Download Unstable Plates slides

PLATE BOUNDARIES
Grade F: Name
the two types of
crust
Grade E: Name
the four different
types of plate
boundary.
Grade D: Describe
the characteristics
of destructive
plate boundaries
Grade C: Describe the theory that
explains why plates move
Grade A/A*: Compare the characteristics
of constructive and destructive plate
boundaries
MOUNT ST HELENS, (MEDC) CASE-STUDY
Causes:
The Juan de Fuca Plate (Oceanic crust) moves eastwards towards the North American Plate
(Continental crust) and is forced downwards.
Effects:
Minor earthquakes in late March 1980 caused a minor eruption of steam and
ash. Minor eruptions daily, which caused a bulge to appear in northern side of
mountain. Main eruption happened on May 18th 1980, 0830 hours.
North side of mountain had been blown off, and reduced the mountain in
height by 390 metres, creating a crater 3km long and 0.5km deep, ash fell on 11
US states, and circled the globe in 15 days.
Human life – 61 deaths, mostly caused by poisonous gases released;
Settlements – several logging camps destroyed
Rivers and Lakes – ash fell into rivers and raised water temperature; sediment and mud choked the channels; killed all
fish in lakes; Spirit Lake filled in
Communication – floodwaters (caused by melting of ice at top of Mountain) washed away several road and railway
bridges; ash hindered smooth running of engines
Forestry – trees deforested in 250km2 area north of blast zone; trees carried down by river caused a log-jam 60km
away; 10 million trees had to be replanted
Services – electricity supplies and telephone wires cut
Wildlife – nothing survived in blast zone
Farming – 12% of crop was ruined by settling dust; crops and livestock lost due to flooding.
Grade E: Name the plate boundary
Grade D: Describe the effects of the eruption
Grade C: Why are eruptions at destructive plate
boundaries so explosive?
Grade B: Explain the economic effects of
the eruption
Grade A/A*: Why was the eruption of Mt
St Helens so successfully predicted?
MONTSERRAT ERUPTION – LEDC CASE STUDY
Montserrat is a volcanic island found on a destructive plate boundary where two oceanic plates meet.
(The island itself was formed as a result of this destructive plate boundary – it is an island arc).
Effects:
From 1995 to 1997 the volcano erupts five times;
Deadly pyroclastic flows (rivers of hot ash, gas, mud and rock moving at high speeds –
gas layer on top of rocks);
Forests were covered in ash
23 people were killed;
Two-thirds of housing destroyed and three quarters of its infrastructure
(e.g. roads) destroyed.
Population declined to 11,000 in 1995 from 14,333 in 1946
By Nov 1997, population fell to 3,500
74% of island’s population forced to relocate to north of island.
By Nov 1997, 18% of the islanders were remaining were still in shelters
Average age of the population had risen from 28.9 in 1990 to 40 in 1997, with the
largest change in the proportion of people aged under 30.
Grade E: What is a pyroclastic flow?
Grade D: Why are pyroclastic flows only found on destructive plate boundaries?
Grade C: Draw a table to list the main effects of the eruption, using headings ‘people’,
‘environment’ and ‘economy’
Grade B: Why were the living conditions on the island so poor?
Grade A/A*: What evidence is there that, given time, the island will recover from the
disaster?
KOBE DISASTER – MEDC EARTHQUAKE
Japan is located on the Pacific Ring of Fire. The Eurasian Plate (continental crust) is being approached by
the Philippines Plate (Oceanic crust) and Pacific Plate (oceanic crust). As the Pacific and Philippines
Plates are heavier, they are being forced under the Eurasian Plate. Over the centuries, volcanic activity
at this plate boundary has created the Japanese island arc. Kobe, the epicentre of the earthquake is on
a minor fault, the Nojima Fault.
Effects:
The earthquake happened at 5.46am on the morning of January 17th. It measured
7.2 on the Richter scale, and lasted for 20 seconds.
200,000 buildings collapsed, 1km stretch of Hanshin Expressway collapsed, long
sections of bullet train route collapsed, several trains on minor lines derailed.
Essential services disrupted (gas, electricity and water);
Fires caused by broken gas mains broke out over the city – made worse by many
houses made out of wood;
Roads grid locked, emergency services delayed;
230,000 people made homeless and had to live in temporary shelters;
Shortage of blankets, clean water and food;
many aftershocks lasted for several days
Many industries, such as Mitsubushi and Panasonic, were forced to close.
Final death toll at 5,500, injured at 40,000, and 180,000 houses destroyed
Grade F: What type of plate boundary is Japan located on?
Grade E: Describe the primary effects of the earthquake
Grade D: Describe the secondary effects of the earthquake.
Grade C/ B: Why are the effects of earthquakes in MEDCs often mainly economic?
Grade A/A*: How did the government and people respond to the disaster?
Laser surveying and …………………
will identify ………………… across a
…………………
Seismometers will ………………… shock
waves from the e……………… of an
earthquake.
The level of
……………… in
wells rises and
falls as the
ground is
………………
before an
……………………
…………………… and
compression of the
………… can be
recorded
automatically and this
data is also sent to
……………
R…………… gas is released from within minerals as
…………… increases during the build up to an
……………………………………. Also, g………………, magnetic
properties of rocks and …………………… to …………………
current all change as ………………… increase during the
build up to an earthquake.
Grade E: Name one technique for predicting earthquakes
Grade D: Why does the level of water rise before an earthquake?
Grade C: How do computers help in predicting earthquakes?
Grade B: Why can MEDCs successfully predict earthquakes?
Grade A/A*: Why can LEDCs not predict earthquakes?
RESPONSES TO EARTHQUAKES
MEDC responses / precautions:
Emergency drills – preparation, e.g. Kobe, September 1st.
Evacuation procedures – routes planned
Building regulations – improved to a higher standard to withstand a magnitude of earthquake;
Building materials – since the majority of Kobe’s houses were built from wood, most houses now are being designed to withstand
fire;
Further regulations control the design of buildings – Kobe’s authorities have encouraged buildings to be spread out to stop fire
spreading.
Also, Fire Authorities have been practising dealing with fires from earthquakes;
Population of Japan have been trained in first aid.
Shelter and food supplies planned.
Essential services have been properly designed – water pipes not to fracture and gas mains.
Relief grants, low cost loans and tax breaks for victims of earthquake have helped the city back on the road to recovery
Emergency funds set up to rebuild infrastructure.
LEDC responses/precautions:
Authorities around the world encouraged Red Cross and other charities to come
into the country to help provide food and shelter.
Emergency shelters set up.
Financial relief from World Bank.
Charities help keep water clean and free from disease or provide essential
services.
Often there is complete disaster in the area, so authorities are slow to rebuild –
Bam, in Afghanistan/Iran had still not responded eight to ten months after the
earthquake. This is due to lack of money, planning and prediction.
Prediction is rare, because authorities have no money to invest.
Planning is often non-existent, so the effects are often worse.
Building structure and design means that they will often collapse completely and
due to high population in the cities means that the death toll is often worse.
Grade D/E: Describe the
responses of MEDCs.
Grade C: Compare the
responses made by MEDCs
and LEDCs.
Grade B: Why is the recovery
time of LEDCS often longer
than MEDCs?
Grade A/A*: Why are the
effects of tectonic hazards
often worse in LEDCs?