1. Chapter 18 - Volcanic Activity

2. Types of Magma
The 3 main types of magma are andesitic, basaltic, and rhyolitic
Basaltic has the same composition as basalt
Hawaii and Iceland are examples of these
Rhyolitic is used to describe the magma that solidifies to form granite
Andesitic has the same composition od andesite
Mount St. Helens is an example of this

3. Magma Composition
There are number of factors that determine type of magma
One is viscosity – the internal resistance to flow

4. Basaltic Magma
This normally forms when rocks in the upper mantle melt and has a low viscosity – flows easier

6. Andesitic Magma
This is found along continental margins, where oceanic crust is subducted into Earth’s mantle
Has intermediate viscosity

7. Rhyolitic Viscosity
Forms when molten materials rises and mixes with the overlying crust
This has a high viscosity

11. Viscosity
The viscosity of magma and lava depend upon both temp and composition
The hotter the magma, the lower the viscosity
The amount of silica increases the viscosity