Drainage and erosion of Cambodia's Great Lake in the middle-late Holocene: the combined role of climatic drying, base-level fall and river capture

We provide evidence for a large-scale geomorphic event in Cambodia’s great lake, the Tonlé Sap, during the middle Holocene. The present-day hydrology of the basin is dominated by an annual flood pulse where water from the Mekong River raises the lake level by c. 8m during the monsoon season. We present new subsurface geophysical data, allied to new and past core studies, which unequivocally show a period of major mid-Holocene erosion across the entire Tonlé Sap basin that is coincident with establishment of the lake’s flood pulse. We argue that this widespread erosion, which removed at least 1.2 m of sediment across the lake’s extent, was triggered by up to three, likely interacting, processes: (1) base-level lowering due to mid-Holocene sea-level fall, leading to (2) capture of the Tonlé Sap drainage by the Mekong River, and (3) a drying climate that also reduced lake level. Longer-term landscape evolution was thus punctuated by a rapid, river capture- and base-level fall-induced, lake drainage that established the ecosystem that flourishes today. The scale of change induced by this mid-Holocene river capture event demonstrates the susceptibility of the Tonlé Sap to ongoing changes in local base-level and hydrology induced by anthropogenic activity, such as damming and sand mining, within the Mekong River Basin