The glider pilot stated that when he reached his intended destination, lift increased and he decided to fly back to the departure airport. As the glider flew closer to the departure airport, the lift decreased and the glider was about 800 feet above ground level, approximately 10 miles away from the departure airport. The pilot was unable to locate another airport and elected to land in a field. While on final approach for the field, the pilot observed a small hill prior to the field and turned left to avoid a straight-on collision. The left wing subsequently struck the hill and the glider came to rest upright in the field. The pilot added that there were no preimpact mechanical malfunctions with the glider. Examination of the glider by a Federal Aviation Administration inspector revealed damage to the left wing, forward fuselage, and tailcone.