This phenomena is predicted to happen when a super volcano erupts. As a super volcano erupts a huge noise could be heard, and since huge vast of noises can cause a sound hole (AKA a black hole) they predicted one of the super volcanoes to form one of those. They called it the Volcanic Difference Phenomena because of the difference of the gravity. They have said that 6 of these can form during a super volcano eruption. The 1816 volcanic eruption of mount tambour might of formed 2. It would then cause another explosions as the black hols quickly evaporate because of their size. So the phenomena for these to form will be extremely deadly and have predicted that some can also form if a gamma ray burst also hits the earth, because of the noises from space impacts the earth making the noise louder it could form these phenomena, also predicted by scientist. The results of these can be extremely loud as they emit huge noises, and when they explode a wave of loud noises will be released, causing ear damage to a 7 mile radius. It is a rare phenomena and two can merge.