By Fred Pearce
The rivers of lava flowed with no apparent end. And then came the earthquakes. Hawai’i’s Kilauea Volcano had been erupting since mid-May. It’s entered a quiet phase now, but what happens next remains uncertain. What’s certain is the damage left in its wake. Similarly, the Canary Island of Lanzarote experienced violent volcanic eruptions nearly nonstop for five consecutive years. This happened three centuries ago. But instead of causing massive destruction, Lanzarote’s eruptions laid the foundation of a rejuvenated agriculture. The following passage from the upcoming revised edition of Fred Pearce’s When the Rivers Run Dry: Water—The Defining Crisis of the Twenty-First Century describes the marvelous benefits the black volcanic stones of the eruptions brought to the island.
Lanzarote, an island off the west coast of Africa, was a tranquil place in the eighteenth century, ruled by Spanish priests and visited occasionally by ships making the transatlantic crossing. Farming was rudimentary and the living poor. The island had less rain than much of the Sahara desert. Then came a series of massive volcanic eruptions that shook the island almost without a break from 1730 to 1735. A priest described how, at the height of the eruptions, “the earth suddenly opened… a gigantic mountain rose and sank back into its crater on the same day, covering the island with stones and ashes”.
It could have been the end for the island’s inhabitants. Yet, far from obliterating its life, the eruptions provided the key to the island’s future prosperity. The black volcanic stones noted by the priest launched a bizarre agricultural revolution. As the farmers returned to their fields, and contemplated the task of removed the stones, they noticed something odd. In the areas covered by stones, their crops were bursting forth, whereas elsewhere they were not. It didn’t take the farmers long to discover why. The black pumice-like stones had shaded the soil from the glare of the sun, reducing evaporation and keeping the soils damp. They were also porous and trapped moisture by capturing night-time dew. We now know the stones—which the local people called picon—cut water loss from the often-parched fields by around seventy-five percent. New crops would grow in the soil, including fruit and vegetables, provided there was a layer of picon at the surface.
Soon the farmers were importing camels from Mauritania to haul stones to fields that had not benefited from the eruptions. Formerly useless hillsides were cleared of brush, cut into terraces, covered in picon and planted with vegetables. By 1776, an anonymous chronicler was recording a “prodigious mutation” of farming on the island. “Marvels abound, with the land being more fertile, becoming fruitful and bearing fruit two or three times a year. Like sponges, the picon soaks up the water, and the crops receive a delicate, gentle watering,” he wrote. “Before the eruptions in 1730, the most the island produced was bread and beef; now on the strength of the picon, it produces grapevines, vegetables, maize, potatoes, pumpkins and other produce.”
Exports of surplus produce began. Grapes did particularly well. The farmers grew prickly pears for the cochineal insects that infested them. The insects are deep crimson inside, and the islanders scraped up the insects with a spoon, dried and ground them, before selling the vivid crimson remains as a dye. Cochineal harvesting was big business in Lanzarote in the nineteenth century, before the advent of synthetic dyes.
The stones revolutionized agriculture. Their water catching abilities remain vital on an island with no permanent rivers, few underground water reserves and rainfall averaging just thirty-seven inches a year. Nowadays, most of Lanzarote’s population make their living from the two million tourists who visit each year. But the black fields produce nearly half a million gallons of wine a year. Lanzarote cochineal is still used in everything from lipstick to strawberry milkshake and Campari.
Farmers reckon fields need to be replenished every thirty to fifty years, as the stones become mixed into the soil. But there are still plenty to go round. “Virtually all cultivated fields in Lanzarote still have a layer of picon today,” says David Riebold, a British forestry scientist on the island, who showed me round. “Without picon, you couldn’t grow crops in most places.”
The technology has some precedents. It seems the prehistoric inhabitants of Easter Island in the Pacific used mulches of volcanic stones to trap moisture, especially after they had destroyed their forests. Some farmers in arid western China cover their fields with gravel from river beds to cut down evaporation. But, like the dew ponds on England, picon remains a remarkably local hydrological phenomenon that goes largely unnoticed both by the world’s agriculturalists and by the millions of tourists taking the sun on this very unusual desert island.
Look for Fred Pearce’s When the Rivers Run Dry: Water—The Defining Crisis of the Twenty-First Century this August!
About the Author
Fred Pearce has reported on environmental, science, and development issues from eighty-five countries over the past twenty years. Environment consultant at New Scientist from 1992 to 2018, he also writes regularly for the Guardian newspaper and Yale University’s prestigious e360 website. His many books include The New Wild, When the Rivers Run Dry, With Speed and Violence, Confessions of an Eco-Sinner, The Coming Population Crash, and The Land Grabbers.