Living with Tectonic Hazards – Risk or opportunity?

Question 1

oceanic-oceanic plate divergence

Answer 1

When two oceanic plates diverge, fractures are formed at the plate boundary.
Sea-floor spreading takes place as magma rises from the mantle, cools and solidifies to form new sea-floor and the mid-oceanic ridge is formed.
Along various points on the ridge, magma builds up and solidifies to form undersea volcanoes.
When these volcanoes grow above sea level, they are known as volcanic islands.

Question 2

o-o plate divergence : example

Answer 2

Example:
North-American plate & Eurasian plate diverge forming the Mid-Atlantic Ridge & Azores found in the Northern Atlantic Ocean

Question 3

continental- continental plate divergence

Answer 3

Two unique landforms found at divergent continental-continental plate boundaries are block mountains and rift valleys.
At such boundaries, tensional forces result in parts of the crust being fractured in a process known as faulting.
Rift valleys form when a central block of land subsides between a pair of parallel faults.
Block mountains form when land masses surrounding a block of land subsides leaving a block of land with steep stones left standing.

Question 4

c-c plate divergence : example

Answer 4

Examples:
block mountain ➢ the Black Forest in Germany
rift valley ➢ East African Rift Valley
⤷ Nubian boundary of African Plate
⤷ Somalian boundary of African Plate

Question 5

oceanic-oceanic plate convergence

Answer 5

When two oceanic plates converge, the denser one subducts under the less dense plate
A subduction zone forms creating a deep depression known as an oceanic trench
The subduction of the oceanic plate causes the solid mantle material to partially melt and magma is formed
The magma rises through the mantle and cracks on the ocean floor to emerge as volcanoes
Eventually a chain of arc of islands called and island arc is formed
Earthquakes may also occur as such boundaries

Question 6

o-o plate convergence : example

Answer 6

Example:
Convergence of Pacific & Philippine plates.
Pacific Plate subducts.
Forms the Mariana Island & Mariana Trench.

Question 7

continental-continental plate convergence

Answer 7

Plates made largely of continental crust may converge with other plates made largely of continental crust.
However, both plates are too thick and buoyant, and have similar densities. Therefore, they resist subduction.
Instead, the plates break, slide along fractures/faults in the crust and fold, forming fold mountains
Earthquakes may occur at such boundaries

Question 8

c-c plate convergence

Answer 8

Example:
Convergence of Indian & Eurasian Plate
Himalayas is formed

Question 9

oceanic-continental plate convergence

Answer 9

When an oceanic plate meets a continental plate, the denser oceanic plate subducts under the less dense continental plate.
A subduction zone forms, creating a deep oceanic trench along the plate boundary.
The subduction of the oceanic plate causes the solid mantle material to partially melt and magma is formed.
The magma rises through the mantle and cracks in the continental crust to emerge as volcanoes in fold mountains
The edge of the thick continental plate folds and buckles to form fold mountains.
Earthquakes may also occur.

Question 10

o-c plate convergence : example

Answer 10

Example:
Formation of the Sunda Trench & Barisan Mountains
Australian plate (oceanic) converge with Eurasian plate (continental)
Trench - Sunda
Fold mountains - Barisan Mountains

Question 11

transforming plate boundary

Answer 11

Plates slide past each other.
There is frictional force.
As they do so, tremendous stress builds up because the boundary isn’t smooth.
This stress is eventually released suddenly, often as a violent earthquake

Question 12

transforming plate boundary : example

Answer 12

Example:
North Anatolian Fault
Anatolian Plate & Eurasian Plate

Question 13

Stratovolcanoes

Answer 13

Not as hot - flows like honey 
High viscosity - high silica content 
Doesn’t spread quickly
Accumulate and grows in height 
Steep slopes - steeper at top, gentler at base 
Traps gas - may develop secondary cones
Explosive eruption

Question 14

Stratovolcanoes : Example

Answer 14

Example:
Mount Pinatubo, Philippines in 1991 emitted 10 million tonnes of lava, 20 million tonnes of sulphur dioxide and a million tonnes of ash

Question 15

Shield Volcanoes

Answer 15

Very hot - flows almost like water
Low viscosity - low silica content
Spreads over large area quickly
Does not grow in height quickly 
gentle sloping sides, broad summit
Does not trap gas
Non-explosive eruption

Question 16

Shield Volcanoes : Example

Answer 16

Example:

Mount Washington in the USA

Question 17

Risks : Massive destruction by volcanic materials

Answer 17

Volcanic materials produced by volcanic eruptions include lava and pyroclasts that consist of rash, rock fragments and volcanic bombs.
A pyroclastic flow can destroy everything in its path with hot rock fragments travelling at speeds greater than 200 m/s. Inhaling the hot ash and gases can also result in serious injury.

Question 18

Risks : Massive destruction by volcanic materials [example]

Answer 18

Example:
The eruption of Nerado del Ruiz in the Andes Mountains of South America in 1985 released a pyroclastic flow. The mixing of pyroclasts and glacial ice triggered lahars which are flows of wet volcanic debris on the side of a volcano. The lahar engulfed the town of Amero and killed more than 20 000 people.

Question 19

Risks : Respiratory Systems

Answer 19

Volcanic eruptions can release thick plumes of ash and gases such as carbon monoxide and sulphur dioxide which may be harmful to people.

Question 20

Risks : Respiratory System - example

Answer 20

Example:
In May 2016, thousands of residents near Mount Sinabung in Northern Sumatra suffered respiratory diseases after inhaling volcanic ash.

Question 21

Risks : Flight disruptions

Answer 21

Volcanic eruptions can produce extensive ash clouds containing tiny particles of abrasive glass, sand and rock that pose a serious danger to aircraft engines.

Question 22

Risks : Flight disruption - example

Answer 22

Example:
In 2010, the eruption of Mount Eyjafjallajokull in Iceland led to a closure of airspace over Europe.
This caused delays to 1.2 million passengers and cost the airline industry US $1.8 billion.

Question 23

Benefits : Fertile Soil

Answer 23

Lava and ash from volcanic eruptions break down to form fertile volcanic soil which are very favourable to agriculture.

Question 24

Benefits : Fertile Soil - example

Answer 24

Example:
The volcanic soils of Java and Bali in Indonesia support the cultivations of crops such as tea, coffee and rice. (Indonesia, Philippines turn to solid because they poor)

Question 25

Benefits : Precious stones and minerals

Answer 25

Volcanic rocks are rich in precious stones and minerals which can be extracted once the upper layers of volcanic rocks are eroded.

Question 26

Benefits : Precious stones and minerals - example

Answer 26

Example:
The old volcanic rocks at Kimberly in South Africa are one of the world’s richest sources of diamonds.
When refined, this precious stone is useful as industrial tools and in scientific research.

Question 27

Benefits : Tourism

Answer 27

Volcanic areas are rich in history and offer beautiful scenery for hiking and camping

Question 28

Benefits : Tourism - example

Answer 28

Example:
The ruins of Pompeii, Italy is a popular dark tourism site visited by 3 million people a year.
This Roman town was buried by ash from Vesurius in 79 CE.

Question 29

Benefits : Geothermal Energy

Answer 29

When groundwater comes into contact with hot rocks beneath the surface, it heats up and erupts as hot water or stream which can be harnessed to drive turbines and produce energy.

Question 30

Benefits : Geothermal Energy - example

Answer 30

Example:
Much of Iceland’s electricity is generated from geothermal power due to the large number of volcanoes in the country.
Over 70% of Iceland’s homes are heated by volcanic steam.