The Trout Lake Mudflow is the youngest large debris flow from Adams and the only large one since the end of the last Ice Age. The flow dammed Trout Creek and covered of the White Salmon River valley. Impounded water later formed Trout Lake. The Great Slide of 1921 started close to the headwall of the White Salmon Glacier and was the largest avalanche on Adams in historic time. The slide fell about and its debris covered about of the upper Salt Creek area. Steam vents were reported active at the slide source for three years, leading to speculation that the event was started with a small steam explosion. This was the only debris flow in Mount Adams' recorded history, but there are five known lahars.