What is a beached whale and why do whales beach themselves?

Between January and February in 2016, 30 sperm whales have become stranded on the sand on the coasts of England, France, Germany and the Netherlands.

When whales are beached like this it can be really dangerous for them and, if they can't make it back into deeper waters, they don't survive.

Marine scientists don't have one clear reason to explain why whales beach themselves.

Jenny has been looking into the theories...