Volcanoes Flashcards
What is a volcano
A volcano is a structure containing a magma chamber from which molten magma moves.
The magma travels up through a vent
and eventually out through a crater.
What is volcanic activity
Through this crater, hot ash, dust ,
volcanic rock bombs and molten magma
erupt
Magma which has moved out of the
crater is known as Lava.
Over time, a landform known as a volcanic cone
develops
Where does volcanic activity occur
The world’s volcanoes occur in three different
areas:
1. DIVERGENT plate boundaries: Where plates pull
apart, magma comes up through a crack.
2. CONVERGENT plate boundaries: Where plates
collide and subduction occurs magma may reach
the surface through a small opening between the
plates.
3. HOTSPOTS: Weakness at the centre of a plate.
What is the Pacific Ring of Fire
This is where over half of the world’s active
volcanoes are located.
It is located around the edge of the Pacific
ocean.
Many of the world’s major plates meet here.
The life cycle of a volcano
ACTIVE VOLCANO: The volcano is still erupting a
frequent intervals, e.g. Mount Etna in Italy
DORMANT VOLCANO: The volcano has been quiet
for a long time (10,000 years) but may erupt again,
e.g Mount Fuji in Japan
EXTINCT VOLCANO: The volcano has not erupted in
recorded history, e.g. Slemish Mountain in Co Antrim
Products of a volcanic eruption
- Lava
- Pyroclasts and Pyroclastic flows
- Poisonous gases
- Ash pumice and dust
- Water vapour
- Lahars
Lava
There are two types of lava that can come to
the earth’s surface: acidic and basic
Depending on which lava comes to the
surface will gives us different landforms
Acidic lava
This type of lava is produced at a destructive plate
boundary. It is sticky and moves slowly. As this lava is sticky, gases can build up causing
great pressure. When this magma is realised it erupts with a massive explosion. These eruptions create dome volcanoes e.g. Mt St Helens
Basic lava
This type of lava is produced at a constructive plate boundary. It is a runny type of lava and it flows quickly. These eruptions create shield volcanoes. E.g. Mauna Loa
Pyroclastic flows
Pyroclasts are hot ash and rock fragments that are
thrown out of the volcano…
Pyroclastic flows are flows of boiling clouds of ash and rock with poisonous gases…
They travel at speeds up to 200km/h
They destroy everything they meet
Poisonous gases
Carbon dioxide
Sulfur dioxide
All these gases are released from the volcano and
they result in people been suffocated
Ash and dust
The power of an eruption shatters rocks
down to dust within the vent and cone…
On eruption this dust and ash can be
thrown many km into the air..
Winds can send this dust across the
world..
Pumice
When lava is thrown from the
volcano air is sucked into it.
This air is trapped into the lava
when it cools (rock) and makes it
a light rock.
This is now known as Pumice.
Lahars
Lahars are debris flows or mudlows, composed of
pyroclasts, rocks, and water… VOLCANIC LANDSLIDES!
Lahars travel at a variety of speed depending on their size.
The larger the lahar the greater the speed (up 80kph). As lahars move they erode the hill sides
Extrusive volcanic landforms
These are volcanic landforms found on the
earth’s surface. These include:
Plateaus
Volcanic cones
Craters and caldera
Plateaus
This landform is a result of
volcanic activity.
It forms when lava flows out
of a fissure and spreads
across the surface of the
earth.
One of the best known
plateaus is the Giant’s
Causeway.
Types of volcanic cones
There are different types of volcanic cones:
These depend on the:
The type of lava
Ash ejected
The different types include:
Shield volcanoes
Dome volcanoe
Shield volcanoes
These have gently sloping sides.
The are a result of basic lava eruptions.
As the basic lava is so runny the lava can spread over many km. Over millions of years these build up of lava forms some of the largest volcanoes in the world.
Example = Kīlauea is an active shield volcano in the
Hawaiian Islands.
Dome volcanoes
These have steep sloping sides.
They are a result of acidic lava eruptions.
As the lava is sticky it does not flow far and cools quickly to turn into rock.
Common on destructive boundaries.
Calderas
These occur in areas that suffer from explosive
eruptions.
They release many cubic km of magma.
This virtually empties the magma chamber.
The ground above the magma chamber collapses into the magma chamber.
Intrusive volcanic landforms
Batholiths
Sills
Dykes
Laccoliths
Lopoliths
Batholith
These are large masses (greater than 100km2) of igneous rock that are formed inside the surface of the earth.
The masses of rock are exposed when the rock layers above it are eroded. Example: granite
Sills
Horizontal sheets of volcanic rock which run
in the same direction (parallel) as the layers
of rock in the ground.
The magma cooled quite close to the
surface
Dykes
Thin, vertical sheets of volcanic rock that run perpendicular to
the layers of rock.
They were formed when lava was forced into VERTICAL cracks/fractures in the rock.
Laccolith
These are formed when lava is forced up in between layers of rock and they push the rock upwards and create it to bulge up
Lopoliths
These are formed when lava is forced in between layers of rock and create it to sag down
Positive effects of volcanic activity
New land created
▪ Iceland, Hawaii, etc.
▪ Physical and economic benefit
Geothermal energy
▪ New Zealand and Iceland
▪ Economic and Environmental benefit
Fertile soil after lava has been eroded (Terra Rossa Soil)
▪ Canary Islands and Brazil
▪ Physical, social and economic benefit
Negative effects of volcanic activity
Lava Flows
▪ These are a danger to human life
▪ Mount Etna, Cumbre Vieja (La Palma, Canary Islands)
Pyroclastic flows
▪ Danger to humans
▪ Mount Pinatubo in Philippines
Tsunamis
▪ A volcanic eruption can trigger a tsunami
▪ Indonesia, 2004
Negative effects of volcanic activity
Lava Flows
▪ These are a danger to human life
▪ Mount Etna, Cumbre Vieja (La Palma, Canary Islands)
Pyroclastic flows
▪ Danger to humans
▪ Mount Pinatubo in Philippines
Tsunamis
▪ A volcanic eruption can trigger a tsunami
▪ Indonesia, 2004
