21 Introduction

Module 6


a range of volcanic mountains, one with steam escaping, and one in the distance with a full plume of smoke
Figure 1. The Mount Bromo volcano on the island Java of Indonesia. Depending on the degree of volcanic activity, the Indonesian Centre for Volcanology and Disaster Hazard Mitigation sometimes issues warnings against visiting Mount Bromo.


In the previous module, we studied different types of igneous rocks and intrusive igneous processes. Now, we are moving on to consider volcanism and extrusive activity. Without doubt, volcanic eruptions are among the most spectacular of Earth’s processes. Activity ranges from gentle eruptions that do not represent significant hazards to humans, as is the case in Hawaii, up to highly explosive and large events that have the potential to impact global climate. In this module, you will learn about the different types of volcanism and the hazards that they represent. In addition, you will read about several specific volcanoes to better understand the processes associated with different eruptions.

How would you like to live on an active volcano? Surprisingly, a lot of people are living on or near active volcanoes, and many more live near volcanoes that are currently considered to be “dormant,” exhibiting a volcanically-quiet period of time over the past 10,000 years, but with the potential to erupt in the future. Are they crazy? Maybe some are, but not all volcanoes erupt explosively; for example, the type of volcano that forms the Hawaiian Islands is a type that erupts effusively, with lava running down the sides (flans) of the volcano. Hawaiian citizens are familiar with this style of eruption, and they are also aware that their particular volcano will not erupt explosively.

Explosive eruptions are more likely for the volcanoes that make up the Islands of Sumatra and Java (Indonesia); these volcanoes are very dangerous, and yet Indonesia is one of the most densely populated countries in the world. So, it would seem very important to know why some volcanoes are dangerous, and why others are not. Of the “dangerous” types that are currently dormant, will we have enough of a warning before they erupt? Is it only the eruption that we should worry about, or are there other hazards that we must be aware of? These questions will be addressed in this module, along with a few other questions that you might have, such as why volcanoes form in certain locations, especially in relation to plate tectonics, and the association of magma type with volcano type and eruptive style.

Select an image to view larger


molten lava flowing down a street burning grass and trees
Figure 2. This photo from the U.S. Geological Survey offer a glimpse into the destructive volcanic eruption now occurring on the East Rift Zone of Hawaii Island.At 07:45 a.m. HST, May 7, 2018, lava from fissure 7 slowly advanced to the northeast on Hookapu Street in Leilani Estates subdivision on Kīlauea Volcano’s lower East Rift Zone.


Two large telescope buildings with a sky full of stars.
Figure 3. Strombolian eruption of Pacaya in Guatamala, 1992.


A view of the inside of a volcano crater, surrounded by clouds of steam
Figure 4. ‘This is the view, as close as I was willing to go, of inside mount Merapi in Indonesia’ – Jimmy McIntyre, Editor of HDR One Magazine
Place alternative tag here.
Figure 5. Casts of some of the Pompeiian victims of Mt. Vesuvius’ eruption in AD 79. The people and buildings of Pompeii were covered in up to 12 different layers of tephra, in total 25 metres (82.0 ft) deep, which rained down for about six hours.


A volcanic mountain with a large crater at the top
Figure 6. Sunset Crater Volcano National Monument, just north of Flagstaff, Arizona. Around 1085 the ground began to shake, and lava spewed high into the air. When the eruption finished, it had changed both the landscape and the people who lived here.
A mountain and laek with a sign that says No lifeguard swimming is not allowed
Figure 7. A lake has filled the caldera at Mt. Pinatubo, Philippines. It is an active stratovolcano that lasterupted in 1993, but its massive eruption in 1991 was arguably one of the largest eruptions inmore than 100 years. It caused a volcanic winter by dropping global temperatures by 1 °C inthe Northern Hemisphere.

Module Objectives

At the completion of this module you will be able to:

  1. Describe the different types of volcanoes.
  2. Explain why there are different types of lava.
  3. Explain how volcanism, igneous rocks and plate tectonics relate.
  4. Describe the hazards associated with volcanism.
  5. Explain how volcanism can impact life on Earth.

Activities Overview

See the Schedule of Work for dates of availability and due dates.

Be sure to read through the directions for all of this module’s activities before getting started so that you can plan your time accordingly. You are expected to work on this course throughout the week.


Physical Geology by Steven Earle

  • Chapter 4 (Volcanism)

Discussion 3

30 points, class participation

For this week’s “Current Events in Geology” discussion. It is important that you feel engaged in this class. Discussion topics are very flexible, and can cover anything in geology or a related field, including hydrology or water resources, environmental or climate science, paleontology, planetary geology, etc. This is a great opportunity for you to learn about topics in geology that interest YOU, and to see that many interesting things relating to geology are currently making headlines in the news. You are also helping your instructor to become aware of what is going on and to learn new things, so I appreciate your efforts and look forward to reading what you find!

Discussion 3 Instructions

Pay close attention to the Course Schedule for when each of your posts are due. Some are due earlier than others. Failure to post on time will result in lost points.

Module 6 Assignment: Exploring Volcanic Features of the United States

15 points

After you complete the reading, you can start working on Module 6 Assignment – Volcanic Features of the United States

Module 6 Quiz

10 points

Module 6 Quiz has 10 multiple-choice questions and is based on the content of the Module 6 readings and Assignment 6.

The quiz is worth a total of 10 points (1 points per question). You will have only 10 minutes to complete the quiz, and you may take this quiz only once. Note: that is not enough time to look up the answers!

Make sure that you fully understand all of the concepts presented and study for this quiz as though it were going to be proctored in a classroom, or you will likely find yourself running out of time.

Keep track of the time, and be sure to look over your full quiz results after you have submitted it for a grade.

Your Questions and Concerns…

Please contact me if you have any questions or concerns.

General course questions: If your question is of a general nature such that other students would benefit from the answer, then go to the discussions area and post it as a question thread in the “General course questions” discussion area.

Personal questions: If your question is personal, (e.g. regarding my comments to you specifically), then send me an email from within this course.


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