# Mt. Vesuvius spewed out 10 billion tons of debris? Really? **URL:** \ **Category:** Factual Questions\ **Created:** [June 10, 2013, 10:08pm UTC](https://boards.straightdope.com/t/mt-vesuvius-spewed-out-10-billion-tons-of-debris-really/660663 "2013-06-10T22:08:11Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Claire98909](https://avatars.discourse-cdn.com/v4/letter/c/8c91f0/32.png) [@Claire98909](https://boards.straightdope.com/u/Claire98909)\ **Post date:** [June 10, 2013, 10:08pm UTC](https://boards.straightdope.com/t/mt-vesuvius-spewed-out-10-billion-tons-of-debris-really/660663/1 "2013-06-10T22:08:11Z")
I love the BBC TV movie “Pompeii: The Last Day”. I watch it all the time. Anyway, the narrator says at the end that by the time the eruption was over, Mt. Vesuvius had “spewed out more than 10,000,000,000 tons of pumice, rock, and ash”. I’m no geologist. I’m interested in geology but can’t even call myself an “amateur geologist”, so I could be completely talking out of my butt. But 10,000,000,000 tons of debris just seems like…a lot. I mean, one ton is 2,000 pounds, and I can’t even multiply that by 10 billion without getting an error on my calculator. Plus, wasn’t the majority of debris pumice and ash, both of which are pretty lightweight? Anybody have any insight on this? Thanks! ---
**Author:** ![bob\_2](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bob_2/32/3341_2.png) [@bob\_2](https://boards.straightdope.com/u/bob_2)\ **Post date:** [June 10, 2013, 10:12pm UTC](https://boards.straightdope.com/t/mt-vesuvius-spewed-out-10-billion-tons-of-debris-really/660663/2 "2013-06-10T22:12:15Z")
Wikipedia says: > [@](#): > > Mount Vesuvius is best known for its eruption in AD 79 that led to the burying and destruction of the Roman cities of Pompeii and Herculaneum. That eruption ejected a cloud of stones, ash and fumes to a height of 20.5 miles, spewing molten rock and pulverized pumice at the rate of 1.5 million tons per second, ultimately releasing a hundred thousand times the thermal energy released by the Hiroshima bombing ---
**Author:** ![Duckster](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/duckster/32/1244_2.png) [@Duckster](https://boards.straightdope.com/u/Duckster)\ **Post date:** [June 10, 2013, 10:18pm UTC](https://boards.straightdope.com/t/mt-vesuvius-spewed-out-10-billion-tons-of-debris-really/660663/3 "2013-06-10T22:18:55Z")
> [@Claire98909](#): > > Anyway, the narrator says at the end that by the time the eruption was over, Mt. Vesuvius had “spewed out more than 10,000,000,000 tons of pumice, rock, and ash”. So did the [Mt. Pinatubo eruption in 1991](http://en.wikipedia.org/wiki/Mount_Pinatubo). ---
**Author:** ![Skald\_the\_Rhymer](https://avatars.discourse-cdn.com/v4/letter/s/ecccb3/32.png) [@Skald\_the\_Rhymer](https://boards.straightdope.com/u/Skald_the_Rhymer)\ **Post date:** [June 10, 2013, 10:23pm UTC](https://boards.straightdope.com/t/mt-vesuvius-spewed-out-10-billion-tons-of-debris-really/660663/4 "2013-06-10T22:23:48Z")
> [@Claire98909](#): > > I love the BBC TV movie “Pompeii: The Last Day”. I watch it all the time. Anyway, the narrator says at the end that by the time the eruption was over, Mt. Vesuvius had “spewed out more than 10,000,000,000 tons of pumice, rock, and ash”. > > I’m no geologist. I’m interested in geology but can’t even call myself an “amateur geologist”, so I could be completely talking out of my butt. But 10,000,000,000 tons of debris just seems like…a lot. I mean, one ton is 2,000 pounds, and I can’t even multiply that by 10 billion without getting an error on my calculator. Plus, wasn’t the majority of debris pumice and ash, both of which are pretty lightweight? > > Anybody have any insight on this? > > Thanks! 10 billion tons sounds like a lot, but it’s infinitesimal compared to the mass of the Earth, which is something like 6 \* 10[sup]24[/sup] kilograms. ---
**Author:** ![bob\_2](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bob_2/32/3341_2.png) [@bob\_2](https://boards.straightdope.com/u/bob_2)\ **Post date:** [June 10, 2013, 10:28pm UTC](https://boards.straightdope.com/t/mt-vesuvius-spewed-out-10-billion-tons-of-debris-really/660663/5 "2013-06-10T22:28:03Z")
If you ever get the chance, go to Herculaneum and see just how deep that town was buried. ---
**Author:** ![lisiate](https://avatars.discourse-cdn.com/v4/letter/l/f05b48/32.png) [@lisiate](https://boards.straightdope.com/u/lisiate)\ **Post date:** [June 10, 2013, 10:31pm UTC](https://boards.straightdope.com/t/mt-vesuvius-spewed-out-10-billion-tons-of-debris-really/660663/6 "2013-06-10T22:31:37Z")
Well the debris completely covered two good-sized towns. Herculaneam was covered by 23 metres of debris. I imagine most of the weight would be in the pyroclastic surges rather than the ash plume. Assuming the average density of the ejecta is approximately that of water you’ve got a volume of 10 billion cubic metres, a cube 2,154 metres to a side, which does seem pretty big, but gets more managable if the average density is greater than that of water. ---
**Author:** ![bob\_2](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bob_2/32/3341_2.png) [@bob\_2](https://boards.straightdope.com/u/bob_2)\ **Post date:** [June 10, 2013, 10:36pm UTC](https://boards.straightdope.com/t/mt-vesuvius-spewed-out-10-billion-tons-of-debris-really/660663/7 "2013-06-10T22:36:52Z")
> [@](#): > > I imagine most of the weight would be in the pyroclastic surges rather than the ash plume. I am not so sure about that. The houses weren’t pushed over as pyroclastic flow would have done, but buried by hot ash from above. It happened so fast that in spite of the high temperature, some wooden artefacts survived. ---
**Author:** ![dracoi](https://avatars.discourse-cdn.com/v4/letter/d/90db22/32.png) [@dracoi](https://boards.straightdope.com/u/dracoi)\ **Post date:** [June 10, 2013, 10:43pm UTC](https://boards.straightdope.com/t/mt-vesuvius-spewed-out-10-billion-tons-of-debris-really/660663/8 "2013-06-10T22:43:16Z")
If you’re having trouble wrapping your head around Vesuvius, then do not look at the following link: [Volcanic Explosivity Index: Measuring the size of an eruption](http://geology.com/stories/13/volcanic-explosivity-index/) or, for emphasis just on relatively recent eruptions, this one: [http://pubs.usgs.gov/gip/msh/comparisons.html](http://pubs.usgs.gov/gip/msh/comparisons.html) Vesuvius is the just the little kid brother in the family of volcanic eruptions. ---
**Author:** ![Great\_Antibob](https://avatars.discourse-cdn.com/v4/letter/g/e47c2d/32.png) [@Great\_Antibob](https://boards.straightdope.com/u/Great_Antibob)\ **Post date:** [June 10, 2013, 10:46pm UTC](https://boards.straightdope.com/t/mt-vesuvius-spewed-out-10-billion-tons-of-debris-really/660663/9 "2013-06-10T22:46:24Z")
> [@Claire98909](#): > > Plus, wasn’t the majority of debris pumice and ash, both of which are pretty lightweight? I think you’re getting density and weight mixed up here. A pound of feathers and a pound of rocks weigh exactly the same - 1 pound. But the pound of rocks will take up less space. Ash and pumice aren’t as dense as solid basalt but a ton of pumice or a ton of ash is still a ton, no matter how much space they take up. To put it into perspective, while that seems like a lot, it’s a burp compared to the size of the Earth, which is roughly 6 \* 10^21 tons or 6 sextillion tons. 10 billion tons would be 0.0000000017% of the total mass of the earth. Another comparison. A cubic yard of water is roughly 1 ton. So, we’d need 10 billion cubic yards of water. What is roughly the same size? That’s about 5000 Sears Tower’s worth of solid water. That’s a lot in human terms, but a very strong rain storm will drop more water than that naturally. And a hurricane definitely drops much more weight in water before it dies out. ---
**Author:** ![Saltire](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/saltire/32/553_2.png) [@Saltire](https://boards.straightdope.com/u/Saltire)\ **Post date:** [June 10, 2013, 11:05pm UTC](https://boards.straightdope.com/t/mt-vesuvius-spewed-out-10-billion-tons-of-debris-really/660663/10 "2013-06-10T23:05:08Z")
Quick googling gets various values for the density of basaltic lava. The values are around 3000 kg/m[sup]3[/sup], more or less. I’ll also simplify by using metric tonnes, 1000 kg. Doing the math, I get a cube of lava about 1900 meters on each side. That amount of molten rock would mass about 10 billion tonnes, and would make a heck of a lot of ash and pumice if sprayed into the air at high pressure. I’m sure I messed up the math somewhere, and that someone will correct me. But I think the point is clear–that much mass isn’t really all that much compared to the mountain it came out of, let alone the Earth. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [June 10, 2013, 11:06pm UTC](https://boards.straightdope.com/t/mt-vesuvius-spewed-out-10-billion-tons-of-debris-really/660663/11 "2013-06-10T23:06:21Z")
> [@](#): > > I think you’re getting density and weight mixed up here. No, it makes sense to me. 10 billion tons of low-density pumice will make a much bigger pile of rock than 10 billion tons of high-density granite. So the debris being low-density pumice makes the debris pile even more implausibly large. ---
**Author:** ![lisiate](https://avatars.discourse-cdn.com/v4/letter/l/f05b48/32.png) [@lisiate](https://boards.straightdope.com/u/lisiate)\ **Post date:** [June 10, 2013, 11:10pm UTC](https://boards.straightdope.com/t/mt-vesuvius-spewed-out-10-billion-tons-of-debris-really/660663/12 "2013-06-10T23:10:40Z")
An 1,800 metre a side cube is a hell of a lot bigger than a 1,200 (Mt Vesuvius’ rough height) metre high cone though. Of course the material ejected doesn’t all come from within what we see of the volcano, it’s from much futher down. ---
**Author:** ![runningdude](https://avatars.discourse-cdn.com/v4/letter/r/e9c0ed/32.png) [@runningdude](https://boards.straightdope.com/u/runningdude)\ **Post date:** [June 10, 2013, 11:20pm UTC](https://boards.straightdope.com/t/mt-vesuvius-spewed-out-10-billion-tons-of-debris-really/660663/13 "2013-06-10T23:20:34Z")
> [@lisiate](#): > > Well the debris completely covered two good-sized towns. Herculaneam was covered by 23 metres of debris. I imagine most of the weight would be in the pyroclastic surges rather than the ash plume. > > Assuming the average density of the ejecta is approximately that of water you’ve got a volume of 10 billion cubic metres, a cube 2,154 metres to a side, which does seem pretty big, but gets more managable if the average density is greater than that of water. If Pompeii and the surrounding environs were a 20km x 20km (~ 14 miles) area, then they would be buried by only 24 meters (~75 feet). Which is comparable to what “lisiate” and “bob++” said. ---
**Author:** ![Claire98909](https://avatars.discourse-cdn.com/v4/letter/c/8c91f0/32.png) [@Claire98909](https://boards.straightdope.com/u/Claire98909)\ **Post date:** [June 10, 2013, 11:41pm UTC](https://boards.straightdope.com/t/mt-vesuvius-spewed-out-10-billion-tons-of-debris-really/660663/14 "2013-06-10T23:41:26Z")
> [@dracoi](#): > > If you’re having trouble wrapping your head around Vesuvius, then do not look at the following link: [Volcanic Explosivity Index: Measuring the size of an eruption](http://geology.com/stories/13/volcanic-explosivity-index/) or, for emphasis just on relatively recent eruptions, this one: [MSH Comparisons With Other Eruptions [USGS]](http://pubs.usgs.gov/gip/msh/comparisons.html) > > Vesuvius is the just the little kid brother in the family of volcanic eruptions. Thanks for those links! I’ve always known that, in relation to other eruptions, the eruption of Vesuvius in 79 AD was quite small, but I think it’s really cool to see that visual representation. I’m just wondering why, in the second link you posted, they didn’t include Lake Toba? ---
**Author:** ![dracoi](https://avatars.discourse-cdn.com/v4/letter/d/90db22/32.png) [@dracoi](https://boards.straightdope.com/u/dracoi)\ **Post date:** [June 10, 2013, 11:51pm UTC](https://boards.straightdope.com/t/mt-vesuvius-spewed-out-10-billion-tons-of-debris-really/660663/15 "2013-06-10T23:51:39Z")
> [@Claire98909](#): > > Thanks for those links! I’ve always known that, in relation to other eruptions, the eruption of Vesuvius in 79 AD was quite small, but I think it’s really cool to see that visual representation. I’m just wondering why, in the second link you posted, they didn’t include Lake Toba? The USGS comparison only goes back to the 5000 BC Crater Lake eruption, and most of the eruptions they show are within the last 200 years. Toba was 74,000 years ago, so I assume it didn’t make the cut just based on date. ---
**Author:** ![Der\_Trihs](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/der_trihs/32/233_2.png) [@Der\_Trihs](https://boards.straightdope.com/u/Der_Trihs)\ **Post date:** [June 11, 2013, 12:27am UTC](https://boards.straightdope.com/t/mt-vesuvius-spewed-out-10-billion-tons-of-debris-really/660663/16 "2013-06-11T00:27:37Z")
> [@Claire98909](#): > > Plus, wasn’t the majority of debris pumice and ash, both of which are pretty lightweight? [Ash](http://en.wikipedia.org/wiki/Volcanic_ash) can been pretty heavy, especially if it gets wet. It’s known for collapsing buildings, among other things. > [@](#): > > The density of individual particles varies with different eruptions. The density of volcanic ash varties between 700–1200 kg/m3 for pumice, 2350–2450 kg/m3 for glass shards, 2700–3300 kg/m3 for crystals, and 2600–3200 kg/m3 for lithic particles. > \ > > Damage to buildings and structures can range from complete or partial roof collapse to less catastrophic damage of exterior and internal materials. Impacts depend on the thickness of ash, whether it is wet or dry, the roof and building design and how much ash gets inside a building. The specific weight of ash can vary significantly and rain can increase this by 50-100%.[8] Problems associated with ash loading are similar to that of snow; however, ash is more severe as 1) the load from ash is generally much greater, 2) ash does not melt and 3) ash can clog and damage gutters, especially after rain fall. Impacts for ash loading depend on building design and construction, including roof slope, construction materials, roof span and support system, and age and maintenance of the building.[8] Generally flat roofs are more susceptible to damage and collapse than steeply pitched roofs. Roofs made of smooth materials (sheet metal or glass) are more likely to shed ash than roofs made with rough materials (thatch, asphalt or wood shingles). Roof collapse can lead to widespread injuries and deaths and property damage. For example, the collapse of roofs from ash during the 15 June 1991 Mount Pinatubo eruption killed about 300 people. ---
**Author:** ![Bartman](https://avatars.discourse-cdn.com/v4/letter/b/779978/32.png) [@Bartman](https://boards.straightdope.com/u/Bartman)\ **Post date:** [June 11, 2013, 12:28am UTC](https://boards.straightdope.com/t/mt-vesuvius-spewed-out-10-billion-tons-of-debris-really/660663/17 "2013-06-11T00:28:05Z")
> [@runningdude](#): > > If Pompeii and the surrounding environs were a 20km x 20km (~ 14 miles) area, then they would be buried by only 24 meters (~75 feet). Which is comparable to what “lisiate” and “bob++” said. It is also worth remembering that a decent portion was ejected into the atmosphere (around 10-20%). Ash several inches thick can be found hundreds of miles away. And traces of ash remained in the atmosphere for a couple of years. ---
**Author:** ![j\_sum1](https://avatars.discourse-cdn.com/v4/letter/j/8baadc/32.png) [@j\_sum1](https://boards.straightdope.com/u/j_sum1)\ **Post date:** [June 11, 2013, 12:54am UTC](https://boards.straightdope.com/t/mt-vesuvius-spewed-out-10-billion-tons-of-debris-really/660663/18 "2013-06-11T00:54:52Z")
> [@Bartman](#): > > It is also worth remembering that a decent portion was ejected into the atmosphere (around 10-20%). Ash several inches thick can be found hundreds of miles away. And traces of ash remained in the atmosphere for a couple of years. Not to mention the large amount of gaseous material. I know that it is low in density but it does propel pretty much everything that comes out and it does contribute to the total ejected mass. ---
**Author:** ![Great\_Antibob](https://avatars.discourse-cdn.com/v4/letter/g/e47c2d/32.png) [@Great\_Antibob](https://boards.straightdope.com/u/Great_Antibob)\ **Post date:** [June 11, 2013, 2:13am UTC](https://boards.straightdope.com/t/mt-vesuvius-spewed-out-10-billion-tons-of-debris-really/660663/19 "2013-06-11T02:13:23Z")
> [@Chronos](#): > > So the debris being low-density pumice makes the debris pile even more implausibly large. Meh. Once you get to a cube a couple kilometers to a side (which isn’t all that implausible to begin with), in the worse case, what difference does an extra kilometer to a side really make? ---
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [June 11, 2013, 3:46am UTC](https://boards.straightdope.com/t/mt-vesuvius-spewed-out-10-billion-tons-of-debris-really/660663/20 "2013-06-11T03:46:15Z")
How do these events compare to meteorite or asteroid impacts on Earth? [Next page](https://boards.straightdope.com/t/mt-vesuvius-spewed-out-10-billion-tons-of-debris-really/660663.md?page=2)