Methane Clumped Isotopologue: the Taleteller

 

Figure 1. A flare burns by a fracking well near Karnes City, Texas.

Aaron M. Sprecher/Associated Press

  Methane (CH₄) is important, not only because it's the major component of natural gas -- widely-used clean energy, but also because it's a powerful greenhouse gas that makes the second largest contribution to global warming after carbon dioxide (CO₂). Although everyone is breathing and using methane, we know little about its detail because methane is not making a self-introduction. Where and how was it formed? What was the temperature of its formation? What kind of journey did it experienced and what partners did it meet before you breathed it in? However, methane might have recorded its story by methane clumped isotopologue, waiting for us to explore.

Figure 2. Radiative forcing (relative to 1750) due to major greenhouses gases (GHGs).

Please note that despite the low atmospheric methane concentration, it contributes a non-negligible radioactive forcing.

(Source: National Academies of Sciences, Engineering, and Medicine. 2018.)

"Wait, what is clumped isotopologue?"

    Clumped isotopologue refers to a molecule that has multiple (usually two) atoms substituted by their rare isotopes. If you feel hard to understand, just imagine yourself stepping into a Starbucks, "I'd like a cup of Latte, double espresso, almond milk, and light ice." Now you are making multiple requirements for that cup of Latte, which can be termed "Latte clumped requirement". The same thing can be done for methane, "I'd like a molecule of CH₄, with a ¹³C substituted for ¹²C and one ¹H replaced by ²H (deuterium or D)." Then you've got a "doubly-substituted methane", or "methane clumped isotopologue" (Figure 3). In a parcel of methane that contains a huge number of methane molecules, the proportion of methane clumped isotopologues is normally quite small because the chance for two rare isotopes meeting and combining on a methane molecular is very small.

Figure 3. A real photo of Latte (left panel) and a conceptual diagram of methane and methane isotopologue (right panel).

"How methane clumped isotoplogue tells story?" It's complex.

    Generally speaking, certain types and degrees of deviations of measured methane clumped isotopologue values from their expected values indicate certain processes during methane formation and/or transportation. I know you got confused, but take a sip of the latte you just bought. As a decent coffee nerd, you immediately find something wrong, "What I required is almond milk but this one uses soy milk." From the special soy milk flavor which deviated from the almond milk flavor you expected, you inferred a process that the barista carelessly used soy milk. Scientists might be able to reveal the hidden story of methane through its clumped isotopologue signature, as long as the behaviors of methane clumped isotopologue are thoroughly understood -- just like how you fully acquainted with every step and raw material of making a cup of latte. However, a variety of factors and processes can affect the signal, such as the formation temperature, the availability of hydrogen sources, microbial mediated formation, and mixing of two parcels of disparate methane. We still have a long way to go before becoming a qualified methane narrator.

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.

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 into thorium, potassium into argon, and aluminum into 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. 

    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 material 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 material was able to travel toward the center of the Earth, while 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. 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 elements 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.

Why So Salty?: A Tale of Freshwater Rivers

On a frigid, snowy day, nothing tastes (or smells!) quite as good as warm, chicken noodle soup. The first thing I usually notice is 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 flavor overwhelmingly salty. Something similar is happening to our sources of drinking water worldwide.

Picture the same cold day, but now think of the roads, sidewalks, and parking lots. We use deicing agents, primarily road salt, as a method to stay safe in inclement weather conditions. Yearly, Maryland buys 230,000 tons of road salt each year, or about 30,000 dump trucks to prevent accidents. The US uses about 10 to 20 million tons of salt each year! I agree it is important for us to use a deicing agent for safety, but where does the road salt goes when the snow and ice melts? The salt dissolves and is transported with the melted snow and ice into groundwater and the nearby streams. Throughout the winter, the streams are getting saltier just like the flavor when we add more salt to soup. The term Freshwater Salinization Syndrome describes the process of increasing salinization over time. Salinization does not only impact areas that use road salt but occurs globally in most of our major rivers. Building and road materials, construction, fertilizers, water softeners, and even our sewage are causing our freshwater sources to get saltier.

Road salt on walkway in College Park, Maryland.

During the winter months, the salinities in rivers in Maryland, New Hampshire, and New York are 25-40% the saltiness of seawater during the winter. Our rivers have the salinity of about 1.5 to 2 cans of Campbell’s Condensed Chicken Noodle Soup! The salinity values remain elevated during the summer months as well. The consistently saltier environment drastically alters the natural chemical balance of the freshwater and creates an inhospitable home to many aquatic organisms. Highly sensitive and native organisms such as fish, plants, and macroinvertebrates are unable to survive in these conditions, altering the food web of the stream. The influx of salt not only harms the aquatic life but also causes the release of toxic metals into the rivers. When ingested in very high doses, these metals can cause a variety of human health effects, such as skin, skeletal, and nervous system disorders.  

Over the years, the specific conductance (a way to measure salinity) has increased at many locations throughout the United States. Notice the red line increasing! (Source: Kaushal et al., 2018)

Freshwater Salinization Syndrome is an increasingly pertinent problem in freshwater sources worldwide. To reduce the impacts of salinization, we must continue research to find methods to properly and holistically manage road salt and other sources of salt to our freshwater environments.  

Sources: 

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

https://www.campbells.com/products/condensed/chicken-noodle-soup/

Could we live in lava tubes on the Moon?

When we think about space exploration the first thought is most likely not about underground tunnels. But as it turns out, that might just be 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 hallow 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 (Sauro, 2020)! Although lunar lava tubes have not been physically accessed yet, they have been studied through orbital imagery, gravity measurements and ground penetrating radar. 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.

            Artists rendering depicting how a lunar rover may enter a lava tube through a skylight. Source: Kerber et al., 2018

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 should 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 will 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 volatiles and 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.

Rock Mechanics and lunar lava tubes

An important question to ask when studying these lava tubes is how exactly do the rocks around the channel behave? Understanding the structure and properties of the material surrounding channels will give great insight on the stability and safety of using lava tubes as a site of a lunar base. The problem? We are not on the moon. In order to study these subsurface structures on the moon, terrestrial analogs must be used. 

The lunar volcanic rock surrounding these lava tubes most likely formed in a similar fashion as some areas with volcanic rock on Earth. Studying these rocks found on Earth is a much more accessible way to understand the volcanic rocks on the Moon. Therefore, geophysical properties measured in the laboratory on analog samples can be used to infer geophysical properties of volcanic rocks on the Moon.

To better understand this process, let’s think about the Apollo missions. Astronauts on the Apollo missions landed on the Moon and collected hand samples to bring back to Earth. These hand samples were then studied in a laboratory where various properties were analyzed in order to characterize the samples. Scientists then use these properties measured on a hand-sample-scale in order to infer large scale subsurface structures on the Moon (in our case lava tubes). Working with our analog study can be thought of as the reverse of this process. Large scale properties can easily be measured in the field on Earth, but hand-sample-scale properties are not well characterized for analog sites. 

Hopefully, by strengthening the link between hand sample properties and large scale properties on the Earth, we can better understand the properties of lava tubes on the moon. 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!

(Top) Apollo 11 astronaut conducting active source seismology. Source: NASA (Right) Student at The University of California performing active source seismic experiments. Source: CSU

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

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 meters in size, with depths ranging up to 1.8 m (Bradford 2017). 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 (Credit: Bradford 2017, originally from National Park Service)

Debatably more accomplished than a gopher, the Earth has created tunnels through a plethora of processes. Lava tubes and their formation are the most applicable process to my research. Generally seen as a “roofed conduit” of actively flowing, drained, or plugged magma, lava tubes on Earth range from meters to kilometers in length, 0.5-30 m in width or height, and anywhere from centimeters to meters in depth below the surface (Sauro et al. 2020). Now this may feel like it puts the gopher’s efforts to shame, but a little perspective and googling will tell you that Earth weighs around 13.17e24 gophers (Cool Cosmos, IPAC). Even more shameful is the fact that Lunar and Martian lava tubes have been found to be 10-1000 times more voluminous than those on Earth (Sauro et al. 2020). 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 outer surface chills and solidifies, insulating the molten lava below and allowing it to maintain a high temperature and low viscosity for longer, and thus farther from the vent. Shallow inflation results in a superficial bulge morphology; for pahoehoe lava flows this bulge forms along the tube's development and the process revolves around uplift of the lava sheet. Elliptical tubes are then formed and can become open after drainage. In juxtaposition, the shallow inflation bulge for a’a flows is found nearer to the end of the lava flow, and due to higher pressure from a form of “stoppage”, a’a flows create larger lava tubes. A step higher, deep inflated-entrenched lava tubes are among the largest found on Earth and involve downward thermic erosion and breakdown. [Sauro et al. 2020]. 

Figure 2. Models of lava tube formation processes (Sauro et al. 2020). Of note are A corresponding to overcrusting, C to pahoehoe shallow inflation, D to a’a shallow inflation, and E to thermal erosion and breakdown.

 

Definitions of technical jargon aside, lava tubes (inferred from the presence of skylights and collapse on sinuous 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 the most likely to be stable award (Sauro et al. 2020). Fortunately for Mars, my research into modelling lava tubes using mesh and seismic wave propagation software looks past this shortcoming. At its current stage, my research focuses on using mesh software (such as GMSH) to create lava tube analogous geometries. My next step is to import this mesh geometry into SPECFEM2D, a spectral-element solver that will allow me to simulate the propagation of acoustic (seismic) waves through the medium (SPECFEM2D 2020). 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/ 

Kimberlite Diamonds: Live Fast, Die Hard

 Just as the world’s most famous diamonds conjure stories of theft and intrigue, of monopolies and power, diamonds also tell of 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, from depths of 150 to over 200 kilometers. For some perspective, the distance from Washington, DC to Philadelphia is roughly 200 kilometers. 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.

Molecular structure of diamond, with red spheres representing individual carbon atoms.

Kimberlites are an igneous rock named for Kimberley, South Africa, where they were first studied. As rocks go, kimberlites are like experienced world travelers, full of exotic stories to tell. Their journeys begin deep in the mantle when a neighborhood of rock begins to melt due to a change in its temperature or pressure conditions. This new magma is less dense than the rock surrounding it, 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. This 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. On the whole, 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. 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.

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 led by James K. Russell at the University of British Columbia 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 long 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.

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

In the years since their discovery, the Russell team’s 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.

 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 (Sirgudsson, 2015). For instance, the legend of Popocatepetl and Iztaccihuatl volcanoes in Mexico involve a romance story where two lovers have been transformed into volcanoes as a result of their deep and tragic love (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 (Berry, 2009) or Armero in Colombia (Saavedra, 2015) 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). Studying the crystals found in the ashes (Fig. 4) it is possible to calculate the pre-eruptive conditions of the magma (i.e. temperature and pressure) as well as to understand what caused the eruption.

Figure 4. Ash fragment with crystals of plagioclase,
 biotite and amphibole.

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 of those crystals, we can generate a model to explain the eruption.

For example, in the Azufral volcano's model: 1) there 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 (Fig. 5a). 2) Then a deeper magma with higher temperatures was injected into the first magma destabilizing the system (Fig. 5b) and creating a rim around the preexisting crystals (Fig. 5c). 3) 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 (Fig. 5d) – 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 occured.

Figure 5. Explicative model for the 3600 yr BP eruption.
 a) While a plug is emplaced in the crater's volcano,  crystals appear in depth; b) deeper magma injection; c) recrystallization of crystals rims;  d) eruption occurrence (Taken from Castilla et al., 2019).

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. Thus, it is quite important to look into the details because it allows generating hypotheses to explain what we see today. That is why geologists have to be very observant of their environment because some answers could be found on a very small scale.   

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.

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