An unglaciated lava flow and an overlying pyroclastic-flow deposit extending east from the summit are the most recent products of Chiginagak.

They most likely originated from a lava dome at 1687m on the SE flank, 1 km from the summit of the volcano.

In early May 2005, a catastrophic release of acidic water from the lake, with an accompanying acidic aerosol component, drained and flooded Indecision and Volcano Creeks with acidic water, traveled 27 km downstream and flowed into the Mother Goose Lake, headwaters of the King Salmon River.

Extensive vegetation damage occurred along the flood route and Mother Goose Lake was acidified (pH of 2.9-3.1), killing all aquatic life and preventing the annual salmon run.

Indecision Creek now usually has a strong sulphur odor, yellow color and a pH of 1.3.