When Little Ice Age glaciers retreated during the 20th century, water filled in the spaces left behind, forming moraine-dammed lakes, which are more common in the Mount Jefferson Wilderness and the nearby Three Sisters Wilderness than anywhere else in the contiguous United States. A number of these lakes breached during the 20th century and inundated Jefferson Park and the Jefferson Creek drainage under Waldo Glacier. These breach events yielded floods and small lahars (volcanically induced mudslides, landslides, and debris flows). The flood on August 21, 1934, at a lake formed near Whitewater Glacier, created a debris flow that reached the Whitewater River drainage and buried parts of Jefferson Park in of debris; another event took place in 1957, but was poorly documented.