poko-poko
The soft, rhythmic sound of small bubbles rising and popping on a water surface — a hot spring bubbling, mud pots percolating, or a gentle boil.
💡A natural hot spring bubbling — 'The hot spring was bubbling poko-poko at the surface.'
温泉がぽこぽこと湧いている。
The hot spring is bubbling poko-poko.
The mud pool was ___ bubbling in the geothermal area.
地熱地帯で泥の池が○○と泡を立てていた。