Dallol hot springs and geysers

These unique phenomena have been created by a rare coincidence of several geological factors.

Danakil Depression

The geology of Afar is unusual – the crust of Earth here slowly is spreading in three directions. In the zone of such spreading the crust of Earth gets thinner and the heat from the depths of Earth breaks through it, forming countless volcanoes, hot springs, and other amazing geological phenomena.

Danakil Depression is located on the northern arm of this Afar Triple Junction. This harsh, inhospitable desert is located very low, up to 119 m below sea level. Several volcanoes are located here – also Dallol Volcano, which rises above the desert but nevertheless is 48 m below the sea level.

Giant lens of salt

Nowadays Danakil Depression is dry desert – but in the past, in Miocene epoch it has been repeatedly inundated by the sea, forming a deep gulf. Every time when this gulf was cut off from the ocean, it dried out, leaving salt deposits.

As a result here has formed more than one kilometre thick layer of salt. Countless caravans have been coming here and mining the salt for centuries – and they still do it today.

Vapour, explosions and maars

Dallol Volcano is not a true volcano. Here, in the thick salt layers has intruded basaltic magma. As the groundwater descends deeper, it meets overheated rocks and turns into vapor. When the pressure of vapor reaches a critical level, the ground (here – salt) above this superheated vapor is blown off in a spectacular explosion, leaving a crater – maar.

Last time such an explosion took place in 1926, some 1.5 km to the southwest from the main crater of Dallol Volcano. Now in the site of this explosion is located deep, 30 m wide, round pit, filled with orange brine.

Will there be more explosions in the future? Most likely – yes. This can happen every second.

The 1.5 by 3 km large crater of Dallol Volcano has formed by the collapse of salt layers. Multiple hot springs above the hot magma have washed out the salt layers, leaving voids, which at some moment have collapsed.

Most colourful place on Earth?

The salts of Danakil Depression are white or transparent – just like the table salt. There have been mixed diverse salts – the well-known halite (NaCl), but also sylvite, carnallite, kainite.

Volcanic heat though brings up from the depths other, more colorful elements – the bright yellow sulfur and the iron. Iron adds lots of colors – green, blue-green, orange, brown.

All of this – the immense layer of salts and the colorful iron compounds and sulfur are blended by the countless hot springs in the crater of Dallol Volcano. This has resulted in one of the most unusual landscapes on Earth.

Crater is filled with small ponds of water (no, not water – a brine and often – sulphuric acid with pH below 1!) in different colors. In one pond the liquid might be in poisonous green color, but right next to it there might be a yellow or blue-green pool.

Ponds are divided by salt – and often this salt is white as snow, but also – green, orange, yellow.

Here have formed also rimstone formations – small stone dams. Again – this is a unique place where can be seen rimstone formations made of salt, maybe the only ones in the world. Elsewhere in the world rimstones are formed from travertine or sinter – and even such travertine rimstones are quite rare.

Salt geysers

The pressure of vapor has created countless geysers in Dallol Volcano. These geysers are not high and not permanent – the salt around the geyser in the depths is easily dissolved and at some moment geyser stops erupting. Water finds other crevices and a new geyser starts erupting nearby.

The erupted brine is very hot and quickly evaporates, leaving salt deposits around the mouth of the geyser. The highest geyser cones are up to 3 m tall, and just like everything else here – colored in garish colors.

When the geyser is "young", the cone is in clear colors – white, green, orange. As it gets older and fades off, the cone is gradually dissolved by the surrounding acid vapor and rain and becomes rusty, dirty.

In January 2011 here took place heavy rainfall. The supply of freshwater changed the hydrological regime and there appeared hundreds of new geysers and hot springs. Inevitably they will disappear one after another… and again there will come up new ones after the next rainfall.

Are we on Earth?

It seems – no other place on Earth is that similar to some alien world. Neon colors, steam, the unbearable smell of sulfur, and no life in sight – this could be Venus or some other planetary system.

Additional effect is created by the unbearable heat. A weather station in the 1960s fixed 34.4°C annual mean temperature – this is a world record. Read once more – annual mean! Including the nights! In daytime temperature above 40°C in shade is a norm – except that there is no shade!

But no – we are not on another planet. Dallol is a part of human Earth. This is reminded by the harsh fact that over the last years Ethiopian militaries are conveying tourists to this place. This is a necessary action to prevent attacks of local mobsters.

Most likely Dallol will never turn into a mass tourist site – it is too hot and too remote. And this is good – because the salt formations are fragile. Visiting the site is not too safe either – you are never sure whether you are not walking over a thin layer of fragile salt with hot acid under it. And remember the terrible maars – every second there can happen a grand explosion.

This sounds menacing – but this ephemeral feel also is a part of the charm of Dallol.

References

1. PhotoVolcanica.com, Dallol Volcano, TravelDope.net. Accessed on June 7, 2011.

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