Why do whales beach themselves?

Does anyone know why whales beach themselves?

It's unlikely that they do it deliberately to die, but that their very strong social ties call them to the 'rescue' if one of the group is in danger - for example, by ending up on a beach as the tide goes out. This is according to an interesting article on http://www.abc.net.au/worldtoday/content/2003/s997632.htm ,

they follow the ocean's currents a lot

and when the current changes suddenly and directs then to the shore, well you know.. thats why...

but it goes depper than that so look at the article that susila2 offered

I remember there was a time where a huge amount of whales beached themselves and later studies discovered that a national guard ship was around the whales and the ship uses some sonar device that creates a lot of noise, and possibly that trigered the whales to move away from it, which resulted in the whales not being able to move further than the shore..