A climatic trigger for catastrophic Pleistocene-Holocene debris flows in the Eastern Andean Cordillera of Colombia

Abstract

The geomorphology and stratigraphy of massive debris flows on the Eastern Andean Cordillera, Colombia, indicate two distinct deposits can be recognized. The lower Chinauta deposit covers 14 km2 and has a thickness of ∼60 m, whereas the upper Fusagasugá deposit covers 20 km2 and has a thickness of ∼20 m. The lower Chinauta section consists of matrix‐supported gravels, with isolated boulders and massive to moderately bedded structure and local inverse grading. The upper section displays sequences of inversely graded, clast‐supported gravels, with boulders >2 m in axial length, capped by massive, matrix‐supported fine gravels. The latter are dissected by coarse, channelized gravels. We interpret these facies as a series of debris and hyper‐concentrated flows dissected by river channels. The Fusagasugá deposit is dominated by massive to inversely graded matrix‐supported gravels with isolated boulders. Single‐grain, optically stimulated luminescence dates of the sandy–silty matrix of debris and hyper‐concentrated flows constrain the timing of deposition of the Chinauta debris flow deposits between 38.9 and 8.7 ka. We postulate that millennial‐scale climate variability is responsible for causing these massive debris flows, through a combination of elevated temperatures and increased rainfall that triggered runoff and sediment transport.

Quaternary drainage network reorganization in the Colombian Eastern Cordillera plateau

“…This capture event is confirmed by several landforms, such as the main knickpoint and elbows of capture along the Bogotá River, the meandering wind gap in the Sumapaz drainage divide, the area test and an observed anomalous basin shape of the Bogotá basin downstream of the main knickpoint (white box labeled D in Figure 9A). Optically stimulated luminescence (OSL) analysis from Hoyos et al (2015) provide an age of 38.9 to 8.7 ka for the terrace deposits in the Sumapaz basin (Figure 9A, pale pink polygon), enhancing our interpretation of a recent capture on the basis of poorly eroded flat surfaces and the presence of a pristine landslide about 2 km long and 0.7 km wide (Figure 9E). In the same location, we observed an ongoing river capture of the longitudinal course located at the eastern side of the landslide.…”

“…The Sumapaz drainage system flows along the Fusagasugá syncline and ultimately joins the Bogotá River (Figure 1). The Fusagasugá syncline exposes Middle‐Late Eocene mudstone and siltstone (Acosta and Ulloa, 1998; Bayona et al, 2003) and is overlain by Pleistocene debris flow and river terrace deposits that date to between 38.9 and 8.7 ka (Hoyos et al, 2015, see later). On the eastern side of the Eastern Cordillera, all the transverse rivers drain from the Eastern flank into the Los Llanos Basin across Cretaceous sandstone and shale formations and an isolated Precambrian‐Paleozoic inlier, named the Quetame massif, that is composed of low and medium grade phyllite and schist (Figure 1; e.g.…”

“…The Eastern Cordillera of Colombia is located in the northern Andes and is composed of Precambrian–Paleozoic basement and a succession of Mesozoic and early Cenozoic sedimentary rocks (Julivert, 1970; Colletta et al, 1990; Cooper et al, 1995; Figure 1A). The Cordillera formed as an extensional basin during the Mesozoic, and became tectonically inverted, deformed and uplifted during the Cenozoic (Colleta et al, 1990, Dengo and Covey, 1993, Mora et al, 2013, Hoyos et al, 2015). As a result of the tectonic inversion, a new doubly‐verging thrust system developed on its two flanks delimiting the upper and inner part of the range characterized by a plateau morphology and the two foreland basins: the Llanos Basin to the east and middle Magdalena basin to the west (Figure 1B).…”

Debris flow events of 4000 a BP and its resulting archaeological site destruction in Qian River gorge, the upper reach of Wei River, central China

“…Mountainous regions are hugely sensitive to debris flows caused by intense or prolonged rainfall, earthquakes, volcanic eruptions, and glacier melt. Climate can play a vital role in initiating debris flows through control of water transport capacity and sediment availability (Benn, Owen, Finkel, & Clemmens, 2006; Hoyos et al, 2015; Jones, Arzani, & Allen, 2014). Through investigation and analysis, we believe that the debris flow incident on the south bank of the Qian River was also triggered by high‐intensity rainfall and earthquakes.…”

“…It is useful to assess the intensity of weathering and pedogenesis during dust accumulation, resulting predominantly from temperature and precipitation change within the semi-arid to semi-humid climate regions (An et al, 2012;Deng, Zhu, Verosub, Singer, & Vidic, 2004;Huang et al, 2010;Liu, 1988;Maher, 2016;Sun, Clemens, An, & Yu, 2006). control of water transport capacity and sediment availability (Benn, Owen, Finkel, & Clemmens, 2006;Hoyos et al, 2015;Jones, Arzani, & Allen, 2014). Through investigation and analysis, we believe that the debris flow incident on the south bank of the Qian River was also triggered by high-intensity rainfall and earthquakes.…”