Volcanic Eruptions

Magma effecting the type of volcano - When magma erupts at the surface as lava, the type of volcano formed depends on: the viscosity (stickiness) of the magma, the volume of gas in the magma, the composition of the magma, the way magma reached the surface.

Effusive - A type of volcanic eruption where low-viscosity (runny) lava flows out of a volcano onto the ground, rather than being explosively ejected into the atmosphere.

Characteristics of a Divergent plate eruption - Low pressure High temperature High gas release Low heat transfer to the crust Highly effusive eruptions

Characteristics of a Convergent plate eruption

High pressure

Low temperature

Low gas release

Low heat transfer to crust

Highly explosive eruptions

Active Volcano Recent history of eruptions, likely to erupt again.

Dormant Volcano Hasn’t erupted in a long time but may do in the

future.

Extinct Volcano Not expected to erupt in the future.

Fissure Volcano

A gentle slope of basaltic

lava with low silica

content.

Shield Vocalno

Gentle slope of basaltic

lava flow, with a low silica

content.

Dome Volcano

Stepp convex slopes from

thick, fast cooling lava,

with a high silica content.

Ash Cinder Volcano

Fine ash released from a

cinder vent, with a low

silica content.

Composite Volcano

Also known as a

Stratovolcano, it releases

ash and lava with branch

pipes of the main vent.

They have a high silica

content.

Caldera Volcano

Multiple cones in a large

crater releasing ash and

magma with a high silica

content.

Explosive Eruptions

Can be catastrophic as it erupts between 10-

1000km3

of magma per eruption. They send ash

clouds more than 25km into the stratosphere.

These have severe environmental and climate

impacts whilst also very hazardous.

Stratovolcanoes Characteristics

Its Andesitic Magma is felsic (high silica content)

with a high viscosity meaning the magma is very

sticky and can’t flow very far. Despite having 30-

35o

slopes.

These are likely to cause explosive eruptions

which may form Caldera Volcanoes.

Shield Volcanoes Characteristics

Its Basaltic Magma is mafic (low silica content)

with a low viscosity meaning the magma is very

runny and can spread out. Has 10o

slopes.

They erupt frequently but not explosively.

Primary Impacts - Lava Flows

Destroy and bury everything in their path but

usually slow enough for people to avoid.

Pahoehoe (ropy/smooth) - Basaltic lava can flow

at 30km/hr

Aa Lava (blocky/rough) - Flow speed depends

on the silica content determining its viscosity.

Primary Impacts - Tephra

Fragments produced during a volcanic eruption.

Ash - <2mm diameter, miles travelled

destroying habitats and buildings.

Lapilli - 2-64mm diameter

Volcanic Bombs - >64mm diameter

Primary Impacts - Sulphur Dioxide

Ejected by volcanoes into the stratosphere

converts sulphuric acid and condenses into

sulphate aerosols. Aerosols increase the

radiation reflection from the sun cooling earths

Troposphere.

Primary Impacts - Volcanic Bombs

Mass of partially molten rock layer than 64mm,

formed when a volcano ejects viscous fragments

of lava during an eruption. Lava cools rapidly as

it passes through the air.

Types - Almond Bombs, Breadcrust Bombs, Twist

Bombs.

Primary Impacts - Flood Basalts

Huge areas of mafic basalt erupted during

fissure eruptions, and degassing of lava also

releases huge amounts of CO2

E.g. Deccan Traps, India, Covers an area of

500,000km

Primary Impacts - Pyroclastic Flows (Nuees

Ardentes)

Fast moving gas and rock called tephra,

travelling at speeds of up to 450mpjs and at

temperatures of about 1000oC.

Secondary Impacts - Lahars (Mudflow)