Pukao are the hats or topknots formerly placed on top of some moai statues on Easter Island. They were all carved from a very light red volcanic stone scoria, which was quarried from a single source at Puna Pau.
Pukao are cylindrical in shape with a dent on the underside to fit on the head of the moai and a boss or knot on top. They fitted onto the moai in such a way that the pukao protruded forwards. Their size varies in proportion to the moai they were on but they can be up to 8 feet tall and 8 feet in diameter.
The pukao was balanced as a separate piece on top of the head of a moai. It is not known how they were raised and placed but theories include them being raised with the statue or placed after the statue was erected. Pukao may have represented dressed hair or headdresses of red feathers worn by chiefs throughout Polynesia.
To date, about 100 pukao have been documented archaeologically, but only at Ahu with fallen statues or at the source quarry. Reference: Wikipedia