The Lesser Antilles island arc lies of the east margin off the central American coast, spanning approximately 750 km in length from the northernmost island of Saba to the southern extent of Grenada. The crescent of volcanic islands is the surface manifestation of the westwards subduction of the American tectonic plate underneath the Caribbean Plate.
From north to south, the islands studied as part of CRITMAG are:
- St Kitts
- St Vincent
- The Grenadines archipelago (Bequia, Isle de Quatre, Mustique, Savan, Petit Mustique, Catholic Island, Canuoan, Mayreau, Petite St Vincent, Ile Caille, Ronde, Carriacou)