scholarly journals Waters from the Djiboutian Afar: A Review of Strontium Isotopic Composition and a Comparison with Ethiopian Waters and Red Sea Brines

Water ◽  
2018 ◽  
Vol 10 (11) ◽  
pp. 1700 ◽  
Author(s):  
Tiziano Boschetti ◽  
Mohamed Awaleh ◽  
Maurizio Barbieri
Keyword(s):  
Red Sea ◽  
Hot Springs ◽  
Ethiopian Rift ◽  
Concentration Data ◽  
Mixing Processes ◽  
Main Ethiopian Rift ◽  
Weathering Processes ◽  
Sea Bottom ◽  
Geochemical Studies ◽  
Freshwater Aquifers

Drinking water is scarce in Djibouti because of the hot desert climate. Moreover, seawater intrusion or fossil saltwater contamination of the limited number of freshwater aquifers due to groundwater overexploitation affect those who live close to the coastline (~80% of the population). Despite this, the geothermal potential of the country’s plentiful hot springs could resolve the increasing electricity demand. Strontium isotopes (87Sr/86Sr) are routinely used to determine sources and mixing relationships in geochemical studies. They have proven to be useful in determining weathering processes and quantifying endmember mixing processes. In this study, we summarise and reinterpret the 87Sr/86Sr ratio and Sr concentration data of the groundwater collected to date in the different regions of the Djibouti country, trying to discriminate between the different water sources, to evaluate the water/rock ratio and to compare the data with those coming from the groundwater in the neighbouring Main Ethiopian Rift and the Red Sea bottom brine. New preliminary data from the groundwater of the Hanlé-Gaggadé plains are also presented.

A discussion on the structure and evolution of the Red Sea and the nature of the Red Sea, Gulf of Aden and Ethiopia rift junction - The structure of afar and the northern part of the ethiopian rift

1970 ◽  
Vol 267 (1181) ◽  
pp. 331-338 ◽  
Keyword(s):  
Red Sea ◽  
Rift Zone ◽  
Ethiopian Rift ◽  
Crustal Extension ◽  
Gulf Of Aden ◽  
Lateral Shear ◽  
Structural Pattern ◽  
Main Ethiopian Rift ◽  
The Individual ◽  
Complex Faulting

The major structural feature of the northern part of the Main Ethiopian Rift is an en échelon belt of Quaternary tensional faulting with the individual faults trending approximately N 20° E. Farther north, towards central Afar, this structural pattern gives way to a zone of complex faulting. Northern Afar is dominated by a linear, axial central rift region, marked by active fissure volcanism, normal faulting and open tensional faults, all trending generally NNW. However, this central rift zone dies out northwards as it is traced towards the Gulf of Zula. Left-lateral shear along the length of the Main Ethiopian Rift is proposed as the cause of the en echelon tensional fault zone, which can be traced into Afar, but is apparently not continuous with the zone of faulting associated with the median trough of the Red Sea. The latter appears to be replaced in an en echelon fashion southwards by zones of crustal extension in central and northern Afar.

scholarly journals Homogenized earthquake catalog and b-value mapping for Ethiopia and its adjoining regions

2019 ◽  
Vol 6 (1) ◽  
Author(s):  
Geremew Lamessa ◽  
Tilahun Mammo ◽  
Tarun K.Raghuvanshi
Keyword(s):  
Red Sea ◽  
B Value ◽  
Moment Magnitude ◽  
Ethiopian Rift ◽  
Rift System ◽  
Earthquake Catalog ◽  
Gulf Of Aden ◽  
East African Rift System ◽  
Main Ethiopian Rift ◽  
B Values

AbstractThe Ethiopian rift which is part of East African Rift system passes through the middle of the country making it one of the most seismically active regions in the world. Thus, significant and damaging earthquakes have been reported and recorded in the past in this region. A homogeneous earthquake catalog is of basic importance for studying the earthquake occurrence pattern in space and time and for many engineering applications including assessment of seismic hazard, estimation of peak ground accelerations and determination of long-term seismic strain rates.The first earthquake catalogue for Ethiopia was prepared by Pierre Gouin and later, different authors attempted to compile a catalogue using different time period intervals and different earthquake magnitude scales. The b-value mapping and its implication never done for Ethiopia and its environs. The main purpose of the study is therefore first compile and homogenize earthquake catalog of Ethiopia including Read Sea and Gulf of Aden regions into Moment magnitude Mw scale through completeness analysis in time and magnitudes. Secondly, mapping b-values for different Seismgenic regions and understand its implications for magma induced Seismicity in the regions.During the present study, a new homogenized earthquake catalog in moment magnitude scale (Mw), covering about 3814 events is prepared for Ethiopia including Red sea and Gulf of Aden regions. The present study area is bounded within Latitude (40N − 200)N and Longitude (340N − 480)N E and have a magnitude range of Mw (3.0–7.1) with a total coverage period of 56 years (1960 to 2016). The catalog has been analyzed for magnitude completeness (Mc) using Gutenberg’s Frequency Magnitude Distribution law and it is found to be complete respectively for Mc ≥ 4.6 ± 0.03, Mc ≥ 4.6 ± 0.03, Mc ≥ 3.2, Mc ≥ 3.1 and Mc ≥ 5.1 for Afar including red sea and Gulf of Aden, Afar rift and Dabbahu Volcano, Northern, Central, and Southern Main Ethiopian Rifts. Further, the corresponding average b-value of the regions Afar including Red Sea and Gulf of Aden, Afar and Dabbahu Volcano separately, Northern Main Ethiopian Rift, Central Main Ethiopian Rift and Southern Main Ethiopian Rift respectively are estimated to be 1.17 ± 0.05, 1.15 ± 0.05, 0.843, 0.826 and 1.03 with respective period of completeness from 2003 to 2014, 2005 to 2014, 2001 to 2003, 2001 to 2003 and 1960 to 2016 for the regions. Later, mapping of the b-values in the Gutenberg-Richter relation from the newly developed catalog was performed by binning the regions into minimum of 0.050x0.050 for Afar and Dabbahu region, 0.10x0.10 for Main Ethiopian rifts and 0.20x0.20 for the other regions. Thus, the b-value characteristics of various seismogenic zones within the area have been discussed. Hence, in this study, we clearly observed that magma chamber movement including mapping of volcanic centers and magmatic segments are mapped using b-values.

Strontium isotopic composition as tracer of weathering processes, a review with respect to James Ross Island, Antarctica

2012 ◽  
Vol 2 (1) ◽  
pp. 20-30 ◽  
Author(s):  
Jitka Míková
Keyword(s):  
Natural Environments ◽  
Polar Regions ◽  
Sr Isotopes ◽  
Mixing Processes ◽  
Rock Interaction ◽  
Weathering Rates ◽  
Weathering Processes ◽  
James Ross Island ◽  
Flow Pathways ◽  
Geochemical Studies

Strontium isotopes (87Sr/86Sr) are routinely used to determine sources and mixing relationships in geochemical studies. They have proven to be useful in determining weathering processes and quantifying end-member mixing processes. A number of studies highlight that Sr isotopes represent a powerful tool helping to constrain weathering reactions, weathering rates, flow pathways and mixing scenarios, even when inherent differences in weathering rates of different minerals, and mineral heterogeneity in natural environments may cause difficulties in defining the weathering component of different geochemical systems. Nevertheless, Sr isotopes are useful when combined with other chemical data, to constrain models of water–rock interaction and mixing as well as geochemical processes such as weathering. This paper presents basic information about Sr isotopic system, new analytical developments, summary of recent published studies in constraining the weathering processes, and indicates studies similar to weathering in polar regions. The aim of this paper is to present rationale of using Sr isotopes as tracer of weathering processes on James Ross Island, Antarctica.

scholarly journals Mapping Hydrothermal Alteration at the Fentale-Dofan Magmatic Segment of the Main Ethiopian Rift

2021 ◽  
Vol 9 ◽  
Author(s):  
Martina Raggiunti ◽  
Derek Keir ◽  
Carolina Pagli
Keyword(s):  
Fluid Flow ◽  
Hydrothermal Alteration ◽  
Hot Springs ◽  
General Pattern ◽  
Hydrothermal Systems ◽  
Tectonic Activity ◽  
Ethiopian Rift ◽  
Volcanic Complex ◽  
Main Ethiopian Rift ◽  
Circular Pattern

The Main Ethiopian Rift (MER) is characterized by extensional tectonics and volcanism, associated with active hydrothermal systems, hydrothermal alteration and fumarolic deposits. The spatial distribution of these hydrothermal products and their link with faults and rock types provides important clues to what controls fluid flow in the subsurface. However, little is known about this in the East African Rift. We address this issue with a multidisciplinary approach in the Fentale-Dofan magmatic segment of the MER, an area characterized by intense volcanic and tectonic activity and a geothermal prospect. Primarily we conduct mapping of hydrothermal alteration and fumarolic deposits, and rock lithologies using a surface feature classification technique of multispectral satellite images. Then we interpret the map using a new database of faults and active hydrothermal manifestations such as hot-springs and fumaroles. We find that the surface hydrothermal alteration and deposits are mainly focused near Fentale and the Dofan Volcanic Complex (DVC). At DVC the hydrothermal products are focused on rhyolites on the western side of the volcano, in an area of intense NNE striking, rift parallel faults. At Fentale volcano the hydrothermal products are mainly associated with ignimbrite and show a circular pattern around the volcanic edifice, but also in places follow the NNE striking faults. At Fentale, the more complex association of hydrothermal products and active manifestations around the edge of the ignimbrite suggests formation contacts may also localize fluid flow in places. At both volcanoes the association between hydrothermal products with either the rhyolites and ignimbrites is likely due to them being relatively easily altered (in comparison to basalt), and also their brittle nature allows for fracturing through which localized fluid flow can occur (as opposed to the sediments). The general pattern of hydrothermal products suggests a stronger structural influence at the DVC with respect to Fentale. The presence of hydrothermal products and active hydrothermal manifestations, along with other lines of evidence such as locus of subsurface dike intrusion at the volcanic centres, suggest that discrete and localized magma reservoirs beneath Fentale and the DVC are the heat source for hydrothermal circulation. Our study also demonstrates that geology, including hydrothermal deposits, can be successfully mapped using automated remote sensing based classification.

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.

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