1. WARM UP!!! Thursday 1/31/08 Describe a magma chamber!

2. Types of Volcanic Eruptions

3. Why do volcanoes erupt? Magma rises to the surface because it is LESS DENSE than the surrounding rock. Gases and magma build up inside the volcano and eventually erupts.

4. Parts of a Volcano… This diagram is located on pg. 185 in your textbook. It would be a good idea to use the book to find out the information about each part!

5. Characteristics of Magma Temperature: –Hotter = Less Viscous (thinner) – Cooler = More Viscous (thicker) Silica Content: –Low Silica = Less Viscous (thinner) –High Silica = More Viscous (thicker) The thicker the magma, the more explosive the eruption!

6. Types of Eruptions 1.Quiet 2.Violent

7. Quiet Eruptions Runny lava oozes from volcano vents Ex. Iceland and Hawaii Produce two types of lava: –Pahoehoe: FAST and HOT –Aa: SLOW and COOL

8. Violent Eruptions Thick and sticky magma plugs vents like a cork. Pressure builds up and eventually explodes. Pieces of lava/rock create a pyroclastic flow of ash, cinders, and bombs. 1.Ash = small pieces 2.Cinders = medium pieces 3.Bombs = large pieces

9. Mount St. Helens BEFORE the eruption…(1980)

10. Mount St. Helens DURING the VIOLENT eruption… Pyroclastic Flow

11. Mount St. Helens AFTER the eruption…

12. Stages of Volcanoes Active: Can erupt at any moment Dormant: May awaken and become active. There is magma still underneath it. Extinct: Unlikely to erupt again. No longer has magma underneath it.