On August 1, 1998, about 1315 central daylight time, a Schweizer SGS 1-34 glider, N7631, registered to Coastal Soaring Association Inc, operated as a 14 CFR Part 91 personal flight, crashed while on approach for a forced landing at Coastal Airport, Pensacola, Florida. Visual meteorological conditions prevailed, and no flight plan was filed. The aircraft was substantially damaged, and the pilot sustained no injuries. The flight originated from the same airport about 10 minutes before the accident. The pilot stated that when he was about 100 feet off the ground, the canopy suddenly opened. He had no indication that it would become unlatched. The canopy remained attached to the glider, hanging on the left side of the fuselage. The pilot kept climbing to 200 feet, released the towing latch, and performed a 180 degree turn to the left to return to the airport for landing. When he was approaching the runway, he realized that his sink rate was very high. While pulling up on the stick to try to clear a wooded area before the runway, the right wingtip brushed the top of a tree. The airplane stalled and crash into the ground about 300 feet before the runway. According to the pilot, the canopy's latching mechanism did not reveal any malfunctions during preflight or postcrash examination.