A common myth says a single big eruption releases more CO₂ than all of humanity. According to the US Geological Survey, all the world's volcanoes, on land and under the sea, emit a few hundred million tonnes of CO₂ a year. Human activities emit more than 35 billion tonnes, around 100 times as much. The chemical fingerprint of the carbon building up in the air bears the mark of fossil fuels.
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.