1. Volcanoes Objective: Identify how magma forms as a result of plate motion Explain why plate boundaries have volcanic activity

2. Volcano The opening in earths crust where molten rock, gases and ash erupt.

3. Magma Formation Magma: molten rock from deep within the earth that rises to the surface.

4. Magma Formation: 3 conditions Diverging boundary: Convection current, creates new crust Hot Spot: Magma from asthenosphere rises through crust, can create island chains Subduction: converging plates, strong volcanic activity, mountains and island arcs

5. Types of Magma Magma is mostly made of Silica Silica determines a magmas viscosity High silica = resistant to flow = Basaltic Low silica = flow easily = Andesitic

6. Types of Magma and Locations Basaltic Magma usually at hot spots and divergent boundaries. Andesitic magmas tend to form at subduction zones. Rhyolitic generally form where hot spots underlie continental plates.

7. Lava Flows Magma that reaches earth’s surface is called LAVA. Basaltic lava types: Pahoehoe: smooth, ropelike, fast moving flow AA: cooler basaltic flow, slow, rough, and jagged.

8. Types of Magma

9. Underwater Lava When lava cools underwater it forms a distinctive round shape. This is called Pillow Lava

10. Local Volcanoes Basalt Mountain: Shield Volcano formed 8.8 mya Triangle Mountain: Sill created from a fissure eruption 1.5 mya Lincoln Creek: Grizzly Caldera 35 mya Grizzly Andesite