Nige
Long time ago I read the direction of the flattened trees, pointed towards the centre, now they say away from centre. This is crucial, pointing towards centre indicates a firestorm or high alt nuclear explosion, pointing away indicates a blast shock wave,
Maybe a high alt Meteor or Asteroid explosion could cause the same effect, but the shock wave should hit first, blowing all trees away from the centre before the updraught sucks them in.