Here is your short paragraph on Avanimulam:
This festival of Tamil Nadu is associated with the life of Manikava-Cakar that occurs in the month of Avani (August-September).
This is observed in all Siva temples but as an incident in said to have happened at Madurai, the festival has a special significance there.
The Myth is that Lord Siva appeared in the form of a horse man on the Avani Mulam day and the incidents pertaining to Manickavacakar happened on the next day. On this auspicious day, devotees take out the procession of God Sundaresa from the river bank to the temple “with a golden basket and a golden spade.”