Before anyone screams "Terrorism, Coverup, ROP, Nothing to see here move along" (surprised the thread made it this far without that spam), how about a little perspective. If it were terrorism, why would they do it in a rural/suburban area instead of inside a city where they could cause far more harm? The likely cause is a broken rail, in the last 24 hours there was a big temperature drop there and the steel rails expand and contract based on the temperature changes. The track is designed to handle that, but occassionally there are breaks, especially after a big shift in temperatures. The railroad, CSX, also has one of the worst safety history of the major railroads and has been repeatedly cited for poor track maintenance. Plus there are other potential causes (axle failure, bearings burn off, sloppy train handling, etc.)
What is scary is seeing that fireman on the ladder spraying water on the fire. There is a somewhat famous film of another derailment 30 years ago in Houston where a firefighter was also up on a ladder spraying down a big fire, where a big after explosion literally blew him off the ladder.