http://www.celestialmonochord.org/2006/05/sidewalk_fulgar.html

For the naysayers out there... Take a look at this beautiful bit of electrical discharge machining done to a sidewalk, likely either by a downed power line or by lightning. I'd tend toward the latter. Real-world arc scarring evidence.

Perhaps we'll be a little more open-minded about EDM on Earth and in space, hmm? If lightning can do this to a terrestrial concrete sidewalk (complete with black glassy concretions)... What do you think it can do on other solid surfaces on earth and in space?

Just a thought... Fairly strong visual, though. Sure as heck ain't "water erosion," that's for sure. Talk amongst yourselves...