Most Western Samoan soils are formed from basaltic volcanic lava flows differing mainly in age and kind of deposit (pahoehoe, aa or scoria), volcanic ash associated with past eruptions, and sediments from volcanic material.
|
Volcanic activity |
Age |
|
Fagaloa |
2.5 million years |
|
Vini |
|
|
Salani |
125,000 years |
|
Mulifanua |
70,000 – 10,000 years |
|
Lefaga |
10,000 – 5,000 years |
|
Puapua |
1850 – 750 years |
|
Aopo |
240 – 120 years |
In addition:
Colluvium occurs on the lower parts of hilly and steepland particularly on Upolu. These deposits, formed by erosion, include many stones and boulders.
Alluvium deposited by the main rivers is not extensive in Samoa but forms the parent material of the most versatile soils.
Coral sand strips along the coastline lie in front of swamps and depressions in which organic deposits overlie coral or basaltic sands. Locally there are estuarine deposits under tidal influence. There are also shallow upland peats in a few small areas in Upolu and in central-eastern Savai'i.
