On a glassed landmass, how long would it take for plants to grow?

Question

My story takes place 60 years after a roughly 250 mile diameter area of a landmass was glassed. Cities were melted, and all living things were incinerated in the blast, down to roughly 20 feet below the surface of the soil, and all rivers in the area were vaporized and underwent the same melting as the rest of the soil. The area was then twisted to resemble spikes, think similar looking to ferrofluid, then flash frozen to hold the shape. (all of this was done using programmed magic. the magic isn't relevant to the question except to explain how this happened and to say that there is no solution to biosphere collapse using this magic) This volcanic rock wouldn't have nearly as many nutrients as volcanic rock in the real world, since it's just melted topsoil and bedrock. Granted, it would have an incredibly high iron content in the areas that were once cities, and would have the nutrients from the ash of the creatures and people that once lived there.

The climate was a mix of grasslands and savanna before the glassing, though there would be a lot more flooding given that the water isn't absorbed by the volcanic rock. Volcanoes don't exist on the planet, since it is completely artificially made and isn't tectonically active, with the magnetosphere artificially created and maintained, so there wouldn't be any environmental precedent for something like this, i.e. no plants are adapted to grow in this sort of situation.

Given all of this, in the best possible circumstances, how much could the biosphere have recovered in the 60 years which followed?

Answer 1

There are two things here:

• The glass itself is going to be extremely rich in a number of elements that don't usually occur at high levels in volcanic rocks, it's also likely to be highly porous. This is because soil, and continental rock for that matter, contains a lot of Carbon and light(er) reactive elements when compared to something like basalt. Much of the glass field may resemble carbonatites in terms of reactivity and dissolve quite readily under normal rainfall. The relatively very high level of aluminium in the melt will also be particularly telling, as will industrial metals like copper and zinc from the destroyed cities. The high level of volitiles incorporated in the melt is going to mean the glass is also full of air pockets making it physically fragile as well.

• There is also an edge, that is going to be subject to erosion. Where the topography outside the edge is higher than the glass zone water and soil are going to run onto/across the glass surface. This directly erodes the surface of the material and also allows plant growth to start. Many pioneer species are nitrogen fixers that produce strong acids at their roots (to the point of lowering soil pH to 2 or less during periods of soil saturation) that will accelerate glass degradation. Where the glass is higher than the unaffected land water will run off and erode the land beyond the edge undercutting the glass slab, glass has poor tensile strength so chunks are going to break off quite quickly once unsupported.

Between these factors the glassed zone will be relatively fragile and erosion along the edges will be quite rapid. Now 60 years is not terribly long on the normal scale of geological processes but depending on the exact chemistry of a given patch of glass it could already be gone after the first decent downpour.

End result; I'd expect the zone to be very patchy after 60 years and several miles to several tens of miles smaller in total radius as the edges get broken up by vegetation, water, and soil motion.

I had been thinking about a mild climate setting, until @AcePL made a good point, if this happens in an area that experiences deep ground frosts then between frost heave and frost wedging porous glassy material is going to fairly disintegrate over a few cycles. Even in climates that don't get frosts but do get a lot of strong sunlight during the day the thermal stress weathering, particularly thermo-mechanic fatigue, could do a lot of damage. After a decade or so you'd have to dig up relatively solid glass nuggets to know what had happened, those more solid pockets of glass will exist but they're unlikely to be particularly large.

Answer 2

Speaking form a purely biological perspective, the answer is "as soon as it's cool enough not to kill anything organic that touches it". In fact, it will start growing basic life such as bacteria the first time that it rains, and everything afterwards will follow.

Bacteria, mold and algae - along with the nutrients that they need - will arrive in the first rain that falls, and will start to form on the surface within days of that, especially in the pools and gullies between the spires\spikes. The surface will start to look dulled and grubby as organisms begin to expand into a niche with no natural competition. They will feed on the nutrients carried in by the rain, and will create a bio-film on which more complicated organisms can live. Which in turn will start to attract animals, that will carry yet more complex organisms with them, including seeds in their droppings.

As the other answers said, dust and debris will be blown in by the wind and will accumulate in nooks and crannies, and hollows, insects will lay their eggs in shaded pools and animals that feed off of them will come, brining vegetation with them in the form of seeds on their coasts\feathers or in their droppings.

Unless the region has a particularly harsh environment you will see substantial greening the following spring.

So, it would go from glass to sparse grassland in the space of one growing season.

Answer 3

Since it's only a limited area to be glassed, all the glass will be accumulating dust and debris carried by weather from all around it.

This means that it won't take long for lichens to start growing, followed by grass, shrubs and small plants the more dust and debris will accumulate. Once vegetation is there, also animal can follow.

At the same time the more exposed part will be sanded by wind carried particles.

My estimate is that in 60 years you might even start to have trees and not notice much differences with the unglassed surrounding regions.

Answer 4

There is an actual close equivalent of this that occurred after the May 18, 1980 explosion of Mount Saint Helens, when large areas of forest were essentially cooked at high temperature (and all trees were physically knocked down by the force of the blast), and all visible life was killed. The entire area became a grey, sterile wasteland.

Several studies have been done of the recovery of nature after this event: you might find it instructive to track down some of these records.

Notably, some plants were beginning to grow again within a year or two after the event (apparently a few seeds survived, perhaps because they were buried under ash and insulated by it from the high temperatures, or perhaps because visiting birds pooped them out), and creatures such as deer, mice, etc. were starting to venture into the area soon after. Within a decade or two, large amounts of the forest have mostly recovered. (Obviously there are still a lot of fallen, dead trees.)

Answer 5

Comparisons:

Look at the speed that wide spread volcanic flows get green again. You want to compare to shield volcanoes where the lava is fairly runny.

Western washington and southern Idaho experieced MASSIVE lava floods -- some 2500 feet of basalt over the course of about 20,000 years. It was episodic. But look at erosion in Washingtion you can see layers 50 feet thick.

Rock and glass are both weak in tension on a large scale. Unless prevented by ongoing magic, the glass will crack with changes in temperature. These cracks allow water, dust to collect. I would expect to see most of it being at least sparsely green (like a desert) within 100 years. I'd expect the edge to start showing green in a very few years.

Answer 6

Expanding from a comment:

The Glass-land would prevent water circulation, since, even when cracked, glass is watertight.

Within months the glassed lands would be filled with ponds, puddles and marshes made of rainwater, and any river that intersected with the glassed area would either spread onto it, or be dammed by it, forming some extra marshland.

You basically created a shallow, cracked aquarium.

Waterborne life would psread quickly: algae, mosquito larvae, then small plants etc. In 60 years, it would look like a mangrove forest or swampland, with odd bits of glass occasionally visible here and there.

If anything, it will become a richer environment than the savanna around it.