Formação de labirintos sob a floresta equatorial Amazônica (Território Federal do Guaporé)

Abstract

            The presence of laterites was first explained in the zone where the "campos cerrados" (savanna-like formation) occurred as the vegetal covering. Lateritic formations (canga) are widely distributed in vast areas of the Brazilian central plateau.

            The various naturalists which traveled in the Amazonian region have sometimes recorded references of the presence of hematites and limonites.

            Prof. Pierre Gourou, in 1948, during field studies in the states of Pará and Amazonas, along the axis of the Amazon river, emphasized geomorphological problems as well as some other problems directly related to the occupation of the land when laterization reaches its last stage, i .e., the formation of lateritic crusts.

            The problem of laterization is, nowadays, one of the most controverted points in respect to its origin.

            Our field trips made in areas where savannas occurred (Senegal and Brazilian central plateau) and in regions of tropical forests (Amazonian region and Portuguese Guinea) we have arrived to the conclusion that laterites are formed either in a zone of savannas or under the forests.

            The only difference between the lateritic process in the above mentioned zones is that in the first case there occurs a concentration of the hydroxides of iron and aluminum at the surface, while in the areas where forest occur, that concentration takes place at a certain depth from the surface, a predetermination of the darwnward migration being noted.

            On the Territory of Guaporé, thick and compact crusts of this neo rock are found, near Pôrto Velho, where the devastation of forests begun in 1907. This same compact laterite is also found under the dense forest as we had the opportunity to record on the vicinity of Km 9 and Km 33 of the road from Pôrto Velho to Cuiabá, locality of Tanques, three km to the northeast of the capital (Pôrto Velho); this formation can also be observed on the site of the "Nucleo Agrícola Pres. Dutra" (Iata) at a distance of about 23 km to the north of the city of Guajará-Mirim.

            Laterization constitutes, therefore, a natural process where the human influence acts as an accelerating agent either to erosion or the lateritic process itself and not, as many authors have advocated, as an originator of laterites.