Tectonic Landscapes and Hazards Flashcards
what are the two types of the Earths crust
continental and oceanic
what is the lisophere
the crust and uppermost mantle which is split into tectonic playes
what are convection currents
the movement of magma below the crust. Hot magma rises cools and sink back down creating circular currents
how do tectonic plates move
convection currents
where are earthquakes/volcanoes most likely to occur
near/on plate boundaries
what is a destructive plate boundary
a plate boundary where oceanic and continental plates move towards each other (converge)
what is a constructive plate boundary
a plate boundary where a continental and oceanic plate move away from each other (diverge)
what is subduction
the process in which a plate is subducted under another plate at a destructive boundary. The denser oceanic plate is pushed under the continental plate. subducting plate melts in mantle
what is a conservative plate boundary
a plate boundary where two plate move against eachother in opposite directions
what causes a destructive/constructive plate boundary
dependent on the way the convection current travels below. If two circles go towards then destructive, if two flow away from each other then constructive
Where/how is an ocean trench formed
where subduction takes place at destructive boundary. e.g. Marina trench
How/where are fold mountains formed
at destructive plate boundary. The continental plate is crushed and folded upwards. e.g. Andes Mountains
How/where are explosive volcanoes formed
at destructive margin as oceanic plate sinks it melts and molten magma rises to surface. e.g. Mount Merapi
How/where is a new crust formed
At constructive plate boundary where two oceanic plates move apart and space created between the two fills with magma. e.g. Mid-Atlantic
How/where is an ocean ridge formed
At constructive margin when lava cools forming a ridge in the ocean. e.g. Mid-Atlantic ridge
How/where are submarine and island volcanoes formed
At constructive plate boundary when submarine volcanoes sometimes rise to the surface. e.g. Surtsey, Iceland
How/where is an rift valley formed
At constructive margin where two continental plates pull apart.
Rift valley example: Thingvellir, Iceland
Iceland slowly being torn apart as North American and Eurasian plate diverges.
- Rift valley 7.7km wide
- average 7mm wider a year
- valley floor subsiding by average of 1mm a year
What is a volcanic hotspot
area in the middle of a plate w/ unusual amount of volcanic activity
how are volcanic hotspots formed
intense radioactivity in core causes massive plume of magma which melts and pushed through crust. Plume then lies at fixed position, as plate moves over new hotspot, upwelling magma creates a line of volcanoes.
What are the types of volcano
shield volcanoes, stratovolcanoes and caldera
features of a shield volcano
constructive boundaries and hotspots; circular shape with gently sloping sides; composition of lave with no layers; runny lava; regular eruptions
how does a shield volcano form
basaltic magma w/ high temp gets to surface via cracks in crust. magma makes fluid lava which travels far before cooling creating gentle slopes.
Features of a stratovolcano
destructive plate boundary; conical shape w/ steep sides; alternate layers (strata) of ash and lava. explosive eruptions
how are stratovolcanoes formed
acidic lava w/ high viscosity that cools quick, doesn’t flow far before solidifying making steep sides. explosive eruptions of ash and lava bombs
what is a caldera
large scale volcanic crater that can be up to several km in diameter
how are calderas formed
either by magma chamber emptying causing roof to collapse; or massive explosive eruption
how does a lava tube form
forms beneath surface when low viscosity develops a hard crust through which lava flows
what is a geyser
a vent in crust that ejects hot water and steam. it erupts when super heated groundwater confined at depth becomes hot enough to blast to surface
Volcanic explosivity index (VEI)
measure of the explosiveness of a volcanic, measures how much is ejected, how high material is thrown up and how long eruption lasts. Logarithmic scale 1-8
what is magnitude
a quantitative measure of the size of an earth quake using Richter scale
what is the Richter scale
a measure of the magnitude of an earthquake. uses logarithmic, each level is ten times stronger from 1 to 10
characteristics of a lava flow
molten rock flowing down volcano, lava from shield goes further. local effect may travel few km endangering close villages/towns
characteristic of lahars
volcanic mudflows of ash and water form rain melted snow etc. travels at great speed down mountain. local effect travels several km endangering close villages/towns
characteristics of ash clouds
ash thrown into atmosphere, blocks sun. settles on everything eg. crops and buildings. Large effect, may reach 10-15 km high and spread over thousands of km
characteristics of pyroclastic flows
burning clouds of gas and ash w/ temps up to 1000°c travelling up to 200km/h. local effect, travel several km
the four earthquake hazards
ground shaking, liquefaction, landslides, tsunamis
physical factors that increase vulnerability to earthquakes
magnitude, duration, predictability, regularity
what is the epicentre
the point on the surface directly above the focus
what is the focus
the originating point of an earthquake
what are aftershocks
ground tremors occurring after a major earthquake but from same focus.
human factors that increase vulnerability
wealth, education, governments, age, health, population density, time of day, emergency services
what is a seismograph
a device used to detect vibration in earths crust. an increase may indicate an oncoming earthquake
monitoring techniques for earthquakes
laser beams - detects plate movement
levels of radon gas, increase indicates earthquake
seismograph
Pacific Tsunami Warning System
uses a network of seismographs and ocean buoys to detect earthquakes that can cause tsunamis. warning given to local centres who warn people
monitoring techniques for volcanic eruptions
remote sensing - satellites monitoring gas emissions w/ thermal imaging
visual signs, seismographs, tiltmeters - monitor shape of volcano
GPS
Hazard map
a map highlighting areas most affected by volcanoes, earthquakes and tsunamis
what does hazard mapping allow authorities to do
limit access to hazardous areas, control development in areas at risk
emergency planning features
education, divert lava flows, emergency services trained and have correct resources, exclusion zone, emergency kits, infrastructure designed to withstand disasters
features of earthquake buildings
steel frame, rolling weights on roof, cross bracing to support frame, open areas for evacuees, shock absorbers in foundation, deep foundation sin solid rock, roof covering area immediately outside building.
