This post was written by Amelia Frizell-Armitage, a plant scientist at UEA and John Innes Centre investigating wheat yield improvement and a friend to a geologist (why she was pestered into writing this blog post). You can follow her on twitter here.
When you think about volcanoes you probably think about their danger as a natural hazard, their destructive power and maybe even a little about their (I have been told) interesting geology. However, as a biologist and self confessed plant geek, I am more interested in how volcanoes have shaped life on earth. We live in a world of contrasts, and volcanoes are no exception: they have the power to both destroy and create.
In general, when a volcano erupts on land it spews out large amounts of lava, destroying the majority of living organisms in the surrounding area. Together with the lava come gases and tephra, with more far reaching effects. Tephra is a mixture of different sized rock fragments. The very largest of these fragments over 64mm in diameter and you would certainly not want to be in the firing line of one of these! Thrown long distances from the volcano, they can cause quite a large amount of damage where they fall. The smallest of these fragments are particles less that 0.1mm in diameter and can remain in the atmosphere for years after eruption.
On the scale between bombs and particles we find ash, which forms a thick carpet in the regions surrounding the volcano and can also spread long distances from the volcano. Of the many things a plant requires to grow, light and water are of the highest importance. Plants covered in ash can become deprived of both of these things and are effectively ‘suffocated’. The effects of ash on vegetation can be far more widespread than other eruption components so can be pretty disastrous for vegetation in the region. Green plants are the basis of most terrestrial food webs, so wiping out the vegetation of an area would have disastrous consequences for consumers further up the food chain (that have managed to actually survive the eruption). With no food they either have to migrate elsewhere, or starve.
I’ve painted a pretty dire picture so far of the immediate aftermath of a volcanic eruption, with the implication that the regions surrounding a volcano are barren and desolate. But we actually find the opposite to be true, with some of the most bio-diverse areas on earth found near volcanoes! This is also the case for other sources of natural disaster such as earthquake epicentres.
The phenomenon can be explained when we think about disturbance in the context of evolution. Evolutionary theory states that the species that is best adapted to its environment (the fittest) will outcompete other less-well adapted species; the fittest survives and the others go extinct. The problem with this is that if we have an environment that remains constant over time we can end up with a few species that ‘win’, and everything else gets wiped out. The upshot is low biodiversity. However, in an environment that is constantly changing we also have low biodiversity because no species are able to adapt to a high level of disturbance. The best scenario for increasing biodiversity long-term is an intermediate level of disturbance, and with a volcano this is exactly what we get. The time between eruptions is enough for many different types of species to evolve in the environment, but not long enough that any one can dominate. Each time there is an eruption most species will be wiped out, but a few individuals (the fittest) will survive. Once the land begins to recover these individuals, plus other newly evolved species and others migrating in, can start to populate it. This means that over the long-term, geological time scale, areas with intermittent disturbance are able to have higher diversity.
The volcanic ash itself can have a much more direct consequence on biodiversity. In order to grow, plants need various nutrients, including nitrogen, potassium and phosphorus. Without these minerals it is impossible for a plant to grow, develop or harvest sunlight. Commonly the most limiting nutrient for plant growth is potassium, a mineral found in large amounts in volcanic ash! Plants cannot access this potassium when the ash first falls (but to be honest most plants have probably been killed under the ash flow anyway!). However, given time to weather, the potassium can be released from the tight bonds that hold it in the ash, and move into the soil. This is also true of many other minerals contained within volcanic ash, the composition of which depends on the particular volcano or region. For example, some ashes are high in sulphur, which when eroded makes the soil more acidic (lower PH). This is great for species that like a low PH such as blueberries.
I will re-iterate that plants are the basis of most terrestrial food webs. The consequence of a region with fertile soil is highly bio-diverse vegetation, and in turn a wide range of higher species such as animals and birds. Humans too can exploit volcanic soils for growing crops; for example, the soils around Mount Vesuvius are now fantastic agricultural lands. It is even possible to buy volcanic soil to improve your garden! A surprising result of this can be that regions around volcanoes can be heavily populated.
I have talked in this blog post about the impacts of terrestrial volcanoes on land-based life. However, volcanoes also exist under the oceans, where 50-80% of the life on earth resides. The short podcast below by The Naked Scientists is well worth a listen. A researcher from Plymouth University discusses ocean volcanoes and biodiversity, and also considers how these volcanoes can be used to predict changes to ocean life in the face of climate change.
“How do Volcanoes affect Ocean Biodiversity” The Naked Scientists with Jason Hall Spencer from Plymouth University, 17th April 2012: