Page 71 - Volcano and Geothermal Tourism

48 Africa

Figure 3.2 The craters of Erta Ale in November, 2002, viewed from the south-east from the helicopter that transported
the expedition members
Source: Jens Edelmann

rises 50–60 metres above the surrounding salt the surface – at least no evidence of magmatic
plains and has approximate dimensions of 1.5 × activity at the surface has been found to date.
3km) and several other features in the vicinity, The circular depression near the centre of
such as the 1926 crater near the ‘Black Mountain’ Dallol Mountain is presumably a collapse crater,
(which consists of manganese-rich halite), about although neither its age nor the exact process
1.5km to the south-west. which led to its formation are known. The south-
Dallol is nested on top of a layer of quaternary west flank of Dallol Mountain harbours impressive
evaporates including large potash (potassium salt) salt canyons formed by erosion processes. Salt
reserves, at least 1km thick. These massive evaporate pillars up to 40 metres high are found rising above
deposits formed as the result of ongoing geological the canyon floors. The pillars consist of hundreds
and tectonic processes in the region. Crustal of layers of slightly pinkish (due to traces of KCl)
spreading has resulted in repeated periods when the halite (NaCl) salt deposits separated by thin layers
low-lying Danakil depression was connected to the of gypsum-like material. They are capped by
sea. Subsequent geological events led to disconnec- gypsum anhydrite and clay beds which have
tion and eventual evaporation of the sea water, protected them from the rainfall-induced erosion
resulting in massive evaporate deposits. Dallol is a which formed the surrounding canyons.
further result of the intrusion of basaltic magma A minor phreatic eruption was reported in
into the oceanic crust covering the floor of the Dallol in 1926 and formed a 30m wide crater.
Danakil Depression, as a consequence of the rifting Since then, no significant volcanic activity has been
process. However, unlike at Erta Ale, the magma reported. Currently, activity is only in the form of
body appears to have caused an upwelling of the hot brine springs. As a result of these Dallol is one
floor of the depression without actually reaching of the few places on Earth where significant

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