The Central American arc is a continuous range of volcanoes running from northwest to southeast through Guatemala, El Salvador, Honduras, Nicaragua, and Costa Rica. These volcanoes lie parallel to, and approximately 100 km to the east of, the plate boundary between the Cocos and Caribbean plates. When active, they vent magmas and volatiles from the underlying mantle wedge. Beginning in Costa Rica, the goal of this and subsequent expeditions is to sample the entire arc through all five countries.