*Spoiler* Can somebody answer my plot question about the recent Narnia movie?

I haven't read the books, but I heard that the books aren't exactly like the movies anyway. But, at the beginning, when the pictures overflows with water and fills the room, how does this happen? They never explain it throughout the entire movie. I get that it's magical, but it still doesn't have an explanation. Can somebody please help me here? I could barely even enjoy the movie because all I could think about the whole time is why that happened.