As of 1993, the moraine for Jack glacier dammed a lake with a volume of , a surface area of , and a maximum depth of . Though this lake did not appear on United States Geological Survey topographic maps made during the 1920s, its presence was documented by a report in 1937. The lake sits precariously; moraines on the volcano are steep, unstable, and populated with boulders. Before September of 1960, there was a partial breach of this moraine-dammed lake that covered an area of near the moraine's base. Since 1960, there have been at least three incidents in which moraine-dammed lakes on the volcano have caused floods down the slopes, including a significant flood and debris flow in 2012. Local soil is thin, and it has been buried by a layer of weathered Holocene tephra from Three Fingered Jack, which has a maximum thickness of .