volcanic hazards Flashcards
volcanoes at destructive plate margins
-subduction at destructive plate margins results in volcanic activity, once oceanic crust dips below continental crust, temperatures rise and melting occurs
-the resulting magma would move slowly to the surface where it erupts through volcanoes and fissures as viscous, andestic lava and tephra
-the vicious magma traps steam and other gases creating explosions and eruptions
volcanoes at constructive plate margins
-at constructive plate margins, tensions in the crust and lithosphere reduced the pressure and allows magma to flow to the surface
-lava, tephra and hot gases erupt through volcanoes and fissures
-most eruptions are on the ocean floor as constructive plate margins are found at mid-ocean ridges
-differences from the volcanic activity at destructive plate margins include;
-> the lava is basalt rather than andestic
-> eruptions are less violent
what are two ypes of effects caused by volcanoes
primary effects: tephra, pyroclastic flows, lava flows, volcanic gases
secondary effects: volcanic mud flows, flooding, acid rain
what is tephra
volcanic bombs and ash which are ejected into the atmosphere
what are pyroclastic flows
also known as nuees and ardente, they are gas and tephra which are extremely hot (over 800 degrees) which flow down the sides of volcanoes a speeds of 700km per hour
what are lava flows
flows or streams of molten rock pour from an erupting vent, the speed at which lava moves depends on:
-the type of lava
-its viscosity
-the steepness of the ground
-whether the lava flows as a broad sheet, through a confined channel or down a lava tube
what are volcanic gases
carbon dioxide, carbon monoxide, sulphur dioxide and chlorine escape through fumeroles
what are volcanic mud flows
these are also known as lahars, they are a combination of melted snow and ice, rock, sand and volcanic ash. flow at high speeds and travel long distances
when does flooding occur
it occurs when eruptions melt ice caps and glaciers
what is acid rain
where the volcano emits gases, when the gas combines with atmospheric moisture it causes acid rain
what is the distribution of volcanoes
along plate margins and subduction zones
what is the measurement for magnitude of a volcano
volcanic explosivity index (VEI)
-logarithmic scale running from 0-8
what are some impacts of volcanoes
-destruction of natural environments
-destruction of human environments
-loss of life
-disruption to travel
-damage and destruction to buildings, settlements and infrastructure
-disruption to livelihoods
-disruption of communication
methods of prediction include monitoring:
-land swelling
-changes to groundwater levels
-chemical composition of groundwater
-gas emissions
-expanding cracks
-looking for shock waves that result from magma moving towards the surface
what are the ways that we can protect and prepare for a hazard
-monitoring can lead to evacuation responses
-risk assessments can lead to a series of alert levels
-land use planning may follow an assessment of the areas most at risk
-it may be possible to divert lava flows away from the built environment
