Volcanoes And Earthquakes Flashcards
(23 cards)
Where are volcanoes found?
Divergent plate boundaries, convergent plate boundaries and hotspots
What is a hotspot?
A small area of the earths crust where an unusually high heat flow is associated with volcanic activity
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
Describe effusive eruptions
Frequent, gentle and free flowing lava, emits gas and lava flows, can create flood basalts, occurs at shield volcanoes, low viscosity
Describe explosive eruptions
High viscosity, long periods of time with no activity, steep sided strato-volcanoes, gas&ash&dust&laval bombs,
Caused by a build up of pressure as magma prevents gases escaping by plugging vents
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.
Features of shallow focus earthquakes
Have a depth of up to 70km
Can cause higher level of damage as energy is released over a smaller area.
Common - 75% of quakes
Fault movements are in brittle, cold rocks or magma movement.
Focus and epicentre are closer to each other so there is a shorter difference in time between Primary and Secondary waves.
How are hotspots caused?
Intense radioactivity in the earths interior creates a high column of upwelling lava known as a plume. This plume pushes upwards and the plastic rocks become molten, pushing through the crust.
Calderas
Calderas can form where the top of the volcano is blown off or sides collapse.
What are sills and dykes?
Horizontal and vertical intrusions in a volcano. Internal lava flows.
Impacts of pyroclastic flow on people
Loss of life, injury, displacement of communities, infrastructure damage.
Impacts on the environment of pyroclastic flows.
Habitat destruction, changes in soil composition affecting agriculture, ash can pollute water supplies, decreased air quality posing health risks.
Ash and tephra
Ash falls back to the ground and creates a think layer, destroying crops, vegetation, killing livestock and causing roofs to collapse.
Why can shallow focus earthquakes still cause a high level of destruction?
Energy released reaches the surface quicker and the crust is thinner so it doesn’t absorb as much energy so more energy reaches the surface quicker
Features of deep focus earthquakes
Happens at a depth exceeding 70km
Less frequent, accounts for 25% of earthquakes
Latter magnitude due to high pressure created by the weight of the plate
Despite more energy initially being released, the earthquakes are often weaker due to the less of energy as the seismic waves travel to the surface.
