MT. ADAMS
Mount Adams is the largest active volcano in Washington State and among the largest in the Cascades. The volcano has produced a larger volume (about 300 km3 or 70 mi3) of eruptive material during the past million years than any other Cascade stratovolcano except Mount Shasta (about 350 km3 or 85 mi3). Mount Adams lies in the middle of the Mount Adams volcanic field—a 1,250 km2 (about 500 mi2) area comprising at least 120, mostly basaltic volcanoes that form spatter and scoria cones, shield volcanoes, and some extensive lava flows. The volcanic field has been active for at least the past one million years. Mount Adams was active from about 520,000 to about 1,000 years ago and has erupted mostly andesite. Eruptions have occurred from ten vents since the last period of glaciation about 15,000 years ago.
QUICK FACTS
Location: Washington, Klickitat County
Elevation: 3,742 (m) 12,277 (f)
Volcano type: Stratovolcano
Most recent eruption: 3,800 years ago
VOLCANIC HISTORY
Andesite and basalt flows formed a 20-to-200-foot (6 to 60 m) thick circle around the base of the Mount Adams, and filled existing depressions and ponded in valleys. Most of the volcano is made of andesite together with handful of dacite and pyroclastic flows which erupted early in Adams' development. The present main cone was built when Adams was capped by a glacier system in the last ice age. The lava that erupted was shattered when it came in contact with the ice and the cone interior is therefore made of easily eroded andesite fragments. The present eruptive cone above 7,000 feet (2,100 m) was constructed sometime between 40,000 to 10,000 years ago. Since that time the volcano has erupted at least ten times, generally from above 6,500 feet (2,000 m).