Going To Ground The Breakdown -- A Short Circuit On A Large Scale

From Popular Science:

Here's a vivid example of an electrical short circuit in a beautiful natural setting. In brief, a short circuit occurs when the normal path of current is bypassed via an alternate route with very low resistance. Since current likes to take the path of least resistance, most of it will flow through the short circuit. Also, according to Ohm's Law (V = IR), reducing the resistance of the circuit will drive up the current. Large currents result in excessive resistive heating in circuits, and we usually want to avoid them.

In the video an unfortunate tree has fallen onto a high-voltage power line. This provides a direct path for current to go into the ground, rather than travelling the normal route through the electrical grid. The resulting surge of moving charge results in sufficient resistive heating to ignite the tree and potentially start a forest fire.

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