Spatial and temporal variation of tectonic uplift in the southeastern Ethiopian Plateau from morphotectonic analysis Liang Xue a , Tadesse Alemu a , Nahid D. Gani b , Mohamed G. Abdelsalam a, ⁎ a Boone Pickens School of Geology, Oklahoma State University, 105 Noble Research Center, Stillwater, OK 74078, USA b Department of Geography and Geology, Western Kentucky University, Bowling Green, KY 42101, USA abstract article info Article history: Received 14 November 2017 Received in revised form 22 February 2018 Accepted 22 February 2018 Available online xxxx We use morphotectonic analysis to study the tectonic uplift history of the southeastern Ethiopian Plateau (SEEP). Based on studies conducted on the Northwestern Ethiopian Plateau, steady-state and pulsed tectonic uplift models were proposed to explain the growth of the plateau since ~30 Ma. We test these two models for the largely unknown SEEP. We present the first quantitative morphotectonic study of the SEEP. First, in order to infer the spatial distribution of the tectonic uplift rates, we extract geomorphic proxies including normalized steepness index k sn , hypsometric integral HI, and chi integral χ from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) digital elevation model (DEM). Second, we compare these rates with the thickness of flood basalt that we estimated from geological maps. Third, to constrain the timing of regional tectonic uplift, we develop a knickpoint celerity model. Fourth, we compare our results to those from the Northwestern Ethiopian Plateau to suggest a possible mechanism to explain regional tectonic uplift of the entire Ethiopian Plateau. We find an increase in tectonic uplift rates from the southeastern escarpments of the Afar Depression in the northeast to that of the Main Ethiopian Rift to the southwest. We identify three regional tectonic uplift events at ~11.7, ~6.5, and ~4.5 Ma recorded by the development of regionally distributed knickpoints. This is in good agreement with ages of tectonic uplift events reported from the Northwestern Ethiopian Plateau. © 2017 Elsevier B.V. All rights reserved. Keywords: Southeastern Ethiopian Plateau (SEEP) Tectonic uplift Geomorphic proxies Knickpoint celerity model 1. Introduction The development of geomorphic features in response to tectonic uplift provides important information regarding nature and spatial and temporal distributions of tectonic forces in contractional and exten- sional tectonic regimes. The distribution of tectonic activities in regions experiencing tectonic uplift can be mapped through geomorphic prox- ies, including normalized steepness index k sn (Whipple, 2004; Kirby and Whipple, 2012), hypsometric integral HI (Strahler, 1952; Gao et al., 2016), and chi integral χ (Perron and Royden, 2013; Willett et al., 2014). In addition, celerity modeling of knickpoints allows for establishing end-member time constraint for the changes of tectonic uplift rates (Berlin and Anderson, 2007; Miller et al., 2012). Here, we use these approaches (in addition to information about precipitation and lithology) to establish the spatial and temporal distribution of the tectonic uplift in the tectonically active southeastern Ethiopian Plateau (SEEP). The Ethiopian Plateau is divided by the Main Ethiopia Rift (MER) and the Afar Depression into the Northwestern Ethiopian Plateau and the SEEP (Fig. 1A). The landscape of this region has been shaped by tectonic uplift, volcanism, and extensional deformation associated with the development of the East African Rift System (EARS) (Fig. 1A; Wolfenden et al., 2004; Simmons et al., 2007; Prave et al., 2016). The development and preservation of such an anomalously high plateau (average elevation of ~2.5 km) within a continental rift setting are caused by the dynamics of the Afar mantle plume (Ebinger and Casey, 2001; Sengor, 2001; Faccenna et al., 2013). Morphotectonic studies to constrain the tectonic uplift history of the Ethiopian Plateau have remained considerably sparse. Hence, several fundamental questions regarding the tectonic uplift history of the plateau remain unanswered. These include: • Was the growth of the Ethiopian Plateau steady or episodic? Results from (U-Th)/He thermochronology studies by Pik et al. (2003) suggest steady-state plateau growth for the Northwestern Ethiopian Plateau since ~29 Ma resulting in ~1 km uplift since then. Conversely, morphotectonic analysis by Gani et al. (2007) and Ismail and Abdelsalam (2012) reported multistage and accelerated growth of the Northwestern Ethiopian Plateau at 30–10 Ma, 10–6 Ma, and 6 Ma–present. This excludes the portion of the plateau away from the escarpment of the MER and the Afar Depression (toward the low- lands of Sudan) where the steady-state model is applicable. Geomorphology 309 (2018) 98–111 ⁎ Corresponding author. E-mail address: mohamed.abdel_salam@okstate.edu (M.G. Abdelsalam). https://doi.org/10.1016/j.geomorph.2018.02.025 0169-555X/© 2017 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Geomorphology journal homepage: www.elsevier.com/locate/geomorph