Plate Tectonics- Vulcanicity

Eruptions at Constructive and Destructive Plate Margins

	Constructive plate margin	Destructive plate margin
Type of magma	Basalt to Andesite	Andesite to Rhyolite
Lava Characteristics	·         Runny ·         Low silica content	·         Slow flowing, very viscous ·         High silica content
Type of eruption	Little violence, gases can easily escape due to not plug	Potentially explosive, as lava blocks up the main vent forming a plug, causing lava to shatter into pieces
Materials erupted	Mainly lava	Lava bombs, ash, dust
Frequency of eruption time	Regular and can be continuous	From time to time, long dormant periods
From of the volcano	Lava Plateau, Shield Volcano	Acid lava dome, composite come

 

There are three main types of magma:

• Basaltic Magma: constructive boundaries - low viscosity, slow cooling, low gas content - shield volcanoes - gentle eruptions

• Andesitic Magma and Rhyolitic Magma: destructive boundaries - high viscosity, fast to solidify, high gas content -composite volcanoes - explosive eruptions - full of impurities from subduction of plate

And two main types of lava:

• Pahoehoe: rope like surface due to partial cooling 
• Aa: block, rough lava flow

Volcanic impacts

Primary effects include:

• Tephra­- solid material, ranging from volcanic bombs to ash particles ejected into the atmosphere
•  Pyroclastic flows- very hot, gas-charged materials (gas and tephra)
• Lava
• Volcanic gases- carbon dioxide, carbon monoxide, hydrogen sulphide, sulphur dioxide and chlorine

Secondary effects include:

• Lahars- volcanic mud flows
• Flooding- due to melting ice caps and glaciers
• Tsunamis- giant sea waves generated by caldera-forming events such as the explosion of Krakatoa
• Volcanic landsides
• Climate change- brought about by the injection of vast amounts of debris into the atmosphere, which can reduce global temperatures