Lago Leopoldo (Lake Leopold) is a body of water located in the Venezuelan Amazon in the westernmost range of the Guiana Shield. It measures about by and and up to deep. The water level was documented at above sea level but may have diminished in recent years. Its name derives from the expedition that King Leopold III of Belgium made in 1952 which motored up the Sipapo, Autana and Umaj-Ajé rivers and set camp several miles from the lake. There is no firm evidence that members of King Leopold expedition actually reached the lake. Lago Leopoldo was first seen from the air as a landmark near the Cerro Autana tepui during the 1950s. The lake was first visited by helicopter in March 1973 by the Spanish naturalist Félix Rodríguez de la Fuente. The following April, the terrestrial route from the original King Leopold III camp was established by a Venezuelan expedition which reached the shores of the lake on April 18, 1973. Lago Leopoldo figures prominently in the oral history and lore of the native Piaroans where it is referred as "Paraka-Wachoe" or the lake in the mountains. Lago Leopoldo now renamed Lago Autana has been included as a natural monument within a protected area which includes the Cerro Autana and adjacent lands.
Description
Lago Leopoldo is located in the westernmost section of the Cuao-Sipapo massif which constitutes the western edge of the Guiana Shield, east of the Sipapo and Orinoco Rivers. It lies between the hydrological basins of the rivers Cuao to the north and Autana to the south. The lake is sited in a mountain top with a prominent scarped side in the north-west edge and a smaller basin edge in the south-east border. Its water collects from rain accumulation; drainage is by a subterranean stream which emerges at a distance from the lake's edge in the south. This stream drains into an affluent of the Umaj-Ajé River which drains into the Autana. The edge consists of nutrient-poor sandy soils originating from the erosion of the surrounding sandstone. Its eroded cliffs contain vegetation typical of transition areas with low shrubs in the upper part and shrubs, palms and large herbs downslope. The base of the cliffs consists of an accumulation of quartzite blocks covered by mosses and algae. Farther from the edge there are stunted trees with trunks and branches covered by mosses, lichens and epiphytes such as ferns, orchids and bromeliads. The shores are light to dark rose or white in color, with sandy soils, rich in quartz, extremely nutrient poor and with low water retention capacity. The site is remote and virtually inaccessible. It does not appear in maps of colonial settlers or of European explorers of the 19th century.
Geology
Lake Leopoldo is located in the strata of the Roraima Group rocks preserved in erosional remnants that rest on eroded Parguaza Granite. Roraima sandstones in the Cuao table-mountains consist of a basal member characterized by graded sandstones with cross-bedding and ripples, wackes and thin discontinuous conglomerates; a middle member consisting of two strata of black and gray shales inter-bedded with quartzitic sandstones; and an upper member consisting of quartzitic sandstone with traces of carbonate, feldspathic sandstones and sandstones with abundant hematite. The lake is likely the result of the collapse of sandstones in a process similar to the formation of the caves of Cerro Autana. The bottom of the lake is composed mostly of sand and small quantities of mud. Sand composition is largely quartz arenite and a small percentage of monomineralic components dominated by quartz and some accessory minerals (zircon, feldspar, hematite, and rutile). Of note is the high concentration of mercury in the sediment which is 2.3 higher than the expected concentration on these remote areas. In the absence of human activity around the lake and the fact that the closest gold mining operation is 250 km (155 miles) to the NE, possible sources of the high concentration of mercury include regional geologic sources through biochemical transformation of the soils, atmospheric transport from remote human sources, and burning of biomasses from the clearing of surrounding forests.