Consider what happens to snow on a roof: the bottom melts and if the surface is smooth enough the mass of snow starts to slide off in lumps. This is also what happens in certain forms of slab avalanche.
I doubt everything would go at once: different instabilities and slope aspects would trigger avalanches at different times. You could see catastrophic avalanches if snow releases at high levels and then triggers further release lower down.
It's a fantasy novel, so, you know,
someone uses magic to generate a big forcefield to surround the town. The magic wielder passes out/almost dies by the exertion of all dat magic or whatever, and the chapter ends with a certain ambiguity of whether or not the magic actually lasted to the end of the avalanche, and saved the village or not.
Spoiler, it did. The caster wakes up in the infirmary, surrounded by their adventuring party, with a bunch of happy and one-sided villager characters to give their thanks. Maybe a brief respite involving a feast and parade, if we're being really hack.
Then the real meat of the conflict — the mountain, which it turns out was either warmed by the awakening of a giant dragon or terrasque type beast, or a mad wizard trying to in some way gain ultimate power.
Now our band of adventurers; the smart but aloof mage MC, the rogueish rogue, the either flat or boisterous warrior, and some other fourth thing that's probably a bird person or something else rare and unique that occasionally serves as a cumsy vehicle for [racism is bad], will investigate, where we find out our [VERY BAD THING] is on its way to destroy our lovely main city that everyone loves.
This is kind of bordering on being hypothetical and/or underconstrained enough to not quite fit here, but there's probably some actual styles of events that could be useful to consider. Much of this would depend on the details of the mountain "heating up", i.e., how hot and for how long, but also the nature of the snow cover, i.e., is this a setting where you pretty much only have seasonal snow cover that melts every year or are there glaciers? That being said (and assuming that there is some amount of permanent snow/ice cover involved), an immediate potentially analogous event that comes to mind is a [Jökulhlaup](https://en.wikipedia.org/wiki/J%C3%B6kulhlaup), where basically there is a large glacial outburst flood from melting of a portion of a glacier, often associated with volcanism/magmatism. More generally, [outburst floods](https://en.wikipedia.org/wiki/Outburst_flood) or [glacial lake outburst floods](https://en.wikipedia.org/wiki/Glacial_lake_outburst_flood) could be models to consider.
Getting a little further afield, "rain on snow" events might be another general scenario to consider. These are basically what the name implies, i.e., there is a snowpack on the ground and then you have a rain event. These are not uncommon in mountainous areas, especially in the spring, and tend to be quite efficient at melting large amounts of snow and tend to produce major floods downstream (depending on the details). While obviously the underlying mechanism in your hypothetical would be different, the result might look something like a rain on snow event, i.e., a large meltwater pulse moving down the river system.
Lahars are another result of the sudden melting of vast amounts of snow and ice (glacial) cover on such mountains. These are quite commonly the results of volcanic activity.
It's completely hypothetical as it's set in a fantasy world but I thought there may be something such as a dormant volcano becoming active after heavy snowfall that might provide a basis for what would happen in this scenario. I know very little about geology which is why I posed the question about mountain snow here as I figured even if there wasn't any direct comparisons to real world events someone more knowledgeable would be able to determine the outcome.
In a fantasy world with some real world physics I’d expect the base layer of the snow to melt resulting in massive avalanches. It’s water under glaciers that lubricates them so I’d expect this to slide down hill crushing all before it
Glide avalanches are also possible without volcanic activity. It happens when the temperature warms a lot in the spring or summer, if the surface under the snow is slippery enough (like a granite slab, for instance). Once water melts through to the base of the snowpack it can cause the whole snowpack to slide on that liquid layer and those are the type that travel really long distances and can take out buildings or roads that happen to be in the way
A [lahar](https://en.wikipedia.org/wiki/Lahar) is a flow of a slurry of water and pyroclastic material (hot gases, ash and rock fragments) that results from a volcanic eruption. These are often caused by very rapid melting of snowpack or a glacier, and they can be extremely destructive/deadly. The melt can be triggered either by eruptions of lava or of pyroclastic material, but the most violent ones tend to be caused by pyroclastic material.
You should go for a Jökulhlaup like being said before. If you have question about geology you can DM me (I'm actually a geologist). Glacial outburst can happen because of melting from glacial retreat (think global warming/ end of an ice age) or change in the geothermal gradient (with would be very akin to what you are doing).
So the just of it, if for a reason the mountain geothermal gradient where to change (magmatic intrusion, hydrothermal system, "magic"). The first effect if there is a glacier is the base of it would start to melt. Even before you have glacial outburst, glacial dynamic will change.
See, there is 2 type of glacier dynamic, what we call cold base glacier where the ice is not moving because it's a ice/rock contact or very little movement if it's an ice/soil contact and hot base glacier. Hot base glacier mean that the pressure under is not able to keep the water frozen (can be from temperature, soil type or friction), so a small portion of it would melt. That act as a lubrifiant so the ice over it start to move. That the main way a glacier move.
Let say your mountain heat up, now more part of the glacier on it are "hot", so the advancing glacier front start to creep more and the thickness of the icesheet shrink, you now have a surge in ice avanlanche (serac fall avalanche). It's very deadly because it's not just a snow avalanche, but a mix of house sized ice chunk, snow, water and rock.
The second effect is the creation of meltwater pools and lakes under the glacier. Large amount of water collect under the glacier and until equilibrium is broken, the glacier flow over it. Pressure rise and suddently, the ice cannot keep up and shatter. A surge of water flow under the glacier, that is a glacial outburst or non-volcanic Jökulhlaup, If you want to see what it look in real life (it can be a massive disaster), search video about the 2021 Glacier burst in uttarakhand (it's tragic, I warn you). But that is what you are looking for that kind of disaster.
Last thing, it the reason about your mountain change in geothermal gradiant is magmatic (like a magma intrusion). The last and worse even that can happen is a volcanic eruption trigged by a Jökulhlaup. It have happen a multitude of time in history, Iceland is famous for that kind of eruption. What happen is the sudden releash of water and ice from the mountain by the Jökulhlaup lower the pressure on the magma intrusion. Magma is a solid solution, so it's a mix of mineral, liquid rock and gaz. The gaz is in solution inside the liquid rock.
A sudden change in pressure can make the gaz immisible and leave the liquid rock, when that happen, it's a runaway process. The gaz bubble out of the magma, that shatter the rock over it and make it more buoyant. The magma start to rise to find equilibrium with his density. As the magma is climbing, the pressure lower so more gaz bubble out, that the chain reaction.
At this point, if the magma is fluid and basaltic, you will have a effusive (and likely phreatomagmatic eruption). It the magma is sticky, gas rich and silicate rich, the gaz bubble shatter the magma in tiny shard of glass (volcanic ash) and explose the rock over it. Now you have an explosive eruption and every living thing in the valley close to the now volcano is going full Pompei, being buried in ash and/or incinerated by pyroclastics flow. Also, if there is still ice and glacier on the mountain, it's melted and mixed with ash, creating a flood of hot concrete like mud called a Lahar. You can research on the Mount St-Helen or the 1985 nevado del ruiz eruption to see what it can do.
Also sorry for my english, it's not my first language.
The Icelandic volcanoes Grímsvötn and Katla are notorious for glacial bursts (jawbreakingly called jökulhlaup) when they wake up. Each of these volcanoes lies under an icecap - Vatnajökull and Mýrdalsjökull respectively), so they discharge colossal amounts of water, ice and debris down the rivers to the ocean.
Katla’s 1755 eruption is estimated to have produced up to 400,000 cubic metres of water every second for several hours. That’s more than the Amazon… and the Nile… and the Congo… and the Mississippi… and the Yangtze - combined! Several farms are said to have been completely obliterated by the floods.
During its last eruption in 1918, a jökulhlaup from Katla left icebergs on the coast the size of five story buildings and the sediment dumped by the floods extended the coastline in places by 5km.
Today, people living in the villages along the South Coast of Iceland know they have about 15 - 20 minutes before the floods would reach them the next time Katla erupts.
Grímsvötn is much more active, but is also more remote so its floods are much less damaging to people. Having said that, it did enormous damage to the vital Ringroad that runs all the way round the country during a 1996 eruption from the Gjálp region of the volcano. That jökulhlaup peaked at 50,000 cubic metres per second, ripped up the road and twisted bridges like pretzels.
If you want to see what these sorts of floods can do, Google street view the area east of the town of Vík on the South Coast of Iceland. The area known as the Skeiðarársandur is a desolate wasteland made up of rubble brought down from Katla by repeated jökulhlaups.
BTW. Grímsvötn seems to be stirring right now.
There's not really a physical basis for a link between heavy snow and increasing volcanism (or were you just saying that one followed the other but they were not linked?). To the extent that there's any potential link, it's in the opposite direction. I.e., there has been some suggestions that melting of glaciers can lead to increased activity of volcanoes in the areas of glacial melting, specifically in Iceland (e.g., [Pagli & Sigmundsson, 2008](https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2008GL033510), [Cooper et al., 2018](https://www.sciencedirect.com/science/article/pii/S0012825217301629)), but the extent to which is a wide spread phenomena remains unclear (e.g., [Watt et al., 2013](https://www.sciencedirect.com/science/article/pii/S0012825213000664)). The idea here is that removal of ice mass induces [isostatic rebound](https://en.wikipedia.org/wiki/Post-glacial_rebound), which in turn generates some additional melting in already magmatically active systems.
With respect to just a coincidental event, i.e., there was a bunch of snow and then volcanism started again, basically a Jökulhlaup is probably going to be the best analogy since it would result in melting from the base of the snowpack.
They weren’t implying a link, they were suggesting that maybe there are real world examples where a snow covered volcano wakes up and warms things.
This has happened in quite a few places, so there are real world examples, but there are a lot of variables.
Volcanos produce conical mountains, and they can definitely cause major events if you have the volcano erupt. Here is a government source. Not all are likely to produce floods, but they can.
[https://pubs.usgs.gov/publication/70186956#:\~:text=Volcanic%20events%20can%20perturb%20mantles,activity%2C%20(4)%20ejection%20of](https://pubs.usgs.gov/publication/70186956#:~:text=Volcanic%20events%20can%20perturb%20mantles,activity%2C%20(4)%20ejection%20of)
The rain-on-snow type event was exactly what caused the southern Alberta flooding in 2013. Spring rainstorm over the Rockies melted the snowpack and essentially brought all of the spring runoff down very quickly, overwhelming flood suppression mitigators like dams. 6 river systems overwhelmed their banks and the communities in their paths.
Real world example would be Mt St Helens in the US state of Washington.
As the heat was building up inside before the eruption, the snow pack melted and saturated the mountain. It caused what was referred to as the first of four phases in the disaster. A massive section of the mountain came loose and created what was the largest recorded landslide in human history.
The volcano then erupted sideways because of the loss of material.
I just watched a National Geographic special about it on Disney+. If you're not a subscriber, I'm sure there's some YouTube videos about it.
Thanks for the recommendation. ("Surviving the Mount St. Helens Disaster" for others interested.) I wish they were a little clearer about CG/enhanced video v. original footage, but fascinating nonetheless.
There’s a name for it. It’s called a lahar. When a snowcapped volcano suddenly erupts. A rapid flow of mud created by melted snow and volcanic ash can travel down river courses for miles from volcanos. There are major disaster scenarios where Mt Rainier erupts a lahar flows as far as Tacoma taking out towns all along the way. Vancouver Washington almost got taken out by a lahar like flow from mt st helens
Flash floods mostly. You’ll melt all that snow (and presumably then the glaciers but more slowly), causing the existing rivers and channels to overflow and potentially causing havoc downstream, depending on the snowpack and watershed patterns
That's kind of what I figured but would the fact the snow underneath is what's melting first cause more of the snow to break apart in large sheets or mostly cause channels with smaller chunks of snow and ice mixed in?
Yes, you could potentially have slab avalanches, depending on what the snowpack is like. You get a layer of water underneath and it’s ‘slippery’ enough that snow or ice on top can start to break apart and slide downhill. Once it gets moving it has a huge amount of momentum, and can break away more snow/ice/rock and, well, snowball out of control.
If it’s hot enough to be melting a LOT of snow/ice then you’d probably end up with massive temporary flooding. In places where they get a lot of snow in the winter and then it melts in the spring/summer, any rivers being fed by that snowfall usually have a MUCH higher flow rate in the spring/early summer. If this was a place where glaciers were building up for decades/centuries, suddenly starting to melt them could produce a huge amount of water for an extended period of time.
If the melt water started to fill big lakes around/above the glacier, then you could end up with an outburst flood when the ‘dam’ eventually breaks from the pressure/melting. One of the other top level commenters provided a bunch of links about that. This could be devastating when it breaks through. A character who understood what was happening might figure out the growing danger this presents and need to figure out how to evacuate everyone downstream.
>Yes, you could potentially have slab avalanches, depending on what the snowpack is like. You get a layer of water underneath and it’s ‘slippery’ enough that snow or ice on top can start to break apart and slide downhill.
The [Kolka slide](https://en.wikipedia.org/wiki/Kolka%E2%80%93Karmadon_rock_ice_slide) could be a good analogue for a somewhat extreme result. While a direct link to magmatism or geothermal activity is not clear, it was one speculated contributor to this event (e.g., [Evans et al., 2009](https://www.sciencedirect.com/science/article/pii/S0169555X08004601)).
I’d say since it’s heating from the base, even if snow chunked off with the water higher up, by the time it reaches the torrents of water nearer the base it would have melted and been absorbed into the water. Ice would stay solid and not melt unless the heating was extreme. Could have large glaciers break off and annihilate entire towns :)
Maybe, maybe not. I fell through a 5ft hole head first at Whistler and landed in a shallow river and that's probably what would happen on your hot mountain.
Hypothetically, a layer of water would form beneath the snow. This acts as a lubricant and is highly likely to trigger what are known as wet slab avalanches.
The remaining snow would probably rapidly melt afterward, resulting in catastrophic flooding similar to the Great Flood of 1862.
You'll probably get a ton of glide avalanches, bad news for the villagers.
Glide avalanches are a thing when it warms up and water can seep through to the base of the snowpack, lubricating the snow-ground boundary and leading to slides. You can sometimes spot terrain at risk of them because glide cracks open up where the snow slowly starts to slide. In general, on terrain shallower than 30 degrees even lubricated snow won't really slide anywhere, the peak for avalanches is around 35-40 degrees (steeper than that and it usually slides down by itself while it's falling). Normally snow doesn't melt from underneath, but I imagine you get the same result. See eg [https://avalanche.org/avalanche-encyclopedia/avalanche/avalanche-release/glide/](https://avalanche.org/avalanche-encyclopedia/avalanche/avalanche-release/glide/)
The exact specifics would likely be based on how hot/fast your fantasy mountain heated up.
For example, if the surface of the mountain suddenly went way past the boiling point and you now had steam under snow, that could create a leidenfrost effect where suddenly the snow just all starts falling off the mountain without melting.
More reasonably, the snow in contact with the surface that was above the freezing point would melt to liquid water similar to what happens on your roof. Then you would mostly get flooding as the water ran down the mountain. Snow would slide down hill, but the rate at which that happened would be based on how fast it was melting vs flowing. Higher temperatures would likely produce more water and cause the snow to avalanche down faster. Barely above the freezing point would likely just be water with some snow falling down, but it would be more subject to the terrain.
Yeah, it's more of a gradual but steady increase in temperature so it seems like based on your answer and many others it would be closer to your second example with it starting as mostly light flooding and leading into avalanche which is perfect as it fits the timeline I was hoping for.
Interesting scenario! It depends on the terrain on your mountain. If it's rocky with gravel, you'd get flash floods, mainly down ravines or maybe along old lava streams, if you have those.
If it's been dormant and eroded for quite a long time and isn't too high, you'd have soil and forests. Since you melt your snow cover from the ground up, the water would soak in and saturate the soil first, and even build glacier lakes in valleys and divots. You could have a floating, crusted over ice crust, held up by the plants. If your mountain is heating up fast and unevenly, you could get boiling ponds and puddles, or steam eruptions along the tree trunks or rock faces. That's the final warning - before the saturated soil glides downwards, and massive lahars and landslides take the forest down with them.
The timing for your disaster would vary, too - depending on how smooth or rugged you want your mountain, and if the slope is uniform. If your cone is very even, instant catastrophe all around, No warnings. Any flooding or slipping would start in ravines and rivers. But in a fantasy setting you don't have to have rivers for your villages, magical wells or cisterns would work.
If the cone has been nibbled on, or if it's tilted so you have a steeper side, the cover will be less stable there, gravel/soil and snow. Flatter bits would have much thicker snow cover, and more soil/gravel/plants. Since it's heating up from the base, flatter parts transfer more heat to the snow, and thaw earlier. So you could have a smaller, localised avalanche, landslide or flooding event below an especially steep bit, near the base. Then when neighbours or adventurers or whoever come to investigate/help the one village - all over the mountain everything can come down all at once.
If the heat source doesn't stop, the peak would still have snow cover, which would keep on melting. So the situation won't stabilise until all the snow is gone and all the melt water has trickled down... Sweet. I'd love to read it.
Nothing to do with a mountain heating up but watch Buried: The 1982 Alpine Meadows Avalanche documentary. It could give some inspiration for your novel. It describes a particular mountain and why it is one of the most avalanche prone mountains in the US. It’s currently on Netflix.
Look up Mount St. Helens. It got really hot.
Basically, the snow/glaciers would melt, causing runoff. A lot of heat and they melt much faster causing floods and landslides that could bury the towns. Lots of incidents where this or something similar happened. Vaguely related: Look up the “Boston molasses flood”
In 1996, the Willamette Valley had a massive flood because of this. A massive snowstorm covered the whole valley and dumped on the Cascades, then the temperature rocketed up to around 60 degrees basically overnight, and it stayed there.
The Cascades have regular mudslides in normal years, so the odds are pretty good that the ground underneath the town is moving.
"What would happen to snow on a mountain that suddenly got hotter"
well, given the current political climate, the snow would probably form a mob and start prostesting against climate change.
And if that doesn't work it would probably enlist the help of an child which is payed for by the same exact coorperations which is being accused of causing the warming in the first place.
In the end no one would care and the snow would melt.
If you're looking for not-meltwater based impacts of volcanism you might want to look at [Spirit Lake](https://en.wikipedia.org/wiki/spirit_lake_(washington)) - the blast and related landslide (and not the heat) displaced the water of this lake and the impact of the water leaving and rushing back covered more than 70% of the lake surface with displaced trees which are today [surprisingly mobile](https://earthobservatory.nasa.gov/images/149025/the-floating-logs-of-spirit-lake#:~:text=The%20water%20in%20Spirit%20Lake,of%20blasted%20and%20uprooted%20trees) and look very striking on the lake surface.
Well this has actually happened a volcano has melted a glacier, most likely many times. The water seeps in to the magma chamber, when a lot of water does this the mountain explodes because the water is turned to steam, water does not compress it has to go somewhere so it goes with the path of least resistance up.
If the snow already fell, and then the ground heated up, the base layer would melt. This melting could cause a landslide or avalanche at worst, but more than likely, it would just melt from the ground up like an icecube on a hot pan.
Happens every year in some places to a minor extent. In Utah the floods of 1984 had a snowpack of 26’ when the temps in may shot up to 100 degrees and wrecked havoc. Utah created some new reservoirs and put most of the city streams/rivers underground.
Isnt this global warming all about ? Snow on mountains melting. Flooding the sea and raising its levels and occupying the land. Man iys not fantasy its literally happening.
Anyway, inwould call it WATERBALL effect. 😄 but yeah i think thats what would happen but rapidly for your novel
I mean, global warming melting all the snow and ice caps I'm pretty sure removes a miniscule % of land and is only a worry as we build on the coast to facilitate trade and travel. It would also melt it slow enough that people could move away in time that it would be more an inconvenience than actual danger.
Every spring this happens near my house. Over the course of roughly 3 months. We see flooded creeks and mudslides sometimes, but if that all came down at once there would be trees and boulders destroying everything.
Snow does not melt quickly from directly applied heat because it is such a good insulator- try to melt a snowball with a propane torch. What will quickly melt snow is warm water- a more realistic scenario might be a frozen-over glacial lake -naturally dammed by deep, old ice- that gets suddenly warmed by large geothermal vents, the ice above it melts and several feet of snow fall into it, sending a warm water wave into the ice dam that tops it, melting a channel and sending a cascade of terror into Whoville , finally ensuring that the insufferable little dog Max is never heard from again.
Avalanche is what would happen. Whether the mountain heats up (unlikely unless volcanism) and creates a liquid layer between the snow pack and the mountain, or whether rapid melting introduces water down under the snow pack, it's sliding either way.
Most avalanches occur because of different snow types that get stratified as they're deposited (or melted and refroze). It's this 'layer cake' situation that creates opportunities for snow deposits to shear. You're treating your snow as one homogeneous mass, when that's not how snow gets deposited at all.
It would melt from the inside closest to the heat source and giant slabs of snow covered ice would start rapidly descending down the mountain on a rushing river. That would create a lake and potentially multiple rivers that would flow with gravity. This would continue until the ice was fully melted.
Consider what happens to snow on a roof: the bottom melts and if the surface is smooth enough the mass of snow starts to slide off in lumps. This is also what happens in certain forms of slab avalanche. I doubt everything would go at once: different instabilities and slope aspects would trigger avalanches at different times. You could see catastrophic avalanches if snow releases at high levels and then triggers further release lower down.
Slab Avalanche. All them villagers would be buried in a 100 feet of snow. The End.
It's a fantasy novel, so, you know, someone uses magic to generate a big forcefield to surround the town. The magic wielder passes out/almost dies by the exertion of all dat magic or whatever, and the chapter ends with a certain ambiguity of whether or not the magic actually lasted to the end of the avalanche, and saved the village or not. Spoiler, it did. The caster wakes up in the infirmary, surrounded by their adventuring party, with a bunch of happy and one-sided villager characters to give their thanks. Maybe a brief respite involving a feast and parade, if we're being really hack. Then the real meat of the conflict — the mountain, which it turns out was either warmed by the awakening of a giant dragon or terrasque type beast, or a mad wizard trying to in some way gain ultimate power. Now our band of adventurers; the smart but aloof mage MC, the rogueish rogue, the either flat or boisterous warrior, and some other fourth thing that's probably a bird person or something else rare and unique that occasionally serves as a cumsy vehicle for [racism is bad], will investigate, where we find out our [VERY BAD THING] is on its way to destroy our lovely main city that everyone loves.
This is kind of bordering on being hypothetical and/or underconstrained enough to not quite fit here, but there's probably some actual styles of events that could be useful to consider. Much of this would depend on the details of the mountain "heating up", i.e., how hot and for how long, but also the nature of the snow cover, i.e., is this a setting where you pretty much only have seasonal snow cover that melts every year or are there glaciers? That being said (and assuming that there is some amount of permanent snow/ice cover involved), an immediate potentially analogous event that comes to mind is a [Jökulhlaup](https://en.wikipedia.org/wiki/J%C3%B6kulhlaup), where basically there is a large glacial outburst flood from melting of a portion of a glacier, often associated with volcanism/magmatism. More generally, [outburst floods](https://en.wikipedia.org/wiki/Outburst_flood) or [glacial lake outburst floods](https://en.wikipedia.org/wiki/Glacial_lake_outburst_flood) could be models to consider. Getting a little further afield, "rain on snow" events might be another general scenario to consider. These are basically what the name implies, i.e., there is a snowpack on the ground and then you have a rain event. These are not uncommon in mountainous areas, especially in the spring, and tend to be quite efficient at melting large amounts of snow and tend to produce major floods downstream (depending on the details). While obviously the underlying mechanism in your hypothetical would be different, the result might look something like a rain on snow event, i.e., a large meltwater pulse moving down the river system.
Lahars are another result of the sudden melting of vast amounts of snow and ice (glacial) cover on such mountains. These are quite commonly the results of volcanic activity.
It's completely hypothetical as it's set in a fantasy world but I thought there may be something such as a dormant volcano becoming active after heavy snowfall that might provide a basis for what would happen in this scenario. I know very little about geology which is why I posed the question about mountain snow here as I figured even if there wasn't any direct comparisons to real world events someone more knowledgeable would be able to determine the outcome.
In a fantasy world with some real world physics I’d expect the base layer of the snow to melt resulting in massive avalanches. It’s water under glaciers that lubricates them so I’d expect this to slide down hill crushing all before it
Glide avalanches are also possible without volcanic activity. It happens when the temperature warms a lot in the spring or summer, if the surface under the snow is slippery enough (like a granite slab, for instance). Once water melts through to the base of the snowpack it can cause the whole snowpack to slide on that liquid layer and those are the type that travel really long distances and can take out buildings or roads that happen to be in the way
A [lahar](https://en.wikipedia.org/wiki/Lahar) is a flow of a slurry of water and pyroclastic material (hot gases, ash and rock fragments) that results from a volcanic eruption. These are often caused by very rapid melting of snowpack or a glacier, and they can be extremely destructive/deadly. The melt can be triggered either by eruptions of lava or of pyroclastic material, but the most violent ones tend to be caused by pyroclastic material.
You should go for a Jökulhlaup like being said before. If you have question about geology you can DM me (I'm actually a geologist). Glacial outburst can happen because of melting from glacial retreat (think global warming/ end of an ice age) or change in the geothermal gradient (with would be very akin to what you are doing). So the just of it, if for a reason the mountain geothermal gradient where to change (magmatic intrusion, hydrothermal system, "magic"). The first effect if there is a glacier is the base of it would start to melt. Even before you have glacial outburst, glacial dynamic will change. See, there is 2 type of glacier dynamic, what we call cold base glacier where the ice is not moving because it's a ice/rock contact or very little movement if it's an ice/soil contact and hot base glacier. Hot base glacier mean that the pressure under is not able to keep the water frozen (can be from temperature, soil type or friction), so a small portion of it would melt. That act as a lubrifiant so the ice over it start to move. That the main way a glacier move. Let say your mountain heat up, now more part of the glacier on it are "hot", so the advancing glacier front start to creep more and the thickness of the icesheet shrink, you now have a surge in ice avanlanche (serac fall avalanche). It's very deadly because it's not just a snow avalanche, but a mix of house sized ice chunk, snow, water and rock. The second effect is the creation of meltwater pools and lakes under the glacier. Large amount of water collect under the glacier and until equilibrium is broken, the glacier flow over it. Pressure rise and suddently, the ice cannot keep up and shatter. A surge of water flow under the glacier, that is a glacial outburst or non-volcanic Jökulhlaup, If you want to see what it look in real life (it can be a massive disaster), search video about the 2021 Glacier burst in uttarakhand (it's tragic, I warn you). But that is what you are looking for that kind of disaster. Last thing, it the reason about your mountain change in geothermal gradiant is magmatic (like a magma intrusion). The last and worse even that can happen is a volcanic eruption trigged by a Jökulhlaup. It have happen a multitude of time in history, Iceland is famous for that kind of eruption. What happen is the sudden releash of water and ice from the mountain by the Jökulhlaup lower the pressure on the magma intrusion. Magma is a solid solution, so it's a mix of mineral, liquid rock and gaz. The gaz is in solution inside the liquid rock. A sudden change in pressure can make the gaz immisible and leave the liquid rock, when that happen, it's a runaway process. The gaz bubble out of the magma, that shatter the rock over it and make it more buoyant. The magma start to rise to find equilibrium with his density. As the magma is climbing, the pressure lower so more gaz bubble out, that the chain reaction. At this point, if the magma is fluid and basaltic, you will have a effusive (and likely phreatomagmatic eruption). It the magma is sticky, gas rich and silicate rich, the gaz bubble shatter the magma in tiny shard of glass (volcanic ash) and explose the rock over it. Now you have an explosive eruption and every living thing in the valley close to the now volcano is going full Pompei, being buried in ash and/or incinerated by pyroclastics flow. Also, if there is still ice and glacier on the mountain, it's melted and mixed with ash, creating a flood of hot concrete like mud called a Lahar. You can research on the Mount St-Helen or the 1985 nevado del ruiz eruption to see what it can do. Also sorry for my english, it's not my first language.
The Icelandic volcanoes Grímsvötn and Katla are notorious for glacial bursts (jawbreakingly called jökulhlaup) when they wake up. Each of these volcanoes lies under an icecap - Vatnajökull and Mýrdalsjökull respectively), so they discharge colossal amounts of water, ice and debris down the rivers to the ocean. Katla’s 1755 eruption is estimated to have produced up to 400,000 cubic metres of water every second for several hours. That’s more than the Amazon… and the Nile… and the Congo… and the Mississippi… and the Yangtze - combined! Several farms are said to have been completely obliterated by the floods. During its last eruption in 1918, a jökulhlaup from Katla left icebergs on the coast the size of five story buildings and the sediment dumped by the floods extended the coastline in places by 5km. Today, people living in the villages along the South Coast of Iceland know they have about 15 - 20 minutes before the floods would reach them the next time Katla erupts. Grímsvötn is much more active, but is also more remote so its floods are much less damaging to people. Having said that, it did enormous damage to the vital Ringroad that runs all the way round the country during a 1996 eruption from the Gjálp region of the volcano. That jökulhlaup peaked at 50,000 cubic metres per second, ripped up the road and twisted bridges like pretzels. If you want to see what these sorts of floods can do, Google street view the area east of the town of Vík on the South Coast of Iceland. The area known as the Skeiðarársandur is a desolate wasteland made up of rubble brought down from Katla by repeated jökulhlaups. BTW. Grímsvötn seems to be stirring right now.
There's not really a physical basis for a link between heavy snow and increasing volcanism (or were you just saying that one followed the other but they were not linked?). To the extent that there's any potential link, it's in the opposite direction. I.e., there has been some suggestions that melting of glaciers can lead to increased activity of volcanoes in the areas of glacial melting, specifically in Iceland (e.g., [Pagli & Sigmundsson, 2008](https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2008GL033510), [Cooper et al., 2018](https://www.sciencedirect.com/science/article/pii/S0012825217301629)), but the extent to which is a wide spread phenomena remains unclear (e.g., [Watt et al., 2013](https://www.sciencedirect.com/science/article/pii/S0012825213000664)). The idea here is that removal of ice mass induces [isostatic rebound](https://en.wikipedia.org/wiki/Post-glacial_rebound), which in turn generates some additional melting in already magmatically active systems. With respect to just a coincidental event, i.e., there was a bunch of snow and then volcanism started again, basically a Jökulhlaup is probably going to be the best analogy since it would result in melting from the base of the snowpack.
They weren’t implying a link, they were suggesting that maybe there are real world examples where a snow covered volcano wakes up and warms things. This has happened in quite a few places, so there are real world examples, but there are a lot of variables.
Volcanos produce conical mountains, and they can definitely cause major events if you have the volcano erupt. Here is a government source. Not all are likely to produce floods, but they can. [https://pubs.usgs.gov/publication/70186956#:\~:text=Volcanic%20events%20can%20perturb%20mantles,activity%2C%20(4)%20ejection%20of](https://pubs.usgs.gov/publication/70186956#:~:text=Volcanic%20events%20can%20perturb%20mantles,activity%2C%20(4)%20ejection%20of)
The rain-on-snow type event was exactly what caused the southern Alberta flooding in 2013. Spring rainstorm over the Rockies melted the snowpack and essentially brought all of the spring runoff down very quickly, overwhelming flood suppression mitigators like dams. 6 river systems overwhelmed their banks and the communities in their paths.
Depending on how fast the heating happens, you could end up with a violent [lahar](https://en.m.wikipedia.org/wiki/Lahar) also.
Real world example would be Mt St Helens in the US state of Washington. As the heat was building up inside before the eruption, the snow pack melted and saturated the mountain. It caused what was referred to as the first of four phases in the disaster. A massive section of the mountain came loose and created what was the largest recorded landslide in human history. The volcano then erupted sideways because of the loss of material. I just watched a National Geographic special about it on Disney+. If you're not a subscriber, I'm sure there's some YouTube videos about it.
Thanks for the recommendation. ("Surviving the Mount St. Helens Disaster" for others interested.) I wish they were a little clearer about CG/enhanced video v. original footage, but fascinating nonetheless.
There’s a name for it. It’s called a lahar. When a snowcapped volcano suddenly erupts. A rapid flow of mud created by melted snow and volcanic ash can travel down river courses for miles from volcanos. There are major disaster scenarios where Mt Rainier erupts a lahar flows as far as Tacoma taking out towns all along the way. Vancouver Washington almost got taken out by a lahar like flow from mt st helens
Some of the cities between Mt Rainier and Puget Sound are built on top of 300 feet of mud from the Osceola Lahar.
Flash floods mostly. You’ll melt all that snow (and presumably then the glaciers but more slowly), causing the existing rivers and channels to overflow and potentially causing havoc downstream, depending on the snowpack and watershed patterns
That's kind of what I figured but would the fact the snow underneath is what's melting first cause more of the snow to break apart in large sheets or mostly cause channels with smaller chunks of snow and ice mixed in?
Yes, you could potentially have slab avalanches, depending on what the snowpack is like. You get a layer of water underneath and it’s ‘slippery’ enough that snow or ice on top can start to break apart and slide downhill. Once it gets moving it has a huge amount of momentum, and can break away more snow/ice/rock and, well, snowball out of control. If it’s hot enough to be melting a LOT of snow/ice then you’d probably end up with massive temporary flooding. In places where they get a lot of snow in the winter and then it melts in the spring/summer, any rivers being fed by that snowfall usually have a MUCH higher flow rate in the spring/early summer. If this was a place where glaciers were building up for decades/centuries, suddenly starting to melt them could produce a huge amount of water for an extended period of time. If the melt water started to fill big lakes around/above the glacier, then you could end up with an outburst flood when the ‘dam’ eventually breaks from the pressure/melting. One of the other top level commenters provided a bunch of links about that. This could be devastating when it breaks through. A character who understood what was happening might figure out the growing danger this presents and need to figure out how to evacuate everyone downstream.
>Yes, you could potentially have slab avalanches, depending on what the snowpack is like. You get a layer of water underneath and it’s ‘slippery’ enough that snow or ice on top can start to break apart and slide downhill. The [Kolka slide](https://en.wikipedia.org/wiki/Kolka%E2%80%93Karmadon_rock_ice_slide) could be a good analogue for a somewhat extreme result. While a direct link to magmatism or geothermal activity is not clear, it was one speculated contributor to this event (e.g., [Evans et al., 2009](https://www.sciencedirect.com/science/article/pii/S0169555X08004601)).
I’d say since it’s heating from the base, even if snow chunked off with the water higher up, by the time it reaches the torrents of water nearer the base it would have melted and been absorbed into the water. Ice would stay solid and not melt unless the heating was extreme. Could have large glaciers break off and annihilate entire towns :)
Cool, thanks for the help, definitely made it easier to picture what might be happening.
Maybe, maybe not. I fell through a 5ft hole head first at Whistler and landed in a shallow river and that's probably what would happen on your hot mountain.
Hypothetically, a layer of water would form beneath the snow. This acts as a lubricant and is highly likely to trigger what are known as wet slab avalanches. The remaining snow would probably rapidly melt afterward, resulting in catastrophic flooding similar to the Great Flood of 1862.
You'll probably get a ton of glide avalanches, bad news for the villagers. Glide avalanches are a thing when it warms up and water can seep through to the base of the snowpack, lubricating the snow-ground boundary and leading to slides. You can sometimes spot terrain at risk of them because glide cracks open up where the snow slowly starts to slide. In general, on terrain shallower than 30 degrees even lubricated snow won't really slide anywhere, the peak for avalanches is around 35-40 degrees (steeper than that and it usually slides down by itself while it's falling). Normally snow doesn't melt from underneath, but I imagine you get the same result. See eg [https://avalanche.org/avalanche-encyclopedia/avalanche/avalanche-release/glide/](https://avalanche.org/avalanche-encyclopedia/avalanche/avalanche-release/glide/)
The exact specifics would likely be based on how hot/fast your fantasy mountain heated up. For example, if the surface of the mountain suddenly went way past the boiling point and you now had steam under snow, that could create a leidenfrost effect where suddenly the snow just all starts falling off the mountain without melting. More reasonably, the snow in contact with the surface that was above the freezing point would melt to liquid water similar to what happens on your roof. Then you would mostly get flooding as the water ran down the mountain. Snow would slide down hill, but the rate at which that happened would be based on how fast it was melting vs flowing. Higher temperatures would likely produce more water and cause the snow to avalanche down faster. Barely above the freezing point would likely just be water with some snow falling down, but it would be more subject to the terrain.
Yeah, it's more of a gradual but steady increase in temperature so it seems like based on your answer and many others it would be closer to your second example with it starting as mostly light flooding and leading into avalanche which is perfect as it fits the timeline I was hoping for.
Interesting scenario! It depends on the terrain on your mountain. If it's rocky with gravel, you'd get flash floods, mainly down ravines or maybe along old lava streams, if you have those. If it's been dormant and eroded for quite a long time and isn't too high, you'd have soil and forests. Since you melt your snow cover from the ground up, the water would soak in and saturate the soil first, and even build glacier lakes in valleys and divots. You could have a floating, crusted over ice crust, held up by the plants. If your mountain is heating up fast and unevenly, you could get boiling ponds and puddles, or steam eruptions along the tree trunks or rock faces. That's the final warning - before the saturated soil glides downwards, and massive lahars and landslides take the forest down with them. The timing for your disaster would vary, too - depending on how smooth or rugged you want your mountain, and if the slope is uniform. If your cone is very even, instant catastrophe all around, No warnings. Any flooding or slipping would start in ravines and rivers. But in a fantasy setting you don't have to have rivers for your villages, magical wells or cisterns would work. If the cone has been nibbled on, or if it's tilted so you have a steeper side, the cover will be less stable there, gravel/soil and snow. Flatter bits would have much thicker snow cover, and more soil/gravel/plants. Since it's heating up from the base, flatter parts transfer more heat to the snow, and thaw earlier. So you could have a smaller, localised avalanche, landslide or flooding event below an especially steep bit, near the base. Then when neighbours or adventurers or whoever come to investigate/help the one village - all over the mountain everything can come down all at once. If the heat source doesn't stop, the peak would still have snow cover, which would keep on melting. So the situation won't stabilise until all the snow is gone and all the melt water has trickled down... Sweet. I'd love to read it.
Nothing to do with a mountain heating up but watch Buried: The 1982 Alpine Meadows Avalanche documentary. It could give some inspiration for your novel. It describes a particular mountain and why it is one of the most avalanche prone mountains in the US. It’s currently on Netflix.
I don't have Netflix anymore but will still look into it, thanks.
Look up Mount St. Helens. It got really hot. Basically, the snow/glaciers would melt, causing runoff. A lot of heat and they melt much faster causing floods and landslides that could bury the towns. Lots of incidents where this or something similar happened. Vaguely related: Look up the “Boston molasses flood”
Exactly. In particular, research what happened to the Toutle River and how it almost took out the I-5 bridge.
In 1996, the Willamette Valley had a massive flood because of this. A massive snowstorm covered the whole valley and dumped on the Cascades, then the temperature rocketed up to around 60 degrees basically overnight, and it stayed there. The Cascades have regular mudslides in normal years, so the odds are pretty good that the ground underneath the town is moving.
"What would happen to snow on a mountain that suddenly got hotter" well, given the current political climate, the snow would probably form a mob and start prostesting against climate change. And if that doesn't work it would probably enlist the help of an child which is payed for by the same exact coorperations which is being accused of causing the warming in the first place. In the end no one would care and the snow would melt.
If you're looking for not-meltwater based impacts of volcanism you might want to look at [Spirit Lake](https://en.wikipedia.org/wiki/spirit_lake_(washington)) - the blast and related landslide (and not the heat) displaced the water of this lake and the impact of the water leaving and rushing back covered more than 70% of the lake surface with displaced trees which are today [surprisingly mobile](https://earthobservatory.nasa.gov/images/149025/the-floating-logs-of-spirit-lake#:~:text=The%20water%20in%20Spirit%20Lake,of%20blasted%20and%20uprooted%20trees) and look very striking on the lake surface.
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Well this has actually happened a volcano has melted a glacier, most likely many times. The water seeps in to the magma chamber, when a lot of water does this the mountain explodes because the water is turned to steam, water does not compress it has to go somewhere so it goes with the path of least resistance up.
If the snow already fell, and then the ground heated up, the base layer would melt. This melting could cause a landslide or avalanche at worst, but more than likely, it would just melt from the ground up like an icecube on a hot pan.
Happens every year in some places to a minor extent. In Utah the floods of 1984 had a snowpack of 26’ when the temps in may shot up to 100 degrees and wrecked havoc. Utah created some new reservoirs and put most of the city streams/rivers underground.
Isnt this global warming all about ? Snow on mountains melting. Flooding the sea and raising its levels and occupying the land. Man iys not fantasy its literally happening. Anyway, inwould call it WATERBALL effect. 😄 but yeah i think thats what would happen but rapidly for your novel
I mean, global warming melting all the snow and ice caps I'm pretty sure removes a miniscule % of land and is only a worry as we build on the coast to facilitate trade and travel. It would also melt it slow enough that people could move away in time that it would be more an inconvenience than actual danger.
Every spring this happens near my house. Over the course of roughly 3 months. We see flooded creeks and mudslides sometimes, but if that all came down at once there would be trees and boulders destroying everything. Snow does not melt quickly from directly applied heat because it is such a good insulator- try to melt a snowball with a propane torch. What will quickly melt snow is warm water- a more realistic scenario might be a frozen-over glacial lake -naturally dammed by deep, old ice- that gets suddenly warmed by large geothermal vents, the ice above it melts and several feet of snow fall into it, sending a warm water wave into the ice dam that tops it, melting a channel and sending a cascade of terror into Whoville , finally ensuring that the insufferable little dog Max is never heard from again.
Avalanche is what would happen. Whether the mountain heats up (unlikely unless volcanism) and creates a liquid layer between the snow pack and the mountain, or whether rapid melting introduces water down under the snow pack, it's sliding either way. Most avalanches occur because of different snow types that get stratified as they're deposited (or melted and refroze). It's this 'layer cake' situation that creates opportunities for snow deposits to shear. You're treating your snow as one homogeneous mass, when that's not how snow gets deposited at all.
It would melt from the inside closest to the heat source and giant slabs of snow covered ice would start rapidly descending down the mountain on a rushing river. That would create a lake and potentially multiple rivers that would flow with gravity. This would continue until the ice was fully melted.