Obon is in the middle of August and is a holiday lasting several days where families visit the graves of their ancestors. Obon is a celebration of the Shinto religion and the belief behind the celebration is that the spirits of one's ancestors returns to Earth to visit. For this reason, lanterns are often light out side of houses to guid ancestors back to homes. At the end of the week, special lanterns are lit and are released into a near by river to guid the spirits back into the spirit realm. In many places in Japan, this special event at a river is called Toronagashi.
In Morioka, however, it is called Funekko Oroshi. This is because part of the celebration involves setting aflame boats (about twenty, one for each neighborhood) full of fireworks on a river. (In Japanese, the word for boat is fune). Although bad for the environment, it is quite a spectacle.
As the people (mostly men, and a few women) who pull the boats down the river are nearly naked, it is also I imagine quite dangerous, since the fireworks and debris could be seen spilling out of the boats.
At the end of the festival, several hundred fireworks were shot off as men set paper lanterns out to float down the river.
Watch the video (about three and a half minutes long, no sound) below. The people are a little compressed because the original video is widescreen but on the internet it has to be a square rather than a rectangle.