Lyman Glacier is located on the north slopes of Mount Adams a stratovolcano in Gifford Pinchot National Forest in the U.S. state of Washington.

[3] The glacier is also within the Yakama Indian Reservation and descends from near the summit of Mount Adams at approximately 11,400 ft (3,500 m) to a terminus near 7,800 ft (2,400 m).

Below 9,000 ft (2,700 m) the glacier splits into three distinct lobes.

[3] Lyman Glacier has been in a general state of retreat for over 100 years and lost 34 percent of its surface area between 1904 and 2006.

[2] Lyman Glacier was named after William Denison Lyman by Claude Ewing Rusk because Lyman was one of the first to describe some of Mount Adams' features and history.