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The question about volcanic ashes

by Eagle9
Tags: ashes, volcanic
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Eagle9
#1
Feb13-14, 11:06 AM
P: 134
Good day
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?
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Simon Bridge
#2
Feb13-14, 06:34 PM
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Quote Quote by Eagle9 View Post
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 infra-red 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/module...nspiration.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.
Chestermiller
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Feb13-14, 07:16 PM
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Quote Quote by Eagle9 View Post
Good day
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?
Sulfate aerosol can evaporate, and there are also gaseous sulphur compound present.

SteamKing
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Feb14-14, 03:33 AM
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The question about volcanic ashes

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
Chestermiller
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Feb14-14, 07:26 AM
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Quote Quote by SteamKing View Post
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
davenn
#6
Feb14-14, 11:05 PM
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Quote Quote by chestermiller
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
Simon Bridge
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Feb14-14, 11:13 PM
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So Tunguska wasn't an impact with a quantum black hole?
Darn Niven... <mutter>

Note:
http://iopscience.iop.org/1009-9271/...a_3_S1_545.pdf
more accessible: http://www.rense.com/general12/gas.htm
... still not volcanic though.

Quibbles over examples aside, I believe the question has been answered.
davenn
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Feb14-14, 11:22 PM
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Quote Quote by Simon Bridge View Post
So Tunguska wasn't an impact with a quantum black hole?
Darn Niven... <mutter>

Note:
http://iopscience.iop.org/1009-9271/...a_3_S1_545.pdf
more accessible: http://www.rense.com/general12/gas.htm
... still not volcanic though.

Quibbles over examples aside, I believe the question has been answered.
hahaha, it was as some believe the engine of an alien space craft exploding
davenn
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Feb14-14, 11:26 PM
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just watching some pinatubo eruption videos on youtube at the moment
it was truely massive
My wife is from the Phil's, she was 21 when the eruption occurred, she remembers it well

Dave
SteamKing
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Feb15-14, 02:49 AM
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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.
davenn
#11
Feb15-14, 03:49 AM
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yes thats true, it is deemed an airburst

but it wasnt a volcanic eruption

D
Eagle9
#12
Feb16-14, 11:15 AM
P: 134
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?

micron size
Thanks
Like you said, sulfuric acid.
But with SiO2, right?
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

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.
davenn
#13
Feb16-14, 06:10 PM
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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
Simon Bridge
#14
Feb16-14, 10:30 PM
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Looking up ash etc properties is straight forward, i.e. a simple google yields:
http://volcanoes.usgs.gov/ash/properties.html

There are also peer review journals devoted to vulcanology and atmospheric chemistry.
eg. http://www.atmos-chem-phys-discuss.n...1481-2012.html
davenn
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Feb17-14, 03:01 AM
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Simon

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

Cheeras
Dave
Ophiolite
#16
Feb17-14, 06:41 AM
P: 274
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.
Chestermiller
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Feb18-14, 12:52 PM
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Quote Quote by Eagle9 View Post
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.
Eagle9
#18
Feb21-14, 12:27 PM
P: 134
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

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


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