Increased land Subsidence and also Sea-Level climb are Submerging Egypt’s Nile Delta coastal Margin
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Jean-Daniel Stanley1*, Pablo L. Clemente2*

1 Mediterranean container (MEDIBA) Program, 6814 Shenandoah Court, Adamstown, Maryland 21710, USA2 Dept. The Geographic and Environmental Systems, college of Maryland, Baltimore County, 1000 Hilltop Circle, Baltimore, Maryland 21250, USA


Abstract

Egypt’s Nile delta, just ~1 m above mean sea level at the Mediterranean coast, is topic to uneven prices of submergence. This is a response to several determinants leading to boosting land lowering (subsidence) that the northern delta and nearby seafloor, add to an accelerating rise in eustatic (world) sea level in the Mediterranean. An median eustatic sea-level climb of ~3 mm/yr represents just ~26% to 45% of full relative sea-level rise measured follow me this margin. Three determinants leading to subsidence room neotectonic lowering, compaction that Holocene sequences, and diminished sediment replenishment by much reduced Nile circulation to Egypt’s coast. Subsidence accounts because that variable average land lowering of ~3.7 mm/yr of section in the NW delta, ~7.7 mm/yr in the N delta, and ~8.4 mm/yr in the NE delta, based on compaction rates of strata thicknesses that decrease down-core between top and also base the Holocene sections in 85 drill cores distributed along the delta margin. Among present critical challenges are significant reduction that Nile water and also sediment listed below the High Aswan Dam that have the right to now reach the delta coast. That is expected that difficulties of new water and energy poverty in the reduced Nile basin are likely to be seriously exacerbated in year ahead by construction of Ethiopia’s grand Renaissance Dam (GERD). Completion of this, the greatest hydroelectric framework in Africa, is this year. Egypt, the Sudan, and Ethiopia must resolve the looming crisis of decreased Blue Nile water and sediment circulation to the lower Nile Basin and also Egypt’s delta margin.

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* E-mails: stanleyjd0
gmail.com; clempa1
umbc.edu

Manuscript obtained 13 July 2016; amendment manuscript obtained 29 Oct. 2016; Manuscript accepted 17 Nov. 2016; Posted virtual 14Feb. 2017

10.1130/GSATG312A.1


Introduction

Recent submergence that many world fluvial-marine deltaic spare is typically attributed to enhanced eustatic (world) sea-level increase responding mostly to raised polar glacial ice melt and thermal growth of seawater linked with an international warming (Hansen et al., 2016). Much less attention has actually been payment to various other mechanisms that might presently play a substantial, or even greater, function in a delta’s seaside submergence. The Nile delta’s margin in northern Egypt is examined below with regard come its continuous submergence by rising sea level (Shaltout et al., 2015), linked with the impacts of land subsidence near its Mediterranean coastline and also seafloor offshore (Fig. 1). The latter incorporate (1) effects of current neotectonic lowering of the delta surface linked with substrate displacement; (2) ongoing compaction of the Holocene sedimentary sequence; and (3) lessened sediment replenishment through the Nile flow at the delta coast and surrounding shelf. We propose the these three phenomena have triggered a greater amount that subsidence that the low-elevation delta margin (~1 m over mean sea level ) and consequent landward coast retreat during the past few thousand year than could have been developed during this time expectations by the enhanced rate the eustatic sea-level increase alone. Components triggering floor subsidence, connecting with increased rise in eustatic sea level, account because that what is generally termed relative sea-level rise.


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figure 1

Map of the Nile basin indicating loved one percentages that fresh-water flow added by the Blue Nile, Atbara River, and also the White Nile to the main Nile in the Sudan and Egypt. GERD—Grand Ethiopian Renaissance Dam.


This inspection highlights raised anthropogenic pressures the augment the affect of this factors and also have negative consequences for populations in the north delta. Of major concern is the recurring reduction that useable land and also fresh water essential for agricultural production in this small but critical breadbasket, one that has actually previously accounted because that 60% that the country’s food production. This continued coastal margin submergence occurs at a time as soon as Egypt, encountering increased financial stress and diminished inner political stability (La Guardia, 2016), must currently import much of its food to feeding its growing populace concentrated in the Nile delta and valley.

Background

The Nile container covers 3,250,000 km2 and extends northward throughout 36° of latitude. The delta creates at the mouth the the Nile, the world’s longest flow (~6700 km), whose water in Egypt is obtained from two north-flowing branches, the Blue and White Niles, that merge as the main Nile in the northern Sudan (Fig. 1). Interpreta­tions concerning Holocene depositional sequences at the delta’s seaside margin (Fig. 2A) are based upon stratigraphic, sedimentological, petrologic, biogenic, and geochemical analyses of >3000 samples selected native 85 radiocarbon-dated drill cores (dots in Fig. 2B). This cores and also supplemental study materials were examined throughout the past 30 years by the Smithsonian Institution’s Mediterranean container (MEDIBA) program (Stanley et al., 1996; Stanley and also Warne, 1998). Full core lengths variety from 20 m come >50 m indigenous the delta surface downward, with numerous sections radiocarbon dated to provide a chrono-stratigraphic framework. The upper component of the so late Pleistocene’s mainly sandy part (Mit Ghamer Fm.) is generally recovered at most core bases; these older sections, in turn, space covered through Holocene nutrient-rich silty mud and also fine sand assignment (Bilquas Fm.) that thicken northward and also eastward follow me the shore (Fig. 2B). Main point sites are spread from east to west in a curvilinear, coast-parallel area of ~7000 km2 that creates the northern third of the delta; many sites room positioned ˂30 km from the current arcuate coast at elevations to ~1 m or lower above msl.


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figure 2

(A) geographic features and localities in the north sector the the Nile delta, consisting of those quote in the text. (B) Map showing typical thickness (in m) the Holocene section (CD) in sectors I, II, and also III of the north delta. (C) Lithologic aspects and also physiographic features in the delta margin and also offshore sector. Arrows highlight three major coastal shifts and reversals v time: I, coast landward retreat in post-glacial time (ca. 16,000 B.C.) to beforehand Holocene (ca. 6000–5500 B.C.); II, shore seaward advancement from at an early stage Holocene (ca. 6000–5500 B.C.) to late Holocene (ca. 2500 B.C.); and III, coastline landward retreat, when again, from late Holocene (ca. 2500 B.C.) to present.


Additional data are derived from various other sources: cores acquired by rather in the delta (Attia, 1954; Marriner et al., 2012); sediment grab samples and also short gravity cores ~ above the surrounding Nile delta shelf (Summerhayes et al., 1978); and also dated vibro-core and also seafloor data at major, now-submerged historical sites of Greek and Roman age seaward that the delta, including major ones in Abu Qir Bay and also Alexandria’s east Harbor (Bernand and also Goddio, 2002; Stanley, 2007; Robinson and Wilson, 2010). Also useful are released analyses the satellite surveys the delta surface and sea-level elevations, deep subsurface stratigraphic and also structural data derived in the northern delta and offshore by means of 2D and 3D geophysical surveys, and associated well main point information. These data space compiled by the hydrocarbon (largely gas) suppliers conducting expedition in this region during the past half-century.

The distance between the delta’s southerly apex close to Cairo and the coastline is 160 km, and also the delta length along its arcuate coastline is ~270 km, indigenous Alexandria in the west to the margin south of the Gulf the Tineh in the east. Four elongate brackish lagoons, positioned from east to west nearby to the delta coast (Manzala, Burullus, Idku, and Maryut; Fig. 2A), room of usual depths, varying to little more than 1 m listed below msl. Lock are open to the sea, and their waters room brackish come saline. The delta’s seaside margin order of late Pleistocene to existing age include Nile fluvial and also desert wind-borne sediment, and also those derived from eroded maritime sections indigenous nearshore deposits. Sandy delta beaches space in component shaped by the Mediterranean’s semi-diurnal microtidal and surge effects, and especially by strong winds the in winter space directed towards the SE. The current coastline’s arcuate kind results from powerful winter wave surges and wave-driven coastal currents the displace sediment mainly toward the eastern (Frihy et al., 2002). Seaside material is preferentially eroded native seaward projecting headlands, consisting of the two Nile distributary promontories and also the bowed-out coast in the Baltim an ar (Fig. 2A). This displaced sediment creates the long, small sand obstacles at the seaward margin of coastal lagoons, if landward-driven masses the wind-blown sand have gathered as considerable dune fields along the north-central delta shore east of Baltim (Figs. 2A and also 2C). A big body that published work summarizes the outcomes of theoretical modeling and field measurements of sediment displaced native various seaside and offshore shelf sectors and also their migrate patterns with time (UNDP/UNESCO, 1978; Frihy and El-Sayed, 2013). Teams examining these troubles have had several global organizations, the seaside Research academy in Alexandria, and other Egyptian study centers and universities. Coast stabilization is currently partially achieved, at the very least locally where efficient protection measures have been implemented, mostly due to the fact that the past half-century adhering to closure in 1965 the the Aswan High Dam.

The much-increased duty of human task through time in this an ar needs to it is in emphasized. In Predynastic time, from ~5000 B.C. Onward, hunters and also gatherers in little numbers moved to the delta native adjoining arid, sand-rich Sahara terrains. The significant cultural-ecological transition to watering farming and urbanism top top the Nile’s delta plain, with its available water and also organic-rich soil, occurred during the early Dynastic to Dynastic at ca. 3000 B.C. This progressed to what Butzer (1976) characterized as very early hydraulic civilization, a socio-economic system based upon deliberate flooding and draining by sluice gates and also use of water containers contained by dikes. The major shift in populace from the Nile sink northward to the delta took place during the Hellenistic period (323–30 B.C.), a time when Egypt’s total populace increased come ~5 million (Butzer, 1976).

At present, the country’s population has reached ~90 million, with a growth rate above 2.0%/yr. The this number, ~45–50 million civilization live in the delta and also its proximity and, of these, approximately 20 million are focused in and around Cairo at the delta’s southerly apex, with another 15–20 million occupying the delta’s southern and central sectors. About 10 million an ext people inhabit the north delta’s coastal region; this number has the 4.5 million people living in Alexandria, Egypt’s second largest city and also its significant port and industrial center. Populace densities are extremely high (to 1000 or more/km2) in much of the Nile delta and valley, two sectors the comprise locations of 22,000 km2 and 13,000 km2, respectively, and also that together type only ~3.5% of Egypt’s complete area. Due to anthropogenic stresses, the Nile delta has been modified to the degree that it no longer features as a organic fluvial-marine depocenter (Stanley and also Warne, 1998).

Neotectonic Effects

Neotectonics refers generally to energetic seismicity and also tectonic activities that space geologically recent, indigenous the Tertiary onward and also continuing to the present. Substantial information ~ above seismicity and tectonics affect the delta’s surface and also subsurface sequences has been released in current years, following energetic exploration in ~ the delta’s hydrocarbon provinces. Data has actually been derived from 2D and 3D seismic surveys, in addition to well main point analysis, in the northern delta and offshore shelf. These and seismograph surveillance stations have helped clear up the relation between Holocene sediment deposits and also their displacement by earthquakes, faults, and also delta surface lineaments, the latter mapped through Landsat. Although identified as a passive margin, northern Egypt is defined by constant earthquake events of shallow beginning and small magnitude (M the 3 or less) and also of moderate quakes (M come 5) that happen less typically (Korrat et al., 2005). Earthquake and fault trends are interpreted as results of ongoing interactions amongst African, Arabian, and Eurasian plates and the Sinai subplate.

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Two active linear belts cross Egypt and intersect in the delta: a SE to NW Gulf that Suez-Cairo-Alexandria trend and a NE to SW east Mediterranean-Cairo-Fayum trend (Fig. 3A), v slip faults associated with this megashears (Kebeasy, 1990; Gamal, 2013). Earthquakes related to significant trends encompass those that recently impacted the Cairo area (in 1992, M = 5.9), and the Alexandria come offshore sector (in 1998, M = 6.7); the latter initiated in ~ a depth of 28 km. Alexandria, in particular, is a high earthquake danger zone that has periodically experienced significant damage, such as the an effective quake and also associated tsunami recorded in 365 A.D. That damaged much of the city (Guidoboni et al., 1994), and major quakes in 1303 and also 1323 A.D. That damaged the renowned Alexandria lighthouse. There is evidence of seismic damage and also fault counter in Alexandria that have disturbed old construction and additionally recently tilted some buildings. Modern earthquakes v M ≥5 occur about every 23 years. Although most quakes are of lower seismicity, with each other they constitute a source of seismic risk for the many who live in the delta and also its seaside margin (El-Ela et al., 2012).