Looking backward: Past eruptions at Volcán Santa Maria

On our way to visit the Santiaguito Volcano Observatory, Gustavo Chigna of INSIVUMEH (the Guatemalan equivalent of the USGS) was kind enough to take an afternoon off and show us some of the older deposits near Santiaguito. Our first stops were at an exposure of the air-fall deposit from the October 24, 1902 eruption of Volcán Santa Maria. This eruption was a devastating one, stripping the land for more than 50 km around the volcano, burying villages and fincas (plantations) in more than 3 meters of ash, mud and rock, and killing more than 7,000 people (the exact number will probably never be known). The area had already experienced months of earthquakes prior to the eruption, and activity at the crater formed in Santa Maria continued for weeks afterward.

This location is about 4 km from the volcano. The 1902 air-fall deposit here is more than 2 meters thick (the photo is only showing the top bit, and Gustavo is standing a few meters behind the outcrop, so the sense of scale is a bit wonky. The big clast in the center is about fist-sized, though.). This fall deposit contains a mix of lithics (old and new lava and country rock) and pumice, and what's really impressive is that many of the lithics are the same size as the pumice (up to 15 cm). Generally, in a fall deposit the material will have had the same terminal velocity, which means the mass of the pumice and lithics should be roughly equal. Because pumice is much less dense than lithics, this usually means that the lithics are much smaller than the pumice. Possibly the lack of difference in clast sizes here has to do with the proximity to the volcano; in other places that we stopped, the pumices were definitely larger than the lithics.

The view from this location was pretty spectacular, and it highlighted the deposits from the November 2, 1929 dome collapse. Here you can just see the summit of Santa Maria, and the El Brujo and other domes in front of it. Brujo is the dark green dome farthest to the left, and the hummocky low hills in front of it are may be the result of that 1929 collapse. Hummocks are a classic sign of a debris avalanche of some sort, and can be seen in places like Mount St. Helens and Mount Shasta. ***Note: After speaking with Rudiger Escobar, a Santiaguito expert and fellow volcanologist (see the comments section), I wanted to note that the hills pictured here probably have more to do with lava flows coming off of Brujo than older collapse deposits, although some portion of them may be collapse remnants. It's also possible that I have faulty notes, as the conversation was mostly being conducted in Spanish at the time, and my Spanish skills are limited. 

After a bit of backroad driving around the fincas, we reached the Rio Tambor, which was the site of many deaths in the 1929 dome collapse. The 1929 event, in which more than 3 million cubic meters of the lava dome collapsed, was mostly described by foreign geologists who interviewed survivors. Their accounts tell of glowing rains of ash and rock; boiling mudflows in the rivers covered with rafts of glowing rock; a blast that rushed back toward the volcano after it blew down the river valleys, scouring the south side of tree trunks; and people suffocating on gases and hot air. More than 3,000 people were killed, mainly because they were on the fincas for a religious holiday rather than in their villages. Sadly enough, this was a very  minor dome collapse by volcanology standards (a large one might be in the hundreds of millions of cubic meters, such as those at Soufriere Hills on Montserrat).

The coffee plantations that were destroyed in 1929 are no longer here, but the new ones are beginning to encroach. Frankly, I'm not sure I'd want to spend my days working in an area where there are outcrops like this:

These photos are looking east across the Tambor at a mudplain created by lahars, and at the 1902 deposit (the white strip at the base of the cliff) overlain by block-and-ash flow and lahar (volcanic mudflow) deposits. Here the 1902 deposit is about 2 meters thick, and overlain by a thinner gray ashy deposit (perhaps from the 1929 collapse, although it hasn't been well studied and it wasn't clear if that guess was right). The upper blocky deposits are probably post-1929, and consist of a mix of lahar and block-and-ash (pyroclastic flow) leavings.

It was a bit difficult to get a scale into this picture, but the cliff is about 10 meters high, and the bigger boulders at the base are roughly the size of me. This is an interesting photo because it shows a very distinct division between two deposits. What we ended up discussing at this site was what kind of deposits these were, and how to tell them apart. Both block-and-ash flow deposits and lahar deposits look similar at first glance: very poorly sorted, with a clast size range from ash (< 2 mm, in the matrix) to boulders (> 25 cm, supported by the matrix). Both deposits are matrix-supported and both have a bit of a mix of angular and rounded clasts.

So how to tell them apart? One clue might be the angularity of the clasts; block-and-ash flows tend to be a bit more violent in terms of knocking rocks around, and they're dry, which means no muddy cushion for the rocks like a lahar might provide. But what happens if the block-and-ash flow goes down a river (like here)? It could become a lahar, which brings up all sorts of messy discussion about naming conventions. A better indicator of a block-and-ash flow would be the lithology of its clasts; lahars will pick up anything in their path and tend to have a big mix of rock types, while block-and-ash flows tend to be monolithological. Again, however, if a block-and-ash flow travels far enough, it may pick up enough clasts from other places to confuse this.

As it turns out, there is one sure indicator that you've got a lahar deposit, and it's not always easy to find (or present). Because a lahar is a wet flow, it will contain bubbles. When the lahar stops, sometimes those bubbles are unable to rise through the muddy liquid and are trapped; when the deposit dries out, the bubbles leave little spherical cavities in the fine-grained matrix. These are really hard to see and it's easy to debate what you're seeing if you're not sure.

So what was the verdict for these deposits? Based on a bit of arguing discussion, we decided that we were fairly sure we saw bubbles in the lower deposit, but that the upper one had more indicators of a block-and-ash flow deposit. So at this outcrop, we have about 4-5 meters of visible lahar deposits overlain by about 5-6 meters of block-and-ash flow deposits. Needless to say, this would not have been a fun place to have been standing for either event. In fact, Gustavo mentioned that very few people will come down to this area after dark, because some of the victims of the 1929 collapse are thought to haunt the riverbed. Having been down there in the evening, I can attest that it does get a little creepy when it's dark, and it would certainly be easy to turn the jungle sounds into the moaning or wailing of ghosts. Better not to stay there too long, ghosts or no ghosts; it is a channel filled with lahar deposits, after all.

Dome collapses

In light of the recent dome collapse at Soufriere Hills, I thought I'd expound a little on the subject, which is a major part of my research. Lava domes, if they last long enough, tend to go through cycles of growth and collapse. These can be relatively short, like the domes at Soufriere Hills or Mt. St. Helens (remember, a few years is short even on a volcanic timescale), or long, like at Casita volcano in Nicaragua or my own study area of Santiaguito. The collapses vary in volume: a smallish collapse might comprise a few million cubic meters of material (the 1929 collapse at Santiaguito was about 3 million cubic meters), but the collapse of an entire dome might be in the 100s of millions of cubic meters. 


There are a number of reasons why domes collapse. One is gravity; domes can grow on steep slopes or overspill summit craters, which means that parts of them can become very unstable and simply collapse because of their own weight. Another trigger might be an earthquake, which can shake loose dome rock; yet another trigger might be an eruption, which could loosen or even blow up significant portions of a dome. (This could be what happened at Soufriere Hills; there have been some pretty spectacular Vulcanian eruptions going on at the same time as dome-building there.)


My research, however, focuses on how water can cause dome collapses over short and long timescales.  In the short term, intense precipitation events (large storms or hurricanes) have been known to cause domes to collapse (especially at Soufriere Hills). This likely has something to do with water saturating the domes to the point where it can penetrate deep into hot dome rock, and either a) sealing in magmatic gases or b) sealing itself in and vaporizing in cracks and fractures. Either way means that pressure builds up in the dome and water can lubricate structural breaks, which reduce the stability of the dome. In the long term, a dome with an active and well-supplied hydrothermal system can form lots of clays, which are very weak and can also trap water. (Some clays even swell when they absorb water, which pushes dome rock around and destabilizes it that way.) This seems to be what happened when some old domes at Casita Volcano in Nicaragua collapsed and formed a devastating lahar, or mudflow of volcanic material.


What I intend to focus on at Santiaguito is why the domes there haven't experienced any major collapses in the 80 years they've been growing, and what part of the complex might be most likely to fail if a collapse did occur. This is going to involve looking at water-dome interaction in both the short and long term; I'm mixing in hydrology and clay mineralogy with my volcanology, and on this trip I hope to collect clay samples from the inactive domes in the complex. (I am not going anywhere near Caliente, the erupting dome, if I can help it; those videos of people standing on the rim during eruptions are just insane. I've met people who were at Galeras when it erupted in 1993, and I've heard enough about what can happen that I have no intention of putting myself in that kind of danger.)


Further Reading:



Barclay, J., Johnstone, J.E. and Matthews, A.J., 2006. Meteorological monitoring of an active volcano: Implications for eruption prediction. Journal of Volcanology and Geothermal Research, 150(4): 339-358.

Calder, E.S., Luckett, R., Sparks, R.S.J. and Voight, B., 2002. Mechanisms of lava dome instability and generation of rockfalls and pyroclastic flows at Soufriere Hills Volcano, Montserrat. Geological Society, London, Memoirs, 21(1): 173-190.

Elsworth, D., Voight, B., Thompson, G. and Young, S.R., 2004. Thermal-hydrologic mechanism for rainfall-triggered collapse of lava domes. Geology, 32(11): 969-972.

Fink, J.H. and Anderson, S.W., 2000. Lava domes and coulees. In: H. Sigurdsson, B.F. Houghton, S.R. McNutt, H. Rymer and J. Stix (Editors), Encyclopedia of Volcanoes. Academic Press, San Diego, California, pp. 307-319.

Harris, A.J.L., Rose, W.I. and Flynn, L.P., 2003. Temporal trends in lava dome extrusion at Santiaguito 1922-2000. Bulletin of Volcanology, 65(2-3): 77-89.

Matthews, A.J. et al., 2002. Rainfall-induced volcanic activity on Montserrat. Geophysical Research Letters, 29(13): 1644-1647.

Sapper, K. and Termer, F., 1930. Der Ausbruch des Vulkans Santa María in Guatemala vom 2-4 November 1929. Zeitschrift für Vulkanologie, 13: 73-100.

Sheridan, M.F. et al., 1999. Report on the October 30 1998 rockfall/debris avalanche and breakout flow of Casita volcano, Nicaragua, triggered by Hurricane Mitch. Landslide News, 12: 2-4.

Taron, J., Elsworth, D., Thompson, G. and Voight, B., 2007. Mechanisms for rainfall-concurrent lava dome collapses at Soufriere Hills Volcano, 2000-2002. Journal of Volcanology and Geothermal Research, 160(1-2): 195-209.

Voight, B. and Elsworth, D., 2000. Instability and collapse of hazardous gas-pressurized lava domes. Geophysical Research Letters, 27(1): 1-4.

Taking a volcano's temperature

While running through my RSS feed, I came across this National Geographic article about using thermal infrared imaging to monitor and forecast volcanic eruptions. I'm currently working on a project that involves using satellite imagery to detect and map hydrothermal alteration products in a volcanic dome, so I was definitely interested, especially because the scientists involved are using data from the same instrument that I am.

First, I have to give them props for using the term "forecast" rather than "predict". I know a number of volcanologists who are touchy about using "predict", because any conclusions about what a volcano may or may not do are necessarily based on probabilities, just like a weather forecast. When people start thinking that we can say for certain when a volcano will erupt, we get the blame when it doesn't, and they have to deal with the consequences of precautionary evacuations - or if it erupts sooner and takes everyone by surprise. It's very important that people know that no scientist can be 100% sure when a volcano will erupt and what it will do - voclanoes are simply too complicated.

I also like the bit about volcanologists being "courageous scientists". I suppose that even though we're very aware of the danger involved in our work, we don't really see ourselves as courageous. It's just another aspect of a job, and for the most part a calculated risk when we venture onto an active volcano to observe eruptions. That said, if there are alternative ways to get the same information with less risk of getting injured or killed (or having to spend an inordinate amount of time and effort getting to hard-to-reach places), I'm all for them.

Anyway, the article discusses how Michael Ramsey and Adam Carter of the University of Pittsburgh are using a combination of ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) satellite images and FLIR (Forward-Looking Infrared Radiometer) camera pictures to monitor active volcanoes on the Kamchatka peninsula. This area of Russia is of major concern to both volcanologists and the aviation industry, because there a number of airplane flight routes go directly over this area. Erupting stratovolcanoes can create ash plumes that rise up to 50 km, far above the normal crusing altitute of a jet. The worldwide Volcanic Ash Advisory Centers already keeps a watch on these volcanoes using the MODIS (Moderate Resolution Imaging Spectroradiometer) and TOMS (Total Ozone Mapping Spectrometer). MODIS detects the thermal signatures of eruptions, and TOMS detects the gases - usually SO2 - associated with plumes.

(ASTER image of Bezymianny volcano lava flow from NASA Visible Earth image archive)

Ramsay and Carter (together with U.S. scientists at the University of Alaska-Fairbanks and Russian experts at Kamchatka's Institute of Volcanology and Seismology) worked at Bezymianny volcano, using the FLIR to record temperature increases in the lava dome just days prior to an eruption. They were able to correlate their ground data with data from NASA's ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) instrument, which records several bands of thermal infrared data. This is particularly significant because it means that for volcanoes with fairly well defined thermal precursors to explosive eruptions, scientists can use satellites to monitor them, rather than traveling to remote locations with expensive, cumbersome equipment.

There are a few caveats. Any thermal satellite image records not only the temperature at any one time in a location, but the temperature history. Thermal emissivity varies with the amount of energy a surface absorbs, and with the rate that the surface re-emits that energy. Some surfaces absorb lots of energy but lose it quickly; some absorb energy and emit it slowly; others don't absorb much at all. All of this shows up in a thermal image, which should be treated more as a time exposure than a single snapshot. The article sums it up pretty well:

"Because the satellite images capture an average temperature reading for the entire volcano at a given moment, the scientists knew the reading in some areas was probably many times higher."

This must be taken into account when analyzing satellite data. A single "bright" ASTER image can mean that temperature increased suddenly, or that temperatures increased steadily over the course of hours or even days, depending on how quickly the lava's surface loses heat. Several images, taken hours or days apart, however, would prove very useful. Unfortunately, obtaining even one line of ASTER data - or data from any satellite that records in the thermal band - is expensive, and requires a special requisition process. Additionally, most thermal data comes from instruments on satellites that also serve other purposes; finding a way to dedicate any satellite entirely to recording thermal imagery of volcanoes would be difficult and expensive (again). Still, it would be extremely useful - and it's exciting research even without that.

The research is being partially supported by the National Geographic Society's Committee for Research and Exploration. A Bulletin of Volcanology article about their work can be found here.

How safe is too safe?

As many of our posts suggest (see A Carnival of Death-Defying Geologists), we can sometimes be a little lax in our safety standards. I have yet to meet a geologist who hasn't at least gotten sunburned or a little dehydrated on a long hike, or bashed a finger with a rock hammer, or spilled dilute HCl on themself in lab. Geology is not a particularly safe job, although we do take precautions to keep it from being truly life-threatening.

That said, when we're teaching it to young 'uns, exactly how stringent should those precautions be? Naturally, if I'm showing a bunch of third- or fourth- or fifth-graders how to identify limestone, I'm going to use vinegar instead of HCl, and make sure they (and I) are wearing those geeky-looking splash goggles because I KNOW they're going to get something in their eyes. Or if I'm out on a field trip with intro geo students, I'm not going to let them swing the hammer or stand near me when I'm trying to knock a hand sample off an outcrop. Common sense. You don't let little kids mess with something that could hurt them, and you don't let older "kids" do something until you're sure they know the proper technique.

One of my projects at the moment is to put together images for a publication where children "doing geoscience" are prominently featured. Because I work for a non-profit, we try to avoid purchasing images from stock photo sources if we already have something public domain or that the organization owns. Free images get used first, and often these have been recycled many times from past years' publications. So we're a little limited in what we can use, and the images can be kind of old. The main point is, we've used the images before, and we've gotten them from places like the USGS, NOAA, NASA, NRCS, USDA, and a hodgepodge of other official letter combinations. And those organizations have seen fit to publish the photos, and in the past, no one's complained about us using them.

Recently, one of the groups to which this particular publication goes (it's a yearly one) has told us that the images don't meet their safety standards, and they can't distribute the publication unless the images are changed or eliminated. Some of their concerns were valid - one person needed to be wearing splash goggles, for instance. But others went completely beyond the realms of reason. If the children were depicted outdoors, the image was unacceptable if they were not wearing long pants, long sleeves, hats and sunglasses (because they might be exposed to UV rays). If a child was collecting water from a stream, they were doing "chemical testing" and needed to be wearing gloves, boots, goggles, a HazMat suit, etc. If the children were anywhere near rocks or dirt and tools, they had to be wearing safety glasses and NOT touching the tools, because something might get in their eyes or they could scratch themselves and get an infection.

The changes, which they requested very late in the publishing process, would have required a great deal more work and money to make, and required us to either stage new photos, or buy them from stock photo sources. Not only that, but some of the same images had been used in previous years in publications that the group has distributed without complaint and without comment from their safety office. But suddenly, this year, the images are not acceptable.

The main point of the publication is to get kids interested in geoscience and get them outside. You know, in the sun and the dirt. I wonder what kind of images would have been acceptable - should we show children rolled in bubble wrap, covered in buckets of sunscreen and locked in a room with walls covered in undyed organic fabric made from non-GM cotton picked by free-range nuns? Sheesh. It's the same attitude that the "disinfect everything" cleaning products companies are espousing: protect the children from every possible danger, because god forbid we should let them develop immunities or common sense. When I was a kid (not very long ago), if I went outside and played in the dirt or climbed a tree or picked up rocks, I got a bath and some band-aids and maybe a little antibiotic cream afterwards, not a disinfecting routine worthy of a cleanroom airlock. If I tripped and fell while I was running, or scraped myself on a tree, or got dirt in my eyes at an excavation (later on in life), I learned from it.

There's a point when the Cover Your Ass attitude has to be balanced out by common sense. Yes, you can be sued if you don't let people know that you should wear goggles when using acid and someone's kid burns their eyeballs after copying your publication. But rejecting an image because there's a faint possibility that someone could interpret it a certain way and potentially do something dumb is just ridiculous. Wow, there's a kid sitting under a tree. If a storm comes along, he could get hit by lightning or a branch could fall on his head or he could be attacked by rabid squirrels or the tree could be cut down by a crazed chainsaw-wielding neighbor, so obviously we can't publish that photo. In fact, all photos of children near trees should be accompanied by a government warning that trees are highly unpredictable natural phenomena, and should be approached with extreme caution.

You can't plan for every idiotic thing that someone could potentially do. Naturally, you shouldn't take unnecessary risks, or let children do obviously stupid or dangerous things. But when you start saying that kids shouldn't be depicted running around in sunlight, or digging in the dirt, or wading in water at the beach, you're just being silly and alarmist. We can't raise a generation of people who have no idea how to handle themselves in the real, dirty, messy, natural world, because they'll just spend their lives inside. And you can't do geoscience from a bubble.

The group ultimately opted not to distribute the publication, which was just fine with us, since it saves us money and the hassle of printing X many thousands of copies. But it's a shame that thousands of teachers and students won't get to see a really great product that encourages them to embrace the geosciences, and get the darn kids outside to do the same.

Disturbing developments

Well, I've just seen something in the news that reinforces my opinion of how far some of our government representatives have moved on from sanity (or at least from representing the interests of some of their constituents). I'm sure this is a rather polarized issue, but I'll risk dissenting commentary, because I think it needs to be brought to peoples' attention. (Gun owners: I personally do not own a gun and do not want to, but I am not saying that I don't think you should, either. This isn't about that; it's my opinion on why we don't need to have weapons accessible in National Parks.)

"Senators Push for Guns in National Parks" showed up in my morning paper, and I didn't even have to go beyond the first sentence before I was sufficiently steamed to start drafting letters to my senators. Apparently, the gun lobby is making a big push to get their in-pocket senators to change National Park Service rules to allow gun owners to carry loaded, accessible firearms onto National Park lands.

The senators write that current policies "infringe on the rights of law-abiding gun owners who wish to transport and carry firearms on or across these lands." Oh really? I just checked the Code of Federal Regulations, Title 36, Parts 1 to 199, and came across Title 36, Chapter 1, Part 2, part of which states:

(3) Traps, nets and unloaded weapons may be possessed within a temporary lodging or mechanical mode of conveyance when such implements are rendered temporarily inoperable or are packed, cased or stored in a manner that will prevent their ready use.

I don't see anything in that sentence that says people aren't allowed to have weapons in a National Park - only that they aren't allowed to have loaded, readily accessible weapons.

Which is how it should be. There is absolutely no reason that the average citizen, visiting a National Park, should need access to a firearm. They are not there to hunt animals because National Parks and Preserves are some of the only places left where animals can live without the threat of being shot (other than in allowed hunting seasons and special situations). There is no need for weapons for defense - the National Park Police 2006 Annual Report listed, among other things, 3 homicides and 138 aggrivated assaults for the entire park system in 2006, from a pool of 272 million visitors. A few hundred crimes that might have prevented with a gun out of 272 million visits? What an absolute hotbed of criminal activity.

I don't buy into the whole "I need a gun for self-defense" argument at the best of times, but I especially don't want people carrying them around me when I'm in a National Park. All right, if you're in a bear-infested area and you need a gun to fend them off, fine. The Park System grants permits and exceptions for that. But if you're not allowed to hunt or target shoot in the park, and the crime rate is lower than a whole lot of other places in the country, why the hell do you need to have access to a weapon? And I don't buy that crap about people needing the laws changed so they can drive through parks with their weapons on the way to hunting areas. They don't need to change the laws. Keep the gun unloaded and locked up in your cabin or your car, or don't drive through the park.

I am seriously disappointed in the whole mentality that's driving this issue, particularly that it's our national heritage to be armed to the teeth wherever we go. Maybe that was necessary two hundred years ago, when law enforcement was scarce or nonexistent, people needed to hunt for food and there actually were enough dangerous animals around to merit carrying a gun, but that certainly isn't the case today. Having spent a great deal of time learning about geology in National Parks, I can definitely say that the thought of allowing people to have access to their firearms in Parks is appalling. I certainly won't feel safer knowing that while I'm out mapping an outcrop, someone might decide to start firing a weapon near me (or at me, since it's apparently pretty easy to get mistaken for a deer, if the amount of neon orange hunting gear for sale is any indicator). National Parks are the only place in this country where I know that weapons are not permitted unless they're essentially useless. I'm perfectly happy that the Park Police have weapons to use if they need them, but the thought of my fellow average citizen having access to a weapon in a park - where, most likely, there would never be enough Park Police to enforce gun safety - scares me.

I'm going to be writing those letters this afternoon, and I hope I can inspire some other people out there to do the same.