La Calima: An Ill Wind Which Blows a Lot of Good

Calimas occur from time to time in Lanzarote, as they do throughout the Canary Islands. They’re unpleasant events while they last, which can be anything from a few hours to three or four days. They arise when dust storms are stirred up by high winds over the Sahara desert and then driven westward across the Canaries. During these spells the air becomes somewhat foggy, due to the presence of minute particles of dust, which eventually settle and leave all exposed surfaces covered with a fine layer of yellow sediment.  At the same time the atmosphere becomes clammy, because aerosol droplets of moisture are formed, which remain suspended in the air because they’re too minute to coalesce and fall to the ground as rain. The air also becomes charged with an excess of positive ions, as always happens when hot air travels at speeds across a large land mass. This can give rise to feelings of lethargy, headaches, tension and increased irritability, just as it does when sirocco and khamsin winds blow over Mediterranean countries.

Atmospheric dust has always had a bad press, yet we need it to form the clouds, precipitate the fall of rain and create beautiful sunsets. Without dust in the sky, water wouldn’t begin to condense until the relative humidity was about 300%, which means that every day on earth would be intolerably muggy. Deprived of clouds, which normally shield about half of the earth from direct exposure to the sun’s rays, the land would become excessively hot.  But there’s something very special about the dust that’s floating in the skies. Most of this comes from particles of sand from the Sahara desert. This inhospitable wasteland is unlike other deserts. They’re covered by layers of solid stone and rocks, whereas the Sahara is made up of loose sand piled up in dunes which rise in places as high as a five-storey building. This fine material is easily carried in the wind. This is particularly true of the particles from one particular dust bowl in the Chad valley, which was formed over six thousand years ago when a major climate change dried out the vast Bodélé lake, which covered an area not much smaller than the modern state of California. Every year about two hundred million tons of dust is blown from this basin across the Canaries towards the Caribbean. Some of it falls on nearby Lanzarote, some reaches Europe, some drops in the Atlantic ocean, and about twenty per cent gets as far as the Amazon rain forest. This is of great benefit to the environment, for the dust is rich in iron and phosphorus, the micronutrients found in commercial plant fertilizers which are essential for the manufacture of one of the key enzymes needed for the life giving process of photosynthesis. When the Bodélé sand particles land in the sea they aid the growth of algae; when they fall in the Amazon basin they nourish the growth of the tropical rain forest. So when next you’re caught in a Calima, give thanks for the good the ill wind is blowing. Be grateful too that the dried up bed of the Bodélé lake – thought to be the dustiest place on earth – is expected to continue yielding its store of nutrient-rich sand for at least another thousand years.

© Donald Norfolk

www.donaldnorfolk.co.uk