Chapters 3 and 4 are about igneous rocks and igneous processes. (Either chapter may be read first). Chapter 4 focuses on volcanoes and igneous activity that takes place at Earth's surface. Chapter 3 describes igneous processes that take place underground. However, you will learn early in this chapter how volcanic as well as intrusive rocks are classified based on their grain size and mineral content.

We begin the chapter by introducing the rock cycle. This is a conceptual device that shows the interrelationship between igneous, sedimentary, and metamorphic rocks. We then begin focusing on igneous rocks. After the section on igneous rocks classification, we describe structural relationships between bodies of intrusive rock and other rocks in the earth's crust. This is followed by a discussion of how magmas form and are altered. We conclude by discussing various hypotheses that relate igneous activity to plate tectonic activity.

Expanded Readings From Chapter 4

Mt. St. Helens, 1980 - North America's Eruption of the 20th Century

An Icelandic Community Battles a Volcano and Wins

HOT! How did you spend your summer vacation? HOT!
Click on the link below to share the experiences of Geoscience students from the University of Arkansas and their professor, Dr. Glen Mattioli, as they survive an explosive volcanic eruption on the Caribbean island of Montserrat during July 2003.

<a onClick="window.open('/olcweb/cgi/pluginpop.cgi?it=gif::Montserrat, October 1997::http://comp.uark.edu/~mattioli/redo_plume3.gif','popWin', 'width=NaN,height=NaN,resizable,scrollbars');" href="#"><img valign="absmiddle" height="16" width="16" border="0" src="/olcweb/styles/shared/linkicons/image.gif">Montserrat, October 1997 (33574K)</a>Montserrat, October 1997

View Dr. Mattioli's photographs of the eruption and its aftermath here, here, or here.

Read a press release about the eruption here.

Read another press release about the eruption here.

Learn more about the Soufriere Hills volcano here.

Learn about the CALIPSO project here.

Contact the University of Arkansas Department of Geosciences here.