1. VOLCANOES & IGNEOUS ACTIVITY CHAPTER 10

2. Section 10.1

4. Origin of Magma  Magma is a complex mixture  Contains:  Partly melted minerals crystals  Dissolved gases  Water

5. MAKING MAGMA  Forms in crust and upper mantle.  Solid rock partially melts  Formation depends on 3 factors:  Increase the temperature (Heat the least important) (Heat the least important)  Decrease the pressure  Introduce water

6. HEAT  Sources of Heat 1.Friction  lithospheric plates slide past each other at subduction zones 2.Mantle Heat  Geothermal gradient – deeper you go, the hotter it gets. 3.Intrusion of hot mantle rock into cooler lithosphere  The least important of the three factors

7. PRESSURE  “Confining Pressure”  pressure increases w/depth  causes increase in melting temperature  DECOMPRESSION MELTING  Drop in “Confining Pressure”  as hot solid rock moves towards the surface it’s melting temperature is lowered, forming magma pockets  Commonly occurs at divergent plate boundaries

8. WATER CONTENT  WATER (VOLITILES) - lowers melting temperature of many minerals.  “wet” rock deep beneath the surface melts at a lower temperature than “dry” rock at same pressure  0.1% water can lower melting point of basalt up to 100°C  Occurs when wet ocean crust descends into subduction zones.

9. Assignment: Sec. 10.1 #1 What three factors affect how magma forms? #1 What three factors affect how magma forms? #2 Using the Graph on page 281 or your notes: What is the melting temperature of basalt at a depth of 7 km? of Granite? #2 Using the Graph on page 281 or your notes: What is the melting temperature of basalt at a depth of 7 km? of Granite? #3 How does higher water content affect rock’s melting point? #3 How does higher water content affect rock’s melting point? Vocabulary: Write the terms and their definitions from the list on page 280

10. Bellringer You have 5 minutes to answer the question on a sheet of paper and turn into the basket * How does magma form? Magma forms in the crust and upper mantle when solid rock partially melts. The formation of magma depends on several factors, including heat, pressure, and water content.

12. DISTRIBUTION OF IGNEOUS ACTIVITY  Divergent Plate Margin  Lithosphere pulls apart reducing pressure on underlying rock  Decompression melting occurs  basalt magma is produced and erupts along spreading ridges  Occurs at Mid-ocean ridges & rift valleys on the continents

13. DISTRIBUTION OF IGNEOUS ACTIVITY  Convergent Plate Margin  Subduction Zone  Descending plate partially melts at about 100-150 km deep due to:  Friction  Temperature, Pressure & water  Oceanic-Continental Plate Boundary  Continental Volcanic Arc forms along edges of Continent plate margins  Oceanic-Oceanic Plate Boundary  Volcanic island Arc forms in ocean at Ocean plate margins

14. DISTRIBUTION OF IGNEOUS ACTIVITY  Ring of Fire  Long belt of volcanoes that circle the Pacific Ocean

16. DISTRIBUTION OF IGNEOUS ACTIVITY  Intraplate Volcanism  Activity within a rigid plate  Basalt magma source  Partial melting of mantle rock rise as plumes of hot mantle material  Can occur in oceans and on continents  Ex: Yellowstone NP  “HOT SPOTS” –  small region of volcanic activity on the surface  40 known “Hot Spots”  Ex: Hawaiian Islands

17. YELLOWSTONE HOT SPOT

18. Bellringer You have 5 minutes to answer the question on a sheet of paper and turn into the basket * What is the relationship between plate boundaries and volcanic activity? Most volcanoes form along convergent and divergent plate boundaries. Some volcanoes form far from plate boundaries above “hot spots” in the crust.

19. Assignment: Sec. 10.1 #1 How are the locations of volcanoes related to plate boundaries? #1 How are the locations of volcanoes related to plate boundaries? #2 What causes intraplate volcanism? #2 What causes intraplate volcanism? #3 What is the Ring of Fire? #3 What is the Ring of Fire? #4 How is magma formed through decompression melting? #4 How is magma formed through decompression melting? #5 What process formed the volcanoes of the Andes? #5 What process formed the volcanoes of the Andes?