8.2 VOLCANIC ERUPTIONS

Where the rock cycle begins

Learning Targets

1. Compare the types of volcanic eruptions

2. Describe a method for predicting volcanic eruptions

Volcanic Eruption1. Magma collects in magma chamber2. Hot magma expands creates

pressure3.Vent: crack in the earth’s surface4. Magma moving through vent =

eruption

How do volcanoes erupt?1. Types of eruptions:

a)Explosiveb) Non-explosive; effusive

Explosive Eruptions1. Can be 1000 times more

powerful than atomic bomb

2. Pressure builds as gases in magma expand

Explosive Eruptions1. Explosion shoots ash and gas

high in the air2. Heavy debris falls; light debris

may float around for years3. Why is ash and gas in the air

important?a) Blocks sunlight, produces poisonous

gas, mixes with water to form acid, global climate change

Explosive Eruptions1. Some magma crystallizes in the

air2. Called pyroclastic material:

ash, lapilli, bomb

3. Can come down miles from the volcano

Non-explosive eruptions1. Another name for non-explosive

eruptionsa)Effusive eruptions

2. Different mix of minerals in magma

3.No gas build up4. Less dangerous but lava flows

are consistent and unstoppable

Magma Formation1. What causes magma to form

a) High heati. Hot Spots; effusive

b) Decreased pressurei. Divergent boundaries; effusive

c) Increased water contenti. Subduction zones; explosive

Lava - Viscosity1. Viscosity: Resistance to flow

a) Honey, ketchup, water2. High viscosity

a) High silica contentb)Explosive eruptions pressure

3. Low viscositya) Low silica contentb)Effusive eruptions no

pressure

Lava formations1.Explosive lava Pyroclastic

materiala) Pyroclast – lava solidifies in the

atmosphereb)Pyroclastic flow – fast moving

current of superheated gas and rocki. Can move hundreds of miles per hour

2.Effusive lavaa) A’a: jagged, gravelly textureb) Pahoehoe: smooth, even lava flowc) Pillow lava: cools underwater forms rounded

lobes

Predicting Eruptions1.History of eruption

a)Active, dormant, extinct2.Earthquakes

a)Pressure of magma causes earthquakes

3.Slope deformationa) Plastic deformation due to pressure

4.Gas emissionsa) Gas escapes before magma

5. Remote Monitoring