How can electrical power lines keep burning even after the wire burns through and breaks?

It happened over 50 years ago, but I can still vividly recall the day the wires in front of my house exploded in a roaring buzz so loud it shook the walls. Over 1 mile of 18,000 volt lines burned that day. The first hint that something was wrong was the sound, an intermittent buzzing that began off in the distance and grew rapidly louder till it overpowered rational thought.

When I ran outside to see what was happening, a terrified neighbor yelled, “The wires are on fire.” I reached the front yard in time to see 5-foot fireballs racing between poles a quarter mile down the road we lived on. They were heading for me. The occasional pause in the roaring sound came when a fireball reached a pole and, for some reason, paused at the supporting insulators before passing on to the next exposed strip of wire.

The traveling fireballs looked like the arc of an arc welding operation and gave of a sound like a buzzer. But both the size of the arc and volume of the sound were as if Paul Bunyan were doing the welding. As the arc passed, it left the wire behind it smoldering and burning, and the burning wire soon broke. What was truly puzzling was that in all, over 1 full mile of wires were destroyed. When the wires between poles broke, the arc-fire continued on unabated. How could this be? Why didn’t the breaking wires (they crumbled almost immediately between each successive pole) cut the circuit and snuff out the fire? I have been puzzled about the physics of this ever since witnessing it.

We later learned that what caused the strange event was an unusual weather pattern. I lived in coastal Virginia, and the breeze had be blowing gently from the sea for 3 full days, with temperatures just right for the formation of fog. It had set up a salt fog that you could actually taste in the air. The highly conductive salty dampness had coated and permeated everything, and when a wet, conductive branch fell over the 18,000 volt lines that carried power to an industrial complex south of us on the Southern Branch of the Elizabeth River, that triggered the cascading failure. Did the damp, salty ground itself serve as the return circuit?