Erta Ale

Erta Ale ( also spelled as Arta Ale , Herta Ale ) is one of the spectacular and unique places in Afar- Ethiopia ( May be in the world ). It is the most active isolated shield Volcano in Ethiopia famed for its long-standing lava lake activity.This volcano is situated in the Danakil depression of Northern Afar along the NNW-SSE trending Erta Ale range. 

Before we go any further , a word about Shield Volcano helps the non specialized reader. A shield Volcano is a large volcano with shallowly-slopping sides similar to a warrior shield. Shield volcanoes are formed by lava flows of low viscosity-lava that flows easily. The fulidity of the lava prevents major explosive eruptions. The most sevier explosions occur if water enters a vent. Also interesting to know that expanding gases in the magma can produce spectacular fountaining of low viscosity lava.Many of the largest volcanoes on earth are shield volcanoes. Other places where shield volcanoes can be found are Hawaii, Wahington,Oregon , the Galapagos Islands and Reunion Island. Maona Loa on the big Island of Hawaii is the largest shield volcano on earth. Shield volcanoes are known to form on other planets too. Olympus Mons on Mars , the largest known shield volcano mountain in the solar system, is one good example. 
Now back to Erta Ale. This basaltic broad volcano is about 50 KMs in diameter and rises more than 600 meters from below sea level. On its Summit, the volcano hosts an elliptical shaped caldera ( mouth of volcano) of about 1600 x 700 meters width. Fresh looking basaltic lava flows fill much of the caldra and have overflowed its rim on the southern side. The northern half of this caldera contains two steep sided pit craters of different size. One on its northern tip and the other a little down south. 

According to Oppenheimer and Francis (1998) Erta Ale's Lava lake has been active for atleast the last 90 years making it one of the longest known historic eruptions. It is also more interesting to know that large amounts of heat are released by the volcano while the amount of lava that actually erupts is relatively small. Why was that? This is because ,as suggested by some, a higher magma density which came as a result of the cooling of the lava lake blocked the eruptions. 

It is believed that the Northern pit of Erta Ale stayed active ( contained lava lake) possiblly between 1906 and 1988 for about 80 years. At the momment this pit contains only a rising steam. An over view of the north pit using fish-eye-lens revealed strange fumarolic deposites along the northern rim of this pit. Also on the north eastern rim of the same pit is seen a remarkable hornito formed by fluid lava. On the southern rim a small pit only a few meters in diameter is found. 
The south crater is ellipsoid shaped of about 160 meters from East to west and 130 meters from north to south. Inside the crater almost half of the area is taken up by a lava lake. The other half is covered by solidified basaltic rock terrace which is found at the depth of 40 to 45 meters from the crater rim. On the other hand the lava lake is about 90 meters deep from the rim. Flictuations on the distance between the rim of the pit and the surface of the lava lake have been observed recently. The lava lake alone when measured from east to west is around 100 meters long. 
Lava fountaining of up to 20 meters high occured in different areas at the crater lake , but mainly in the west, south and center. There are some records which tell that some very adventurous (Should we say crazy ?) earth scientists have dared to walk on top of the temporarily crusted lava with the intention to document the activity of the lava lake from the inside. 

The surface near the crater rim is broken by cracks of different width that run in concentric circles around the crater pit. Many parts of the edge can be seen hanging over the empty space. The crater walls are very instable and rock falls ( avalanches) are not uncommon. If one happens to be there at the time of such rock falls one is very likely to see a dramatic cloud of Orange brown dust covering the pit. Recently , after the dramatic eruption of 2005, both the crater pit and the lava lake within have been found to have expanded remarkably. The composition of the rock at Ertale ranges from basalt to rhyolite. According to earth scientists, Erta Ale has erupted seven times in the past 125 years and has been erupting continuously since 1967.

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