This is a mud pool in Akan National Park, in Hokkaido, Japan. Mud pools are often called “bokke,” which means “boiling” in Ainu, the language of the Ainu people who have lived in Hokkaido for thousands of years.
OK, so it’s not quite as enchanting as the soft bubble of champagne, but the bubbly mud pots can be romantic too! When water seeps down from the surface of the earth, it eventually gets to the bottom of the crust. When there’s magma hanging out close to that crust, the water gets heated.
Hot things rise, so that water rises up through volcanic vents called fumeroles along with steam and, in the case of mudpots, hydrogen sulfide, which combines with the water to make sulfuric acid. When that sulfuric acid meets the surface rock – voila! Mud! Bubbling mud, in fact. See, I told you it was romantic.
Mudpots like this one are often really smelly. That sulfuric acid that meets the surface and makes the mud also makes sulfur dioxide, the stuff that smells like rotten eggs.
Some of the most famous mudpots are in Yellowstone National Park. The park website has some recordings of them, if you just can’t get enough of the bubbly.
Sound recorded by snotch on freesound.
* A quick note: the description on the recording calls it a mud volcano. Mud volcanoes do exist, but they’re more rare, and they’re different, although the distinction is often blurry. Mud pots are depressions full of bubbling fluid, while mud volcanoes actually erupt, like a lava volcano would. Mud pots can become mud volcanoes if the pressure of the rising gas or water changes enough – more pressure means more explosive eruptions.