enquiry 1 Why are some locations more at risk from tectonic hazards Flashcards Preview

Tectonics > enquiry 1 Why are some locations more at risk from tectonic hazards > Flashcards

Flashcards in enquiry 1 Why are some locations more at risk from tectonic hazards Deck (27):
1

Hazard

the potential threat to human life

2

natural hazard

can be:
hydro-meteorological (climatic processes)
geophysical (land processes)

3

Divergent constructive (continental)

2 continental
magma plume pushes up and causes the crust to fall = rift valley
fluid basaltic magma from upper asthenosphere reaches the surface
east Africa rift valley

4

Divergent constructive (oceanic)

magma pushes up and out of the surface
grows as new molten rock takes its place
magma is from the partial melting of the asthenosphere
fluid basaltic lava
VEI 1-3
effusive and frequent
mid-Atlantic ridge

5

Convergent collision

2 continental with same density move together
crumple and fold
fold mountains
Himilayas
usually no associated tectonic hazard

6

Convergent destructive

denser oceanic sinks under continental
melt in subduction zone into andesitic explosive magma
slab pull speeds up the process
high on the VEI
magnitude 7-9 earthquakes
triggers tsunamis
less frequent

7

Conservative

2 continental move past each other
friction builds and slips
shallow focus
San Andreas

8

Benioff zone

area of deep earthquakes

9

elastic rebound theory

Locked fault
stress builds
stress exceeds threshold= failure
strain energy releases seismic waves

10

Volcanoes

all plate boundaries
highest magnitude= conservative
pacific ring of fire= 70%
intra-plate earthquakes= middle/interior of plate (Hawaii)

11

Tsunamis

secondary hazard associated with earthquakes
destructive only

12

volcanoes

violence depends on amount of gas in magma and how easily it can escape
more explosive = convergent and divergent
composite
less explosive= constructive and divergent
shield
P waves= immediate shock
S waves=longer wavelengths and arrives seconds later
L waves=travel through crust (crustal fracturing and secondary hazards like landslides)

13

palaeomagnetism

The 1960s
showed magnetic patterns were arranged in direction of earths magnetic field
used to date the age of the crust
mid-Atlantic ridge

14

convection currents

hot core heats up rock in lower mantle

hot rock rises slowly

as it rises it slowly cools and cant rise due to solid crust so it goes sideways

cools further and falls back down

15

plate tectonic theory

earths crust divided into plates
radioactive reactions occur in core= convection currents
at mid-ocean ridges = slab push and pull (Pacific plate)

believed to be correct due to:
Wegners CONTINENTAL DRIFT THEORY
seismic waves- Benioff zone shows subduction of oceanic crust

16

sea-floor spreading

sea floor widens

17

secondary hazards

soil liquefaction leads to lateral spreading which creates fissures (damages roads)

Landslides- travel several miles and grow in size
rarely occur at less than mag 4
exacerbated by saturated ground (2015 Nepal summer monsoon rain)

18

Mantle plumes

Concentrated areas of heat convection

At plate boundaries they are sheet like

Hot spots they are column like

19

Plate boundary

The narrow linear zone where two tectonic plates meet

20

Arthur Holmes 1930s

Earths internal radioactive heat was driving force of mantle convection that move tectonic plates

21

Tuzo Wilson 1965

Transform faults

22

Epicentre

Point in the earths surface directly above the focus

23

Crustal fracturing

2004 Indian Ocean created a rupture line for up to 1000km

Energy pulses generated along entire daily length

24

Pyroclasts

Any rock fragments ejected from a volcano (ash/tephra)

25

Volcanic hazards

Jokulhlaup- floods caused when volcano erupt beneath glaciers and ice caps (common in Iceland)

Gas eruption- eruption of co2 and sulphur dioxide which can poison people (composite/shield)

Ash fall- ash particles and larger tephra particles can blanket huge areas, killing veg/ collapsing buildings/ poisoning water courses (constructive plate margin cinder cone or fissure eruption/ composite)

26

Deadly tsunamis

2004 Indian Ocean

Magnitude 9.2

Wave height 24m

Deaths 230,000

2011 Japan

Magnitude 9

Wave height 9.3m

Deaths 16,000

27

Tsunami generation

Sub marine earthquake displace sea bed vertically

Result of movement along a fault line at a subduction zone

Displaced large volume of water in ocean water column

Moves outward in all directions from point of displacement

Moves as ‘bulge’ in open water

Usually hit coast as ‘wave train’