Pirunkirkko Cave, meaning “Church of the Devil” in English, is located in the famous Koli National Park and is known for its intermittent knocking sounds.
The knocking sounds emanating from Pirunkirkko Cave. (Video: University of Helsinki)
A research team from the University of Eastern Finland has discovered the cause of the strange noises in Pirunkirkko Cave, as reported by Mail on November 27. According to researchers Riitta Rainio and Elina Hytonen-Ng, it is due to a special resonance.
Pirunkirkko is a Z-shaped cave that is 34 meters long. According to legend, it is a meeting place for sages to communicate with the spirit world. In their recent study, scientists explored whether the acoustic features of the cave could help explain the legends associated with it. The analysis revealed that the characteristic resonance both amplifies and extends sounds at specific frequencies.
A rare resonance phenomenon in natural environments.
The research team suggests that this phenomenon is caused by standing waves formed between the smooth, parallel walls of the cave. This creates a sound at the cave’s natural frequency of 231 Hz, which can be heard a second after sounds such as claps, drumbeats, or thumps.
Researchers also interviewed and recorded a modern-day shaman who uses the cave for rituals. They found that the sounds produced by the individual were amplified by the cave at its natural frequency.
While resonance is quite common in buildings, it is relatively rare in natural environments, mainly due to the lack of parallel solid surfaces. For this reason, the research team believes that the resonating sounds in the cave may make visitors feel as if a spirit is present.
