My dissertation examines social impacts of glacier retreat and disaster mitigation projects in Peru's Cordillera Blanca mountain range, which contains more than 700 glaciers and has produced the most deadly glacier, caused catastrophes in world history. Glaciers worldwide have receded considerably in the last 150 years, and in Peru lakes have formed after glacial ice melted. In the 1940s, these lakes began bursting through their natural dams and producing deadly disasters for Cordillera Blanca residents. My research examines how these local inhabitants not only perceived of and responded to retreating glaciers and glacial lake outburst floods, but also how non-local experts who arrived in the region to study glaciers and mitigate for future disasters affected environments, local power structures, and people's perceptions of nature. On the one hand, locals benefited from flood prevention, new jobs, and hydro-electric power generation. On the other hand, glaciers became the domain of experts, conflicts over water use increased, and vilification of glaciers occurred. Analysis of Peruvian government reports, scientific studies, and oral histories will illuminate this complex and contradictory history. This important and timely research reveals the role of climate in shaping the past while also suggesting implications for future climate change.