Do you know what this is?
Bokke by Scienceline
Go on, listen again! Any idea? The answer is after the picture -
which might give you a clue.

That sound is a mud pool! That mud pool is in
Akan National Park, Japan. Mud pools are often called "bokke,"
which means "boiling" in Ainu, the language of the Ainu people who
live near Akan National Park.
When water seeps down from the surface of the earth, it
eventually gets to the bottom of the crust - the outer layer of the
Earth's surface. When there's magma - very hot molten rock -
hanging out close to that crust the water gets
very hot.
Hot things rise, so the water rises up through volcanic vents,
along with steam.In mudpots, hydrogen sulfide
rises too, which combines with the water to make sulfuric
acid. When that sulfuric acid meets the surface rock -
what do you get? Mud! Bubbling mud, in fact.

How mud pools are
formed
Mudpots are often really smelly. The sulfuric
acid that meets the surface and makes the mud smells like rotten
eggs. Ew!
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 stuff.
Sound recorded by snotch
on freesound.
This article was written by Rose Eveleth and is
provided by Scienceline, a project of New York
University's Science, Health and Environmental Reporting
Program.