Plate tectonics (KQ2) Flashcards
What are some examples of tectonic landforms?
- fold mountains
- rift valleys and block mountains
- volcanoes
How are fold mountains formed?
- they are formed along convergent boundaries
- compressional force creates immense pressure
- this causes rocks to buckle and fold
- increasing compressional force on one limb may cause it to fracture and ride over the other limb
What are some examples of fold mountains?
- Himalayas
- The Andes
- The Rockies
How are rift valleys formed?
- they are formed at divergent plate boundaries
- tensional forces cause parts of the plate to fracture
- this forms faults
- as the plates are further pulled apart, a central block of land will sink between a pair of parallel faults to form a rift valley
How are block mountains formed?
- they are formed at divergent plate boundaries
- tensional forces cause parts of the plate to fracture
- this forms faults
- as the plates are pulled apart, land masses surrounding a block of land will sink to form a block mountain between a pair of parallel faults
What are some examples of rift valleys?
- East African Rift Valley
Where are volcanoes found?
- covergent + divergent plate boundaries
How are volcanoes formed?
- magma rises from subduction zones which accumulates in magma chamber where pressure builds up
- it then forces its way up onto the earth’s surface through vents (lava)
- lava builds up around the vent, solidifying to form a small crater (volcanic cone)
What happens during an eruption?
- during an eruption, lava, ash and rock fragments are released
- the force of the eruption depends on the amount of pressure and gas in magma
- summit may also be blown off during an explosive eruption
- sides of the crater collapse inwards due to the loss of structural support, creating a large depression
- lava covers the ash layer and builds up the volcano again
- during the formation, the vent may be blocked
- thus, this forces the magma to find a new exit route (secondary cones)
What are the 2 types of volcanoes
- stratovolcano
- shield volcano
What does the type of volcano depend on?
- type of lava
What is the difference between the two types of lava?
- shield volcanoes, which have low-silica lava have less viscous lava
- stratovolcanoes, which have high-silica lava have more viscous lava
What are the characteristics of shield volcanoes?
- low-silica lava
- they have gentle slopes + broad summits
- lava does not trap as much gas, which leads to less explosive eruptions
- successive eruptions increase the size of the volcano as lava accumulates
- common near divergent plate boundaries, such as Mt Washington, USA
What are the characteristics of stratovolcanoes?
- high silica lava
- they have steep slopes + narrow summit
- developed from successive eruptions of lava + ash
- after initial eruption, the subsequent eruptions eject lava which covers the soft ash and prevents it from being eroded away
- over time, a high volcano with a slightly concave profile develops
- secondary cones may also develop from vent seeps at the sides and erupt
Other than lava, what else is ejected during an eruption of a stratovolcano?
- pyroclastic flows
- these are hot rock fragments + superheated gases
- they move down the slope of the volcano at high speeds
- lahars
- they are a mixture of pyroclasts + melted ice
What are earthquakes?
- vibrations in the earth’s crust caused by a sudden release of stored energy
- energy released in the form of seismic waves
- found in rocks along plate boundaries and fault lines
What is an earthquake made up of?
- seismic waves
- focus
- the focus is a point of sudden energy release
- epicenter
- the epicenter is the point on the earth’s surface directly above the focus
- aftershocks
- aftershocks are smaller earthquakes that occur after the initial earthquake as a result of stress within crusts
Where is the location of the focus?
- deep focus: 70-700km below earth’s surface
- shallow focus: <70km below earth’s surface
What impact does focus have on land?
- deep focus:
- smaller impact
- longer traveling time of seismic waves which leads to less energy
- shallow focus:
- large impact
- shorter traveling time of seismic waves leads to more energy
What are the factors that affect the impact of an earthquake?
- magnitude of earthquake
- population density
- level of preparedness
- distance from epicentre
- time of occurrence
- type of soil
How does population density affect the impact of an earthquake?
- densely populated urban areas are more likely to be more heavily impacted by an earthquake compared to less densely populated rural areas
How does level of preparedness affect the impact of an earthquake?
- having evacuation plans, trained rescue workers and action plans can reduce the damage done by earthquakes
how does the distance from the epicentre affect the impact of an earthquake?
- it affects the strength of the earthquake in the area
- this affects the damage done to the area
- the closer an area is to the epicentre, the more likely that it will sustain more damage
How does the magnitude of an earthquake affect the impact of an earthquake?
- it affects the strength of the earthquake
- for example, stronger earthquakes cause more damage than weaker earthquakes
How does time of occurence affect the impact of an earthquake?
- when an earthquake occurs at night, when people are unconscious, they cannot react and carry out the emergency plans as quickly as during the day
How does type of soil affect the impact of an earthquake?
- loose and unconsolidated soil can cause liquefaction of the ground
- this can cause damage especially to buildings
What is a tsunami?
- a tsunami refers to a large sea wave
How are tsunamis formed?
- the movement of the seafloor during a large earthquake at the subduction zones
- an underwater volcanic eruption
- an underwater landslide
- a landslide above sea level that causes materials to plunge into the sea
What are some benefits to living near volcanic areas?
- fertile volcanic soil
- precious resources
- tourism
- geothermal energy
Why is fertile volcanic soil a benefit of living near volcanic areas?
- lava + ash from volcanic eruptions break down to form fertile soil that is favorable for agriculture
What are some examples of fertile volcanic soil?
- volcanic soils of Java and Bali have been able to support large rural populations for decades
Why are precious resources a benefit of living near volcanic areas?
- volcanic rocks can produce precious stones and materials
- diamonds are formed in volcanic pipes due to intense heat and pressure
- can sell this stuff for money
- brings about economic growth
What are some examples of volcanic areas with precious resources?
- diamonds are mined from old volcanic rocks in Kimberly, South Africa
Why is tourism a benefit of living near volcanic areas?
- volcanic areas provide a variety of activities such as hiking, camping sightseeing and some even have historical value
- more tourists = more money
What is an example of tourism in volcanic areas?
- the ruins of Pompeii, Italy which was a city buried in layers of ash by mt Vesuvius, a volcano in 79 CE
Why is geothermal energy a benefit of living near volcanic areas?
- geothermal energy refers to heat derived from the earth’s crust
- groundwater in contact with hot rocks underground heats up and erupts as hot water or steam
- this is then harnessed to drive turbines
- this then produces electricity
- more environmentally friendly source of energy
What is an example of geothermal energy near a volcanic area?
- 70% of Iceland’s domestic heating is produced by geothermal energy
