| Climate and Geology | ||
 Bogotá-annual
rainfall. photo credit: IDEAM
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The Bogota basin is an intermontane depression in the Eastern Cordillera of Colombia located at an altitude of about 2550 m, near the upper Andean tree line. Rainfall in the basin is dominated by the twice-a-year passage of the Intertropical Convergence Zone, creating two distinct rainy seasons (March–May and September– November) and two dry seasons. The mean annual temperature is 13.5 °C and the mean annual precipitation is 1000 mm. |
The basin has received wind-blown volcanic ashes originating from volcanoes in the Central Cordillera active throughout the late Pleistocene and Holocene. Accumulation of the volcanic ashes combined with colluvial sedimentation and concomitant weathering results in the formation of silty-clayey loams . Soil profiles in the Bogota basin reveal the existence of two distinct episodes of weathering, one corresponding to the modern (Holocene) soils and a second corresponding to paleosols formed on volcano-colluvial deposits before 13 000–16 000 14C yr B.P. A sharp contact locally showing root casts separates the upper (Holocene) silty- clay loam from a buried, slightly siltier loam and represents an erosional period, probably caused by the expansion of alpine glaciers. Available radiocarbon dates indicate that the buried paleosols developed during the last glacial stage, between 15 000 and 31 000 14C yr B.P. Dates bracketing the sharp contact indicate erosion between 13 000 and 15 000 14C yr B.P. The Holocene soils and the paleosols contain B-horizons with abundant kaolinite minerals that formed as a result of volcanic-ash weathering, providing an opportunity to reconstruct paleoclimatic conditions for the tropical Andes during the last glacial stage. |
Approximate reconstruction of Bogota's wetlands. credit: encolombia.com  | |