I work for a major power company in the midwest. Shorting two phases together on high voltage lines can cause very high dollar amounts of damage. The person (retired) who was in my cubicle before me collected cuttings of the conductors that have failed for various reasons. Each sample has a small note on it explaining what it was and how it failed. There is one that says:
This is a piece of 447kcmil [about an inch in diameter] ACRS that was part of a 69kV circuit... The circuit was heavily loaded (overloaded might be a better word). It sagged into the 12kV circuit located lower on the poles. The small burn marks from where contact was made belie the damage done. More than $250,000 in damage was done to customer owned stuff. Fortunately no one was injured and no building were burned.
Some of the other notes a funny however:
This peice of triplex (neutral conductor) that has been chewed up by a squirrel. Like all rodents they have to keep their teeth ground down or they will grow too long. this sort of damage is less likely on the phase wires because the squirrel is usually dispatched with the first on second bite.
The piece of wire the note is discussing is where two conductors were spliced together. The splicing "shell" is almost completely chewed through.
Major damage from shorts are rare however, because the circuit is usually cut off within 1s of the fault being detected. Regardless, high voltage power lines are not something you want to mess around with. it only takes about 22kV to overcome the resistance in 1 inch of air (typical). Some high power lines are 340-785kV; that means the current can jump gaps of up to 3 feet in the right conditions.
An 8000amp 785kV fault current is basically an instagib, even for 1 second.