Volcanoes Flashcards
Benioff zone
The point at which the sun ducted plate melts
As the plate begins to melt it begins to rise up through fissures and cracks in the continental plate and burns their way through overlying rock. Eventually forming explosive volcanoes
Andesitic lava
Has a viscous nature (flows less easily) this creates explosive volcanoes
Shield volcanoes
Gentle slopes and wide base
Frequent erosion of basaltic lava
Lava flows at high speeds for long distances before cooling
Usually non violent eruptions
Non- viscous lava due to basaltic composition
Found at constructive boundaries
Composite volcanoes
Steep sided with distinctive cone shape
High with narrow base
Explosive eruptions of lava and ash
Layers of alternating ash and lava
Viscous lava builds up in layers and does not flow far from the crater
Found at destructive boundaries
Secondly or parasitic cones formed when the main vent gets blocked
Manama viscosity; Silica levels
More silica, more viscous, meaning it flows more slowly
High silica- more explosive
Low silica- effusive
Viscosity
How easy a liquid flows
A thicker magma means that the gases in the volcano (CO2) can’t escape
Eruption styles: pinian
Highly explosive, large eruption column (up to 45km), range of rephrased and pyroclastic fallout, including flows
Eruption styles: Pelean
Explosive eruptions with range of tephra with nuee ardent, pyroclastic flows
Eruption styles: Icelandic
Low viscosity and highly effusive. ,au have water therefore phreatic
Eruption styles: Hawaiian
Effusive, minor explosively, with fire fountain and low viscosity lava flow
Eruption styles: Vulcanian
Higher gas build up than Strombolian, highly viscous lava. A series of shots lived explosions, with tephra bombs
Eruption styles: Strombolian
Eruption with gas bubbles so eject tephra (ash)
Primary effects
Occur immediately along with the event
Secondary effects
Direct consequence of the event but not immediately
Mudflows
Flows of water than contains large amounts of suspended particles and silt. It has a higher density and viscosity than a streamflow and can only the coarsest part of the load; this causes irreversible sediment entrainment
They may rush down mountainsides at speeds as great as 100km per hour, and can cause great damage to property. Can be 3-6m wide
What to do in case of a mudflow: drive carefully, leave area, watch for patterns in storms water drainage
Tephra
Fragment material produced by a volcanic eruption regardless of composition, fragment size
Once clasts have fallen to the ground, they remain as tephra unless hot enough to fuse together into pyroclastic rock or tuff
Largest fragments, blocks and bombs have a diameter of 2.5 inches
What to do: stay inside or leave area
Lava flows
A mass of flowing or solidified lava
Least hazardous
Streams of molten rock that pour from an erupting vent. The speed at which lava moves across the ground depends on several factors, including type of lava and viscosity, steep end of ground over which it travels.
Happens at shield volcanoes
Can move 1.3km and be 100m thick
Melt snow and ice, causing floods
What to do: get to higher ground or evacuate
Gases
The must abundant volcanic gas is water vapour, which is harmless. However significant amount of CO2, sulphur dioxide, hydrogen sulphide and hydrogen halides can also be emitted from volcanoes
These gases are toxic and can harm people
What to do- leave area to avoid breathing in or contact with gases
Acid rain
Rainfall made acidic by atmospheric pollution
Can cause environmental harms mainly to forest and lakes
Caused by emissions of sulphur dioxide and nitrogen oxygen, which react with the water molecules in the atmosphere to produce acid
What to do- stay inside or evacuate
Ash fallout
Volcanic ash is formed during explosive volcanic eruptions when dissolved gases in magma expand and escape violently into the atmosphere.
Occurs immediately after and eruption
What to do- stay inside or evacuate
Pyroclastic flows/ Nuées Ardentes
Fast moving current of hot gas an volcanic matter that moves away from volcano about 100km/h on average but can reach 700 km/h
Destructive and deadly
What to do- evacuate as soon as or before eruption occurs
Lanark’s
Mixture of joy or cold water and rock fragments which flows down the steep side of a volcano
For, when eruption volcanic material gets saturated during periods of heavy rain. This does not have to be during or immediately after an eruption but may be some time afterwards
Can grow as they travel
Destroy anything in their path
Monitoring volcanoes: seismic activity
Measured using local seismographs . Monitoring infra sound sub audible sound below 20 hertz. As many volcanoes are found at or on plate boundaries, it’s very difficult to observe seismic activity. All volcanoes react differently
Monitoring volcanoes: gas emissions
As magma nears the surface, gases escape, SO4 emitted, increasing amounts suggest a rise in magma. Drop in gas before eruptions suggest sealing of gas passage by hardened magma. Measure emissions at volcano or dirtier afield from a safer distance
Monitoring volcanoes: geological observations
GPS- calculate vertical movement by satellite
Distance measurement- electronic distance measurement measure horizontal movement
Slope angle- a tilt meter is used to measure changes in the slope on a volcano side. Installed When volcano active, when magma rises to chamber volcano expand
