Young fiction mystery/action about plot to divert a river for underground fire

[Jennifer]

Greetings!
I am looking for a book I read from my school library (middle or high) in the late 80's or early 90's.
This book is about a teenaged girl who is put in an institution because she believes her father was kidnapped by his employer. She escapes and inadvertently kidnaps a teen boy by hijacking a small plane he was to take a ride in. This boy has an old Native American friend who passes away (I think his name is Joe?).
They crash the plane and end up discovering the river they are following suddenly stops flowing. They end up finding a facility where a gas company (that her father works for) is diverting the river to create an underground fire for the purposes of gasification. (I think it's gasification). The girl reunites with her father and they all escape.
This book is likely out of print. Any help finding the name of this book is appreciated !!

Thank you!
Jenn