The civilization that is often noted for its sudden disappearance is the Tiahuanaco civilization. Tiahuanaco was a significant pre-Columbian civilization located near Lake Titicaca in what is now Bolivia. Its decline remains a subject of research and speculation, with theories including climate change, agricultural decline, and sociopolitical factors contributing to its disappearance.
The Inca civilization, while it did experience significant decline after Spanish conquest, did not exactly "disappear" in the same manner as Tiahuanaco. The Aymara people are still present in the region today.
So, the correct answer is Tiahuanaco.