1. Volcanoes

2. Let’s Talk Magma… Felsic Magma Mafic Magma High silica content Thick
Light colored
Slow moving
Mafic Magma
Low silica content
Thinner
Dark colored
Easy flow

3. Magma’s Journey
Magma rises from the asthenosphere to cracks in the lithosphere
On its way to the surface, decreasing pressure lets dissolved gases expand
Once on the surface, magma becomes LAVA (because previously dissolved gases have escaped to the atmosphere and new materials have been added, the chemical composition has changed)

4. Lava Fragments Tephra: solid fragments of lava
Ash: smallest pieces of tephra
Blocks: large pieces of tephra erupted as solids
Bombs: large pieces of tephra erupted as liquid (they harden as they fall)
Tephra + Gases = Superheated cloud

5. Types of Volcanoes Cinder Cones Shield Volcanoes Composite Volcanoes
Volcanic Domes

6. Shield Volcanoes
The common product of hotspots, but they can also be found along subduction-related volcanic arcs or all by themselves
Almost exclusively BASALT (which is very fluid when erupted)
Slow, steady, non-explosive flow gives it a shield-like shape
Magma mixes with only oceanic crust on the way to the surface
Lava has a LOW silica content (50%), so it has a LOW viscosity (resistance to flow)

7. Composite Volcanoes
Occur from the build-up of multiple eruptions that can be hundreds of years apart
Almost exclusively ANDESITE
Volcanologists call these "strato-" volcanoes because they consist of layers of solid lava flows mixed with layers of sand- or gravel-like volcanic rock called cinders or volcanic ash.
Magma mixes with oceanic (basalt) and continental (rhyolite) crust on the way to the surface
Lava has an intermediate silica content (60%), so…it moves at a medium pace

8. Volcanic Domes Highly explosive! Mainly RHYOLITE
Magma is typically too viscous to move far from the vent before cooling and crystallizing. So…they are very steep sided
Magma mixes only with continental crust on way to surface
Lava has a high silica content (70%) and moves slowly!