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If you take a giant whale out of the water and put it on land for long enough, it will crush itself under its own weight. Why doesn't the animal get crushed under its own weight when it's in water?

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When it's in water the buoyant pressures are distributed more evenly over the whale's natural surface contour, resulting in less internal strain in the whale's body.

On land, the pressures are all concentrated in a planar surface at the bottom. The whale's body is not naturally planar, so significant strain develops as the body attempts to conform to the planar surface in order to distribute the forces resisting gravity.

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One place this issue is discussed is here. The key paragraph is

Whales can withstand this pressure because their bodies are more flexible. Their ribs are bound by loose, bendable cartilage, which allows the rib cage to collapse to some degree under high pressure that would easily snap our bones. A whale's lungs can also collapse safely under pressure, which keeps them from rupturing. When the lungs collapse, the air inside them is compressed, maintaining a balance between inward and outward pressure. These adaptations are particularly important to sperm whales, which dive to depths of 7,000 feet (2,133.6 m) or more, hunting for the giant squid that live at these great depths.

which is pretty cool. But then this leads to another problem addressed here:

Collapse of the lungs forces air away from the alveoli, where gas exchange between the lungs and blood occurs ... the lungs of the deep diver cannot serve as a source of oxygen during the dive. Instead deep-diving whales and seals rely on large oxygen stores in their blood and muscle. Several adaptations enable this.

At the same time, as the article points out, the lack of gas exchange is useful in the sense that it circumvents the problem of nitrogen getting absorbed into the blood that would then bubble out at lower depths.

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