🌋3.1.5.3 - Volcanic Hazards Flashcards
What type of lava is rich in silica?
Slow flowing, viscous lava
What is generally erupted from volcanoes at destructive margins?
Lava bombs, ash, dust
What are lava flows?
Streams of molten rock that pour or ooze from an erupting vent
What are the two types of lava?
Pahoehoe and A’a
What are the characteristics of pahoehoe lava?
Smooth, billowy surface, relatively thin
What are the characteristics of A’a lava?
Rough, jagged surface and thick lava
When lava solidifies, what does it form?
Igneous rock
What are the main gases that lead to acid rain?
Carbon Dioxide and Sulphur Dioxide
How can acid raid impact the environment?
Polluting waterways and soil, killing plants and trees, dissolving rock
What is ash made up of?
Fragments of pulverised rock, minerals and volcanic glass
How is ash formed?
When dissolved gases in magma expand and escape violently into the atmosphere in explosive eruptions
How fast can pyroclastic flows move?
700km/h
How do pyroclastic flows form?
Form collapse of an eruption column, colapse of lava domes, or ‘boiling over’
What are lahars triggered by?
Heavy rain or large amounts of ground water flowing through rocks as it causes the top layer of soil to be removed
How can tephra lead to a pyroclastic flow?
If the rock fragments are hot enough to fuse together
How can tephra cause a temperature drop?
If they reflect light and heat from the sun while in the atmosphere
What can form part of a nuees ardentes?
Pyroclastic flow
What attempted control was used on Mauna Loa in 1935?
Bombing lava tubes
How was Eldfell’s lava controlled on Heimay in 1973?
It was blasted with freezing sea water to cool it rapidly
How was Mount Etna controlled in 1983?
Barriers of rock and ash were constructed to divert the lava
How can volcanoes be monitored using geological observations?
A tiltmeter can be used to measure slope angle and bulges, and GPS to measure horizontal movements caused by expansion before an eruption
How can volcanoes be monitored using seismic activity?
Seismographs measure earthquakes around a volcano as it prepares to erupt
How can gas emissions be used to monitor volcanic activity?
As magma nears the surface and pressure decreases, gases escape. Sulphur dioxide is released as large amounts reach the surface, and concentrations can be measured
What is the main disadvantage of monitoring volcanoes using seismic activity?
Most volcanoes are on plate boundaries, so it can be difficult to distinguish between volcanic earthquakes and routine tremors
Formation of shield volcanoes
Plates move apart
Magma rises to surface, cools = new crust
Sea floor spreading
Layers built by eruptions
Sea floor spreading = plates move apart
Shield volcano example
Eyjafjallajokull, Iceland
Shield volcano characteristics
Gentle sloping sides
Wide base
Low viscosity lava - BASALTIC
Frequent, basic lava eruptions
Shield volcano explosivity
Low, as magma under little pressure
Composite volcano boundary
Destructive
Formation of composite volcanoes
Plates move towards eachother
Oceanic, denser, subducts
Beinoff Zone
Less dense molten material rises
Layers of ash and lava build
Composite volcano example
Montserrat
Composite volcano characteristics
Steep sided
Layers of ash, dust, lava
Viscous lava - RHYOLITIC
Long dormant periods
Composite volcano explosivity
High, as magma rises in plumes through fissures in buckled continental plate- high pressure
Volcanoes in rift valleys formation
Rising magma
Brittle continental crust buckles and fractures
= Fault lines
Plates move further apart
Crust between parallel faults drops down
= Rift Valley
Thin crust
Magma forces its’ way to the surface
Volcanoes at hotspots formation
Concentration of radioactive elements below crust
Plume of magma rises
Breaks through surface
Why do extinct volcanoes subside at hotspots?
As they have put so much pressure on the crust
Volcanic Explosivity Index
Volcanic Explosivity Index
VEI meaning
Logarithmic scale (0-8)
Measures height of eruption column and volume of tephra erupted
Disadvantages of VEI
Doesn’t consider climate impact
Ash, lava and lava bombs all treated alike
Icelandic Eruption
Basaltic lava flows gently from fissures
Highest and Lowest Categories on VEI?
Icelandic = lowest
Plinian = highest
Plinian Eruption
Highly explosive and violent, with tephra and pyroclastic fall out
Tephra Meaning
Solid material (ash-bombs) ejected into the atmosphere
Pyroclastic Flow / Nuees Ardentes Meaning
Fast moving current of hot gas and tephra
Up to 1000°c
Little warning = death and destruction
What are the secondary effects of pyroclastic flows?
Snow melt
Damming streams
What are the secondary effects of tephra?
Grounding air traffic
Destroy vegetation- famine
Improve soil fertility
What 4 factors affect the distance tephra travels?
Height of eruption column
Temperature of air
Wind speed
Wind direction
What 4 things are lava flows affected by?
Land steepness
Extrusion rate
Silica content
Flow temperature
What temperatures are lava flows between?
550°c - 1400°c
Why are lava flows not a big hazard?
Because of their slow speed
Mudflow / Lahar Meaning
Volcanic material + water (rainfall or ice melt)
What’s the difference between mudflows and lahars?
Lahars set like concrete
Name some of the gases released by a volcano
Water vapour
Carbon dioxide
Sulphur dioxide- acid rain
Where does CO2 seep through the volcano and kill plants?
Mammoth Mountain
Why are tiltmeters and GPS used to monitor volcanoes?
Measure slope angles
Indicates expanding magma chamber
Why are seismometers and seismographs used to monitor volcanoes?
Microquakes
Rising magma fractures overlying rock
Why are magnetometers used to monitor volcanoes?
Changing magnetism indicates rising iron-rich magma
Protection- Land Use Planning
Build houses away from high risk areas
Preparation- Why should there be good communication systems?
To alert and update people
Preparation- There should be suitable ____ put aside to deal with an emergency
Funds
Preparation- Residents in high risk areas…
Need evacuating
Preparation- What should an emergency supply kit contain? Where should it be placed?
Tinned food
Battery radio
Torch
Cash
Breathing mask
IN A CAR
Preparation- What should be included in a family emergency plan?
How to contact eachother
How to meet
What you will do in an emergency
East African Rift Valley
African plate
Splitting into Somali and Nubian
Created Kilimanjaro
3 ps
Prediction, protection and preparation
Bombing lava tubes
. In theory, bombs would destroy the lava tubes, ruining transport channel + exposing lava to air cooling it
. But in practice, while bombs created craters in parts of the tubes, they were soon filled again by the lava
What are lava tubes
Cooled and hardened outer crusts of lava which provide insulation for the faster-flowing, molten rock inside
Lava control: water
. Lava stoped in the 1970s on Haimey (Iceland)
. For five months in 1973, sea water was blasted through cannons towards the lava
. As water hit the superheated rock, it turned into steam, allowing the lava’s heat to dissipate
. But conditions were right and lava was slow moving
Lava control: build a barrier
. Mount Etna, in March 1983
. Barriers of rock and ash were constructed to divert the lava
. One of the first barriers, 18m high and 10m wide, was overrun, but a second barrier blocked lava from moving further west
Lahars
. Mixture of hot or cold water and rock fragmented which flow down the steep side of a volcano
. Grow as they travel picking up material
Eruption styles: Icelandic
. Low viscosity and highly effusive
. May have water therefore phreatic
. Lava flows gently from fissures
. Basaltic lava
Eruption styles: Hawaiian
. Effusive, minor explosivity, with fire fountain and low viscosity lava flow
. Lava flows gently from a central vent
. Basaltic lava
Eruption styles: Strombolian
. Eruption with gas bubbles so eject tephra
. Frequent explosions of tephra and steam
. Occasional, short lava flows
. Thicker basaltic magma
Eruption styles: Vulcanian
. Higher gas build up than Strombolian highly viscous lava
. A series of short lived explosions, with tephra including bombs, ash and gases
. Thicker basaltic, andestic and rhyolitic magma
Eruption styles: Pelean
. Explosive eruptions with range of tephra with nuee ardent (glowing cloud) pyroclastic flows
. Andesitic and rhyolitic magma
Eruption styles: Plinian
. Highly explosive, large eruption column (up to 45km) range of tephra and pyroclastic fallout, including flows
. Torrential rainstorms cause Lahars
. Rhyolitic magma
