Erta Ale
Erta Ale is an active
shield volcano in
Ethiopia, known for its long-standing
lava lake activity.
This
volcano is quite broad, about 50 km in diameter. It has an elliptical
caldera some 0.7 x 1.6 km wide. The caldera contains two pit craters, both of which have had lava lake activity. The south pit crater has seen the most continuous lava lake activity, and the larger north pit crater has been less frequently so.
Erta Ale has erupted seven times in the past 125 years. Three of the early eruption dates, 1873, 1903, and 1904 are uncertain. However, 1906, 1940, 1960, and 1967 are well established events. Erta Ale has been erupting continuously since 1967. Observation of this volcano is limited due to the harshness of the
Afar Triangle, as air temperatures can exceed 50°C (123°F), and the indigenous
Afar people have a rather fierce reputation.
Two new studies on Erta Ale have recently been published.
*Oppenheimer and Francis (1998) looked at the implications of long-lived lava lakes. They believe that Erta Ale's lava lake has been active for at least the last 90 years (making it one of the longest known historic eruptions). Large amounts of heat are released by the volcano but the amount of lava that erupts is relatively small. They speculated that a higher magma density (caused by the lava lake cooling) inhibits eruptions. They proposed that most of the magma accumulates in the underlying crust as
dikes and
sills. Since the Afar region is under extension, conditions are favorable for injection of dikes and sills.
*Barrat and others (1998) looked at the chemistry of the rocks at Erta Ale. Rocks range in composition from
basalt to
rhyolite. They found that two mantle sources were tapped for the basalts: one similar in composition to the source for
mid-ocean ridge basalts (called MORB by geochemists) and one similar in composition to the source for ocean-island basalts (called OIB). Their data did not show a significant contribution of
sialic material from the
continental crust. The silica-rich volcanics are derived from fractional crystallization of basaltic
magmas.
As of January 2004, visiting scientists have reported that the lava lake in the south pit crater has solidified at the surface, leaving only a small incandescent lava lake remaining. From 21 to 24 September 2005, Erta Ale erupted, probably in a
Strombolian manner according to the locals, as inferred by scientists who visited afterwards. The south pit crater and its lava lake both have also enlarged considerably since.
George Kourounis, A storm chaser & adventurer from Canada is one of the few people in the world to have documented the
Erta Ale lava lake from the inside. During an expedition in 2005, he was able to walk on top of the temporarirly crusted lava inside the crater.
* Barrat, J.A., et al, 1998. J Volc Geotherm Res. 80, pp 85-100.
* Oppenheimer C, Francis P, 1998. "Implications of longeval lava lakes for geomorphological and plutonic processes at Erta 'Ale volcano, Afar", J Volc Geotherm Res. 80: pp 101-111
*
Global Volcanism Program entry*
Erta Ale: Index of Volcanic Activity Reports
