Science ~ chapter 6 volcanoes

1. Science ~ chapter 6volcanoes Miss Nelson

2. Section 3 Volcanic Landforms

3. Anticipatory set When you picture a volcano, what shape is it? Are all volcanoes shaped this way?

4. standards S 6.1.f – Students know how to explain major features of California geology in terms of plate tectonics S 6.7.g – Interpret events by sequence and time from natural phenomena

5. The big idea What landforms do lava and ash create? How does magma that hardens beneath the surface create landforms?

6. Key terms • Sheild volcano – a wide, gently sloping mountain made of layers of lava; formed by quiet eruptions • Cinder cone – a steep, cone-shaped hill or small mountain made of volcanic ash, cinders, and bombs • Composite volcano – a tall, cone-shaped mountain in which layers of lava and ash alternate • Caldera – the large hole at the top of a volcano formed when the roof of a magma chamber collapses

7. Key terms • Volcanic neck – hardened magma in a volcano’s pipe • Dike – a slab of volcanic rock formed when magma forces itself across rock layers • Sill – a slab of volcanic rock formed when magma squeezes between layers of rock • Intrusion – an igneous rock layer formed when magma hardens beneath Earth’s surface • Batholith – a mass of rock formed when a large body of magma cools inside the crust

8. Volcanic eruptions Read “Volcanic Landforms” on page 229 of your textbook

9. Landforms from lava and ash Volcanic eruptions create landforms made of lava, ash, and other materials Include shield volcanoes, cinder cone volcanoes, composite volcanoes, and lava plateaus

10. Shield volcanoes • At some places on Earth’s surface, thin layers of lava pour out of a vent and harden on top of previous layers • These gradually build a wide, gently sloping mountain called a shield volcano • Shield volcanoes created the Hawaiian Islands

11. Cinder cone volcanoes • If a volcano’s lava is high in silica, it may produce: • Ash • Cinders • Bombs • These materials build up around the vent in a steep, cone-shaped hill or small mountain called a cinder cone

12. Composite volcanoes • Sometimes lava flows alternate with explosive eruptions of ash, cinder, and bombs • The result is a composite volcano • Tall, cone-shaped mountains in which layers of lava alternate with layers of ash • Examples: • Mount Fuji in Japan • Mount Shasta in California

13. Lava plateaus • Some eruptions form high, level areas called lava plateaus • First, lava flows out of several long cracks or fissures • Then, thin/runny lava travels far before cooling and solidifying • This happens over and over again • After millions of years, these layers form high plateaus

14. calderas • The huge hole left by the collapse of a volcanic mountain is called a caldera • Filled with pieces of volcano that have fallen inward, as well as some lava and ash • Form when enormous eruptions empty the main vent and the magma chamber becomes a hollow shell • With nothing to support it, the top of the mountain collapses View figure 13 on page 232 of your textbook

15. Soils from lava and ash • People often settle close to volcanoes to take advantage of the fertile volcanic soil • Over time, the hard surface of the lava breaks down to form soil • As it breaks down, it releases potassium, phosphorus, and other substances that plants need • Some volcanic soils are among the richest soils in the world

16. Landforms from magma • Sometimes magma forces its way through cracks in the upper crust, but fails to reach the surface • The magma cools and hardens into rock • Over time, the forces that wear away Earth’s surface (wind, flowing water, ice) may strip away the layers above the hardened magma and finally expose it

17. Landforms from magma Features formed by magma include volcanic necks, dikes, sills, and batholiths

18. Volcanic necks • A volcanic neck looks like a giant tooth stuck in the ground • Forms when magma hardens in a volcano’s pipe • The softer rock around the pipe wears away, exposing the hard rock of the volcanic neck

19. Dikes and sills • Magma can force its way across or between rock layers • Magma that forces itself across rock layers hardens into a dike • When magma squeezes between horizontal layers of rock, it forms a sill • Dikes and sills are examples of igneous intrusions • An intrusion is always younger than the rocks around it

20. batholiths • Form the core of many mountain ranges • Mass of rock formed when a large body of magma cools inside the crust

21. Check for understanding What are the three main types of volcanoes? What features form as a result of magma hardening beneath Earth’s surface?

22. Check for understanding What are the three main types of volcanoes? The three main types of volcanoes are shield, cinder cone, and composite. What features form as a result of magma hardening beneath Earth’s surface?The features that form as a result of magma hardening beneath Earth’s surface are volcanic necks, dikes, sills, and batholiths.

23. Guided practice What are two ways in which mountains can form as a result of magma hardening beneath Earth’s surface? After millions of years, what landform forms from hardened magma in the pipe of an extinct volcano?

24. Guided practice What are two ways in which mountains can form as a result of magma hardening beneath Earth’s surface?Mountains can form when uplift forces hardened magma to bend rock upward, and is then exposed as the hardened magma wears away. After millions of years, what landform forms from hardened magma in the pipe of an extinct volcano?A landform that would form from hardened magma in the pipe of an extinct volcano after millions of years is a volcanic neck.

25. Independent practice Complete Volcanoes 6-3 Independent Practice