Lava flows from the summit vent erupted between 30,000 and 10,000 years ago, and during the final stages of edifice construction, blocky pyroclastic flows entered the volcano's southeastern drainages. An eruption from Sherman Crater 6,600 years ago erupted a blanket of ash that extended more than to the east. Today, sulfurous gases reach the surface via two fumarole pathways: Dorr Fumarole, northeast of the summit, and Sherman Crater, south of the summit. Both are sites of hydrothermal alteration, converting lavas to weak, white-to-yellow clays; sulfur is a common mineral around these fumaroles. At Sherman Crater, collapses of this weakened rock generated lahars in the 1840s.