Meager is known for its last major eruption about 2,350 years ago. The strange thing about the eruption was the fact it released the debris from the northeast side of the volcano, as rock and ash blocked a major river called the Lillooet River. The river was dammed to a height of at least 100 meters, forming a lake. The lake reached a maximum elevation of 810 meters and was at least 50 meters deep. The breccia soon eroded from water activity within the lake, forming Keyhole Falls. There was a massive flood when the water first broke through the breccia, carrying small house sized blocks of breccia. During this eruption, ash was hurled into the air over 20 kilometers above sea level. The ash was carried eastward as far as Alberta.