Creating a User via the UI without specifying a password; what is the defaulted password?

The Admin user can create User accounts via the Identity Management UI without specifying the password. How is it possible to authenticate the new account without knowing the password? I.e. how does the owner of the new account find out what their password is?

I'm assuming that when creating a User account if the password field is not filled in then the system creates a default password. If so, how do you find out what it is?