The question about volcanic ashes

In summary, the article states that volcanoes can have a cooling effect on the Earth's climate by making aerosols that cool the atmosphere. These aerosols come in different sizes and compositions, and are distributed differently in the stratosphere. They are also subject to the solar radiation, which can evaporate or decay them.
  • #1
Eagle9
238
10
Good day :smile:
It is well-known fact that the volcanic eruptions cause the global decrease of average temperature. I quickly reviewed the article in wikipedia and several questions arised regarding this issue. There is written in this article (I do not trust Wikipedia very much):
A volcanic winter is a reduction in global temperatures caused by volcanic ash and droplets of sulfuric acid obscuring the Sun and raising Earth's albedo (increasing the reflection of solar radiation) after a large particularly explosive volcanic eruption. Long-term cooling effects are primarily dependent upon injection of sulfide compounds in aerosol form into the upper atmosphere—the stratosphere—the highest, least active levels of the lower atmosphere where little precipitation occurs, thus requiring a long time to wash the aerosols out of the region. Stratospheric aerosols cool the surface and troposphere by reflecting solar radiation, warm the stratosphere by absorbing terrestrial radiation, and when combined with anthropogenic chlorine in the stratosphere, destroy ozone which moderates the effect of lower stratospheric warming. The variations in atmospheric warming and cooling results in changes in tropospheric and stratospheric circulation.
1) So, the most dangerous/active factor that cools our planet is aerosols that are made of volcanic ash+ sulfuric acid, right?
2) What about the sizes of these aerosols?
3) What can you tell me about their exact chemical composition?
4) How are they distributed in stratosphere? Do they occupy the thickness of 10–50 km (these are lower and upper boundaries of stratosphere) equally?
5) After some amount of time (months, years) the effect of “Volcanic winter” weakens, apparently because of the weight of the volcanic aerosols. Do they (chemically) decay or do they sink down towards the Earth’s surface?
6) Are they subjected to the solar radiation? Can this radiation (if strong) evaporate/decay them? :rolleyes:
 
Earth sciences news on Phys.org
  • #2
Eagle9 said:
1) So, the most dangerous/active factor that cools our planet is aerosols that are made of volcanic ash+ sulfuric acid, right?
Define "dangerous".
I understand that there is a difference of opinion about what is currently having the largest "cooling effect" on the climate. It seems a fair bet that volcanoes both heat the atmosphere directly and cool it indirectly ... volcanic activity is usually considered to have had an important role in the pre-industrial climate.

2) What about the sizes of these aerosols?
Yes. What about the size of these aerosols? Is there something you want to know about this?
Ejecta from a volcano varies from simple gas molecules to huge rocks.
Expect aerosols in the entire range that can be called by the name "aerosol".

3) What can you tell me about their exact chemical composition?
Not much - the exact composition varies too much so the list would be rather large for this forum.
You can find papers listing various compositions for different eruptions in journals of vulcanology.
Most models would use average compositions of the major substances of concern.

4) How are they distributed in stratosphere?
TLDR: It's complicated.
Especially in light of the request for "exact compositions" prev.

Do they occupy the thickness of 10–50 km (these are lower and upper boundaries of stratosphere) equally?
No. Different chemicals would be distributed differently at different elevations.

You can find examples in atmospheric studies.

5) After some amount of time (months, years) the effect of “Volcanic winter” weakens, apparently because of the weight of the volcanic aerosols. Do they (chemically) decay or do they sink down towards the Earth’s surface?
They are generally heavy - they sink. They also get caught up in rainwater and washed down.

6) Are they subjected to the solar radiation?
Yes. Everything is subject to solar radiation.

Can this radiation (if strong) evaporate/decay them?
If strong yes - but define "strong". The term "solar radiation" is very general and covers a very wide range of energies. Most solar radiation is in the form of infrared light - which won't do much to the relative concentrations of volcanic ash in the upper atmosphere.

I think you need to have a closer look at what the processes of "evaporation" and "decay" actually are. It will help you ask more specific questions.

In evaporation, a liquid droplet breaks up into much smaller droplets ... allowing a more even distribution. Solar radiation can help this along by heating the parent droplet.
http://techalive.mtu.edu/meec/module01/EvaporationandTranspiration.htm
... usually droplets in the upper atmosphere are already smallest for vapor phase, but they can condense on suspended dust particles and these bigger drops evaporate.

Of course, solar radiation can also vaporize a liquid droplet - turning it into a gas.

In "decay" - depends on the kind. In nuclear decay, for eg, higher energy radiation would get captured by the atoms in the droplet, forming an unstable isotope. i.e. oxygen 19 beta-decays into Florine. This would require regular oxygen 16-18 gaining neutrons from the solar radiation flux or secondary interactions.I think you will benefit from asking more specific questions, but you need more grounding in regular science in order to do this carefully. You seem to be trying to ask very careful questions. I'd suggest leaning on your inexperience and just ask less-careful questions.
 
Last edited:
  • #3
Eagle9 said:
Good day :smile:
It is well-known fact that the volcanic eruptions cause the global decrease of average temperature. I quickly reviewed the article in wikipedia and several questions arised regarding this issue. There is written in this article (I do not trust Wikipedia very much):

1) So, the most dangerous/active factor that cools our planet is aerosols that are made of volcanic ash+ sulfuric acid, right?

Volcanic eruptions that put material into the stratosphere (causing temporary cooling) are very isolated events. Most eruptions are not strong or high enough to inject significant mass. Some famous eruptions that did have a cooling effect were Krakatoa in 1883, and Tunguska in the early 1900s. Krakatoa put 1 cubic mile of debris into the stratosphere, and there was said to be no summer in the northern hemisphere that year. Snow fell in June.
2) What about the sizes of these aerosols?

micron size
3) What can you tell me about their exact chemical composition?
Like you said, sulfuric acid.
4) How are they distributed in stratosphere? Do they occupy the thickness of 10–50 km (these are lower and upper boundaries of stratosphere) equally?
The stratospheric aerosol layer is located in the very lower stratosphere, close to the tropopause.

6) Are they subjected to the solar radiation? Can this radiation (if strong) evaporate/decay them? :rolleyes:

Sulfate aerosol can evaporate, and there are also gaseous sulphur compound present.
 
  • #4
  • #5
SteamKing said:
Although the eruption of Krakatoa in 1883 disrupted global weather for about 5 years afterward, I think you have its effects mixed up with the earlier eruption of Mount Tambora in 1815. The after effects of that eruption led to 1816 being called the 'Year Without a Summer' for the unseasonable conditions which prevailed that year:

http://en.wikipedia.org/wiki/Year_Without_a_Summer

http://en.wikipedia.org/wiki/Mount_Tambora

Yes. You're right. Sorry for any misinformation I created.

Chet
 
  • #6
chestermiller said:
and Tunguska in the early 1900s

Tunguska wasnt an eruption ... not sure where you heard that from ??
it was a comet/meteorite type impact

a more recent eruption, 1991, Mt Pinatubo in the Philippines put out enough material to slightly affected global temps

from wiki...
The effects of the eruption were felt worldwide. It ejected roughly 10,000,000,000 tonnes (1.1×1010 short tons) or 10 km3 (2.4 cu mi) of magma, and 20,000,000 tonnes (22,000,000 short tons) SO
2, bringing vast quantities of minerals and metals to the surface environment.[citation needed] It injected large amounts of particulate into the stratosphere – more than any eruption since that of Krakatoa in 1883. Over the following months, the aerosols formed a global layer of sulfuric acid haze. Global temperatures dropped by about 0.5 °C (0.9 °F), and ozone depletion temporarily increased substantially.[7]


Dave
 
  • #9
just watching some pinatubo eruption videos on youtube at the moment
it was truly massive
My wife is from the Phil's, she was 21 when the eruption occurred, she remembers it well

Dave
 
  • #10
It's not even clear that Tunguska was an impact event. Like it recent event over Chelyabinsk, it appears that a meteorite exploded above the surface, and the shock wave produced did all the damage on the ground.

http://en.wikipedia.org/wiki/Tunguska_event

Due to the remote location, and the amount of time elapsed until scientists could survey the damage, it is not clear if some of the fragments of the explosion made it to the ground. In any event, it appears that none have been recovered so far, unlike in the Chelyabinsk event.
 
  • #11
yes that's true, it is deemed an airburst

but it wasnt a volcanic eruption :smile:

D
 
  • #12
Simon Bridge
Yes. What about the size of these aerosols? Is there something you want to know about this?
Ejecta from a volcano varies from simple gas molecules to huge rocks.
Expect aerosols in the entire range that can be called by the name "aerosol".
The huge rock will fall down on Earth quickly, the gas molecules will not at all. I want to know the size of the aerosols that block solar radiation and stay in stratosphere relatively long-several months/years.
Not much - the exact composition varies too much so the list would be rather large for this forum.
You can find papers listing various compositions for different eruptions in journals of vulcanology.
Most models would use average compositions of the major substances of concern.
But probably the most common chemical found in aerosols will be SiO2, right?
You can find examples in atmospheric studies.
Where exactly?

Chestermiller

Volcanic eruptions that put material into the stratosphere (causing temporary cooling) are very isolated events. Most eruptions are not strong or high enough to inject significant mass.
What means “high” in this case? Do you mean the height of the column of the volcanic ashes?
rC1afKS.png

micron size
Thanks :smile:
Like you said, sulfuric acid.
But with SiO2, right? :rolleyes:
The stratospheric aerosol layer is located in the very lower stratosphere, close to the tropopause.
That is at the altitude 10 km, right?

SteamKing
Although the eruption of Krakatoa in 1883 disrupted global weather for about 5 years afterward, I think you have its effects mixed up with the earlier eruption of Mount Tambora in 1815. The after effects of that eruption led to 1816 being called the 'Year Without a Summer' for the unseasonable conditions which prevailed that year
No, I did not mix them up. I know that eruption of Tambora was much stronger than eruption of Krakatoa :wink:

davenn

The effects of the eruption were felt worldwide. It ejected roughly 10,000,000,000 tonnes (1.1×1010 short tons) or 10 km3 (2.4 cu mi) of magma, and 20,000,000 tonnes (22,000,000 short tons) SO2, bringing vast quantities of minerals and metals to the surface environment.[citation needed] It injected large amounts of particulate into the stratosphere – more than any eruption since that of Krakatoa in 1883. Over the following months, the aerosols formed a global layer of sulfuric acid haze. Global temperatures dropped by about 0.5 °C (0.9 °F), and ozone depletion temporarily increased substantially
Well, as I see the aerosols from this eruption was made up with ONLY sulfuric acid, apparently in solid/frozen state, right? But what about the SiO2 that must have been there? Our planet contains this substance in much larger amount than sulfuric acid.
 
  • #13
What means “high” in this case? Do you mean the height of the column of the volcanic ashes?

yes, the height's of the volcano in comparison are small, a mountain of say ~ 2- 3,000 metres
compared to the ash column that may go up to 15 - 20,000 metres or more

oh and in general, the SO2 doesn't become sulphuric acid till it mixes with the water (vapour) in the atmosphere

Most of the SiO2 will be in a big enough particulate size that it will either fall out under gravity or be washed out with rain ... that doesn't stop it from staying up long enough to encircle the world
I remember when living in New Zealand, the incredible sunsets caused by the Pinatubo ash high in the atmosphere
The aerosols on the other hand are primarily micron size to gasses

Dave
 
Last edited:
  • #15
Simon

thanks particularly for that first link
had a quick scan ... think I am going to learn some new things from that
when I get a chance to read it fully :)

Cheeras
Dave
 
  • #16
I see no reason why SiO2 should be dominant among the ash. Many volcanoes contain no free silica (quartz). Granted that explosive eruptions are more likely with an acidic lava, but in these the quartz percentage rarely exceeds 35%. Perhaps the OP means silicate minerals, including the feldspars and ferromagnesians as well.
 
  • #17
Eagle9 said:
Chestermiller

Where exactly?

Try the prestigious Journal of Geophysical Research. Also check out the book by Susan Solomon and Guy Brasseur on atmospheric chemistry (I forgot the name). Also check out Prupacher and Kleck (again, l I forgot the name) which covers atmospheric physical chemistry, particularly with regard to ice and other aerosols.
What means “high” in this case? Do you mean the height of the column of the volcanic ashes?
Both altitude and and quantity of injectate. 1 cubic mile of injectate into the stratosphere will do the trick for causing a big effect.
That is at the altitude 10 km, right?

The tropopause is located at roughly 8 - 15 km, depending on latitude - closer to 15 km at the equator, and 8 km at the poles.
 
  • #18
davenn
yes, the height's of the volcano in comparison are small, a mountain of say ~ 2- 3,000 metres
compared to the ash column that may go up to 15 - 20,000 metres or more
And as I guess only such volcanoes with long/high ash column can cause global cooling, right?
oh and in general, the SO2 doesn't become sulphuric acid till it mixes with the water (vapour) in the atmosphere

Most of the SiO2 will be in a big enough particulate size that it will either fall out under gravity or be washed out with rain ... that doesn't stop it from staying up long enough to encircle the world
I remember when living in New Zealand, the incredible sunsets caused by the Pinatubo ash high in the atmosphere
The aerosols on the other hand are primarily micron size to gasses
So, we can conclude that mainly SO2 (plus water, that is sulfuric acid eventually) causes global cooling, right? But SiO2 also can stay a long time in stratosphere, right?

Simon Bridge
Looking up ash etc properties is straight forward, i.e. a simple google yields:
http://volcanoes.usgs.gov/ash/properties.html
Thanks :smile:

Chestermiller
Try the prestigious Journal of Geophysical Research. Also check out the book by Susan Solomon and Guy Brasseur on atmospheric chemistry (I forgot the name). Also check out Prupacher and Kleck (again, l I forgot the name) which covers atmospheric physical chemistry, particularly with regard to ice and other aerosols.
Thanks, I think that the information gained in this topic will be enough for me :rolleyes:
 
  • #19
So, we can conclude that mainly SO2 (plus water, that is sulfuric acid eventually) causes global cooling,
Not really - "SO2 (etc) causes global cooling" is a bit of a strong statement - what we'd say is that these substances are contributing factors to global climate models - with a short-term cooling effect.

The greatest volcanic impact upon the Earth's short term weather patterns is caused by sulfur dioxide gas. In the cold lower atmosphere, it is converted to sulfuric acid by the sun's rays reacting with stratospheric water vapor to form sulfuric acid aerosol layers. The aerosol remains in suspension long after solid ash particles have fallen to Earth and forms a layer of sulfuric acid droplets between 15 to 25 kilometers up. Fine ash particles from an eruption column fall out too quickly to significantly cool the atmosphere over an extended period of time, no matter how large the eruption.

Sulfur aerosols last many years, and several historic eruptions show a good correlation of sulfur dioxide layers in the atmosphere with a decrease in average temperature decrease of subsequent years. The close correlation was first established after the 1963 eruption of Agung volcano in Indonesia when it was found that sulfur dioxide reached the stratosphere and stayed as a sulfuric acid aerosol.

Without replenishment, the sulfuric acid aerosol layer around the Earth is gradually depleted, but it is renewed by each eruption rich in sulfur dioxide. This was confirmed by data collected after the eruptions of El Chichon, Mexico (1982) and Pinatubo, Philippines (1991), both of which were high-sulfur compound carriers like Agung, Indonesia.

-- http://volcanology.geol.ucsb.edu/gas.htm

Note: if H2SO4 aerosols mean cooler planets, then Venus should be very chilly right?
In fact Venus is very hot. The greenhouse agents sustaining it are water vapour, carbon dioxide and sulphuric acid aerosols. Sound familiar?
http://www.esa.int/Our_Activities/Space_Science/Venus_Express/Greenhouse_effect_clouds_and_winds
(... or pretty much any tract on Venus.)

... right? But SiO2 also can stay a long time in stratosphere, right?
See the first link - solids from eruptions generally don't stay a long time in the atmosphere.
 
  • #20
Simon Bridge
Well, thanks a lot for this information; this was what I wanted to know :smile:
 
  • #21
Had a feeling...
... no worries then.
Enjoy.
 
  • #22
Simon Bridge said:
Note: if H2SO4 aerosols mean cooler planets, then Venus should be very chilly right?
In fact Venus is very hot. The greenhouse agents sustaining it are water vapour, carbon dioxide and sulphuric acid aerosols. Sound familiar?
http://www.esa.int/Our_Activities/Space_Science/Venus_Express/Greenhouse_effect_clouds_and_winds
(... or pretty much any tract on Venus.)
Came across this older thread when I was looking for information on how the sulfuric acid clouds contribute to Venus' surface temperature--a number of sources emphasized their warming effect (for example, p. 224 of this book says "Although carbon dioxide is the most significant greenhouse gas on Venus, the presence of sulfur dioxide and clouds of sulfuric acid enhance its action"), but then I came across this post from a climate scientist which says:
A key feature of the atmosphere of Venus is the sulfuric acid cloud deck. These clouds account for the high reflectivity of Venus, but because they also reflect infrared back to the surface (unlike water clouds, which absorb and emit), they have a warming effect as well, and constitute the second most important factor in the greenhouse effect of Venus after carbon dioxide. Radiation model calculations demonstrate that the clouds have a pronounced net cooling effect on the planet, when both factors are taken into account.
So if I'm understanding correctly, he's claiming that Venus would actually be significantly hotter if the sulfuric acid clouds were removed while everything else remained the same. I wonder if this is an issue on which there is widespread agreement or if it's somewhat controversial among climate modelers.
 
  • #23
Oh the RealClimate blog?
See comment #14 on the same post.
 
  • #24
Simon Bridge said:
Oh the RealClimate blog?
See comment #14 on the same post.
What about that comment, specifically? He mentions there that the clouds have both a warming influence (scattering radiation coming from the surface back downwards) and a cooling influence (reflecting incoming radiation from the Sun, preventing it from reaching the surface) but he doesn't say anything to contradict his earlier statement that the cooling influence predominates.
 
  • #25
Never said he did - it clarifies some of the other mechanisms.
Bottom line: it's complicated.

There are other comments about how the aerosol size is important too.
AFAIK this is the only source asserting that Venuses clouds have an overall cooling effect on the planet.
 
  • #26
Sorry, I misunderstood your meaning. As for your point that most other sources seem to disagree, I think it would be worth looking into the nature of these sources--whether they are technical sources by climate scientists/planetary scientists, or just things like popular articles and general introductions to the solar system like this one I posted earlier (many such sources might just be repeating information they had come across in other non-technical sources, or some older technical source that had become outdated). I also found that the author of that RealClimate post, Raymond Pierrehumbert, has written a textbook called "Principles of Planetary Science", and if you use the "search inside the book" feature on the book's https://www.amazon.com/dp/0521865565/?tag=pfamazon01-20 to look for the phrase "dynamically maintained by the sulfur cycle" you'll see the following on p. 346:
The net influence of the sulfuric acid clouds of Venus presents a particularly interesting problem, because they are dynamically maintained by the sulfur cycle of the planet; it could well be that Venus has gone through periods when these clouds were absent. Would such a Venus be hotter or cooler? Venus clouds act on the OLR through a mix of absorption and scattering, and the estimate of their net effect depends moreover on what the solar-spectrum albedo of Venus would be if you took the clouds away. The few calculations that have been done on this problem tend to suggest that the solar albedo effect wins in this case, and Venus would become considerably hotter without clouds. This is a problem that involves many subtleties and would repay further study, particularly in view of the fact that Venus represents an archetype for the climate evolution of hot, dry planets.
So it seems like he's saying there have been relatively few calculations in the climate science/planetary science literature which have actually tried to figure out in detail whether the warming effect or the cooling effect is stronger, but the ones that he's aware of have indicated it's the cooling effect (the increase in albedo).
 
Last edited by a moderator:

1. What causes volcanic ashes to form?

Volcanic ashes are formed when molten rock, gases, and other materials are expelled from a volcano during an eruption. These materials are then broken into small pieces by the force of the eruption and carried into the atmosphere.

2. Is volcanic ash harmful to humans?

Yes, volcanic ash can be harmful to humans if inhaled. The tiny particles in volcanic ash can irritate the eyes, nose, and throat, and can also cause respiratory issues. It is important to wear protective gear when in areas with volcanic ash.

3. How far can volcanic ash travel?

Volcanic ash can travel thousands of kilometers away from the eruption site, depending on factors such as wind direction and strength. Some volcanic eruptions have even caused ash to reach the other side of the world.

4. Can volcanic ash affect the climate?

Yes, large volcanic eruptions can have a significant impact on the Earth's climate. The ash and gases released during an eruption can block sunlight and cause a temporary cooling effect on the planet.

5. How are volcanic ashes used in scientific research?

Volcanic ash is used by scientists to study past eruptions and understand the history and behavior of volcanoes. By analyzing the composition and characteristics of volcanic ash, scientists can also make predictions about the potential impact of future eruptions.

Similar threads

Replies
2
Views
2K
  • Earth Sciences
Replies
7
Views
2K
  • Sci-Fi Writing and World Building
Replies
5
Views
1K
  • Earth Sciences
Replies
2
Views
5K
  • Sci-Fi Writing and World Building
Replies
21
Views
807
  • DIY Projects
Replies
13
Views
1K
Replies
54
Views
11K
Replies
18
Views
6K
Replies
28
Views
27K
Back
Top