I find it difficult to wrap my mind around volcanoes. I mean, they’re basically portals to the depths of Earth that spew flaming molten rocks—and there’s really no way to stop them. The most we can do is monitor them, make approximations about when they might erupt, and then high-tail it out of the area. At best, they’re humbling reminders of our powerlessness. At worst, they’re deadly.

People who study volcanoes must have a sense of larger-than-life concepts, like geological time and the movement of continental plates. So I was a bit sheepish when I asked volcanologist Janine Krippner of Concord University whether it’s fair to compare volcanoes to soda bottles. I was delighted when she told me that it is one of her favorite analogies.

Let’s get shaking.

If I asked you to imagine a volcano, you’d probably picture a stratovolcano—a cone-shaped mountain that erupts explosively. These guys contain magma (i.e., underground lava) that is quite thick and viscous. The magma isn’t very liquid-y, so it is able to trap gases in the depths, allowing the pressure inside the volcano to build. When these volcanoes erupt, they explode with a bang.

The more explosive volcanoes are kind of like soda bottles with lots of trapped gas.

Shield volcanoes, on the other hand, are usually much more gentle (if that can be said about a mountain bubbling molten rock). These volcanoes are created when layers of lava ooze out of the volcano and harden. Over the course of many years, shield volcanoes grow into giant domes that look like warriors’ shields. Kilauea, the volcano in Hawaii that is currently erupting, is a shield volcano.

Does this look like a warrior’s shield yet?

Shield volcanoes spew lava that is comparatively thinner and runnier than stratovolcanoes. The result is that gas can more easily escape, so their eruptions tend to be less dramatic. In fact, Kilauea has been erupting continuously since 1983, and while lava has made its way into neighborhoods in the past, for the most part, people have been able to live on the volcano’s flanks.

Gas can escape from runny lava (and seltzer) more easily than from thick lava.

So, what changed? Why is Kilauea suddenly pouring lava into residential communities? Watch our seltzer-infused video to find out.

More on Hawaii’s Kilauea volcano