Source: Laboratory of Alan Lester - University of Colorado Boulder

Igneous rocks are the products of cooling and crystallization of magma. Volcanic rocks are a particular variety of igneous rock, forming as a consequence of magma breaching the surface, then cooling and crystallizing in the subaerial environment. 

Magma is liquid rock that typically ranges in temperature from approximately 800 °C to 1,200 °C (Figure 1). Magma itself is produced within the Earth via three primary melting mechanisms, namely the addition of heat, addition of volatiles, and decompression. Each mode of melt generation tends to produce specific types of magma and, therefore, distinct eruptive styles and structures.

Figure 1. Fresh lava breakout on Kilauea, Hawaii. Lava is the term for magma that is on Earth’s surface.

1. CO₂ Volcano

1. Fill a plastic container with a thin neck (a 16-oz. soda bottle for instance) about half-full with warm water.
2. Bury the bottle beneath modeling clay or dough, leaving just the neck (opening) of the bottle exposed, simulating the structure of a volcano.
3. Add a few drops of dishwashing liquid (in order to make the liquid frothy and likely to produce bubbles).
4. Using a folded piece of paper as a funnel, add 4 teaspoons (approximately 15-20 mL) of baking soda.

1. CO₂ Volcano

During the CO₂ experiment, some of the material will flow outwards like a lava flow. The frothy nature of the flow is reminiscent of lava that is charged with volatiles. Most volcanic eruptions are linked to volatile loss. Those that are particularly explosive will have considerable volatile emanations. If the container is corked, then the initial eruption will involve pyroclastic-type material that is ejected into the air above the volcani

Volcanism and associated rocks are of great interest to geologists. Not only do volcanic eruptions pose a threat to nearby communities, it is important to recognize that they can also lead to scenic landscapes, and positively influence soil and agricultural productivity.

Recognizing volcanic rocks in the field, linking them to specific eruptive styles, and ascertaining regions of past activity are part of fundamental geologic assessments for regions in which people live and/or work. Volcanic r