The study of Monks Mound itself — its construction history, its composition, and the challenges its structure has posed — illustrates how much remains to be learned about Cahokia even after more than a century of archaeological investigation.

The mound has experienced significant slumping on its western face.

The western slope of the mound has moved and shifted over the centuries, creating an irregular profile that is different from the original construction.

Archaeological investigation of the slumpage has revealed something surprising: beneath the upper construction stages of the mound, in areas affected by the slumping, there is evidence of buried ponds or wetlands.

The builders of Monks Mound appear to have begun construction in an area that included natural low spots or water features, and the presence of these soft, water-saturated sediments beneath portions of the mound has contributed to the instability that produced the slumping over subsequent centuries.