During the last ice age, ice sheets several kilometres thick pushed Earth's crust down into the mantle. Since they melted, the ground has been slowly springing back, like a cushion regaining its shape. Around Hudson Bay or the Gulf of Bothnia it is still rising by about a centimetre a year, leaving some old harbours far from the sea.
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.