Volcanoes

Question 1

How many volcanic eruptions happen every year?

Answer 1

60

Question 2

Which two factors determine the shape of a volcano?

Answer 2

The amount of silica and the nature of the eruptions.

Parts of the volcano can be destroyed from a big exmplosion

Question 3

What is the viscosity of the lava?

Answer 3

Viscosity is the thickness of magma, largely determining an eruptions power and the shape of the volcano

Question 4

What 3 factors determine the viscosity of magma?

Answer 4

Temperature, Dissolved Gas and Chemisty

Question 5

How do Temperature, dissolved gas and chemistry determine magma viscosity?

Answer 5

Temperature - Higher temperature means lower density of magma
Dissolved gas - Greater the amount of dissolved gases, the more fluid the magma
Chemistry - Higher the silica content, the more viscous the magma.

Question 6

What are the two main types of magma?

Answer 6

Mafic Magma and Felsic Magma

Question 7

What is mafic Magma?

Answer 7

• Most Abundant
• Formed from meeting of material from the upper mantle, commonly occuring at hotpots and rifts. Upwelling mantle decreases pressure of the hot rock and causes partial melting.
• Low silica content (45%-52%)

Question 8

What is Felsic Magma?

Answer 8

• Forms froms the melting of an oceanic plate, meaning it has a different composition from baslatic lava.
• The rising of the melted plate causes continental rock near it to melt
• These mix together forming Felsic Magma

Question 9

What types of volcanoes and eruptions are found at divergent (and constructive) plate boundaries?

Answer 9

• Plate boundaries are moving away from each other
• Magma is produced by the partial melting of the mantle deep below the surface
• Volcanoes often erupt frequently, but not violently so have low viscosity lava.

Question 10

What type of volcanoes are found at convergent (and destructive) plate boundaries?

Answer 10

• Plate boundaries are moving towards each other
• One plate subducts whilst the intense pressures and heat cause melting of rocks and sediments
• This results in the form of an acidic magma chamber.
• The lava is viscous and resistant, eruptions are violent and dangerous involving ash and pyroclastics

Question 11

What scale is used to measure explosiveness of an eruption

Answer 11

The VEI scale - Volcano Explosivity Index

Question 12

What are the 8 stages of the VEI scale?

Answer 12

• Non explosive
• Gentle
• Explosive
• Severe
• Cataclysmic
• Paroxysmal
• Colossal
• Super Colossal
• Mega Colossal