I have an idea for a region of the world I am working on, and I'm not sure how realistic it is.

Basically, the area is an equatorial jungle, closely bordering the ocean on one side. As a result there is a lot of heat, and frequent rainfall from ocean winds bringing tropical storms. However, in semi-recent history (say 1000 years) the area has become an active volcanic area, resulting in several small volcanoes (mix of both strato and shield) and semi-regular eruptions, earthquakes and steam vents in the jungle.

Obvious effects of this would be that:

  • The lava from such eruptions would be highly likely to start forest fires and kill off local animals
  • The volcanic ash would limit sunlight in the area and create a pseudo-winter after major eruptions
  • Most sources of groundwater would be high mineral content and toxic to conventional life
  • But the rich volcanic soil left afterwards should promote rapid regrowth of plant life

Assuming these volcanoes don't kill off the entire area of jungle, the idea is that after the eruption and after the lava solidifies, the jungle vegetation quickly expands back over the new land to reclaim it, covering most of the active volcano in the process. The result of this process repeated over and over is a very rocky and hilly area, appearing much like Karst landscapes, with complex underground structures formed from cooled lava tubes, earthquake crevices and petrified trees creating pockets underground of stone forests and rivers. It also promotes the evolution of fast-growing and resilient plants with a high heat and sulfur tolerance, but which cannot spread to cooler and less mineral-rich areas.

Basically, my main questions with this scenario is How long after an eruption would vegetation be able to reclaim the area? How long would it take for soil to cover the cooled lava flows enough to support trees? This would help me determine how often the eruptions happen.

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    $\begingroup$ Welcome to worldbuilding. First of all, we answer 1 question per post, and here you have 3. Secondly, have you done any research on your own? On our planet we don't have volcanoes only at the poles. More info about our standards in the help center $\endgroup$ – L.Dutch - Reinstate Monica May 4 at 4:35
  • $\begingroup$ Can you provide more detail? How many volcanoes, how large is the region, how frequent are eruptions, etc? Earth has numerous tropical jungles and volcanoes, so what is it about this scenario that wouldn't be plausible? $\endgroup$ – rek May 4 at 5:04
  • $\begingroup$ This article about Mount Saint Helens, 35 years after the eruptions might give you some of the answers you are looking for. $\endgroup$ – Henry Taylor May 4 at 5:16
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    $\begingroup$ Kīlauea? $\endgroup$ – Adrian Colomitchi May 4 at 5:45
  • $\begingroup$ Thanks for your suggestions, it seems there's not a specific answer, only that it depends on a lot of factors. I'm just going to post what I've found as an answer to close the question. $\endgroup$ – Kyrrith May 4 at 6:11

Sorry for self answering, I'm still pretty new to this. I've done some more research on the matter, checked out the links given in the comments, and from what I've found, the answer varies given just about every factor there is, and nobody has a specific time-frame, so I'm just going to close it here with what I've found. (Although if anyone has any better answer, feel free to jump in)

Some sources say that certain types of underground-based vegetation can survive even under stone layers, and eventually erode and grow through thin enough stone back to the surface. Others say that within as little as 1-3 years some plants can be seen in the calderas of previous eruptions. This seems similar to the 'secondary succession' of areas after extensive fires, and applies mostly to burned and ash-covered areas.

However, on the other hand, many sources say that even after 50+ years, there is just barely small clumps of plants and patchy trees in these areas, a far cry from the surrounding environment, and yet others say that even 100+ years later it is still largely barren. The main reason it isn't the same as normal secondary succession is because the affected area is stone, not soil, which means the development of soil has to begin anew.

The amount of soil present depends on erosion of the volcanic rock, the quantity and composition of the volcanic ash, the climate, and presence of other plants/animals in the area, but generally seems to take hundreds of years per cm of soil. It seems that there's no set number I can find for the specific time taken to develop soil on a volcanic island, although volcanic rock is much more prone to erosion than most. This development of soil seems to be aided by algae, lichen and mosses growing on the porous stone, assisting the erosion and decomposing, creating the foundation for other plants such as ferns and shrubs, and eventually even larger plants.

Given this is a tropical and populated area, I'd like to put it at the lower end of the range, but that's still a long time from what I can find. So I'm going to say that realistically, it would take at least 200 years for a decent spread of small plants to form on the volcanic rock with 1 inch of topsoil, and maybe 2000 years for even a thin forest to form (which from what I can tell needs at least 2 feet of soil), let alone a thick jungle.

(Which means that while the idea that I had in mind for this biome is technically possible, it'd have to happen on a time-frame a lot longer than I was expecting, more like 50,000 years, and the eruptions wouldn't occur more than once in a millennium to allow time for soil formation in between.)

Main Source: https://www.atlasobscura.com/articles/how-do-forests-recover-from-lava

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  • $\begingroup$ A lot is going to depend on the type of eruption. An explosive eruption - Mt. St. Helens, for instance - leaves mostly fine particulates. Given ample water, these can be re-vegetated in a few years. Flows of liquid lava, OTOH, require breakdown of the solid rock into soil. But you will get pockets of vegetation where dust &c collects in depressions. Craters of the Moon National Monument is a fairly good example (though located in a low rainfall area). $\endgroup$ – jamesqf May 5 at 18:08

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