1. Homework Metamorphic rock lab due Monday Read section 9.3
Q’s 1-4 on pg 201

2. Definitions
Section 9.2

3. Magma and Erupted Materials
Viscosity: A substance’s resistance to flow (high viscosity = honey, low = water)
Lava: Magma that reaches Earth’s surface

4. Pahoehoe: Solidified basaltic lava flow on land that has formed with smooth, ropelike surfaces
Aa: A solidified basaltic lava flow on land that has formed with rough, jagged surfaces

5. Lahar: a fast-moving mudflow that occurs when heat of a volcano melts the snow and ice on top of a volcano
Pillow Lava: Lava that cools underwater, taking on a distinctive pillow-like shape as it hardens

6. Pyroclastic material: solid rock fragments that are ejected during a volcanic eruption
Pyroclastic flow: A dense, superheated cloud of gases and pyroclastic materials that moves rapidly downhill from an eruption volcano

8. Felsic and Mafic Magmas
Felsic (Feldspar Silica) magma: high silica, low density, light-colored, slow moving and typically come out of explosive volcanoes
Mafic (Magnesium ferric) magma: low silica, high density, more fluid, darker in color and flow more easily. Usually flows smoothly onto the surface

9. Characteristics of Magma

10. Please copy this chart in your notes
Basaltic Magma
Andesitic Magma
Rhyolitic Magma
Silica Content
Gas Content
Viscosity
Type of Eruption
Melting Temp.
Location
Example

11. Silica Content Least (~50%) Intermediate (~60%) Most (~70%)
Basaltic Magma
Andesitic Magma
Rhyolitic Magma
Silica Content
Least (~50%)
Intermediate (~60%)
Most (~70%)
Gas Content
Viscosity
Type of Eruption
Melting Temp.
Location
Example

12. Gas Content Least Intermediate Most Basaltic Magma Andesitic Magma
Rhyolitic Magma
Silica Content
Least (~50%)
Intermediate (~60%)
Most (~70%)
Gas Content
Least
Intermediate
Most
Viscosity
Type of Eruption
Melting Temp.
Location
Example

13. Viscosity Least viscous Most viscous Basaltic Magma Andesitic Magma
Rhyolitic Magma
Silica Content
Least (~50%)
Intermediate (~60%)
Most (~70%)
Gas Content
Least
Intermediate
Most
Viscosity
Least viscous
Most viscous
Type of Eruption
Melting Temp.
Location
Example

14. Type of Eruption Rarely explosive Sometimes explosive
Basaltic Magma
Andesitic Magma
Rhyolitic Magma
Silica Content
Least (~50%)
Intermediate (~60%)
Most (~70%)
Gas Content
Least
Intermediate
Most
Viscosity
Least viscous
Most viscous
Type of Eruption
Rarely explosive
Sometimes explosive
Usually explosive
Melting Temp.
Location
Example

15. Melting Temp. Highest Lowest Basaltic Magma Andesitic Magma
Rhyolitic Magma
Silica Content
Least (~50%)
Intermediate (~60%)
Most (~70%)
Gas Content
Least
Intermediate
Most
Viscosity
Least viscous
Most viscous
Type of Eruption
Rarely explosive
Sometimes explosive
Usually explosive
Melting Temp.
Highest
Lowest
Location
Example

16. Rifts, oceanic hot spots Subduction Boundaries Continental hot spots
Basaltic Magma
Andesitic Magma
Rhyolitic Magma
Silica Content
Least (~50%)
Intermediate (~60%)
Most (~70%)
Gas Content
Least
Intermediate
Most
Viscosity
Least viscous
Most viscous
Type of Eruption
Rarely explosive
Sometimes explosive
Usually explosive
Melting Temp.
Highest
Lowest
Location
Rifts, oceanic hot spots
Subduction Boundaries
Continental hot spots
Example

17. Mount St. Helens, Washington Yellowstone caldera, Wyoming
Basaltic Magma
Andesitic Magma
Rhyolitic Magma
Silica Content
Least (~50%)
Intermediate (~60%)
Most (~70%)
Gas Content
Least
Intermediate
Most
Viscosity
Least viscous
Most viscous
Type of Eruption
Rarely explosive
Sometimes explosive
Usually explosive
Melting Temp.
Highest
Lowest
Location
Rifts, oceanic hot spots
Subduction Boundaries
Continental hot spots
Example
Kilauea, Hawaii
Mount St. Helens, Washington
Yellowstone caldera, Wyoming

18. Goofy but informational! Mt. Etna