Geography notes weather

The Earth’s structure

The crust is the surface of the earth; it is a rock layer forming the upper part of the lithosphere. The lithosphere is split into tectonic plates. The plates move slowly on a layer called the asthenosphere.
Meteorites can tell us what the earth is like-these are rock and metal fragments which fall to earth from space. We know the earth’s core is hot through hot spring geezers and volcano lava.
2 types of crust
OCEANIC CRUST: it is found under the oceans; it’s thin and has a low density as it is made from an igneous rock called basalt. It is 6-8 km thick.
CONTINENTAL CRUST: this forms the land, made from granite which is low density igneous rock. It is on average 30-50km
Earths heat engine
Geothermal is heat from inside the earth the heat is produced by radioactive decay.

Convection current is in the mantle and are cause by the heat of the core. This heat is created due to both the pressure of the overlying material but also produced by the radioactive decay of uranium etc in the core and mantle. As heat rises from the core it creates convection currents in the liquid outer core and mantle. These convection currents move the tectonic plates on top of them.

Pumas
The Parts were convectional current moves towards the surface are called plumes. Plumes bring magma to the earth surface. If magma breaks through the crust it erupts as lava in a volcano.
Pangaea
The continents were once all joined together which formed a super continent called Pangaea. We know this as identical fossils and rocks have been found in western Africa and Eastern South America. Today the lithosphere is split into 15 tectonic plates. Where 2 plates meet together = plate boundary
Different plate Boundaries
Constructive plate boundary
• Where two oceanic plates are moving apart from each other.
• New oceanic crust is forming constantly in the gap created.
• The magma is injected between the two plates. As it cools it forms new oceanic crust.
• The magma is runny. Shallow sided volcanoes form
Convection currents from the mantle bring magma towards the surface. Magma is forced between the plates, cools and forms new oceanic crust.
HAZARDS:
Small earthquakes are formed by friction as the plates tear apart. Volcanoes that are not very explosive/dangerous. Examples are Iceland – the Mid Atlantic Ridge

Destructive plate boundary
• Where an oceanic plate meets a continental plate.
They are moving towards each other.
• The denser oceanic plate is subducted beneath the less dense continental plate.

Subduction describes oceanic crust sinking into the mantle at a destructive plate boundary. As the crust subducts it melts back into the mantle.

HAZARDS: very destructive earthquakes tsunami Very explosive, destructive volcanoes which cool to be steep sided.
Examples are Andes Mountains, Peru, Chile

Conservative boundary
Formed where two plates are sliding past each other. HAZARDS: destructive earthquakes small earth tremors daily. no volcanoes
Example is San Andreas Fault, California

Collision Zone
A type of destructive boundary where two continental plates move towards each other. As they meet they push upwards forming mountain ranges e.g. Himalayas. HAZARDS: destructive earthquakes landslides
Volcanoes are rare

Volcanoes in developed world
Sakurajima, Japan
Plate: Destructive (pacific is subducted beneaththe Eurasion)
Volcano: Stratovolcan- they are extrmly dangerous and explosive. They erupt andesite lava
Risks:
Good products that may be destoryed
7200 people live in the area of volcano
650000 people live in Kagoshima
Sheltered bay mkes good port for fishing
Area is a national park so attract many tourists
Volcanic bombs 3km from crater,procyclastic flows 2km long
Very fertile
Sakurajima is an island connected toTarumizu it wasconnectedby larva flow

Predicting volcanoes
Aircraft used to measure the amount of gas the volcano gives off Tiltmeters detect when the volcano swells up as it fills with magma
Seismometers monitor earth tremors which will increase as magma rises Boreholes to measure water temperature as magma heats up

Protection from volcanoes
Concrete shelters prtect against volcanoes and ash
Evacuation routes clearly marked
Concrete lahar channels divert flows
Regular evacuation drills

Volcanic Explosivity Index (VEI): Measures the destructive power of a volcano on a scale from 1 to 8.
Volcanoes are measured uses a seismograph, or seismometer, which is an instrument used to detect and record earthquakes.
Volcanoes can produce lava flows but they do not kill people as can be out run.

Developing world Volcano Hazards
Risk
Live in risky areas because they have no where else to live
Cant afford safe well built homes
Don’t have insurance
Governments don’t have aid and money
Communications are bad so bad warning and evacution
Mount Nyirago, Democratic republic of Congo in Africa
Plate: Constructive- where the continent of Africa is being pulled away
Date: January 2002
Hot balsalt lava poured out of Mount Nyirgo. Lava 1000m wide flowed 20km into city. 14 villages were detroyed.
Result:
100 pople died form poisonous gas
Lava trigged earthqauke
12500 homes destoryed
400,000 people were evacutcated
People became refugee diseases spread quickly
Releif effort:
United nations sent 260 tonnes of food
TV appeals
$35million to help refugees
Emergancy vaccination

Volcano Hazards
Ash and gas
Prevailing wind
Eruption cloud
Acid rain
Ash fall builds up on roofs causing buildings to collaps
Lava bobmbs can kill
Pyroclastic flow-deadly clouds of hot ash and gas
Lava flow
Lahar (volcanic mudslide) occurs when rain or snow mixes with volcanic ash

Earth quakes
They cant be predicted. Undergroud plates push together building pressure, the pressur is sudenly released along faults (cracks in the crust) sending huge pulse of energy.
Earthquakesstart at the focus. The epi centreis the point on the Earths surfar sbove the focus and is first place to shake.
Earthquake waves travel in any direction.
Magnitude is a measur eof how much the ground shakes.

Niigata, Japan
When: July 2007
Strength: 6.8

Kobe,Japan
When:1995
Strengtht6.8
The city around it had affected90,000 pople, 11 died, 1000 were injured
City of 1 milion
Farms,villages affected
5000 died 26000 were injured
350 buildings destroyed
Damage $2billion
Tsuanmi warning but false alarm
Epicentre clos to Kobe
Epicentre off shore
Soft ground made shaking worse
Happended at 6pm
Happended 6am
People were awake and remembered what to do
People were asleep and confused
Planning:
Earthquake drills
Emergancy service practicing
Emergancy kits containg- torch,radio food and water
Buildings:
Damper on roof prevents builing form swaying
Cross bracing stops floors collapsing
Shock abosrbers
Strong steel frame stops cracking
Double glazed windows stops glass shattering
Very deep foundations to prevent collaps
Developing world
Sichuan, China
Magnitude: 8.0
Date: 12 May 2008
Primary effects:
70,000 people died
400,000 people injured
5 million made homless
$75 million of damage
There were upto 200 aftershocks on 27 May a magnitude of 6.0 caused 42,000 buildings to collaps
Primary effects: caused instantly by earthqaueks
Secondary effects: in hours/days afterwards (fires break out, diesease spread)
Aftershock: often occurs as fault settles inot new positionn (can kill or injure resucuers destorys buildings that wereweakend by the earthquake)
Local and international responses usually help when a natural disaster occurs.
Buildings in developing world to stop so much damage:
Cross bamboo wood frame
Lightweight thatch roof
Walls made from mud and straw packed between wooden slats
Simple steel rod foundations
Concrete ring ties the walls to the foundations