CAVEAT: I am not a Geologist, Seismologist, Ornithologist, Hematologist, Banker (I have a soul), Congressman (I knew my parents), Auto Mechanic (well, professionally I’m not) or formally trained in any of this. I am an amateur, just like you. In other words, take it with a grain of salt, I can be wrong.
This sort of falls in with my previous “It’s a Gas” post from August 14th of LAST year (Originally “this” year, but the Mayan Doom thing came and went and went before this post made it out… it is 2012 that it refers to.)
The other day, I was a bit stoked by finally locating an SO2 dataset for the southern hemisphere. I knew it was out there, many times data from that have been mentioned in various papers. The data set is from the Taylor Dome, located at latitude 77.66°S. GISP, the source for the Northern data set is at around 65°N. Plotted together (with the Taylor Dome set inverted so that each can be clearly seen), you get a reasonably decent look at SO2 for both hemispheres.
Note that both of these plots are for Total SO2, and not just Volcanic SO2. All we are interested in are the peaks/spikes. (Likely volcanic in origin).
Interesting things in the plot:
52.9 BC shows a sizable spike in the Northern plot. According to GVP, Apoyeque in Nicaragua went up around this time with a VEI-6, so it’s a candidate (± 100 years).
78.2 AD could be Vesuvius, there is enough slop in the resolution to where it could be a fit with the 79 AD (historical record) eruption that killed Pliny the Elder (and gave us the archetype for a Plinian Eruption based on the writings of Pliny the Younger). An additional candidate (or co-emitter) could be Furnas in Portugal (80 AD ± 100 years) Both of them are listed as (or likely) VEI-5.
640.1 AD may be Shiveluch. GVP places an event there at 650 AD ± 40 years.
1612 BC is quite interesting. There is a monster spike in the Southern Hemisphere, and smaller one in the Northern hemisphere. GVP places the Santorini VEI-7 in this time frame, but logic says that it should have had the greatest effect in the northern hemisphere… so what happened about this time in the south? Fuego (Guatemala), Chacana (Ecuador), and Taapaca (Chile) all erupted with unknown VEI around 1580 BC, (± 75, 10, 75 years respectively), so any or all of them could be a candidate.
Since we are now in the southern hemisphere, that topic that came up when I posted the original plot: “Where is Taupo?” To put it simply… it ain’t there. Taupo went big in 230 AD at VEI-6. Yet not a blip. It also had a large event in 1460 BC (± 40 years), again.. nothing in the SO2 record to speak of.
dfm noted that the Taylor Dome series may be stunted in what it can record due to the “roaring 40s.”
For those of you that don’t know… 40°S latitude is notorious for it’s storms and high winds… it’s fairly persistent feature of that latitude. There is almost no land along that latitude… maybe 1100 km total out of 30,384 km of latitudinal track. It’s also right at the boundary of the Southern Hadley Cell and the Southern Mid-Latitude Cell.
At the surface, stuff north of the boundary tends to flow north, stuff south tends to flow south. That is, unless you shove the plume up towards the stratosphere where the flows reverse… and then if it gets to the stratosphere, well, things are different there. The stratosphere is above something called the “Tropopause.” The Tropopause is the very top of the troposphere. All weather that we encounter… Hurricanes, Tornadoes, Thunderstorms, Derechos, Typhoons, Monsoons, Lightning, Gales, Gusts, Waterspouts, Snow, Sleet, Rain, Hail… are products of the troposphere. The stratosphere is above that. It’s called the stratosphere due to it being layered… layered in temperature. The reason it is layered, is that not a lot goes on there. Well, not a lot of mixing, at least as compared to the one below it. Yet stuff still goes on there. This is the region where SO2 in a volcanic column is converted to Sulfate and can operate as a screen, reflecting sunlight.
You can see the boundary region in an averaged tropopause height plot. The red region around the equator are the two Hadley cells straddling the equator. Just north and south of these two regions are the mid-latitude cells that run to about 50°N and 50°S. Beyond there and you are into the Polar cells.
So… did Taupo produce an SO2 signal but both GISP and Taylor Dome ice miss it?
In Bolivia, there is a “extinct” stratovolcano called Nevado Sajama. GVP doesn’t have a listing for it, so that implies that it has had no Holocene activity. Davidson et al (1995) places the Nazca Plate Benioff Zone at between 150 to 175 km under the volcano, so it is likely that it is outside (barely) the region that produces magma for arc volcanism. However, that paper also lists Sajama as a Holocene volcano. Some of the ejecta from it overlies 2.2 mya material. So its last activity is at least younger than that. But the thing about Sajama that we care about, is that it has glaciers.
From the Sajama Ice Core descriptor:
In June-July 1997, two ice cores to bedrock were recovered from the summit of the extinct Sajama volcano, Bolivia (18°S, 69°W, elevation 6540 m) and were subsequently transported back in a frozen state to the cold room facility at the Byrd Polar Research Center (BPRC).
This record goes back to about 23000 BC. It only has 100 year resolution, but it at least gives us a peek at something inside the Southern Hadley cell.
An important note: This is Sulfate, not SO2. Sulfate is the end product after SO2 is converted through interaction with water and radicals.
But we are still left with the question of where is the Taupo SO2 signal? The best bet? There isn’t one.
In a previous post on the topic of the TVZ, we found that Taupo’s last eruption showed almost no zonation. Zonation is where different levels of the magma chamber have chemical signatures representative of the crystal formation process that was present at the time of the eruption. As the eruption progresses, different groups of signatures come out as the point source of the eruption gets to them. With no zonation, the likely reason is that that chamber was well mixed and highly dynamic. Convective currents were keeping everything stirred up really well and the chamber was very homogenous. It doesn’t explain the lack of SO2, but it may lend a clue. (something for you and I to ponder)
Is it possible that since Taupo is under a lake, that the SO2 was leached out early in the eruption by the large quantity of water?
Havre Seamount in the Kermadec Islands of New Zealand erupted (significantly) in July of this year… here is the Aura OMI Level 3 SO2 vertical column for that period. (May through August in order to make sure we caught it)
Hmm… nada. Up north around Vanuatu there are emissions, but nothing in the Havre Seamount area. It doesn’t prove the point, but it supports the idea of the SO2 being leached early.
Now we move on to 1258. It shows up on the GISP data set, but not in the Taylor Dome set. It also seems to be missing from the Sajama core, but as noted, it has a 100 year resolution and could still miss it. No matter how you slice it, there is still that glaring item about it showing up in the North Hemisphere, but not the South. If it were an equatorial event, one would expect a coincidental signal in both sets…. weather permitting. Zooming in on that year, sure enough, there is a signal in both sets.
But the northern signal is 6.4 times the size of the southern one. Whoever comes up with the source for the 1258 SO2 spike is going to have to address that. If not, it will be a rather large monkey wrench to deal with .
And now for something completely different. (maybe…)
Ever hear of e-folding? How about continuous interest compounding on a banking instrument? They are related. E-folding comes to us from the world of atomic physics. Continuous interest compounding comes to us from … banks. Both have to do with how you figure out how much “stuff” you have after a certain amount of time.
The top equation would be used to find out how much “stuff” you would have left in a half life equation with a given decay rate of “r” time. “t” is the amount of elapsed time.
The bottom equation does the same thing, but instead of the rate to wind up with “half”, it’s the rate to wind up with 1/e. “e” being a natural logarithm. (about 2.718281828)
The only reason I bring it up, is because Bluth et al (1997) did in their paper “Stratospheric Loading of Sulfur from Explosive Volcanic Eruptions” They come up with the conclusion, that SO2 blown into the atmosphere, is converted to sulfate at an e-folding rate of 35 days. That means that after 35 days, 1/e of the material will be left. (about 36.7%). Sulfate, on the other hand, shows an e-folding rate of about 12 months for the really prolific SO2 eruptions, and 6 months for the more moderate emitting eruptions. In both cases, wintertime sulfate removal rates are slowed down by about 20%.
Not having a handy eruption to run the equations on… let’s go back to my fictitious Mt Gibbons. For the sake of argument, Mt Gibbons erupted 1.0 Mt of SO2. Here is how it would play out according to Bluth et al.
What this plot does, is to apply the SO2 conversion and the Sulfate removal rates simultaneously (well, as close as I can get) to the eruption… which for the model, is assumed to be one large ejection of the SO2. As you can see, peak loading occurs about 2 to 3 months after the eruption.
Where the model fails, is when the SO2 is emitted over time, as in a series of SO2 emissions. Keep that in mind as you ponder how this works.
Okay.. that’s the show. Hopefully you weren’t bored by the post.
OT side note for the true purveyors of arcane bits of knowledge.
Refer back to the Tropopause graphic. Notice anything interesting about it? Hint: Earth’s aphelion is in the first week of July. Thats the furthest point of our orbit. Perihelion, or the closest we get to the Sun is in the first week of January.
Now notice the tropopause heights at each time of the year. In January, the equatorial regions swell quite a bit, and then this flattens towards the poles in mid-year, around July. At that point, the poles are more inflated than during perihelion.
Essentially, the orbit of the Earth drives an oscillation in the atmospheric thickness.
No reason to note it other than it’s quite cool to see it plotted out.
“Stratospheric Loading of Sulfur from Explosive Volcanic Eruptions” Bluth et al (1997)
“Late Cenozoic magmatism of the Bolivian Altiplano” Davidson et al (1995)
Sajama Ice Core Data