An explosion from Japan’s Sakurajima caught via webcam – you can see blocks from the explosion hitting the slopes of the volcano (small, grey spots). Image from July 24, 2012 courtesy of the Japanese Ministry of Land, Infrastructure, Transport and Tourism.
Very brief post today, but I wanted to share the video of yesterday’s eruption of Sakurajima. Regular readers of this blog will know that Sakurajima is almost always erupting, usually in the form of small explosions from one of the craters (Minami-dake and Showa). However, occasionally things get a little noisier at the restless volcano – and over the last few days, the explosions were especially impressive, sending ash to Kagoshima, located across the aptly-named Kagoshima Bay. Some of the plumes from these explosions reached as high as ~6 km / 20,000 feet.
You can watch the video of some of the explosions here – and it shows some impressive shockwaves caused by the explosions at the vent (however, I am a little frustrated that they decided to speed up the eruptive action). There is also a great compilation of timelapse video from the volcano over the last few days (courtesy of Eruptions reader Sherine). Don’t forget, there are abundant webcams pointed at Sakurajima as well, so you can see some of this action as it happens.
It wasn’t too long ago that Galeras was the only show in town in Colombia. After Nevado del Ruiz settled from its eruptions during the 1980s, there wasn’t much other volcanic activity in the South American nation than the ever-active Galeras near Pasto. However, now it seems that more volcanoes are getting the attention of the INGEOMINAS (the Colombian Geological Survey). With all this news of Colombian volcanoes, I thought I’d offer a brief tour of the action. Remember, Colombia has a few dozen potentially active volcanoes, so this activity shouldn’t be too surprising. You can check out this page to see what each of the INGEOMINAS alert status mean.
A webcam capture of the June 30, 2012 eruption of Nevado del Ruiz in Colombia. Most of the volcano is obscured by clouds, but the grey-brown ash plume spread ash across the countryside. Image courtesy of INGEOMINAS.
Machín, a neighbor of Ruiz, has also seen elevated levels of seismicity over the past few years. Nothing has occurred beyond earthquakes that suggest rock fracturing that could be hydrothermal or magma movement under the volcano. Machín hasn’t erupted in over 1100 years and not much is known about the dome complex that sits within a 3-km caldera. INGEOMINAS currently has the volcano at Yellow Alert III due to the continued seismicity.
Huila
After over 450 years of quiet, Nevado del Huila came back to life in 2008 with a series of small explosions that has produced ash falls, lahars and lava domes at the summit of the volcano (totally a VEI 3 eruption so far). The eruption is considered to be ongoing, although right now the volcano is merely steaming from fumaroles at the summit and experienced tens to hundreds of small earthquakes each week. Huila currently sits at Yellow Alert III.
The steaming summit of Cumbal seen on August 1, 2010. Fumarolic activity such as this is common at Cumbal, but increased seismicity has prompted an increase in the alert level. Image courtesy of INGEOMINAS.
Cumbal
The latest volcano to join the parade of elevated activity is Cumbal (see above), a composite volcano that last erupted in 1926. A report that was issued yesterday (July 11) from INGEOMINAS has raised the alert status to Yellow Alert III after noticing increases in earthquake swarms under the volcano, along with an increase in the temperature of fumaroles at the summit of Cumbal. There has also been reports of noises coming from the volcano in the past few week as well. Much like Machín, not much is known about Cumbal, with only one other known eruption (in 1877). However, Cumbal has rumbled before without producing any eruption.
Sotará
Even less is known about Sotará, a small volcano near Popayán. There have been no known historic eruptions of Sotará, however in late June, seismometers recorded a swarm of over 900 small earthquakes under the volcano. INGEOMINAS did not raise the alert status for Sotará after the swarm, and the swarm seems to be very transitory in nature – not much activity before and after the June 30 swarm.
Galeras
The southernmost volcano in Colombia, Galeras continues to sit at Yellow Alert III. The volcano has not been as eruptively active over the last few months than in recent years, but seismicity continues as does sulfur dioxide emissions. INGEOMINAS describes the current activity as “a reflection of an evolving process that initiated mainly by the intrusion of magmatic material that began to emerge in mid-March 2012″ – that suggests a period of slow dome growth at Galeras right now.
Does all this activity mean that volcanism is on the rise in Colombia? Probably not – in fact, this might be a great case on how increased volcano monitoring helps us become more aware of how restless volcanoes can be when they aren’t erupting or about to erupt. Many of the volcanoes on Yellow Alert III status, like Cumbal and Machin, are only experiencing earthquakes are no one on the surface would even notice. So before many of these volcanoes were wired with seismometers, they could have experienced activity like this and no one would notice. The same can be said for volcanoes worldwide – we can capture so much more subtle information about volcanic activity today than we could even 15 years ago. This can give that false impression that there is more volcanic activity, but rather, we’re just getting more information about what volcanoes do all the time.
Cleveland (background) and Carlisle (foreground) volcanoes in Alaska seen from an Alaska Airlines 737 in May 2012. Image by Cyrus Read, courtesy of AVO/USGS.
This is pretty much all that is going on in the Aleutians right now – Iliamna, another volcano that showed some restlessness earlier this year, has settled in a pattern of low-level (yet above background) seismicity that leaves it at Yellow alert status. However, the Aleutian’s northern Pacific cousins in Kamchatka are definitely keeping busy, especially Shiveluch, where the volcano has been producing frequent ~6-8 km / 20,000- to 26,000-foot plumes.
The ash-rich plume from Nevado del Ruiz in Colombia, seen on May 29, 2012. Image courtesy of INGEOMINAS.
I might have guessed that just after reading an article about how USGS geologist left Colombia this week after helping set up monitoring for Nevado del Ruiz that the volcano do something. Sure enough, today the volcano experienced a series of explosions that produced ash that fell on the city of Manizales, ~30 km from the volcano. The volcano had recently been lowered from Orange to Yellow status by INGEOMINAS, however a new earthquake swarm that started at 3 A.M. on Tuesday (May 29)prompted the return to an Orange alert, meaning an eruption in days to weeks. These new explosions are spreading ash in the region near Ruiz, but I have yet to see any information about the nature of the ash – is it juvenile (new) magma or just pulverized rock fragments caused by increasingly intense steam explosions at the summit. If it is juvenile, then we might be seeing magma reaching the surface at Ruiz, with this morning’s earthquakes being the precursor signs of the magma on the move.
UPDATED MAY 30
MSNBC posted some video of the ash fall near Ruiz – looks to be a few millimeters to a centimeter in some parts of Manizales. The video also mentions that the plume reached ~1 km. The latest INGEOMINAS update mentions that the volcano is experiencing constant tremor, similar to what occurred during the 1985 and 1989 eruptive periods, however INGEOMINAS director Marta Calvache reported that ash emissions were down this morning. It seems that the webcams for Nevado del Ruiz are only intermittently working, but the webicorder shows just how much tremor the volcano is feeling right now. You can also seen how prominent the sulfur dioxide emissions from Ruiz were on Sunday (May 27), two days before these new explosions.
The explosions have put enough ash into the skies to prompt the closure of airports in Manizales, Armenia (~60 km) and Pereira (~40 km – and my mother’s home town). Government officials have also issued evacuation orders for 500 people living near the volcano as part of the first level of response to an eruption at Ruiz. Dust masks are also beginning to be distributed to local residents as well.
There are three INGEOMINAS webcams pointed at Nevado del Ruiz, so you can check them out when conditions are right to see what the volcano might be doing.
3D bathymetric view of Monowai caldera in the Kermadec Islands. The red cone in the foreground is Monowai cone. You can see the scars of collapses on its slopes along with new domes near the summit. Image courtesy of Oregon State University by Susan Merle.
I saw (and was sent) a lot of articles about the findings from Anthony Watts and others in Nature Geosciences on the submarine volcanism in the Kermadec Islands north of New Zealand. A group of geologists were lucky enough to stumble across an eruption of Monowai in 2011 and in doing so, they set off a series of discoveries that seem to indicate that Monowai is a very active submarine volcano. Monowai is a fairly complex caldera volcano that has seen quite a bit of activity that has been captured either through subsurface acoustics or by finding the telltale signs of an eruption beneath the sea – discolored, bubbling water, pumice rafts – stuff like what we saw during last year’s activity at El Hierro. Watts and his collaborators were able to carefully map the volcano to find what the changes at Monowai have been during these eruptive periods and it boils down to something we find familiar for terrestrial volcanoes: collapse and healing, sometimes quite rapidly.
If you’re a close watcher of volcanic activity, you know that if a volcano erupts andesite, dacite to rhyolite, you can produce sticky domes of lava that can oversteepen and collapse. That is what happens on a regular basis at places like Soufriere Hills on Montserrat and Shiveluch in Kamchatka (amongst many others). These domes or spins can become incredibly impressive – the spine that formed at Pelee in Martinique in 1902-1903 was almost 300 meters tall and it eventually collapsed in 1903. However, these examples are all from terrestrial volcanoes.
Figures 6a and 6b from Watts et al. (2012) showing the changes in the shape of Monowai in the Kermadec Islands over the last 8 years. You can see the growth and destruction of domes and spines on the volcano across the years.
This new study at Monowai may have captured a collapse like this, followed by new growth of a dome at a submarine volcano. Over the course of 14 days of mapping, the team found that the seafloor depth changed, first dropping almost 19 meters, then surging back almost 72 meters. That is quite a dramatic shift for only 2 weeks. This activity coincided with earthquake activity at Monowai was well, so even though the eruption was seen, the clues of changing seafloor depth – possibly a collapse followed by new lava – and seismicity all point to eruptive activity. If you look at their vertically-exaggerated views of the seamount (Figure 6a and b, above), it becomes quite clear that domes or spines of lava come and go from the summit area of Monowai, just like you might seen at its terrestrial brethren. Now, these cycles had been recognized at Monowai before, but this is the first time that the results of an eruption was caught in the act.
One of the implications that the authors push in the article is that these rates of activity are very rapid – and surely they are. The estimates of ~0.001-0.008 km3 of new material erupting within a few weeks – that works out to annual eruptive rates of ~0.11-0.63 km3*. I do worry a bit about their comparision of average growth rates at global volcanoes with these data, even looking at the last few years are Monowai. Volcanoes are notoriously inconsistent with their growth and have periods of heightened activity that punctuate long periods of low activity – they even point this out by comparing the average growth rate between 2007-2011 (0.08 km3) versus the rate they observed in the two weeks in 2011 (which would have produced, if constant over 4 years, ~2.8 km3). Whether or not “growth rates at Monowai are larger than all other oceanic volcanoes, including Montserrat, Azores, Hawaii, Iceland and the Canary Islands” is truly significant and not merely a product of small sample sizes we have for the volcanic history of many submarine volcanoes is unclear. However, it does show how dynamic some submarine arc volcanoes might be, which should come as little surprise considering the mischief their terrestrial counterparts can produce.
*Note: A few readers wondered why certain articles on this study insisted on reporting all volumes as “Olympic size swimming pools” of lava. Beats me, honestly. I know some writers love those comparators, but maybe we can give the reading audience some credit after you mention the comparison once.
The plume from Popocatépetl in Mexico seen on May 6, 2012. Webcam capture by Eruptions reader Kirby.
Quick updates on current activity at a number of volcanoes while I am mired in grading jail:
Popocatépetl: The Mexican volcano is still churning away (see above). Thus far, most of the activity has been subplinian plumes from the crater area as the new magma rises and fragments, but Mexican officials are not taking any chances. They will be distributing almost half a million dust masks to people living near the volcano if/when a larger explosive eruption occurs that could drop significant ash across much of the area. You can see what is going on at Popocatépetl on the CENAPRED webcams for the volcano.
Iliamna: We haven’t heard much from Iliamna in the past month or so after the volcano was downgraded to Yellow Alert status by AVO after a period of increased seismicity and degassing. The seismicity was reported to be back on the upswing at the end of last week according to the Alaska Dispatch (who looks to be getting into the game of webicorder watching). However, this blip (if real) didn’t cause AVO to change the status of Iliamna as the latest update just mentions seismicity at the volcano is “slightly above background”. Iliamna has a webcam as well as a webicorder so you can follow along at home.
Lokon-Empung: Another volcano that has been quite active is Lokon-Empung in Indonesia. Thevolcano had an explosive eruption earlier last week, producing a 2.5 km / 8,200 foot plume. Although evacuations have not been called yet, the National Disaster Mitigation Agency (BNPB) has begun to set up evacuation centers in case the activity increases. Seismicity has been increasing at Lokon-Empung since last week’s eruption, but the alert status (Level III) is unchanged.
Slight discoloration of the sea at Fukutoku-Okanoba (bottom right) may suggest eruptive activity. Image taken April 19, 2012 by the Japanese Coast Guard.
The Moon: Really, it is your friend. Image courtesy of NASA.
{This article was originally posted on March 11, 2011. I’ve reposted it today because of another so-called “Supermoon” on May 6, 2012}
I’ve had a number of questions lately about a couple of events coming up this month astronomically and how they might effect geologic events – namely earthquakes and volcanoes – on Earth. I can tell you right now, without much doubt, that the answer, even before I tell you the question, is very, very little.
Now, the questions: (1) How will the close passage of Comet Elenin and Earth cause geologic catastrophes on March 15 and (2) How will the so-called “Supermoon“, a full moon when the moon is closest to Earth in its orbit, cause geologic catastrophes?
I know there has long been a desire to show about the gravitational resonance of planets/comets/asteroids/the sun might play a role in Earth’s geologic activity – and with some logic. We see the interaction of the Earth’s surface with the Moon’s gravity (and to some extent the Sun’s) with the tides in the oceans. Water has low viscosity so the tidal tugging of the moon as it rotates around the Earth sloshes the oceans back and forth to create our tides. One could imagine that the Earth’s crust/mantle/core might feel some of that gravitational interaction as well – and they do. John Vidale, a seismologist at the University of Washington, mentions that during full and new moons – when the moon is oriented between or opposite the Earth and the sun – there is potentially as much as a 1% increase in earthquake activity worldwide (and a slightly higher effect on volcanic activity). Let me repeat that: 1%. In any natural, geologic process that is mostly distributed randomly through time like earthquakes, 1% or there about is well within the “noise” of processes, so would these alignments produce much of a discernable increase? Probably not and this is with the two bodies that play the largest role in tidal forcing on Earth. There are other studies that suggest that this tidal tugging and pulling can cause small shifts in fault systems like the San Andreas, but one might argue that the moon is, in fact, “passively” releasing seismic energy on the fault, thus preventing or delaying large earthquakes! Trying to say that any other astronomical body might, even in some specific alignment, might cause more than a 1% increase in the chance of activity is remote at best.
Some of the so-called evidence for this moon-earthquake relationship is specious at best. From aNational Geographic article on the “lunar connection” back in 2005: “At least two major quakes may support [James A.] Berkland’s theory. The December 26, 2004, magnitude 9.1 in Sumatra, Indonesia, occurred on the day of a full moon. Likewise, the March 27, 1964, magnitude 9.2 earthquake in Alaska occurred on the day of maximum high tide. According to Berkland, such correlations are more than coincidences. They demonstrate a true connection between the moon and earthquake activity.” First off, two earthquakes coinciding with full moons is hardly scientific, statistically-sound evidence. How many “large” earthquakes (and who defines that anyway?) occur when it isn’t a full moon? And how many full moons have we had when there wasn’t a “large” earthquake? I’ve said this before, but it is an easy trap – correlation does not mean causation. Full moons happen 12 (maybe 13) times a year, so if you randomly sprinkle earthquakes through time, many large ones are bound to coincide with the full moon. USGS seismologist Dr. John Bellini followed up on Berkland’s theories: “Bellini questioned the scientific validity of Berkland’s predictions. He said they appear to be “self-selected statistical analysis of historical seismicity rates and are so vague in time and location that they are certain to be correct.”
Now, as for the Moon’s relative position to Earth and its effect, the Moon when it is at least closest is 356,401 km from the Earth’s surface and at its furthest, it is 406,700 km (with an average distance of 384,401 km. That is a difference of ~50,300 km ~ in other words, when the Moon is closest to Earth, it is ~12% closer than it is at its furthest. Newtonian physics tells us that the attraction between the Earth and the Moon is dictated by F = GM1M2/R2, where M1 and M2 are the masses of the Earth and Moon, G is the gravitational constant and R is the distance between the two bodies. Even a ~12% change in that value means that the force of gravity, in Newtons, only changes by ~30% at maximum (and only ~11% difference from average), a change that happens gradually as the Moon moves around its orbit. We see this fairly small change with different sized tides, but even those changes are not “disastrous”. When you consider the energy needed to move tectonic plates (or even the oceans), this change in gravitational energy from the Earth-Moon system is small. Remember, that the Moon is at its closest once a month, so just because it happens during a full moon doesn’t mean that the gravitational pull from the Moon is any stronger than it would be at any other perigee. Remember, the Moon reaches perigee every month and you don’t see massive earthquakes and eruptions every time this happens.
Some planetary bodies do see a profound effect of tidal forces. The moons of Jupiter areconstantly being tugged by the high gravity of Jupiter as the whiz around the gas giant. You can see that constant, frictional energy being imparted on the rocks of the moons in the relative geologic activity on the Galilean satellites – closest to Jupiter lies Io (at ~420,000 km), the most volcanically active body in the solar system. It gets tugged by a force 300% more than the Moon pulls on Earth. Next comes Europa (at ~664,000 km), where there are suggestions that liquid or slushy subsurface water exists due to tidal heating. Ganymede and Callisto, even further from Jupiter, show much fewer signs of liquid water or extensive tidal heating. The gravity of Jupiter is the direct cause for the geologic activity on these small planetary bodies.
The lava flow from the Kamoamoa Fissure snaking around an old crater on Kilauea, as seen on March 10, 2011. This eruption did not start during a full/new moon. Image courtesy of HVO/USGS.
As I mentioned before, this sort of “correlation” of astronomical alignments and geologic disasters have been predicted before – with results that were coincidental at best. Back in 2006, there was rampant speculation about how a full moon was going to trigger an eruption of Mayon in the Philippines … and it didn’t. In a USGS article about volcanoes and the moon, they make the point that it does appear that activity at some volcanoes, like Kilauea, are effected by lunar cycles – however, this does not mean that an eruption at any specific volcano worldwide can be predicted using lunar cycles. There are just too many other variables, so unless the volcano is already erupting, such as Kilauea (see above from an eruption that didn’t start on a new/full moon), don’t expect the Moon to bring volcanoes to life. Even if the volcano is predisposed to be close to eruption (and even defining that is difficult), there is no data to support this (to borrow a quote from a paper that Chris Rowan’s uses in a post on the subject): “We found no conclusive evidence for a general correlation between volcanic activity and lunar tidal phase. This result is consistent with recent work which indicates that diurnal and fortnightly tidal stresses may be too short-lived and strain rates too high to effect a significant viscous response in partially molten regions of the Earth’s subsurface.” (Mason et al., 2004). During this Mayon hype in 2006, Phil Plait also took on these predictions and points out the biggest flaw with many of these “correlations”: “It’s small number statistics, like flipping a coin three times and having it come up heads each time. It’s rare, but it does happen on average one out of every eight times. You need bigger samples to get good statistics.”Science requires data that can show a valid correlation, not picking what fits best to your ideas. UPDATE: Phil takes on the “Supermoon” as well.
If anything, we should be concentrating on terrestrial forcing for “predicting” earthquakes. It could be that changes in the strength of the Earth’s magnetic field, due to the thickness and composition of the Earth, but might help find earthquake-prone locations. A study in Science by Song and Simons from 2003examined the gravity anomaly (how much the gravitational field from the Earth varies from the norm) along a subduction and then compared it to a long historical record of seismicity. It found that “within a given subduction zone, areas with negative gravity anomalies correlated with increased large earthquake activity. Areas with relatively high gravity anomalies experienced fewer large earthquakes.” However, how we can use the changes in gravity anomaly to predict earthquakes is still very unclear.
So, what can we take away from all this?
The Moon plays a very small role in increasing seismicity and volcanic activity on Earth – potentially increasing activity ~1% during full/new moons.
The change in the gravitational pull from the Moon during apogee and perigee is small.
Beyond this, there is no statistically-sound evidence that geologic disasters can be predicted based on lunar alignments or distance (or any other astronomical phenomena).
The keys to understanding how to predict earthquakes or eruptions (if at all possible) lie within the Earth, not deep in space.
From Chris Rowan: “The moon does not magically load up plate boundary faults or fill magma chambers … The most the moon can do is slightly alter the timing of an earthquake or eruption that was on the verge of happening anyway.”
Merapi in Indonesia seen on December 7, 2011. Image from Yudha Aria / Flickr.
I did want to pass along this piece of news I saw this morning on Merapi in Indonesia. Dr. Masako Iguchi from the Disaster Prevention Research Institute at Kyoto University has been studying deformation at Indonesian volcanoes using GPS for the past two years, specifically targeting Merapi, Sinabung and Guntur. Of those three, it looks like Merapi has already entered in a cycle of inflation after the impressive (and deadly) eruptions of 2010. Sadly, the article in the Jakarta Post does not offer any sense of magnitude of the inflation, but Dr. Iguchi does say that Merapi appears to experience rapid inflation before a new eruptive cycle begins. In other Merapi news, Gadjah Mada University (UGM) and the National Space and Aviation Agency (Lapan) released images of the summit area of Merapi taken by a styrofoam drone – one of the first uses of drones to image active volcanoes that I’ve seen. The images from the drone that feel ~400 meters above the summit will be used to create a 3D map of the volcano. I’ll keep my eyes peeled for more news on Merapi.
The small steam plume from Nevado del Ruiz, seen on March 27, 2012. Image from INGEOMINAS Colombia.
Some news brought to my attention by Eruptions reader Sherine merited a quick Saturday post. Thedeveloping volcanic crisis at Nevado del Ruiz in Colombia looks like it is continuing to escalate. INGEOMINAS, the Colombian geological survey, released a “special bulletin” this afternoon elevating the alert status at Nevado del Ruiz to Orange Level (II). This means that the signs of activity at the volcano suggest that an eruption is likely in the days to weeks timescale. Marta Calvache from INGEOMINASmentioed that over the past few days the volcano has experienced tremor related to “fluid motion” (likely magma), rock fracture earthquakes at the summit have been increasing in pulses and sulfur dioxide emissions continue to be high.
So far, INGEOMINAS thinks any potentially eruption will be smaller than the activity seen during Ruiz’slast eruptive period between 1985-1989. The major hazard from Ruiz is the lahars that can be generatedas ash and other volcanic material mix with melted snow and ice at the summit. There is also the potential for ash fall (especially hazardous for those with respiratory problems) on towns and cities in the area, including Manizalez and Pereira, both of which are less than 50 km from the volcano, and Bogotá, only ~120 km from Ruiz. If you live in the area around Ruiz, be sure to examine the INGEOMINAS volcanic hazard map to see the places with the highest probability of lahars and pyroclastic flows. Taking a look at the INGEOMINAS Azufrado webcam for Ruiz, a plume can be seen coming from the summit area (see below) while the webicorder shows the increasing seismicity as well. You can also get a glimpse of the volcano from an INGEOMINAS webcam in Manizalez.
Webcam capture from March 31, 2012 showing a small plume from Nevado del Ruiz in Colombia.
The plume from a lateral blast at Pinatubo in the Philippines seen on June 15, 1991. The eruption may have helped stifle hurricane activity in the Atlantic for three years afterwards.
We have had many discussions over the years here on Eruptions about the relationship betweenvolcanic eruptions and weather/climate (remember, they are different things). Most of the time, the concern is how weather will become worse (i.e., much colder or much hotter) due to volcanic aerosols or ash that are kicked high into the atmosphere during large eruptions. Remember, ash plumes from manyplinian eruptions can tower over 35-50 km up, so material can be injected into the upper atmosphere and spread around the world in a matter of weeks. It would be very surprising if these sorts of eruptions – which are relatively rare, only occurring maybe once or twice a decade – didn’t effect weather and climate for years until the aerosols can all settle out.
So, I was quite interested when I saw a new paper in the Journal of Geophysical Research titled “Atlantic hurricane activity following two major volcanic eruptions” by Amato Evan. My instant thought was I actually wasn’t sure what to expect – I mean, how would a large eruption effect the activity of such major, hemisphere-spanning events like hurricanes? Would it make hurricanes worse? As it turns out, this study suggests that major eruptions in the tropics (or close) might actually subdue Atlantic hurricane activity for years after the eruption.
Figure 2B from Evan (2012) showing the drops in sea surface temperature (SST) in the Atlantic after the eruptions of El Chichón (1982) and Pinatubo (1991)
Evan (2012) looks at two eruptions in particular – the1982 eruption of El Chichónin Mexico and the 1991 eruption of Pinatubo* in the Philippines. Both were large eruptions, ranking as VEI 5-6. Both eruptions injected large volumes of aerosols and ash into the upper atmosphere in the tropics, reducing theoptical depth of the atmosphere to 0.1-0.2 (normally it should be closer to 0.01). To give you an idea, that is almost as bad as other large eruptions such as Krakatau in 1883, famous for the vibrant skies it produced worldwide. All these aerosols in the atmosphere increase the albedo of the planet – that is, the planet will reflect more sunlight back into space. This means less sunlight hitting the surface of the Earth, and in particular, less on the oceans in the tropics. This produces colder surface and near-surface waters in what is called the Atlantic Main Development Region (MDR) for hurricanes – between 8-20°N/20-65°W (see right). This decrease in sea surface temperature, in turn, lead to an increase in vertical wind shear in the MDR.
What Evan (2012) found was that the total number of hurricanes in the three years before each eruption and three years after the eruption were markedly different – ~12 per season prior to the eruption and 6-8 per season after the eruption. Not only that, but the storms in the three years after the eruption were weaker and didn’t last as long as prior to the eruption. Even beyond this, the location that hurricanes formed changed as well, where before the eruptions most hurricanes were found in the MDR, after the eruptions there were dominantly found along the eastern United States. So, the long and short becomes large volcanic eruption leads to lower sea surface temperatures and higher vertical wind shear in the locations where hurricanes form, thus fewer hurricanes occur and those that do are weaker.
Now, bear in mind, this study only looked at two major eruptions in the last 35 years – and unfortunately both coincided with an El Niño, so one can’t conclusively link the eruptions and the change in hurricane activity. Evan (2012) mentions that there are at least three other major eruptions that could effect hurricane activity – Agung in 1963**, Santa Maria in 1902 and Krakatau in 1883. However, no pattern emerges from these eruptions as hurricane activity did decrease after Krakatau, it wasn’t effected by Santa Maria and appeared to increase after Agung. Evan (2012) suggests that the Agung eruption might have cooled the South Atlantic preferentially, causing the increase in North Atlantic hurricane activity.
Hurricane Irene off of Cuba and Florida, seen on August 24, 2011. Can volcanic eruptions help or hinder hurricane activity? It is still unclear.
Clearly, there is still a lot of noise in these correlations of hurricane activity and volcanic eruptions. The eruptions that Evan (2012) examined are the big ones – so, what if any effect would smaller eruptions in the tropics have (such as Merapi in 2010 or Nabro in 2011). Taking a look at the hurricane counts for the past century, you can see a number of periods of lower hurricane activity – can these all be correlated with eruptions like Katmai in 1912 (well out of the tropics) and what is causing the low hurricane counts in 2005-08? There are many unanswered questions here – but clearly, a closer examination looks to be in order – or, as the author of the paper suggests, maybe we need a large eruption in the tropics to test this theory out.
* Lockwood and Hazlett (2010) note that a typhoon/hurricane might have helped cause the cataclysmic eruption of Pinatubo in 1991. The lowest atmosphere pressure from the Typhoon Yunya passed over Pinatubo just 3 hours before the largest eruption. It likely didn’t cause the eruption (that was an injection of magma into the system over the prior few weeks), but it could have played a role in pushing the volcano pass the “tipping point” for an eruption.
** This eruption is listed in the paper as 1964, but the activity lasted from February 1963 to January 1964.
{Hat tip to Alex Witze for pointing out this article to me.}
Image 1: Pinatubo erupting in 1991. Image by Richard Hoblitt/USGS
Image 2: Figure 2B from Evan (2012), Journal of Geophysical Research
Image 3: Hurricane Irene in 2011. Image from the NASA Earth Observatory.
