A volcano is any location where magma comes to the surface, or has done so within the past several million years. This can include eruptions on the ocean floor (or even under the water of a lake), where they are called subaqueous eruptions, or on land, where they are called subaerial eruptions. Not all volcanic eruptions produce the volcanic mountains with which we are familiar; in fact most of Earth’s volcanism takes place along the spreading ridges on the sea floor and does not produce volcanic mountains at all—not even sea-floor mountains.

Colorado has a great deal of volcanic rock, with most of it being relatively young. Despite the relatively young ages, Colorado is not a place where volcanic eruptions are much of a worry in modern times (we’ll look at why in chapter 10). We’ll look at a few of these volcanoes in some detail toward the end of this chapter, but a few of them are shown on Figures 4.0.1 and 4.0.2.

The study of volcanoes is critical to our understanding of the geological evolution of Earth, and to our understanding of significant changes in climate. But, most important of all, understanding volcanic eruptions allows us to save lives and property. Over the past few decades, volcanologists have made great strides in their ability to forecast volcanic eruptions and predict the consequences—this has already saved thousands of lives.

Figure 4.0.1 The Dotsero cinder cone volcano (the crater or depression in the foreground), just off of Interstate 70 in the town of Dotsero, Eagle County, CO. The rim of the crater is at an elevation of 6,783 feet. It last erupted approximately 4,200 years ago.

Figure 4.0.2 Mount Saint Helens, in Washington state, erupting on the morning of May 18, 1980. Notice how the volcano possesses a stereotypical “cone shape”, and the column of ash erupting from it. Not all volcanoes look like this, nor do all of them produce ash.

Media Attributions

• Figures 4.0.1, 4.0.2: Wikimedia Commons