More on the Great Rift Valley

In 2001 I prepared an essay describing the Great Rift Valley from its origin in the Jordan Valley to Mozambique.  In the essay I described its structure and expressed my views on the possibility of the rift rupturing at the many faults from movements of the tectonic plates.  While my views were entirely speculative and didn’t appear to be seriously considered by the scientific community, the facts of the matter were that the tectonic plates were slowly tearing apart eastern Africa.  

In a July 2006 story posted by Sara Goudarzi, Staff Writer for LiveScience, she reported that the Earth’s crust had split along a 37-mile section of the East African Rift [part of the Great Rift], in Afar, Ethiopia.  As she put it, “The Red Sea is parting again, but this time Moses doesn’t have a hand in it.”

 The East African Rift is a small part of the Great Rift Valley, which extends about 3,000 miles from southwest Asia through a series of faults to eastern Africa, from the Jordan River valley to Mozambique.  In my essay of 2001, I described the route of the Great Rift in some detail and concluded my paper with the possible effects of the rift on Eastern Africa in geological time.  One of my described risks was the formation of an inland sea, a subject included in Sara Goudarzi’s story.  Another possible event included in my essay, but not discussed in the LiveScience report, was the possibility of part of Eastern Africa breaking away from the mainland due to the weight of infiltrating water on the fault areas.  Once again, time is geological time.  This problem of infiltrating water is well known to scientists who have studied the problem for the past 10-20 years and possibly longer.  These studies have been made primarily of the rift in the Kenya / Tanzania regions where an increasing flow of water, probably from an aquifer, deep well, underground river or such other water source, has been infiltrating parts of the Great Rift for years.  While the local and short-term irrigation benefits of such flows are obvious, there is concern of the long-term effects. 

What is happening?  Nature reports that Earth’s tectonic plates are moving away from each other, stretching the Earth’s crust and widening the southern end of the Red Sea.  This movement has been verified by images from the European Space Agency’s Envisat radar satellite.  

Specifically, over a period of three weeks, the crust on the sides of the rift moved apart by 26 feet over a 37-mile section, and magma moved from storage chambers at depths of 1.9 to 3 miles into the vertical crack, forming new crust.  Scientists estimate that enough magma was released to fill a football stadium 2,000 times.         

When the Great Rift leaves the Dead Sea and the Jordon trough, it is 1,292 feet below sea level, the lowest point on Earth.  From the Dead Sea, it continues to and through the Gulf of Aqaba, a northern arm of the Red Sea, which separates Egypt’s Sinai Peninsula from Jordon and Saudi Arabia, into the Red Sea. The Red Sea, as part of the Rift Valley, separ-    ates northeast Africa from the Arabian Peninsula.  It includes the area from the Gulf of Aqaba and the Straits of Tiran at the northern end to the Bab el Mandeb at Djibouti at the southern end, where it meets the Gulf of Aden.   The Red Sea did not exist 20 million years ago.  At that time, the Great Rift was the center of a trough in a land mass, which included the Arabian Peninsula.  The Red Sea was formed from a long-term tug-of-war between the Arabian Plate (moving northeast) and the African Plate (moving southwest).  The trough in the land mass widened and deepened over time from the two plates pulling away from each other.  Eventually, the strain caused a rupture in the land that is now Egypt and Sinai and the Mediterranean Sea poured into the trough forming the Red Sea.  

The Great Rift continues to form the boundaries of the tectonic plates in the Red Sea and the Gulf of Aden.  However, it is far  more complex than two plates pulling against each other, and it is this complexity that creates the possibility, the probability, of a new inland sea.

                                                                               

The Arabian Plate is moving northeast, but the Eurasian Plate and the Indian Plate restrict its movement.  The combined effect of the two plates is only to slow the movement of the Arabian Plate, not stop it.  The African Plate has two parts: the Nubian part southwest of the Arabian Plate and the Somalian part south of the Arabian Plate and southwest of the Indian Plate.    

The Great Rift Valley - Kenya/Tanzania Area

 The Afar Triangle is a plate tectonic triple junction located in the Afar Region of Ethiopia, where three plates are pulling away from one another: the Arabian Plate and the two parts of the African Plate causing splitting along the East African Rift Zone.  The Afar Triangle is also called the Afar Depression or the Danakil Depression.  It is a geological depression in the Horn of Africa, where it overlaps the southern extension of Eritrea and northwest Djibouti.  However, the greater part of the depression will be found in Ethiopia.  Over millions of years, geologists expect the Red Sea to erode through the barriers surrounding the Afar Depression and flood the valley.  In about 10 million years, geologists predict that the whole 6,000 km length of the East African Rift will be submerged, forming a new sea as large as the Red Sea is now.   

In terms of the Great Rift, the Afar or Danakil Depression is where the Great Rift returns to land after moving the length of the Red Sea from the Gulf of Aqaba. 

 In her report, Sara Goudarzi notes that this is the first rifting episode to have occurred since 1970, but it is the largest single rip in the Earth’s continental crust during the satellite-monitoring era.  It was preceded by 163 earthquakes in the Afar rift alone. 

This latest split, added to the long-term rifting process, which is tearing the northeast of Ethiopia and Eritrea from the rest of Africa, could eventually create a huge new sea.  What has scientists especially excited. Is that this event has given scientists an unprecedented opportunity to monitor the rupture in real time.  This region of Africa will undoubtedly be one of the most investigated in the future of all the geological places of interest on Earth.  

In the preparation of this article, liberal use has been made of the story by Sara Goudarzi, Staff Writer for LiveScience.  Maps are from the main World Atlas, MapQuest, information on the Afar Region and Depression is from Wikipedia and the Encyclopædia Britannica 2006 Ultimate Reference Suite CD, references to geomorphology are from NASA, and references to the route of the Great Rift Valley and other references are from my original essay of 2001.    

January 2007   

LFC