Download Y10GeUA3_2 Tectnic Nov16_7 PP

Introducing Volcanoes
With a bit of revision first
Structure of the Earth
• The Earth is
Mantle
made up of 3
main layers:
 Core
 Mantle
 Crust
Outer core
Inner core
Crust
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Plate Tectonics
• The Earth’s crust is divided into 12 major
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plates which are moved in various directions.
This plate motion causes them to collide,
pull apart, or scrape against each other.
Each type of interaction causes a
characteristic set of Earth structures or
“tectonic” features.
The word, tectonic, refers to the
*deformation of the crust as a consequence
of plate interaction.
* deform = change shape
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World Plates
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Plate Movement
• “Plates” of crust are moved around by the
underlying hot mantle convection cells
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Three types of plate movements
What happens at
the margins of
plates moving in
this way?
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Where do earthquakes form?
Figure showing the tectonic setting of earthquakes
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• Just to remind you – here are
the plates and …
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… and this is where the
earthquakes occur
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Earthquakes
• Earthquakes occur mainly on
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•
•
plate boundaries that are
moving towards, past or away
from each other
Over many years pressure
builds up until eventually the
rocks snap along a weak area
called the FAULT LINE
The point of origin of an
earthquake is the FOCUS – this
is the point where it starts
from
The place at the surface
directly above the focus is
called the EPICENTRE
What sort of
margin is this?
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• The stored energy is released, travelling
outwards in SEISMIC WAVES
• Seismic Waves are strongest at the epicentre
of an earthquake – this is where the most
damage is caused
• Seismic Waves spread out from the focus like
ripples
• *AS SEISMIC WAVES TRAVEL OUTWARDS
THEY LOSE ENERGY*
The closer to
the surface the
focus of the
earthquake is
and the softer
the rocks, the
higher the
magnitude of
the seismic
waves and the
greater the
damage
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The magnitude of an earthquake is
measured on the Richter Scale
• An earthquake’s magnitude (the strength)
is measured using a seismograph.
• Each subsequent level is x10 more
powerful than the previous on was.
• The scale is continuous (has no end)
although nothing above 9.2 has not been
recorded on land.
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Measuring Earthquakes – one way
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But the only problem with Richter is …
• That it tells you about the strength of the earthquake
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at focus/epicentre and so each earthquake only has 1
value.
But obviously, this tells you nothing about what it is
like further away – is there any damage? How great is
the damage?
So there is another measure of earthquakes, which
when you are looking them up you may come across.
It is called the Modified Mercalli Scale - it is often
measured using Roman Numerals I, II, III, IV etc
Go to the animation where you can get an appreciation
of what an earthquake may feel like as variuous points
on the scale
http://newigcsenotes.wikispaces.com/3+Hazardous+env
ironments
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An example
• On September 29 there was an
earthquake under the sea, south of
Samoa and American Samoa had a
Richter scale of 8.0 (or 8.3 depends
who you read).
• But the Mercalli scales for these were
Samoa felt (V) and (IV) at American
Samoa.
• But it was the tsunami that did the
damage. At least 149 people killed in
Samoa, 34 people in American Samoa
and nine people killed and four injured
on Niuatoputapu, Tonga. Widespread
damage to infrastructure at Pago Pago
and Samoa.
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What is an earthquake like?
There are 2 types of waves in an
earthquake
• Body waves and surface waves.
• Body waves travel outward in all directions,
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including downward, from the quake's focus -that is, the particular spot where the fault first
began to rupture.
Surface waves, by contrast, are confined to the
upper few hundred miles of the crust.
They travel parallel to the surface, like ripples
on the surface of a pond out from the focus.
They are also slower than body waves.
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Following an earthquake …
• ..the body waves (P-wave) strike first and are the fastest
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kind People often report a sound like a train just before
they feel a quake, which is the P-wave moving as an
acoustic wave in the air.
Then the secondary, or S-waves, arrive. A person in a
building perceives the arrival of S-waves as a sudden
powerful jolt, as if a giant has pounded his fist down on
the roof.
Finally, the surface waves strike. In very strong
earthquakes, the up-and-down and back-and-forth
motions caused by surface waves can make the ground
appear to roll like the surface of the ocean, and can
literally topple buildings over.
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In Washington State 2001
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In Washington State 2001
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Now for Volcanoes
• Just to remind you – here are the
plates and …
• Where are the places the volcanoes
occur most commonly?
• Why is that?
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Ring of Fire
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The main effects of a volcanic eruption
include:
• Often earthquakes occurring near a volcano can be one
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of the first warnings of things to come
Larva: it can be thick, viscous (sticky) lava or much more
runny.
The thick lava moves relatively slowly and hardens quickly
to form new rock – and so forms a cone shape a cone
shape. Eruptions tend to be violent.
Eruptions that give out the thin, runny lava tend to be
frequent but relatively gentle and come from a shield
volcano
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The main effects of a volcanic eruption
include:
• Pyroclastic flow: some vlocanoes do not
give out lava alone but a mixture of hot
steam, ash, rock and dust.
• A pyroclastic flow can roll down the sides
of a volcano at very high speeds and with
temperatures of over 400° C.
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Direct
measurements of
pyroclastic flows
are extremely
dangerous!!!
• A truck carrying
volcanologists and a film
crew attempting to out
run a pyroclastic flow ….
• the pyroclastic flow was
traveling at about 25-30
meters per second…..
• they made it….
• just!
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The main effects of a volcanic eruption
include:
• Ash clouds may affect more than the immediate area.
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They consist of water vapour, sulphur gas as well as small
rock fragments and tiny pieces of glass.
Many of these will return to earth and add a layer of
dust to a wide area.
However, the gases may be carried a long way by the
wind once they have reached high enough into the
atmosphere. This may be carried all around the world ad
has in the past had a lasting impact on the climate,
lowering the temperature for a year or more. E.g.
Krakatoa in 1883 is the largest volcano eruption in
recorded history for which we have data.
Average global temperatures fell by as much as
1.2 degrees Celsius in the year following the eruption.
Weather patterns continued to be chaotic for years and
temperatures did not return to normal until 1888.
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Finally Lehars
• These can occur at the same time as a volcanic eruption
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but may also occur over succeeding years.
Lahars form when water from intense rainfall, melting
snow and ice, or the sudden failure of a natural dam,
mixes with loose volcanic material, creating mudflows
that can be particularly dangerous and destructive.
Although lahars contain a lot of volcanic ash and rock
fragments–making them dense and viscous like wet
concrete–they actually flow faster than clear-water
streams.
These mudflows can rush down the flanks of a volcano at
speeds as great as 65 kilometres per hour and can travel
more than 80 kilometres. Lahars that contain the most
debris move the fastest and are the most destructive.
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We can measure storms and measure
earthquakes, why not volcanoes?
• Measuring movement of plates and the kind of damage
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done is fairly straight forward. Measure storms is simple
– it is the wind speed that tells the story.
But measuring volcanoes is a whole lot more complicated.
What do you measure? The clouds of dust, the speed of
the lava, how much lahar there is? Different volcanoes
behave in their own special way – it is not possible to
have universal measures that apply to all circumstances.
However, local methods of issuing warning are being
developed – some use a colour code system, some
numbers – most use 1 as low level and 4 or 5 as high levels
of danger – but then again some use a reverse order with
1 being the highest level of alert.
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Alert Level
Criteria
Interpretation
1
Aktif Normal
Monitoring of visual, seismicity and other volcanic
event do not indicate changes.
No eruption in foreseeable
future.
2
Waspada
Increasing activity of seismicity and other volcanic
events, and visual changes around the crater.
Magmatic, tectonic or
hydrothermal disturbance, no
eruption imminent.
3
Siaga
Intensively increasing of seismicity with supported by If trend of increasing unrest
other volcanic monitoring, obvious changes of visual continues, eruption possible
observation and crater. based on observation data
within 2 weeks.
analysis, the activity will be followed by main
eruption.
4
Awas
Following the main eruption, the initial eruption begin Eruption possible within 24
to occur as ash and vapor. Based on observation data hours.
analysis, the activity will be followed by main
eruption.
Green
Volcano is in typical background, noneruptive state or, after a change from a higher level,
volcanic activity has ceased and volcano has returned to noneruptive background state.
Volcano is exhibiting signs of elevated unrest above known background level or, after a
Yellow change from a higher level, volcanic activity has decreased significantly but continues to
be closely monitored for possible renewed increase.
Orange
Red
This is scale
used in
Indonesia
This is scale
used in Alaska
Volcano is exhibiting heightened or escalating unrest with increased potential of eruption,
timeframe uncertain, OR eruption is underway with no or minor volcanic-ash emissions.
Level
Possible Scenario
Eruption is imminent with significant emission of volcanic
ash into the atmosphere likely
OR eruption is underway or suspected with significant emission of volcanic
ash into
The volcano
couldthe
be on a state basis that characterized the period of rest or
atmosphere.
stillness, or record seismic activity, fumarole or other manifestations of activity
IV Active volcano
in that area are predominantly the most immediate or near the center of the issue,
and stable
so it does not represent a risk for the populations and economic activities in its
area of influence.
Variations in the levels of the parameters derived from the monitoring indicating
that the volcano is above the threshold base and that the process is unstable and
III Changes in the may evolve by increasing or decreasing these levels. Phenomena can be
behavior of volcanic registered as swarms of earthquakes, some of them senses; emissions of ash,
activity
lahars; morphological changes, noise, smells of volcanic gases among others,
which can alter the quality of life of the populations in the zone of volcanic
influence.
Significant changes in the development process of volcanic derived from the
II Likely eruption in
analysis of the indicators of the parameters of surveillance, which can evolve in
days or weeks
the event (s) Eruptive (s) of an explosive or effusive.
I Eruption imminent The eruptive phase is explosive or effusive can be composed of several episodes.
or in progress
The time for preparation and response is very short.
This is scale
used in
Columbia in
South America
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Why am I telling you this?
• As you might suppose you might need it in your
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homework.
I want you to find out about as least one recent
earthquake and one recent volcanic eruption – no specific
time limits but there have been a number of quite serious
earthquakes in the last 6 months but few volcanic
eruptions, so I would suggest you might need to go
further back for volcanoes perhaps.
I want to know where it is with a map if possible (and
most sites about disasters do have maps), what happened
and what was the impact of it on the place – short term
and long term. And only if you happen to come across it,
how they coped/are coping – who is helping etc. [DO NOT
SEARCH FOR THIS LAST PART]
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