Over the course of the past century, five or more lahars have occurred at the Three Sisters and Broken Top, either as a result of glacier-outburst flooding or the failure of moraine-dammed lakes. However, these only affected undeveloped areas, as they extended less than roughly from their original source. Future dam failures leading to similar events would likely still only affect the proximal hazard zone with a diameter of , but they might reach more distal areas if they originate from certain lakes, such as Carver Lake or the unnamed lake on the eastern side of Broken Top draining to Sparks Lake. Lakes with less threat of reaching the distal hazard zone include small lakes in the headwaters of Whychus Creek and the basin below Collier Glacier.