Volcanoes Flashcards
What type of slope does a shield volcano have?
Gentle slopes built from previous eruptions.
What type of lava is released by shield volcanoes?
Runny lava
How often do shield volcanoes erupt?
Frequent eruptions
Are shield volcano eruptions mild or severe?
Mild
What are the slopes of composite volcanoes like?
They have steep sides.
What type of volcano can be found at hotspots?
Shield
How are seamounts formed?
Extinct volcanoes apply too much pressure on the crust so subsidence occurs. This, combined with erosion creates sea mounts.
What type of volcano is found at subduction zones?
Composite
What type of volcano is found at constructive plate boundaries?
Shield
How do volcanoes form at destructive plate boundaries?
When the oceanic plate melts in the subduction zone, plutons of magma rise to create volcanoes.
How do volcanoes form at oceanic ridges?
They occur as a result of sea floor spreading as magma rises through gaps in the crust and makes its way to the surface.
What type of lava is found at oceanic ridges?
Low viscosity, balsatic lava
How do volcanoes form at rift valleys?
When the crust drops down, the magma rises through the gaps as the crust becomes thinner.
What is meant by the term “active”?
An eruption is currently going on
What is meant by the term “dormant”?
It has not erupted in the last 2000 years
What is meant by the term “extinct”?
The volcano will not erupt again.
Give an example of an active volcano
Mauna Loa, Hawaii
Give an example of a dormant volcano
Mt Rainier, USA
Give an example of an extinct volcano
Mount Snowden, Wales
Where are shield volcanoes found?
Hotspots and constructive boundaries
What are composite volcanoes made of?
Alternating layers of ash and lava from previous eruptions.
What are shield volcanoes made of?
Lava
Where are composite volcanoes found?
Destructive plate boundaries
What are eruptions of composite volcanoes like?
Pyroclastic flows
What are eruptions of shield volcanoes like?
Lava flows
What is lava made of?
Silicon, oxygen, aluminium, iron, magnesium, calcium, sodium, potassium, phosphorus, and titanium
How do high viscosity lavas flow?
Slowly
How far do high viscosity lavas flow?
They cover small areas.
How do low viscosity lavas flow?
Quickly
How far do low viscosity lavas flow?
They cover thousands of square kilometres
Why do low viscosity lavas not result in violent eruptions?
Gases are allowed to escape so pressure does not build up.
Why do high viscosity lavas lead to violent eruptions?
Gas pressures build up.
What is the character of volcanoes largely controlled by?
The viscosity of the lava.
How is the magnitude of volcanoes measured?
Using the VEI
What does VEI stand for?
Volcanic Explosivity Index
What is the VEI measured on a scale of?
0-8
What does a VEI score of 0 suggest?
Non-explosive
What does a VEI score of 8 suggest?
Very large
Why might eruptions with the largest VEI scores not have the worst effects?
Volcano could be in a rural area with a small population
Prediction and evacuation
LIC/HIC
Population density
List 4 potential primary impacts of volcanic eruptions
Tephra
Volcanic gases
Lava flows
Pyroclastic flows
What is tephra?
Solid material of varying size that ranges from volcanic bombs to ash, all ejected into the atmosphere.
What are the volcanic gases released by volcanoes?
CO2, CO, SO2, CL2 and hydrogen sulfide
Give an example where volcanic gases have caused a problem
In 1986, CO2 emissions from a lake in the crater of Nayos, Cameroon killed 1700 people.
What are lava flows?
Streams of molten rock that pour from an erupting vent
What are pyroclastic flows?
Very hot, gas charged, high velocity flows made up of a mixture of gas and tephra.
Give an example where pyroclastic flows have caused problems in the past
Pompeii was destroyed by pyroclastic flows from Mt Vesuvius in 79AD.
What are 6 potential secondary impacts of volcanic eruptions?
Lahars Flooding Volcanic landslides Tsunamis Acid rain Climate change
What are lahars?
Melted snow and ice as a result of the eruption combined with volcanic ash forms mud flows that can move down the course of river valleys at high speeds.
Give an example of a deadly lahar
1985, a lahar destroyed the Columbian town of Armero after Nevado Del Ruiz erupted, only 25% of the population survived.
Why can flooding occur after an eruption?
The eruption may melt glaciers and ice caps.
When has flooding as a result of an eruption been a problem?
Iceland 1996, after the Grimsvotn volcano erupted.
What are volcanic landslides?
Large masses of wet/dry rock and soil that fall, slide or flow rapidly under the force of gravity.
What are volcano-related tsunamis caused by?
Violent volcanic eruptions
Give an example when a tsunami caused by an eruption has been deadly
Krakatoa, Indonesia 1883, estimated 36,000 dead
Why can eruptions cause acid rain?
Volcanic gases released containing sulphur mix with atmospheric moisture.
Why can eruptions cause climate change?
Volcanic debris can reduce global temperatures.
What are the 3 methods of mitigation?
Preparation, prevention and adaptation
What visual change can suggest a volcano may erupt?
Ground deformation
What do seismometers detect?
Small earthquakes
What are the small earthquakes caused by? (In a volcanic context)
Magma rising up through cracks in the Earth’s crust
What do thermal imaging techniques and satellites detect?
Rising temperatures as volcanic activity increases.
What are gas samples and chemical sensors used for?
Detecting high sulphur levels which may indicate that the volcano will erupt soon.
What are long-period events?
These indicate the movement of magma as a result of increased pressure on the rock and can be seen on seismometer readings.
How many lives did the knowledge of long-period events save when Popocatepetl erupted?
30,000
When did Popocatepetl erupt?
2000
Where is Popocatepetl?
Mexico
How do you spell the name of the Icelandic volcano that erupted in 2010?
Eyjafjallajokull
What did the volcanic ash cloud released by Eyjafjallajokull in 2010 cause?
Flights in and out of the UK to be cancelled.
Were there any deaths when Eyjafjallajokull erupted?
No
What is expected for Eyjafjallajokull in the future?
Larger eruptions
Tectonic plate boundaries are home to what percentage of volcanoes?
80%
What type of plate boundary is Iceland on?
A constructive plate boundary?
What is significant about Iceland’s location on a constructive plate boundary?
It will continue to grow
What are 5 ways in which people can adapt for volcanic eruptions?
Monitoring systems Redrafted action plans Relocation Building techniques Concrete shelters
How can building techniques be used to mitigate the risks from volcanic eruptions?
Retrofit buildings
Stronger structures
What are redrafted action plans based on?
Previous events
What are 6 ways in which death and destruction by volcanic eruptions can be prevented?
Location of infrastructure Building techniques Lava channels Warning systems Evacuation Evacuation routes
Where should businesses/schools and homes be built?
Away from volcanoes
What type of building should be strategically placed?
Hospitals
What do lava channels do?
Redirect lava away from buildings and people
Why are clear evacuation routes important?
They can save lives and reduce the number of injuries.
What are 7 ways in which people can prepare for volcanic eruptions?
Emergency funds Emergency supplies Hazard maps Evacuation Exclusion zones Communication systems Education
What do hazard maps show?
Pathways of expected eruption products
What is important when planning an evacuation?
That there are places to temporarily relocate people.
What is a benefit of exclusion zones?
They reduce disruption
Why are communication systems important?
For coordinating rescue and give warnings or evacuation orders.
