Scholars' Mine Masters Theses Student Theses and Dissertations Summer 2011 Morpho-tectonic analysis of the Tekeze and the Blue Nile drainage systems of northwestern Ethiopian Plateau, Ethiopia Elamin Hassan Dai Ismail Follow this and additional works at: https://scholarsmine.mst.edu/masters_theses Part of the Geology Commons, and the Geophysics and Seismology Commons Department: Recommended Citation Ismail, Elamin Hassan Dai, "Morpho-tectonic analysis of the Tekeze and the Blue Nile drainage systems of northwestern Ethiopian Plateau, Ethiopia" (2011). Masters Theses. 4974. https://scholarsmine.mst.edu/masters_theses/4974 This thesis is brought to you by Scholars' Mine, a service of the Missouri S&T Library and Learning Resources. This work is protected by U. S. Copyright Law. Unauthorized use including reproduction for redistribution requires the permission of the copyright holder. For more information, please contact [email protected]. i MORPHO-TECTONIC ANALYSIS OF THE TEKEZE AND THE BLUE NILE DRAINAGE SYSTEMS OF NORTHWESTERN ETHIOPIAN PLATEAU, ETHIOPIA by ELAMIN HASSAN DAI ISMAIL A THESIS Presented to the Faculty of the Graduate School of the MISSOURI UNIVERSITY OF SCIENCE AND TECHNOLOGY In Partial Fulfillment of the Requirements for the Degree MASTER OF SCIENCE IN GEOLOGY AND GEOPHYSICS 2011 Approved by Mohamed Abdelsalam, Advisor Stephen Gao David Rogers ii © 2011 Elamin Hassan Dai Ismail All Rights Reserved iii DEDICATION To My late mother, late father and late brothers Ismail and Agabna To My late friend Mansour M. Farag To My family Siham, Sahar, Dali, Eiman and Mohamed My aunt Fathia and my brothers and sisters iii ABSTRACT This study examines the morpho-tectonic evolution of the drainage system in the northwestern Ethiopian plateau by focusing on the Tekeze and the Blue Nile Rivers. The plateau is underlain by Precambrian crystalline rocks, overlain by Mesozoic sedimentary section that is topped with a 1-3 km thick pile of Oligocene-Quaternary volcanic rocks. It is bounded in the east and southeast by the Afar Depression (AD) and the Main Ethiopian Rift (MER). Satellite derived Digital Elevation Models are analyzed using ArcGIS and RiverTools to extract morpho-tectonic parameters of tributaries of the Tekeze and Blue Nile Rivers including Normalized Steepness Index (Ksn), Concavity (θ), Regression Fit (r2), and spatial distribution of major and minor knickpoints and faults. Two end-member models have been previously proposed: 1) a steady-state rate of incision since the beginning of the development of these drainage systems (~30 Ma) or 2) a rate of incision that increased through time. This study shows that the incision history of these drainage systems is more complex than can be explained by these two end-member models. Nevertheless, the models are still valid explanations for specific regions of the plateau. The evolution of the drainage systems on the NW plateau is influenced by three tectonic and geological events: 1) The rising of the Afar mantle plume (~30 Ma) created a moderate increase in the incision rate of the entire plateau, 2) a localized increase in the incision rate associated with the shield volcanoes build-up event (~22 Ma) and lastly 3) a significant increase of the incision rate in the eastern part of the northwestern plateau due to rift-flank uplift on western escarpment of the AD and the northwestern escarpment of the MER. This uplift diminishes westward leaving the drainage system in the lower reaches of the Tekeze and Blue Nile Rivers relatively tectonically undisturbed, hence establishing a long-lived hydrological stability and reaching steady-state equilibrium. iv ACKNOWLEDGEMENTS I am grateful to my family, Siham Eltayeb, Sahar, Dali, Eiman and Mohamed for their patience and support. I would like to thank Dr. Mohamed Abdelsalam as advisor, friend and colleague for the effort and advice to complete this work and my appreciation to my committee members, Dr. Stephen Gao, Dr. John Hogan, Dr. Francisca Ikuenobe, Dr. David Wronkiewicz and Dr. David Rogers. My thanks to Dr. José Vicente Pérez- Peña from the Department of Geodynamics, University of Granada, Spain for providing me with CalHypso extension software he and his colleagues has developed, and for linking me with indispensible resources for tectonic geomorphology. I would like to thank the Geology and Geophysics Program at Missouri University of Science and Technology for the financial assistance they made available to me through the Radcliff endowment. I am very thankful for the Geological Engineering program and faculty for making my transition to the PhD program in Geological Engineering. Special thanks to my colleagues Dr. Kamal Sharafaldin Ali, Dr. Osama Awadelkarim and Dr. Mahgoub Ali for encouraging me to go back to school. Special thanks to Ahmed Elsheikh and to the remote sensing lab group for their support and advices. I am grateful to Dr. Lulu Tisege for his overwhelming assistance during my field work in Ethiopia and for all those in the Geological Survey of Ethiopia and the Tekeze Hydro-electric power project for making my field work in Ethiopia an unforgettable experience. Field work of this project was funded by the National Science Foundation (NSF) through a project entitled “Modeling Drainage Incision on the Ethiopian Plateau”. v TABLE OF CONTENTS Page ABSTRACT ....................................................................................................................... iii ACKNOWLEDGMENTS ................................................................................................. iv LIST OF ILLUSTRATIONS ............................................................................................. vi LIST OF TABLES ........................................................................................................... viii SECTIONS 1. INTRODUCTION .......................................................................................................1 1.1. STATEMENT OF THE PROBLEM AND OBJECTIVES ............................. 1 1.1.1. Statement of the Problem ......................................................................... 1 1.1.2. Objectives ................................................................................................. 5 1.2. OVERVIEW OF THE TEKEZE RIVER AND THE BLUE NILE ................ 6 1.3. TECTONIC SETTING ...................................................................................9 1.4. GEOLOGY ...................................................................................................11 2. DATA AND METHODS ..........................................................................................16 2.1. DATA ............................................................................................................ 16 2.2. METHODS .................................................................................................... 16 3. RESULTS ..................................................................................................................18 3.1. RESULTS OF THE GEOLOGICAL ANALYSIS ........................................ 18 3.2. RESULTS OF THE MORPHO-TECTONIC ANALYSIS.......................... 21 3.2.1. The Normalized Steepness Index (Ksn) .................................................. 21 3.2.2. Results of Long profiles ......................................................................... 26 3.2.3. Spatial Distribution of Knickpoints and Faults.......................................33 4. DISCUSSION ............................................................................................................39 5. CONCLUSIONS .......................................................................................................43 APPENDIX .......................................................................................................................44 BIBLIOGRAPHY ........................................................................................................... 100 VITA ............................................................................................................................... 106 vi LIST OF ILLUSTRATIONS Page Figure 1.1: Digital Elevation Model (DEM) of Ethiopia showing topography, tectonic elements, and the drainage systems of the northwestern and southeastern Ethiopian plateaus, MER = Main Ethiopian Rift ……............................…2 Figure 1.2: Geological map of Ethiopia showing the Ethiopian Plateau underlain by Precambrian crystalline rocks and topped with Oligocene – Quaternary volcanic rocks. 1 = Blue Nile and the Gorge of the Nile. 2 = Tekeze. 3 = Ter Shet. Red lines represent the approximate trends of the Afar Depression and Main Ethiopian Rift border faults…....……................….3 Figure 1.3: Location and physiographic setting of the Tekeze River and the Blue Nile Rivers..…..………………………...........................………...............…….7 Figure 1.4: The Tekeze and Blue Nile Horton–Strahler Stream Order with pruning of three. The Tekeze River is a sixth order stream, and the Blue Nile is seventh order stream……….…………..........…………................……….8 Figure 1.5: Geological map of the Tekeze and the Blue Nile River basins with the location of cross-sections shown as P1 to P11…….............................…..12 Figure 1.6: Stratigraphic columns comparing the stratigraphy of the Tekeze River (This Study) with those of the Blue Nile (Gani et al., 2009) and the Mekele Outlier (Beyth, 1973)…............................................................... 13 Figure 3.1: Geological sections