Well, first you might want to get in for a sleep study. Not for your rem cycles, but for your body temperature. Often times, things in our dreams reflect how our body is physically feeling while we sleep (like dreaming of water when you have to pee). There's a chance, considering the feeling of heat stays after waking, that the heat sensation starts physically and translates to lava in the dream. In the meantime, maybe get a fan to cool you off while you sleep.

The imagery of mass destruction is often attributed to a cataclysmic change in your life, or one that is perceived/anticipated (even if it's not based in reality). Are you anxious about some upcoming event/issue? Has something major come up in your life that you haven't been able to resolve? That it's a world-changing event translates to the fear that whatever is driving this fear is inescapable.

There's also another theme here - fire. The heat of lava/fire often symbolizes determination, passion, and change. It's destructive and driving. It's captivating and devastating. This is a more vague perspective, and will probably take second chair to the theme of destruction. ((Is your life changing in major ways that you are feeling you're losing control over?))

Something to consider - what were the other people like? How do you relate to them? All characters in the dream are essentially projections of different parts of yourself. Getting to know the characters may help you understand what parts of your own personality are felt as being threatened. Look for commonalities between them, and consider events in your waking life that might be influencing that part of yourself.