The Vallée des Couleurs is endowed with a wide stretch of multiple coloured earths arranged in bands and domes. Some 23 coloured earths have been identified and scientifically described.
The vallée des Couleurs is located around 1 km downstream to the south east of Bassin Blanc volcano which was in eruption some 100, 000 years ago making it one of the most recent and young volcanoes of the Island. The particularity of Bassin Blanc volcano is that it was of the strombolian type i.e it was slightly explosive due to the presence of underground water near the active vent of the volcanic structure.
This means that for more than one hundred thousand years, the volcano has been emitting pyroclastic materials (pyro means fire and clastic means broken) ranging from clinkers to lapilli, tuffs, cinders and volcanic ash. Millions of tons of volcanic ash of different metallic composition and chemical characteristics have been emitted and have carpeted the region south and East of Basin Blanc.
Since the Vallée des Couleurs is located almost at the foot of the volcano, it has received the full load of the volcanic ashes and with the waning down of volcanic eruption has sprayed ashes which are more varied in quality and quantity than elsewhere. The ashes with different metallic and non-metallic composition which have puffed out from the crater and deposited in the valley were as constituted as follows ; Iron ( Fe ), Aluminium ( Al), Manganese ( Mn), Calcium( Ca ), Magnesium ( Mg), Sodium ( Na), with zinc( Zn) and Copper ( Cu) in lesser quantities. The air born ashes were deposited in bands along the valley based on the their density and weight which gave the following order;
Copper -> Iron -> Manganese -> Aluminium ->Sodium -> Magnesium -> Calcium.
The ashes compacted close together after they fell to the ground thus increasing the bulk density of the deposits . The bulk density of any ash fall deposit can be variable, with weight ranging between 1,000 and 2,000 kg/m3 . This is why they stayed put where they had fallen. In addition, volcanic eruptions usually inject water vapour (H2O), carbon dioxide (CO2), sulfur dioxide (SO2), hydrochloric acid (HCl), hydrofluoric acid (HF) and ash into the atmosphere. HCl and HF will dissolve in water and fall as acid rain whereas most SO2 is slowly converted to Sulfuric acid (H2SO4) aerosols.
With time and in the presence of moisture, water, oxygen and carbon dioxide, they started to change their composition and developed different colours. Iron when oxidized and further oxidized and when mixed with clay develops different distinct colours ranging from dark red to brown and light yellow.
Similarly, other metals decomposed and with time developed permanent colours ranging from dark red to purple, bluish and greenish. It is important to note that the ashes having different metallic composition have deposited in successive bands and later on with gully surface erosion have developed rounded shapes , a landscape which we can call a “ basket of eggs topography”.
The 23 colours of the volcanic ashes which are exposed at the Vallée des Couleurs have distinct and internationally recognized colours ranging from shades of red, brown, green, grey ,blue and yellow. The 23 colours are exposed in the geology museum with appropriate colour description and chemical composition.
The different metals emanate positive vibrating energy. Anyone who spends a few minutes observing the coloured earths in quiet meditation will receive and absorb such energy. The energy that will enter mind-body will avert anxiety, fear, worry, stress and negative emotions and will bring calmness and inner peace.