Diamond Kimberlites: Live Fast, Die Hard

Just as the world’s famous diamonds conjure stories of theft and intrigue, of monopolies and power, diamonds also tell an equally exciting geological story. Diamonds are made of carbon molecules arranged in a very tight, unique arrangement, which is what makes them so hard. It takes high pressures to squish the carbon molecules into that kind of interlocking structure, which is why diamonds form very deep in the Earth’s crust at depths of 150 to over 200 kilometers (roughly the distance from Washington, DC to Philadelphia). The Kola Superdeep Borehole, the deepest hole ever dug, was only a little over 12 kilometers deep, and it did not even break through Earth’s crust into the mantle. So, we do not dig for diamonds in the crust – they come to us! Diamonds are brought near to the surface by an unusual type of volcanic structure known as a kimberlite pipe.

A diamond in the rough in a kimberlite. Wikipedia.

Kimberlites are igneous rocks named for Kimberley, South Africa, where they were first studied. Their journeys begin deep in the mantle when a neighborhood of rock begins to melt due to a change in temperature or pressure conditions. This new magma is less dense than the surrounding rock, and so it begins to rise like a balloon. As it rises the magma picks up diamonds, which exist naturally at those depths, and carry them along for the ride. The magma ascends through the mantle in a vertical chimney-like structure known as a kimberlite pipe (not exactly an open hole, but more like a network of cracks and channels). The kimberlite pipe ferries the magma all the way up into the crust, where it eventually cools into kimberlite and deposits its diamonds. This process is not so different from more conventional types of magmas, which come from shallower neighborhoods of the Earth. What makes kimberlite magmas unique is the speed with which they traverse such great distances. Evidence from the minerals in kimberlites show that they ascend at rates of 1 to 10 meters per second, which means their total travel time is anywhere from less than 10 hours to about 2 days (it takes about 3.5 hours to drive from Washington, DC to Philadelphia). This is the equivalent of a geological high-speed train, carrying diamonds up from the mantle through solid rock at rates faster than the flow of the Mississippi River.

A kimberlite diamond mine situated on top of a kimberlite pipe. Diamonds have been mined from only about 30 localities on Earth. Wikipedia.

For a long time, geologists puzzled over the driving force behind such an ascent; no other magma travels that far through the Earth, and at such high speeds. In 2012, a team of researchers modeled an exciting explanation for the phenomenon. The answer lies in the magma’s changing chemistry. When they first form from melting mantle rocks, kimberlite magmas are very basic (the opposite of acidic) and they contain a lot of carbon. They do carry diamonds with them, but kimberlite magmas also scrape off solid chunks of rock from the walls of the kimberlite pipe during their journey upwards. These chunks of rock are known as xenoliths (Greek for “foreign rock”) and they begin to dissolve as they are carried along. The xenoliths are not basic, and they actually make the kimberlite magma more acidic as it rises (similar to how a sugar cube makes your coffee sweeter). Increasing the acidity changes the properties of the magma such that it can no longer carry the dissolved carbon with which it started out. As more and more xenoliths are incorporated into the magma (by the end of its journey, the magma is almost 25% xenolith by volume), the dissolved carbon separates from the magma and combines to form carbon dioxide instead. This process effectively foams the magma and increases its buoyancy, making it shoot upward for the same reason a soda bottle foams over after being shaken. Kimberlite magmas travel one of the most remarkable geological journeys, and they are essentially propelled by the Earth-equivalent of a soda machine.

Caption from previous: Diagram of kimberlite pipe with xenoliths, with modern day equivalent for comparison. Kansas Geological Survey, and Coca Cola.

In the years since its discovery, this hypothesis has become the accepted mechanism for kimberlite volcanism.  Although it is a relatively simple trick of chemistry, the process it drives is worthy of the gem’s lore. The diamonds that we mine and wear and burglarize have all been carried to the crust by a hot, fizzing column of magma champagne, racing behind a popped cork that’s flown 200 kilometers away.

For more information:

Russell, J.K., Porritt, L.A., Lavallée, Y., and Dingwell, D.B. 2012. Kimberlite ascent by assimilation-fuelled buoyancy. Nature, 481. 352-356.

Russell, J.K., Sparks, R.S.J., and Kavanagh, J.L. 2019. Kimberlite Volcanology: Transport, Ascent, and Eruption. Elements, 15. 405-410.

Could we live in lava tubes on the Moon?

 When we think about space exploration, our first thought is most likely not about underground tunnels. But as it turns out, that might just be the best place to start exploring!

What are lunar lava tubes?

Lava tubes are void structures formed when the surface of a lava flow cools, crusts over, and hardens. The lava underneath this crust continues to flow and drain out, leaving behind a hollow channel with hard rock surrounding it. Terrestrial lava tubes, or the lava tubes found here on Earth, differ from lunar lava tubes most drastically in their size. Terrestrial lava tubes average a width of about 10-100 meters, while lunar lava tubes are estimated to be 1000 times that of terrestrial tubes! Although lunar lava tubes have not been physically accessed yet, they have been studied through various other methods including images captured from space. Through these techniques, basic information has been provided about lunar skylights (collapsed sections of lava tubes) and sinuous rilles (elongate features resembling channels) as well as void spaces beneath these surface features.

Figure 1. Artists rendering depicting how a lunar rover may enter a lava tube through a skylight.

Why should we care about lunar lava tubes?

Lunar lava tubes pose as a suitable location for future lunar bases. The large size of these void spaces means there may be a large amount of useable floor space in these tubes in order to set up instrumentation and future housing for astronauts. Since these lunar lava tubes have a "roof", they will also provide protection from radiation, micrometeorites hitting the surface of the moon, and extreme temperature fluctuations. In addition to shelter, lava tubes provide possible access to resources, such as frozen water, that may be trapped in the volcanic material. These resources can potentially be accessed and used by astronauts as a source for useable water and potential rocket fuel.

If these tubes are underground…how do we find them?

Because these lava tubes on the Moon are typically buried beneath the ground, one of the main concerns in studying lunar lava tubes is actually being able to find where they are on the Moon. Scientists have to use special techniques that include sending signals in the form of waves into the Moon’s interior that then bounce off the rocks and create a sort of image of the lava tube. These waves will bounce off certain rocks differently depending on those rocks’ physical properties. Laboratory experiments can help characterize these differences in properties which are used to help scientists understand what’s going on in the images they capture.

These waves that scientists send into the moon are very similar to the way doctors use X-rays to image the inside of a body. When a doctor takes an X-ray, they are actually using waves to create an image of the inside of a patient’s body. X-rays pass through bone differently than it passes through tissue and muscle. These differences are what makes it possible to see an actual image. The waves that scientists pass through the Moon act in a similar fashion. These waves will pass through hard solid rock differently than it would soft loose sediment and differently again as it would an empty lava tube. It is for this reason that scientists can actually create an image of the inside of the Moon!

Figure 2. X-ray showing the inside of a person’s hand (left). Sketch of how waves travel through the ground and can be used to produce an image of the lava tube beneath the surface (right).

 

Hopefully, by combining the knowledge obtained from measurements taken in a laboratory with this technique for imaging the interior of the Moon, scientists can more readily locate lunar lava tubes. And while we may still be years out from starting entire cities on the Moon, lava tubes may just be the key to continuing our long journey of exploring our Solar System and beyond!

References

Alex Beall. CSU System. News. The Faults in our Earth. https://www2.calstate.edu/csu-system/news/Pages/the-faults-in-our-earth.asp

NASA, 2017. Apollo 11 Seismic Experiment. https://moon.nasa.gov/resources/13/apollo-11-seismic-experiment/

Sauro et al., 2020. Lava tubes on Earth, Moon and Mars: A review on their size and morphology revealed by comparative planetology, Earth-Science Reviews, Volume 209, 2020, 103288, ISSN 0012-8252.

Why gophers are cooler than people but not planets 2.0

The average American gopher, weighing roughly 1-2 lbs, lives a solitary life in a burrow consisting of multiple tunnels. Whether used for foraging, storage, or rest, these tunnels can reach up to hundreds of square yards in size, with depths ranging up to six feet below the surface. With an assumption that I can consider myself an average America, this feat is more than I expect to accomplish in my lifetime (Minecraft excluded). 

Figure 1. Gopher, ft. burrow (National Park Service)

Debatably more accomplished than a gopher, the Earth has created tunnels through a plethora of processes; lava tubes and their formation being the most applicable process to my research. Generally seen as a “roofed conduit” (or tunnel) of actively flowing, drained, or plugged magma, lava tubes on Earth are yards to miles in length, 0.5-30 yards in width or height, and anywhere from centimeters to meters below the surface. Now this may feel like it puts the gopher’s efforts to shame, but to put it in perspective Earth weighs around 13,170,000,000,000,000,000,000,000 gophers. Even more shameful is the fact that Lunar and Martian lava tubes have been found to be 1-3 times larger than those on Earth. As of the writing of this blog I do not know of any gophers having conducted interstellar travel.

Volcanoes’ process of digging is a degree more heated than gophers’, with the three main mechanisms being overcrusting, shallow inflation, and deep inflated-entrenched tubes. Overcrusting of magma occurs when the surface chills and solidifies, insulating the molten lava below and allowing it to maintain high temperature and lower thickness for longer. Imagine placing a napkin over freshly microwaved soup where the napkin insulates the liquid, keeping it hot longer than it would stay without a cover. The second form, shallow inflation, results in a bulge morphology. To deviate from the food and animal metaphors, consider that you have a family member who loves packaging peanuts, so you decide to mail them some. As you shove the peanuts into your inadequate envelope it will inflate and form a bulge either in the middle or towards the far end as you keep pushing. 

The magma used as an analogue for the Moon and Mars is termed basaltic due to its composition, and has two broad variants: pahoehoe and a’a, with the first being more liquid and less rough than the latter. For pahoehoe lava flows, the inflation process results in a central bulge of the lava sheet (packaging peanuts relatively evenly shoved into the envelope) and a sequence of elliptical lava tubes form below the surface. In contrast, the shallow inflation bulge for a’a flows is found nearer to the end of the lava flow (packaging peanuts shoved to the opposite side) due to higher pressure, these a’a flows create larger lava tubes than pahoehoe flows. The final variant, deep inflated-entrenched lava tubes, are the largest found on Earth and involve downward erosion. Compared to the previous three lava tube formation mechanisms, deep inflated-entrenched tubes lack identifiable surface features. 

Figure 2. Models of lava tube geometries and associated surface features. Of note are top left corresponding to overcrusting, top right  to pahoehoe shallow inflation, bottom left  to a’a shallow inflation, and bottom right to thermal erosion and breakdown (Sauro et al. 2020).

 

Definitions of technical jargon aside, lava tubes (inferred from the presence of skylights and collapse along winding features) on the Moon and Mars were created through similar processes; overcrusting and shallow inflation for Mars, and deep inflation-entrenchment for the Moon. Unfortunately for Mars, lunar lava tubes are the current candidate for “most likely to be stable and not collapse - as much”. Fortunately for Mars, my research into modelling lava tubes looks past this shortcoming. At its current stage, my research focuses on using mesh (interconnected shapes, a latticework shown below) software to create lava tube analogous geometries - a circle or cylinder representing a tube inside of a rectangle representing the surrounding subsurface. My next step is to import this mesh geometry into a solver software that will allow me to simulate the movement of seismic waves generated by a hammer hitting the surface through the subsurface. As the surrounding rock and vacuum space of the lava tube are different compositions, these simulations will present estimates of the lava tube’s location and dimensions. These estimates will hopefully allow for steps to be taken by astronauts to reach and utilize the tubes. A step not taken by your average American gopher.

Figure 3. Example of a simple lava tube mesh geometry (created by me using GMSH software).

References

A. Bradford. Facts About Gophers, Live Science (2017), 

https://www.livescience.com/57623-gopher-facts.html 

Cool Cosmos. How much does Earth weigh and how is this measured? IPAC. 

https://coolcosmos.ipac.caltech.edu/ask/61-How-much-does-Earth-weigh-and-how-is-this

-measured

F. Sauro, R. Pozzobon, M. Massironi, et al., Lava tubes on Earth, Moon and Mars: A review on 

their size and morphology revealed by comparative planetology,

Earth-Science Reviews (2020), https://doi.org/10.1016/ j.earscirev.2020.103288

SPECFEM2D User Manual (2020). https://specfem2d.readthedocs.io/en/latest/ 

So Much Water but None to Drink!

Figure 1. Warm bowl of chicken noodle soup.
Source: TasteofHome.com

On a frigid, snowy day, nothing tastes (or smells!) quite as good as warm, chicken noodle soup. After the first spoonful, I usually notice the soup tastes delicious but needs a little extra flavor. My solution: salt! We use salt on our foods to enhance and balance the flavors in our meal. But at a certain point, one too many grinds of the saltshaker can make the soup overwhelmingly salty. Something similar is happening to our freshwater sources worldwide.

Figure 2. Road salt on boardwalk in
College Park, MD

Throughout the same cold day, trucks are applying road salt to roads, sidewalks, and parking lots. Road salt is applied to the roads to melt the snow and ice for safety purposes. Yearly, Maryland buys 30,000 dump trucks worth of salt each year, or about 230,000 tons, which costs $11 million! The United States uses almost 2 million dump trucks of salt per year, 45 to 87 times the amount Maryland buys. Where does the road salt go after the roads are clear? The salt dissolves and is transported with the melted snow and ice into groundwater and the nearby streams. After multiple winter snowstorms, the streams accumulate more salt, a process called salinization. A study found rivers in Maryland, New Hampshire, and New York have a quarter to a half the saltiness of seawater during the winter and remain elevated during the summer. Our rivers have the salinity of about 1.5 to 2 cans of Campbell’s Chicken Noodle Soup!

Figure 3. The salt concentration is increasing over recent years in
many freshwater sources globally.
Modified from Kaushal (2016).

The term Freshwater Salinization Syndrome describes the process of increasing salinization over time. Salinization does not only impact snowy cold regions but is a global issue. Other sources of salt include building and road materials, construction, fertilizers, water softeners, and even our sewage. The consistently saltier environment drastically alters the chemistry of the water and creates an inhospitable home to many aquatic organisms. Highly sensitive and native organisms are unable to survive in these salty conditions. Salt-tolerant species, on the other hand, thrive in a range of salinities and can easily repopulate and live in the saltier waters. The increase of salt-tolerant species and decline of native or highly sensitive species alters the food web and the ecosystem of the river. 

The influx of salt not only harms aquatic life, but also causes the release of toxic metals into rivers. The metals are attracted to the soil like the positive and negative side of a magnet and want to be touching (Figure 4a). Like a magnet, the soil and the metal also have charges - the soil has a negative charge, and the metals have a positive charge.  When we add salt (Figure 4b), we are adding positive charges into the stream that are more attracted to the soil. The metal is not strong enough to stay attached to the soil particle and is released into the water. The metal flows with the water downstream to the drinking reservoir or to a well where we get our drinking water. In very high doses, these metals can cause a variety of health effects, ranging from nausea, vomiting, and diarrhea to cancers, learning deficiencies, and skeletal abnormalities. 

Figure 4. (a) Without an influx of salt, the metal and soil are attracted to each other.
(b) When salt is added, the salt is attracted to the soil and the metal is released into the river.

Freshwater Salinization Syndrome is an increasingly pertinent problem in freshwater sources worldwide. It is highly unlikely we will stop using road salt. Even if we did, it is extremely difficult to pinpoint all the other sources of salt in our rivers. Therefore, we must continually monitor and sample these impaired rivers year-round and create regulations with consequences for exceeding the salt levels. Currently, the US Environmental Protection Agency has set general salt limits for our rivers, but each state can ignore when the limit is exceeded. We must continue to monitor and holistically manage sources of salt to our freshwater environments before it is too late. 

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References: 

https://www.baltimoresun.com/bal-te.journal18feb18-column.html

https://mde.state.md.us/programs/Marylander/Documents/2013_Stranko_Road_Salt_(final)_TMF_edits.pdf

Kaushal, S.S., Groffman, P.M., Likens, G.E., Belt, K.T., Stack, W.P., Kelly, V.R., Band, L.E., Fisher, G.T., 2005, Increased salinization of fresh water in northeastern United States: Proceedings of the National Academy of Sciences of the United States of America, v. 102, p. 13517-13520.

Schuler, M.S., Canedo-Argulles, M., Hintz, W.D., Dyack, B., Birk, S., Relyea, R.A., 2018, Regulations are needed to protect freshwater ecosystems from salinization: Philosophical Transactions of the Royal Society B, v. 374.

https://www.baltimoresun.com/news/bs-xpm-2006-02-12-0602110117-story.html

The Core of Earth's Structure

    It’s a hot day, and you need a refreshing drink. You order a nice, big cup of boba, like the one pictured here on the right. It’s a nice sight - the milk tea and the tapioca pearls all in one tasty drink. Now, imagine that cup of boba is our Earth, but instead of being made up of tea and tapioca, it consists of a crust, mantle, and core. The fact that Earth is structured this way may be common knowledge, but how exactly this structure came to be may be a mystery to some.

    To start with, Earth hasn’t always looked the way it does now. Early on in Earth’s history, our planet was hot enough to be partially molten. This heat came from a couple of different sources: impacting material and the decay of radioactive elements. Radioactive elements are atoms that are unstable, and tend to decay to a more stable form. For example, over time, uranium can decay to thorium, potassium to argon, and aluminum to magnesium. These decay processes, among others, can generate significant amounts of heat inside the Earth. Aluminum in particular was a substantial heat source during Earth’s formation. This specific isotope, referred to as aluminum-26, has a short half life, meaning that it decays relatively quickly. This means that all of the aluminum-26 was used up when it was heating Earth, and actually doesn’t exist anymore!  

    Our other main heat source, impacting material, is very different in nature. Think of what happens when you clap your hands together. Depending on how hard you do it, your hands will get warm (and maybe even sting a little bit). Now, instead of your hands, imagine a massive planetary body, like an asteroid or planetesimal, crashing into Earth at an extreme speed. Events like these occurred often as the planets in our Solar System formed, and Earth was no exception. These collisions generated large amounts of heat - enough to trigger localized melting. 

    All of this heat and melting made it easier for the now molten material within the Earth to move around and separate from one another. This process is called planetary differentiation, and it’s the reason Earth is structured the way it is. Denser, molten material was able to travel toward the center of the Earth, while the less dense material rose toward the surface. This is why Earth’s core is primarily made up of iron and nickel - two relatively dense metals. In contrast, the crust and mantle are made up of minerals called silicates, which are much lighter. To go back to the boba analogy, the iron and nickel would be our tapioca balls sinking to the bottom of the cup. The tapioca is denser than the overlying milk tea, just like how Earth’s core is denser than the lighter minerals that comprise the crust and mantle. Earth is exactly like boba! Just maybe a little bit harder to drink.

    This process doesn’t just apply to Earth, though. Similar processes took place on the other planets in our Solar System, as well as on their moons, and on a variety of asteroids. This reorganization of material gives planetary bodies their characteristic layering, and can tell us a bit about what’s going on in their interiors - even though we may not be able to see them up close. Fortunately, we’re able to use meteorites that fall to Earth to learn more about these other planetary bodies - whether it be Mars, the Moon, or some far-off asteroid! For example, the meteorite pictured below is composed nearly entirely of iron and nickel, meaning that it was likely part of the core of a planetary body that had broken apart at some point. This meteorite, and the thousands of others that have been discovered across Earth, can tell us a lot about the planets and asteroids that we share our Solar System with!

How Methane Tells a Story of its Origin

A flare burns excess methane from an energy-producing well near Karnes City, Texas.

Aaron M. Sprecher/Associated Press

Methane is important, not only because it's the major component of natural gas -- a widely-used clean energy that can power the electric lamp, but also because it's a powerful greenhouse gas that traps the heat of the sunlight and is the second-largest contributor to global warming after carbon dioxide. Given its great importance, we may wonder where and how was it formed? What was the temperature of its formation? What kind of journey did it experience before it is finally exposed to the atmosphere? The answer might have recorded by a small group of rare methane molecules, waiting for us to explore.

Radiative forcing due to major greenhouse gases (GHGs). The y-axis represents the energy trapped by the gas per square meter area, which is termed radiative forcing. The longer the bar, the stronger the contribution to the greenhouse effect. The red bar corresponds to carbon dioxide. The green bar is for methane. Please note that despite the atmospheric methane concentration is about 200 times lower than carbon dioxide, the contribution of methane is equivalent to about 1/3 of carbon dioxide. (Source: National Academies of Sciences, Engineering, and Medicine, 2018.)

The Rare Methane Molecules

Methane (CH4) is a chemical with one atom of carbon (C) and four atoms of hydrogen (H).  Although still composed of one carbon and four hydrogens, rare methane molecules have uncommon flavors for atoms. For simplicity, imagine yourself stepping into a Starbucks, "I'd like a cup of Latte, triple espresso, almond milk, and strawberry sauce." Now multiple uncommon flavors are gathering in a cup of Latte, which makes it a "rare Latte". The same thing can be done for methane, "I'd like a molecule of methane, with the carbon atom slightly heavier than usual, and one normal hydrogen atom replaced by a twice heavier hydrogen atom." These heavier atoms you required are termed "isotopes". Anyway, now you get a rare methane molecule. 

 A real photo of common Latte (left panel) and a conceptual structure diagram of common methane and rare methane (right panel). A common methane molecule has four hydrogen atoms with a relative mass of 1 and one carbon atom with a relative mass of 12. A rare methane molecule here has three hydrogen atoms with a relative mass of 1, one hydrogen atom with a relative mass of 2, and one carbon atom with a relative mass of 13. This rare methane molecule is an example of methane clumped isotopologue.

In a parcel of methane that contains a huge number of methane molecules, the proportion of rare methane molecule is normally quite small because the chance for two rare isotopes meeting and combining on one methane molecular is very small. 

"How do rare methane molecules tell a story?" It's complex.

Generally speaking, it's the proportion of rare methane molecules (or how clumping the parcel of methane is) that conveys information. To get an idea of what is "how clumping", let's first check our university.

UMD is a diverse campus. Students have different genders, ages, nationalities, and majors. If socializing happens completely randomly on campus, you will have the same probability of becoming friends with anyone. However, a student majoring in geology may find himself or herself surrounded by friends from the geology department because they both like rocks. A Chinese student may find that (s)he usually chats with Chinese because of their common language and background. These are examples of the clumping phenomenon. The clumping is determined by the inherent attributes of students, such as major and nationality. The combination of each person's social circle shapes the social network of UMD that has a unique clumping signal.

Social network visualization plot. The circles represent the members inside the network. The lines indicate the interactions (e.g. emails) between two members. Larger circles correspond to more interactions for the individual. The areas with large and dense circles indicate the social center, or more clumping area. The areas with small and sparse circles belong to people who are less involved in social activities, or less clumping area. (Source: Grandjean, 2014.)

However, this balance can be broken by certain processes. COVID is a good example. Due to the outbreak of the epidemic, everyone follows social distancing. The clumping signal is significantly reduced.

The same principle can be applied to methane. The substitution of normal atoms with rare atoms will change the energy of the methane molecule, just like using strawberry sauce instead of caramel syrup will make a Latte with a different flavor. The energy difference, combined with the ambient temperature, determines the specific characteristics of clumping which may directly reflect the formation temperature of methane. However, processes such as microbial activity and mixing will change the clumping signal in a specific direction. In these cases, although we lost the information of temperature, we may infer the processes that methane went through. Taken a sip of the Latte, you can tell the syrup it uses. Given a sample of methane, I may tell you the story of its origin.

References:

National Academies of Sciences, Engineering, and Medicine. 2018. Improving Characterization of Anthropogenic Methane Emissions in the United States. Washington, DC: The National Academies Press. doi: https://doi.org/10.17226/24987.

Grandjean, Martin (2014). "La connaissance est un réseau". Les Cahiers du Numérique 10 (3): 37-54. DOI:10.3166/LCN.10.3.37-54.

Following volcanoes clues Study case: Azufral Volcano, SW Colombia: Version 2.0

 Following volcanoes clues

Study case: Azufral Volcano, SW Colombia

Figure 1. Popocatepetl and Iztaccihuatl: A Tragic
 Romance of Aztec Legend (Klimczak, 2016)

Human beings have always felt fascinated by the majesty and imposing presence of volcanoes. This is why many legends have tried to explain the occurrence of these particular fire mountains. For instance, the legend of Popocatepetl and Iztaccihuatl volcanoes in Mexico involves a romance story where a brave warrior - Popo - to be able to marry his truly love, the princess Izta, goes to the most difficult battle chagenlled by Izta's father. After a long waiting, Izta is told by one love rival that Popo had died and incapable to support her pain, she passed away. When Popo returned victorious from the battle, found Izta dead. He decided to carry her love until a great mountain where he built her a great tomb. He sat in front of her love, kissed her lips and waited until the snow covered completely their bodies transforming them into these beautiful volcanoes (Fig. 1)

As geologists, we understand the importance of volcanoes in the cycle of Earth life. Nevertheless, history, and the geological record, have shown how these "titans" can destroy entire civilizations with only one "sneeze" or eruption. Pompeii in Italy or Armero in Colombia are clear examples of how an eruption can end in tragedies.

Fundamentally, past eruptions are the best tellers of what we can expect in the future, therefore volcanologists have made huge advances to learn and understand how these complex systems have worked. Now maybe you are wondering: How can we  predict the behavior of volcanoes that we haven't seen erupt? Well, the products - ashes - erupted by them have the clues!

To clarify this, we are going to look deeper into Azufral Volcano. This volcano is located in Colombia and is quite touristic due to its beautiful crater lake named “Laguna Verde” (Fig. 2).

Figure 2. Crater lake called “Laguna Verde”. Nariño, Colombia.

Figure 3. Deposit of ashes, behind
 it is seen the crater lake.

Close to the crater you can find the ashes erupted by this volcano thousands of years ago (Fig. 3). If you see carefully this picture, you will see different layers such as the layers you see in a cake. Each of these layers represent one small eruption accumulated one after the other. In this manner, layers close to the surface are younger than those in the bottom.  

Figure 4. Ash fragment with crystals (red rows). 
vesicles representing the bubbles of the
 magma (yellow rows), and a colourless
groundmass representing the magma (blue rows).

The ashes erupted by the volcano are photos of the magma just after the eruption. If we study the ashes and the crystals contained in them (Fig. 4) we will be able to reconstruct the conditions of the magma as well as to understand what caused the eruption. 

Figure 5. Desequilibrium texture in plagioclase crystals.
You can notice how the center of the crystal is completely 
dirty or reabsorbed and the rim is totally clear.

Imagine a coke bottle - the bottle is the volcano conduit and the coke is the volcano’s magma. This magma contains bubbles (gases) and crystals that are created at different depths and conditions inside the volcano – or bottle. By knowing the different depths and studying the disequilibrium textures (Fig 5.) of those crystals, we can generate a model to explain the eruption.

For example, in the Azufral volcano's model (Fig. 6) there is a first stage where it was a plug emplaced in the center of the crater - the cap of the coke bottle – and some crystals began to appear in the volcano's magma. Then in a second stage a deeper magma with higher temperatures was injected into the first magma destabilizing the system and creating a rim around the preexisting crystals. In the third stage, this new magma also caused the system to overpressurize –  similar to many bubbles accumulated inside the coke. This overpressure removed the plug and triggered the explosion in the fourth stage – such as when the bottle cap is removed. Finally, the ashes we see today close to the Azufral crater are volcanologist's target because they represent the evidence of what occurred.

Figure 6. Explicative model for the eruption.  First stage: while a plug is emplaced in the crater's volcano, crystals appear in depth. Second stage: deeper magma injection. Third stage: recrystallization of crystals rims. Fouth stage: eruption occurrence.

Certainly, not all volcanoes systems act in the same way, but that is volcanologist's job, to find clues in the field and the lab to create scenarios that we can expect in future eruptions. Legends and stories from communities that live close to the volcano have also been very helpful to volcanologists to understand the most recent volcano's behavior. As well, written stories and painted draws have been used to know when the volcano has erupted in the past. In Mexico, the legend says that every time the great warrior Popocatepetl remember his beloved princess Izta, his heart begins to beat faster and the fire and passion cause the eruptions of this volcano.

References

Berry, J. (2009). Pompeya (Vol. 13). Ediciones AKAL.

Castilla, S. C., Pardo, N., Larrea, P., Zuluaga, C. A., Sarmiento, S., Noguera, D., & Sarmiento, G. A. (2019). Pre-eruptive conditions and pyroclastic emplacement of the last known vulcanian eruption of Azufral Volcano, SW Colombia. Journal of South American Earth Sciences, 91, 372-386.

Klimczak, N. (2016). Popocatepetl and Iztaccihuatl: A Tragic Romance of Aztec Legend. Mexico. https://www.ancient-origins.net/myths-legends/popocatepetl-and-iztaccihuatl-tragic-romance-aztec-legend-005779

Saavedra, M. (2015). ARMERO: “UNA CATÁSTROFE ANUNCIADA”. godues. https://godues.wordpress.com/2015/11/16/armero-una-catastrofe-anunciada/

Sigurdsson, H., Houghton, B., McNutt, S., Rymer, H., & Stix, J. (Eds.). (2015). The encyclopedia of volcanoes. Elsevier.Klimczak, 2016