While terms such as solidarity and communitas are invoked, sometimes interchangeably, to characterize the feeling of togetherness supporting mutual aid during the emergency phase of disasters, they are not identical phenomena. This article examines the 2017 Peruvian huiaco disaster to understand the role communitas and reciprocity play in the mobilization of emergency aid and the growing sense of togetherness buttressing its distribution. Via an in situ qualitative study conducted as the disaster unfolded, we analyze how the huaicos or flashfloods and mudslides caused by the El Niño phenomenon activated a temporary but structured humanitarian exchange that filled voids left by disrupted markets and debilitated local, regional, and national governments. This aid resulted from a media-fueled sense of togetherness that motivated an asymmetric exchange based on principles of redistribution and generalized reciprocity. While the short-Term feeling of togetherness offered a glimpse of possible societal transformation, once communitas ended, the humanitarian exchange further reproduced pre-existing social structures and exacerbated vulnerability. With an understanding of how temporary post-disaster communitas operates, the challenge lies in the strategic importance of prolonging the experience of communitas to address the new relational vulnerability created by humanitarian exchange.