1. How are volcanoes formed?
Lesson 25 – pages 21-22

2. Lesson Aims To learn how shield volcanoes form.
To learn how composite cone volcanoes form.
Key Skill = Communication

3. Rift Valleys

4. Shield Volcanoes Gentle slopes and wide base
Frequent eruptions of basic lava (Mount Elgon is now considered extinct)
Lava flows more easily, travels longer distances before cooling
Usually non-violent.
Layers are of similar basalt lava flows.
The basalt weathers to form a very fertile soil.
Shield Volcanoes

5. Shield Volcanoes Draw a labelled sketch of a shield volcano.
Describe its characteristics.
Explain its characteristics.

6. Composite Cone Volcano
Steep-sided cone shape
High with narrow base
Alternate layers of lava and ash
Lava may cool inside the vent - the next eruption is very explosive to remove the plug
Subsidiary cones and vents form.
Composite Cone Volcano

7. Composite Cone Volcano
Draw a labelled sketch of a Composite Cone volcano.
Describe its characteristics.
Explain its characteristics.