The rivers are becoming muddy

Some time ago, Erhart (1968), traveling by ship along the Congo and Amazon rivers, was puzzled by the lack of turbidity in the water - no sediments, no clays, nothing of the brown colour that one expects of mighty rivers draining such large basins. Eventually, he realized that the clear water was natural. These large streams flowed from rain-forest basins, where there was no erosion. Chemical processes of organic origin predominated. Although the water in these rivers was carrying salts, resulting from the leaching of ions from the soils they drained, no sediments were being transported. Ions of calcium, sodium, potassium, magnesium, and silicon and carbonates, phosphates, and chlorides were carried in the water in small proportions, producing a gradual increase in the salinity of the sea and supplying raw materials for the shells of sea organisms.

Erhart also realized that the old processes of soil formation (weathering) in rain-forest environments were the origin of limestone. Today’s calcareous mud at the bottom of the ocean is the current equivalent of the ancient limestones formed (by biostasy) 100 or 200 million years ago during the Mesozoic era, when dinosaurs roamed the Earth. However, the calcareous muds of the past were buried by younger sediments, composed of claystones, siltstones, and associated sandstones (what geologists call “flysch”), during a drier period that followed the humid period that produced the limestones. Erhart concluded that the forest had disappeared and that subsequently the soils had been eroded; he called this situation, in which mechanical processes predominated, rhexistasy.

Today, large forests are disappearing even faster as a result of human action. Deforestation is widespread. Forests are logged or burned, leading to soil erosion; rivers are becoming filled with muddy sediments. Flying over the Amazon brings new surprises every year: its tributaries are becoming yellow or brown in colour; the Amazon itself is no longer dark green; and in geological terms, the forest is starting to die.

In ancient times, forests would die, but others were born. There were always sufficient trees to maintain a low level of CO2. Now, as all forests are being cut back at the same time, we suspect there is considerable risk to the planet’s dynamics.