Environmental disasters are escalating in frequency and intensity, with climate change largely exacerbating these conditions. Research on disasters suggest that volunteers are invaluable assets that can help contribute to vulnerability reduction and emergency response. Much of the literature on volunteerism have focused on individual variables and there is a dearth of research examining disaster volunteerism as a form of collective action. This study examined whether the Social Identity Model of Collective Action (SIMCA) can be used in predicting collective volunteerism in times of natural disasters. Results of surveys with 299 public and private university students, confirmed that intentions to volunteer in collective disaster activities was influenced significantly by collective efficacy, social norms, and group-based emotion of anger. These three factors also significantly mediated the connection between social identity and intentions to volunteer. The study also showed that among the various emotions of shame, guilt, sympathy, and anger, it was the latter that significantly predicted intentions to volunteer. The findings suggest that volunteerism behavior during disasters can be encouraged by making identity salient, by encouraging group efficacy and shaping group norms, and by harnessing emotions towards collective action.