Editing Tagus (section)

== Geography ==

=== Source ===
The Tagus River originates at an elevation of 1,593 meters above sea level in a place known as Fuente García, within the municipality of [[Frías de Albarracín]] in Teruel, Spain. Its source is located between the Muela de San Juan (1,830 m) and Cerro de San Felipe (1,839 m), in the Sierra de Albarracín, which belongs to the Montes Universales in the western branch of the Iberian System.<ref>{{cite web  |author=Redaragón  |title=Nacimiento del Tajo  |url=http://www.redaragon.com/turismo/que_hacer/default.asp?accion=pagina&CosaQueHacer_ID=1664  |website=Redaragón  |access-date=2024-06-30  |language=es  |archive-url=  |archive-date= }}</ref>

=== Course ===
The river flows through Spain for {{Convert|816|km|abbr=on}}, passing through four autonomous communities (Aragón, Castilla-La Mancha, Madrid, and Extremadura) and a total of six provinces (Teruel, Guadalajara, Cuenca, Madrid, Toledo, and Cáceres). After forming a {{Convert|47|km|abbr=on|adj=on}} border between Spain and Portugal, it enters Portugal.<ref>The 47 km stretch where the river forms the border between Spain and Portugal is known as the "International Tagus".</ref> In Portugal, it flows for {{Convert|145|km|abbr=on}} through the traditional regions of Beira Baixa, Alto Alentejo, Ribatejo, and Estremadura, which include the districts of Castelo Branco, Portalegre, Santarém, and Lisbon.

The most important cities along its course are Aranjuez, Toledo, and Talavera de la Reina in Spain; and Abrantes, Santarém, and Lisbon in Portugal.

=== Basin ===
The Tagus basin has a total area of {{Convert|80,600|km2|abbr=on}}. It is the most populated basin in the Iberian Peninsula, with more than ten million inhabitants. It includes the Madrid metropolitan area and the Lisbon region. The Tagus basin has a total reservoir capacity of around {{Convert|14,500|hm3|e9cuft|abbr=unit}}.

=== Geology ===
The lower Tagus region in Portugal is a seismically active area. Major [[earthquake]]s in the Lower Tagus include those of 1309, [[1531 Lisbon earthquake|1531]], [[1755 Lisbon earthquake| 1755]], and [[1909 Benavente earthquake|1909]].<ref>{{cite book|first=William Herbert|last=Hobbs|author-link=William Herbert Hobbs|title=Earthquakes: An Introduction to Seismic Geology|publisher=D. Appleton and Company|location=New York|year=1907|pages=142–144}} [https://archive.org/details/earthquakesanin00hobbgoog/page/n200 <!-- pg=142 quote=Tagus. --> Downloadable Internet Archive]</ref><ref name="Diário de Notícias">{{cite web |title=Sismo sentido em Lisboa na mesma zona dos grandes abalos de 1531 e 1909|trans-title=Earthquake felt in Lisbon in the same area as the great earthquakes of 1531 and 1909 |url=https://www.dn.pt/sociedade/sismo-sentido-em-lisboa-ocorreu-na-mesma-zona-dos-grandes-abalos-de-1531-e-1909--13472236.html |publisher=[[Diário de Notícias]] |access-date=29 October 2021 |language=Portuguese |date=18 March 2021}}</ref>

=== Inverted delta ===
{{unreferenced section|date=September 2024}}
The Tagus river is one of the few rivers in the world to have an [[Inverted river delta|inverted delta]]. Its delta is wider at the beginning and narrows down as it approaches the sea, contrary to a typical [[River delta|delta]]. This is because it flows into the sea through a small opening in a valley. Although due to sedimentation, this delta is now only very partially inverted, with the valley now mostly filled with sediment. The delta is about {{Convert|15|km|4=0|abbr=on}} wide and {{Convert|25|km|abbr=on}} long, but its exit into the sea is only {{Convert|2|km|abbr=on}} wide. It thus forms a large lagoon with large and very shallow sand banks which go uncovered during low tides. The delta used to be even bigger thousands of years ago.