✅HAZARDS 3.1.5.3 - Volcanic Hazards Flashcards
What are the characteristics of shield volcanoes?
Gentle slopes, wide base
Frequent eruptions, basic lava
High speed and low viscosity basaltic lava
Non-violent eruptions
Where are shield volcanoes found?
Constructive boundaries
What are the characteristics of composite volcanoes?
Steep sides, cone shape High with narrow base Explosive eruptions Layers of alternating ash and lava Secondary/parasitic cones
Where are composite volcanoes found?
Destructive boundaries
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 primary effects?
Occur immediately along with the event, as a result of it
What are secondary effects?
Direct consequence of the event but not immediate
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
How are gases released from magma?
As it rises to the surface and pressure decreases, gases are given off from the liquid portion
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
What impacts can ash have?
It can disrupt aviation, critical infrastructure eg electric power supply, and impact health
What is a pyroclastic flow?
A high density mix of hot lava blocks, pumice, ash and volcanic gas
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’
Why are pyroclastic flows considered the most dangerous of volcanic hazards?
Their speed makes them inescapable, and due to high temperatures, it is impossible to survive one
What is a lahar?
A moving mass of soils or mud made fluid by rain or snow moving down a steep slope
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
What are tephras?
Rock fragments and particles thrown into the air by volcanic eruptions
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 are nuees ardentes?
Clouds of gas ash and lava fragments ejected from the volcano
What can form part of a nuees ardentes?
Pyroclastic flow
What are the main volcanic gases?
Sulphur Dioxide, Carbon Dioxide, Hydrogen Flouride, Hydrogen Chloride, water vapour
How can volcanic gases have an impact?
Sulphur dioxide can cause acid rain and global cooling, Carbon Dioxide can cause global warming and Flourides can be lethal to animals
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 y 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
Magma type: Basaltic
Silica content: less than 50% (low viscosity/ very runny)
Forms Basalt
Magma Type: Andesitic
Silica: 50-70% (medium viscosity)
Forms Granite
Magma type: Rhyolitic
Silica: over 70% (high viscosity, not runny)
Forms Granite
Plinian/ Vesuvian Eruption Features, example
Mt. St. Helens 1980
High silica content (makes eruptions long, up to days, and less frequent)
Rhyolitic
Explosive
Big plume
Fast Lava
Vulcanian Eruption Features
All types of magma
Violent gas explosions
Very viscous lava
Clearing of a blocked vent, releases lots of ash
Katmai, Alaska
Icelandic/ Fissure Eruption Features
Lots of basaltic, from a fissure
At constructive boundaries
Such as Deccan Plateaux, India
Hawaiian Eruption Features
Basaltic, Lava very runny. Can form shield volcanoes when solidifies
Constructive
Generally not explosive
Strombolian Eruption Features
Basaltic magma
But viscous lava due to silica
Short bursts of thick lava
Constructive
Mt Etna (used to have vulcanian but change in pressure makes them strombolian now)
Stratovolcano (composite) Volcano features
Made of layers of ash and andesitic lava
Destructive margins
Explosive
Basic Shield Volcano
Gently sloping cone of basaltic Lava
constructive margins
Gentle Eruptions
Mauna Loa, Hawaii
Acid Dome Volcano
Steep- sided cone formed from Rhyolitic lava which can’t travel far solidifies in vents making explosive unpredictable eruptions
Destructive margins
Mt Pelee
Caldera volcano
Cauldron-shaped summit, can fill with water. E.g., Lake Nyos, Cameroon
Formed by gases built up beneath blocked vent
Big eruptions
Destructive margins
Fissure Volcano
Elongated spit
Basaltic Lava
Constructive margins, ocean ridges
Creates lots of plateaus due to fast flowing lava solidifying
Heimaey, Iceland
Active Volcano definition
Has had an Eruption in the last 10,000 years
Could still be dormant
Extinct Volcano definition
Hasn’t erupted in the last 10,000 years & isn’t expected to in comparable time scale
Features of Block lava flow
High acidity so doesn’t flow well. Forms block shapes
Features of A’a lava flows
More basaltic than block lava flows, so not as rough
Slow
Irregular
Features of Pahoehoe lava flows
Lower viscosity, flows further
Can form lava tubes/ caves due to far distance
When cools down becomes more viscous, can become A’a
Pillow Lava flows
Flows under water that have become solid rock, spherical shape.
