Hazardous Earth SG1 Flashcards
What are the three main types of plate boundary?
Divergent, Convergent, Conservative
What are the three types of convergent plate boundaries?
Ocean/Continental (OC), Ocean/Ocean (OO), Continental/Continental (CC)
Which plate boundaries have volcanoes?
Divergent and Ocean/Continental Convergent
Define Magma
Molten rock beneath the surface
Define Lava
Molten rock above the surface (700-1200 degrees temp)
Are magmas/lavas with high silica contents viscous or non-viscous?
Viscous - they don’t flow easily
Are magmas/lavas with low silica contents associated with infrequent explosive or frequent effusive eruptions?
Frequent effusive eruptions
What is the silica content of andesite?
62%
What is the silica content of rhyolite?
71%
What is the silica content of basalt?
48%
What are the two types of volcanic eruption?
Explosive and effusive
What temperature is basaltic magma when it erupts?
1,200 degrees Celsius
What boundary do explosive eruptions happen on?
Convergent (where subduction is taking place)
What boundary do effusive eruptions happen on?
Divergent
What % of earth’s individual volcanoes do composite cones make up?
60%
What can make composite volcanoes more complex in shape?
Secondary or parasitic cones
Why is a composite volcano called that?
It is made of alternating layers of lava flows and volcanic ash
Define Dyke
Igneous rock layer cutting across beds of rock
Define Sill
Igneous rock layer following/running between beds of rock
Define Caldera
Large circular depressions (1-20km across) caused by the collapse of the top of a volcano following an explosion
What are the three stages in the formation of a caldera?
1) Build up of pressure as magma rises to the surface
2) Magma level in chamber lowers after an eruption and fractures form in unsupported rocks
3) Top of the volcano collapses inwards due to the weight of the rock
What happens to a caldera over time?
It fills with water and a new volcano begins to form from the previous magma chamber
Which caldera is 3700m high in Lombok, Indonesia?
Rinjani Volcano Caldera
How is a shield volcano characterised?
Gentle slopes of less than 10 degrees leading away from a central vent
Where do most effusive eruptions occur and what are the exceptions?
Most occur unseen on the ocean floor apart from in Hawaii and Iceland
How many recorded eruptions has Kilauea (the world’s most active volcano) had in its current cycle?
More than 60 - it has been erupting on a continuous basis since 1983
Despite the volcanic activity, what benefits come from living on Hawaii?
Fertile land is good for agriculture, Tourism
What is a lava plateaux/fissure eruption?
Lava spills out from a fissure to form sheets of lava over the pre-existing landscape
What were the impacts of the 8 month fissure eruption in Laki, 1783?
Killed 1/3 of Iceland’s population, Caused two years of extremely cold winters and summers globally
How high were the fire fountains in Laki?
500m high
What is the Ring of Fire?
A major area in the Pacific Ocean where many earthquakes and volcanoes occur
How big is the Ring of Fire?
40,000km (25,000 miles) horseshoe shape
How many earthquakes and volcanoes have occurred in the Ring of Fire?
90% of the worlds earthquakes, All but 3 of the world’s 25 largest volcanic eruptions of the last 11,700 years
Who first proposed the hot spot theory in 1963 to explain intraplate volcanic activity?
Tuzo Wilson
What did Tuzo Wilson suggest?
The Hawaiian chain is the product of a single ‘hot spot’ fixed in the mantle. As the pacific moved over the hot spot a chain of volcanic islands form
Which island in the Hawaiian Islands chain is currently over the hot spot?
Hawaii - there is only volcanic activity on Hawaii
Which seamount will form an island in 10,000 years time?
Loihi - it is the youngest sea mount in the Hawaiian Islands chain
Why are the oldest volcanoes now below sea level?
Erosion and they are sinking as the crust gets colder
What do guyots represent?
The oldest volcanoes to have formed as a result of the hotspot in the Pacific ocean
Define Guyot
An undersea mountain with a flat top
How long is the Great Rift Valley?
4,000km
Which is the highest active volcano in the Great Rift Valley?
Mount Kilimanjaro
How was the Great Rift Valley formed?
Crustal stretching causes tension within the local rocks., resulting in rifting with magma forcing its way to the surface and creating a line of active volcanoes
Where else can hot spots occur?
On plate boundaries - Iceland is over a 100 mile wide, 370 mile deep hot spot and a divergent plate boundary
Define Supervolcano
A volcano that erupts more than 1,000 cubic km (km3) in a single eruption event. They exist as giant calderas
What is an example of a supervolcano?
Yellowstone
What can a volcano be classified based on?
Plume type (ash cloud) and height
What are the six types of classification for volcanoes?
Icelandic, Hawaiian, Strombolian, Vulcanian, Pelean, Plinian
What does the Volcanic Explosivity Index (VEI) measure?
Magnitude (amount of material erupted) and Intensity (the speed at which the material is erupted)
What is the scale for the VEI?
0 (least explosive) to 8 (most explosive) - each increase in number represents nearly a tenfold increase in explosivity
What is a limitation of the VEI?
There can be conflicting results - the height and amount of material produced might not fit into the same category
Define Active Volcano
A volcano that has erupted in the last glacial period or within the past 10,000 years - 1,500 volcanoes fit in this category
Define Dormant Volcano
A volcano that has not erupted in the last 10,000 years but is expected to erupt in the future
Define Extinct Volcano
A volcano that is not expected to erupt again
What are the 4 local primary hazards created by a volcano?
Lava flows, Pyroclastic flows, Tephra, Volcanic gases
What are the 4 local secondary hazards created by a volcano?
Landslides, Tsunami, Lahars, Flooding
What is a global secondary hazard created by a volcano?
Climate change
Strategies to mitigate against the event:
Not yet possible for the majority of volcanic eruptions
Strategies to mitigate against vulnerability:
Education, Prediction and warning, Constant monitoring, Hazard resistant buildings, Hazard mapping, Land use zoning, Community preparedness
Strategies to mitigate against losses:
Disaster response teams, Emergency aid, Closure of airports, Insurance and government compensation schemes
What are three methods to predict volcanic eruptions?
Ground deformation, Seismicity, Gas emissions
