Geological Frightfest: El Monstruo de los Volcanes

Tonight's post will be a short one, because it's Friday and I just spent the last hour carving a pumpkin. This Frightfest offering comes via the suggestion of a devoted reader (thanks, Mom!), and I had to post it, even though I can't find out a lot about the movie. This is the best I could dig up for El Monstruo de los Volcanes: A yeti-like creature with the power to hypnotize its victims stalks the slopes of Mount Popocatepetl, attacking construction workers who are building an inclined railway on the volcano.

Yep, a 1962 horror movie about a volcano yeti. I don't think I can add much to that. (Here's a Spanish website with a short blurb about the movie, for those of you who can read it. Oh, and funicular is another word for an inclined railway, if you get stuck translating it.)

On the volcanic side of things, Volcan Popocatepetl (the name means "smoking mountain" in the Aztec language) is a large stratovolcano about 70 km SE of Mexico City. Its most recent  eruption began in January 2005 with a series of phreatic explosions, and has continued since with explosive eruptions of ash and the extrusion of a lava dome. (Check out the GVP's monthly and weekly summaries for more details!)

Distinguishing deposits from andesitic eruptions

Telling apart different kinds of deposits associated with volcanic eruptions isn't always easy. There are a lot of factors that can affect their appearance: the location and type of eruption, the magma/lava type, where they're emplaced, etc. On Montserrat, volcanologists are lucky to have both ancient and modern deposits; they can look at what's currently being erupted and compare it to the older volcanics on the island. We did quite a bit of this on our field trip, and one of our assignments was to summarize the characteristics of andesitic eruption deposits on Montserrat. (I emphasized that because the characteristics we saw are not necessarily going to be the same for all volcanic eruptions, or even for all andesitic eruptions. I've tried to generalize a bit, but apply these cautiously if you're going into the field to look at other volcanic deposits; things may look very different in your field area.)

Block and ash flows are a kind of pyroclastic density current. "Pyroclastic flow" is a kind of catchall term, but there are more specific ones that better describe the makeup of one of these currents. "Block and ash flow" implies that the flow is composed of blocks (either of denser lava or pumice or both) and ash; "pumice flow" means that the contents are mainly pumice and ash, "ash flow" that there are few blocks and mostly ash in the current.

Faint reverse grading in a block and ash flow deposit at Old Road Bay

Block and ash flows contain a range of clast sizes from mm-sized ash to m-scale boulders. The clasts are usually somewhat angular and tend to be a combination of lithics (lava) and pumice. The matrix of these deposits (what larger clasts are embedded in) is generally ashy and may be crystal-rich. The deposit may be clast or matrix supported (which describes whether there is enough matrix that the clasts are not touching) and poorly sorted (clasts are not separated by size). Oxidation and alteration of clasts as well as fractured blocks (including radially jointed clasts) may occur if the flow is deposited into water and cools quickly. Sometimes you can see grading in the deposits (i.e., a change from small to large clasts, or the reverse), which has to do with the energy of the pyroclastic current and the conditions under which clasts are being deposited from it.

Pointing out matrix in a deposit on the side of the Belham River Valley

Debris avalanches form from older volcanic material that's unstable enough to collapse, either because of erosion or alteration or both. They form "hummocky" deposits that are very obvious in aerial photos, but in cross section they're also fairly easy to identify.

Panorama of a debris avalanche deposit near Jack Boy Hill. Different colors mark chunks of preserved stratigraphy.

Debris avalanche deposits contain mm to m sized clasts (or larger), as well as chunks of material from older deposits that retain their original stratigraphy. These clasts and chunks are poorly sorted, and rounded to angular in shape. Clast compositions are almost always mixed, and the matrix is often clayey and highly altered. Jigsaw jointing is apparent in individual clasts, with clast fragments separated by matrix material but orientation with respect to neighboring clasts preserved. Clasts or deposit blocks may be "smeared" out into trains or show internal faulting.

A "jigsaw" fractured block in a debris avalanche deposit

Lahars form when water mixes with volcanic material and flows downslope. These can have the consistency of soup to concrete, and they're a major concern even when a volcano isn't erupting (especially if the volcano is located in a tropical area that gets lots of rain.)

House buried in lahar deposits in the Belham River Valley

Clasts in a lahar deposit range from mm to multi-meter size. They are matrix supported, poorly sorted, and often contain clay or silt in the matrix. The clast shapes vary from rounded to angular and may be either monolithologic (all one rock type) or mixed rock types, depending on the source material. Sometimes the deposits show bedding features such as cross-bedding. There is one absolutely diagnostic feature for lahars: preserved voids where bubbles of air were trapped in the matrix mud. The voids are spherical and usually pretty tiny, but they don't form in pyroclastic currents. (The lack of these voids does not, however, mean that a deposit is not a lahar, so this feature is only useful if it's present.)

Cross-section of a fairly recent lahar deposit. There's not much in the way of sorting or grading here.

A fourth type of pyroclastic current, called a surge, also shows up on Montserrat, but they're not often preserved because they consist of a blast of ash and hot gases (sometimes derived from block and ash flows), and they leave very thin deposits. I don't have any good photos of them, but they tend to be fine-grained (mm to cm sized clasts at the most), and sometimes show cross-stratification. It's rare that they're preserved, especially in a tropical environment, because the fine material washes away very easily.

February 2010 dome collapse deposits at Soufriere Hills

If you ever want to visit a post-apocalyptic wasteland, someplace that's been run over by pyroclastic flows would be a great choice. On February 11 of this year, a partial dome collapse on the northeastern flank of the Soufriere Hills lava dome produced spectacular pyroclastic flows, surges, and a 50,000 ft (~15 km) high ash plume. The pyroclastic flows extended the eastern coastline significantly in the area of the old Bramble Airport, and surges were observed flowing out over the ocean on the eastern side of the island.

Here's a photo from the edge of the collapse deposits, below the Jack Boy Hill overlook. In the distance of this photo, you can (just) see a chimney stack. This is one of the only visible structures left in the whole area; even the old Bramble Airport (which would have been visible to the left of the chimney) is now completely buried.

The chimney stack is part of an old sugar mill, and I'm pretty sure that what's visible isn't the whole chimney. To give you a sense of scale, here's yours truly standing next to the stack. 

Walking on pyroclastic deposits isn't difficult, but it's not the most pleasant hike I've taken. Ash is nasty stuff, especially when you're kicking it up whenever you walk somewhere. In addition, these deposits are still(!) quite hot; a few inches down is enough to make it uncomfortable to stand in one place too long, and digging less than a foot down, they become hot to the touch.

Here's what the deposits look like in cross-section. Those dark streaks are degassing structures, which are cut off by the most recent deposits on the top of the sections. 

As I mentioned before, the Montserrat Volcano Observatory scientists brought us on this hike; in the khaki hat and olive shirt is Dr. Paul Cole, the Director of the Observatory. We're examining one of the boulders that was transported downslope in the collapse - and while it looks pretty big, it's actually one of the smaller boulders that we saw. The largest were the size of small houses! (Definitely not something you want to get hit by, which is why it's a good thing that the people on Montserrat pay attention to the exclusion zones.)

On several of the boulders, we saw examples of marks that are interpreted to have been created by the impact and scraping of one boulder against another during transport. They could be described as slickensides, except here they're glassy surfaces that were created very quickly during an impact, rather than slowly during the scraping of a fault surface. (The study I linked to mentions that in the largest marks, frictional melting formed pseudotachylite, which is basically glass.)

Things like the friction marks above, and this next photo, remind you of just how dangerous pyroclastic flows are. Aside from giant boulders smashing into each other, you also get stronger-than-hurricane-force blasts, poisonous gases and extremely high temperatures. To give you an idea of what that does to the landscape, here's a view of the end of a pumice flow lobe that carried trees with it. All the wood here is carbonized; my best guess is that temperatures of around 400°C (or higher!) were involved. That's about twice as hot as your kitchen oven will go.

Did I mention the force involved in pyroclastic flows? Here's an example: a tree limb thicker than my arm that was snapped in half and then pretty much welded into that position. 

Another interesting feature just beyond the pumice lobe were these pit craters, formed when the flow buried a water source, which was then heated to steam and exploded up through the new material.

I think the water in question was probably part of this drainage (this is looking roughly to the west), which we walked down on our way back to the vehicles. While these deposits do retain their heat, there doesn't seem to be enough time to really weld them together, so they're pretty easily washed away by precipitation, and form these sorts of drainage channels.

The channels do make it much easier to see cross-sections, though! There are at least five (probably more) different deposition events represented here, with a lovely pumice-filled channel right in the middle. 

I'll try to get to a post on how to distinguish different types of deposits next (and hey, maybe some annotated photos!)

UPDATE: Claire Howard (one awesome reader) sent in some photos of the factory chimney at Trants from May 1995, 6 months before the beginning of the eruption. Turns out that chimney was a lot taller than it is now. Enjoy - and thanks to Claire!

In the Humorous Vein #14

I'm still getting ready for the semester here, so at the suggestion of A Lifelong Scholar, I'm resurrecting an old series I was working on and giving you a humorous interlude. (This is one of the photos from my travels this summer; can anyone guess where it was taken?)

The Santiaguito Volcano Observatory needs your help!

While I was in Guatemala working at the Santiaguito lava dome complex, my field group had a lot of help from the Instituto Nacional de Sismologia, Vulcanologia, Metereologia e Hidrologia (INSIVUMEH). And when I say a lot, I mean "helped organize every logistical detail of the trip and gave us a place to stay at the Santiaguito Volcano Observatory". I could never have done any of this work without their help, and now I'm going to try and help them out in return.

The Santiaguito Volcano Observatory needs our help.

Unlike the geological organizations in the U.S. and Europe, INSIVUMEH doesn't have a lot of money to throw around. The scientists and observers at Santiaguito (and at other volcanoes in Guatemala) don't have the equipment they need to easily and accurately monitor active volcanoes. It's not a matter of needing big pieces of high-tech instrumentation; the folks at the Observatory don't even have the basics that we all take for granted - such as digital cameras, radios, and GPSs. What's more, even though they have a seismic station collecting data about the Santiagutio domes, there's no way to receive or process the information at the Observatory, because they don't have the computers to do it. 

In light of the recent large eruptions at Santiaguito and Pacaya, this is dismaying. The people who live and work around Santiaguito depend on the Observatory to help keep them safe, and INSIVUMEH's scientists don't have the basic tools they need to do their work. I've talked about the hazards of living near an active volcano in the past, and the key to doing it safely is to have diligent, well-equipped scientists monitoring volcanic activity. The INSIVUMEH volcanologists and observers are incredibly dedicated to their work, but there's a point when equipment needs simply hamper their ability to be effective. Because the average person in Guatemala lives on US$2 or less a day, there's no way they can afford to spend their own money to supplement their equipment. But we can, and that's why I'm making this announcement - and asking for your help.

Donate to the International Volcano Monitoring Fund!

The International Volcano Monitoring Fund (IVMF), which was created by Dr. Jeff Witter, has been set up specifically to help volcano observatories in developing countries. Dr. Witter has agreed to extend their current endeavors to purchasing equipment for the Santiaguito Observatory, and has just launched a new webpage where you can find out how to help: http://www.ivm-fund.org/guatemala/. He and I have been working with Gustavo Chigna, the director of INSIVUMEH's volcanology programs, and Rudiger Escobar, a Guatemalan PhD student in volcanology at Michigan Technological University, to develop a list of what the Santiaguito Volcano Observatory needs.

The equipment they've requested runs all the way from smaller items like tape measures and rock hammers to more expensive things like desktop computers (to receive and process seismic signals) and laser rangefinders. Each item comes with a dollar amount needed to purchase it and a description of how it will be used. You don't even have to purchase the whole item - like the DonorsChoose campaign that the geobloggers participate in every year, every little bit helps. The IVM Fund is a non-profit organization, so you can be assured that as much of your donation as possible will be going toward funding Guatemalan volcanologists.

Please, help my colleagues in Guatemala do their work! I'm incredibly lucky that I don't have to worry about being able to afford my equipment, and I want to make it possible for the volcanologists at INSIVUMEH to do their work without the same problems. Because any fundraising effort is a long-term endeavor, I'm going to place a permanent link on the blog and periodically update you all as the IVM Fund collects enough to start purchasing equipment. (I also think that t-shirts may be in the works for the future - you'll be able to donate toward volcano monitoring efforts and add to your geologic wardrobe!)

Eruptions - especially the ones that we've seen this year - remind us all that it's necessary for volcanologists to keep a close eye on active volcanoes. Like any scientist, they need the proper tools to do that. When they have them, volcanologists can do a lot to help safeguard peoples' lives, livelihoods and homes. If you think you can spare a little money, please help the volcanologists at the Santiaguito Volcano Observatory do just that!

Volcano Vocab #5: Caldera

Part of my research this summer involves visiting Los Alamos to learn how to work with a computer model; in addition to one of the world's greatest research laboratories, northern New Mexico also hosts the Valles caldera, a major volcanic center north of Albuquerque. (Pretty much everything around me is volcanic, which means that whenever I drive or bike anywhere, I'm always staring at the scenery and going "holy crap, that's amazing!")

Caldera ("cal-dare-uh") is a Spanish word meaning "cauldron", and it describes a type of large, bowl-shaped volcanic structure. Calderas are created by collapse of the roof of a magma chamber after the chamber's contents have been removed, either in effusive or explosive eruptions. They're technically not craters, which are smaller and usually located on the summit of a volcano, but much larger features that form when a volcano expels the contents of a big magma reservoir and then collapses. (If activity continues after this happens, it can even create new stratovolcanoes within the caldera.)

The eruptions that form calderas are big - hundreds to thousands of cubic kilometers of material is involved. Collapse features that form over magma chambers that large are often not recognized as volcanic features until they're seen from the air, because they're simply too large to distinguish from the ground. On the volcanic explosivity index (VEI), caldera-forming eruptions top the chart - and in the case of some, are too big to even show on the chart:

VEI figure from the USGS Volcano Hazards Program Photo Glossary.

To give you an idea of what this translates to in reality, here's part of the Valle Grande in the Valles caldera:

This meadow is only a fraction of the whole caldera, and you can't even see the far walls because they're hidden behind the resurgent and smaller domes. Here's a map of the whole caldera:

View Larger Map

The Valle Grande is the light green patch in the southeast; the hills in the background of the photo are the Redondo Peak resurgent dome and smaller lava domes, which are pretty common post-caldera-eruption features. Resurgent domes are thought to be related to rebounding of the caldera floor, possibly due to new magma intrusion; the lava domes represent later eruptions through fractures. (If you want to know more about the specific geologic history of the Valles Caldera, Garry Hayes over at Geotripper has a great post from last year.) Some well-known examples of calderas in the United States are Yellowstone in Wyoming, Crater Lake in Oregon, Long Valley in California, but there are plenty of others:  Krakatau and Tambora in Indonesia, Santorini in Greece, and Colli Albani and Campi Flegrei in Italy, to name a few. 

I'll leave you with a photo from the rim of the Colli Albani caldera in Italy, with the Faete stratovolcano to the left of center:

Volcanoes everywhere...Is there a link? (EARTH Magazine article)

Like Brian over at Clastic Detritus and Callan of Mountain Beltway, I've also recently contributed an article to EARTH Magazine's website. Mine talks about the recent eruptions at Pacaya and Tungurahua, with a little bit of exposition on the inevitable question of whether they're linked. (Nope!) 

I'm digging into some research in the next few weeks, so posting will be a little sparse (again). I'll try to get the Volcano Vocab feature started up again, though - I've been sadly neglecting it. 

Perception of volcanic hazards in Iceland

The eruption may be subsiding a bit, but there is still a lot of discussion (and arguing) centered around the Eyafyallajökull event. It's not entirely surprising; most people in Europe don't have to deal with active volcanoes, and the last time an Icelandic one caused widespread trouble was in the 18th century. But what about the Icelandic response? One might assume, given the prevalence of volcanic and geothermal activity in Iceland, not to mention hazards caused by volcano-water interaction, that Icelanders might be better prepared than other Europeans to deal with natural hazards. But is that really the case?

In "Resident perception of volcanic hazards and evacuation procedures", published in 2009 in Natural Hazards and Earth Systems Science, Australian and Icelandic scientists set out to evaluate how Icelanders perceived risk and what their response would be to an evacuation drill for a jökulhlaup hazard. The study was conducted in March 2006 in the jökulhlaup hazard zone of Rangávallasýsla, a region immediately adjacent to the Mýrdalsjökull and Eyafyallajökull glaciers and the Katla volcano, which is notorious for producing jökulhlaups.

Figure 1 from Bird et al. (2009). The jökulhlaup hazard zone of Rangávallasýsla. The hazard zone is the maximum area that a  catastrophic jökulhlaup is expected to flood. Evacuation centers are represented by blue triangles.

The authors of the study used a combination of methods to assess the reactions of residents and emergency officials: they directly observed an evacuation drill, did face-to-face interviews with officials and residents, and distributed surveys to those involved in the drill. The authors also discuss the parameters of the drill:

If an eruption is imminent residents would be notified via a text message to their mobile phone. If residents do not have a registered mobile phone number a recorded message would call through to their landline. Upon receiving this message residents have 30 minutes to prepare to evacuate. However, if an eruption occurs without precursory activity, residents will be instructed to evacuate immediately. Before leaving, they are required to hang the evacuation sign outside their house to indicate that they have left. Certain residents in each region have volunteered to ‘sweep’ their local area to ensure their neighbours have left for the evacuation centres...

To test the proposed evacuation plan the ICP conducted a full scale evacuation exercise on 26 March 2006 in Rangávallasýsla. Approximately 1200 residents live within the hazard zone (K. Þorkelsson, personal communication, 2006) and for the purpose of fully testing the evacuation plan residents were not informed of the timing of the eruption scenario. Instead residents were instructed to go about their business as usual until they received an evacuation message (R. Ólafsson, personal communication, 2006). The mock eruption began at 10:55 local time (LT) and the first evacuation message was communicated to residents at 10:59 LT. Residents then had 30 minutes to complete the instructions on the hazard sign (Fig. 2) before evacuating their homes to their designated centre.

So what were the results of the evacuation drill and the study?

• Many residents did not receive notice of the evacuation, but about 65% of the local population still registered at evacuation centers. Some of the reasons cited by the remaining 35% for their non-participation included lack of communication from officials, reluctance to leave their livestock, or that they were simply not interested in the drill. The response from those who did participate, however, was overwhelmingly in favor of the drill.
• 71% of evacuation participants were able to correctly describe the evacuation procedures they were supposed to follow during the drill, and 94% were able to define what a jökulhlaup was (and knew that it was the major hazard associated with an eruption of Katla).
• Many of the residents of towns on higher ground stated that they would remain in their homes rather than evacuate, citing that it was safer there than on roads and that they thought the flood stage of the glacial drainage would be too low to reach them.
• Many of those surveyed - especially farmers - did not think that 30 minutes was enough time to prepare for an evacuation, since they had livestock to care for in addition to dealing with their homes and families.
• "None of the participants from the 18–30 year age group and very few from the 31–50 year age group could correctly describe a brief volcanic history of Katla." Some residents who had family members who had seen the 1918 Katla eruption had knowledge of what Katla was capable of, but this has apparently not been passed down to their children.

This paints an interesting picture. Most of the residents, even if they didn't participate in the drill or completely understand the potential hazards associated with an eruption of Katla, were still very well informed about what they should do in an emergency. Many evacuated even though they didn't receive a direct message from emergency officials (mostly because of community volunteers who helped spread the word of the drill). But it is troubling that a large number of people living near Katla (and Eyafyallajökull) knew very little about the past activity of the volcanoes. This is often the case when volcanic disasters have passed partially or completely out of living memory, but given that volcanic activity is extremely common in Iceland, it's not particularly reassuring. The authors suggest that a lack of outreach by public officials may be the cause for this:

Our participants are aware of jökulhlaup, tephra, lightning and rock fall hazards but they have not been provided with enough information to enable them to make an informed decision on whether to evacuate or take shelter in place and how to best protect their livestock.

Finally, the authors comment on some of the underlying problems with the evacuation itself, most having to do with communication issues (again):

Results from our study highlighted problems associated with communication during the evacuation exercise and the possible need to find alternative modes which do not rely so heavily on technology. In light of this, scientists and emergency management officials should collaborate with media agencies and the public in order to promote the use of media resources and, to ensure hazard information is accurately distributed in an understandable form. Furthermore, the importance of the sweepers’ role during an evacuation should be emphasised as they may provide the only communication link between emergency management and farming communities. Recent public meetings which involved residents in risk mitigation efforts are a positive step toward empowering residents with evacuation procedures and preparedness strategies.

What's the bottom line? It's an interesting one: people near this volcanic center in Iceland seemed to be fairly well informed about what they should do in an evacuation. But they weren't necessarily as knowledgeable about the hazards that necessitate the evacuations, even though they live very close to an active (and now erupting) volcanic center. (Given the recent eruptions, I suspect that a follow-up study would show a distinct change in this observation. If anyone comes up with one, I'd be interested to see it.) This study does emphasize again the importance of good communication between scientists, emergency officials and the public; in an emergency, if people are better informed about hazards and what they should do to avoid them, evacuations will run more smoothly and officials will waste less time dealing with confusion and misinformation.

Bird, D., Gisladottir, G., & Dominey-Howes, D. (2009). Resident perception of volcanic hazards and evacuation procedures Natural Hazards and Earth System Science, 9 (1), 251-266 DOI: 10.5194/nhess-9-251-2009

Volcano Vocab #4: Lahar

As suggested by a commenter on the last Volcano Vocab post, here's a water-and-volcano-related term for you: Lahar ("lah-haar"). 

Lahar is an Indonesian word for a mudflow of volcanic material - that is, a mass movement of volcanic debris that contains some amount of water. (A dry flow of volcanic material would usually just be called a debris flow or debris avalanche.) The key thing that distinguishes a lahar from a "regular" mudflow is the presence of volcanic material in the flow, which can include tephra, ash, hydrothermal alteration products, blocks of lava flows, and other pyroclastic materials. Some descriptions liken this mixture to a flow of cement, and it's capable of moving house-sized boulders huge distances from their source.

Lahar deposits characteristically show poor sorting (lots of different sizes of material, from boulders to sand), multiple rock types, rounded clasts, and muddy matrix supporting the clasts. (Sometimes in deposit matrices you can find rounded voids where bubbles of air were trapped as the deposit hardened around them!) Lahars are most common on stratovolcanoes, but (as we've seen in Iceland), other types of volcanoes can also create the correct conditions to form a lahar. Lahar formation depends on having lots of loose material, and the addition of lots of water over a short period of time (such as from a melting glacier, a hurricane or storm, or a breached crater lake, among other things). They do not require the volcano to be actively erupting, which is one reason why they are so dangerous.

Here's a video of a lahar from Mount Ruapehu in New Zealand (March 2007):

Lahars are an especially dangerous volcanic hazard because they appear and disappear so quickly. Lahar debris that's deposited in a riverbed can easily be eroded by normal river flow, and lahars that have spread beyond valleys and drainages can easily become reclaimed by vegetation. In fact, one of the most devastating lahars to have come from Mount Rainier in Washington State (the Osceola Mudflow)  is now covered with small towns. Because the people in the area are now aware of the danger a repeat lahar would present, they are required to hold evacuation drills. Lahars are somewhat easier to monitor and avoid; acoustic flow monitors (specially calibrated seismometers) can be placed in source zones, and a timely warning can be sent downstream when lahar signals are detected. Sometimes evacuation can be simply a matter of climbing to a higher elevation, although on a floodplain it could be necessary to travel much greater distances to safety, but it does require advance warning.

Armero, Colombia, destroyed by lahar on November 13, 1985. Photo from the USGS CVO website.

Lahar warnings aren't always heeded, however. It's impossible to mention lahars without also mentioning the town of Armero in Columbia. On November 13, 1985, a small eruption of the nearby volcano Nevado del Ruiz melted part of the snow and ice capping the volcano's summit, and produced a lahar. Volcanologists knew that river valleys on the volcano's flanks could channel lahars toward populated areas, and sent warning to towns in the lahar's path; unfortunately, local officials either received incomplete or conflicting information, and/or decided not to listen to the scientists' warnings. As a result, more than 23,000 people were killed in Armero and nearby villagees, when they could have reached safety by climbing only a short distance up the slopes on the sides of their valley. This tragedy drove a USGS scientist to develop the Acoustic Flow Monitors mentioned above, in hopes that more deaths could be avoided; the system is now used at lahar-prone volcanoes worldwide.

Volcano Vocab #3: Tephra

Today's volcano word is tephra, another term that's directly related to the Eyjafjallajökull- Fimmvörduháls eruptions going on in Iceland at the moment. Tephra ("teff-rah") refers to any fragmented material thrown from a volcanic vent during an explosive eruption. It comes in different sizes, all of which have their own names (just to make things even more difficult!)

Bombs or blocks are large rocks - 64 mm and greater in diameter (cobble to boulder sized; see the photo at left, which is an example of a really big bomb on a scoria cone on Mount Etna). Lapilli are smaller, from 2 mm to 64 mm (the size of the material underneath the bomb at left). Ash is any material smaller than 2 mm, and is one of the main constituents of a volcanic eruption column, such as the one that's disrupting air traffic over northern Europe at the moment. Volcanic ash is composed of fragmented glass, rock, and phenocrysts (crystals), unlike the ash you get from fires (which is mostly carbonized organic material).

The other things that make up an eruption column are typically gases (including water vapor), ambient air that's been entrained and heated, and some lapilli and bomb-sized particles. Some recent news reports have been saying things like "ash and smoke" to describe the Eyjafjallajökull-Fimmvörduháls eruption column, which is incorrect. There is no "smoke" in an eruption column, at least in the sense that most people think of it (as a byproduct of burning materials). The column appears to be smoky, but only because of the presence of the ash, which is generally some shade of gray or black.* (The photo below, from a February 2010 eruption of the Caliente dome at Santiaguito, is quite gray to begin with, but I can guarantee that it's not because something in the vent is burning.)

Tephra is a major hazard associated with volcanoes. Bombs tend to be more of a problem in the vicinity of a volcano, but as many people in northern Europe are finding out, smaller particles like lapilli and ash can travel much higher and farther. Ash from a powerful eruption can reach the upper atmosphere, far higher than airplanes can fly; and because glass makes up a good portion of those ash particles, any plane that does fly through an ash cloud risks sucking glassy particles into its engines, where the glass can melt and re-solidify. This is bad - it could mean total engine failure, which is what happened to a flight over Alaska in 1989. No sane pilot is going to fly a plane into that.

So if you're stuck waiting for a flight to or from Europe, just remember: it's a lot better than risking a plane crash. And you can probably look forward to some spectacular sunsets.


*Okay, maybe some lichen is getting toasted, but that still doesn't mean you can call ash "smoke".

Volcano Vocab #2: Jökulhlaup

Today's obscure volcanologically-related word is jökulhlaup ("yer-kul-hloyp", "YO-kel-yawp" and "yo-kul-h-loip" in varying pronunciations), which is an Icelandic word for glacial outburst floods, both of water and lahars, formed when a subglacial eruption occurs. The water for these floods is formed when heat from those eruptions melts glacial ice, forming lakes that eventually become unstable enough to break through channels in the base of the glacier and flow out from underneath it. (Apparently the word can also refer to flooding caused by geothermal heat rather than a subglacial eruption, but since it's hard to see what's going on under a glacier in the first place, I wouldn't be too picky about the generation mechanism; suffice to say that some sort of volcanic activity is involved.) To give you an idea of what an unstable subglacial lake would look like, here's a diagram from an excellent overview paper:

Figure 3 from Björnsson (2002), showing a stable sub-glacial lake (a) and (b) an unstable lake likely to form jökulhlaups.

How big are these floods? Here's a quote from the same paper, talking about jokulhlaups from formed by the Grímsvötn volcano under the Vatnajökull glacier:

Jökulhlaups from Grímsvötn have occurred at 1– to 10–year intervals, with peak discharges of 600 to 4–5×10⁴ m³s⁻¹ at the glacier margin, a duration of 2 days to 4 weeks and a total volume of 0.5–4.0 km³.

Obviously, this is not a good thing to be in the way of. (By way of comparison, the mean discharge at Niagara Falls is about 1770 m³s⁻¹ , or about a quarter one-thirtieth of the peak discharge during one of those floods.) I don't have any personal or public domain photos of a jökulhlaup, but the Global Volcanism program has some excellent photos from a 1998 event during an eruption of Grímsvötn.

This topic is quite relevant at the moment because of the recent volcanic activity in Iceland. While the fissure that's erupting at Eyjafjallajökull isn't in danger of melting much ice, there are several other volcanoes that are, such as Katla volcano under the Mýrdalsjökull glacier. Since roughly 10% of Iceland is covered in glacial ice, and the country has more than 30 volcanoes that have been active in the last 10,000 years, this is a major concern (see Ole Nielsen's post on jökulhlaups here).

If you're interested in more Icelandic geologic vocab, the USGS has an English-Icelandic glossary here. And here is the full citation for the Björnsson paper:

Björnsson, H., (2002), Subglacial lakes and jökulhlaups in Iceland. Global and Planetary Change, v. 35, p. 255–271. http://dx.doi.org/10.1016/S0921-8181(02)00130-3


UPDATE: Whoops! Totally forgot about this page over at Andrew Alden's About.com Geology. Lots more detail there!

Volcano Vocab: Guyot

I don't want to steal the thunder of any of the Skepchicks (especially Evelyn, who's doing a fantastic job on the Geology Word of the Week feature), but I thought I'd start a bi-weekly post on obscure or specialized volcanology words. (Yes, it's really just an easy way for me to post, since I've got the Glossary of Geology sitting here and all I have to do is flip a page to get a post idea, but I'll try to include a little discussion along with the posts.) We'll see if I'm any more successful with this weekly feature than I was the last time.

So what's the first word o' the half-week? By dint of me opening to the glossary of a volcanology textbook and pointing blindly: Guyot!

A guyot ("gee-oh") is basically a flat-topped seamount, or underwater volcano. The glossary in Bardintzeff & McBirney's Volcanology (2000) adds a bit about why it's got a flat top:

A submarine volcano with a flat top produced by wave erosion before the island was submerged. 

A guyot is one of the stages in the life cycle of an ocean island volcano, and the form occurs when a volcano is no longer actively growing and unable to replace what is lost to the erosive force of wind and waves. Here's a diagram to illustrate:

(This came from a powerpoint someone gave me a while back, and I don't know where they nabbed it from - looks like a textbook. If anyone recognizes it, let me know and I'll put in an attribution!)

Unfortunately, it's a bit hard to show off a photo of a guyot, since they're generally underwater. Here's something that looks similar, however, from Hawaii's Big Island. These photos were taken somewhere along Rt. 11 (Mamalahoa Highway) on the way to Punalu'u Black Sand Beach and Ka Lae (South Point).  I remember that there was some discussion going on about guyots, but I'm not sure if these are the real item. Does anyone else know if these are 'stranded' guyots?

Video Friday

Still waiting to hear on some info for the next Santiaguito Observatory post, but in the meantime, here's a neat video to keep your attention: A view of an eruption filmed with a Forward-Looking-Infrared, or FLIR camera. (These are the cameras that you sometimes see on ghost-hunting shows when they're trying to find "cold spots", or what you might use to look for heat leaks if you're evaluating your house for heating efficiency.) Enjoy - espectially BHC, who requested it!

This is a "double" eruption of ash and gas filmed in March of 2009 from the Santiaguito Observatory. The FLIR video converter has sped it up for some reason, so it's about 12 times faster than the actual eruption, but you can always pause it and advance it slowly if you'd like to get the full effect. In FLIR video, the warmer colors (white, yellow, and orange) indicate higher temperatures, and the cooler ones lower temperatures. The highest temperature in this video is about 150C (although this can vary due to atmospheric and distance effects, so it's not an exact temperature). 

(Sorry for the poor resolution - Blogger's video tool has gotten worse, for some reason.)

The Santiaguito Volcano Observatory

It's Friday! Which means picture day, because pictures are easy and fun. I thought - as a lead-in to a fundraising project I'm starting, and which I'll talk about in the next post - that I'd give you all a tour of the Santiaguito Volcano Observatory. I've been there twice, on my last trip to Guatemala and for a couple of days on this year's trip. After five days of camping next to an active lava dome complex, this is pretty much the lap of luxury. Beds, electricity, running water - heaven! Plus it's set in the middle of a lovely coffee plantation, and the views are incredible. 

Seriously, you can't compete with this for a first-thing-in-the-morning vista. You do have to get up early to see it - things cloud in by about 10 in the dry season, and probably even earlier in the rainy season (if you can see it at all). This view is looking northwest toward the cone of Santa Maria and the Caliente dome of Santiaguito. In the foreground is the Observatory's weather station, the front door, and a nicely informative sign.

See? Location and elevation. The Observatory is located on the land of one of the local fincas, which is owned by sells to Starbucks. The building, water and electricity are (if I'm remembering correctly) all The land was donated to INSIVUMEH, who built the observatory, and visitors who stay there pay a small fee for the drinking water and cooking gas that they use. There are usually two or three INSIVUMEH observers there full time - they have bedrooms and a nice little kitchen - and there are bunks for visiting scientists.

The Observatory's capabilities are pretty limited, however. The observers have been working there for years and know a lot about the volcano, but they're not academic scientists, and they don't have much equipment to speak of. Eruptions at Santiaguito are watched through the north-facing window in this photo, and reports are radioed back to Guatemala City and recorded on the typewriter. There's a pair of binoculars for closer observations, since it's a pain to drive much further toward the volcano from here, but that's mostly it.

The trusty (but noisy!) typewriter. If you see a report on Santa Maria in the Global Volcanism Program's newsletter, it was written up here first. There's no internet access at the Observatory, so whatever they want to report has to go out by radio or cell phone. They're working to change that, though - more on that later.

My favorite part of the Observatory! This is part of their rock collection, and a scale model of Santa Maria and the domes (made with actual rock and ash from the domes). If I was watching a volcano and had my view rained out for half the year (and a good bit of the clear days), I'd totally make one of these.

Another view, first thing in the morning. All the plants in the foreground are official Starbucks coffee plants, which are apparently unaffected by being ashed on every once in a while. (The finca office will sell you ground coffee for considerably less than Starbucks, and it's delicious. Probably because it hasn't been burned, which SB seems to like to do for some reason. Oddly enough, most Guatemalans don't drink coffee from the fincas - either they can't afford it, or they prefer the instant kind. Go figure.)

Our dual FLIR-video camera setup.Watching eruptions with a thermal camera is amazing, because you can see how the thermal currents rise in an eruption column (even when there's no more material coming from the vent).

And you get to see things like this - the top of an eruption cloud being sheared off by the wind. The wind patterns around Santa Maria have regional trends that change with the season, but locally they can change day by day. Eruptions occur at Santiaguito every few hours, so there's a near constant supply of ash to the areas surrounding the volcano. On the most recent trip we were fortunate enough to avoid having to deal with much ash (only a little on the first day), but people who live and work on the fincas and the Xela area have to put up with it all the time. Imagine having all that ash in your coffee!

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.