Lyman Glacier lies on the north slopes of Mount Adams in Washington, within Gifford Pinchot National Forest and the Yakama Indian Reservation. Beginning near the summit at about 11,400 feet, it descends to a terminus near 7,800 feet, and below about 9,000 feet its ice divides into three distinct lobes. The glacier has been shrinking for more than a century, losing 34 percent of its surface area between 1904 and 2006. Named by Claude Ewing Rusk for William Denison Lyman, it is significant both as part of Mount Adams’s volcanic landscape and as a clear example of long-term glacial retreat.