Physical Geography - Tectonic Processes & Hazards

Question 1

L4 1.3a What scale do scientist use to measure earthquakes and what does it measure?

Answer 1

Moment Magnitude Scale - measures total energy released at the moment it occurs, uses size of the waves, amount of rock movement, area broken by the earthquake, resistance of the affected rocks

Question 2

L4 1.3a How does the Moment Magnitude Scale work?

Answer 2

Logarithmic scale, goes from 1 (smallest) to generally around 10 (largest)

Question 3

L4 1.3a What does the Mercalli scale do?

Answer 3

Takes observations from people who experienced the earthquake and rates them from I (hardly noticed) to XII (catastrophic)

Question 4

L4 1.3a What kind of earthquakes occur at divergent boundaries?

Answer 4

Shallow focus, low mag. (5-6)

Question 5

L4 1.3a What kind of earthquakes occur at convergent (o/c) boundaries?

Answer 5

range of focal depths, high mag. (8-9)

Question 6

L4 1.3a What kind of earthquakes occur at convergent (o/o) boundaries?

Answer 6

range of focal depths, moderate to high mag. (7-9)

Question 7

L4 1.3a What kind of earthquakes occur at convergent (c/c) boundaries?

Answer 7

shallow to moderate focal depths, moderate mag. (6-8)

Question 8

L4 1.3a What kind of earthquakes occur at conservative boundaries?

Answer 8

shallow focus, moderate mag. (6-8)

Question 9

L4 1.3a What is the Wadati-Benioff zone?

Answer 9

Where most pressure is built up and then released during an earthquake. Understanding its depth can help to understand how destructive an earthquake will be

Question 10

L4 1.3a Describe primary waves

Answer 10

Arrives first, travels through crust, mantle, and core, longitudinal wave

Question 11

L4 1.3a Describe secondary waves

Answer 11

Slower than p-waves, travels through crust and mantle, transverse wave

Question 12

L4 1.3a Describe Rayleigh waves

Answer 12

Surface waves, rolling motion (up/down & side/side), responsible for most shaking

Question 13

L4 1.3a Describe Love waves

Answer 13

Surface waves, fastest surface wave, moves side/side as it travels (zig zag pattern)

Question 14

L5 1.3a Describe what liquefaction is and what damage it causes

Answer 14

Loosely packed, water-logged sediments near the ground’s surface which lose their strength due to strong ground shaking, it can cause flash flooding and the uprooting of infrastructure like pipes and manholes

Question 15

L5 1.3a Explain how earthquakes can lead to mass movement and what damage it causes

Answer 15

Seismic waves shake the ground and cause slopes to destabilise and slip, can bury roads, towns, and infrastructure which makes rescuing those in affected areas difficult

Question 16

L5 1.3a Summarise the Christchurch Earthquake Feb. 2011

Answer 16

6.3 mag. shallow focus earthquake, liquefaction was exaggerated because shockwaves of contrasting resonances occurred in the soft horizontal layers underground, 30m thick soft upper layer smacked into the solid layer beneath sending vibrations back to the surface

Question 17

L5 1.3a What engineering was put in place in Christchurch after the 2011 earthquake to protect against the impacts of future events?

Answer 17

Cone Perimeter Testing (CPT) was carried out to assess the susceptibility of soil to liquefaction in different areas of Christchurch (quick and inexpensive but in some places boreholes were dug to explore deeper), new buildings built with stone columns (10m in ground), geogrid of plastic matting, and compacted gravel above to redistribute the weight of the building

Question 18

L5 1.3c What is a tsunami and how is it caused?

Answer 18

A series of larger-than-normal waves which are usually caused by volcanic eruptions or underwater earthquakes

Question 19

L5 1.3c Summarise the causes and impacts of the 2004 Boxing Day Tsunami

Answer 19

Caused by an earthquake off the coast of Sumatra, Indonesia that was 9.0-9.3 mag., thrust moved ocean floor 15m towards Indonesia

Coastal settlements were devastated (70% of residents killed in some villages, 1500 villages destroyed in Sumatra), much infrastructure was destroyed (Andaman & Nicobar cut off as jetties destroyed), economies devastated (60% of fishing fleet & industrial infrastructure destroyed in Sri Lanka, tourism industry lost £25m in Thailand - 120k jobs lost), ecosystems destroyed, vegetation & topsoil destroyed, freshwater supplies contaminated with seawater, $10bn total cost

Question 20

L6 1.2c, 1.3a,b+c Where are volcanoes usually located? Give an example for each location

Answer 20

Along plate boundaries (e.g. Pacific Ring of Fire), at mid-ocean ridges (e.g. mid-Atlantic ridge), and at hotspots which can be in the centre of plates (e.g. Hawaii)

Question 21

L6 1.2c, 1.3a,b+c How do plate boundaries influence what type of eruption occurs?

Answer 21

At divergent plate boundaries lava is usually basaltic so eruptions are less viscous and effusive (shield volcanoes). At convergent plate boundaries lava is usually andesitic or rhyolitic. This means the gas content is higher so the eruptions are more explosive (composite cone volcanoes)

Question 22

L6 1.2c, 1.3a,b+c Summarise the features of a composite volcano. What is its alternative name? What types of lava does it contain?

Answer 22

Steep sides, high silica content - viscous lava, explosive, layers of solidified lava, found on destructive plate boundaries

Contains andesitic and rhyolitic lava

Also known as a strato volcano

Question 23

L6 1.2c, 1.3a,b+c Summarise the features of a shield volcano. What type of lava does it contain?

Answer 23

Gently sloping sides, low silica content - less viscous lava, effusive, found on constructive plate boundaries and hot spots

Contains basaltic lava

Question 24

L6 1.2c, 1.3a,b+c Describe the features of basaltic lava

Answer 24

• Hottest type (1000-1200°C)
• Low silica (50%)
• Low gas content (0.5-2%)
• Low viscosity
• Effusive
• Darker colour
• Found at shield volcanoes

Question 25

L6 1.2c, 1.3a,b+c Describe the features of andesitic lava

Answer 25

• 800-1000°C
• Intermediate silica (60%)
• Intermediate gas content (3-4%)
• Intermediate viscosity
• Moderately explosive
• Lighter colour
• Found at composite volcanoes
• Formed by the subducted oceanic plate melting

Question 26

L6 1.2c, 1.3a,b+c Describe the features of rhyolitic lava

Answer 26

• Coolest (650-800°C)
• High silica (70%)
• High gas content (4-6%)
• High viscosity
• Very violent, cataclysmic
• Lighter volcano
• Found at composite volcanoes (& supervolcanoes)
• Formed by the subducted plate melting

Question 27

L6 1.2c, 1.3a,b+c How do we measure the strength of volcanic eruptions? What is the scale based on? Describe what happens at levels 0, 2, 4, 6, 7, & 8

Answer 27

Volcanic Explosivity Index (VEI) - Logarithmic scale, it is based on the volume of erupted material, the height of the eruption, and the duration of the eruption

0 - gentle flow
2 - bi-weekly
4 - 1-2 yrs
6 - 50-100 yrs, largest in living memory -> global change in temperature (Pinatubo eruption, 1991 -0.5°C global temps)
7 - 500-1000 yrs (Mt. Tambora eruption, 1815, 0.5°C cooling, 90,000 deaths due to famine)
8 - every 50,000 yrs, super eruption, extinction level event

Question 28

L6 1.2c, 1.3a,b+c What is a phreatomagmatic eruption?

Answer 28

When a volcano erupts through water/ice, this can cause large amounts of ash to be emitted