i'm assuming you're intent is to want to have been dead prior to jumping into the volcano so you don't experience any further pain, and i'm assuming it also helps in the case where you're body is harder to find and you "disappear" in a sense
i do feel sympathize for you and you're method in a way. i've always thought of just getting a boat and going out deep into the ocean, and just shooting myself in the head, and falling overboard pre-planned so my body just falls into the depths of the ocean and is never found. so i definitely understand you wanting to jump into the volcano after death, as a person who doesn't want their body found.
everyone has their own choice of method and we shouldn't feel the need to assume and measure the seriousness of another persons suicidal ideation; we don't know eachother on this forum well-enough to assume and judge just like that and it isn't fair to OP. criticizing and judging another persons method in a negative manner further derails the thread and it also prevents positive interaction and discussion amongst the thread and forum in general and again and IT WILL NOT BE TOLERATED.
to each their own, i definitely respect you're decision and method, as there's also plenty of other methods you can look into as well if you're not confident and that maybe more suitable for you, but that's for you to judge.
take care.