A first-of-its-kind study on Twitter use during 5 of the costliest US natural disasters offers potentially life-saving insights. The research finds that Twitter users with small networks (100-200 followers) increase activity more than those with larger networks in these situations. It also finds that each disaster type (hurricanes, tornadoes, floods) has a unique pattern of social media use. The results have important implications for government and organizations responsible for emergency preparations.