Friday, March 27, 2009

Santiaguito lava dome complex

If seeing this first thing in the morning doesn't both make you want to jump up and down in excitement AND say, "Oh, shit, I just spent the entire night unconscious and three klicks away from an erupting volcano," you are either clinically dead or an alien.

A composite of Santiaguito, gently steaming in the 6AM sunlight. This is both a fascinating and depressing time - fascinating because I could see a volcano erupt for a few hours, but depressing because at this point I had already been up and dealing with thermal imaging equipment for an hour, sans food or drink thanks to my recovering stomach.

Santiaguito is a strange place. The first of the lava domes in the complex, Caliente (the one erupting in the first photo, and the farthest to the right in the one above) began extruding from the 1902 eruption crater in Santa Maria in 1922. By 1929, the year that a 3 million cubic meter collapse and pyroclastic surge occurred, the dome had grown to about half a cubic kilometer in size. In the next 80 or so years, the other three domes - La Mitad, El Monje, and El Brujo - formed as the active vent migrated westward.

Then, after a brief period when both Caliente and El Brujo were active, everything shifted back to Caliente. Currently, Caliente is looking more and more like a mini-stratovolcano - the old rubbly dome has long since been covered over by talus slopes and lava flows. At the summit, however, is a very strange situation. The main vent consists of two structures: an outer ring-shaped fracture set, and an "inner annulus", or smaller ring-shaped vent. During an eruption, jets of gas and ash are expelled from various points around these rings, and the both rings heat up. In addition, the eruptions are pushing out a blocky, viscous lava flow onto the SW slope of Caliente.

A Forward-Looking InfraRed (FLIR) view of the top of Caliente from the summit of Santa Maria. The outer ring is clearly visible as a bright, hot area, and there are radial fractures leading to the "inner annulus", which is somewhat harder to see. The pinkish patch on the opposite side of the dome summit is the lava flow, and there are several fumaroles below the summit on the near side. Temperatures are in Celsius, and brighter colors mean the surface is hotter.

A clip from a FLIR video of an eruption. The lava flow is clearly visible on the left side of the dome, and several jets are apparent in the eruption plume. These eruptions last for several minutes, and it's common to see the hot jets of ash and gas migrate around the ring fracture.

Caliente's eruptions occur every few hours. That's right - not days, or weeks, or months - hours. It's amazing to watch, and even more incredible to listen to, because these eruptions sound exactly like a jet flying overhead. (Interestingly enough, people looking at infrasound - way below human hearing range - have found that volcanoes sound like jet engines there, too.) Occasionally these eruptions are large enough to produce pyroclastic flows, which eventually expand and drift and turn into a really annoying, view-blocking cloud around the base of the volcano.

This particular eruption, on the 15th of March, got reported in the local news the next day. The eruption plume, which came from both the vent and the pyroclastic flow on Caliente's SW slope, drifted to the SE, toward a number of small towns, rather than to the SW, which is where it usually goes and where there are mostly coffee plantations. It's not unusual to see ash coating coffee plants when you're driving through the fincas, although it seems that the nearby towns don't see it that often.

Another interesting feature of eruptions is that they are often preceded and followed by rockfalls. These are really easy - and neat - to watch on infrared camera, and sometimes you can hear the cracking of house-sized blocks tumbling down the slopes. They're likely from the front of the lava flow, where oversteepened blocks are detached by the push of extrusion or just the shaking of the eruption itself.

video

It's really amazing to see all this activity happening all the time. What's surprising is that the monitoring abilities at the Santiaguito Volcano Observatory are really limited. There are several observers on staff all the time, but they don't receive any telemetered data from the instruments on the volcano - it all goes straight to Guatemala City. This limits them to, basically, what they can see out the back door - and after about 10 in the morning, even in the dry season, that isn't much. I suspect this results in the number and height of eruptions being underreported, since even if you can hear something going on (sometimes possible) when the volcano is covered in clouds, you can't see it. It also makes for some pretty anxious moments, like when you realize just how screwed you really are if you're within a few km of the domes and something big happens.

Still, the observatory folks do a great job with what they have. And getting to the observatory isn't easy, either - it either takes an hour of walking up and down some very big hills over a narrow road, or a really bumpy ride in the back of a pickup (if you're lucky enough to catch a ride in with the finca workers at 6:30 in the morning). Coffee, however, is readily available, since the observatory sits right in the middle of a field of coffee bushes, and the finca office is right down the road. (Interestingly enough, this finca is owned by Starbucks, so those of you geologists with a taste for expensive coffee can be assured that your daily grind has been raised on the finest volcanic ash Santiaguito can produce.)

Next up: a visit to the valleys below the volcano, and a little bit about the 1929 pyroclastic surge.


Bibliography:

Bluth, G.J.S., Rose, W.I. (2004): Observations of Volcanic Activity at Santiaguito Volcano, Guatemala. J. Volcanol. Geotherm. Res. 136:297-302.

Harris, A.J.L., Rose, W.I., Flynn, L.P. (2003): Temporal Trends in Lava Dome Extrusion at Santiaguito, 1922-2000. Bull. Volcanol. 65:77-89.

Johnson, J.B., Harris, A.J.L., Sahetapy-Engel, S.T.M., Wolf, R., Rose, W.I. (2004): Explosion Dynamics of Pyroclastic Eruptions at Santiaguito Volcano. Geophysical Research Letters 31:L06610.

Rose, W.I. (1972a): Santiaguito Volcanic Dome, Guatemala. Geol. Soc. Am. Bull. 83:1413-1434.

Rose, W.I. (1973): Pattern and Mechanism of Volcanic Activity at the Santiaguito Volcanic Dome, Guatemala. Bull. Volcanol. 37:73-94.

Rose, W.I. (1987b): Volcanic Activity at Santiaguito Volcano, 1976-1984. Spec. Pap. Geol. Soc. Am. 212:101-111.

Rose, W.I., Stoiber, R.E., Bonis, S.B. (1970): Volcanic Activity at Santiaguito Volcano, Guatemala June 1968 - August 1969. Bull. Volcanol. 34:295-307.

Rose, W.I., Pearson, T., Bonis, S. (1977): Nuee Ardente Eruption from the Foot of a Dacite Lava Flow, Santiaguito Volcano, Guatemala. Bull. Volcanol. 40:23-38.

Sahetapy-Engel, S.T.M., Flynn, L.P., Harris, A.J.L., Bluth, G.J., Rose, W.I., Matias, O. (2004): Surface Temperature and Spectral Measurements at Santiaguito Lava Dome, Guatemala. Geophys. Res. Lett. 31:L19610.

Williams, S.N., Self, S. (1983): The October 1902 Plinian Eruption of Santa Maria Volcano, Guatemala. J. Volcanol. Geotherm. Res. 16:33-56.

Tuesday, March 24, 2009

Sweet irony

Guess who isn't commenting on the eruption of Mount Redoubt?

Sometimes nature has really perfect timing.

Friday, March 20, 2009

Lava domes, coffee, and a little bit of shaking

I'm finally back from my first attempt at field work in the volcanic highlands of Guatemala, and reasonably alive - no thanks to being laid out flat halfway through the trip by a truly nasty case of food poisoning. There is a distinct disadvantage to doing field work in a developing country, and it's never more apparent than when you're so sick you can't eat for three days. However, aside from a major restructuring of our plan of attack, we were able to collect enough data to keep me busy until the next trip.

The first thing I noticed? Guatemala is FULL of volcanoes. It's almost impossible to live somewhere on the Pacific coast where you can't see one. Flying in was incredible - peak after peak went by the window, all beautiful symmetrical cones (except for 'my' volcano, of course, but that will come up later). There are more than twenty-five volcanoes (depending on how you count domes), twenty-two that have been active in the Holocene and at least ten in historical times. The capital city has a lovely view of its own stratovolcano, Agua, and Volcáns Fuego, Pacaya and Santa María are currently active.

Volcán Pacaya Agua from the car on the drive out of Guatemala City. Yes, that's a nice little planned community down there, if by 'nice' you mean 'potentially toast'.

Guatemala is an interesting place. It's a developing country, which means that the infrastructure that a lot of us take for granted is much reduced, or even lacking. The government of Guatemala is still struggling to throw off a truly staggering atmosphere of corruption, which also extends to the judicial system and anything meant for infrastructure upkeep. As a result, the country doesn't have much in the way of sanitation, which means that the first thing you notice is a lot of trash, everywhere. It's a bit startling until you realize that most people hardly see it anymore. Most people get places by walking, or riding chicken buses - so-called because it's not unusual to see farm animals on board, along with everything else.

The "chicken bus" formerly known as Marlene. These are all old American school buses, painted over in really bright colors. Safety is definitely not a main concern, and the buses always get the right of way.

We mainly spent our time away from the capital (which is commonly referred to as Guate - confusing if you're not sure whether the person is talking about the country or the city). The highland city of Quetzaltenango is about 150 km (or a 3-6 hour drive, depending on your route) away from Guate, and is also called Xela (pronounced Shay-la, short for
Xelajú) after the old Mayan name. It's a very popular place for gringoes to go and study Spanish, and has a charming central park (where I spent some time peoplewatching from a rooftop cafe). Parts of the city are actually quite beautiful - not very much of the actual old colonial architecture is left, since it gets destroyed by earthquakes every so often, but they've rebuilt in a sort of neo-Classical style here.

Parque Central, where everyone ends up at some point. This is early in the morning, before the vendors got down to business.

A view of some of the uphill parts of Xela, which is built in the middle of old lava dome complexes, debris avalanche deposits, and on the back slopes of Volcan Santa María. (The volcano is hidden behind the hills.)

While we were in Xela, we were (lucky?) enough to feel some fairly large earthquakes - a M4.9 about 80 km south of the city, and a M5.3 off the coast south of Guatemala City. One more geological experience for me - being woken up in the middle of the night by the bed shaking!

Guatemala is unlike some other Central American countries (Costa Rica, for example) in that there are many more indigenous people still around, mainly in the highlands. Some of them have adopted the Westernized customs and dress of the Spanish-descended lowland populations, but many still wear traditional dress - mostly the women. They wear an amazing amount of color - in fact, I think they try to wear as much as possible at one time, with some truly eye-popping results. Women and children often carry loads on their heads - something I briefly tried in private, without much success - and it's common to see a woman throw a folded cloth over her head instead of a hat. (These never fall off, and I couldn't figure out why not.)

Women in a parade for International Women's Day (March 8). The ones on the right are doing the cloth thing.

One of the street vendors with her basket. See the heels? Now imagine a little old lady wearing heels like that, and carrying a twenty-pound bag of flour on her head, and maybe a baby or two in a sling.

My research is centering around the lava dome complex of Santiaguito at the Volc
án Santa María. The volcano and domes are just SW of Xela, in the middle of what are now coffee, banana and macadamia nut plantations (called fincas), and the whole lot sits at the head of several active river drainages that lead directly to the coast.

View of Volcán Santa María and the Santiaguito dome complex from the Santiaguito Observatory, about 3 km to the south.

Santa Mar
ía first erupted in 1902, creating a huge Plinian column, extensive ash and tephra falls, and blowing a large crater in the flank of the volcano. (Possibly some slumping was also involved, although I'm not entirely sure.) Twenty years later, the first of the Santiaguito lava domes (Caliente) began growing in the crater. The lava domes have been growing ever since, migrating westward with time and eventually returning to the Caliente dome for the last twenty or so years. There have been several major dome collapses (one in 1929 that killed thousands of people and destroyed a number of the coffee plantations that drape the slopes below the domes), and many lahars, some of which destroyed the town of El Palmar in the late 1980s.

A closer view of the 1902 eruption crater, in which part of the dome complex sits (Caliente's eastern slope is visible on the left). I've done a bit of fiddling with exposure and contrast on this one so you can see it better - the haze from crop burning obscures a lot at this time of year.

There has not, however, been a major dome collapse (involving more than the 3 million cubic meters of the 1929 collapse). My research is focusing on determining the probability of that happening, where it might occur, and what the runout distance of the debris could be. It combines structure mapping, investigations into the hydrothermal system of the domes, and computer simulations, and I eventually hope to turn it all into a new hazard map of the volcano. On this trip we weren't able to actually make it out to the domes, but I did get to spend a lot of time observing eruptions - something that happens every few hours at Caliente, the active dome. It's pretty exciting, but also really scary at times, since it makes you realize just how close thousands of people - and you - are to a very active volcano.

An eruption on March 15 that produced a moderately large pyroclastic flow (on the western flank of the Caliente dome). This turned into a large ash cloud that hung around for a while and even made it into the news, although it was by no means an indication of activity increasing dramatically.

Which brings me to a darker side of the work that I'm going to be doing. The populations of the fincas (coffee plantations) live in much the same way they did in 1929 - without paved roads, motorized vehicles, or much communication with people far beyond the local towns. There is probably no one left who remembers the '29 event, and since nothing major has happened at the volcano since then, they have no way of conceiving of the magnitude of a major collapse event. Perhaps they understand the dangers, but what could they do to avoid them? There is no infrastructure that could initiate, organize or support a large-scale evacuation. Data from seismic stations and from the observatory is transmitted directly to the country's geological survey, INSIVUMEH, in the capital, and it is by no means a large organization with the clout of, say, the USGS.

It's a sobering thought. My work may help people in the future - in fact, I hope that it will help give the INSIVUMEH scientists the support they would need to convince people of the need for an evacuation - but it's a very small chance. More likely is that a major dome collapse will someday happen, and people won't be able to get away from it even if they have warning.

It's a pity to end on a depressing note. In the next few posts I'll talk a little bit about some of the thermal imaging we did with a FLIR (Forward-Looking InfraRed) camera, and show off more of the nifty images you see when you're watching a volcano that erupts every few hours; I'll also do a little tour of some of the areas below the volcano, and what happened there in the 20s and 80s.

Tuesday, March 3, 2009

For my spring break...

I will not be blogging, because I will be here:


View Larger Map

Staying out of the way of this:




And looking for things like this:

Some people spend their spring breaks at the beach. I spend them hauling my butt up a steep, very active Guatemalan volcano looking for clay and structural weaknesses in a bunch of lava domes.

Ah, life. Well, I'll at least have some very good photos to share, providing I make it back to the States with myself and my camera intact.