Editing Horn of Africa (section)

===Geology and climate===
[[File:horn of africa.jpg|thumb|The Horn of Africa as seen from the [[NASA]] [[Space Shuttle]] in May 1993. The orange and tan colors in this image indicate a largely arid to semiarid climate.]]

The Horn of Africa is almost [[:wikt:equidistant|equidistant]] from the [[equator]] and the [[Tropic of Cancer]]. It consists chiefly of mountains uplifted through the formation of the [[Great Rift Valley (geographical concept)|Great Rift Valley]], a fissure in the Earth's [[crust (geology)|crust]] extending from [[Turkey]] to [[Mozambique]] and marking the separation of the African and Arabian [[plate tectonics|tectonic plates]]. Mostly mountainous, the region arose through faults resulting from the Rift Valley.

Geologically, the Horn and [[Yemen]] once formed a single landmass around 18 million years ago, before the [[Gulf of Aden]] rifted and separated the Horn region from the [[Arabian Peninsula]].<ref name="Ranrestar">{{cite web|title=2007 Annual Report|url=http://www.rangeresources.com.au/fileadmin/user_upload/Financial_Reports/RRS_Annual_Report_2007__PRINTERS_FINAL_.pdf|publisher=Range Resources|access-date=14 July 2012|archive-url=https://web.archive.org/web/20120321194039/http://www.rangeresources.com.au/fileadmin/user_upload/Financial_Reports/RRS_Annual_Report_2007__PRINTERS_FINAL_.pdf|archive-date=21 March 2012|url-status=dead}}</ref><ref name="Rrloageappabh">{{cite web|title=Oil and Gas Exploration and Production – Playing a Better Hand|url=http://www.rangeresources.com.au/fileadmin/user_upload/research_Reports/lloydsEJ_feb12.pdf|publisher=Range Resources|access-date=14 July 2012|archive-url=https://web.archive.org/web/20121017183314/http://www.rangeresources.com.au/fileadmin/user_upload/research_Reports/lloydsEJ_feb12.pdf|archive-date=17 October 2012|url-status=dead}}</ref> The [[Somali Plate]] is bounded on the west by the East African Rift, which stretches south from the [[triple junction]] in the [[Afar Depression]], and an undersea continuation of the rift extending southward offshore. The northern boundary is the [[Aden Ridge]] along the coast of [[Saudi Arabia]]. The eastern boundary is the [[Central Indian Ridge]], the northern portion of which is also known as the [[Carlsberg Ridge]]. The southern boundary is the [[Southwest Indian Ridge]].

Extensive [[glacier]]s once covered the [[Simien Mountains|Simien]] and [[Bale Mountains]] but melted at the beginning of the [[Holocene]].<ref>{{cite book|last1=Kaser|first1=Georg|last2=Osmaston|first2=Henry|title=Tropical Glaciers|year=2002|pages=150, 164|publisher=Cambridge University Press |isbn=9780521633338}}</ref> The mountains descend in a huge [[escarpment]] to the [[Red Sea]] and more steadily to the [[Indian Ocean]]. [[Socotra]] is a small island in the Indian Ocean off the coast of Somalia. Its size is {{convert|3,600|km2|sqmi|abbr=on}} and it is a territory of Yemen.

The [[lowland]]s of the Horn are generally arid in spite of their proximity to the equator. This is because the winds of the tropical [[monsoon]]s that give seasonal rains to the [[Sahel]] and the [[Sudan (region)|Sudan]] blow from the west. Consequently, they lose their moisture before reaching Djibouti and northern part of Somalia, with the result that most of the Horn receives little rainfall during the monsoon season.<ref name="Desert">{{cite book|last=Warner|first=Thomas T.|title=Desert Meteorology|pages=99–104|isbn=978-0-521-81798-1|year=2004}}</ref>

[[File:Nasa Horn of Africa.JPG|thumb|left|The Horn of Africa. [[NASA]] image]]

In the mountains of Ethiopia, many areas receive over {{convert|2,000|mm|in|abbr=on}} per year, and even [[Asmara]] receives an average of {{convert|570|mm|in|abbr=on}}. This rainfall is the sole source of water for many areas outside Ethiopia, including [[Egypt]]. In the winter, the northeasterly [[trade wind]]s do not provide any moisture except in mountainous areas of northern Somalia, where rainfall in late autumn can produce annual totals as high as {{convert|500|mm|in|abbr=on}}. On the eastern coast, a strong [[upwelling]] and the fact that the winds blow parallel to the coast means annual rainfall can be as low as {{convert|50|mm|in|abbr=on}}.<ref name="Desert"/>

The climate in Ethiopia varies considerably between regions. It is generally hotter in the lowlands and temperate on the plateau. At [[Addis Ababa]], which ranges from {{convert|2200|to|2600|m|ft|0|abbr=on}}, maximum temperature is {{convert|26|C|F|1}} and minimum {{convert|4|C|F|1}}. The weather is usually sunny and dry, but the short (''belg'') rains occur from February to April and the big (''meher'') rains from mid-June to mid-September. The [[Danakil Desert]] stretches across 100,000&nbsp;km<sup>2</sup> of arid terrain in northeast Ethiopia, southern Eritrea, and northwestern Djibouti. The area is known for its volcanoes and extreme heat, with daily temperatures over 45&nbsp;°C and often surpassing 50&nbsp;°C. It has a number of lakes formed by lava flows that dammed up several valleys. Among these are [[Lake Karum|Lake Asale]] (116 m below sea level) and [[Lake Afrera|Lake Giuletti/Afrera]] (80 m below sea level), both of which possess cryptodepressions in the [[Danakil Depression]]. The Afrera contains many active volcanoes, including the Maraho, [[Dabbahu Volcano|Dabbahu]], [[Afdera (volcano)|Afdera]] and [[Erta Ale]].<ref name="Stobin">{{cite book|last1=Marco Stoppato|first1=Alfredo Bini|title=Deserts|date=2003|publisher=Firefly Books|isbn=978-1552976692|pages=[https://archive.org/details/deserts00stop/page/160 160–163]|url=https://archive.org/details/deserts00stop/page/160|access-date=17 September 2014}}</ref><ref name="Etpame">{{cite book|last1=Facts On File, Incorporated|title=Encyclopedia of the Peoples of Africa and the Middle East|date=2009|publisher=Infobase Publishing|isbn=978-1438126760|page=7|url=https://books.google.com/books?id=stl97FdyRswC|access-date=17 September 2014|archive-date=15 March 2023|archive-url=https://web.archive.org/web/20230315191257/https://books.google.com/books?id=stl97FdyRswC|url-status=live}}</ref>

In Somalia, there is not much seasonal variation in climate. Hot conditions prevail year-round along with periodic [[monsoon]] winds and irregular rainfall. Mean daily maximum temperatures range from {{convert|28|to|43|C|F}}, except at higher elevations along the eastern seaboard, where the effects of a cold offshore current can be felt. Somalia has only two permanent rivers, the [[Jubba River|Jubba]] and the [[Shebelle River|Shabele]], both of which begin in the [[Ethiopian Highlands]].<ref name="Hadden">Hadden, Robert Lee. 2007. [https://web.archive.org/web/20090327102547/http://handle.dtic.mil/100.2/ADA464006 "The Geology of Somalia: A Selected Bibliography of Somalian Geology, Geography and Earth Science."] Engineer Research and Development Laboratories, Topographic Engineering Center</ref>