Volcanoes

A volcano is an opening in the Earth’s crust through which lava, volcanic ash, and gases escape to the surface. This can include eruptions on the ocean floor (or under a lake), called subaqueous eruptions, or on land, where they are called subaerial eruptions. Not all volcanic eruptions produce volcanic mountains; most of Earth’s volcanism occurs along the spreading ridges on the seafloor and does not produce peaks or mountains.

Many Canadians are unaware that western Canada lies along the Pacific “Ring of Fire” and has active volcanoes. In fact, there have been at least 49 volcanic eruptions in British Columbia and the Yukon Territory during the last 10,000 years (Figures 4.1 ). The forces that produce volcanoes are still active, and some of them will erupt again, although we don’t know when.

Although volcanic rocks exist in many other Canadian regions and ancient volcanoes are found (e.g. the Monteregian Hills of Quebec are 60 million-year-old intrusives), the magmatic events that created them are no longer active.

The study of volcanoes is critical to understanding the Earth’s evolution and the significant changes in our climate system. But, most important of all, understanding volcanic eruptions allows us to save lives and property. Over the past few decades, forecasting volcanic eruptions and predicting the consequences has already saved thousands of lives.

Learning Outcomes

After studying this chapter, you should be able to

• know the plate-tectonic settings of volcanoes
• understand variation in magma characteristics and composition that control eruption types
• decribe the eruption sequence
• differentiate between eruption styles
• differentiate between volcanic landforms