VOLCANOES Flashcards
Briefly explain the term active volcano.
An active volcano is a volcano that erupts regularly or is likely to erupt soon. Mount Etna in Italy is an example of an active volcano.
Briefly explain the term dormant volcano.
A dormant volcano is a volcano that has not erupted in recent history but is likely to erupt again in the future. Mount Kilimanjaro in Tanzania is an example.
Briefly explain the term extinct volcano.
An extinct volcano is a volcano that has not erupted in recent history and is not expected to erupt again in the future as the magma is no longer forcing its way into the chamber. Slemish Co. Antrim is an example.
Briefly explain the term lava.
Lava is the name given to magma once it reaches the surface. Lava can be either acidic or basic and the type of lava emitted determines whether an eruption will be violent or gentle.
Acidic lava features (3)
Volcanoes at convergent boundaries
Moves slowly
Violent eruption
Basic lava features (3)
Volcanoes at divergent boundaries
Moves quickly
Gentle eruption
What comes out of a volcano other than lava?
Pyroclastic material (tephra) - ash, dust, and rock fragments
Gases - Carbon dioxide, carbon monoxide, and hydrogen.
Volcanoes occur at convergent plate boundaries when an…
Oceanic plate collided with another plate.
When the plates collide what process occurs?
Subduction. The heavier plate subducts into the mantle.
What depth does the subducting plate reach to melt?
100km
What is released from the plate? (Convergent)
Water vapour and gases e.g CO2
What happens to the gases released (convergent)
Get trapped in the magma.
When the gases get trapped in the magma what happens to the magma?
It’s forced to rise upwards through the overlying plate.
As the magma melts it’s way through the crust it forms a…
Magma chamber
What prevents the gases from escaping?
The viscosity of the lava.
Since the gases can’t escape what happens on the magma chamber?
Pressure builds.
When the pressure becomes so great what happens? (Convergent)
It burns its way through the overlying rock and erupts explosively onto the surface.
Does the pressure travel far? (Convergent)
No
Since the pressure doesn’t travel far what does that lead to? (Convergent)
Formation of
steep sided volcanic cones of alternating layers of tephra and lava.
Convergent volcanoes are known as
Stratovolcanoes
What’s an example of a stratovolcano?
Mount St. Helens
What are the two convergent boundaries that volcanoes form at?
Oceanic oceanic
Oceanic Continental
(OO) Repeated eruptions cause what?
The build up of volcanic material to form volcanic island arcs.
Example of a volcanic island arc.
Philippine Island Arc - formed form subduction of Pacific plate beneath Eurasian plate
(OC) Chains of volcanic mountains are known as..
Volcanic arcs
Example of OC volcanic arc.
The Andes - Nazca and South American (Cotopaxi = peak)
D: what two plates separate?
Oceanic plates
D: As they separate what happens
Fissures form between them
D: What rises through these fissures?
Magma onto the sea floor as lava.
D: Magma has a ____ silica content
Low
Low silica content means that gases
Escape easily
If gases escape easily are the eruptions violent or gentler
Gentler
Once lava comes in contact with sea water it
Cools quickly and hardens to form basalt.
As the basalt builds up it forms what landform?
Mid ocean ridge
The Mid Atlantic Ridge has what plates involved?
North American and Eurasian
A chain of volcanoes form volcanic arcs but also
Hotspots
Unlike other volcanic formations hotspots are located
Away from plate boundaries
The usually occur on what plates (hotspots)
Oceanic
What are hotspots
Areas of Earths mantle that are much hotter than the magma around it
Hotspots: the magma is so hot that
It melts through the oceanic plate to form a volcano
The magma for hotspots is low or high in silica content
Low
Landforms created from volcanoes can be either
Extrusive - on the surface
Intrusive - inside the crust
An extrusive landform is
Volcanic cones
Where do volcanic cones form at?
Convergent and divergent plate boundaries and hotspots.
What are the four types of volcanic cones?
Composite cones
Cinder cones
Calderas
Shield volcanoes
What are composite cones also known as?
Stratovolcanoes
Where do composite cones form at?
Convergent boundaries
What are composite cones made up of?
Alternating layers of pyroclastic material and acidic lava.
Example of a stratovolcano?
Mount Fuji, Japan.
Cinder cones rarely reach heights of more than.
300m
What is the most common type of volcano found on the earth?
Cinder cones
What are cinder cones made up of?
Pyroclastic material that stuck together after explosive eruption.
What volcanic cone only erupts once?
Cinder cone
Why do cinder volcanoes only erupt once?
The eruption is so powerful that it destroys its shape.
Over 100 cinder cones surround
Mauna Lao in Hawaii
How are calderas formed?
When composite cones explode violently
What is a depression and how is it formed?
An area of land that sank downwards after fractured rock collapsed into an empty magma chamber.
Where do shield volcanoes form?
Divergent boundaries and hotspots.
How are shield volcanoes formed?
From gentler eruptions of basic lava which spreads over a wide area.
Example of a shield volcano
Mauna Lao in Hawaii
What type of volcanic cone is the largest?
Shiel volcano
How is a lava plateau formed?
large streams of basic lava are released onto the surface from fissure eruptions. Lava spreads over a wide area and cools and hardens. Repeated eruptions lead to the formation.
Example of a lava plateau
Antrim-Derry Plateau
Hexagonal columns at A-D Plateau are known as
The Giants Causeway
Examples of intrusive landforms.
Batholith and Sill
What are batholiths?
Large areas of igneous rock that form when magma cools slowly inside the Earths crust.
When do batholiths form
During fold mountain building.
Example of a batholith and what plates collided to form it.
Leinster Batholith - North American and Eurasian
How can you predict volcanic activity?
Historic records - studying past eruptions to find patterns e.g. time before eruptions.
Gas emissions - increases in gas like CO2 being released in volcano can mean that its close to erupting
How can you predict volcanic activity? p.2 not HR or GE
Ground deformation: If a volcano’s cone changes in steepness, it can be close to erupting. Tiltmeters are used to check this: an air bubble in water moves if the slope changes.
Seismic activity: It increases under a volcano before an eruption because magma and gas are forcing their way into a magma chamber. Seismographs - as magma moves it records vibrations in the crust.
What are some positive impacts of volcanoes?
New land is created - Iceland formed after a build-up of basalt on Mid Atlantic Ridge (North American and Eurasian plates)
Tourism - Tourists are attracted to landforms formed. Iceland’s economy has been boosted because of the activity. Foreign tourists = 42% of income. Employment goes up. Tourists go hiking or sightseeing.
Geothermal energy - Renewable energy. Iceland uses it. Igneous rock absorbs heat from magma causing groundwater to heat up. Groundwater turns into steam and taken to power stations then filtered through turbines and then produces electricity.
