A mountain range floats on the mantle, a bit like an iceberg on water. To bear its weight, the crust thickens downward: beneath the Himalayas and Tibet it reaches about 70 km, compared with 30 to 40 km under most continents. The hidden part of a mountain is far bigger than the part you can see.
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.