How do tectonic processes result in earthquakes?
- Due to the sudden release of energy
- Earthquakes occur along plate boundaries which contain fractures
When does earthquake occur?
- Rock masses on either side of a fault are pushed by tectonic forces
- Friction causes them to get locked and stress build up
- When the stress exceeds the strength of the fault, the rocks snap or suddenly move to a new position
- This sudden movement causes seismic waves to be released resulting in ground shaking
Parts of an Earthquake
- The focus is the point in the earth’s crust where seismic waves are released
- The epicentre is the point on the Earth’s surface directly above the focus
Deeper focus VS shallower focus
Deeper focus have seismic waves that travel longer and lesser shaking felt on Earth’s surface because more energy is being lost
How to measure earthquakes?
- Richter Scale: calculates the earthquake magnitude using the height of the largest wave recorded on seismometers
- Moment Magnitude Scale: based on the total energy released during the earthquake
How do tectonic processes result in volcanic eruptions?
A volcano is only formed when lava erupts onto the Earth Surface, it may form a cone-shaped mountain as more lava erupts and accumulates over time
Describe the process where volcanic eruptions occur at divergent plate boundaries
1: Plate move apart where the crust stretches and fractures developed.
2: The decrease in overlying pressure causes parts of the underlying mantle to melt, forming magma.
3: Magma contains dissolved gases and is less dense than the surrounding materials
4: Therefore, magma rises through weak areas in the crust to erupt as lava causing a volcanic eruption
5: Lava cools, solidifies, and accumulates over time, forming a volcano
Describe the process where volcanic eruptions occur at Convergent plate boundaries
- Plates move towards each other and the denser plate subducts under the less dense plate
- As the subducting plate sinks into the mantle, the high-pressure forces water out its oceanic crust.
- Water lowers the melting point of the overlying mantle, causing it to melt, forming magma
- Therefore, magma rises through weak areas in the crust to the Earth’s surface to erupt as lava causing a volcanic eruption
- Lava cools and solidifies and accumulates over time forming a volcano
Differences in volcano
- High silica magma is more explosive, more viscous magma, gas cannot escape easily, more pressure builds up resulting in violent, explosive eruptions. [Stratovolcanoes]
- Low silica magma is less viscous, that’s why gas can escape easily, less pressure builds up. Resulting in gentle, effusive eruptions [shield volcano]
How are volcanic eruptions measured?
- The Volcanic Explosivity Index measured based on:
- The ejected material
- The height of the eruption cloud
- The duration of the eruption
How are earthquakes and volcanoes distributed?
- Earthquakes occur at plate boundaries
- The largest concentration of earthquakes and volcanoes is at the Pacific Ring of Fire
The 4 Hazards associated with earthquake
- Ground shaking
- Soil liquefaction
- Landslides
- Tsunamis
How does ground shaking affect us
- Ruptures oil and chemical factories will pollute land and water
- Weakens buildings, bridges, roads, and railways causing them to collapse (making it difficult to rescue people)
- Electricity and communication cables break affecting important communication services
- People may get trapped under collapsed buildings and infrastructure
How does soil liquefaction affect us
- Liquefied soil may enter rivers and smother aquatic plants, causing them to die
- Buildings and infrastructure can sink in and tip over
- Electricity and communication cables can sink in and snap, disrupting supply off these services
- People can get trapped under collapsed buildings
How do landslides affect us
- Fast moving debris can bury huge areas of forest and wetlands
- Debris can bury villages destroying properties
- Roads and Railways can be blocked by debris, making it difficult to rescue people
- Debris can block rivers resulting in floods
How does Tsunami occur?
- An undersea earthquake causes the seabed to be displaced
- A large volume of water is lifted, forming waves of great wavelength and low height of less than 1 metre
- The wave travel towards land at high speeds around 800 km/h
- On approaching the coast, greater friction with the shallower seabed slows the waves down
- The waves get closer together and increase in height
- Before a tsunami occurs, the sea may recede from the shore
How do tsunamis affect us?
- The seawater can flood huge areas of coastal wetlands and forests
- Fast moving waters and the large amounts of debris can sweep away buildings
- Fast moving waters can snap electricity and communication cables, disrupting services
- Sweeping water can drown people.
How does tephra affect us?
- Ash can be carried thousands of kilometres, polluting huge areas of forests rivers and other habitats
- When saturated with water, the weight of ash can double, causing building roofs to collapse
- Ash particles can damage plane engines, leading to closure of airspaces
- Volcanic bombs can hit people
How does volcanic gases affect us
- Sulfur dioxide results in acid rain when it reacts with water in the air which can damage in vegetation
- Sulfur dioxide results in acid which can corrode buildings and infrastructure
- Sulfur dioxide irritates skin, eyes, nose and throat
How does lava flows affect us
- Hot, low-silica lava can travel over some distances, destroying forests
- Lava can burn through homes
- Lava can destroy electricity and communication cables
How does pyroclastic flows affect us
- Thick layers of ash cover the path of the flows, polluting huge areas of forests
- The hot flows can burn through all homes
- The hot flows can destroy electricity and communication cables
- The extreme temperature can burn and kill people
How does lahars affect us
- Lahars can cover forests with thick mud which hardens like concrete
- Lahars can bury houses and buildings, destroying them
- Roads and Railways can be blocked by debris making it difficult to rescue people
- Lahars can bury houses and trapped people
How does volcanic landslides affect us
- Debris from landslides pollutes rivers, killing aquatic life
- Debris buries villages
- Debris can snap electricity and communication cables
- Debris block river resulting in floods which can drown people
What are the benefits of volcanic eruptions
- Volcanic rocks break down to form fertile soils to allow locals to grow a variety of crops or earning more from higher crop yields
- When some magma solidifies, the locals may be able to extra precious minerals like silver or gold, allowing the government to generate revenue
- Geothermal energy can be derived from the heat in the Earth’s crust, locals can benefit from cheaper electricity
- The different volcanic features can attract tourists to visit the country, from here the locals can have more job opportunity boost local economic development
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GIEL Topic 1.1 (Relationship between people and nature)10
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GIEL Topic 1.2 (sense of place)3
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GIEL Topic 1.3 (Relationship between locations and neighbourhood)2
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GIEL Topic 1.4 (Organisation of neighbourhoods in SG)5
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Geography In Everyday Life topic 223
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Geography In Everday Life topic 318
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Tectonic Topic 116
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Tectonic Topic 224
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Tectonic Topic 334
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Tourism Topic 130
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Tourism Topic 213
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Tourism Topic 326
