2. Eruptions Earth science near the end .pptx

Eruptions Earth science

1. Chapter 18 Section 2 & 3 Earth Science

2. How does magma type influence volcanic activity?

3. How are features formed from magma that solidified under Earth’s surface described?

4. Eruptions Copyright © McGraw-Hill Education Making Magma A volcano’s explosivity depends on the composition of the magma. Lava from an eruption can be thin and runny or thick and lumpy.

5. Eruptions Copyright © McGraw-Hill Education Making Magma Temperature Depending on their composition, most rocks begin to melt at temperatures between 800°C and 1200°C. In addition to temperature, pressure and the presence of water and dissolved gases also affect the formation of magma.

6. Eruptions Copyright © McGraw-Hill Education Making Magma Pressure Pressure increases with depth because of the weight of overlying rocks. As pressure increases, the temperature at which a substance melts also increases, which explains why most of the rocks in Earth’s lower crust and upper mantle do not melt.

7. Eruptions Copyright © McGraw-Hill Education Composition of Magma The composition of magma determines a volcano’s explosivity, which is how it erupts and how its lava flows. Understanding the factors that determine the behavior of magma can aid scientists in predicting the eruptive style of volcanoes.

8. Eruptions Copyright © McGraw-Hill Education Composition of Magma Dissolved gases In general, as the amount of gases in magma increases, the magma’s explosivity also increases. Important gases in magma are water vapor, carbon dioxide, sulfur dioxide, and hydrogen sulfide.

9. Eruptions Copyright © McGraw-Hill Education Composition of Magma Dissolved gases Minerals in the mantle, such as albite , melt at high temperatures. The presence of dissolved water vapor lowers the melting temperature of minerals, causing mantle material to melt into magma.

10. Eruptions Copyright © McGraw-Hill Education Composition of Magma Viscosity The physical property that describes a material’s resistance to flow is called viscosity . Temperature and silica content affect the viscosity of a magma.

11. Eruptions Copyright © McGraw-Hill Education Types of Magma The silica content of magma determines not only its explosivity and viscosity, but also which type of volcanic rock it forms as lava cools.

12. Copyright © McGraw-Hill Education Eruptions Types of Magma Basaltic magma When rock in the upper mantle melts, basaltic magma typically forms. Basaltic magma contains less than 50 percent silica. Its low silica content produces low-viscosity magma. The resulting volcano is characterized by quiet eruptions.

13. Copyright © McGraw-Hill Education Eruptions

14. Copyright © McGraw-Hill Education Eruptions Types of Magma Andesitic magma Andesitic magma is 50 to 60 percent silica and is found along oceanic-continental subduction zones. The source material for this magma can be either oceanic crust or oceanic sediments.

15. Copyright © McGraw-Hill Education Eruptions Types of Magma Andesitic magma The higher silica content of Andesitic magma results in a magma that has intermediate viscosity. Thus, the volcanoes it fuels are said to have intermediate explosivity.

16. Copyright © McGraw-Hill Education Eruptions Types of Magma Rhyolitic magma When molten material rises and mixes with the overlying continental crust rich in silica and water, it forms rhyolitic magma. Rhyolitic magma contains more than 60 percent silica .

17. Copyright © McGraw-Hill Education Eruptions Types of Magma Rhyolitic magma High viscosity, along with the large volume of gas trapped within rhyolitic magma, makes the volcanoes fueled by this magma very explosive.

18. Copyright © McGraw-Hill Education Eruptions Visualizing Eruptions As magma rises due to plate tectonics and hot spots, it mixes with Earth’s crust. This mixing causes differences in the temperature , silica content, and gas content of magma as it reaches Earth’s surface. These properties of magma determine how volcanoes erupt.

19. Copyright © McGraw-Hill Education Eruptions Explosive Eruptions When lava is too viscous to flow freely from the vent, pressure builds up in the lava until the volcano explodes, throwing lava and rock into the air. The erupted materials are called tephra .

20. Copyright © McGraw-Hill Education Eruptions Explosive Eruptions Tephra are classified by size. The smallest fragments, with diameters less than 2 mm, are called ash. The largest tephra thrown from a volcano are called blocks .

21. Copyright © McGraw-Hill Education Eruptions Pyroclastic Flows Violent volcanic eruptions can send clouds of ash and other tephra down a slope at speeds of about 80 km/h. Rapidly moving clouds of tephra mixed with hot, suffocating gases are called pyroclastic flows .

22. Copyright © McGraw-Hill Education Eruptions Pyroclastic Flows In 1902, a pyroclastic flow from Mount Pelée on the island of Martinique in the Caribbean Sea was so powerful that it destroyed the entire town of St. Pierre in only a few minutes.

23. Intrusive Activity Copyright © McGraw-Hill Education Plutons Most of Earth’s volcanism happens below the surface because not all magma emerges at the surface. Before it gets to the surface, rising magma can interact with the crust in several ways.

24. Intrusive Activity Copyright © McGraw-Hill Education Plutons Magma can force the overlying rock apart and enter the newly formed fissures. Magma can cause blocks of rock to break off and sink into the magma. It can melt its way through the rock into which it intrudes.

25. Intrusive Activity Copyright © McGraw-Hill Education Plutons Plutons are intrusive igneous rock bodies, formed through mountain-building processes and oceanic-oceanic collisions. They can be exposed at Earth’s surface due to uplift and erosion and are classified based on their size, shape, and relationship to surrounding rocks.

26. Intrusive Activity Copyright © McGraw-Hill Education Plutons Batholiths and stocks Batholiths , the largest plutons, are irregularly shaped masses of coarse-grained igneous rocks that cover at least 100 km 2 and take millions of years to form. Batholiths are common in the interior of mountains.

27. Intrusive Activity Copyright © McGraw-Hill Education Plutons Batholiths and stocks Irregularly shaped plutons that are similar to batholiths but smaller in size are called stocks . Both batholiths and stocks cut across older rocks and generally form 5 to 30 km beneath Earth’s surface.

28. Intrusive Activity Copyright © McGraw-Hill Education Plutons Laccoliths A laccolith is a lens-shaped pluton with a round top and flat bottom. Compared to batholiths and stocks, laccoliths are relatively small; at most, they are 16 km wide.

29. Intrusive Activity Copyright © McGraw-Hill Education Plutons Sills A sill forms when magma intrudes parallel to layers of rock. Because it takes great amounts of force to lift entire layers of rock, most sills form relatively close to the surface.

30. Intrusive Activity Copyright © McGraw-Hill Education Plutons Dikes A dike is a pluton that cuts across preexisting rocks and often forms when magma invades cracks in surrounding rock bodies. A volcanic neck occurs when the magma in a volcano conduit solidifies. Dikes are often associated with the conduit but do not always form the neck.

31. Intrusive Activity Copyright © McGraw-Hill Education Plutons Dikes The coarse-grained texture of most sills and dikes suggests that they formed deep in Earth’s crust, where magma cooled slowly enough for large mineral grains to develop. Dikes and sills with a fine-grained texture formed closer to the surface where many crystals began growing at the same time.

32. Intrusive Activity Copyright © McGraw-Hill Education Plutons and Tectonics Many plutons form as the result of mountain-building processes. In fact, batholiths are found at the cores of many of Earth’s mountain ranges.

33. Intrusive Activity Copyright © McGraw-Hill Education Plutons and Tectonics Scientists think that some of the collisions along continental-continental convergent plate boundaries might have forced continental crust down into the upper mantle where it melted, intruded into the overlying rocks, and eventually cooled to form batholiths.

34. Intrusive Activity Copyright © McGraw-Hill Education Plutons and Tectonics Plutons are also thought to form as a result of oceanic plate convergence. When an oceanic plate converges with another plate, water from the subducted plate causes the overlying mantle to melt. Plutons often form when the melted material rises but does not erupt at the surface.

35. Lets make some Volcanoes Cut the top off a small paper cup to make it 2.5 cm tall. Put the cup in the middle of a piece of graph paper and trace around it. Tape the cup onto cardboard. Mark north, south, east, and west on the cardboard and graph paper. Fill a large cup halfway with baking soda. Put a spoonful of baking soda in the small cup. Pour vinegar into another large cup. Slowly pour vinegar into the small cup to make an eruption. When the eruption stops, trace around the lava with a pencil. Clean up the spill with paper towels. Cover the area with play dough. Draw the lava flow on graph paper with a matching colored pencil. Repeat steps 6-12 for each color of play dough. You can clean the small cup between eruptions. If you run out of time, cover the volcanoes with plastic wrap and continue the next day.

36. Homework Read Chapter 19 Quiz Due on the 19 th Before You Leave!! Hand ins: Weekly Questions Lab Worksheet