Nature And Distribution Of Volcanoes Flashcards
Where do most volcanoes occur?
Plate boundaries.
Name 4 places volcanoes occur?
Oceanic ridges.
Subduction zones
Rift valleys
Hotspots
What are the plates doing at oceanic ridges?
Plates moving apart.
Magma then forced its way to the surface, cooling and forming new crust.
As plates moves further apart , new crust is carried away from ridge.
As plates moves further apart , new crust is carried away from ridge. What is this called?
Sea floor spreading.
Example of oceanic ridge.
Mid Atlantic ridge where Iceland represents a large area formed by volcanic activity.
What are the eruptions like at oceanic ridges (Iceland)?
Fairly gentle shield volcanoes.
Low viscosity lava - basaltic.
Frequent yet gentle
Where does subduction occur ?
Ring of fire at Pacific Ocean.
Describe process of subduction.
Denser oceanic plate subjects underneath continental plate into Benioff zone in mantle.
Further it descends the hotter surroundings become.
This together with heat generated from friction begins to melt oceanic plate into magma.
Less dense molten magma begins to rise in plutons.
Eventually reaches surfaces as volcano.
What type of volcanoes does andesitic lava create?
Due to is viscous slow moving nature it creates complex composite and explosive volcanoes.
What happens if subduction eruptions take place off shore?
A line of volcanic islands known as island arcs can form
How else can island arcs form?
When 2 oceanic plates meet one is forced under the other, subsequent subduction occurs.
What is happening on western side or Pacific Ocean?
Pacific plate being dragged under smaller Philippine plate.
A line of volcanic island including Guam and Marianas has formed.
Where do Rift valleys form ?
At constructive margins in continental areas
When plates move away
Example of Rift Valley
East Africa
Brittle crust fractures as sections move apart.
Areas of crust drop down between parallel faults to form Rift Valleys.
Crust here is much thinner than neighbouring crust meaning tension and friction is causing plague to split.
Thinning plate allows magma to force its way up to the surface to form volcano.
How do hotpots form ?
Concentration of radioactive elements.
