1) This has been an active leak for many years.
2) The original installation of the post or shingles were done incorrectly. Roofing tar or patching compound should never be the primary means of deflecting water. Roofing tar should not even be used on a asphalt shingle roof.
3) incorrect flashing caused a leak which then was improperly repaired with tar. Or the original install was tar and it soon began to leak becaus thats what roofing tar does.
4) The leak was ignored or undetected and the roof rafters suppporting the post began to rot. The weight of the power lines is pulling the post into the decomposing wood and opening a big hole.
5) Finally, no one has inspected this roof for several years. This did not happen over night.
6) The water from this hole must be draining somewhere, causing decay, corrosion and mold. As it turned ot the water was leaking through the first floor wall and down the basement wall.
This all could have been prevented by a properly installed fifty cent piece of flashing. It might take 20 minutes to do. It is extremely important to have an independent inspection done after hiring a contractor for any project. Don't expect the city inspector to protect you. City inspector do not always drive out to check on a re-roof. They rely on the reputation of the contractor or picture the contractor provides. If they do drive to the site they almost never go up on the roof. The example above is not visible from the ground. They have NO liability to you. Remember, it is not about dishonest contractors. Sometimes things are missed, forgotten or they simply has a rookie on their crew that someone forgot to watch closely.
You generally can get someone to do a single point inspection such as a roof for $100.00 or less. A very good investment.