Definitions Section 9.2

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

Pahoehoe: Solidified basaltic lava flow on land that has formed with smooth, ropelike surfaces Aa: Same as Pahoehoe except has rough, jagged surfaces

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

Pyroclastic material: solid rock fragments that are ejected during a volcanic eruption Pyroclastic flow: Dense, superheated cloud of gases and pyroclastic materials that moves rapidly downhill

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

Characteristics of Magma

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

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

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

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

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

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

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

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

Goofy but informational! Mt. Etna