Delta size variability at Lake General Carrera, Patagonia

Abstract

Punctuated lake level drops at Lake General Carrera, Chile, over the last ~13 ka are recorded in multiple stacked deltas that differ in scale. Fifteen delta terrace suites are studied to examine the factors that influence deposit morphology. Surprisingly, the pronounced longitudinal precipitation gradient is inversely correlated with the observed variations in delta size. We find the drainage basins with long-term water storage in glaciers are associated with larger deltas. In these cases, the added contribution of rare, high-magnitude ice meltwater release events (> 600 m3/s) is suggested as the differential driver to enhance delta growth. The overall progradation rate is modest (0.2-1 m/yr), and appears to have slowed over time. For the youngest deltas, we estimate the range in the intermittency factor, a dimensionless measure of the frequency of floods, is 1x10-2 to 4x10-5. Our results illustrate the natural variability of delta growth in a small region (<20,000 km2), and better characterize understudied glaciogenic deltas.