2.1 Earthquakes and volcanoes Flashcards
What is a ‘volcano’?
An opening in the Earth’s crust through which hot molten magma (lava), molten rock and ash are erupted onto the land.
Where are most volcanoes usually found?
Plate boundaries although there are some exceptions, or a hotspot.
What is a ‘hotspot’?
A relatively small area where magma rises through a continental or oceanic plate.
What is ‘magma’?
Molten materials inside the Earth’s interior.
What is ‘lava’?
When the molten material is ejected at the Earth’s surface through a volcano or a crack at the surface.
What is ‘chamber’?
The reservoir of magma located deep inside the volcano.
What is ‘crater’?
The depression at the top of a volcano following a volcanic eruption.
What is ‘vent’?
The channel which allows magma within the volcano to reach the surface in a volcanic eruption.
What is a ‘tectonic plate’?
The theory that the Earth’s outer shell is divided into several plates that glide over the mantle.
What are the two main types of volcanoes?
- Strato-volcanoes (composite cone)
- Shield volcano
What is an ‘epicentre’?
The point on the Earth’s surface vertically above the focus of an earthquake
What is a ‘focus’?
The position within the Earth where an earthquake occurs.
What is the “Ring of Fire”?
A ring of volcanoes around the Pacific Ocean that result from subduction of oceanic plates beneath lighter continental plates.
Name the features of ‘strato-volcanoes’ + one example.
- Narrow and steep
- Explosive
- Destructive
- Silica lava
- Only have one or a few vents to release lava
- When the lava cools, these layers of lava become the sides
e. g. Mount St Helens
Name the features of ‘shield volcanoes’ + one example.
- Wide and gentle slopes
- Non-violent
- Constructive
- Basaltic
- Occur at hot spots under the Earth’s surface
- Erupt frequently, with lava spilling out from many vents
e. g. Mauna Loa
Name the three types of movements of plate boundaries.
- Convergent
- Divergent
- Transform
Convergent + example
when two plates are pushing toward each other
e.g. the boundary between the Eurasian plate and the Indian plate at the Himalayas
Divergent + example
marks two plates that are moving apart from each other
e.g. the boundary between the African plate and the Arabian plate in the Red Sea
Transform + example
occurs where the two plates slide past each other
e.g. the boundary between the Pacific Plate and the Australian plate, crossing New Zealand
What are the four types of plate boundaries?
- constructive plate boundary
- destructive plate boundary
- conservative plate boundary
- collision plate boundary
Constructive plate boundary + example
- the two plates move apart from each other causing sea-floor spreading.
- this causes new oceanic crust to form, creating mid-ocean ridges.
- volcanic activity is common.
- new land is created.
e. g. North American plate and Pacific plate
Destructive plate boundary + example
- the oceanic crust moves towards the continental crust and sinks beneath it due to its greater density
- this causes deep-sea trenches and island arcs to form
- the continental crust is folded into fold mountains; volcanic activity is common
e. g. Nazca plate and South American plate
Conservative plate boundary + example
- the two plates move pass each other in opposite directions, or same direction at different speed
- no new land is created
- no land is destroyed
e. g. Pacific plate and North American plate
Collision plate boundary + example
- the continental crusts collide, as neither can sink they are folded up into fold mountains
e. g. the Indian plate and Eurasian plate -> Himalayas
Plate boundary
when two plates join
Oceanic crust
- found under the oceans
- younger than continental
- can be destroyed
- can be made
- denser
- thinner
Continental crust
- found under land
- older
- thicker
- less dense
- can’t be made
- can’t be destroyed
How do convection currents work?
- magma near the outer core is heated
- as the magma expands it becomes less dense
- the less dense magma then starts to rise towards the crust
- as magma gets near the crust it begins to cool
- the cooling magma becomes denser and begins to sink
- the currents create friction with the crust above and causes it to move
What are ‘earthquakes’?
any movement in the earth’s crust; they happen everyday but not felt by humans
Aftershock
an earthquake that happens after the main earthquake. if the initial earthquake is strong, then the aftershock can be very strong
Richter scale
measures the magnitude (strength of force) of earthquakes by a seismometer (on a seismograph)
Mercalli scale
measures the intensity and effects of an earthquake or in other words the energy released
The amount of damage done by an earthquake depends on
- the amount of energy released
- the depth of the focus
- the density of the population
- how the structures have been built
- the type of bedrock - liquefaction
Preparedness and vulnerability in MEDCs
- hazard mapping and zonal planning
- strict building codes against earthquake damage
- the population would be educated about the hazards of earthquakes
- hazards will be better monitored for predictions to inform the public
- tents, blankets, food and water for anyone who lost their home
Preparedness and vulnerability in LEDCs
- don’t follow building codes
- poorer -> less money for medical care and rescue teams
- poorer transport and communication
- services like electricity and water will take longer to fix
- high population densities -> more people are affected
- less money spent on prediction methods
Short-term effects of earthquakes
- death
- injury
- panic and fear
- infrastructure damage
- secondary hazards
Long-term effects of earthquakes
- homelessness
- unemployment
- dependency
- disease
- post traumatic stress disorder
- rebuilding costs
Why do people live in tectonic active locations?
- poverty
- inertia
- infrequency
- overpopulation
- building design
- education and preparation
- economic opportunities
Why do people choose to live near volcanoes?
- their beauty
- minerals
- geothermal potential
- tourism
- hot springs near volcanoes
- poverty
- home
- shortage of space
- fertile land for agriculture
Name a volcano where people choose to live near.
Mount St Helens - Washington, USA
why?
- its natural beauty
- home to people who like the outdoors
- tourist destination because of its beauty
- a good spot for fishing
- it is well monitored, so people feel safe living near it
- most would not leave because they are either scientists studying the volcano or residents who couldn’t bring themselves to leave their homes
Name a volcano eruption.
Mount St Helens - Washington, USA
- located in Washington, USA
- sits on a destructive plate boundary where the Pacific plate and the Juan de Fuca plate subducts under the North American plate
Causes:
- been dormant for nearly 120 years until 18th may 1980, a 5.0 earthquake triggered a huge landslide and pyroclastic flow
Effects:
- the pyroclastic flow traveled for 25km and flattened everything on its path
- around 7000 animals died, and every tree within 30km of the volcano
- 63 people died
- a reduction of touristry and a total of £100mill damage to crops and machinery
- destruction of 250 homes, 47 bridges, 15 miles of railways and 185 miles of highway
- ash, steam and debris were sent to about 60,000 feet
solutions:
- temporary shelter were sent almost immediately by the US government
- 198 lives were saved
- money sent out by the government
Name an earthquake + its causes + effects + solutions.
Christchurch earthquake
Causes
- 22/02/2011
- an earthquake of 7.1 magnitude and an aftershock of 6.3 magnitude on the Richter scale
Effects
- 184 people died and 164 people were severely injured
- people were trying to get in touch with family and friends, which caused roads and cell phone lines to be jammed
- up to 10,000 buildings were damaged ad 10,000 needed to be demolished
- water and sewage pipes were damaged
- liquefaction
Solutions:
- groups from different areas come to help (volunteers) by bringing food
- rescue teams from all over the world came to supply essentials like bottled water, toilets etc.
- national emergency was declared.
