Objective: the present work aims to learn about the subjective theories of the prosocial behavior of young volunteers during the response and recovery stages of a socionatural disaster. Method: a qualitative case design was used by selecting, through intentional sampling, 11 university students who volunteered in the face of the hydrometeorological disaster occurred in Atacama, Chile. Data was collected through semi-structured interviews and a discussion group, using the coding process in grounded theory as an analysis strategy. Results: we found that (i) volunteers understand prosocial behavior as a process of limited-temporality humanitarian aid which depends on empathy towards those affected; the perception of institutional (in)capacity; a subjective risk assessment; self-perceived abilities; and a sense of social responsibility in the face of a disaster; (ii) its development is linke...