Tectonics Gateway 2

Question 1

Formation of fold mountains

Answer 1

Fold mountains are formed along convergent plate boundaries. The compressional force causes the layers of rocks to buckle and fold. This process is known as folding. The crust is uplifted to form fold mountains.

Question 2

Distribution of fold mountains

Answer 2

Found along convergent plate boundaries.
E.g.
-The Himalayas in South Asia
-The Alps in Southern Europe
-The Andes along North America
-The Rockies along South America

Question 3

Rift valleys and block mountains

Answer 3

A rift valley is a valley with steep sides formed along fault lines. E.g the East African Rift Valley. A block mountain is a block of land with steep sides and had a steep gradient.

Question 4

Formation of rift valleys and block mountains

Answer 4

Rift valleys and block mountains are formed at divergent plate boundaries. The tensional forces result in part of the crust being fractured. Faulting forms fracture in the rocks along which the rocks are displaced. A rift valley is formed with the central block sinking relative to the surrounding blocks. A rift valley with steep sides is formed along fault lines. The block mountains are the blocks of crust left standing above the valley.

Question 5

Formation of volcanoes

Answer 5

Magma is formed by the melting of mantle and crust at divergent and convergent plate boundaries. The magma rises through faults in the earth’s crust. Magma emerges onto the earth’s surface as lava. The lava solidifies and over successive eruptions, a volcano is formed.

Question 6

Shield volcanoes

Answer 6

-Gently sloping sides and broad summit
-Made of low-silica lava with lower viscosity.
- It allows gases to escape easily and flows more easily through the vent. -Does not erupt explosively but erupts effusively.
-Lava flows over a larger area before solidifying, forms volcanoes with gently sloping slides and a broad summit (has a convex profile).
-Found near divergent plate boundaries
-e.g Mount Washington, USA

Question 7

Stratovolcanoes

Answer 7

-Steeper sides and narrow summit
-Made of high-silica lava with higher viscosity
-Traps gases more easily which results in pressure building up below the earth’s surface.
-Erupts explosively ejecting ash and rock fragments
-Lava flows over a smaller area before solidifying, forming volcanoes with steeper sides and narrow summit (has a concave profile)
-Found at convergent plate boundaries
-E.g. Mount Mayon, Philippines

Question 8

Distribution of volcanoes

Answer 8

Found where plates converge. E.g. West cost of North and South America. Western side of Pacific Ocean, down through the Pacific islands. The Mediterranean

Found where plats diverge as well. E.g. The middle of the Atlantic Ocean. In East Africa (along the Great Rift Valley)

Question 9

Active, Dormant, Extinct volcanoes

Answer 9

Active volcanoes refer to volcanoes that are currently erupting or are expected to erupt in the future

Dormant volcanoes are currently inactive but may erupt in the near future

Extinct volcanoes refers to volcanoes without currently seismic activity

Question 10

Risks of living near volcanic areas: Destruction by volcanic materials

Answer 10

Point: Destruction by volcanic materials

Elaboration: Lava has temperatures between 500 to 1400 degrees Celsius and burns anything in its path. Pyroclastic flows of hot ash, rock fragments and super heated steam flow down the volcano under the force of gravity and can travel up to 80km/h destroying everything in its path. Volcanic bombs are rocks ejected forcefully during an eruption causing damage to property. These can range in size from a few centimeters to the size of cars. Landslides can occur due to the structural collapse of a volcanic cone during an eruption. The landslides can obstruct the flow of rivers which causes floods, block roads, and bury villages and farmlands. This may hamper rescue efforts from reaching affected areas and may destroy the livelihood of many farmers.

Example: The ongoing eruption of Kilauea in Hawaii since 1983 of low-silica lava, which has flowed over long distances and destroyed many houses and roads.

Question 11

Risks of living near volcanic areas: Pollution

Answer 11

Point: Pollution

Elaboration: Ash particles form the eruption may block sunlight, suffocate crops and causes severe respiratory problems for people and animals. The release of gases like sulfur dioxide and carbon monoxide may also be harmful to people. The volcanic ash can block out the sunlight and lower visibility making it a transport hazard.

Example: An eruption of a volcano in Iceland in 2010 produced an extensive cloud of volcanic ash, which posed serious danger to aircraft. This resulted in the closer of air space over much of Europe and caused many flights to be cancelled.

Question 12

Benefits of living near volcanic areas: Fertile volcanic soil

Answer 12

Point: Fertile volcanic soil

Elaboration: Lava and ash from the volcanic eruptions break down to form fertile volcanic soils making it favourable to agriculture. People can grow more crops here than elsewhere and can earn an income selling their excess crops.

Example: The volcanic soils of Java and Bali have made it possible to support the cultivation of crops. This is the reason that these two islands have been able to support large rural populations over many decades.

Question 13

Benefits of living near volcanic areas: Building materials, and precious stones and materials

Answer 13

Point: Building materials, and precious stones and materials

Elaboration: Volcanic rocks can be rich in precious stones and minerals. There resources can only be formed in a volcanic area after millions of years. People living around volcanoes can earn a living mining these minerals and precious stones.

Example: Diamonds are created deep underground and are brought closer to the surface when magma forces its way upwards from the mantle. Old volcanic rocks at Kimberly in South Africa are one of the world’s biggest source of diamonds.

Question 14

Benefits of living near volcanic areas: Tourism

Answer 14

Point: Tourism

Elaboration: Volcanic areas offer a variety of activities for tourists to engage in. People visit volcanoes because of their beautiful scenery. They are also places rich in history. People living around volcanoes can make a living providing services such as accommodation, food, guiding and souvenirs to tourists who visit the area

Example: Pompeii was partially destroyed and buried under 4-6m of ash and pumice in the eruption of Mount Vesuvius in CE 79. It is now a major tourist attraction in Italy.

Question 15

Benefits of living near volcanic areas: Geothermal energy

Answer 15

Point: Geothermal energy

Elaboration: Geothermal energy is derived from the head in the earth’s crust. When ground water comes into contact with hot rocks beneath the surface, it heats up and may change to steam. The hot water or steam can be harnessed to produce electricity.

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

Question 16

Formation of earthquakes

Answer 16

-When plates diverge, converge or move past each other, the movement is not smooth.
-This results in the slow build up of stress on the rocks on either side of the faults.
-When the rocks can no longer withstand the increasing stress they can suddenly break and move many metres.
-This results in the sudden release of stored energy in the rocks found along fault lines causing an earthquake. The energy released travels along the surface of earth causing it to shake violently.

Question 17

Distribution of earthquakes

Answer 17

-Found along convergent, divergent and transform plate boundaries.
-They are found along the Pacific Ring of Fire which stretches up the west coast of North and South America,
-Down the eastern side of Asia, and down through the Pacific islands
-Also found across the Himalayas in Asia, and the Mediterranean region and down through East Africa

Question 18

Factors that affect the amount of damage and the casualty rates: Magnitude

Answer 18

Magnitude:
-The greater the magnitude the greater amount of energy is released by the earthquake.
-This could potentially cause more damage to an area than an earthquake with a lower magnitude by causing more buildings to collapse.

Question 19

Factors that affect the amount of damage and the casualty rates: Population density

Answer 19

Population density:
-The greater the population density the more casualties can be expected.
-This is usually also because more densely populated areas tend to have more high-rise buildings that may collapse and injure or kill people.

Question 20

Factors that affect the amount of damage and the casualty rates: Time of occurrence

Answer 20

Time of occurrence:
-Greater casualties are expected if an earthquake occurs at night when people are at home and may be sleeping as they may be trapped in their homes. During the day, people are more likely to be able to react quicker and moor people are outdoors
-E.g. Sun Moon Lake region in Taiwan (1999) 2400 people were killed when a 7.3 magnitude earthquake occurred at 1:47am

Question 21

Factors that affect the amount of damage and the casualty rates: Level of preparedness

Answer 21

Level of preparedness:
-The more prepared the people and authorities are to handle earthquakes, the lower the casualty rates.
-Preparations include knowing what to do in an earthquake, having evacuation plans, trained rescue workers and other action plans.
-Also includes infrastructure and buildings that can withstand earthquake shocks

Question 22

Factors that affect the amount of damage and the casualty rates: Distance from epicentre

Answer 22

Distance from epicenter:
-Damage from an earthquake usually decreases as the distance from epicenter increases.
-This is because as distance increases, the strength of the earthquake waves decrease, causing less damage to buildings.
-E.g. Christchurch (2011) destroyed many buildings in the city when a 6.3 magnitude earthquake occurred 6.7km from the city centre.

Question 23

Factors that affect the amount of damage and the casualty rates: Type of soil

Answer 23

Type of soil:
-Places built on sediments that are loose and unconsolidated are more likely to suffer more damage.
-This is compounded if the sediment are saturated with water.
-The earthquake causes the ground to become unstable and behave like a liquid, causing many buildings to collapse. This is known as liquefaction.
-E.g. Christchurch (2011) many buildings and houses had to be abandoned due to liquefaction

Question 24

Impact of people living in areas prone to earthquakes: Threat to tsunamis

Answer 24

Point: Threat to tsunamis

Elaboration: Tsunami refers to an unusually large sea wave. Tsunamis may be formed by the movement of the sea floor during a large earthquake at subduction zones. Tsunamis can cause widespread destruction at coastal areas when it sweeps inland.

Example: In 2004, a 9.2 magnitude earthquake triggered a tsunami with waves spreading throughout the Indian Ocean. The tsunami created was 4-40m tall and travelled as far as 10km inland causing damage to coastal communities in 12 countries.

Question 25

Impact of people living in areas prone to earthquakes: Disruption of services

Answer 25

Point: Disruption of services

Elaboration: An earthquake can disrupt services such as the supply of electricity, gas and water as pipes and cables are snapped due to the violent vibrations in the ground. This can leave people without energy for heating or cooking. Earthquakes may rupture gas pipes and this can provide fuel to start fires. The fires can destroy homes and businesses and may cause many deaths.

Example: The earthquake in Kobe, Japan, in 1995 disrupted electricity, gas and water supplies to about a million of Kobe city’s in 1.4 million residents. The earthquake in Kobe, Japan, in 1995 caused extensive fires that raged on for two days. Damaged water pipes meant that firefights could not control the fires and fires spread quickly because of the strong winds created by the heat of the fires.

Question 26

Impact of people living in areas prone to earthquakes: Landslides

Answer 26

Point: Landslides

Elaboration: Landslides are rapid downslope movements of soil, rock and vegetation debris. The shaking of the ground during an earthquake can weaken the slopes of hills and mountainsides resulting in a landslide. Landslides can bury houses or cause buildings to be knocked down, trapping or killing people within.

Example: An earthquake in Peru in 1970 triggered a landslide from a volcano. The landslide travelled more than 160km/h and destroyed a nearby town, killing more than 18,000 people.

Question 27

Impact of people living in areas prone to earthquakes: Destruction of property

Answer 27

Point: Destruction of property

Elaboration: Earthquakes can cause destruction to many homes and cause many people to be without homes after the disaster. They may have to live in temporary shelters for many months while homes are being rebuilt.

Example: The Tohoku earthquake in Japan in 2011 caused a tsunami, which travelled up to 10km inland from the coast. Hundreds pf thousands of people were left homeless and had to live at temporary shelters set up by the government. `

Question 28

Impact of people living in areas prone to earthquakes: Destruction of infrastructure

Answer 28

Point: Destruction of infrastructure

Elaboration: Earthquakes may cause cracks to form in infrastructure such as roads and bridges. Transportation can be disrupted, as it is unsafe to use the damaged roads. This can prevent help from reaching affected areas and slows down the evacuation of people from areas devastated by the earthquake.

Example: After the earthquake in Kobe, Japan in 1995, rescue teams had difficulty reaching many parts of the city due to the damaged roads

Question 29

Impact of people living in areas prone to earthquakes: Loss of lives

Answer 29

Point: Loss of lives

Elaboration: Earthquakes and their associated hazards often threaten the lives of those living in earthquake zones. People may be killed in the initial earthquake due to the collapsing of buildings or succumb to their injuries later if medical help is slow to arrive

Example: The earthquake that hit Haiti in 2010 killed around 300,000 people as the people were not prepared for the earthquake and emergency aid to those affected was slow in coming.