Eruption (1977)

Set in Ohau, Hawaii, Sandra is a wealthy heiress whom persuades insurance salesman, Peter, to sell her husband a $2 million life insurance policy, and then persuades Peter to kill him to get the money. The murder goes off without a hitch, but when a persistent investigator threatens to uncover the plot, Peter begins to suspect that Sandra may betray him and turns to her promiscuous teenage stepdaughter, Angie, to help turn the tables on her and Angie's boyfriend, Scott, whom is apparently in cahoots with Sandra.