Evolution
of lakes and internally-drained basins
Interplay
between tectonics, climate, and fluvial transport during the
evolution of tectonic lakes.
On geological time scales, lakes are ephemeral water bodies that, once the mechanism generating the topographic basin ceases, dissapear by erosion of their outlet and/or overfill with sediments brought by tributaries. Therefore, the evolution of a lake and the potential formation of a closed (internally-drained, endorheic) basin depend both on tectonic and climatic factors. How does climate affect the life of a lake at long time-scales? Is the evaporation at the lake's surface as relevant as the tectonic uplift generating the lake? What are the tectonic/climatic conditions under which a lake develops and what are the ones under which a lake becomes internally-drained? These questions are addressed via computer simulations incorporating physico-mathematical approaches to the processes of tectonic uplift and river erosion.
Details in this GSA special publication (Garcia-Castellanos, 2006).
The animation below is
an example of a cross-section computer simulation of the evolution of
a lake created by tectonic uplift across an river profile initially
in equilibrium. The horizontal axis corresponds to distance along the
river flow. This evolution has been calculated using the software tAo
assuming a constant precipitation and evaporation rate through the
entire domain, an uplift rate of 2 mm/yr during the 1st million
years, and a transport capacity proportional to water discharge and
slope.
Bedrock
in brown, sediments in yellow, water in blue. Time is indicated in
millions of years. Note
that the closure of the lake (when evaporation in the lake surface
compensates the water collected upstream and therefore the output
water decreases to 0) occurs at 0.6 Myr, and the abrupt opening by
lake capture (due to
the regressive erosion at the escarpment to the right) occurs at 1.7
Myr.
Abstract. A quantitative model is proposed for the long-term evolution of lakes and internally-drained basins resulting from tectonic vertical motions, sediment infill, outlet erosion and climatic regime. The model accounts for the formation of a water body in topographic basins created by tectonic uplift across a river, which incision capability is approached with a stream power-law, and addresses the notion that, after cessation of tectonic forcing, such lakes are transitory phenomena over geological time scales. High uplift rates across an antecedent river, in combination with low upstream precipitation, result in river defeat and lake formation. In addition to geometrical, lithological, and tectonic parameters, the evaporation rate at the lake surface is revealed as a key factor triggering drainage closure (endorheism) and significant lake life extension by preventing outlet erosion. Post-tectonic lake extinction is ensured by sediment overfill and/or outlet erosion. Once uplift comes to an end and drainage reopens (lake capture), shallow lakes at high altitudes undergo a faster reintegration in the drainage network and extinction. Vertical isostatic movements of the lithosphere significantly delay this process in lakes larger than 50-200 km. The development of an internally-drained basin out of an open lacustrine basin requires that uplift across the outlet persists until the lake is large enough to evaporate all collected water. The evolution of tectonic lakes has therefore similar dependency on geometrical constraints (initial relief, length of the river, hypsometry of the catchment), lithological parameters (rock erodability), tectonics (uplift rate, duration, and its spatial distribution), and climate (precipitation and evaporation rates).