When an avalanche of dry sand slides down a dune's steep face, it can produce a deep, sustained drone, like an organ pipe or a distant propeller plane. Around thirty such singing dunes are known worldwide. The sound, close to 100 hertz, can last several minutes and carry nearly 10 km. Physicists still debate the exact mechanism.
On 27 August 1883, the eruption of the Indonesian volcano Krakatoa was heard as far away as Rodrigues Island, nearly 4,800 km away. Its pressure wave was picked up by barometers worldwide and circled the globe several times. The tsunamis that followed killed more than 36,000 people.
The deepest known point in the ocean, Challenger Deep, lies roughly 10,900 m below the Pacific surface. Drop Everest in and its summit would still sit about 2 km underwater. Down there, the pressure is more than 1,000 times what you feel at sea level, roughly a tonne pressing on every square centimetre.