In this paper, we examine riverbank erosion in Bangladesh, a crisis that affects millions of people, but has largely been overlooked in the ICT4D and crisis informatics literature. Through a two-month field study in four districts of Bangladesh, we explored how people managed the impacts of erosion. Our study reveals that riverbank erosion resulted in material loss, forced migration, and social displacement. Victims faced many challenges but received little institutional support. We combined the ethnographic field study with an online social media study to present a holistic picture of the activities of crisis response. In the field sites, we observed that ICT use was limited to phone calls because the internet was inaccessible. However, our analysis of online social media activity in two nearby regions revealed strong Facebook activism. Activists used Facebook to raise public awareness about riverbank erosion and push for political change.