Spurr

Geography & Climate

Spurr is located in United States, within the Alaska Peninsula Volcanic Arc of the broader North America Volcanic Regions. Situated at 61.30° N, 152.25° W in the Northern Hemisphere, the volcano lies within a subarctic climate zone. At 3,374 meters above sea level, Spurr rises above the surrounding terrain into montane or subalpine conditions. The elevation creates distinct ecological zones along its flanks, from forested lower slopes to exposed rocky terrain near the summit. The volcanic landform is characterized as a composite, which describes the physical shape and structure of the volcanic edifice as observed from the surface.

Geological Context

Spurr sits in a subduction zone, where one tectonic plate dives beneath another, creating intense heat and pressure that generates magma. Subduction zones are responsible for many of the world's most explosive volcanoes and deadliest eruptions. For communities in United States near Spurr, this tectonic setting means the volcano is capable of producing powerful explosive eruptions, pyroclastic flows, and lahars that can threaten populated areas within tens of kilometers of the summit. The dominant rock type is andesite / basaltic andesite, a dark, fine-grained volcanic rock that forms from rapidly cooling, low-viscosity lava. Basaltic eruptions tend to be less explosive and produce fluid lava flows that can travel long distances. While less immediately dangerous than explosive eruptions, basaltic lava flows can destroy structures and infrastructure in their path, and volcanic gases released during these eruptions can affect air quality over a wide area.

Eruption History Summary

Spurr has 7 recorded eruptions in the geological database, spanning from 6050 BCE to 1992 CE. The most powerful recorded event was a cataclysmic eruption with ash columns reaching the stratosphere in 1992 CE, reaching VEI 4 on the Volcanic Explosivity Index. Notable eruptions include 1992 CE (VEI 4), 1953 CE (VEI 4). This eruption frequency indicates a moderately active volcanic system with periodic reawakenings. The most recent eruption in 1992 CE places this volcano within the modern era of volcanological observation.

Significance

With a maximum recorded VEI of 4, Spurr has demonstrated the capacity for significant explosive eruptions that can impact regional aviation, agriculture, and communities tens of kilometers from the summit. VEI 4 eruptions produce ash columns reaching 15-25 kilometers into the atmosphere. With 7 recorded eruptions on file, Spurr has enough documented activity to help scientists identify patterns in its eruptive behavior. Given its recent activity, Spurr is closely monitored by geological survey organizations to provide early warning of future unrest.

GVP Reference Summary

Mount Spurr is the closest volcano to Anchorage, Alaska (130 km W) and just NE of Chakachamna Lake. The summit is a large lava dome at the center of a roughly 5-km-wide amphitheater open to the south formed by a late-Pleistocene or early Holocene debris avalanche and associated pyroclastic flows that destroyed an older edifice. The debris avalanche traveled more than 25 km SE, and the resulting deposit contains blocks as large as 100 m in diameter. Several ice-carved post-collapse cones or lava domes are present. The youngest vent, Crater Peak, formed at the southern end of the amphitheater and has been the source of about 40 identified Holocene tephra layers. Eruptions from Crater Peak in 1953 and 1992 deposited ash in Anchorage.

— Smithsonian Institution, Global Volcanism Program