Volcanoes Ch 22.6 Page 690

A. A volcano is a mountain that forms when magma reaches the surface B. Examples: Mount St. Helens, Kilauea

C. Formation of a Volcano Page Under certain conditions, small amounts of mantle rock can melt, forming liquid magma. The magma rises upward through the crust, erupting at the surface of a volcano

2. How a Volcano Erupts- magma is under pressure and contains dissolved gases. The volcano erupts when the gases bubble out through a crust, propelling magma to the surface

3. Structure of a Volcano

a. Magma collects in a magma chamber b. Magma rises to the surface through a narrow, vertical chamber called a pipe

c. An opening in the ground where magma escapes to the surface is called a vent

d. Top of a central vent is a bowl- shaped crater pit called the crater e. If the shell collapses inward, it creates a huge depression, called a caldera

D. Quiet and Explosive Eruptions Page Volcanoes erupt explosively or quietly, depending on the characteristics of the magma

2. Three main factors determine the viscosity (resistance to flow) of magma

a.Temperature- higher temps, lower the viscosity so it flows easily b. Water content- high water content also helps it flow easily c. Silica content- high silica content also has high viscosity therefore does not flow easy

3. Quiet Eruptions a. Very hot, low-silica b.Lava flow travels for great distance c.Mt. Kilauea

4. Explosive Eruptions a. High- silica magma b. Mt St Helens

E. Location and Types of Volcanoes Page Most volcanoes occur along plate boundaries or at hot spots in the crust

2.Ring of Fire- volcanoes formed along trenches in the Pacific Ocean 3.Hot spot is a region where hot rock extends from deep within the mantel to the surface

4. Three major types of volcanoes

a.Shield volcano- a wide, flat volcano produced from quiet eruption of low-viscosity lava produces

b.Cinder cone- a small, steep sided volcano formed when an eruption is entirely ash and cinders

c. Composite volcano- a volcano that forms from explosive eruptions that produce a combination of lava and ash

F. Other Igneous Features Page Igneous features formed by magma include batholiths, sills, dikes, and volcanic necks

2.A batholith is the largest type of intrusive igneous rock mass

3. If the crack is parallel to existing rock layers, the magma hardens into a structure called a sill

4.If the crack cuts across rock layers, the hardened magma forms a dike

5. When magma hardens in a volcano's pipe, a structure called a volcanic neck may form

Plate Boundaries

Volcano Song Raging Volcano video