Recently the Dorset Geologists' Association (of which I am a member) published in their newsletter a postcard sent by a friend of a member on holiday in Mauritius, showing coloured earths in a gully. Mauritius is a small volcanic island in the middle of the Indian Ocean, comprising mainly basalts (now tropically weathered) as befits a small volcanic island in a tropical ocean. In tropical regions, weathering of the primary minerals in rock is more intense and occurs to greater depths than in other climates. Looking at it simply, organic matter is rapidly degraded and rarely becomes incorporated below a thin surface layer, unlike in temperate climes. Consequently, weathering occurs mainly by hydrolysis in near-neutral conditions at depths well below the influence of acidic organic decomposition products. Tropical weathering down to depths greater than 100 metres are not uncommon due to the warm, damp conditions conducive to rapid (but taking tens to hundreds or thousands of years) decomposition of rock to soil.
展开▼
