Climatic control of the late Quaternary turbidite sedimentology of Lake Kivu, East Africa: Implications for deep mixing and geologic hazards

Abstract

The Lake Kivu catchment in the East African Rift is subject to various geologic hazards, including frequent volcanic eruptions, earthquakes, and potential limnic overturns and degassing events. Integration of high-resolution seismic reflection data, 14 C dated sediment cores, and lake-floor bathymetry reveals large axial and transverse turbidite systems in the eastern basin of the lake. The turbidites were sourced by hyperpycnal river flows during exceptional floods, and the temporal occurrence of the turbidites was climatically controlled. The turbidite record over the past ~12 k.y. is correlated with the regional paleohydrologic records from tropical East Africa. Our study suggests that flood-introduced turbidites preserved in deep lakes are indicators of hydrological changes, and that extreme floods in Lake Kivu's recent history may have triggered deep mixing events. This study also has implications for the current degassing efforts in Lake Kivu; potential geologic hazards may be triggered by extraordinary turbidity currents, and need to be considered in the design and deployment of gas extraction facilities.

Holocene carbonate record of Lake Kivu reflects the history of hydrothermal activity

“…Haberyan and Hecky (11) reported coarse material, including cobble sized, in deep water cores and suggested water levels may have fallen in the late Pleistocene as much as 300 m below the modern level. Similarly, Zhang et al (6) concluded, from a suite of more recently obtained cores, that water levels fell at least 380 m below the modern level 12,700 cal y BP, which would have placed the water level below our K19 coring site (Fig. 1).…”

“…S1). We also used a younger date of 2,172 ± 95 cal y BP in another piston core from Lake Kivu (K13-20A), which Zhang et al (6) correlated stratigraphically to ∼15 cm above the base of the lower carbonate interval in core 19A, i.e., at ∼313 cm blf. We used these dates to construct an age model for this core ( Fig.…”

Extreme events in the sedimentary record of maar Lake Pavin: Implications for natural hazards assessment in the French Massif Central

“…5) suggests deep-water mixing and upwelling of nutrient-rich waters to enhance algal productivity (Zhang et al, 2014). As with the AD 600 event, violent waves would have resulted from this large subaquatic slide; the waves are the likeliest explanation for reworked sand deposits (RDL1) at core PAV09-C5 site.…”

Turbidite systems of lacustrine rift basins: Examples from the Lake Kivu and Lake Albert rifts, East Africa

“…Lake Kivu has experienced drastic water-level fluctuations in the late Pleistocene (Zhang et al, 2014;Wood et al, 2015). The most recent lowstand occurred at~12.2 ka, during which lake-levels were~380 m below present, indicated by paleodeltas on seismic reflection profiles and sediment cores that reveal shallow-water ooids overlying deltaic sands (Zhang et al, 2014). This pronounced lowstand is also evidenced by drowned drainage systems (Fig.…”

“…Today, Lake Kivu discharges south to Lake Tanganyika via the Ruzizi River, and is the major contributor to the salt budget of Lake Tanganyika (Stoffers and Hecky, 1978). Lake Kivu has experienced drastic water-level fluctuations in the late Pleistocene (Zhang et al, 2014;Wood et al, 2015). The most recent lowstand occurred at~12.2 ka, during which lake-levels were~380 m below present, indicated by paleodeltas on seismic reflection profiles and sediment cores that reveal shallow-water ooids overlying deltaic sands (Zhang et al, 2014).…”