It sounds like microbial anaerobic respiration heated things up and then conditions were right for a smoldering burn to propagate. It's a shame all that detaile

It sounds like microbial anaerobic respiration heated things up and then conditions were right for a smoldering burn to propagate. It's a shame all that detailed historical cultural information will be lost to future landfill researchers. On the upside, the high temperatures and anaerobic conditions might reduce metals to their base forms as sperules which would make future mining for material re-use a lot easier.