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Imagine a couple of people are at the side of a huge volcano, halfway to the summit, when it erupts. There's an opening to the Chambers right beside them.

Fire belched from its riven summit. The skies burst into thunder seared with lightning. Down like lashing whips fell a torrent of black rain.

All about it the earth gaped, and from deep rifts and pits smoke and fumes leaped up. Behind them the Mountain was convulsed. Great rents opened in its side. Slow rivers of fire came down the long slopes towards them. Soon they would be engulfed. A rain of hot ash was falling.

Given the description, does it necessarily mean deadly inescapable pyroclastic flow follows?

Can they survive the initial outburst, and stay alive until maybe hours later til rescue comes?


In case it's not obvious, I'm describing the situation J.R.R.Tolkien's protagonists were in. I want to know if it's still possible for Frodo and Sam to survive a real eruption.

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It's always hard to interpret the intentions of an author. But to me, "a rain of hot ash" does not sound like a pyroclastic flow, but rather like a tephra fall, which is a different volcanic hazard. "Slow rivers of fire" seems more obvious and probably refers to lava flows. "Smoke and fumes" can be interpreted as volcanic gas. So this eruption seems to present at least three of the main volcanic hazards. For a full list of volcanic hazards, see for instance this USGS poster (public domain):

enter image description here

Compared to other volcanic hazards, tephra falls, lava flows and volcanic gases rarely kill. See for instance Volcanic disasters and incidents: A new database (Witham, 2005). There is a compilation of 278,341 volcano-related deaths from the year 1600, sorted by volcanic hazards (Table 15). Here is an excerpt:

Hazard Deaths %
Lava 1564 0.56
Tephra/ballistic 13 981 5.02
Gases and acid rains 2018 0.73

Lava flows rarely kills because they are slow. There are some cases of fast lava, which have been deadly, like the 1977 eruption of Mount Nyiragongo. But Tolkien said the rivers of fire were "slow", so we can rule out this hazard as potentially lethal for the protagonists.

Tephra falls mostly kill by roof collapse: when a thick layer of tephra accumulate on a roof, it will eventually collapse, killing the people inside. This is what killed most victims during the 1991 eruption of Mount Pinatubo. So, as long as the protagonists stay outside, they should also be safe from this hazard.

Volcanic gases rarely kill. Most of the deaths listed in this database are the 1746 victims of the Lake Nyos disaster. Other than this exceptional event, you'd have to stay very close to the gas source to get asphyxiated.

So, what are the hazards that do kill lots of people? Here is the top 4:

Hazard Deaths %
Disease, starvation etc 97 330 34.97
Pyroclastic flows/debris avalanches 63 877 22.95
Tsunami 44 610 16.03
Lahar/jokulhlaups 39 042 14.03

Let's skip the first one, as it is considered as an indirect hazard and needs time to be "efficient". That leaves three hazards that could kill the protagonists: pyroclastic flows, tsunamis and lahars. In the passage you quoted, nothing evokes the first two. The "torrent of black rain", on the other hand, could very well trigger a lahar. Lahars tends to be confined to valleys (as shown on the USGS diagram), so the protagonists would be at risk of dying if they were running in a valley.

Pyroclastic flows do not necessarily occur; they occur only if part of the ash plume collapses. But even in that case, it does not have a 360° impact. For instance, this map shows the area impacted by the pyroclastic flow (black outline) that killed ~28,000 people during the 1902 eruption of Mount Pelee (Alfred Lacroix, public domain):

enter image description here

The impacted area covers only ~50° to the SW of the volcano. If the protagonists were anywhere outside this area, they would have been perfectly safe. People in towns outside this outline, like Le Morne-Rouge, actually survived (only to be killed later that year during subsequent volcanic activity, but that's another story).

In summary, even if a "deadly inescapable pyroclastic flow" follows (which is not granted given the description), the protagonists would have a chance to survive if they were on the "good" side of the volcano!

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    $\begingroup$ What a great answer and neat database! $\endgroup$ Commented Oct 8, 2022 at 16:26
  • $\begingroup$ Does it means pyroclastic flow doesn't necessarily occur (or is huge enough to devour everything around) during an eruption? Even in one that shoots "fiery ruin" that kills nine huge birds (the flying steeds of the Nazgûl) in the sky (rushing towards the mountain though)? $\endgroup$
    – Eugene
    Commented Oct 9, 2022 at 2:02
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    $\begingroup$ As a side remark: if I recall well, the volcano has a lava lake. Lava lakes occur only at basaltic shield volcanoes, while pyroclastic flows generally occur at stratovolcanoes. $\endgroup$ Commented Oct 10, 2022 at 13:39
  • $\begingroup$ I agree with answer, but for an explosive eruption, as occurred at Mount St Helens in 1980, no-one would have a chance of surviving such "eruptions" if they were on such a volcano when it "erupts". $\endgroup$
    – Fred
    Commented Oct 10, 2022 at 17:34
  • $\begingroup$ Many thanks! I'm still worried about this "long cave or tunnel that bored into the Mountain's smoking cone". I imagine most of the power got released through the summit, and the tunnel didn't explode behind the Hobbits. $\endgroup$
    – Eugene
    Commented Oct 11, 2022 at 2:33

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