We live on an active planet. Every year, some 50 to 70 volcanic eruptions occur somewhere in the world, some featuring slow pyroclastic flows, others causing violent explosions. As the recent eruption of the Popocatepetl volcano near Mexico City reminds us, many of these hotbeds of activity sit dangerously close to population centers. Following are 10 volcanoes that the International Association of Volcanology and Chemistry of the Earth’s Interior is closely monitoring due to their potential for eruption and their proximity to large populations. The list is in no particular order, as the IAVCEI did not rank the specific threats posed by these volcanoes.