Hazards

Question 1

What is the theory of plate tectonics?

Answer 1

Alfred Wegener- 1912
Believed all the continents were once joined together- Pangea
Until about 200 million years ago Pangea was still intact
Idea that continents are slowly drifting apart- Continental drift

Question 2

What is a hazard?

Answer 2

A threat that has the potential to cause loss of life, injury, property damage, socio-economic disruption or environmental degradation

Question 3

Continental fit

Answer 3

South America and Africa can fit together like a jigsaw
African and Arabian plates can be fitted together if Red Sea is closed
Red Sea is young- 30 million years old

Question 4

Geological sequences

Answer 4

Same kinds of rocks in Africa and South America

Question 5

Climatic evidence

Answer 5

Glacial evidence
If continental drift had not occurred then the ice sheet would have extended from the South Pole to the equator

Question 6

Biological evidence

Answer 6

Land based fossils- can’t swim to different continents
Same fossils found in different continents
Mesosaurus, lystrosaurus, Glossopteris (same plant found in all continents)

Question 7

Paleomagnetism

Answer 7

Discovery of the ridge of mountains along the middle of the Atlantic Ocean- Mid Atlantic ridge
British geologists, Vine and Matthews, discovered magnetic stripes
Stripes correspond to times when the Earth’s magnetic field reversed from North to South
Discovered Earth’s polarity was not constant

Question 8

What are plates?

Answer 8

Sections of the Earth’s crust and lithosphere

Question 9

What is the crust?

Answer 9

Top layer
2 types- Oceanic and Continental

Question 10

Oceanic crust

Answer 10

High density (3.0g/cm3)
New
Darker in colour
Can be destroyed
Basalt
5-10km thick

Question 11

Continental crust

Answer 11

Lower desnity 2.7g/cm3
Old
Lighter in colour
Can’t be destroyed
Granite
25-100km thick

Question 12

The mantle

Answer 12

Zone of molten siicates and other minerals
Molten so it moves- convection currents
2,900km thick

Question 13

Asthenosphere

Answer 13

Upper part of the mantle approx 80km deep
rocks in semi molten state

Question 14

What is the core made of?

Answer 14

Iron and nickel

Question 15

Inner core

Answer 15

Solid due to high pressures
3700 degrees

Question 16

How do plates move?

Answer 16

Convection currents
Require a source of heat
Earth’s core heats up rocks in the lower mantle
Rocks in lower mantle melt and expand
Pockets of heated, molten rocks are less dense than the surrounding rock so rise away from the core
As molten rises, reaches crust, spreads sideways
Thick, molten rocks stick to the tectonic plates and drags it along
As it gets further way from the core it cools and sinks back down

Question 17

How does divergent move?

Answer 17

Plates moving in opposite directions
Convection currents move

Question 18

What types of hazards are found on divergent plate boundaries?

Answer 18

Earthquakes and volcanoes

Question 19

How is a mid ocean ridge formed? (divergent)

Answer 19

As plates move apart it leaves lines of weaknesses that allows magma to escape
Magma fills the gap and eventually erupts onto the surface and cools as new land
Creates huge ridges of undersea mountains and volcanoes

Question 20

How is a rift valley formed? (divergent)

Answer 20

As magma rises the overlying rocks can be forced upwards into a dome
Rigid lithosphere put under pressure and can fracture along parallel faults
Produce underwater rifts
Forms when plates move apart in continental areas

Question 21

What is pillow lava? (divergent)

Answer 21

Cooled magma

Question 22

What are black smokers? (divergent)

Answer 22

Superheated jets of water containing metal sulphides

Question 23

What is a graben? (divergent)

Answer 23

A sunken valley

Question 24

How does convergent move?

Answer 24

Plates move towards eachother

Question 25

Oceanic-continental plate margins (convergent)

Answer 25

Oceanic plate is denser and continental is less dense Pushed together by convection currents Oceanic plate pushed down- more dense Creates a deep ocean trench- depths of 6000-11000m As it descends friction melts the plate, increases pressure and heat from asthenosphere Molten material works its way up- collects in magma chambers Magma can re emerge to create volcanic mountains Can cause Earthquakes

Question 26

Oceanic-oceanic plate margins (convergent)

Answer 26

Both oceanic More denser one will sink Descending plate melts, magma rises to the surface and forms chains of volcanic islands known as Island Arcs Japan

Question 27

Conservative movement

Answer 27

2 plates either slide past eachother in opposite directions or 2 plates slide past eachother at different speeds

Question 28

How are Earthquakes created?

Answer 28

Conservative plate movement Friction, grind on one another When stress energy is released it sends shock waves through the Earth's crust San Andreas faults in California

Question 30

What is an effusive eruption?

Answer 30

A volcanic eruption that releases low viscosity lava steadily onto the surface.

Question 31

What is an explosive eruption?

Answer 31

A violent volcanic eruption driven by trapped gas and high viscosity lava

Question 32

What is the typical lava type in an effusive eruption?

Answer 32

Basaltic lava

Question 33

What is the typical lava type in an explosive eruption?

Answer 33

Andesitic or rhyolitic lava

Question 34

Where are explosive eruptions located?

Answer 34

Convergent plate boundaries

Question 35

What are hot spots?

Answer 35

Eruptions that don't take place at plate boundaries

Question 36

What causes hot spots?

Answer 36

Plumes of hot mantle that rise deep within the Earth. Plume reaches the base of the lithosphere, it partially melts, producing magma that can break through the crust and form volcanoes

Question 37

What is an example of a hot spot?

Answer 37

Hawaiian chain of islands Pacific plate moved NW over the Hawaiian hotspot. Vast amounts of basalt have accumulated on the ocean floor to produce Hawaiian islands

Question 38

Shield volcanoes

Answer 38

Shape: Broad, gently sloping sides Lava type: Basaltic (low viscosity) Eruption style: Effusive, frequent, less violent Formation: Repeated outpourings of runny lava Example: Mauna Loa, Hawaii Formed at hotspots and divergent plate boundaries

Question 39

Stratovolcanoes

Answer 39

Shape: Steep-sided, classic cone shape Lava type: Andesitic or rhyolitic (high viscosity) Eruption style: Explosive, infrequent, highly hazardous Formation: Alternating layers of ash, tephra, and viscous lava Example: Mount St Helens, Mount Fuji Formed at convergent plate boundaries

Question 40

How is a supervolcano formed?

Answer 40

Mantle heat causes partial melting of continental crust. Silicic magma accumulates in a huge chamber. Pressure builds over thousands of years. When the chamber ruptures, the eruption is catastrophic, emptying the chamber. The ground collapses → caldera.

Question 41

What is a type of supervolcano?

Answer 41

Yellowstone- 3 huge eruptions have happened in the last 3 millions years

Question 42

How is volcanic activity assessed?

Answer 42

Volcanic Explosivity Index (VEI) Combines magnitude and intensity into a single number on a scale of 0 to 8 Each increase represents a ten fold increase in explosivity

Question 43

Limitations of VEI

Answer 43

No differentiation between different types of material ejected Does not take into account the power output of an eruption

Question 44

Why do people live near volcanoes?

Answer 44

500 million live at risk from volcanic hazards Fertile soils- Mt Vesuvias 1 in 5 Sicilians live on slopes of Mt Etna Geothermal activity- heats up 70% of homes in Iceland Minerals- lava can crystallise to form gold, silver, copper, sulphur Tourism- Hawaii, Yellowstone national park, Japan, Iceland Volcanologist Take the risk

Question 45

Lava Flows