Volcanoes And Earthquakes Flashcards
Where are volcanoes found?
Divergent plate boundaries, convergent plate boundaries and hotspots
What is a hotspot?
Plums of superheated rock move to the surface via convection currents and melt through the crust. They usually occur away from plate boundaries.
Where are eruptions more powerful divergent or convergent plate boundaries and why?
Convergent plate boundaries – the magma is more viscous and rises due to the subducting plate increasing magma to the surface.
What indicators does the volcanic explosivity index (VEI) use?
Volume of material ejected
Eruption height into the atmosphere
Duration of the eruption.
(Magnitude (volume) and intensity (duration) )
Describe what a shield volcano looks like
Broad bases with gently sloping sides
Describe what a composite volcano looks like
Steep sided volcano with layers of ash and lava making it up
What occurs at shield volcanoes?
Divergent plate boundaries. Low viscosity (thin) and gentle flow of basaltic lava. (Effusive eruption of fluid lava)
What occurs at composite volcanoes?
Convergent plate boundaries. Erupts thick magma with a high silica. Lava can cool and plug vents in the side of the volcano cause pressure to build. Causes EXPLOSIVE eruptions.
Calderas can form where the top of the volcano is blown off or sides collapse.
What is a Caldera and at which volcano type does it usually occur at?
A Caldara is when the top of a volcano is removed by eruptions or when the side of the volcano collapse due to the underground magma chamber empty after an eruption so cannot support the sides of the volcano.
What is a pyroclastic flow?
Cloud of hot volcanic gases, ash, and rock fragments that travel at high speeds. They are hazards associated with volcanos.
What is tephra?
Hazard associated with volcanoes where material is ejected from a volcano. It can range from fine material to large debris.
How are floods caused from volcanoes?
Volcanic eruptions beneath an ice field of glaciers, causing rapid melting and floods.
What is a lahar?
A violent hazard from volcanoes where a flow composed of rocky debris and pyroclastic material
What is the difference between a focus and an epicentre of an earthquake?
Focus is the point in the earths crust where the stress is released. Immediately above this point on the surface is the epicentre.