Accelerated rifting in response to regional climate change in the East African Rift System.

Continental rifting is influenced by interactions between tectonic, magmatic, and surface processes, with the latter strongly dependent on regional climate. We test the role of regional climate variability on rift system behavior, by investigating fault slip rate changes in the South Turkana Basin (Lake Turkana Rift, northern Kenya) at the end of the African Humid Period. Throw rates on 27 faults examined during the African Humid Period (9,631-5,333 yr BP) and post-African Humid Period (5,333 yr BP-present) exhibit a mean 0.17 ± 0.08 mm/yr increase during the drier, post-African Humid Period. Numerical simulations reveal Coulomb stress changes from two loading sources that may explain these changes: (1) reduced vertical loading from a 100-150 m lake level drop, and (2) increased magmatic loading from enhanced mantle melt production due to reduced lake loading. An increase in magma flux of > 0.1 km3/kyr below the South Turkana Basin results in Coulomb stress changes exceeding those expected from a 100-150 m lake level drop. We provide the first empirical evidence of increased fault activity in response to climate-induced lake level changes in the East African Rift System over time scales of 103-104 years, and reveal that climate-tectonic interactions are enhanced in magmatically active rift systems.