Science

January 22, 2010 This is our Notes on Volcanos we have recently done chapter 12. Volcanoes Chapter 12 Pages 330-355 Vocabulary 1. A volcano is an opening in Earth that erupts (A) gases, (B) ash, and (C) lava.
 * 1) volcano
 * 2) vent
 * 3) crater
 * 4) hot spot
 * 5) shield volcano
 * 6) tephra
 * 7) cinder cone volcano
 * 8) composite volcano
 * 9) batholith
 * 10) dike
 * 11) sill
 * 12) volcanic neck
 * 13) caldera
 * __ Section 1 – Volcanoes and Earth’s Moving Plates – Pages 330-335 __**

2. Volcanoes can (A) kill people, (B) destroy property, and (C) disrupt the environment.

3. Lava and pyroclastic flows can bury cities and towns in their paths.

4. Sulfurous gases from volcanoes can create acid rain, which can kill organisms and pollute water.

5. Volcanoes form when magma flows out of a surface opening called a vent: a steep-walled depression around the vent is called a crater.

6. Volcanoes often form where plates are moving apart (divergent boundaries), moving together (convergent boundaries), and at hot spots.

7. Plates move apart at divergent boundaries. The Mid-Atlantic Ridge is a divergent plate boundary that forms rifts through which lava can flow.

8. At convergent plate boundaries, volcanoes form where one plate sinks beneath another plate. Volcanoes tend to erupt more violently at convergent plate boundaries than they do in other areas.

9. At the boundary between Earth’s mantle and core, unusually hot areas form hot spots, such as at the Hawaiian Islands.

Where do volcanoes tend to form?
 * DISCUSSION QUESTION: **

1. The amount of water vapor and other gases present is one factor that determines whether a volcanic eruption will be quiet or explosive.
 * __ Section 2 – Types of Volcanoes – Pages 336-343 __**

A. Gases can be trapped in magma by pressure of surrounding magma and rock; eventually they cause an explosive eruption.

B. Magma at convergent plate boundaries can contain a lot of water vapor that can cause explosive eruptions.

2. The composition of magma is a second factor affecting the nature of a volcano’s eruption.

A. Low-silica magma, called basaltic, is fluid and produces a quiet, nonexplosive eruption.

B. High-silica magma produces explosive eruptions. 1. Andesitic magma is more silica rich than basaltic magma. 2. Granitic magma is more silica rich than andesitic magma.

3. Three types of volcanoes form from the three types of lava.

A. As quiet eruptions of basaltic lava spread out in flat layers, they form a broad volcano with gently sloping sides called a shield volcano.

B. As tephra (bits of rock or solidified lava) falls to the ground, it forms a steep-sided loosely packed cinder cone volcano.

C. A composite volcano forms from alternating layers of quiet and more explosive tephra.

What two factors account for the varying force of volcanic eruptions?
 * DISCUSSION QUESTION: **

1. Many intrusive igneous features form underground and are later exposed. A. Batholiths are rock bodies formed when magma bodies that are being forced upward from inside Earth cool slowly and solidify before reaching the surface. B. Dikes are magma that hardens after being forced into a crack cutting across rock layers. C. Sill is magma that hardens after being forced into a crack parallel to rock layers.
 * __ Section 3 – Igneous Rock Features – Pages 345-349 __**

2. A volcanic neck forms when the cone in eroded away, leaving a solid igneous core. A. The large depression formed when the top of a volcano collapses is a caldera. B. Weathering and erosion wear down surface rock and expose igneous rock features.

How do a dike and a sill differ?
 * DISCUSSION QUESTION **