One of the most critical decisions to be made when a volcano eruption threatens is whether to issue an evacuation order. If the threat turns out to be unfounded, the evacuation order will not only have disrupted thousands of lives and often fragile economies, it also means people will be less likely to heed the next order to leave-an order that could save their lives. Elizabeth Rusch chronicles the work of scientists at the Volcano Disaster Assistance Program of the U.S. Geological Survey, based in the Pacific Northwest, and their colleagues in various parts of the world where eruptions threaten. They work collaboratively to monitor quickly changing situations and determine whether alerts and evacuation orders should be issued. She focuses on two specific eruptions, looking at how scientists from Indonesia and the Philippines worked with VDAP staff to monitor and evacuate people around Mount Pinatubo in the Philippines in 1991, and Mount Merapi in Indonesia in 2010. In the midst of a pending eruption, scientists in the U.S. work collaboratively with their international colleagues, including locally trained observers, drawing on evidence from satellites around the world, to help make these critical decisions in this fascinating entry in the "Scientists in the Field" series. (Ages 11-14)