1. Volcano and Mountain Activities

2. What is a volcano?
A mountain formed of lava and or pyroclastic material

3. Factors Affecting Eruption
The primary factor that determines whether a volcano erupts violently or quietly include magma composition, magma temperature, and the amount of dissolved gases in the magma

4. Viscosity Dissolved Gases Is a substance’s resistance to flow
Hotter the magma, more fluid and less viscous
Directly related to its silica content (more silica, greater its viscosity)
Dissolved Gases
Water vapor and carbon dioxide
More gases, the more violent the eruption

5. Volcanic Materials Lava Flow
Pahoehoe: lava flow resembles the twisted braids in ropes
Aa: lava flow that has a surface of rough, jagged blocks with dangerously sharp edges and spiny projections

6. Gases Pyroclastic material Fragments ejected during eruptions
70% water vapor
15% carbon dioxide
5% nitrogen
5% sulfur
Pyroclastic material
Fragments ejected during eruptions
Varies in size from very fine and volcanic ash to pieces that weigh several tons

7. Composite Cone or Stratovolcano
Types of Volcanoes
Type
Description
Picture
Shield
Broad, slightly domed
Produced by the accumulation of lava flow
Ex: Hawaiian Island
Cinder Cone
Small volcano built primarily of pyroclastic material ejected from a single vent
Determined by a steep-sided slope
Composite Cone or Stratovolcano
Large, nearly symmetrical structure composed of layers of both lava and pyroclastic deposits
Most dangerous
Explosive Eruptions

8. Pyroclastic Flow Lahar
Consist of hot gases, glowing ash, and larger rock fragments racing down the steep slope
Lahar
Mudflow that occurs when volcanic debris becomes saturated with water and rapidly moves down steep volcanic slopes