scholarly journals Main Ethiopian Rift landslides formed in contrasting geological settings and climatic conditions

2021 ◽  
Vol 21 (11) ◽  
pp. 3465-3487
Author(s):  
Karel Martínek ◽  
Kryštof Verner ◽  
Tomáš Hroch ◽  
Leta A. Megerssa ◽  
Veronika Kopačková ◽  
...  
Keyword(s):  
Normal Fault ◽  
Climatic Conditions ◽  
Arabian Plate ◽  
Ethiopian Rift ◽  
Vegetation Density ◽  
Regional Study ◽  
Main Ethiopian Rift ◽  
Landslide Occurrence ◽  
Precipitation Seasonality ◽  
Steep Slopes

Abstract. The Main Ethiopian Rift (MER), where active continental rifting creates specific conditions for landslide formation, provides a prospective area to study the influence of tectonics, lithology, geomorphology, and climate on landslide formation. New structural and morphotectonic data from central Main Ethiopian Rift (CMER) and southern Main Ethiopian Rift (SMER) support a model of progressive change in the regional extension from NW–SE to the recent E(ENE)–W(WSW) direction, driven by the African and Somali plates moving apart with the presumed contribution of the NNE(NE)–SSW(SW) extension controlled by the Arabian Plate. The formation and polyphase reactivation of faults in the changing regional stress field significantly increase the rocks' tectonic anisotropy, slope, and the risk of slope instabilities forming. According to geostatistical analysis, areas prone to landslides in the central and southern MER occur on steep slopes, almost exclusively formed on active normal fault escarpments. Landslide areas are also influenced by higher annual precipitation, precipitation seasonality, vegetation density, and seasonality. Deforestation is also an important predisposition because rockfalls and landslide areas typically occur on areas with bushland, grassland, and cultivated land cover. A detailed study on active rift escarpment in the Arba Minch area revealed similar affinities as in a regional study of MER. Landslides here are closely associated with steep, mostly faulted, slopes and a higher density of vegetation. Active faulting forming steep slopes is the main predisposition for landslide formation here, and the main triggers are seismicity and seasonal precipitation. The Mejo area situated on the uplifting Ethiopian Plateau 60 km east of the Great Rift Valley shows that landslide occurrence is strongly influenced by steep erosional slopes and a deeply weathered Proterozoic metamorphic basement. Regional uplift, accompanied by rapid headward erosion forming steep slopes together with unfavourable lithological conditions, is the main predisposition for landslide formation; the main triggers here are intense precipitation and higher precipitation seasonality.

scholarly journals Main Ethiopian Rift landslides formed in contrasting geological settings and climatic conditions

2021 ◽  
Author(s):  
Karel Martínek ◽  
Kryštof Verner ◽  
Tomáš Hroch ◽  
Leta A. Megerssa ◽  
Veronika Kopačková ◽  
...  
Keyword(s):  
Active Tectonics ◽  
Normal Fault ◽  
Climatic Conditions ◽  
Ethiopian Rift ◽  
Vegetation Density ◽  
Regional Study ◽  
Main Ethiopian Rift ◽  
Landslide Occurrence ◽  
Precipitation Seasonality ◽  
Slope Instabilities

Abstract. The Main Ethiopian Rift (MER), where active continental rifting creates specific conditions for landslide formation, provides a prospective area to study the influence of tectonics, lithology, geomorphology, and climate on landslide formation. New structural and morphotectonic data from CMER and SMER support a model of progressive change in the regional extension from NW – SE to the recent E(ENE) – W(WSW) direction driven by the African and Somalian plates moving apart with the presumed contribution of the NNE(NE) – SSW(SW) extension controlled by the Arabic Plate. The formation and polyphase reactivation of faults in the changing regional stress-field significantly increase the rocks' tectonic anisotropy and the risk of slope instabilities forming. According to geostatistical analysis landslides in the central and southern MER occur on steep slopes, almost exclusively formed on active normal fault escarpments. Landslides are also influenced by higher annual precipitation, precipitation seasonality, vegetation density and seasonality. A detailed study on active rift escarpment in the Arba Minch area revealed similar affinities as in regional study of MER. Landslides here are closely associated with steep, mostly faulted, slopes and a higher density of vegetation. Active tectonics and seismicity are the main triggers. The Mejo area situated on the uplifting Ethiopian Plateau 60 km east of the Rift Valley shows that landslide occurrence is strongly influenced by steep erosional slopes and deeply weathered Proterozoic metamorphic basement. Rapid headward erosion, unfavourable lithological conditions and more intense precipitation and higher precipitation seasonality are the main triggers here.

Modelling constraints on rifting in the Afar region: the birth of a triple junction

2020 ◽  
Author(s):  
Hany Khalil ◽  
Fabio Capitanio ◽  
Peter Betts ◽  
Alexander Cruden
Keyword(s):  
Boundary Conditions ◽  
Triple Junction ◽  
Large Scale ◽  
Structural Features ◽  
Arabian Plate ◽  
Ethiopian Rift ◽  
Far Field ◽  
Triple Junctions ◽  
Main Ethiopian Rift ◽  
Afar Region

<p>Rifting in the Afar region is considered to be the only known example of the formation of an incipient divergent triple junction. Taking the Afar region as an example, we use three-dimensional (3D) laboratory experiments to test hypotheses for the formation and evolution of divergent triple junctions. We systematically evaluate the role of mechanical weakening due to plume impingement versus inherited weak linear structures in lithospheric mantle under both far-field orthogonal and rotational extensional boundary conditions. The interaction between far-field boundary forces and inherited rheological heterogeneities results in a range of complex rift propagation geometries and structural features, such as rift segmentation and ridge jumps, which are comparable to those observed in the Afar region. The combination of rotational boundary conditions and inherited linear heterogeneities favours the formation of rifts that connect at high-angles. Lithospheric weakening associated with a mantle plume triggers different rifting styles but has little influence on large-scale continental breakup. When compared to the Afar region, our results suggest that the rotation of the Arabian plate since the Oligocene led to rifting of the Red Sea and the Gulf of Aden, which are distinct from the formation of the Main Ethiopian Rift. We suggest that rifting in the Afar region is not consistent with the incipient divergent triple junction hypothesis. Rather, the Afar triple junction formed as a result of complex multi-phase rifting events driven by far-field tectonic forces.</p>

scholarly journals Local seismicity near the actively deforming Corbetti volcano in the Main Ethiopian Rift

2020 ◽  
Author(s):  
Derek Keir ◽  
Aude Lavayssiere ◽  
Tim Greenfield ◽  
Mike Kendall ◽  
Atalay Ayele
Keyword(s):  
Gravity Data ◽  
Local Population ◽  
Normal Fault ◽  
Velocity Model ◽  
Ethiopian Rift ◽  
Magma Body ◽  
Main Ethiopian Rift ◽  
Source Mechanisms ◽  
Seismic Swarms ◽  
The City

<p>Corbetti is currently one of the fastest uplifting volcanoes globally, with strong evidence from geodetic and gravity data for a subsurface inflating magma body. A dense network of 18 stations has been deployed around Corbetti and Hawassa calderas between February 2016 and October 2017, to place seismic constraints on the magmatic, hydrothermal and fault slip processes occurring around this deforming volcano. We locate 122 events of magnitudes between 0.4 and 4.2 were located using a new local velocity model. The seismicity is focused in two areas: directly beneath Corbetti caldera and beneath the east shore of Lake Hawassa. The shallower 0-5km depth below sea level (b.s.l.) earthquakes beneath Corbetti are mainly focused in NW-elongated clusters at Urji and Chabbi volcanic centres. This distribution is interpreted to be mainly controlled by a northward propagation of hydrothermal fluids from a cross-rift pre-existing fault. Source mechanisms are predominantly strike-slip and different to the normal faulting away from the volcano, suggesting a local rotation of the stress-field. These observations, along with a low Vp/Vs ratio, are consistent with the inflation of a gas-rich sill, likely of silicic composition, beneath Urji. In contrast, the seismicity beneath the east shore of Lake Hawassa extends to greater depth (16 km b.s.l.). These earthquakes are focused on 8-10 km long segmented faults, which are active in seismic swarms. One of these swarms, in August 2016, is focused between 5 and 16 km depth b.s.l. along a steep normal fault beneath the city of Hawassa, highlighting the tectonic hazard for the local population.</p>

scholarly journals The effect of hydrogeological and hydrochemical dynamics on landslide triggering in the central highlands of Ethiopia

2021 ◽  
Vol 29 (3) ◽  
pp. 1239-1260
Author(s):  
Tesfay Kiros Mebrahtu ◽  
Andre Banning ◽  
Ermias Hagos Girmay ◽  
Stefan Wohnlich
Keyword(s):  
Hydrostatic Pressure ◽  
Groundwater Flow ◽  
Volcanic Rocks ◽  
Chemical Characterization ◽  
Unconsolidated Sediments ◽  
Ethiopian Rift ◽  
Main Ethiopian Rift ◽  
Groundwater Level Fluctuations ◽  
Landslide Mass ◽  
Landslide Triggering

AbstractThe volcanic terrain at the western margin of the Main Ethiopian Rift in the Debre Sina area is known for its slope stability problems. This report describes research on the effects of the hydrogeological and hydrochemical dynamics on landslide triggering by using converging evidence from geological, geomorphological, geophysical, hydrogeochemical and isotopic investigations. The chemical characterization indicates that shallow to intermediate aquifers cause groundwater flow into the landslide mass, influencing long-term groundwater-level fluctuations underneath the landslide and, as a consequence, its stability. The low content of total dissolved solids and the bicarbonate types (Ca–Mg–HCO3 and Ca–HCO3) of the groundwater, and the dominantly depleted isotopic signature, indicate a fast groundwater flow regime that receives a high amount of precipitation. The main causes of the landslide are the steep slope topography and the pressure formed during precipitation, which leads to an increased weight of the loose and weathered materials. The geophysical data indicate that the area is covered by unconsolidated sediments and highly decomposed and weak volcanic rocks, which are susceptible to sliding when they get moist. The heterogeneity of the geological materials and the presence of impermeable layers embodied within the highly permeable volcanic rocks can result in the build-up of hydrostatic pressure at their interface, which can trigger landslides. Intense fracturing in the tilted basalt and ignimbrite beds can also accelerate infiltration of water, resulting to the build-up of high hydrostatic pressure causing low effective normal stress in the rock mass, giving rise to landslides.

scholarly journals Water Quality Threats, Perceptions of Climate Change and Behavioral Responses among Farmers in the Ethiopian Rift Valley

Climate ◽  
2021 ◽  
Vol 9 (6) ◽  
pp. 92
Author(s):  
Tewodros R. Godebo ◽  
Marc A. Jeuland ◽  
Christopher J. Paul ◽  
Dagnachew L. Belachew ◽  
Peter G. McCornick
Keyword(s):  
Climate Change ◽  
Water Quality ◽  
Surface Water ◽  
Water Availability ◽  
Agricultural Sector ◽  
Local Development ◽  
Irrigated Agriculture ◽  
Ethiopian Rift ◽  
Adaptation Mechanism ◽  
Main Ethiopian Rift

This work aims to assess water quality for irrigated agriculture, alongside perceptions and adaptations of farmers to climate change in the Main Ethiopian Rift (MER). Climate change is expected to cause a rise in temperature and variability in rainfall in the region, reducing surface water availability and raising dependence on groundwater. The study data come from surveys with 147 farmers living in the Ziway–Shala basin and water quality assessments of 162 samples from groundwater wells and surface water. Most groundwater samples were found to be unsuitable for long term agricultural use due to their high salinity and sodium adsorption ratio, which has implications for soil permeability, as well as elevated bicarbonate, boron and residual sodium carbonate concentrations. The survey data indicate that water sufficiency is a major concern for farmers that leads to frequent crop failures, especially due to erratic and insufficient rainfall. An important adaptation mechanism for farmers is the use of improved crop varieties, but major barriers to adaptation include a lack of access to irrigation water, credit or savings, appropriate seeds, and knowledge or information on weather and climate conditions. Local (development) agents are identified as vital to enhancing farmers’ knowledge of risks and solutions, and extension programs must therefore continue to promote resilience and adaptation in the area. Unfortunately, much of the MER groundwater that could be used to cope with declining viability of rainfed agriculture and surface water availability, is poor in quality. The use of saline groundwater could jeopardize the agricultural sector, and most notably commercial horticulture and floriculture activities. This study highlights the complex nexus of water quality and sufficiency challenges facing the agriculture sector in the region, and should help decision-makers to design feasible strategies for enhancing adaptation and food security.

scholarly journals Rainfall and landslides in Karditsa county (Greece): a statistical approach

2007 ◽  
Vol 40 (4) ◽  
pp. 1722 ◽  
Author(s):  
L. Pyrgiotis ◽  
G. Koukis ◽  
N. Sabatakakis
Keyword(s):  
Representative Sample ◽  
Statistical Approach ◽  
Mountainous Area ◽  
Systematic Data ◽  
Landslide Occurrence ◽  
Quantitative Expression ◽  
Steep Slopes

The mountainous area of Karditsa County, being geologically a representative sample of Olonos- Pindos geotectonic zone, is characterized by rainfall- induced landslides on steep slopes of high relief. After a systematic data inventory concerning landslides and their quantitative expression, the correlation between landslide occurrence and rainfall is investigated. Following the analyses performed a close interrelation between landslides and precipitation is established. Finally, a characteristic example of rainfall- induced landslide in the wider area of the county is given

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