Incident Overview
A glider pilot reported that while flying at 3,500 feet AGL over a western plateau, thermal activity produced lift of about 2 to 4 knots and sink of 4 to 6 knots. The pilot characterized the lifts as ill-defined, and the flight mostly involved flying into sink areas.
Descent and Decision to Return
As the glider descended to 2,500 feet AGL, the pilot turned back toward the departure airport. However, the glider continued to experience sink rates of 4 to 6 knots. The pilot then began searching for a suitable field for an off-airport landing.
Approach and Collision
The pilot overflew a potential landing field at 2,000 feet AGL and determined that a fairly constant sink of 6 knots existed in the area. While approaching the field, the pilot reported that the sink increased, and the glider subsequently collided with trees at the approach end of the intended landing field.