Volcanoes Flashcards
What is a hotspot ?
Areas of the mantle have more radiogenic heat than others around it, because they are hotter magma is less dense so a plume rises peircing the crust and creating volcanic activity.
What is vulcanicity ?
Refers to the rising of molten magma or other gaseous materials beneath earths crust onto the surface
What is the nature of vulcanicity ?
The forms, characteristics and behaviour of magma rising to and breaking through to earths crust, it includes ; type of eruption, types of volcano, types of lava
Characteristics of basic or basaltic lava ?
Low silica content, Low viscosity, Very hot (1200 degrees), Eruptions are frequent but relatively gentle, Lava and stream ejected, Found at constructive plate margins where magma rises from mantle.
Characteristics of andesitic or acid lava ?
High silica content, High viscosity, Less hot (800 degrees), Eruptions are less frequent but are violent due to build up of gases, Ash, rocks, gases steam and lava ejected, Found at destructive margins where oceanic crust is destroyed.
What is the distribution of volcanoes and what type of volcanoes do they create ?
Along constructive plate margins - Gentle sides due to low viscosity basaltic lava and effusive eruptions tend to happen.
On or around ‘subduction zones’ - Andesitic lava, complex composite and explosive volcanoes.
Over hotspots - Low angled slopes made from low viscosity basaltic lava.
What is the measurement of magnitude for volcanoes ?
Volcanic Explosivity Index (VEI)
What happens to gases in non-viscous lava ?
Gases may escape easily
What happens to gases in viscous lava ?
Gases do not move freely and can build up lots of pressure.
How can explosive eruptions affect the atmosphere ?
It can blow volcanic dust into high atmosphere, reducing the amount of incoming solar radiation and causing short-term global climate change.
How can you determine the frequency of volcanoes ?
Its previous history of activity can be interpreted by volcanologists using the deposits associated with the volcano itself and those within the wider region it can affect.
Primary effects of volcanic activity ?
Tephra (volcanic bombs), Pyroclastic flow, Lava flows, Volcanic gases
What is Tephra (volcanic bombs) ?
Solid material of varying grain size ejected into the atmosphere - generally the large tephra particles travel a shorter distance and small fine ash can be thrown high into the atmosphere where strong winds can blow it around the earth, reducing incoming radiation and cooling the earth.
What are pyroclastic flows (nuees ardentes) ?
Very hot, gas charged, high velocity flows made up of a mixture of gas and tephra. These usually hug the ground and flow down the sides of the volcano up to 700kph.
What are lava flows ?
Flow of lava ranging from 700 - 1200 degrees, rarely cause injury to anyone as they are low velocity however they are unstoppable and can damage anything in its site
What are secondary effects of volcanic activity ?
Lahars (volcanic mudflows), Flooding, Volcanic landslides, Tsunamis, Acid rain, Climate change
What are lahars (volcanic mudflow) ?
Unconsolidated ash from a recent eruption combined with water may be swept down river valleys in the form of hot, dense, fast moving mudflow.
What is flooding following a volcanic eruption ?
When an eruption melts glaciers and ice caps.
What are volcanic landslides ?
The high velocity and great momentum landlside which can cross between valleys and run up slopes
What is an explosive eruption ?
Lots of gases are trapped in the magma and eventually explode out of the volcano.
What is an effusive eruption ?
When magma has a low viscosity and gases can escape easily so when magma erupts at the surface it forms lava flows.
What is a fissure volcano ?
Cracks, 2 constructive plates moving apart ejected through cracks
What is a basic or shield volcano ?
Lava flows out of a central vent and spreads over wide areas.
What is an acid or dome volcano ?
Acid lava solidifies when exposed to air which produces steep-sided convex cone.
What is an Ash and Cinder volcano ?
Ash and cinders building up into a symmetrical cone.
What is a composite volcano ?
Alternating types of eruption (effusive + explosive) in which first ash is ejected and then lava.
What is a caldera volcano ?
Build up of extreme gases, huge explosions may clear the magma chamber beneath the volcano and remove the top of the cone causing sides of the crater to subside thus widening the opening.
What is the regularity of volcanos ?
Occur at known locations, Explosivity largely determined by the plate boundary
How can we predict volcanos ?
Tiltmeter, Changes in CO2 and sulphur dioxide
What is the eruption style dependant on ?
Characteristics of the magma.
How can you mitigate against an eruption ?
Possible redirection of lava flow away from built environment, Barriers to protect settlements
How can you prevent against an eruption ?
There is no way
