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 Eruption

1. 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 Eruptions

1. Can be 1000 times more powerful than atomic bomb

2. Pressure builds as gases in magma expand

Explosive Eruptions

1. Explosion shoots ash and gas high in the air

2. Heavy debris falls; light debris may float around for years

3. 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 Eruptions

1. Some magma crystallizes in the air

2. Called pyroclastic material: ash, lapilli, bomb

3. Can come down miles from the volcano

Non-explosive eruptions

1. Another name for non-explosive eruptions

a)Effusive eruptions

2. Different mix of minerals in magma

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

are consistent and unstoppable

Magma Formation

1. What causes magma to forma) High heat

i. Hot Spots; effusive

b) Decreased pressurei. Divergent boundaries; effusive

c) Increased water contenti. Subduction zones; explosive

Lava - Viscosity

1. Viscosity: Resistance to flowa) Honey, ketchup, water

2. High viscositya) High silica contentb)Explosive eruptions pressure

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

pressure

Lava formations

1.Explosive lava Pyroclastic material

a) Pyroclast – lava solidifies in the atmosphere

b)Pyroclastic flow – fast moving current of superheated gas and rock

i. 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 Eruptions

1.History of eruptiona)Active, dormant, extinct

2.Earthquakesa)Pressure of magma causes

earthquakes

3.Slope deformationa) Plastic deformation due to pressure

4.Gas emissionsa) Gas escapes before magma

5. Remote Monitoring