Question

Write a hypothesis for how did the Hawaiian island chain form

Answer 1

Always remember that a hypothesis always begins with "if"

If the hot spot is underwater and erupts on the sea floor, then it makes logical sense to how the Hawaiian Islands are formed.
 
I am thinking this is somewhat what you were looking for.

Answer 2

It may have formed from volcanoes, which would be your hypothesis, and then you'd have to explain how the variables caused this.