Social media have become an established feature of the dynamic information space that emerges during crisis events. Both emergency responders and the public use these platforms to search for, disseminate, challenge, and make sense of information during crises. In this talk, I will review the social processes that unfold in communities during disaster events and how these processes can be studied at scale with behavioral trace data. I illustrate this approach in studies of rumoring behavior and mass convergence of attention. Understanding these processes has important practical implications for effectively leveraging social media for emergency management.