The pilot elected to attempt a landing at a field. The tail wheel equipped airplane touched down on the main wheels in a "tail low" attitude. The pilot did not initially realize that the snow was too soft and deep. He added full power and pulled back on the stick, but he was unable to prevent the airplane from nosing over. It slid for approximately 7 feet before coming to rest. The vertical stabilizer and rudder were damaged when the airplane nosed over. After the accident, the pilot determined that the snow was about 14 inches deep. He commented that although the airplane was equipped with large diameter tires, the snow was too deep. He reported that there were no malfunctions or failures associated with the airplane prior to the accident.