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Volcanoes: Origin, Types and Eruptions

Samir G. Khoury, Ph.D., P.G.

Every year a few volcanoes erupt with sufficient intensity somewhere around the world to cause significant disruption to our modern way of life and capture our full attention to the remarkable event that is taking place. For example, the recent eruption of Eyjafjallajokull, in Iceland, has disrupted for weeks on end the pattern of air flights to and from major airports around the world. Similarly, the eruption Mount Merapi, in Indonesia, has forced the shortening of a presidential visit to the Far East. Of course these disturbances are in addition to the real havoc, destruction and the loss of life that these volcanic eruptions cause in their immediate vicinity.

Understandably volcanoes have always terrified mankind. Yet it should be remembered that they also play a constructive role in shaping the very top layer of the earth on which we all live. Volcanoes are the source of some of the world’s richest soils, the site of some of the most magnificent vistas and scenic views we all enjoy, and they also replenish our accessible mineral, gas and water resources.

Following a brief introduction of the myths and fanciful speculations that surrounded the subject of volcanic eruptions throughout most of human history, this course explains how our modern understanding of this mighty natural phenomenon began to develop. Starting with a description of the internal structure of the earth, which we now know is composed of a dense core with a radius of about 3,400 km, a lighter mantle that is about 2,900 km thick, and a still lighter crust that is mostly rigid and up to 60 km in thickness, the course proceeds to explain our present understanding of the processes that are active within the deep reaches of our planet and how these processes lead to the development and the eruption of volcanoes. The concepts of plate tectonics and subduction, whereas an oceanic plate is pushed under the leading edge of a continental plate, are also explained and illustrated.

Based on their mode of origin and distinctive internal morphology, four main types of volcanoes can be recognized namely: Cinder Cones, Composite Cones, Shield Volcanoes, and Lava Domes. Next, the volcanic Explosivity Index (VEI), a scale to estimate the size of volcanic eruptions, is presented and its use by volcanologists to compare quantitatively the magnitude of volcanic eruptions worldwide explained.

The next section of the course describes some of the historically famous volcanic eruptions. This part of the course is followed by a section on Supervolcanoes that explains how these oversized features are identified from their geologic record and the size of their eruptions estimated.

Lastly, a glossary of terms and acronyms used in this course is presented following the Summary Section. It will provide the students with a handy reference to assist them in following the concepts that are presented and discussed throughout the text.

This course on volcanoes is presented as a complement to courses G175-Earthquakes: Basic Principles and G207-Tsunamis: Basic Principles for the benefit of those students who want to learn more about the deep seated processes in our earth that are responsible for the generation of these natural phenomena. However, courses G175 and G207 are not pre-requisites for taking this course. This course on volcanoes is a stand-alone presentation that can be taken independently of the other two.

This course includes a multiple-choice quiz at the end, which is designed to enhance the understanding of the course materials.

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