geog book 4 chap 2 Flashcards
what is an earthquake
the shaking of the Earths ground due to sudden release of energy in the Earths lithosphere
generally pccurs along plate boundaries and contain faults
how do earthquakes occur
- Rock mass on one side of fault are pushed by tectonic forces
- friction causes rocks to get locked causing stress to build up
- when the stres exceeds the strength of the fault, rocks snap to a new position
- sudden movement causes seismic waves to be released causing ground shaking
what is the focus
point on earths crust where seismic waves are released
origin of the earthquake
what is the epicentre
point on earths directly above the focus
shaking is generally felt the most strength here
what are seismometers
sensitive instruments that detect ground vibrations and determine the magnitude of an earthquake
the higher the seismic energy released during an earthquake, the higher the magnitude
what is rhe richter scale
calculates earthquake magnitude using the height of the largest wave recorded on seismoneters and max seismic intensity reached rather than total seismic energy released
scale is logarithmic and is from 1-10
what is the limitation of the richter scale
would rate an earthquake with a single drastic spike in wave energy to have a higher magnitude than a long earthquake with many large and intense waves and underestimates longer earthquakes that release more overall energy that may cause more damage
hence it is not commonly used except for small local earthquakes
what is the moment magnitude scale
rates earthquake magnitude based on estimated total energy released during the earthquake
more accurate especially for earthquakes with magnitude 8 and above
thus scientists have adjusted magnitudes of past earthquakes such as the 1964 Prince William Sound Earthquake in Alaska from magnitude 8.6 to 9.2
scale is logarithmic
what is a volcano
a landform created when lava erupts onto the earth’s surface
may form a cone-shaped mountain as more lava erupts and accumulates over time
eruptions occur at dpb and cpb
how do tectonic processes at dpb result in volcanic eruptions
plates move apart causing the crust to stretch and fractures to develop
the decrease in overlying pressure causes parts of the underlying mantle to melt forming magma
magma contains dissolved gases and less dense than the surrounding materials
magma rises through weak areas in the crust to the earth’s surface and erupt as lava causing a volcanic eruption
lava cools and solidifies over time forming a volcano
how do tectonic processes at cpb result in volcanic eruptions
plates move towards each other and the denser plate subducts under the other
subducting plate sinks into the mantle and the high pressure forces water out of the oceanic crust
water lowers the melting point of overlying mantle causing it to melt forming magma
magma contains dissolved gases and is less dense than surrounding materials
hence magma rises through weak areas in the crust to the earths surface and erupt as lava causing a volcanic eruption
lava cools, solidifies and accumulates over time forming a volcano
what is high silica magma?
usually associated w stratovolcanoes
more viscous
as magma rises to the earths surface, dissolved gases in the magma cannot escape easily
more pressure builds up until gases escape explosively causing violent and explosive eruptions
give an example an explain a volcano with viscous magma yet does not result in an explosive reaction
Mt merapi is a stratovolcano but its eruption in 2006 was not explosive as viscous magma rose in a way that allowed dissolved gases to escape easily
what is low silica magma
usually associated with shield volcanoes
less viscous
as magma rises to the earths surface dissolved gases in the magma can escape easily
less pressure builds up resulting in gentle effusive eruptions
explain the formation of stratovolcanoes and name an example
high viscosity magma rises through weak areas in the crust to the earths surface and erupts explosively as lava, ash and rocks
ash and rocks settle on the sides of volcano and are later covered by lava
over successive eruptions, a tall volcano consisting if alternating layers of ash and lava develops
as high viscous lava travels a shorter distance before cooling and solidifying, volcano has steep sides and narrow summit
Mt Mayon Philippines
explain the formation of shield volcanoes and name an example
low viscosity magma rises through weak areas in the earths crust to the earths surface and erupts effusively
over successive eruptions, a volcano consisting of layers of lava develops
as the low viscosity lava travels a longer distance before cooling and solidifying, causing the volcano to have gentle sloping sides with a broad summit
Kilauea Hawaii
name the structure of a volcano
- magma chamber
- layers of rock
- pipe/ conduit
- layers of ash
- layers of lava
- lava flow
- vent
- volcano cone
- secondary cone
- crater
- pyroclasts
what is a magma chamber
a reservoir of molten rock beneath the Earth’s crust
as more magma seeps into the magma chamber,
pressure in the magma chamber builds up
giving rise to a volcanic eruption
what is a pipe/conduit
where magma flows from magma chamber to vent
what is a vent
opening in the earth’s surface with a pipe leading into magma chamber
how is the secondary cone formed
during formation of the volcano the vent may be blocked
forcing magma to find new exit route to surface
secondary cone of newer mantle material develops
what are pyroclasts
ash and rock fragments and volcanic bombs ejected during volcanic eruption
mixed with superheated gas, form pyroclastic flow which can reach up to 200m/s
becomes lahar when mixed with water of melted snow/ice causing fast moving mudflow if 40m/s
how is a caldera formed
the summit of a volcano may be blown off durint an explosive eruption
sides of the crater may collapse inwards due to loss of structural support
creates a much larger crater than original volcanic vent
a caldera, large basin-shaped volcanic depression is formed
over time, magma chamber beneath caldera solidifies and volcano bexomes extinct
caldera may then fill with water to form a lake
how are volcanic eruptions measured?
volcanic explosivity index measures magnitude if different volcanic eruptions based om explosivity
the greater the vol of ejected material -> higher VEI
the greater the height of eruption cloud -> higher VEI
the longer the duration of eruption -> higher VEI
measured on a scale of 0-8
- effusive 0 or 1 as they are non explosive with less than 0.0001km³ of material ejected
- value of 8 -> mega-colossal explosive eruption, eject more than 1000km³ of tephra and eruption cloud column height of over 25km
scale is logarithmic
how are earthquakes distributed
occur along all types of PB
largest conc of earthquakes r at PRoF
at PB, plates are pushed by tectonic forces causing stress to build up and energy to be released
- narrow belt of eq along CPB in PRoF
- narrow belt of eq along DPB at MAR
- narrow belt of eq along TPB at SAF
eq occur more commonly along CPB at subduction zone as mo4e stress builds up during eq
an exception are eq that occur away from PB - eg within Eurasian Plate
what is PRoF
broad belt around the Pacific Ocean where most eq and active volcanoes occur
compromise of all 3 types of PB
CPB: pacific & philippine
DPB: pacific & cocos
TPB: pacific & na at saf
how are volcanoes distributed
generally located near cpb and dpb
at these pb, magma rises to the surface forming volcanoes
belts of volcanoes observed along
- CPB: belt of volcanoes along subduction zones at PRoF
- DPB: belt of volcanoes along DPBs between NA and EUAS plates
unlike eq, volcanoes not found near TPB and CC-C (magma does not rise to the surface)
hotspot volcanoes are exceptions found away from PB
name an example of a hot spot volcano
Piton de La Fournaise is a HSV located on the island of Reunion in Indian Ocean away from PBs
how are tectonic hazards distributed - eq
often localised
generally located within same geographic region as the eq
as eq are found along pb, hazards are also found near pb
how are tectonic hazards distributed - volcano
volcanic hazards generally found near volcanoes at DPB and CPB
however not all are localised
- tsunamis & volcanic ash may spread beyond geographic regions where eq and volcanoes are located
> may travel thousands of km
> tsunami: travel great distances without loss of energy
> ashfall: depends on wind conditions and vol of ash erupted and height of ash thrown into atmosphere
give an example of ashfall spreading away from volcanic eruption
eruption of mt pinatubo 1991 resulted in ash spread across SEA
what are the earthquake hazards
ground shaking
soil liquefaction
landslides
tsunamis
what are the volcanic eruption hazards
tephra
volcanic gases
lava flows
pyroclastic flows
lahars
volcanic islands
what are the impacts of ground shaking on natural and human systems
- destroys ecosystems
- ruptures oil and chemical factories polluting land and water
- ruptures and uproot trees causing widespread tree injury and death and damaging wildlife habitats - destroys properties and infrastructure
- weakens buildings, bridges, roads and railways causing them to collapse and makes it difficult to rescue people - disrupts services
- snaps water and gas pipes causing water shortages and disruptions to gas supply
- electricity & comms cables break affecting important systems such as tsunami warnings and tv broadcasts - causes injury and fatalities
- people may get trapped under collapsed buildings & infrastructure causing loss of life and injuries
give an example of the impacts of ground shaking
2010 haiti eq
surrounding areas around factories polluted
debris polluted areas
more than 250 000 houses collapsed due to violent vibrations
about 220 000 people killed
water pipes ruptured causing water shortages
what is soil liquefaction
occurs when the violent ground shaking causes saturated, loose soil to lose its soil structure and transforms into a thick fluid
what are the impacts of soil liquefaction on human and natural systems
- destroys ecosystems
- trees on liquefied soil sink and tip over damaging habitats and causes loss of biodiversity
- liquefied soil may enter rivers causing aquatic plants to die
- sewage pipes may be broken and untreated waste materials can pollute rivers killing aquatic species - destroys properties and infrastructure
- buildings and infrastructure can sink in a tip over causing damage that makes it difficult to rescue people - disrupts services
- electricity and comms cables and water and gas pipes can sink in and snap disrupting supply of these services
- roads ans railways above liquefied soil can sink in and get damaged making rescue diffucult - causes injuries and fatalities
- people may get trapped under collapsed buildings
give an example of soil liquefaction impacting human and natural systems
2010-2011 Christchurch NZ eqs
triggered severe liquefaction as city lies above former swamp area where soil is loose and saturated
more than 60 000 residential buildings and infrastructure covering 1/3 of city damaged
liquefied soil entered rivers and untreated sewage from broken pipes polluted rivers causing loss of biodiversity
what are landslides
occur as the violent vibrstions from cracks on steep slopes loosen the rocks and soil, and trigger the loose rocks and soil downslope
what are the impacts of landslides on human and natural systems
- destroys ecosystems
- fast-moving debris can bury huge areas of forests and wetlands
- rivers can be polluted w debris killing aquatic life
- rivers can be blocked causing floods that can damage nearby ecosystems and properties - destroys properties and infrastructure
- debris can bury village and farms destroting properties and infrastructure - disrupts services
- debris snap electricity cables water and gas pipes disrupts supply of these services
- roads and railways can be blocked by debris difficult to rescue people - causes injuries and fatalities
- debris can bury people
- debris can block rivers drowing ppl
give an example of landslides and its impact on the natural and human systems
2018 Papua New Guinea eq mw 7.5
triggered landslides and caused high amounts of debris to enter rivers
caused flooding
polluted waters and killed fish
what are tsunamis
a series of ocean waves which can be caused by undersea earthquakes
tsunamis can travel over thousands of km and devastate huge areas of coastline
how do tsunamis occur
- undersea eq causes seabed to be displaced
- a large vol of water is lifted forming waves of great wavelength and low height of less than 1m
- the waves travel towards land at high speeds - 800km/h
- on approaching the coast, greater friction with shallower seabed slows waves down
- the waves get closer together and higher in height
- before a tsunami occurs
- seabed may recede from the shore as sea water fills in the void caused by displacement of seabed
give characteristics of a tsunami
can reach up to 15m or more in height
travel at a speed of 30-50km/h
devastate shorelines as the waves hit
what are the impacts of tsunamis on human and natural systems
- destroys ecosystems
- seawater can flood huge areas of coastal wetlands and forests damaging habitats
- large amount of debris carried by the waves can pollute these areas damaging ecosystems and killing wildlife - destroys infrastructure
- fast moving waters and large amt of debris carried in by the waves can sweep away buildings and destroy them - disrupts services
- fast moving waters and the large amount of debris carried in by the waves snap electricity and comms cables -> disrupting supply
- “ sweep away roads roads and railways making rescue difficult - injuries and loss of lives
- sweeping waters can drown ppl
- large amts of debrid carried in by waves can hit and kill ppl
give an example of a tsunami impacting human and natural systems
2011 tohuku eq mw 9.0
triggered a tsunami up to 40m in height
waves destroyed buildings
tsunamis carried debris inland causing flooding and pollution
Sendal suffered extensive damage and half its population killed
70 000 pine trees knocked down in Iwate causing biodiversity loss
tsunami hit pacific islands devastating ecosystems
what are the impacts of tephra on human and natural systems
- destroys ecosystems
- ash can be carried thousands of km by prevailing winds polluting huge areas of ecosystems
- ash can infiltrate and kill wildlife
- ash can cause blindness to birds - destroys buildings
- volcanic bombs can hit properties damaging them
- ashfall accumulates on roofs
- when saturated with water, ash can double in height causing roofs to collapse
- corrosive, weakening building structures -> more likely to collapse
- thick blankets of ash damage farmland suffocating crops and destroying livelihoods - disrupts services
- ash particles can damage plane engines -> closure of airspaces and disruption of air transport - causes injury and fatality
- volcanic bombs can hit people causing injury and loss of lives
- ashfall can cause respiratory problems, eye irritation and suffocation
give an example of tephras impact on natural and human systems
1991 mt pinatubo eq
emitted huge amts of ash
buried more than 180km² of forests in 25cm ash
destroyed 800km² of rice fields affecting livelihoodd of many farmers
airports closed and many flights cancelled disrupting transport
some places damaged
what are the impacts of volcanic gas on natural and human systems
can release large amts of toxic gases such as co2 and so2
- destroys ecosystems
- so2 results in acid rain when it reacts with water in air -> damaging vegetation soil & kill wildlife
- cold co2 heavier than aif -> becomes concentrated in low-lying volcanic areas
- higher amt of co2 in air -> kill wildlife and destroy vegetation - destroys properties and infrastructure
- so2 results in acid rain corroding buildings and infrastructure - threatens public health & security
give an example of volcanic gas having impact on natural and human systems
1979 Dieng Volcano eruption Indonesia
- released deadly amts of co2 and killed 150 ppl
what are the impacts of lava flows on natural systems and environment
extremely hot and can travel distances within geographic region
deaths by LF are low as people can easily move away
- destroys ecosystens
- hot low silica lava can travel distances destroying forests and other habitats and ecosystems - destroys properties and infrastructure
- lava can burn through homes properties and structures - disrupts services
- lava can destroy electricity and comms cables water and gas pipes disrupting supply of these services
give an example of lava flows impacting natural and human systems
2018 Kilauea eruption in Hawaii
far reaching LFs destroying >600 homes
destroyed huge areas of forests and ecosystems
telephone and power lines damaged causing widespread comms outages
what are pyroclastic flows
hot cloud of gas, ash and rocks travelling down slopes of volcano at great speeds >200kmh
occur when a column of hot ash and gas gets thrown up into the air and falls back to the ground under the pull of gravity
temp of up to 700°C making it the most devastating volcanic hazards
travels several km
how does pyroclastic flows impact natural & human systems
- destroys ecosystems
-huge areas of forests destroyed causing biodiversity loss
- thick layers of ash cover the path of the flows polluting huge areas of forests - destroys properties and infrastructure
- hot flows burn through HPI in their path - disrupts services
- hot flows can destroy electricity and comms cables disrupting supply of these services - injuries and fatalities
- extreme temps burn and kill ppl instantly
give an example of pyroclastic flows impacting natural and human systems
2010 merapi eruption Indonesia
blasted a series if PFs down slops inhabited by villagers
about 350 deaths
huge areas of forests burned
what are lahars
mudflows comprising water and ash
formed when huge amts of rain and rocks ejected during an eruption mix with water
can flow at high speeds of up to 200kmh and cover considerable distances within geographic region
how are lahars formed
PFs melt ice, snow and mix with water on volcanic cone as they travel down
intense rainfall washes down ash
what are the impacts of lahars on natural and human systems
- destroys ecosystems
- lahars can cover forests and other ecosystems with mud that hardens destroying them
- can pollute rivers killing aquatic life - destroys properties and infrastructure
- can bury homes and buildings, destroying them
- can cober farms with mud that hardens damaging them - disrupts services
- roads and railways blocked by debris making it difficult to rescue ppl
- can damage comms cables and water and gas pipes disrupting supply of services - TPB and IF
- can bury houses & its residents causing LoL
give an example of lahars impact on natural and human system
1985 nevada del ruiz eruption in columbia
released huge amts of ash and volcanic ash melted snow and ice
meltwater mixed with ash and rocks form lahars
fast-moving lahars buried more than 20000 ppl instantly
rivers highly muddied by lahars killing many fish
what are volcanic landslides
common on tall and steep volcanic cones comprising thousands if solidified lava layers and loose tephra
blast from an explosive eruption trigger downward movement of loose volcanic materials causing a landslide
high velocity and great momentum of landslides allow them to travel considerable distances in the geographic region
what are the impacts of volcanic landslides on natural and human systems
- destroys ecosystems
- fast moving debris can bury huge areas of forests and wetlands
- debris from landslides pollutes rivers killing aquatic life
- debris block rivers causing fliids and damaging nearby ecosystems and properties - destroying properties and infrastructure
- debris bury villages and farms destroying properties and infrastructurr - disrupts services
- debris can snap electricity and comms cables and water and gas pipes disrupting supply
- debris can block railways and roads -> difficult for rescue - CIF
- debris can hit ppl causing injuries and LoL
- debris block rivers causing flooding drowning people
give an example of volcanic landslides impacting natural and human systems
1980 mt st helens usa
north face of volcanic cone collapsed causing landslides that travelled 23km
destroyed huge areas of land and killed many
explain the benefits if volcanic eruptions and living near volcanoes - farming
over thousands of years, volcanic rocks break down and undergo weathering to form fertile soils ss they produce high crop yields and locals benefit from it
explain the benefits if volcanic eruptions and living near volcanoes - extracting precious materials and fossil fuels
magma cools and solidifies beneath volcanoes forming precious materials
source of income for locals employed to mine them
govt can sell them to generate revenue can be used to provide social services to locals
volcanic materials such as ash and solid materials may also be mined and used as construction materials
explain the benefits if volcanic eruptions and living near volcanoes - harnessing geothermal energy
derived from heat in earths crust
can be harnessed in tectonically active areas
beneath earth’s surface hot rocks heat up groundwater forming steam harnessed to generate energy
locals benefit from cheaper local energy and can be employed to work at geothermal power plants
explain the benefits if volcanic eruptions and living near volcanoes - tourism activities
tectonic movements can be attractive to tourists such as hiking and sightseeing
provides locals w employment opportunities such as tour guides, sellinf products and providing accommodation
hence boosting local economy
give an example of the benefit of farming with fertile soil at volcanic regions
best rice-growing regions in indonesia are near volcanoes in Bali -> Mt Agung
give an example of the benefit if extracting precious minerals and fossil fuels
at mt merapi, thousands of locals employed to mine volcanic sand suitable for construction
give an example of the benefit of harnessing geothermal energy
iceland: most electricity generated from geothermal power plants
give an example of the benefit of tourism activities at volcanic regions
Hawaiian islands are popular tourist locations for it scenic volcanic landscapes and tourism generates an annual income of ~usd 8mil and provides locals w thousands of jobs
