Download Tectonic Impacts #3

Tectonic Impacts
1 Lithospheric
plates and their
motion
 describe the characteristics of
lithospheric plates
 identify the relationship between
the general composition of
igneous rocks and plate boundary
type
 gather and analyse
information from secondary
sources about the forces
driving plate motion
 outline the motion of plates and
distinguish between the three
types of plate boundaries
(convergent, divergent and
conservative)
 describe current hypotheses used
to explain how convection currents
and subduction drive plate motion
Lithospheric Plates
Feature
Average Density
Average Thickness
Composition
Continental
2.7g/cm*3
35km
Felsic rocks, sedimentary,
igneous, andesite and granite
Oceanic crust is composed of four major layers:
1) Sediment layer
2) Pillow basalt, basaltic breccius
3) Sheeted dike, gabbro
4) Thin layer of upper mantle material
Oceanic
3.0g/cm*3
7km
Mafic rocks, basalt and gabbro
Igneous rocks and plate boundaries
Location
Divergent boundaries
Convergent
boundaries
Hot spots
Type of movement
Mid – ocean ridge
Magma formation
Mafic magma
Continental rift
Mafic magma
Oceanic - oceanic
Mafic rich magma
Oceanic – continental
Mafic rich magma
Continental collisions
Small amounts of felsic
magma
Mafic magma
Under continental
crust
Under oceanic crust
Mafic magma
Lava produced
Mafic lave erupts to
form pillow basalt.
Forms basalt dykes and
gabbro
Mafic lava erupts and
forms basalt. Felsic
lavas forms to produce
rhyolite
Eruptions are mafic to
intermediate. Early
eruptions are mainly
mafic
Eruptions are mainly
intermediate. Some
mafic magma. Felsic
magma. Plutons
None. plutons
Mafic lava produces
basalt. Felsic lava form
rhyolite
Mafic lava erupts
Plate boundaries
Convergent, Divergent and transform Boundaries
-
Earthquake focus is the point at which rocks break or move above the epicentre
Subduction is where one plate subducts under another
Convergence (Destructive boundary) – Collision of two plate boundaries usually resulting in
subduction. The overriding plate usually becomes folded and volcanic to produce mountain chains
Divergence (Constructive boundary, Extensional boundary – Where two plates separate. The
spreading centre is where new crust is formed. The mid ocean ridge is a divergence of multiple
plates.
Transform (conservative) – Where two plates move past one another, the plate movement is
parallel to the direction of the boundary
Convergent Boundaries
Oceanic – continental convergence
-
-
Summary of features: subduction indicated by trench, intensely folded mountain range,
andesitic volcanism and granite magma intrusions, regional and contact metamorphic
rocks, shallow to deep focus earthquakes, growth of continental crust
Example – mountain ranges of the Andes in South America
Oceanic – Oceanic Convergence
-
Summary of Features – trench, island arc chain, volcanoes, regional and contact
metamorphic rocks
Example – Mariana Trench in the pacific beneath Japan
Continental – Continental convergence
-
-
Summary of features – intensely folded mountains, regional metamorphism, shallow to
medium focus earthquakes, usually no subduction or little, no volcanoes or magma
intrusions, no trenches or contact metamorphism
Example - Himalayas
Divergent Boundaries
-
Summary of features – Youngest rocks at boundary, fissure eruptions typical, boundary
characterised by an elevated rift valley, little or no metamorphism, shallow focus
earthquakes only
-
Example – Mid Ocean ridge, marks he divergence of several plates
Transform Boundaries
-
-
Summary of features: Rarely volcanism, shallow focus earthquakes, opposite and parallel
movement on either side of the boundary, builds elastic potential energy until it releases
in seismic waves
Example – San Andreas fault
Plate motion
-
There are two theories for the movement of plates:
o Convection currents
o Slab pull
o Ridge push
-
The accepted theory of plate movement is convection currents
Convection currents occur in all unevenly heated fluids. When part of a liquid is heated it
rises and cools and moves horizontally before it descends.
-
It is believed that as the currents move horizontally they push the plates with them
It is now being debated that convection currents alone are not powerful enough to move
crustal plates
The slab pull model suggests that as a plates are subducted or diverge they pull the plate in
the direction of the subduction/divergence due to gravity
The slab pull model has not been proven
The Ridge push model suggests that the driving force of plate tectonics are divergent
boundaries
Suggests that as divergent boundaries are elevated above the rest of the ocean floor they
push the lithospheric plates as they diverge
It is likely that all these forces are contributing to tectonic movements
-
2 The movement of plates results in
mountain building
 distinguish between mountain belts formed
at divergent and convergent plate
boundaries in terms of general rock types
and structures, including folding and faulting
gather, process and present information
from secondary sources which compares
formation, general rock type and structure
of mountain belts formed as a result of
thermal uplift and rifting with those
resulting from different types of plate
convergence
Mountain building
Process of formation
Example
Rock types
Thermal uplift
Blue mountains
Rifting
Great dividing range,
rift valley
Hariana trench
Any rock type/depends
on ocean/continent.
No one answer
Basaltic, igneous rocks
Oceanic – oceanic
convergence
Oceanic – continental
convergence
Andes, south America
Continental –
continental
convergence
Himalayas
Regional and contact
metamorphic rocks.
Andesite magmas
Regional and contact
metamorphic rocks.
Granite intrusions
Regional metamorphic
rocks
Structures of
mountains
Folds, faults of all
types
Plateau, escarpments
in the rift valley
Island arcs and chain
Intensely folded
mountain ranges
Intensely folded
mountain ranges
- Compression forces can produce folds and faults
- Rocks which bend or fold produce arches called anticlines and downfolds called synclines
- If the compression forces are large or the rocks brittle, they may snap to produce faults
3 Continents evolve
as plate
boundaries move
and change
 outline the main stages involved in
the growth of the Australian
continent over geological time as a
result of plate tectonic processes
 summarise the plate tectonic supercycle
-
analyse information from a geological or tectonic map of Australia in terms of age
and/or structure of rocks and the pattern of growth of the continent
present information as a sequence of diagrams to describe the plate tectonic supercycle concept
Craton – old geologically stable area. No new rock formation/metamorphism occurring.
Mobile Belts – Areas that are still geologically active, they are unstable
Fold Belt – An area that is greatly folded due to compression forces
Growth of the Australian Continent
-
the formation of Australia was west to east
the western parts of Australia are the oldest land forms on the earth
the east coast of Australia formed from a subduction zone, this subduction zone has
since moved eastward and now lies in New Zealand and Tonga
Timeline
-
Mount narrayer forms (4.4bya)
Yilgarn block begins to forms (3.5bya)
Crust begins to form, rivers, igneous intrusions (3.4 – 3.09bya)
Yilgarn block forms (3.09 – 2.7bya)
Banded iron formations form, emerging crust, large tectonic forces (2.7 – 2.32bya)
Large crustal areas form in the north coast, west coast and south coast (1.93 –
1.55bya)
Formation of the east coast begins through oceanic – continental convergence, east
coast formed by island arcs from subduction zone (500mya)
Plate tectonic super cycle
-
-
Twice in the earths history continents have joined together and formed a super
continent until later it broke apart. This process is cyclic
There may have been more than two times, however, it is unknown
The super continents:
o Rodinia – broke up around 750mya
o Pangaea – Broke up around 280mya
Pangaea separated into Laurasia and Gondwana
Why do the super continents break apart
-
When there is a super continent it insulates the mantle resulting in heat build up and
eventual expansion
The continents begin to rise and eventually cracks appear which begin to rift
(diverge) apart
The upwelling of hot material creates an ocean floor
4 Natural disasters
are often
associated with
tectonic activity
and
environmental
conditions caused
by this activity
may contribute to
the problems
experienced by
people
 identify where earthquakes and
volcanoes are currently likely to
occur based on the plate tectonic
model
 describe methods used for the
prediction of volcanic eruptions
and earthquakes
 describe the general physical,
chemical and biotic characteristics
of a volcanic region and explain
why people would inhabit such
regions of risk
 describe hazards associated with
earthquakes, including ground
motion, tsunamis and collapse of
structures
 describe hazards associated with
volcanoes, including poisonous gas
emissions, ash flows, lahars and
lava flows and examine the impact
of these hazards on the
environment, on people and other
living things
 justify continued research into
reliable prediction of volcanic
activity and earthquakes
 describe and explain the impacts of
shock waves (earthquakes) on
natural and built environments
 distinguish between plate margin
and intra-plate earthquakes with
reference to the origins of specific
earthquakes recorded on the
Australian continent
 gather, process and
present information from
secondary sources to chart
the location of natural
disasters worldwide
associated with tectonic
activity and use available
evidence to assess the
patterns in terms of plate
tectonics
 gather information
from secondary sources to
identify the technology
used to measure crustal
movements at collision
boundaries and describe
how this is used
 gather information
from secondary sources to
present a case study of a
natural disaster associated
with tectonic activity that
includes:
– an analysis of the
tectonic movement or
process involved
– its distance from
the area of disaster
– predictions on the
likely recurrence of the
tectonic movement or
process
– technology
available to assist
prediction of future events
– an investigation of
possible solutions to
minimise the disastrous
effects of future events
Locations of earthquakes and volcanoes
-
-
Volcanoes can occur on convergent boundaries, divergent boundaries and hotspots
Earthquakes may occur on convergent boundaries, divergent boundaries, transform
boundaries. Intraplate earthquakes are earthquakes which occur on continents not
necessarily close to plate boundaries and often occur on faults
Divergent plate boundaries tend to produce low magnitude and shallow earthquakes
Transform plate boundaries tend to create shallow earthquakes
Convergent plate boundaries then to produce the most destructive earthquakes
which can be shallow
Prediction methods of earthquakes and volcanoes
Earthquakes:
-
-
Little ways to plan or predict earthquakes in long term, more in short term
Seismic Gaps – when no earthquake has occurred along a known fault one is more
likely
Animal behaviour – The strange behaviour of animals is present shortly before a
earthquake this was evident in an earthquake in China in 1975
Wells – Changes in the level of water in local wells
Radon gas – an increase or fluctuation in the amount of radon gas released in deep
wells
Electrical conductivity of rocks – in the area around earthquakes
Seismographs – are able to monitor the small earthquakes that occur before a larger
one
Lasers – uses to measure the change In length of lines across a known fault line
Strainmeters – fitted in boreholes to monitor the build up of force in earthquake
prone regions
Creepmeters – used to measure stretch in their length due to gradual movements
along a fault
No prediction method is totally successful and mostly it is difficult to inform and
move millions of people from a potential earthquake hazard if a short term
prediction method is used
Volcanoes:
-
-
Seismic activity – Earthquakes provide early warning of a possible volcanic eruption
Geophysical monitoring – prior to an eruption magma moves closer to the surface
this can be monitored by:
o Infra red photos
o Alterations of magnetic properties
o Gravitational properties of an area
Topographical monitoring – The shape of the volcano may change prior to an
eruption
-
Volcanic gases – The amount of gases released may change in particular the rate at
which sulphur dioxide is produced
Why people live near volcanoes
-
Very fertile soil – new minerals are brought to surface
Born in the area/family
Topographic and orographic rainfall may increase amounts of water in area
9/10 people living in volcanic areas are in developing nations and are often
uneducated/unaware of volcanic dangers
Earthquake hazards
Earthquake
Tsunamis
Nature
A series of waves
caused by
displacement of a large
volume of water
Building collapses
Due to seismic waves
which travel and cause
to ground to shake
Fire
Liquefication
Effect on environment
Can cause devastating
damage on ecosystems
and organisms, marine
life, trees, land
Can destroy human
environment. May
pollute the biophysical
environment through
water and pollutants
Caused by downed
Can cause damage to
powerlines, explosions. human environment,
Can spread rapidly
may damage
through a destroyed
biophysical
city
environment
Saturated soil looses
Building can loose
strength in response to support, can cause
stress. Earthquakes
damage to piping
cause water in to soil
systems
upwards to the surface
Effect on people
Can kill large amounts
of people in coastal
areas. People are
swept away and
buildings may collapse
Potential loss of life,
homes and economic
damage
Potential loss of life,
destroys homes
Economic damage
Causes death to
people especially if
inside a building
Volcano Hazards
Volcanic hazard
Poisonous gases
Nature of the hazard
Magma contains
dissolved gases which
are released into
atmosphere
Pyroclastic flows
fast moving
superheated rock and
gas
Lahars
Mudflow of debris.
Flow composed of
pyroclastic, rocky,
water
Generally do not move
fast, lava flows from
the volcano
Series of waves caused
by displacement of
water
Lava flows
Tsunamis
Effect on environment
Acid rain has a huge
impact on
environment. Fertile
soils. Destruction of
flora/fauna
Destroys trees and
wildlife. Extensive
damage to
environment close to
volcano
Kills all natural things
in its path
Destroys all natural
things in its path
Can destroy the
environment and kill
wildlife
Effect on people
Respiration illness
Pulmonary edima
Death
Dizziness/headaches
Hot gases and high
speeds make
pyroclastic flows lethal
17% of volcanic deaths
If fast can kill all in its
path
Can destroy homes
Least hazardous
people are generally
able to avoid lava flows
Can kill thousands of
people without
warning
Earthquake waves
-
Focus – The place often underground where an earthquake starts
Epicentre – A point on the surface of the earth which is directly above the focus of
an earthquake and where earthquake waves reach first
Primary (P) waves – The first seismic wave that reaches a seismograph from an
earthquake; a compression wave. Minor tremors
Secondary (S) waves – The second waves to arrive at a seismograph from a
earthquake; transverse wave. Minor damage
Long (L) (love) (tertiary) waves – An earthquake wave that travels over the surface
of the earth. Destructive waves
Rayleigh waves – waves which travel vertically through ground shaking it
Intraplate and plate margin
Plate margin – occur on plate boundaries such as convergence. About 95% of all
earthquakes occur on plate margins
Intraplate – Occur on along the edges of crustal plates caused by stresses and strains of the
crustal plates moving across the athenosphere
5 Plate tectonics
and climate
 predict the possible effects of
explosive volcanic activity on
global and local climates
 describe and explain the potential
and observed impacts of volcanic
eruptions on global temperature
and agriculture
 identify data, choose resources, gather and analyse secondary data on recent volcanic
activity to determine the relationship between the eruption of ash and gas from an
explosive volcanic eruption and the subsequent decrease in global temperature
Volcanoes and climate
Short Term:
- Volcanoes dust clouds can obscure the sun
- Sulfuric acid droplets can absorb the suns radiation
- This can cause a solar radiation filter, reducing the amount of sunlight reaching the
earths surface
- This can cause a global drop in temperature. (large volcanic eruptions may decrease
global temperature by up to 1c)
- Short Term impacts do not last a long time
Long Term:
- The large amounts of dust ejected into the atmosphere can produce a global solar
radiation filter, that could potentially in accord with other factors such as changes in
the earths orbit and variation in solar activity produce ice ages
Volcanoes and Agriculture
-
Effects on local agriculture are large, the blocking of sunlight in conjunction with
sulphur dioxide can kill livestock and crops in the local area.
Furthermore, pyroclastic flows and other volcanic hazards can destroy any
immediate agriculture
This is evident in Iceland in 1783 where the volcano Laki killed 75% of livestock in
Iceland and caused a famine killing 25% of the population
More globally however, the results are less severe. There may be a drop in global
temperature which can result in poor harvests