Lecture 8 - After the Eruption Flashcards
What is Ash Fall?
-Rain of volcanic ash (microscopic glass shards)
-Can occur miles from the volcano
-Severity depends on the the thickness of the layer and grain size
What are the Effects of Ash Fall on Humans?
-Can be irritating or deadly
-Small particles (<4micrometres) can be breathed into the base of the lungs
-Ash and water in the lungs forms a concrete which causes chronic respiratory problems (Pneumonoultramicroscopicsilicovolcanoconiosis)
What are the Effects of Ash Fall on Plants?
-Ash cloud can block out the sun for days to years
-Ash covering leaves reduced ability to photosynthesise
-Plants die which has a cascade effect on surrounding ecosystems
What are the Effects of Ash Fall on Buildings?
-Layers of ash covers roofs
-10cm of dry ash weighs 50kg
-Wet ash is even heavier causing roofs to collapse
-Rain is also made more possible after an eruption as ash causes water vapour to condense into droplets
What are the Effects of Ash Fall on Electrical Systems?
-Wet volcanic ash is conductive
-This shorts electrical systems and damages powerlines
What are the Effects of Ash Fall on Air Travel?
-BA flight from Heathrow to Auckland
-Flew through volcanic ash south of Jakarta from mount Galunggung eruption in 1982
-Ash scratched the windows so pilots couldn’t see and caused all 3 engines to seize up
What is St Elmos Fire?
-Type of volcanic lightning
-Caused by ionisation of the air around sharp objects in a strong electrical field
-Nitrogen and oxygen in the atmosphere cause blue fluorescence
-The electrical field is formed by static build-up in the volcanic ash cloud
What is a Lahar?
-Volcanic mudlfow
-Made of water, ash, pyroclastic material and rock
-Consistency is similar to wet concrete which solidifies when it stops
-Can travel 10s of metres per second
-E.g. Nevado Del Ruiz lahar 1985 (killed 23,000 and buried the city of Armero)
What causes a Lahar?
-Melting snow or glaciers in contact with lava/ pyroclastic material
-Rainfall on ash deposits after an eruption
-Breakout of a crate lake
-Can form during the eruption or several months afterwards
How is a Caldera Formed?
-Magma chamber below volcano empties
-The void can no longer support the roof of rock above
-This rock falls into the hole left behind by the erupted magma
-A caldera (meaning cauldron) is formed
How do Sulphurous Gasses affect the World after an Eruption?
-Laki Iceland eruption in the 18th century covered Europe in a cloud of sulphurous gas
-Around 300,000 died
-It mixed with fog to form acid rain, and persistent fog
-This caused leaves and fruit to drop off trees, and breathing problems and heart palpitations for many people
How do Volcanic Eruptions Change the Climate?
-If enough SO2 is released into the upper atmosphere, albedo is increased (sunlight is reflected into space)
-E.g. Kraktau and Lake Toba eruptions
How do Volcanoes Erode?
-Volcanoes are very weak structures
-The shape is maintained by volcanic activity
-Once this volcanism stops, it rapidly erodes and eventually only the plug remains
