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Jul 1 • 16 tweets • 6 min read
#FridayPhysicsFun – I got a question today: are there pyroclastic flows from volcanoes elsewhere in the solar system?
Pyroclastic flows are the result of explosive volcanic eruptions, a mix of hot gas and volcanic matter hurtling downslope at potentially more than 100 km/h, burning and suffocating everything. Basically a landslide mixed with hot, dense gas and dust.
en.wikipedia.org/wiki/Pyroclast…
Why do landslides move in the first place? The Varnes classification suggests there are falls, topples, slides, spreads and flows.
geology.cz/projekt681900/…
onlinepubs.trb.org/Onlinepubs/sr/…
Gravitational potential gets turned into movement (and damage to stuff), and especially flows get a lot of velocity if they are of the right type.
In a landslide flow there is fluidization: the solid material bounces, rolls and shakes enough to behave like a fluid. The more material there is (and hence more energy) the further the flow tends to go.
sciencedirect.com/science/articl…
doi.org/10.1016/S0013-…
There can also be entrained fluid that helps trigger the slide and later lower friction. In pyroclastic flows there might be gas trapped under high pressure under the solids that help them flow longer distances.
nature.com/articles/s4156…
OK, where in the solar system do we get volcanos? At present besides Earth it is Io and Venus. Mars may or may not be extinct, and the Moon (1 Gya) and Mercury are definitely extinct. Plus some cryovolcanos (see below)
en.wikipedia.org/wiki/List_of_e…
The Moon likely had pyroclastic flows, and it has been suggested that rilles are due to them (a theory that is no longer in fashion) agupubs.onlinelibrary.wiley.com/doi/abs/10.102…
On the other hand, lack of atmosphere and low gravity make the solids spread out 6 times further by ballistic trajectories rather than flows.
lpi.usra.edu/exploration/CL…
Mercury seems to have been similar.
Io volcanism tends to send plumes of vapour and "volcanic snow" hundreds of km up and to the side, or sulphur or basalt lava flows. Simulations suggest pyroclastic flows of dust carried by volcanic gases helped by the low gravity.
en.wikipedia.org/wiki/Volcanism…
lpi.usra.edu/meetings/lpsc2…
Mars seems to have had pyroclastic flows, e.g. at Tyrrhena Patera.
doi.org/10.1016/j.jvol…
Generally the lower gravity likely makes pyroclastic flows run several times longer than on Earth. Plus, low gravity = low buoyancy => rare but bigger eruptions => longer flows. agupubs.onlinelibrary.wiley.com/doi/10.1029/94…
On Venus the high air pressure prevents normal volcanic plume formation but may make pyroclastic flows more common, adding to the hellishness of the landscape.
agupubs.onlinelibrary.wiley.com/doi/full/10.10…
On Enceladus, Titan, Triton and maybe Pluto there is cryovolcanism when particles are ejected by cold gas or liquid. Cryoclastic flows might happen, although the low gravity and gas density likely makes them more snow-like than avalanche-like.
agupubs.onlinelibrary.wiley.com/doi/full/10.10…
In 1969 Freeman Dyson suggested volcanoes on neutron stars as an explanation for star-quakes. As far as I can tell few believe in this possibility, but were it true one could get some fantastic nuclear-powered pyroclastic flows. adsabs.harvard.edu/full/1969CoASP…

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More from @anderssandberg

Anders Sandberg Profile picture
Jul 2
There is an old Swedish rhyme about the cuckoo: "södergök är dödergök, västergök är bästergök, östergök är tröstergök och norrgök är sorggök."
Roughly: "south-cuckoo is death-cuckoo, west-cuckoo is best-cuckoo, east-cuckoo is consolation-cuckoo, north-cuckoo is grief-cuckoo".
If you take the rhyme seriously each cuckoo hence radiates a kind of field in cells, like a cellphone tower for superstition. It presumably declines as 1/d^2 with the sound intensity. Image
In a forest different cuckoos presumably generates a mixed random field as they move about. It is a bit unclear if they show constructive or destructive interference: maybe a west and a south cuckoo cancel, your enemies die, or you get a monkey's paw situation. Image
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Anders Sandberg Profile picture
Jun 29
I knew my youthful forays into ceremonial magic and neural networks would pay off eventually... But not simultaneously, for the same application.
I think the essay gets at something deep. We are not just being pre-scientific or pre-engineering with current prompt design ("ha ha, it's black magic"), but the domain has many similarities to magic because it draws on an overlapping source.
The Internet *is* the collective (un)conscious today. We have externalized it by putting enough data from ourselves there that we have a collective exoself with a collective unconscious defined as a statistical latent space.
Read 4 tweets
Anders Sandberg Profile picture
Apr 15
It is interesting that the same people who would strongly endorse "societal change without caring about quarterly revenue" in the abstract likely oppose these particular people doing it. Meandering🧵
There is often (1) an assumption about what values are embodied by non-revenue aims, and (2) the assumption that such change must be joint by a group rather than unilateral by an individual.
(1) is largely from a world-view that doesn’t recognize that people interested in acquiring money may have non-money goals too. This is just mistaken.
Read 17 tweets
Anders Sandberg Profile picture
Apr 8
This Monday, I explained in the FHI kitchen why my AGI timelines were long. Over the *past three days* they have shortend a fair bit.
It is not that I think PaLM, DALL-E 2 or Socratic models in themselves are huge steps towards AGI. It is that they demonstrate rapid improvement in three entirely different domains, looks like it can be generalised to a lot of tasks, and surprise "experts" like me.
The surprise part suggests that one cannot rule out early arrival given past evidence: it is not just that progress may be faster than expected, it is that surprising synergies and tricks also clearly can show up.
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Anders Sandberg Profile picture
Apr 7
Using LAION for designing book covers looks somewhat feasible. It might not be DALL-E II, but it knows how book covers usually looks. Image
I find the "spelling" and typography fascinating. Image
Saying "with space theme" biases it towards SF novel covers. Image
Read 6 tweets
Anders Sandberg Profile picture
Feb 20
Yesterday, when an friend heard I worked on the end of the world I was asked what I thought about the imminent social collapse. I was confused: "why do you think there is one?"
The reasons given were basically that people are stupid and listen to stupid people, that civic virtues are decaying, and it all depends on unsustainable activities. Which has been the case for the past few millennia. Why *now*?
Digging a bit deeper (and factoring out the important and IMHO real vulnerabilities that might lead to a random systemic implosion for non-social reasons) it seemed to be more a criticism of everything bad phrased as a prediction of doom.
Read 11 tweets

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