Volcanic deposits that can be classified as deltas are rare, but have been documented as either cones of lava and hyaloclastite advancing into the sea or aprons of volcaniclastic material. Beach sands com- posed of grains of basalt can be found along the coasts of many volcanic islands; they exhibit a high degree of textural maturity, but their compositional maturity is very low, consisting mainly of unstable lithic fragments. An association with carbonate
sediments is quite common and the fringes of volcanic islands are ideal locations for carbonate sedimentation because of the absence of terrigenous clastic detritus: in the periods between volcanic eruptions faunal communities are able to develop and provide a source of carbonate as bioclastic sands or reef build-ups.