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
