the caribbean parts of the kingdom consist of two zones with different geographic origins. the leeward islands (saba, sint eustatius and sint maarten) are all of volcanic origin and hilly, leaving little ground suitable for agriculture. the leeward antilles (aruba, bonaire and curaçao) are largely lacking in volcanic activity: the island arc occurs along the deformed southern edge of the caribbean plate and was formed by the plate's subduction under the south american plate.