9.2 Magma and Erupted Materials

1. 9.2 Magma and Erupted Materials Purpose: After completing this lesson we learn what materials erupt from volcanoes.

2. Types of Magma • Magma is molten rock. The main “ingredient” in rocks is a mineral named silica (SiO2); besides silica, there are many other minerals. • Magma also contains significant amounts of fluids dissolved in the molten rock: water vapors and carbon dioxide are most common • Silica, however, is the one that determines the type of magma in every igneous activity. • Silica determines the viscosity (resistance to flow) of magma as well.

3. Types of Magma • There are three types of magma, depending on the content of silica: 1. Basaltic 2. Andesitic 3. Rhyolitic

4. Basaltic Magma Some characteristics of basaltic magma are: • it has about 50% silica • has a small amount of gases dissolved • flows easily (least viscous) • the eruption is rarely explosive • it has the highest melting point (>1300 C degrees)

5. Basaltic Eruption • Lava flows easily, due to reduced viscosity

6. Andesitic Magma • contains about 60% silica • Has a moderate amount of gasses • Sometimes it generates explosive eruptions • The melting temperature is around 1000 C degrees

7. Andesitic Eruption • This is an explosive eruption

8. Rhyolithic Magma • Contains most silica ( over 70%) • Contains a significant amount of dissolved gasses • It has a high viscosity (flows very slowly) • The eruptions are usually explosive and create tremendous damage. • The melting point is below 900C degrees.

9. Rhyolithic Eruption • This type is highly explosive

10. Location of Each Type of Magma Each type pf magma form in certain areas: • Basaltic magma is found at rifts and hotspots • Andesitic magma is found at subduction boundaries • Rhyolitic magma is found at continental hot spots.

11. Magma versus Lava • Magma is the molten material that rises from the deep. It contains a significant amount of volatile compounds; water vapors and CO2 are most common. As the magma reaches the surface of the earth, it loses very quickly the volatiles, because of the difference in pressure. (Shake a can of soda and open it quickly; the fizz is nothing else but the CO2 which is released from the liquid) • Lava is magma which has lost most of its volatile components. Lava has temperatures between 700 and 1200 C degrees.

12. Other Volcanic Products • Lava is the main product that is released from a volcano. • Pyroclastic materials (“pyro” means hot and “clast” means fragment in Greek). These are hot, solid materials of different sizes. Sometimes the lava cools down on the pipe, creating a plug; the magma is climbing up the pipe at great pressures, and breaks apart this plug, creating fragments of different sizes. • The most common pyroclastic materials are: -volcanic ashes (the particles have less than 2 mm in diameter) -lapilli- pebbles with diameters between 2-64 mm - bombs or blocks, are fragments larger than 64 mm

13. Types of Lava Flow • Pahoehoe is lava with smooth, ropelike surfaces.

14. Pillow Lava • Lava that cools under water has a rounded, pillow like form.

15. Aa • Aa is lava that cools quickly with a rough, jagged surface.