USGS HOME
Contact USGS

  • About
  • Observatories
  • Activity
  • Education
  • Publications

Summit of Glacier Peak Divided in Three Parts

The uppermost 800 m (2,600 ft) of Glacier Peak can be subdivided into three parts, two false summits and the actual summit. The summit of Glacier Peak is covered by the uppermost parts of the Chocolate Glacier on the east, but is partly exposed on the west and south. It consists of a massive 50-m-thick (165 ft) lava flow. The lava is believed to be a remnant of a dome eruption during one of the major mid-Holocene eruptions perhaps about 5,500 years ago. There are two smaller peaks equally spaced to the north and south of Glacier Peak's summit block. Approximately 250 m (820 ft) to the north is a small plateau with the remnants of a recent lava dome. A small dacite lava flow extends from near the center of this false summit to the headwall of Dusty Glacier on the volcano's northeast slope. Disappointment Peak is a dacite lava dome located 250 m (820 ft) south of Glacier Peak's summit. This large dome flowed almost 800 m (2600 ft) down the south and southwest side of the volcano more than 13,000 years ago.