Did I say spark, I actually meant cracks, just happened to be talkeing to a power trader about sparks on IM while typing the last message.
You are right , sparks are very volatile and power vs. nat gas spreads are certainly not for faint hearted.
One of the things to look out for is the building correlation between US NG and UK Gas, this is a good candiate for convergence as there is an increasingly important market growing in European delivered and US delivered LNG which will, over the next few years correlate these markets basis a freight spread.