Iceland is one of the few places where the Mid-Atlantic Ridge rises above the sea. The North American and Eurasian plates are pulling apart there by about 2 cm a year, opening fissures in the open air. In one of them, Silfra, filled with glacial water of exceptional clarity, divers swim right through the rift zone separating two tectonic plates.
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.