SoilsSoils

Soils

The soils of North Keeling Island are calcareous and derived from coral breakdown. They comprise a relatively thin layer of sandy loam which in places grades into moderately and/or very stony sand comprising considerable amounts of coral clinker. They overlay a highly permeable sub-stratum which allows rapid leaching of nutrients. On the main (southern) atoll, long-term leaching has led to deficiencies in iron, potassium, copper, manganese, magnesium and other minerals (Cameron McNamara Consultants 1984). This leaching has probably also occurred on North Keeling Island. Similarly, the soils of North Keeling Island are expected to be highly alkaline, as on the southern atoll, with pH levels of between 8.0 and 8.5. Soils abutting the outer shore are subject to wave erosion during high tides and storm surges.

The lagoon shore of the island slopes gradually and deepens slowly. At low tide, its maximum depth is less than 2 m. The bottom, and much of the beach, is a fine, greyish, sandy silt, much of which is derived from decaying vegetation. Towards the eastern recesses, this is greyer and darker and in the north-east corner, the beach is composed of a fine, dark, brownish mud. In a few places, particularly towards the southern end, the sand is replaced by a bare breccia slope and jagged fragments occur all down the west side.

Along the sheltered sides of the island, the shore is composed partly of coral shingle and partly of patches of white sand. However, periodic storms and changes in wave alignments alter the distribution of beach sand on an annual cycle. On the south and east coast (the windward sides) the bank is almost entirely coral shingle.