White bands of coral in the southern sector, at a height of , above the present water level, shows that the area was once marine and that the water was much deeper than present. The chronological development of the outer barrier spit of the lake has been dated by Optically stimulated luminescence studies of minerals. This was done on sixteen samples of the lake bed. The studies indicated doses of between 153 ± 3 mGy and 2.23 ± 0.07 Gy, corresponding to ages from 40 years at the top of the spit to 300 years at the bottom. The youngest ages are consistent with the age of the overlying vegetation. A clearly defined period of > of barrier construction 40 years ago is identified. Prior to that the deposition rate was relatively constant for 300 years.'"