It has a destroyed crater to the northwest. Prehistoric lava flows on its western flank; one of them, the so-called Florida flow, was perhaps created by Platanar's most recent activity. Cerro Porvenir has a truncated caldera at the summit with a cone inside. Both of these are part of a composed stratovolcano of Upper Pleistocene age that on Platanar's side overlies the remains of Palmera's collapsed caldera, of probable late Pleistocene age. Platanar has erupted lavas ranging from basalts to andesites in composition.