Seismometers such as this one (foreground) installed near Mount Spurr (background) were critical for scientists of the Alaska Volcano Observatory to monitor the earthquake activity beneath the volcano during its 1991-92 activity. View is north toward Mount Spurr.

The summit of Mount Spurr was built by a series of lava flows and domes erupted from the center of a large caldera formed during a large landslide and explosive eruption. The ancestral summit area of the volcano was destroyed by the landslide, which traveled at least 25 km down the Chakachatna River and carried blocks of the volcano as large as 100 m. In the photo above, the west and east rim of the caldera can be seen just left of the antenna and below the word "Peak," respectively.

Crater Peak is the youngest volcanic feature at Mount Spurr, located in the breach of the caldera about 3.2 km from the summit. Crater Peak has been the source of all eruptive activity at Spurr in the past several thousand years.