A shot of part of the stunning Glass House Mountains in Queensland, Australia. Photo taken April 2019.
I have been terribly neglecting my blog this year. However, I have a good excuse: over the past few months I have accepted a new job working as a geologist for Anglo American… and I have moved my family to beautiful Brisbane, Australia. On top of that, I am mother to a young son (18 months old now) and I’m also studying part-time… so, I have my hands very full!
However, now that the chaos of moving is over, I thought I would revive my blog… once again! There is much new geology to see here in our new home country, so I’ll try to share some georneys (geology journeys!) here more regularly!
As a start, here is a picture of the majestic, magical Glass House Mountains in Queensland. These mountains are young (26-27 million year old) volcanic plugs. I’ll blog more about their geology soon! For now, enjoy this teaser shot.
A view of Kangaroo Point Cliffs, taken from across the river, December 2018.
Happy New Year! I’m going to try to keep up with my “Monday Geology Picture” posts in 2019. I did okay with these in 2018, although I missed some weeks here and there when I was very busy with work or family life.
To start off a new year of pictures, here is a picture that I took during a recent visit to Brisbane, Australia. This picture shows a place known as Kangaroo Point Cliffs. These cliffs are not completely natural but were rather formed by a combination of river erosion and quarrying for stone that was used to make several buildings throughout the city. The geology of the cliffs is quite interesting — the cliffs are comprised of Brisbane tuff, a welded ignimbrite that is Triassic in age. I’ll blog more about these fascinating rocks in future.
Here’s a little more information from a sign located across the river from the cliffs:
Sign with some information on the Kangaroo Point Cliffs. Click to enlarge.
The first paragraph says:
The rocks in the Kangaroo Point Cliffs are the debris of an ash flow from an exploding volcano 220 million years ago. The cliffs have been slowly carved by the river and from the 1820s stone was quarried from the cliffs to build the new Brisbane Town.
Last week I shared a lovely view of Santorini taken by my friends Patrick and Nia during their vacation back in June. This week I thought I’d share several more of their Santorini shots. Some of them are quite stunning. Enjoy!
When Patrick and Nia sent through these pictures to me, my husband commented:
Ah, a geologist’s nightmare. Photographs without scale! Except for the one with the boat… and the one with Nia…
Despite the lack of scale in some of them, these photographs are still pretty neat! If you are familiar with Santorini geology, please feel free to point out notable features. There are some great volcanic rocks in these pictures!
Santorini #2, with sailboat for scale.Santorini #3.Santorini #4, with some houses for scale.Santorini #5, with Nia for scale.Santorini #6.Santorini #7.Santorini #8, with some beach visitors for scale.Santorini #9, with flag and a building for scale.
Beautiful Santorini. The boats are travelling across an enormous, water-filled volcanic caldera.
Courtesy of my friends Patrick and Nia, here is a lovely picture of Santorini, a Greek island that is a the remnant of a volcanic caldera. Patrick and Nia were on vacation in Greece back in June. I’ll share a few more of their Santorini pictures for next week’s “Monday Geology Picture” post.
One of my favorite new songs is “Pompeii” by the UK band Bastille. I’m not sure how popular this song is in the USA, but in the UK and also here in South Africa it’s quite popular at the moment. If you haven’t heard the song yet, please take a listen.
The song has a geological theme and makes reference to the famous eruption of Mt. Vesuvius in AD 79, which destroyed and buried the Roman cities of Pompeii and Herculaneum. Here are the lyrics:
I was left to my own devices
Many days fell away with nothing to show
And the walls kept tumbling down
In the city that we love
Great clouds roll over the hills
Bringing darkness from above
But if you close your eyes,
Does it almost feel like
Nothing changed at all?
And if you close your eyes,
Does it almost feel like
You’ve been here before?
How am I gonna be an optimist about this?
How am I gonna be an optimist about this?
We were caught up and lost in all of our vices
In your pose as the dust settles around us
And the walls kept tumbling down
In the city that we love
Great clouds roll over the hills
Bringing darkness from above
But if you close your eyes,
Does it almost feel like
Nothing changed at all?
And if you close your eyes,
Does it almost feel like
You’ve been here before?
How am I gonna be an optimist about this?
How am I gonna be an optimist about this?
If you close your eyes
Oh where do we begin?
The rubble or our sins?
Oh where do we begin?
The rubble or our sins?
And the walls kept tumbling down
In the city that we love
Great clouds roll over the hills
Bringing darkness from above
But if you close your eyes,
Does it almost feel like
Nothing changed at all?
And if you close your eyes,
Does it almost feel like
You’ve been here before?
How am I gonna be an optimist about this?
How am I gonna be an optimist about this?
I really like this song. The music is nice, and I also appreciate the lyrics. I am sure that there is metaphor and that there are many ways to interpret the lyrics, but for me the lyrics of “Pompeii” express what it must feel like to be suddenly caught up in a devastating volcanic eruption– or any sudden natural disaster. The environment around you changes so quickly and so shockingly that you are left in a state of disbelief. Your mind can’t keep up. You feel, almost, that if you closed your eyes and opened them again everything would return to normal.
What do you think of the song? Does anyone else have geology-themed songs they enjoy? Perhaps we can start a geoblogging meme!
Here is Part II of the views that I observed during a flight from Amsterdam to Cape Town back in September 2012. Part I is here. I believe that all of these shots were taken over Algeria. There are some stunning desert views. Although I grew up in relatively lush New England, I have always liked deserts. I think I first became enchanted by deserts when I was an exchange student and lived in Jordan for 5 months when I was 15 years old. My school in Jordan took me on visits to places such as Wadi Rum and Petra, and I quickly fell in love with the sands, rocks, animals, people, and historical ruins of the deserts there. Visiting the Jordanian deserts certainly helped inspire me to study geology.
I’ve never been to Algeria, but the desert views I observed while flying over Algeria are certainly enchanting. The young, volcanic Hoggar Mountains look particularly enticing. I hope that I can one day visit the deserts of Algeria. Has anyone been there?
Enjoy the desert views below. And, as always, feel free to point out interesting locations and geological features.
I still have some more views to share from this flight, so stay tuned for Part III!
Algeria #2.Algeria #3.Algeria #4.Algeria #5.Algeria #6.Algeria #7. Sand ripples.Algeria #8. Sings of man.Algeria #9. A lone fire.Algeria #10. Another view of the fire.Algeria #11. Sand, sand, sand.Algeria #12.Algeria #13.Algeria #14. Signs of salt.Algeria #15.Algeria #16.Algeria #17. Red, white, and blue desert hues.Algeria #18.Algeria #19. A winding wadi leading into the Hoggar Mountains.Algeria #20.Algeria #21.Algeria #22.Algeria #23.Algeria #24.Algeria #25.Algeria #26. Volcanic mountain tops.Algeria #27.Algeria #28.Algeria #29.Algeria #30.Algeria #31.Algeria #32.Algeria #33.Algeria #34.Algeria #35.Algeria #36.
Note: Dr. Olivier Galland, a senior researcher at the Physics of Geological Processes Center of Excellence at the University of Oslo, presented a talk, “Ground deformation associated with shallow magma intrusions” at the LASI V conference in Port Elizabeth, South Africa in October 2012. The article below is based on this talk and also an interview with Dr. Galland. Over a few weeks, I am highlighting some of the research that was presented at the LASI V workshop. This is the fourth post in that series.
The landscape around an active volcano is dynamic: as magma moves about, the ground may change shape, inflating or deflating depending on how the magma is moving (Steps 1-2 of Fig. 1). The deformation may be caused either by the deep movement of magma or by the shallow intrusion of magma as sills or dykes. The movement can be dramatic (hundreds of meters) or it can be barely noticeable (a few millimeters). Big or small, ground deformation at volcanoes is important to monitor as it can provide clues to what is going on under the surface and, importantly, about when and where a volcanic eruption might occur.
At many volcanoes, geologists monitor ground deformation using a variety of techniques, including physical devices such as GPS and tiltometers, remote sensing techniques such as InSAR, and photogrammetry, which is the analysis of photographic images (Step 3 of Fig. 1). From surface measurements of ground movements, geologists can try to model what is going on underneath the surface (Step 4 of Fig. 1). However, linking observations of surface deformation to magma movements is no easy task (Step 5 of Fig. 1). That’s because geologists cannot generally directly observe the insides of a volcano. An analogy might be trying to understand why a kitchen sink is broken—why it is leaking or not flowing, perhaps— without being able to open up the cabinet door and look at the sink’s plumbing. Geologists can observe ancient volcanic plumbing, so to speak, in places where the tops of volcanoes have eroded away. However, observing the plumbing of active volcanoes is very difficult to impossible. Therefore, geologists generally rely on fancy computer models to try to link surface deformation with subsurface magma movement.
Fig. 1. Schematic diagram illustrating the principle of ground deformation analyses on active volcanoes. Numbering gives the succession of the stages of the analyses. 1. Magma intrudes in volcano, feeding magma reservoir or forming a sheet intrusion (dark gray intrusion). 2. Magma intrusion triggers ground deformation at surface, leading to modified topography (dashed line). 3. Topography variation is measured by geodetic techniques (GPS, InSAR, Photogrammetry, etc.). 4. Geodetic data are compared with modelling of ground deformation due to various intrusion shapes. 5. The best fit between models and ground deformation data provides a calculated intrusion shape (light gray dashed intrusion) responsible for the measured ground deformation. Nevertheless, the calculated intrusion shape is not a unique solution, and no direct observation is available to validate the calculation results.
Computer models are extremely helpful in trying to understand the insides of active volcanoes. However, they do have their limitations. This is because the shapes of magma chambers and shallow magma intrusions can be complex. Computer models can easily accommodate simple shapes such as circles or flat bodies. However, they have a harder time simulating more complex shapes, such as cones or saucers. Computer models also have trouble taking into account all environmental factors, such as the various stress fields and the realistic behavior of rocks. Finally, it is difficult to be completely confident in the results of computer models since the results of such models cannot generally be compared with direct observations.
One way to try to bridge the gap between surface observations of ground deformation and subsurface movements of magma inferred through computer models is through laboratory experiments. Dr. Olivier Galland is one scientist who conducts such experiments. Dr. Galland describes his experimental set-up (Fig. 2a) as, “Actually, it’s very simple. It’s just a box filled with silica flour, which is a fine-grained, granular material that is simulating the brittle crust. And into that material I inject a vegetable oil, which represents the magma, and the pressure of that oil is monitored. And then it’s possible to simulate the transport of magma and the formation of dykes and sills in this box.” Although such procedure seems simplistic, robust dimensional analysis of the method shows that the experimental results at the lab scale are valid at the geological scale.
Fig. 2. a. Drawing of the experimental apparatus. b. Representative oblique view photograph of the model surface during an experiment. The surface exhibited a smooth relief, at the rim of which the oil erupted. Dashed white line locates the section in the next image. c. Representative oblique view photograph of the model after the end of the experiment. The oil solidified and the intrusion was excavated, such that its top surface can be observed. The section showed that the intrusion was a thin sheet, resulting from hydraulic fracturing. Thus, the top surface of the intrusion was representative of its whole shape.
In a recent experiment (Galland, 2012) Dr. Galland used this silica flour and vegetable oil set up to simulate three types of shallow magmatic intrusions: a cone sheet, a dyke connected to a cone sheet, and a saucer-shaped sill. The motivation for this experiment was to provide additional data about the deformation that occurs when these shallow magmatic bodies are emplaced and, in addition, the deformation that occurs when they breach the surface and erupt. While the silica flour and vegetable oil set-up can’t simulate everything about a real volcano, it can provide plenty of important information, especially about the shapes of various intrusions and the pressures of the magma which produces these intrusions. This is possible because the oil is solid at room temperature, such that the final intrusion can be excavated out of the silica flour and its 3D shape analyzed (Fig. 2c).
Dr. Galland explains, “When a volcano is about to erupt or as it is erupted it either inflates or deflates, and this movement can be monitored. And then afterwards this movement is analyzed and inverted by geophysicists who try to calculate the geometry of the magma conduits. The problem is that we can never test these modeling results because we don’t see the intrusions because they are buried. The only way to really test these inversion techniques is to have a system where you measure the deformation and also know the shape of the intrusion and the pressure into the intrusion. And this is what we are doing in our experiments. We can quantify the shape of the intrusion and measure the pressure into the intrusion and measure the surface deformation, and then we can use this dataset to help test the inversion tools used by the geophysicists.”
Already, Dr. Galland’s experimental work is providing some interesting clues as to what is going on under the surface at volcanoes. “Recently, we figured out that there is clearly a link between how magma rises towards the surface and the pattern of the deformation at the surface,” Dr. Galland says. “Interestingly, this pattern develops very early during the experiments in the very early stages. So, we can observe some asymmetric development of this pattern which indicates where the magma is rising. So, if we can analyze that in real time, we could theoretically use it to predict where an eruption will occur. Obviously, in terms of volcanic hazard that is very important.” This is illustrated in the Figure 3, which shows the good match between the shape of the intrusion with the resulting ground deformation.
Fig. 3. Correlation between the shape of the ground deformation and the underlying intrusion in a characteristic experiment. a. Topographic map of model surface before the eruption of the oil. b. Plots of the temporal evolution of topographic profiles across the ground deformation pattern. The profiles are located on the map described in a. Each curve of the plots represents a transient stage of the model surfaces during each experiment. One can notice an initial symmetrical ground deformation, evolving to asymmetrical. c. Topographic map of the top surface of the excavated intrusion. The grey scale indicates the depth in mm below the initial surface. The locations of topographic profiles are the same as on the map of model surface in a, such that the profiles of the ground deformation and of the intrusions can be compared. d. Plots of topographic profiles of the model surface (top) and the underlying intrusion (down) parallel to the X-axis (X-profile). e. Plots of topographic profiles of the model surface (top) and the underlying intrusion (down) parallel to the Y-axis (Y-profile). Notice the vertical scale dilation for the profiles of the model surface. The correlation between e and d show that the ground deformation pattern reflects the shape of the underlying intrusion. This suggests that the asymmetrical development of the ground deformation pattern can be analysed to predict where the magma rises towards the surface.
However, Dr. Galland doesn’t spend all of his time in the laboratory. He believes that it is important for him to regularly go into the field to directly observe volcanoes, modern and ancient. He is particularly interested in observing subvolcanic systems, such as the saucer-shaped sills exposed in South Africa’s Karoo region and intrusive complexes formed in compressional settings exposed in the Neuquén Basin in the north Patagonian Andes. Dr. Galland explains, “My approach is to go to the field and really observe and do some detailed work and then out of that comes a question and then these questions can be subsequently addressed with experiments.” After all, that field knowledge is important for turning silica flour into the Earth’s crust and vegetable oil into magma.
Reference:
Galland, O. 2012. Experimental modelling of ground deformation associated with shallow magma intrusions. Earth and Planetary Science Letters, Vol. 317-318: 145-156.
***Note: Thanks very much to Dr. Galland for providing the three figures and captions.***
Brown and black products of Quaternary glaciovolcanic activity, with Paleozoic granite in the background, northern Victoria Land Antarctica. John Smellie for scale. Photo Credit: National Antarctic Research Program of Italy.
Note: Dr. Sergio Rocchi, an associate professor at the University of Pisa in Italy, presented a talk, “Intravolcanic sills, lava flows, and lava-fed deltas (Victoria Land, Antarctica): Paleoenvironmental Significance” at the LASI V workshop in Port Elizabeth, South Africa in October 2012. The article below is based on this talk and also an interview with Dr. Rocchi. Over a few weeks, I am highlighting some of the research that was presented at the LASI V workshop. This is the third post in that series.
When volcanoes erupt underneath and in the vicinity of glaciers and ice sheets, a unique geological record is created that provides information about both the volcanism and the snow and ice which interacted with the lava as it was being erupted. “Glaciovolcanism” is the term used to describe the interaction of lava with ice, snow (in all its forms, such as “firn” or compacted snow), and meltwater.
Glaciovolcanism includes study of modern examples in places such as Iceland and Antarctica as well as study of ancient examples. For the ancient examples, the ice and snow have generally long since melted away as a result of changing climate over the ages. Furthermore, the sediments and sedimentary rocks—tills and moraines and diamicts— associated with the glaciers and ice sheets have also often long since eroded away. However, volcanic rocks which interacted with the ice and snow are harder and slower to erode, and they often remain long after ice and sediment have disappeared.
Dissected late Pliocene volcano, northern Victoria Land Antarctica. John Smellie for scale. Photo Credit: National Antarctic Research Program of Italy.
Glaciovolcanic rocks can provide much valuable information about ancient glaciers and ice sheets. For example, study of glaciovolcanic rocks can help geologists identify if ice was present and, if so, can help geologists learn about the thickness of the ice, the elevation where the ice was present, the temperature conditions at the base of the ice, and the structure of the ice. A limitation is that volcanic eruptions do not occur continuously. Depending on the circumstances, they may occur at intervals of 10s—or even of 100s or 1000s— of years. Also, over time even hard glaciovolcanic rocks can erode away. Nevertheless, study of glaciovolcanic rocks is a powerful tool for reconstructing past ice cover and conditions, which in turn provides much information about past climate that can complement other paleoclimate studies—for example, study of sedimentary and coral records. Volcanic rocks are also fairly easy to date using isotopic techniques, so they can provide clear age constraints to help with paleoclimatic reconstructions.
Dr. Sergio Rocchi is a volcanologist who has studied glaciovolcanic rocks in Antarctica along with his colleague Dr. John Smellie and other co-workers. Dr. Rocchi explains, “Volcanic eruptions in subglacial environments generate some glacial volcanic lithofacies [units of rocks with certain characteristics] which can tell us the thickness and also the type of ice that was present at the time of the eruption. Additionally, the volcanic rocks can be dated by isotopic means, so the combination of the age and thickness of the ice can be a very useful source of paleoenvironmental information.”
Sergio Rocchi flying over Mt Melbourne Volcano, northern Victoria Land Antarctica. Photo credit: National Antarctic Research Program of Italy.Sergio Rocchi over Campbell Glacier, northern Victoria Land Antarctica. Photo credit: National Antarctic Research Program of Italy.
As an example, Dr. Rocchi and his co-workers have studied Late Miocene glaciovolcanic rocks of Victoria Land, Antarctica. There, hyaloclastite-rich glaciovolcanic rocks, including some “lava-fed deltas” (features which form when lava enters water either in a marine/lacustrine or a glacial meltwater environment), have enabled reconstruction of Late Miocene glacial cover over Victoria Land. The glaciovolcanic rocks indicate that at this time Victoria Land was covered by a thin (<300 m thick) cover of ice. This ice sheet is much thinner than that predicted by some modeling studies and implies a more complex climatic transition in the Miocene than previously thought.
While most work regarding glaciovolcanism to date has been carried out in Antarctica, study of glaciovolcanism can also be done in many other places. “Similar work can obviously been done wherever there are or were volcanoes and ice,” says Dr. Rocchi. “The main places where volcano-ice interaction can be studied are Antarctica, Iceland, and British Columbia in the northern Cascades. A future project for which we are raising funding is making a comparison of the glaciovolcanic record in Antarctica with that in Iceland.”
In the future, study of glaciovolcanism will no doubt continue to help geologists and climate scientists unravel the history and nature of past glaciers and ice sheets. Combined with other paleoclimate records, study of glaciovolcanism will help scientists to better understand how Earth’s climate used to be and how climate changes over time. This information is invaluable in a time when humans are experiencing the effects of anthropogenic climate change and when scientists need as much information as possible in order to evaluate what may happen to Earth’s climate in the coming years.
Smellie, J., Wilch, T., and Rocchi, S., 2013. ‘A‘ā lava-fed deltas: A new reference tool in paleoenvironmental studies. Geology. (to be published in the April issue).
Smellie, J., Rocchi, S., and Armienti, P. 2011. Late Miocene volcanic sequences in northern Victoria Land, Antarctica: products of glaciovolcanic eruptions under different thermal regimes. Bulletin of Volcanology, Vol. 73: 1-25.
Smellie, J., Rocchi, S., Gemelli, M., Di Vincenzo, G., and Armienti, P. 2011. A thin predominantly cold-based Late Miocene East Antarctic ice sheet inferred from glaciovolcanic sequences in northern Victoria Land, Antarctica. Palaeogeography, Palaeoclimatology, Palaeoecology, Vol. 307: 129-149.
Smellie, J., Johnson, J., McIntosh, W., Esser, R., Gudmundsson, M., Hambrey, M., van Wyk de Vries, B. 2008. Six million years of glacial history recorded in volcanic lithofacies of the James Ross Island Volcanic Group, Antarctica Peninsula. Palaeogeography, Palaeoclimatology, Palaeoecology, Vol. 260: 122-148.
Note: Dr. Steffi Burchardt, a senior lecturer in Structural Geology at Uppsala University in Sweden, presented a talk, “Xeno-pumice erupted offshore El Hierro, Canary Islands: A tale of stoped blocks in magma chambers?” at the LASI V workshop in Port Elizabeth, South Africa in October 2012. The article below is based on this talk and also an interview with Dr. Burchardt. Over a few weeks, I am highlighting some of the research that was presented at the LASI V workshop. This is the second post in that series.
Following a period of intense seismic activity, on October 10th, 2011 a submarine eruption began approximately 1 kilometer off the coast of El Hierro, the youngest and westernmost island in the Canary Islands, which is a group of volcanic islands believed to have been formed through hotspot volcanism. The eruption was evident from the unusual conditions on the sea surface: the sea bubbled, like a Jacuzzi, and was stained green. The large green stain was easily observable from space. In the midst of these strange conditions, some highly unusual rocks were erupted. For several days after the sea started bubbling, strange floating rocks were observed and collected off the coast of La Restinga, the closest town to the undersea eruption. These floating stones were generally tens of centimeters in size and resembled lava bombs in shape. The outsides of these floating rocks consisted of basanite , a rock type commonly observed in the Canary Islands and other volcanic ocean islands. Basanites don’t generally float. However, these basanite shells floated because their insides were filled with a white to light grey, pumice-like material. Pumice is a highly vesicular rock, which means that it is a rock full of voids or bubbles, which make the rock light enough to float on water.
Figure showing the green stain on the sea during the early days of the 2011 El Hierro eruption. Figure from Troll et al., 2012.A restingolite bomb with a basanite crust and a white, pumice-like interior. Photo courtesy of Dr. Steffi Burchardt.
While the pumice-like centers explained why the rocks floated, they also raised a multitude of questions and triggered some heated debates amongst geologists. This is because pumice is not commonly produced in the Canary Islands* or in other oceanic island hotspot environments, such as Hawaii and Iceland. The lavas erupted at oceanic island hotspots are generally mafic, low viscosity lavas such as basalts (and basanites). Viscosity is, in essence, a measure of how resistant lava is to flowing. The less viscous a lava, the more likely that lava is to flow. Therefore, low viscosity lavas such as basalts tend to flow easily and also tend to regularly release volatiles such as water and carbon dioxide. Therefore, the pressures in these lavas remain relatively low, and violent eruptions are uncommon. Pumice is most commonly produced during eruptions of felsic, highly viscous, volatile-rich lavas, which are found in environments such as island arcs, not oceanic island hotspots. The voids or bubbles in pumice represent places where volatiles have been rapidly released due to a pressure change, often during a violent eruption.
So, what was pumice-like material doing in an oceanic island eruption? A number of theories were put forward to try to explain the floating rocks that were erupted off of La Restinga. Some scientists thought the pumice-like material represented juvenile, highly silicic, highly viscous magma (such as rhyolite), which is very explosive. Other scientists proposed that the pumice-like material represented re-melted magmatic material, altered volcanic rock, or reheated hyaloclastite or zeolite from the slopes of El Hierro. Mysterious in origin, the floating stones were called “restingolites” after the nearby town of La Restinga.
After extensive analysis, a group of scientists (Troll et al., 2012) proposed an alternative hypothesis to explain the pumice-like material found in the restingolites. Based on the material’s high silica content, lack of igneous trace element signatures, and high oxygen isotope values as well as the presence of remnant quartz, jasper, carbonate, and wollastonite, Troll et al. concluded that the pumice-like material in the restingolites in fact represented xenolithic material from pre-island sedimentary layers that were picked up and heated by ascending magma, which caused the layers to partially melt and bubble. Looking like pumice and originating as xenoliths, Troll et al. dubbed the restingolites “xeno-pumice”.
Dr. Burchardt elaborates, “Xeno-pumice is definitely not an established term. We have coined it for the first time in the case of El Hierro eruption. The name comes from adding the preface ‘xeno-‘, which means foreign, to ‘pumice’. We used this term because the floating rocks of El Hierro present the characteristics of pumice, but they are actually not pumice in origin; they are actually xenoliths. We found out, based on mineralogy and also the fact that they contain detrital sand grains and fossils, that they are actually not magmatic in origin but rather that they are xenoliths from the sedimentary layers that underlay the Canary Islands. So, they are older than the volcanism. When the magma was rising, it stagnated at this level and interacted with the sedimentary rocks, sandstone and minor carbonate, and the magmas transported the xenoliths up with them to the ocean floor, where they were erupted. But in the process of the ascent of these xenoliths, they were subject to heat from the magma, so they started to melt. Since they contain a lot of water, this water started to boil and formed bubbles. The end product was something that looked like a pumice: lots of bubbles surrounded by a glassy matrix.”
Schematic from Troll et al. 2012 illustrating how the El Hierro restingolites may have formed.
Even though xeno-pumice was not a known rock type before the 2011 El Hierro eruption, Dr. Burchardt and her colleagues think that xeno-pumice may actually be a common—if not commonly recognized—rock type in other parts of the world.
Dr. Burchardt explains, “The El Hierro eruption was a very fortuitous circumstance for our work because my colleagues and I had been working on similar rocks from volcanoes worldwide, but that they were not previously recognized as xeno-pumice. The El Hierro eruption was therefore some kind of a breakthrough for our research in this field, and there will be a whole series of papers dealing with xeno-pumice from different parts of the world.”
By November, the xeno-pumice rocks were no longer being erupted, and worries that a dangerous, explosive eruption could occur at El Hierro abated. The identification of the restingolites as xeno-pumice was also good news for the hazard risk at El Hierro.
Dr. Burchardt explains, “It was good news that these xenoliths are sedimentary in origin because it means that there is no rhyolitic magma beneath the island, which means that a big explosive eruption isn’t likely.”
While the xeno-pumice rocks do not carry the message that an explosive eruption is likely to occur at El Hierro, they do carry other important messages from the deep. The unusual xeno-pumice rocks observed erupting at El Hierro in 2011 can provide much direct information about the interaction of magma and oceanic sediments and also may indicate that recycling of oceanic sediments into magma is an important process at ocean islands. Further study of xeno-pumice from the Canary Islands—and also from other parts of the world—will go a long way towards helping geologists better understand how volcanic eruptions at ocean islands interact with oceanic crust and sediments as they make their way to the surface.
*Update: Commentor Siim Sepp points out that intermediate composition pumice is found on the Canary Islands, most notably on the island of Tenerife. This is a very good point. I have perhaps oversimplified the explanation– pumice can be found at volcanic ocean islands under certain conditions. Thanks for pointing this out, Siim!
Reference:
Troll, V.R., Klügel, A., Longpré, M.-A., Burchardt, S., Deegan, F. M., Carracedo, J. C., Wiesmaier, S., Kuepper, U., Dahren, B., Blythe, L. S., Hansteen, T., Freda, C., Budd, D., Jolis, E. M., Jonsson, E., Meade, F. C., Harris, C., Berg, S. E., Macini, L., Polacci, M., and Pedroza, K. 2012. Floating stones off El Hierro, Canary Islands: xenoliths of pre-island sedimentary origin in the early products of the October 2011 eruption. Solid Earth, Vol. 3: 97-110.
Note: Dr. Dougal Jerram—aka “Dr. Volcano”— presented a talk, “When Shallow Intrusions Make Silver Mines—A Journey into Superman’s Cave, Naica, Mexico” at the LASI V workshop in Port Elizabeth, South Africa in October 2012. The article below is based on this talk and also an interview with Dr. Volcano. Over the next few weeks, I will be highlighting some of the research that was presented at the LASI V workshop. This is the first post in that series.
The title of this blog post, “Dr. Volcano in the Cave of Crystals”, may sound like the title of a comic book or a science fiction story, but I can assure you that both Dr. Volcano and the Cave of Crystals are very much real. I had the pleasure of meeting Dr. Volcano and hearing about his visit to the Cave of Crystals at the LASI V workshop back in October 2012.
Dr. Volcano is also known as Dr. Dougal Jerram, who in June 2011 left his academic position at Durham University to set up DougalEARTH Ltd. and embark on an exciting new career as an independent geological consultant, researcher, and also a media consultant, becoming involved in science outreach and popular science entertainment. On his website DougalEARTH, Dr. Jerram states that he is, “aiming to make science more accessible to the general public and promoting our understanding of the planet.” In his science outreach and media work, Dr. Jerram is known as “Dr. Volcano.” The title is certainly appropriate since he has published dozens of scientific research articles about volcanoes and has also penned two books about volcanoes, The Field Description of Igneous Rocks (with Nick Petford, 2011) and Introducing Volcanology: A Guide to Hot Rocks (also 2011). For his scientific outreach and media work, Dr. Volcano has appeared on television programs for stations such as the BBC, The History Channel, and National Geographic.
The Channel 9 News Team in the Cave of Crystals. Picture courtesy of Andy Taylor.
As part of his media work, Dr. Volcano had the extraordinary opportunity to visit a place in Naica, Mexico known as Cueva de los Cristales or the Cave of Crystals (http://en.wikipedia.org/wiki/Cave_of_the_Crystals) in the Fall of 2011. Dr. Volcano visited the cave as part of a news team for a 60 Minutes documentary for Channel 9 News, Australia. The cave is also known as the Giant Crystal Cave and Superman’s Cave, since it resembles the Arctic home of the comic book character Superman. Located about 1000 feet (about 300 meters) below the Earth’s surface, the cave contains gigantic crystals of selenite (gypsum, CaSO4•2H2O) that are some of the largest known crystals on Earth. The largest crystals in the cave are nearly 40 feet (12 meters) tall!
The Cave of Crystals was first discovered in 2000 by miners who were excavating a new tunnel for the silver, zinc, and lead mine owned by the Industrias Peñoles mining company. Previously, a similar cave known as Cueva de las Espadas or the Cave of Swords was discovered in 1910. This cave is also located at Naica but at a shallower depth of about 400 feet (about 120 meters). However, the selenite crystals in the Cave of Swords are smaller, with a maximum size of about 6 feet (2 meters). In addition, many of the crystals from the Cave of Swords have been removed from the cave and transported to other places, such as museums.
A map of the Naica mine showing the locations of the Cave of Swords and the Cave of Crystals. Figure taken from Garcia-Ruiz et al. (2007).
Dr. Volcano explains, “We had the very lucky opportunity to go into the Naica caves in Mexico. These caves are very special because they have—arguably—the largest crystals on the planet. These crystals are gypsum, which is calcium sulphate (dihydrate). We were able to get into these caves after two years of negotiation with the Mexican mine and the government there.”
Prior to mining, the Cave of Crystals was underwater. The cave is only exposed because the mining company has pumped water away, lowering the groundwater level so that mining can proceed deeper. Naturally, the groundwater level is about -110 meters. Once pumping stops, the Cave of Crystals will again fill with groundwater. And not just any groundwater. The cave will fill with very hot groundwater since the Earth is quite warm at 300 meters depth. Research (e.g. Ruiz-Garcia et al., 2007) suggests that the enormous selenite crystals found in the Cave of Crystals likely formed in low-salinity fluids that were at a temperature of approximately 54 degrees Celsius. The selenite crystals grew very slowly over hundreds of thousands of years, enabling the crystals to reach their enormous sizes.
While no longer filled with hot fluid, the Cave of Crystals nevertheless remains an inhospitable environment for humans. Temperatures in the cave are 45 to 50 degrees Celsius, and the humidity ranges from 90 to 100%. While the mining shafts are cooled for the workers, the Cave of Crystals is not cooled, which helps preserve the giant selenite crystals. Visiting the Cave of Crystals is therefore no easy feat.
Dr. Volcano describes, “You go inside the cave, and you’re in temperatures of around 50 degrees Celsius, and the humidity is around 100%. One of the biggest problems when you go into an environment like that is that your body is unable to cope with that environment, and you effectively start dying the minute you enter the cave.”
In such an extreme environment, humans can only survive unaided for a few minutes.
Dr. Volcano elaborates, “The biggest problem you have is that when your body temperature is the lowest temperature in the cave, everything that your body does to try to cool itself doesn’t work. It tries to sweat, but the sweat doesn’t evaporate because there’s 100% humidity, so there’s no cooling from evaporation. You breathe in air, but the air is hotter than your internal body, so it starts heating up your body. You start to pant, like a dog, which is a natural reaction to try to cool yourself, but as a result you end up heating the interior of your body more quickly. We found that after 9 minutes in the cave without any sort of protection, our body temperatures rose to 39.5 degrees Celsius, which is quite dangerous. We had an Australian medic with us (David Rosengren), and he said that if your body temperature goes over 40 degrees Celsius, you could very rapidly deteriorate and even die.”
Fortunately, the Channel 9 news team came prepared.
Dr. Volcano explains, “We had a kind of solution, which we called ‘Formula 1 Geology.’ We used the same sort of suit that people in extreme sports, such as Formula 1 racing, use in environments where they can get very hot very quickly. It’s a close-to-the-body suit with piping inside that pumps cold water around the body. You wear a backpack with ice water, and an electric pump moves that cold water around the suit. With the suit, we could safely stay in the cave for about 25-30 minutes. Ultimately, if other people could refill the backpacks with more ice cold water, people could possibly stay in the cave much longer.”
As difficult as it is for humans to explore the Cave of Crystals at present, if mining ever stops at the Naica mine then it may become impossible to visit the cave since it will again fill with hot fluid.
Dr. Volcano wonders, “The giant crystal caves are only exposed because man is pumping the groundwater out. The biggest dilemma that we have for this natural wonder of the earth is: if the mining stops, then in principle the water level will rise again, and the Naica caves will be underwater again. I pose to the general public: what should be done—if anything—to save the Naica caves?”
I wonder that, too. It may be that the unique and remarkable Cave of Crystals will only be accessible for a brief time, only as long as the Naica mine remains in business.
Georneys 