Hi Padre,
Well as allways i remain dubious of anything attributed to demons, the very fact that the activity ceased after the electrical supply was terminated speaks volumes,and there are many things that could cause it, one thing that springs to mind is the fact that this area is volcanic, volcanos as we all know create a great deal of potential energy (geothermal) also a broad spectrum of flammable and toxic gases,Its possible that these natural gases build up, and after a while are ignited by a dodgey electrical system or natural static charges from volcanic activity, It does not take 15 gigawatts to ignite gas, after all, one can ignite flatulence with a lighter (mythbusters).
And why the heck would Aliens want to travel billions of light years to set fire to a toaster ?

, As for the cable bursting into flame without being plugged in, I have personally experienced a static charge fom a thirteen amp plug that was'nt attatched to the electrical supply, I think that there is a natural explanation for this, not a diabolical one.
Jane