Air travel disruptions following major volcanic eruptions

Following major volcanic eruptions, plumes of ash and steam raise many kilometers into the atmosphere where ash can be dispersed over a wide area. The injection of this material into the atmosphere effects the evolution of atmospheric chemistry and can influence short term weather patterns. The ash in the atmosphere also makes it unsafe for airplanes to travel through, as was the case following the eruption in Iceland last April which resulted in tens of thousands of flight cancellations.

Extent of the Plume from the Eyjafjallajökull Volcano in Iceland, from earthobservatory.nasa.gov

A volcanic plume has to be buoyant to reach 10's of km into the atmosphere. The hot gases and ashes cool as the plume rises in the atmosphere, and the plume expands. This keeps the plume less dense than the surrounding atmosphere and keeps the plume rising, in the same way bubbles rise in a glass of soda.

Sarychev Peak Eruption June 12, 2009 taken from the International Space Station, from earthobservatory.nasa.gov

Work was completed at NASA's Goddard Space Flight Center to investigate how these plumes rise. While there are numerous conditions that are looked at, the effects of vent geometry has on supporting a buoyant plume was investigated. Computer models of volcanic plumes originating from linear and circular vents were constructed. From the simulations the maximum height at which a buoyant plume can reach was determined. Simulations were done with different vent openings to see if a linear vent can produce a plume which can reach heights similar to that of plumes from circular vents.

Maximum predicted plume heights on Earth as a function of vent area. The linear vent results are shown for multiple choices of active fissure length

The results show that when buoyancy is sustained, linear vents appear to be equally capable of injecting ash and volatiles into the atmosphere. For analogous mass flux rates at the vent, the maximum heights to which linear and cylindrical plumes can rise are comparable. However, in some cases where the length of an active linear vent is smaller than the radius of the circular vent, the entrainment area of the linear plumes is significantly less than the cylindrical equivalent. Thus the range of vent widths that can sustain a buoyant plume is narrow and linear plumes are more likely to collapse and not inject ash high into the atmosphere.

For a more detailed description, please see the paper Glaze et al., 2011

Glaze, L. S., S. M. Baloga, and J. Wimert (2011), Explosive volcanic eruptions from linear vents on Earth, Venus, and Mars: Comparisons with circular vent eruptions, J. Geophys. Res., 116, E01011, doi:10.1029/2010JE003577.

Sub-zero temperature acid-weathering on Mars

In a recent study, acid-weathering in sub-zero temperatures was found to occur at rates and magnitudes comparable to those from 0 °C to at least room temperature. This type of weathering may have been an important process on Mars. Temperatures today range from about -90 to -5 °C and the sulfate-rich sediments suggest weathering via an acidic medium, possibly sulfuric acid. Further, the temperature of Mars in the past is an issue of contention because it has implications for the presence of stable liquid water on the Martian surface. Many features on Mars appear to have been created by flowing liquid water, such as gullies, outflow channels, and valley networks, but the evidence is not conclusive. Some of these features may have been formed through the periodic melting of permafrost. This leaves the fundamental question of how warm or cold was Mars? The aforementioned study was conducted in order to expand our understanding of acid-weathering to the sub-zero temperature regime and to investigate a possible low temperature source for sulfate-rich sediments on Mars that were discovered by the hugely successful Opportunity Mars Exploration Rover. The research concerning the genesis of these sediments may provide a clue to Mars’ past climate.

Mars, as seen by the Opportunity rover, in foreground. For scale, the distance between tire tacks is about 1 meter. Image is a photomosaic, courtesy NASA/JPL Photojournal.

Upon landing, Opportunity found a vast, sandy, windblown plain. This plain is essentially a large-scale deposit of sulfate-rich sediment, characterized by fine layering, cross-bedding, and hematite spherules, which are tiny spheres of an iron oxide mineral – or as they are better known, “blueberries”. Finally, a mineral called jarosite, an iron sulfate, was found in abundance. The origins of the sediment and the depositional features are debated, but a popular hypothesis suggests that they originated through alteration processes in a groundwater-fed evaporative dry lake bed. Alternatively, it has been suggested that the sediments were altered via acid-weathering in a massive dust-ice deposit and later reworked by wind. These hypotheses differ mainly in the temperature of the region. Were the sediments altered to their present state in a warmer or colder climate? To test the ice-weathering hypothesis, sub-zero temperature acid-weathering must first be understood. Reaction kinetics are necessarily slower below 0 °C. However, acid-weathering, especially the effect of temperature on acidity and the effect of acidity on weathering, below 0 °C is not as well understood as it is at >0 °C. The situation is complicated by the formation of ice. As ice forms, the remaining acidic solution becomes more and more concentrated. The acid concentration can therefore increase as temperature decreases, which may mitigate the effect of the cold.

The fine layering of the sediments can only be seen inside craters. This image was taken inside Endurance Crater. Image is a photomosaic, courtesy NASA/JPL Photojournal.

A preliminary study was conducted in order to investigate the rate of acid-weathering at very low temperatures. In this study, olivine, a magnesium- and iron-bearing silicate mineral ((Mg,Fe)₂SiO₄), was exposed to sulfuric acid under different temperature conditions (the lowest of which was -52 °C) for varying amounts of time. The resulting solution was analyzed for dissolved Mg²⁺ and Fe²⁺ ions, which would indicate weathering of the olivine. The solid residue was examined for evidence of weathering using a sophisticated microscope with imaging and qualitative chemical analysis capabilities.

Images of two olivine grains. A. is a residue grain from the longest duration -20 °C sample. B. is from the least weathered sample (-52 °C, 1 hour) for comparison, though the two samples are not related. Chemical analyses are also shown, showing differing Mg:Si between the two samples. This ratio change indicates some degree of weathering.

The results of the analyses, as stated previously, suggest that acid-weathering occurred in even the coldest temperatures. Both Mg²⁺ and Fe²⁺ were found in all the solutions, with the samples in the coldest conditions having the lowest concentrations. Additionally, the concentration of the acid seemed to compensate for the colder temperatures in the first 24 to 40 hours. However, the rate of weathering drops off very quickly in the coldest temperatures, indicating that the temperature does play a large role in slowing the reaction kinetics. Furthermore, the images and chemical analysis of the solid residue give compositional and textural evidence of sub-zero temperature acid-weathering. The ratio of Mg to Si is much lower than typical Mg-rich olivine composition in darker colored areas and spots (color differences indicate compositional differences in these images), showing that some degree of weathering has occurred. It seems, then, that the ice-weathering hypothesis is possible, but that will not end the debate of the role of liquid or ice water on Mars or its part in Mars’ past climate.

For additional information about this study and references, see the abstract.

Isotope Partition Function ("The Urey Equation")

The partition function for determining equilibrium isotope fractionation factors as formulated by Urey (1947) for diatomic molecules (sometimes called the "Urey Equation"):

Where,

σ = symmetry number for molecule
I = moment of inertia for molecule
M = molecular mass
h = Planck's Constant
c = Speed of Light
ω = vibrational frequency
k = Boltzmann's Constant
T = Temperature

The subscripts 1 and 2 refer to two isotopologues that are undergoing an isotope exchange reaction.   

Isotopologue definition: Molecules that differ from one another only in isotopic composition, e.g., C¹⁶O and C¹⁸O.

Mass-Independent Fractionation (MIF)

Equation for the detection of mass-independent fractionation of sulfur isotopes

Δ³³S = ((^33/32S_sample/^33/32S_reference – 1) x 1000) – 0.515 x ((^34/32S_sample/^34/32S_reference – 1) x 1000)

Effective Permeability Equations

The effective permeability through a material will vary directionally, particularly if the material has a layered structure. If we consider a simple layered material as illustrated below, we can use 2 equations to define the effective permeability horizontally and vertically through the material.

Equation for Horizontal Permeability:

Equation for Vertical Permeability:

Before describing what each equations means, it is important to understand the parameters or symbols they use.

k = permeability (the ability of a material to transmit fluid)

• In these equations we are solving for keff, which is the effective permeability. The term effective denotes that we want the permeability for the entire material, not just one or a few of the layers within it.

• When ki is used in the equations, we are referring to the permeability of a specific layer, i. We are using "i" as a placeholder for the actual position of the layer, where "i" can be any number. For example, if we are referring to the 2nd layer in a material, "i" would equal 2 and the permeability would be expressed as k2. We will use the subscript "i" here, because we will need to consider individual permeability values for each layer in order to get the total keff.

h = layer height

• These equations use h for the height of the layers in the material. As with the permeability, the subscript "i" will also be used with h as hi to denote the height of the individual layers, as the layers will typically vary in height.

• The h with the overlying bar is used to represent the total height of the material or the sum of h1 through the h of the last layer of the material.

In the above diagrams, you will also see that an l term is included which represents the length of each layer. This term is not included in the permeability equations, and is negligible if all the layers are the same length.

Formula

Basalt Is Hard to Chew: A Liquid Supported Seafloor Biosphere

Life on Earth may be even more ubiquitous than previously thought.  At least that is one of the main implications of a recently emerged hypothesis that states that exposed oceanic crust (composed of basalt) may host a substantial “rock-eating” microbial biosphere.  This biosphere is thought to occupy both the surface of the seafloor and beneath, far from sunlight and substances traditionally thought of as food.  This hypothetical zone of life—termed the Seafloor (or Subseafloor) Biosphere—is generally believed to subsist on the energy-releasing chemical reactions that take place when basalt reacts with seawater (called chemical weathering, a form of rock alteration).  In order to investigate the potential for oceanic crust to host life, a group of colleagues and I investigated the initial stages of alteration of one of the most chemically reactive components of oceanic crust—basaltic glass—at the Loihi Seamount, a young and active submarine volcano in the Hawaiian Islands.  We found that warm hydrothermal fluids—enriched in some of the same chemicals found in basalt—were more important than local basalt weathering in delivering the rock chemicals these microbes need for energy, meaning that any Seafloor (or Subseafloor) Biosphere may be liquid supported, rather than rock supported.

Cartoon illustrating how basalts were collected from the Loihi Seamount in the Hawaiian Islands.  Samples were collected using an ROV (remotely operated vehicle) named Jason II controlled from a research vessel above.  We sampled all along the length of the seamount to the edge of the abyssal plain below.  The ship and ROV are not to scale (Loihi is much bigger than both!).

ROV Jason II in action: Collecting fragment of pillow basalt from Loihi on the FeMO 2008 research cruise to the seamount.  The basalts are covered with a coating of orange (iron-rich) minerals and, thus, have been altered since the time of their formation.  Where did this "rust" come from?

The Loihi Seamount is a gradually rising underwater volcano that may someday become the next Hawaiian Island.  Like the rest of oceanic crust, Loihi is made of basalt and its surface is covered with fresh pillow basalts.  The surfaces of these pillow basalts are glassy and often covered with a layer of orange (iron-rich) alteration materials that resemble rust.  This "rust" has associated with it a large diversity of microbial life, including microbes that can turn inorganic carbon (e.g., carbon dioxide) into organic matter for growth by oxidizing (i.e., “rusting”) the iron and manganese compounds found in basalt.  (In other words, much of the rust is the waste product of this certain type of microbial metabolism, meaning it is essentially "microbe poop".)  Because these types of microbes are associated with basaltic glass at Loihi, it has been supposed that these microscopic ‘bugs’ are  living off of the basaltic glass itself.  However, it isn't clear whether this rust has been derived from the underlying basalt glass or has been deposited by the low-temperature, iron- and manganese-rich hydrothermal fluids found all over Loihi.  We aimed to test the hypothesis that the biomass associated with these alteration materials was directly supported by basalt weathering by determining the source of this secondary material.

Hydrothermal vent site within Pele's Pit, a pit crater formed by the collapse of Loihi's summit during a violent eruption in 1997.  The orange chimney structures and coatings are made primarily of rust-like iron minerals that have precipitated out of iron-rich vent fluids.  Iron- and manganese-oxidizing microorganisms make their living off of the redox (or “energy”) gradient between the reduced ("non-rusting") vent fluids and the oxidizing ("rusting") ambient seawater.  Distance between laser points is approximately 10 cm.

Using various techniques (many of them synchrotron-based), we examined and characterized  in great detail the glassy surfaces and associated rust coatings of a variety of basalts collected at numerous sites along the length of the seamount.  This included sites adjacent to hydrothermal vents and sites where no obvious venting was occurring.  At all locations, we found little to no evidence that any significant chemical alteration of our glasses occurred, and that there was simply too much iron and manganese in the rust to have been sourced from the underlying glass.  We also found that many of the minerals in the rust structurally resembled those known to have been biologically precipitated from vent fluids, further lending support to the notion that these materials were externally sourced.  Thus, it appears that at Loihi the microbes in question aren’t directly eating the rocks, but are rather living off of chemicals leached from rocks deeper in the volcano by hot fluids.  This might mean that any Seafloor (or Subseafloor) Biosphere is on "liquid life support", and may be restricted to volcanically active areas of oceanic crust (e.g., in proximity to mid-oceanic ridges) where shallow subseafloor hydrothermal circulation is an important process.
 

The full study can be found here: http://www.nature.com/ngeo/journal/v2/n12/full/ngeo696.html.  A short video about the Big Island of Hawaii and nearby Loihi can be found here.  To snag some of the ‘hot’ future real estate Loihi is sure to provide, see: http://www.petroglyphs.com/loihi/real-estate-future-value.html.