What Am I Riddles

Question: What kills a lot of people but is harmless?

Question: ***What can so easily be broken and could never be spoken?***

Question: I break down buildings I crumble mountains You can't see me What am I?

Question: People are scared of me but I am loved by some. I can be your best friend but could become your enemy in a blink of an eye. What am I?

Question: I float when I am born, lay down when I am alive, and run when I am dead. What am I?