What a thunder can do...

[boiseengineer]

Maybe it was "positive" lightning strike.

NOAA: "Its flash duration is longer, and its peak charge and potential can be ten times greater than a negative strike; as much as 300,000 amperes and one billion volts!"
http://www.srh.noaa.gov/jetstream/lightning/positive.htm

 

[Sgeirk]

Good point, either way, it looks like dynamite went off inside the transmitter shack.

 

[boiseengineer]

Or something volatile was stored in there & the lightning lit it off.