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Buy a small bottle of pop (you don’t have to drink it!) and open the lid. The bottle will become soft because the pressure is released, and small bubbles will start forming. If you put the lid back on and shake the bottle (best to do this outside!) you’ll enhance the processes of bubble formation, and when you open the lid the pop will come gushing out, just like an explosive volcanic eruption.
A pop bottle is a better analogue for a volcano than the old baking soda and vinegar experiment that you did at elementary school, because pop bottles, like volcanoes, come pre-charged with gas pressure. All we need to do is release the confining pressure and the gases come bubbling out. Of course, champagne is better still![i]
[i] Niells Noordhoek, 2012, CC BY SA 3.0, http://upload.wikimedia.org /wikipedia/commons/6/64/Champagne_uncorking_photographed_with_a_high_speed_air-gap_flash.jpg
| Type | Tectonic setting | Size and shape | Magma & eruption characteristics | Example |
| Cinder cone | Various. Some form on the flanks of other volcanoes | Small (10s to 100s of m) and steep (>30˚) | Most are mafic and form from the gas-rich early stages of a shield- or rift-associated eruption | Eve Cone, northern BC |
| Composite volcano | Almost all are at subduction zones | Medium size (1000s of m) and moderate steepness (10 to 30˚) | Magma composition varies from felsic to mafic, and from explosive to effusive. | Mt. St. Helens |
| Shield volcano | Most are at mantle plumes, some on spreading ridges | Large (up to several 1000 m high and 200 km across), not steep (typically 2 to 10˚) | Magma is almost always mafic, and eruptions are typically effusive, although cinder-cones are common on the flanks of shield volcanoes | Kilauea, Hawaii |
| Large igneous provinces | Associated with “super” mantle plumes | Enormous (up to millions of km2) and 100s of m thick | Magma is always mafic. Individual flows can be 10s of metres thick | Columbia River basalts |
| Sea-floor volcanism | Generally associated with spreading ridges but also mantle plumes | Most of the oceanic crust formed at spreading ridges | At normal eruption rates pillows form. At faster rates lava flows develop. | Juan de Fuca ridge |
| Kimberlite | Older parts of continents | The remnants are typically 10s to 100s of m across | Most appear to have had explosive eruptions forming cinder cones. The youngest one is over 10 ka, and all others are over 30 Ma. | Lac de Gras kimberlite field, NWT |