The Earth Story

The Devil's Cauldron

We recently posted on some sedimentary rocks deposited in the world's youngest forming sea in the Afar triangle (see http://on.fb.me/1791Pmn), mentioning that the continental rifting involved also resulted in a variety of volcanic events. These range from the volcanic plateaus of Ethiopia, through the chains of Africa's Great Rift to the coastal smaller scale basaltic volcanic fields on both coasts of the Red Sea, both clearly visible as zones of dark rock in satellite photos.

Somewhat south of the Danakil Depression, right on the tip of the Horn of Africa curling into the sea towards Yemen is the tiny Republic of Djibouti, one of whose volcanic treasures is the bay of Ghoubbet Al-Karab. There are many fissures here that have leaked lava as the continent is slowly pulled apart like a pizza surrounded by starving teenagers, resulting in extensive volcanic fields, many of whose features formed in a single eruption. Between eruptions, coral reefs grow in the lava.

The bay is 20km long by 20 wide, on the borders of Lake Assal, itself a volcanic crater. Djibouti also sits on the triple junction between the Indian, African, and Eurasian tectonic plates. As the new oceanic spreading centre creates new marine crust between them, they are being pushed apart as the Red Sea grows. The process in ongoing, with new faults opening up and spewing lava every now and again.

The bay is surrounded by 600 metre cliffs and supposedly the haunt of fiery devils, who drag down unwary sailors to Davy Jones's Locker. The waters are deep, some 200 metres, and sealed off from the main body of the sea by powerful currents. The sea level can show up to a metre in difference between the bay and the surrounding gulf. Within the bay are a couple of old volcanic cones, known as the Devil's Islands. Whales and sharks abound in these waters, along with dolphins, barracuda and other predatory fish.

Loz

Image credit: Bernhard Edmaier

http://www.bernhard-edmaier.de/en/portfolio.html http://www.yannarthusbertrand2.org/index.php?option=com_datsogallery&Itemid=0&func=detail&catid=82&id=1648&lang=en&l=1366 http://www.visitdjibouti.dj/explorer http://www.cntraveller.com/news/2013/january/the-best-undiscovered-dive-sites/page/goubet-al-kharab,-republic-of-djibouti

AFAR DEPRESSION; ERITREA, DJIBOUTI AND ETHIOPIA The Afar Depression (aka the Danakil Depression) is a geological depression caused by the Afar Triple Junction, part of the Great Rift Valley. The Afar Depression overlaps Eritrea, Djibouti and the entire Afar Region of Ethiopia. The Afar Triangle includes the Danakil Depression and Lake Asal, which is the lowest point in Africa at 155 metres below sea level. The photo shows a hot spring within the Afar Depression. Dallol (https://www.facebook.com/photo.php?fbid=385595664834817&set=a.352867368107647.80532.352857924775258&type=3&theater) is also part of the depression. The floor of the Afar Depression is composed of mostly basaltic lava. The name Afar Triangle refers to the area being the product of a tectonic triple junction, where the spreading mid ocean ridges that form the Red Sea and the Gulf of Aden emerge on land and meet the East African Rift. These three pieces of the Earth’s crust meet around Lake Abbe. Beneath this Lake is a source of volcanic heat which causes hot water to rise through the layers of salt and anhydride products. The area is extremely dry with annual rainfall average about 10 to 18 centimetres; temperatures range from 25°C in monsoons to 48°C in the dry season. Aside from Iceland, the Afar Depression is the only place on Earth where a mid-ocean ridge can be studied on land. In the Depression itself, the Earth’s crust is rifting apart at the rate of 1-2 centimetres a year along each of the 3 rifts which form the triple junction. The consequence of this is a continuous sequence of earthquakes. Eruptions have occurred at Dabbahu and Erta Ale volcanoes (https://www.facebook.com/photo.php?fbid=380997365294647&set=a.352867368107647.80532.352857924775258&type=3&theater), as well as in Teru and Aura woredas. In 2005, 2.5 cubic kilometres of molten rock was injected into one of the plates along a dyke between depths of 2 and 9 km, forcing open an 8 metre wide gap on the surface, known as the Dabbahu fissure. The area also contains many salt deposits; in some places the salt deposits are 5 km thick. The salt deposits have been created by water from the Red Sea flooding the Afar Depression and then evaporating. The Red Sea is expected, over millions of years, to erode through the highlands surrounding the Afar Depression and flood the valley. In 10 million years the whole 6,000 km of the East African Rift is expected to be submerged and form a new sea.  Afar is also known as one of the cradles of hominids, containing the Middle Awash, the site of many fossil hominid discoveries such as Ardi, (Ardipithecus ramidus); the Gona (Gawis cranium); and Hadar, site of Lucy, the fossilised specimen of Australopithecus afarensis. -TEL Read more: http://ngm.nationalgeographic.com/2012/01/afar-depression/morell-text; http://broadcanvas.blogspot.co.nz/2012/04/danakil-depression-hottest-place-on.html;http://www.nature.com/nature/journal/v442/n7100/full/nature04978.html Photo: Carsten Peter for National Geographic http://maxcdn.fooyoh.com/files/attach/images/1097/439/006/001/danakil.jpg Other TES posts on this area: http://on.fb.me/1r9pNGC http://on.fb.me/1Cb148S http://on.fb.me/1JwpjQU http://on.fb.me/1CfddXC http://on.fb.me/1GAJ87f

AFAR DEPRESSION; ERITREA, DJIBOUTI AND ETHIOPIA The Afar Depression (aka the Danakil Depression) is a geological depression caused by the Afar Triple Junction, part of the Great Rift Valley. The Afar Depression overlaps Eritrea, Djibouti and the entire Afar Region of Ethiopia. The Afar Triangle includes the Danakil Depression and Lake Asal, which is the lowest point in Africa at 155 metres below sea level. The photo shows a hot spring within the Afar Depression. Dallol (https://www.facebook.com/photo.php?fbid=385595664834817&set=a.352867368107647.80532.352857924775258&type=3&theater) is also part of the depression. The floor of the Afar Depression is composed of mostly basaltic lava. The name Afar Triangle refers to the area being the product of a tectonic triple junction, where the spreading mid ocean ridges that form the Red Sea and the Gulf of Aden emerge on land and meet the East African Rift. These three pieces of the Earth’s crust meet around Lake Abbe. Beneath this Lake is a source of volcanic heat which causes hot water to rise through the layers of salt and anhydride products. The area is extremely dry with annual rainfall average about 10 to 18 centimetres; temperatures range from 25°C in monsoons to 48°C in the dry season. Aside from Iceland, the Afar Depression is the only place on Earth where a mid-ocean ridge can be studied on land. In the Depression itself, the Earth’s crust is rifting apart at the rate of 1-2 centimetres a year along each of the 3 rifts which form the triple junction. The consequence of this is a continuous sequence of earthquakes. Eruptions have occurred at Dabbahu and Erta Ale volcanoes (https://www.facebook.com/photo.php?fbid=380997365294647&set=a.352867368107647.80532.352857924775258&type=3&theater), as well as in Teru and Aura woredas. In 2005, 2.5 cubic kilometres of molten rock was injected into one of the plates along a dyke between depths of 2 and 9 km, forcing open an 8 metre wide gap on the surface, known as the Dabbahu fissure. The area also contains many salt deposits; in some places the salt deposits are 5 km thick. The salt deposits have been created by water from the Red Sea flooding the Afar Depression and then evaporating. The Red Sea is expected, over millions of years, to erode through the highlands surrounding the Afar Depression and flood the valley. In 10 million years the whole 6,000 km of the East African Rift is expected to be submerged and form a new sea. Afar is also known as one of the cradles of hominids, containing the Middle Awash, the site of many fossil hominid discoveries such as Ardi, (Ardipithecus ramidus); the Gona (Gawis cranium); and Hadar, site of Lucy, the fossilised specimen of Australopithecus afarensis. -TEL Read more: http://ngm.nationalgeographic.com/2012/01/afar-depression/morell-text; http://broadcanvas.blogspot.co.nz/2012/04/danakil-depression-hottest-place-on.html;http://www.nature.com/nature/journal/v442/n7100/full/nature04978.html Photo: Carsten Peter for National Geographic http://maxcdn.fooyoh.com/files/attach/images/1097/439/006/001/danakil.jpg