A22 Techtonic Activity Flashcards
Describe liquefaction and tsunamis
How can their impact on people be reduced by accurate earthquake prediction
Liquefaction -
a process where shaking of soft or unconsolidated ground by earthquakes causes it to lose cohesion and act as an unstable base.
Water may be forced to the surface but buildings pipelines and other structures may have their foundations undermined and sink with serious consequences
Tsunamis -
Huge waves oft generated by the movement of plates on the ocean floor. They travel at high speed and grow to great heights when approaching a coastline.
They can reach 30m in height and travel several kilometres inland in low lying coastal regions
Buildings and infrastructures should avoid areas prone to liquefaction or unconsolidated soils and avoid low lying coastal areas as they are easily t by tsunamis.
Tsunamis - real time warning system, alert people of the likelihood or a tsunami arriving allowing areas to be evacuated and cleared
How does ocean floor evidence and plate evidence explain the movement of plates according to continental drift/plate tectonic theory
Ocean floor evidence - age of rocks Mid ocean ridges Deep ocean trenches Sedimentation Palaeo magnetism
Plate evidence
Distribution of earthquakes and volcanic activity
Parallel coastlines
Geological evidence on continental drift fossils and mountain trends
Topography of oceans studies - mid ocean ridges
Huge linear underwater mountain ranges with deep central valleys
Ran in continuous line for 50,000 km around Earth
Expected ocean floor to get deeper near centre but it was younger
Ocean rocks dated in millions not billions and sediment was thin near centre - recently formed
Plate evidence
Distribution volcanic and earthquake activity -
Distance and repeated patterns of volcanic and seismic activity emerged.
Presence of volcanic and earthquake activity at constructive and destruction margins helped shape plate tectonic concepts
Trends occurred in long linear bands through oceans or along coasts
Hazards of volcanic activity
Explosion - force of explosion can be enormous elsewhere even though explosion does not cause violence. Explosions can generate tsunami
Lava - flow destroys property, rarely threatens life. Swamps and buildings start fires. LAVA FLOW DOWN MT ETNA IN ITALY DESTROYED CABLE CAR STATIONS HOUSES HOTELS FARMLANDS
Nuée ardentes/pyroclastic material - wide variety of solid material ejected by volcano other than lava. Potentially lethal mixtures of super heated gas, ash, and rock fragments that travel rapidly down side of mountain 29k DEATHS IN ST PIERRE IN CARRIBEAN ISLANDS IN 1992
Volcanic gases - hot and toxic. Can cause mass suffocation
Landslides - building of volcano as magnetic pressure builds beneath surface. Formation of steep slopes may cause landslide. ERUPTION OF MT ST HELENS IN 1980 COLLAPSE OF SIDE OF MOUNTAIN LARGEST LANDSLIDE EVER RECORDED ON FILM
Lahars - volcanic mud flows. Hot ash can mix with rain or river water. Flows as thick hot mixture at great speed. Can flood valleys burn environment and grown people
Jokulhlaups - floods caused by volcanic eruption beneath ice sheets or glaciers
Economic social and environmental impacts of volcanos
ECONOMIC
damage to farmland, tourist attractions and commercial may take decades of restoration
Takes very long to re-establish economy
Lava flows destroy built structures like housing factories hotels roads farms
Infrastructure damage costs to agriculture industry and government
SOCIAL
lava flows destroy anything in its path, damage to homes and property
Traumatic event which can have psychological impact on people
Children and elderly can die of disease
Homelessness/deaths/refugees/injuries
People can refuse to return to area even with it is safe to do so
ENVIRONMENTAL
Major volcanic event or series of them can impact global climate
Volcanos are capable of re-writing landscapes
Explosions that emit ash and lava can destroy vegetation and animal life
Eruptions could fill atmosphere with dust and reduce level of insulation entering earths atmosphere
1m FARM ANIMALS DIED WITH MT PINATUBO ERUPTED IN 1981
Benefits of volcanic activity
LAND CREATION
ash and lava can create new land. SUMMIT OF MT SURTSEY DISCOVERED IN 1963. ISLAND PROVIDED SCIENTISTS WITH GOLDEN OPPORTUNITY TO STUDY VOLCANIC ACTIVITY AND ECOLOGICAL SUCCESSION
FERTILE SOILS
some lava flows and ash falls can be weathered into rich fertile soils. Deposits that are rich in potassium or phosphorus highly valued.
ENERGY
ICELAND NEW ZEALAND ITALY AND USA all naturally produced volcanic stream is generated to produce electricity. REYKJAVIK good example - volcanic hot springs supplies over 50,000 homes with heated water
TOURISM
strong tourist attractions. Adventure seekers and tourists enjoy natural beauty. eg YELLOWSTONE NATIONAL PARK IN USA GENERATES THOUSANDS OF VISITORS ANNUALLY.
What is volcanic prediction
Prediction of volcanic activity that involves monitoring and research to predict the time and severity of volcanic eruptions
Necessary to predict time and length of eruption and scale and nature of impacts
What are warning signs of volcanic activity
Local seismic events, tilting of ground and gas release
Other observations eg melting of snow caps, disappearance of creator lakes and death of local vegetation
What are methods of monitoring
Tilt meters used on slopes and on edge of volcano craters to monitor rises, falls or bulges in surface levels that reflect underground movement of magma
Study of gas emissions emitted by volcanos. New technologies such as laser monitoring can be used to detect small changes in gas across surface or creator of volcano
Seismometers used to detect earthquakes as hundreds of earthquakes caused by rising of magma
Thermal imaging around volcano to detect rises in heat
What is sea floor spreading and subduction
Sea floor spreading is when new oceanic crust is created as magma rises through the weak zones in the crust.
The weak zones in the crust are being pulled apart along a ridge crest.
This creates mid Atlantic ridge and rock is very young and they become older as they move away from ridge.
SUBDUCTION
subduction is when denser oceanic plate is Subducted by lighter continental or oceanic plate which melts the plate and destroys it at destructive plate boundaries.
This explains why earth does not get bigger besides sea floor spreading
Why rocks at the centre of the ocean base are much younger than continental rocks
Constructive plate boundary
Hot spots deep in mantle cause magma to rise
Forces plates above to stretch
Break along a fault line
Line of weakness can be seen by Rift Valley
Magma solidifies to create new plate material
Features - mid ocean ridge, Rift Valley and linear sea
Explanation of constructive boundary
As divergence process continues stretching plate and Rift Valley allow ocean to spill in initiating formation of new ocean basin
Shallow earthquakes are associated as movement of magma towards surface
Destructive plate boundary
Plates forced towards each other at margin by convection currents
Ocean and continental -
Heavier oceanic plate forced down under light her continental plate creating a trench.
Subduction ^
Plate forced under melts and breaks up
As plate melts molten magma rises forming volcano at distance away from trench
Region of seismic event is known as Benioff zone - contact point between places
EG NAZCA PLATE AND SOUTH AMERICAN PLATE
Collision plate margins
Plates move towards each other by convection currents in the asthenosphere
Both plates carry continents
Edges of the plate and any sediment in between is crushed upwards producing fold mountain
FOLD MOUNTAIN - HIMALAYAS
BETWEEN INDIAN AND EURASIAN PLATE
Conservative plates
Plates slide past one another
No creation or destruction of plate material - no significant volcanic activity
Frequency cause of earthquakes
What are hot spots
Hotspots - localised source of high heat energy that sustains volcanism
Not all volcanoes occur at plate boundaries. Can occur in the middle of a plate due to hotspots
Seen as the driving force of convection currents and the creation of lines of construction and destruction at plate margins
Oceanic plate above a hotspot may cause volcanic eruptions to occur if plate margin left unbroken
Description
Mantle plume rises from athenosphere into lisp sphere, and continues into plate where it erupts
As plate moves away it can carry volcano or volcanic island away from hotspot and becomes dormant/extinct.
A new one grows in its place. Former islands cool, subside and erode with distance form hotspot.
