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There's an important aspect of my headworld involving volcanoes which I planned many years ago. Recently I revisited this concept to refine it further, only to run into a few questions that I've been struggling with. My geology knowledge is quite limited and I can't find much information on these matters online.

Basically, I have a creature species that has adapted to living in colonies settled inside craters of massive extinct volcanoes. The rough concept was that, although the environment around these volcanoes is extremely harsh with low temperatures and constant, powerful wind currents, the volcanoes still emanate enough heat to provide a good settlement for this species. The heat consistently melts down the accumulating snow at the top of the crater walls, then the water streams down and pools up inside the crater. These pools make for the colony's water source, and there are fissures/openings in the rock that allow for the water to stream out too. In some cases this even forms waterfalls outside.

I was wondering, is it plausible for completely extinct volcanoes to still emit heat in such ways? Some time ago I read about an extinct volcano that still has magma simmering in its chamber(link), while its own structure prevents an eruption from happening again. However, I'm not very knowledgeable on the details of these cases and couldn't find much information on how common that is.

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Volcanoes become extinct when their magmatic chamber is no longer supplied with new magma from the mantle.

But like when you turn off the fire under a pan of boiling water its content stops boiling but stays hot for a while, so does the magmatic chamber. The heat from the molten lava will slowly diffuse outward, until, over geological time, the lava will solidify.

Meanwhile people living above the chamber might enjoy thermal baths and other related secondary volcanic activities.

An example of this is Larderello in Italy.

The region of Lardarello has experienced occasional phreatic eruptions, caused by explosive outbursts of steam trapped below the surface. The water is contained in metamorphic rocks where it is turned to steam which is then trapped beneath a dome of impermeable shales and clay. The steam escapes through faults in the dome and forces its way out in the hot springs. It possesses a dozen explosion craters 30–250 m in diameter. The largest is the Lago Vecchienna crater which last erupted around 1282, now filled by the Boracifero Lake.

Larderello now produces 10% of the world's entire supply of geothermal electricity, amounting to 4,800 GWh per year and powering about a million Italian households. Its geology makes it uniquely conducive to geothermal power production, with hot granite rocks lying unusually close to the surface, producing steam as hot as 202 °C

In 1911, the world's first geothermal power plant was built in the Valle del Diavolo ("Devil's Valley"), named for the boiling water that rises there. It was the world's only industrial producer of geothermal electricity until 1958

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Yes, there are many “extinct”, or more precisely, dormant volcanos that still emit heat that drives hydrothermal activity.

Perhaps the best known example is Yellowstone. It has not erupted in a while and it’s not going to erupt in a while. However, the pools in the Yellowstone area support unique ecosystems of microorganisms and larger animals.

Hakone in Japan is another example. It is relatively dormant, compared to the neighbouring Mount Fuji. However, it is still thermally active and this activity supports, again, a unique ecosystem.

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    $\begingroup$ Your examples are not extinct volcanoes, but merely dormant ones. There is a big difference. $\endgroup$ – Arkenstein XII Sep 25 '19 at 3:49
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    $\begingroup$ @Gimelist The definition of dormant volcano is one that's erupted within the last Ice Age, making it 10,000 years old at best. Source: worldatlas.com/articles/… $\endgroup$ – Halfthawed Sep 25 '19 at 4:00
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    $\begingroup$ @LilianSilva to give you a short answer, a volcano that has not erupted in million of years is extremely unlikely to be thermally active. $\endgroup$ – Gimelist Sep 25 '19 at 4:09
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    $\begingroup$ @LilianSilva If your species is somehow limited to a single volcano, yes. However, there have always been and always will be dormant volcanoes. Assuming they can move between them, there's no problem. $\endgroup$ – Arkenstein XII Sep 25 '19 at 4:09
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    $\begingroup$ Consider Iceland. There's usually a recently active volcano or two somewhere around, $\endgroup$ – jamesqf Sep 25 '19 at 4:17

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