome frictional restraint, and the two blocks will slip relative to each other leading to an earthquake.
Beyond this, the plate melts, becoming a liquid, so there is no friction or tension as rocks are able to deform without breaking.
how does magnitude affect earthquake impact
Magnitude (Richter scale); depth of focus.
6.0 on the Richter scale is 100times more powerful than one of 4.0 – Japan earthquake 2011 9.0 on the Richter Scale greater than Lincolnshire 2008 5.2 on Richter Scale.
The more aftershocks, the more damage is done.
Earthquakes that occur near the surface do more damage than deep focus earthquakes, (more of the energy is absorbed by overlying rocks).
Northridge and Bam both 7-10km away from surface, shallow earthquakes.
specific forecasting of EARTHQUAKES
difficult as the mechanisms that cause earthquakes are located deep within the ground. This means that the presence of sensors that analyse the strain in rocks, unusual behaviour in groundwater, release of radon gas, or they can be completely unexpected.
This occurred in Bam, Iran (2003) and North-Ridge in California (1994), when it was not actually known the settlements were situated on an active fault zone.
the experiment carried out by the US Geological Survey in Park field, California (1980s/90s) to see if earthquakes could be predicted, ultimately failed.
gentle P waves can be sense by a seismograph, allowing a warning to be issued before the slower and more destructive S waves
distributed by mobile phones and interruption to TV broadcasts. Warning in the 10s of seconds – enough for buildings to be evacuated, crouching under desks
general preperation of EARTHQUAKES
Steel lattice framed superstructures are placed around buildings, shock absorbers built into a buildings structure, absorbing shaking forces; after Kobe in 2005, Japan enforced regulations to prevent the domino effect of buildings, ensuring they are appropriately spaced.
California and Japan enjoy this technology; in Bam, Iran mud bricks led to 75% of houses destroyed.
Tsunami walls can be built, such as along the east coast of Japan; but in 2011 tsunami overtopped the land causing great damage – structures only effective to a certain extent.
HIC hazard perception of earthquakes
well managed in countries such as Japan, ensured through education. Earthquake simulation as school children visit fire stations ensures appropriate, first-hand knowledge of the hazard.
immediate response to EARTHQUAKES
digging through the rubble to rescue people via search and rescue teams; establishing centres for refugees that have become homeless;
social media to search for survivors.
short term response to EARTHQUAKES
After the earthquake in Bam aid and personnel were sent in by 44 countries, while the UN World Food Programme sent in 100,000 rations of food. Tents, blankets and medical supplies were also airlifted in, coordinated by the UN.
Japanese defence force mobilised response internally; motorway fully functional 6 days after, 98% of electricity, 96% of water supply restored. Taiwain raised money via concerts.
long term response to EARTHQUAKES
Long term reform of policy towards building design, the Iranian government established a framework to deal with the construction of earthquake proof buildings and agreed to rebuild Bam with buildings with following specific codes.
The water supply was damaged in the quake, hurting the date growing industry – the Iranian government rebuilt and improved these plantations.
problems with forecasting tsunami
often predicted at a much smaller scale than in reality – waves were predicted of 6m when they were 39m for Japan 2011
Difficulty forecasting specific events as earthquakes, landslides and underwater volcanic eruptions are impossible to predict in themselves.
Monitoring equipment is expensive and requires HIC investment domestically, or via aid e.g. UN Meteorological Agency after Indian Ocean
general prediction of TSUNAMI
hazard mapping – ranging from white to red, the risk of tsunami occurrence is published every year in a choropleth map by the Japanese meteorological agency: highest risk at Iwate in North West Japan
specific forecasting of a TSUNAMI
achieved via monitoring
monitoring: 180 seismic stations across Japan and 80 water borne stations monitored 24 hours a day
If an event is forecast, more immediate warning is issued via TV and social media alerts, warning sirens and loud speaker systems etc
This generally gives people 20m to get to higher land
By contrast, the Indian ocean tsunami had no short-term warning and contributing to its large death toll.
general preperation for TSUNAMIS
Japan has concrete floodgates and breakwaters protecting ports and costal areas.
In conjunction with hazard maps, areas at high risk often take out insurance, have emergency aid kits at home, and a pre-planned evacuation route.
However, 40% of Japan’s 10m tsunami walls toppled in 2011
specific preperation for TSUNAMIs
Preparing for a specific event e.g. evacuation plans into action – after receiving a superimposed alert from Japanese meteorological agency people are advised to swiftly get to higher ground.
hazard perception for tsunamis
in HIC countries well managed e.g. Japan
more important in LIC countries e.g. prior to Indian Ocean Tsunami 2004, locals and holidaymakers had never experienced a destructive hazardous effect and so had no perception of the scale of the danger they were facing.
short term tsunami response
Japanese Self Defence Force coordinated rebuilding efforts; just 6 days after a motorway was repaired and fully functional; 100% of expressway restored, 96% of electricity supply, 98% of water supply etc.
Over 116 countries and 28 NGOs offered assistance e.g. Taiwan raised over $252 million in aid; local governments acted to fundraise through concerts etc.
Affected by the political climate – following the 2004 Indian Ocean tsunami, only 30% of those eligible for aid received it in Sri Lanka; allegations of local officials giving aid only to supporters, some of whom not victims of tsunami.
long term reponse to tsunami
tsunami wall raised to 12.5m, 250 miles long in 2016 at a cost of £4.6bn
why is sustainable managment possible in Eldfell
Hazardous areas can only be managed sustainably if the hazards are understood well.
The problems and threats of hazardous environments are balanced with the opportunities.
Iceland’s low population (3 people per square km), strong economy and stable democratic government provide fertile ground for effective long-term planning.
how is the volcanic hazard managed sustainably in iceland
preparedness for an event, regular monitoring
short term response in difficult and inneccesible terrain
long term response creation of opportunities
