A key institution responsible for river management and disaster response, particularly on the Mississippi River and other hazardous sites. The Corps' mission and methods are often examined and questioned by various characters throughout the book.

An officer who oversees operations on the Mississippi River and leads the Mississippi River Commission. His role highlights the tension between military strategy and civilian needs in the Corps' management practices.

A Cajun man who manages a navigation lock to control the Atchafalaya River on behalf of the Army Corps. He is a proponent of the Corps' efforts.

A Cajun native who manages the Army Corps' control mechanism at Old River, directing water flow. Initially skeptical of the Corps' objectives, he grew to support their mission.

A former general counsel of the National Wildlife Federation and law professor who challenges the Army Corps' approach to controlling the Mississippi. He raises concerns about military versus civilian priorities.

A Cajun fisherman whose livelihood depends on the Mississippi River and its management. He advocates for better support of local industries like crawfishing by the Corps.

The director of the Hawaii County Civil Defense Agency, tasked with managing lava flows in Hilo. He interacts with various experts to assess and respond to volcanic challenges.

An Icelandic physicist who devised a method to cool lava flows to protect his hometown. His innovation significantly impacted local geography and economy.

A military officer who assisted with Thorbjorn's lava cooling project in Iceland, bringing a managerial perspective to the scientific effort. He later shared his experiences in Hawaii.

A resident and former mayor of Heimaey, Iceland. He provides local historical context and decision-making under volcanic threat.

An upper-middle-class family living near Los Angeles, whose home was nearly destroyed by a debris flow. Their experience highlights issues with local infrastructure management.

An eccentric individual who built a castle using debris boulders near the Los Angeles mountains. He discusses debris basins and enjoys a unique view of the natural landscape.