ESC 1000 Earth and Space Science Video Lecture Notes

                                                              Name: ________________

Earth Revealed #13: Volcanism (1992)

Please watch the video in class. Take notes on the Earth Revealed Disc #13 Volcanism circle each of the Chapter 9 vocabulary words discussed in the video. When the film is finished and after reading Chapter 9 write questions with answers that a student should be able to answer if she/he viewed this video. You should have at least two or more questions for each chapter. List the most significant discovery you made about Volcanoeswhich you did not know before watch the film.

Play Video:

Chapter 9: Volcanoes and Other Igneous Activity

Key Concepts

Mt. St. HelensCh. 9: Volcanoes and Other Igneous Activity

After reading and studying Ch. 9, you should be able to:

Concept 1: List the factors that contribute to and determine the violence of volcanic eruptions.

Concept 2: Describe the various types of volcanoes and other features produced by volcanic activity including materials extruded and hazards associated with eruptions.

Concept 3: List and describe several intrusive igneous features.

Concept 4: Discuss the role of heat, pressure, and composition (including volatiles) in the origin of magma.

Concept 5: Describe the relationship between igneous activity and plate tectonics


The following statements summarize and describe many of the key terms and concepts presented in the chapter.

  • The primary factors that determine the nature of volcanic eruptions include the magma's temperature, its composition, and the amount of dissolved gases it contains. As lava cools, it begins to congeal, and as viscosity increases, its mobility decreases. The viscosity of magma is directly related to its silica content. Rhyolitic lava, with its high silica content, is very viscous and forms short, thick flows. Basaltic lava, with a lower silica content, is more fluid and may travel a long distance before congealing. Dissolved gases provide the force that propels molten rock from the vent of a volcano.
  • The materials associated with a volcanic eruption include lava flows (pahoehoe and aa flows for basaltic lavas), gases (primarily in the form of water vapor), and pyroclastic material (pulverized rock and lava fragments blown from the volcano's vent, which include ash, pumice, lapilli, cinders, blocks, and bombs).
  • Successive eruptions of lava from a central vent result in a mountainous accumulation of material known as a volcano. Located at the summit of many volcanoes is a steep-walled depression called a crater. Shield cones are broad, slightly domed volcanoes built primarily of fluid, basaltic lava. Cinder cones have steep slopes composed of pyroclastic material. Composite cones, or stratovolcanoes, are large, nearly symmetrical structures built of interbedded lavas and pyroclastic deposits. Composite cones produce some of the most violent volcanic activity. Often associated with a violent eruption is a nuée ardente, a fiery cloud of hot gases infused with incandescent ash that races down steep volcanic slopes. Large composite cones may also generate a type of mudflow known as a lahar.
  • Most volcanoes are fed by conduits or pipes. As erosion progresses, the rock occupying the pipe is often more resistant and may remain standing above the surrounding terrain as a volcanic neck. The summits of some volcanoes have large, nearly circular depressions called calderas that result from collapse following an explosive eruption. Calderas also form on shield volcanos by subterranean drainage from a central magma chamber, and the largest calderas form by the discharge of colossal volumes of silica-rich pumice along ring fractures. Although volcanic eruptions from a central vent are the most familiar, by far the largest amounts of volcanic material are extruded from cracks in the crust called fissures. The term flood basalts describes the fluid, waterlike, basaltic lava flows that cover an extensive region in the northwestern United States known as the Columbia Plateau. When silica-rich magma is extruded, pyroclastic flows consisting largely of ash and pumice fragments usually result.
  • Igneous intrusive bodies are classified according to their shape and by their orientation with respect to the host rock, generally sedimentary rock. The two general shapes are tabular (tablelike) and massive. Intrusive igneous bodies that cut across existing sedimentary beds are said to be discordant, whereas those that form parallel to existing sedimentary beds are concordant.
  • Dikes are tabular, discordant igneous bodies produced when magma is injected into fractures that cut across rock layers. Tabular, concordant bodies called sills form when magma is injected along the bedding surfaces of sedimentary rocks. Laccoliths are similar to sills but form from less-fluid magma that collects as a lens-shaped mass that arches the overlying strata upward. Batholiths, the largest intrusive igneous bodies with surface exposures of more than 100 square kilometers (40 square miles), frequently make up the cores of mountains.
  • Magma originates from essentially solid rock of the crust and mantle. In addition to a rock's composition, its temperature, depth (confining pressure), and water content determine whether it exists as a solid or liquid. Thus, magma can be generated by raising a rock's temperature, as occurs when a hot mantle plume "ponds" beneath crustal rocks. A decrease in pressure can cause decompression melting. Further, the introduction of volatiles (water) can lower a rock's melting point sufficiently to generate magma. Because melting is generally not complete, a process called partial melting produces a melt made of the lowest-melting-temperature minerals, which are higher in silica than the original rock. Thus, magmas generated by partial melting are nearer to the granitic (felsic) end of the compositional spectrum than are the rocks from which they formed.
  • Most active volcanoes are associated with plate boundaries. Active areas of volcanism are found along oceanic ridges where seafloor spreading is occurring (divergent plate boundaries), in the vicinity of ocean trenches where one plate is being subducted beneath another (convergent plate boundaries), and in the interiors of plates themselves (intraplate volcanism). Rising plumes of hot mantle rock are the source of most intraplate volcanism.


Earth Revealed #13. Volcanism
Volcanoes provide clues about what is going on inside Earth. Animations illustrate volcanic processes and how plate boundaries are related to volcanism. The program also surveys the various types of eruptions, craters, cones and vents, lava domes, magma, and volcanic rock. The 1980 eruption of Mount St. Helens serves as one example.

Play Video:

Video Notes:





Chapter 9: Volcanoes and Other Igneous Activity

AA flow


Pyroclastic Flow 


Geothermal Gradient

Pyroclastic Material  


Hot Spot

Scoria Cone 

Cinder Cone 

Intraplate Volcanism

Shield Volcano 

Columnar Joint

Island Arc


Composite Cone


Strato volcanoes 




Continental Volcanic Arc 

Mantle Plume



Muee Ardente


Decompression Melting 

Pahoehoe Flow

Volcanic Island Arc 


Parasitic Cone

Volcanic Neck 


Partial Melting


Fissure eruption 



Flood basalt


















Student Questions (with Answers):











Most Significant Discovery (discoveries):




Video Study Guide: Earth Revealed

Episode 13: Volcanism

Why does magma rise to the surface?



Where are most of the world's active volcanoes?



What is pillow lava?



Describe the Hawaiian hotspot.



Describe basaltic (mafic) magma and why it commonly forms shield volcanoes.



What are rift zones?



Why are the volcanoes around the Pacific rim called composite volcanoes?



What common gasses occur in composite (intermediate) magmas?



What factors influence the explosiveness of volcanoes?



Discuss andesitic (intermediate) magmas associated with composite volcanoes.



Describe pumice and how it is formed.



Discuss viscosity and how it relates to the formation of pahoehoe and aa lavas.


How do lava tubes form?


Describe cinder cones and how they differ from composite and shield volcanoes.



What tectonic settings are most volcanoes associated with?


What is obsidian and how is it formed?


Discuss the clues that volcanologists use to predict eruptions.


Discuss how volcanoes relate to ore deposits and geothermal energy.


What are some of the beneficial aspects of volcanoes?