Hearing the word volcano immediately makes us think of a destructive, explosive, and violent agent that provokes fear. However, volcanic activity has been very important in shaping the Earth's surface, forming continents and islands, and transforming ecosystems.
When a volcano becomes active, it expels lava, ash, and gases. The lava (molten rock) can cover a forest, turning the area into a barren space for decades or even centuries; the time it takes for plants to colonize the lava depends on the nature of the volcanic material and the climate. But the volcano can also spew ash and fertilize poor soil, allowing abundant vegetation to grow there.
Volcanic ash is full of nutrients that enrich the soil: it is composed of fine particles of minerals such as potassium, phosphorus, calcium, magnesium, and sulfates, all of which are essential for plant growth. In addition to providing rich material for plant nutrition, volcanic ashes contain crystals that retain large amounts of water and provide moisture to the soil. However, they also have their negative side: released in large quantities by a volcano near urban areas, they can clog sewers and prevent good drainage in the city; they can also destroy fields of crops or accumulate in the stratosphere, modifying the climate by blocking the normal passage of the sun's rays.
But let's look at the positive side: for a farmer who owns a piece of land devoid of crops, an ash eruption that forms a layer less than 20 centimeters thick can be wonderful. It has been seen that in places with periodic ash expulsions, soils remain fertile. This is the case on the terraces of Java where rice is grown for a large number of inhabitants. In tropical areas, soils are usually poor; they are very old and the parent rock that could provide minerals is at a great depth; these soils manage to remain rich thanks to the constant supply of organic matter.
By removing their vegetation cover, they are also stripped of their fertility. In this way, regions of Sumatra that were once home to abundant and diverse flora were impoverished by being exploited for crops of interest to the villagers. But from 1883 onwards, after the eruption of Krakatoa, ash emissions fertilized the soil and turned these areas into very prosperous agricultural areas.
In Italy, the periodic eruptions of ash from Vesuvius over the last twenty centuries have allowed incredible wine production in the area. Similarly, the Chichonal in Mexico, in 1982, spewed ash that fertilized the agricultural fields farther away from the volcano. However, in the closest areas, the ash deposits reached more than 15 m and all life was extinguished.
It is important to mention that the fertilization of soil by the contribution of ashes depends on the nature of the ashes. Those rich in crystals are the most appreciated because they are easily degraded and quickly release many nutrients. Popocatepetl, which in Nahuatl means "the mountain that smokes", spewed silica-rich ashes many years ago.
Silica is difficult to degrade and therefore takes a long time to fertilize the soil. Farmers in the region remove the top layers containing silica-rich pumice and planted them in deeper soils 2000 years ago. These soils are very rich because they have received for hundreds of years the slow runoff of nutrients released by this type of ash.
In this way, corn, beans, pumpkin, squash, vegetables, flowers, and fruit trees are grown on the slopes of the Popo. Nowadays, the volcano is also known as "Don Goyo", causes uncertainty in the population living in its surroundings, and this is understandable. A volcano can, at any given moment, change its behavior, but in this case, people can rest assured that their constant observation and study will help prevent any disaster.
By Verónica Bunge Vivier, Source: Correo del Maestro No. 31