A Strong Start to the 2017 Keck Gateway Project

June 22nd, 2017

Guest Blogger: Addison Thompson (’20 Pitzer College and Team Keck Member)

The 2017 Keck Gateway Team.

Amid our first official day at the College of Wooster, spirits were high as we embarked on the five week Keck Gateway Project.  The Gateway Project encompasses two different scientific enquiries which will span three states; Ohio, Utah, and Alaska.  The goal of the project centered in Utah is to determine the age of geologically young lava flows (now igneous rock) in the Ice Springs Volcanic Field of central Utah in order to add another piece to the unsolved puzzle of the Earth’s geologic history.  The goal of the project centered in Alaska aims to gain a better idea of why Cedar trees in Juneau are in decline.  The information gained from the students working in Alaska will help pinpoint specific environmental factors that are adversely affecting ecosystems, trees in particular.  This portion of the project is one week long.

Evidence of a tree core.

Once the data from the Utah and Alaska field sites are complied, both teams will return to the College of Wooster to complete lab tests in order to answer each respective hypothesis. This portion of the project is roughly three weeks long.  The participants of the project also have the opportunity to attend and present the findings of their research at the GSA’s (Geological Society of America) annual conference in Seattle in mid-October.

The first full day of the project was a beautiful one and we dove into the topic material with gusto.  We began at 9am in the geology department which is located in Scovel Hall and had a discussion about the rules of authorship and the details of what mentoring means with Dr. Pollock and Dr. Wiles.  Following that, details for the field work trips (Utah and Alaska) were coordinated and supplies like rock hammers and chisels were evenly distributed.  At that point it was time to break for a much needed lunch.  The Keck group met back at Scovel Hall around 1:30, just in time for a jaunt around the Oak grove led by Dr. Wiles, during which the group cored three trees to determine their age.

The processing of coring trees involves inserting a hollow drill into the tree, then removing the sample of the tree located in the hollow drill.

An excited Team Alaska member extracts her tree core.

The Alaska team will use this method hundreds of times in order to determine the health of trees in a large area.  With the first day complete, our group looks forward to strengthening our bonds and embarking on our geology research.

On the second day, the Utah group and the Alaska group split to their respective labs to discuss the minutia of the trips.

The Utah group examined basaltic rocks from the Black Rock Desert, the location where they will be conducting their fieldwork.

These rocks had previously been dated via two techniques: one being Varnish Microlamination (VML) which aims to date the rocks by measuring the coating on rock surfaces, the other being Cosmogenic Nuclide Dating which measures the accumulation of radioactive isotopes in the surfaces of the lava flows.

Meanwhile the Alaska group learned more about tree coring, a practice they will become very familiar with during their stay in the last frontier.

This concluded our work for the day, and we broke for lunch.  The rest of the day was spent preparing for our arduous journeys to the field sites the following morning.  We went shopping to stock up on various items for the trips.  The day came to a conclusion with a delicious dinner and some frisbee outside Douglas Hall.

Much to their chagrin, the Alaska group was departing the College of Wooster at 4am on the third day.  The Utah group was given a more lenient departure time, 6am, because their destination was 2,113 miles closer to the College.  There were no issues rising bright and early and both groups headed to Cleveland Hopkins Airport with anticipation of the journey ahead of them and slightly weary eyes.  To make matters more interesting for the Alaska group, their travel plans routed them through Dallas Fort Worth…not quite in their desired direction but they were sports nonetheless. And so the day went, a travel day.  The Utah group touched down in Salt Lake City in the mid afternoon and began the two hour drive to the town of Fillmore, only stopping once for a much needed dinner.  Eventually the group made it to their campground and settled in their cozy cabins.  After a long day of travel and two hours lost, a rest is what the doctor ordered.  As of writing this, the Alaska group is currently still in transit to Juneau.  Tomorrow marks the first official day of field work in the Black Rock Desert for the Utah group and there is an excited fervor hanging in the air.  All the tools and measurement devices are prepped and ready to go.

 

 

 

 

Isotope analysis by TIMS is FUN

May 23rd, 2017

Chapel Hill, NC – Wooster Geologists have been hard at work preparing samples for isotope analysis. Now that sample preparation is complete, the next step is to analyze them on the thermal ionization mass spectrometer (TIMS). In the TIMS, a sample heats up until it ionizes, created a beam of charged particles.

The charged particles are sent through a mass spectrometer, which accelerates the ions through a curved path in a magnetic field. The ions separate based on their mass to charge ratio. The separated beams of ions are sent to collectors that convert the ions into an electrical signal that can be used to determine the sample’s isotopic composition. Figure from Revesz et al. (2001).

For a complete overview of how the TIMS works, check out this website at SERC.

 

Our tiny samples get loaded onto tiny filaments that heat up in the instrument. The filaments are stored in neat, orderly rows in a cabinet in the TIMS lab. If you look closely, you’ll see the flat ribbon onto which we’ll mount our samples.

You can imagine that the filament loading process is as meticulous as the sample preparation work. Here, Ben Kumpf (’18) pipettes a sample onto the filament.

This is what our sample looks like before we heat up the filament. It’s a single drop.

The filaments will get loaded into the TIMS instrument. This is one of the TIMS instruments here at the University of North Carolina Chapel Hill that we’ll use to analyze for strontium (Sr).

This is the exciting part, when we hope that all of our hard work as paid off. It’s a lot of effort for a single data point, but we know it’s well worth it.

References

Revesz, K.M., Landwehr, J.M., and Keybl, J. 2001. Measurement of bigsymbol13C and bigsymbol18O Isotopic Ratios Of CaCO3 using a Thermoquest Finnigan GasBench II Delta Plus XL Continuous Flow Isotope Ratio Mass Spectrometer with Application to Devils Hole Core DH-11 Calcite: USGS Open-File Report 01-257. US Government Printing Office.

Extracting a single element from a rock

May 20th, 2017

Chapel Hill, NC – As you know, Ben Kumpf (’18) and I are working in the Isotope Geochemistry lab at UNC Chapel Hill. We are measuring isotopes of strontium (Sr), lead (Pb) and neodymium (Nd) in basaltic pillow lavas from northern British Columbia. In order to measure the elements, we need to isolate them from the rest of the elements that make up our rocks. We purify individual elements using the method of column chemistry. A column is like a filter for elements; we pass our sample through the column and the column captures the element of interest, then we release and collect the element off the column to be analyzed later.

The first step to preparing our samples is to dissolve our rock powders in an acid solution. Ben Kumpf (’18) weighs small amounts of rock powder into Teflon vials. We add a series of acids to the vials and let them sit on a hotplate for a day or two until the powders are completely dissolved.

Once the samples are dissolved, we measure out a small amount of the solution into a new vial to run it through the column chemistry process. The first step to make a column “load” solution is to dry the sample solution down to a powder on a hotplate.

To the dried-down powder, we add an acid that is appropriate for the column that we’re using. For Sr, we’re adding nitric acid to the vials.

Now we’re ready to set up the columns. Dr. Ryan Mills (psychedelic lab coat) is showing Ben Kumpf (’18) how to add the resin.

This is what a column looks like up close. It’s suspended above a waste beaker. The white material that is filling the tube and neck is the resin. You can see it still settling out of solution. The resin that we use to isolate Sr was developed in response to the Chernobyl accident when it became necessary to remove radioactive Sr from milk (Vajda and Kim, 2010).

The chemical column process involves adding a series of solutions to the columns in a sequence that cleans the resin, conditions the resin for the sample load solution, introduces the sample, and rinses the sample through the resin. There’s a lot of pipetting and waiting for the solutions to move through the column during this stage.

Samples are centrifuged prior to loading. The centrifuge separates any undissolved solids from the liquid so that we only add the liquid portion to the column.

These columns are loaded with our Pb solutions.

Now that our sample has passed through the column, we release all of the Sr or Pb off of the column and collect it in our sample vial.

The last step in the process is to dry down the sample one final time. This makes a tiny bead at the bottom our vial. We will load this bead into a mass spectrometer to measure the isotope composition.

Now you can see why we need do our sample preparation in a clean lab.

References

Vajda, N. and Kim, C.-K. 2010. Determination of radiostrontium isotopes: A review of analytical methodology. Applied Radiation and Isotopes 68: 2306-2326.

What is a clean lab?

May 16th, 2017

Chapel Hill, NC – Ben Kumpf (’18) and I are at the University of North Carolina at Chapel Hill to use their lab facilities for isotope analysis. We’re working with small amounts of sample and the instrument has a high degree of analytical precision and sensitivity, so all of our sample preparation occurs in the class-1000 clean lab. A clean lab is a room that is specifically designed to limit the amount of airborne contaminants. Special air filters and air distribution systems keep the environment clean so that we can minimize contamination while we separate and purify the isotopes.

Clean labs are classified based on the amounts of specifically sized particles allowed in a cubic meter (~35 cubic feet) of air. If we sample a cubic meter of air in the class-1000 lab and measure the amount of particles that are 5 microns in diameter, we would count no more than 293! For comparison, human hair has a diameter of about 50 to 100 microns, so we’re talking about really tiny bits of airborne dust. Class-1000 refers to Federal Standard 209E, where class-1 is the cleanest space and class-100,000 is the dirtiest (but still pretty darn clean). Federal Standard 209E has been replaced by International Organization for Standardization ISO 14644-1 standards. The new standards include one dirtier and two cleaner classifications and are numbered ISO-1 to ISO-9. Class-1000 is equivalent to ISO-6. UNC Chapel Hill also has a class-100 (ISO-5) clean lab where they process zircons for U-Pb dating.

Before we enter the clean lab, we gear up in the gowning room. The garments are designed to protect the wearer and minimize contamination from the wearer’s body. We wear standard lab safety attire, like glasses, gloves, and a lab coat. We also remove our shoes and exchange them for designated (comfy) slip-on shoes that only go in the clean lab.

Ben Kumpf (’18) models the clean lab outfit, complete with matching Carolina Blue accents. I see a theme.

Let the summer research commence!

May 15th, 2017

Chapel Hill, NC – As the College of Wooster Commencement ceremony was just finishing, our rising seniors were starting their summer research. Ben Kumpf (’18) and I are visiting the labs in the Department of Geological Sciences at the University of North Carolina at Chapel Hill. We are using their Isotope Geochemistry Lab to measure Sr-Nd-Pb isotopes of pillow lavas from our study site in northern British Columbia. The first step in the process is to dissolve our rock powders using several strong acids. Fortunately, we were able to send some of our samples in advance, and the good folks here at UNC dissolved about half of our samples for us.

Ben Kumpf (’18) went straight from his flight to the lab and is already hard at work. He measured portions of the dissolved samples into new vials so that we can prepare them for Sr isotope analysis. The dissolved samples will be made into solutions that we’ll use tomorrow.

Look for our posts in the following week to learn more about how isotopes are analyzed and what we hope to learn.

The 30th Annual Keck Symposium and the Importance of Presentation in the Undergraduate Research Experience

May 11th, 2017

Middletown, CT – Wesleyan University recently hosted the 30th annual Keck Symposium. The Keck Symposium is one of the key features that separates Keck projects from other types of undergraduate research experiences. Most other REU programs are confined to the summer, but Keck projects continue through the following academic year and culminate in the Symposium. Research groups reunite to synthesize their individual results and present their work to a broader scientific community. The Symposium is also a best practice and an essential part of the undergraduate research experience. By presenting their research, students transition from private to public discovery and contribute knowledge to the scientific discourse. They develop confidence in their abilities and advance their independence as scientists (Lopatto, 2009).

Wooster Geologists, Andrew Conaway (’17), Chloe Wallace (’17), and Meagen Pollock are happy passengers headed to the Keck Symposium.

The Keck Symposium format involves two sessions of oral presentations followed by poster presentations. With coffee and muffins in hand, the Keck Iceland group is ready for the morning session.

Each research group provides an overview of their projects. Students present their work in a brief 5 minutes. Andrew Conaway (’17) tells the audience about the history of land use around the Wisconsin lakes that he studied.

The oral sessions are followed by poster sessions, where the students can discuss their work in detail. Andrew Conaway (’17) talks about his research on magnetic susceptibility in lake cores.

Chloe Wallace (’17) discusses her research on volatile contents of pillow lavas from a subglacial ridge in southwest Iceland.

Team Iceland celebrates the end of our poster session with a final group photo. The Symposium also provides an opportunity for faculty to catch up and network. It’s an important professional development opportunity, particularly for early-career faculty.

Another important thing that happens at the Keck Symposium is the review of copy-edited short contributions. Each student writes an extended abstract of ~2500 words and 5 figures, which is compiled and published in a Symposium Volume. Team Iceland goes through their short contributions one last time at the lunch break.

It’s an intense weekend, but the smiles on our faces at the end of it all (despite the early morning flight) show that it’s worth the effort.

Last Wooster Geologist Presentation at #GSA2016

September 28th, 2016

Denver, CO – The honor of the last presentation at #GSA2016 goes to Amineh AlBashaireh (’18), who has a poster on her summer work at Black Mountain in San Diego, CA.

Amineh AlBashaireh ('18) has been conducting research on the occurrence and mobilization of arsenic.

Amineh AlBashaireh (’18) has been conducting research on the occurrence and mobilization of arsenic.

Congratulations, Wooster Geologists, on another successful GSA meeting!

 

Association for Women Geoscientists Breakfast at #GSA2016

September 26th, 2016

Denver, CO – The Association for Women Geoscientists (AWG) held their annual breakfast at #GSA2016, where they recognized those people who make exceptional contributions to their mission. AWG seeks to encourage the participation of women in the geosciences, exchange information (technical, educational, professional), and enhance professional growth and advancement. After this morning’s inspirational stories, who wouldn’t want to become a member? One notable part of the program was the recognition of women geoscientists from the Mongolian Chapter of AWG.

Representatives from the Mongolian Chapter of AWG were recognized for their efforts to support women geoscientists. They began as an informal club in 2012 and were officially recognized as an international chapter of AWG in 2014.

Representatives from the Mongolian Chapter of AWG were recognized for their efforts to support women geoscientists. They began as an informal club in 2012 and were officially recognized as an international chapter of AWG in 2014.

 

This year’s Outstanding Educator Award winner was Barbara Dutrow, a renowned mineralogist.

Barbara Dutrow accepts the Outstanding Educator Award. One of her nominators was a former student who was profoundly affected by her undergraduate research experience with Barbara.

Barbara Dutrow accepts the Outstanding Educator Award. One of her nominators was a former student who was profoundly affected by her undergraduate research experience with Barbara.

 

 Me and my research students, Rachel Heineman ('17, Oberlin) and Amineh AlBashaireh ('18), at the AWG breakfast. My students had the opportunity to network with lots of influential mentors, including a CUR Councilor, GSA Fellow, potential graduate advisors, and the Outstanding Educator Award Winner.

Me and my research students, Rachel Heineman (’17, Oberlin) and Amineh AlBashaireh (’18), at the AWG breakfast. My students had the opportunity to network with lots of influential mentors, including a CUR Councilor, GSA Fellow, potential graduate advisors, and the Outstanding Educator Award Winner.

 

Keck GSA Abstracts

July 25th, 2016

Wooster, OH – The summer portion of the Keck Iceland project is officially over, but our research isn’t finished. We’ll be working together throughout the academic year and will synthesize our final results at the Keck Symposium at Wesleyan University in April 2017. Along the way, we’ll be presenting at GSA in Denver, Colorado. We wrote and submitted 4(!) abstracts based on our work this summer. Here they are:

Cara Lembo ('17, Amherst) stands next to a ridge-parallel dike intruding through a tephra cone. Helgafell, a hyalocastite edifice, is in the distance.

Cara Lembo (’17, Amherst) stands next to a ridge-parallel dike intruding through a tephra cone. Helgafell, a hyalocastite edifice, is in the distance.

NEW INSIGHTS ON THE FORMATION OF GLACIOVOLCANIC TINDAR RIDGES FROM DETAILED MAPPING OF UNDIRHLIDAR RIDGE, SW ICELAND

HEINEMAN, Rachel1, LEMBO, Cara2, ENGEN, Carl-Lars3, KOCHTITZKY, William4, WALLACE, Chloe5, ORDEN, Michelle4, THOMPSON, Anna C6, KUMPF, Benjamin5, EDWARDS, Benjamin R.4 and POLLOCK, Meagen5, (1)Department of Geology, Oberlin College, 52 West Lorain St, Oberlin, OH 44074, (2)Department of Geology, Amherst College, 11 Barrett Hill Dr, Amherst, MA 01002, (3)Department of Geology, Beloit College, 700 College Street, Box 777, Beloit, WI 53511, (4)Department of Earth Sciences, Dickinson College, 28 N. College Street, Carlisle, PA 17013, (5)Department of Geology, The College of Wooster, 944 College Mall, Wooster, OH 44691, (6)Department of Geology, Carleton College, One North College Street, Northfield, MN 55057, rheinema@oberlin.edu

Undirhlíðar ridge on the Reykjanes Peninsula in southwest Iceland is a glaciovolcanic tindar formed by fissure eruptions under ice. Previous work in two quarries along the ridge shows that this specific tindar has had a complex eruption history. Here we report new results from investigations along the length of the ridge (~3 km) between the quarries. We have identified aerially significant fragmental deposits and a potential vent area on the ridge’s eastern side. The newly mapped tephra deposits are dominated by lapilli- and ash-size grains that are palagonitized to some degree (~20-60%) but locally contain up to ~75% fresh glass. Basal units are tuff breccia to volcanic breccia with basaltic and rare gabbroic lithic clasts. Upper units are finely bedded with few large clasts and some glassy bombs. Locally, lapilli-tuff units show repetitive normally graded bedding and cross bedding. Measured bedding attitudes suggest that present exposures represent a moderately eroded tephra cone that was subsequently intruded by basaltic dikes. Extending north and south of the tephra cone, the upper surface of the ridge comprises pillow rubble with outcrops of massive basalts showing radial jointing and concentric vesicle patterns. All of the outcrops appear to be similar coarse-grained, olivine- and plagioclase-bearing basalts; ongoing petrographic and geochemical analysis will determine if the bodies represent “megapillows” or if they are related to intrusions that are present in both quarries. Along the western side of the ridge, lapilli tuff and/or volcaniclastic diamictites overlie pillow lava (or volcanic breccia made of pillow fragments) that is locally intruded by dikes. In northern gullies, at least two stratigraphically distinct units of pillow lava are present. In order to communicate the implications of our detailed research to a broad audience, we are constructing two “map tours” of the ridge: one that is centered on the abandoned and accessible Undirhlíðar quarry, and another that describes features along the upper part of the ridge between the quarries. Stops along the tour include exposures of dikes, pillow lavas, and erosional alcoves within the tephra cone. The goal of these tours is to compare similar units across the ridge and quarry and to show the general anatomy of a glaciovolcanic ridge.

Rachel Heineman ('17, Oberlin) stands next to a potential "megapillow."

Rachel Heineman (’17, Oberlin) stands next to a potential “megapillow.”

Cross section of a pillow lava, with Michelle Orden's ('17, Dickinson) head for scale.

Cross section of a pillow lava, with Michelle Orden’s (’17, Dickinson) head for scale.

PHYSICAL CHARACTERISTICS OF GLACIOVOLCANIC PILLOW LAVAS FROM UNDIRHLIDAR, SW ICELAND

THOMPSON, Anna C1, ORDEN, Michelle2, LEMBO, Cara3, WALLACE, Chloe4, KUMPF, Benjamin4, HEINEMAN, Rachel5, ENGEN, Carl-Lars6, EDWARDS, Ben2, POLLOCK, Meagen4 and KOCHTITZKY, William2, (1)Department of Geology, Carleton College, One North College Street, Northfield, MN 55057, (2)Department of Earth Sciences, Dickinson College, 28 N. College Street, Carlisle, PA 17013, (3)Department of Geology, Amherst College, 11 Barrett Hill Dr, Amherst, MA 01002, (4)Department of Geology, The College of Wooster, 944 College Mall, Wooster, OH 44691, (5)Department of Geology, Oberlin College, 52 West Lorain St, Oberlin, OH 44074, (6)Department of Geology, Beloit College, 700 College Street, Box 777, Beloit, WI 53511, thompsona@carleton.edu

Pillow lavas are one of the most abundant lava morphologies on Earth, but are relatively inaccessible because of their submarine or subglacial eruption environments. Our research location in a former rock quarry in southwest Iceland provides a unique opportunity to view cross-sections through well exposed pillow lavas on land. The quarry is located at the northern end of Undirhlíðar, which is a glaciovolcanic ridge on the Krisuvik fissure system, and exposes thousands of individual pillow lavas. This study uses detailed field and laboratory observations of vesicle distributions and jointing patterns to better constrain the mechanisms that control vesiculation, bubble transport, and cooling rates during emplacement of pillow lava. From detailed analysis of >40 exposed pillow cross sections, we have identified 7 fracture characteristics that make up a combination of fracture patterns within the pillow lavas. These characteristics include: short (<5 cm) fractures at the outer edge of a pillow, fractures within pillow cores, fractures between the core and the edge of a pillow, long fractures (up to 40 cm) that go through the entire pillow, ‘web’-like fractures, fractures that branch from other fractures, and curvilinear fractures that cut through bands of vesicles. The distributions of vesicles are more diverse, with at least 12 different patterns defined by characteristics including: concentric banding, moderately/highly vesicular cores, non-vesicular cores, and open cavities. We identified 6 vesicle pattern combinations in the field, and are using image analysis of nearly 50 field photographs to characterize the patterns. These characteristics will constrain physical modeling to better understand how variations in emplacement conditions (abrupt pressure changes, lava discharge rates, water infiltration along fractures) are recorded by the lavas. These pillow lavas are the only lasting record of a preexisting englacial lake presumably formed during the eruption of the lavas, so understanding the details of their textures may provide new insights into the hydrology of the enclosing ice (occurrence of syn-eruption jokulhlaups, efficiency of sub-ice drainage).
Chloe Wallace ('17, Wooster) samples glassy pillow lava rinds for geochemical analysis by XRF and FTIR.

Chloe Wallace (’17, Wooster) samples glassy pillow lava rinds for geochemical analysis by XRF and FTIR.

GEOCHEMICAL CONSTRAINTS ON THE MAGMATIC SYSTEM AND ERUPTIVE ENVIRONMENT OF A GLACIOVOLCANIC TINDAR RIDGE FROM UNDIRHLíðAR, SW ICELAND

WALLACE, Chloe1, KUMPF, Benjamin1, HEINEMAN, Rachel2, LEMBO, Cara3, ORDEN, Michelle4, THOMPSON, Anna C5, ENGEN, Carl-Lars6, KOCHTITZKY, William4, POLLOCK, Meagen1, EDWARDS, Ben4and HIATT, Alex1, (1)Department of Geology, The College of Wooster, 944 College Mall, Wooster, OH 44691, (2)Department of Geology, Oberlin College, 52 West Lorain St, Oberlin, OH 44074, (3)Department of Geology, Amherst College, 11 Barrett Hill Drive, Amherst, MA 01002, (4)Department of Earth Sciences, Dickinson College, 28 N. College Street, Carlisle, PA 17013, (5)Department of Geology, Carleton College, One North College Street, Northfield, MN 55057, (6)Department of Geology, Beloit College, 700 College Street, Box 777, Beloit, WI 53511, cwallace17@wooster.edu

Glaciovolcanic tindar ridges are landforms created by the eruption of magma through fissure swarms into ice. The cores of many of these ridges comprise basaltic pillow lava, so they serve an accessible analogue for effusive mid-oceanic ridge volcanism. Furthermore, similar landforms have been identified on Mars, and thus they may also serve as models for planetary volcanic eruptions. To better understand pillow formation and effusive glaciovolcanic eruptions, we are investigating Undirhlíðar ridge, a pillow-dominated tindar on the Reykjanes Peninsula in southwest Iceland. Our detailed mapping and sampling in two rock quarries along the ridge and in the ~3 km area between the quarries show that this specific tindar ridge has had a complex eruption history. In the northern quarry (Undirhlíðar), Pollock et al. (2014) demonstrated that at least two geochemically distinct magma batches have erupted. Further trace element and isotope analyses in the southern quarry (Vatnsskarð) suggest that the ridge is fed by a heterogeneous mantle source. Isotopic Pb data show a spatially systematic linear array, which is consistent with a heterogeneous mantle mixing between depleted and enriched endmembers. The occurrence of multiple magma batches in dikes and irregular intrusions suggests that these structures are important to transporting magma within the volcanic edifice. Glassy pillow rinds were sampled for volatile analysis by FTIR in order to determine how paleo-water pressures vary along the ridge. In Undirhlíðar quarry, paleo-water pressures decrease with stratigraphic height (1.6-0.7 MPa). In Vatnsskarð quarry, paleo-water pressures show evidence of two separate eruptions, where pressure values decrease with an increase in stratigraphic height from 1.1 to 0.7 MPa over ~30 m, at which point pressure resets to 1.1 MPa and continues to decrease with elevation. When comparing the two quarries, paleo-water pressures in the upper units of Undirhlíðar and all the units in Vatnsskarð have similar values (0.7-1.1 MPa), and these are lower than the basal units of Undirhlíðar (1.2-1.6 MPa). Overall, compositional variations correlate with stratigraphy and spatial distribution along axis, suggesting that glaciovolcanic eruptions and their resulting landforms show a higher level of complexity than previously thought.

A view looking NE into Undirhlidar quarry on a moody Icelandic day. (Photo Credit: Ben Edwards)

A view looking NE into Undirhlidar quarry on a moody Icelandic day. (Photo Credit: Ben Edwards)

3-D

MAPPING OF QUARRY WALLS TO CONSTRAIN THE INTERNAL STRUCTURE OF A GLACIOVOLCANIC TINDAR, SW ICELAND

EDWARDS, Benjamin R.1, POLLOCK, Meagen2, KOCHTITZKY, William1 and ENGEN, Carl-Lars3, (1)Department of Earth Sciences, Dickinson College, 28 N. College Street, Carlisle, PA 17013, (2)Department of Geology, The College of Wooster, 944 College Mall, Wooster, OH 44691, (3)Department of Geology, Beloit College, 700 College Street, Box 777, Beloit, WI 53511, edwardsb@dickinson.edu

Documentation of the internal structures of volcanoes are critical for understanding how edifices are built over time, especially for glaciovolcanoes, which have rarely formed historically and are inaccessible during eruptions. We have been unraveling the internal structure of a complex glaciovolcanic ridge (tindar) in southwestern Iceland for the past 5 years in order to better understand the sequence of events that built the ridge. Undirhlidar ridge is ~5 km long, and has been dissected by two different aggregate mines along its axis. The northern mine (Undirhlidar quarry) is inactive and has walls up to 40 m in height that fully expose several critical stratigraphic relationships including multiple sequences of separate pillow lava flows, cross-cutting dikes that locally feed overlying pillow flows, and ridge parallel, continuous massive jointed basaltic units that may be the remnants of internal lava supply networks. The second quarry, ~3 km to the southwest (Vatnsskard quarry) is presently active and continually has new exposures. This quarry only penetrates halfway through the width of the ridge but has ~500 m of exposure along strike. It also has remnants of what appears to be the internal magma distributary system, and many components clearly show evidence that they were (and some still are) open lava tubes. While both quarries contain excellent exposures, many of the structures are difficult to safely access or are inaccessible due to mining activity. In order to overcome access issues, we have used Structure-from-Motion techniques to make 3-D maps of the quarry walls. A series of overlapping pictures were taken from points constrained with D-GPS using a Trimble GeoXH data logger and external antennae. The image locations with corrected positions were imported into Photoscan software to create a point cloud representative for each quarry and to derive a Digital Elevation Model with a reported vertical resolution of less than 1 m. Field testing of a preliminary, low resolution DEM shows that measurements of dyke widths on the DEM have errors of ~5% relative to measurements on the ground. Measurements made from the field-generated DEM will provide significantly better constraints on deposit thicknesses and volume estimates compared to traditional methods of estimating unit thicknesses on vertical faces.

Black Mountain GSA Abstract

July 21st, 2016

Wooster, OH – If you’ve been following our summer research adventures, you know that Amineh AlBashaireh (’18) has been hard at work studying the compositions of soils around abandoned mines in Black Mountain Open Space Park in San Diego, CA. She wrote the following abstract for the Geological Society of America Annual Meeting in Denver, Colorado this September.

Amineh AlBashaireh ('18) collecting a soil sample surrounded by miner's lettuce outside of Koala Mine in Black Mountain Open Space Park, San Diego, CA.

Amineh AlBashaireh (’18) collecting a soil sample surrounded by miner’s lettuce outside of Koala Mine in Black Mountain Open Space Park, San Diego, CA.

Evaluation of Arsenic Extent and Mobilization in Soil and Vegetation surrounding abandoned, ultra-enriched Arsenic Mines in Black Mountain Open Space Park, San Diego, California to GSA

ALBASHAIREH, Amineh B.1, JOHNSTON, Elizabeth2, O’SHEA, Bethany2 and POLLOCK, Meagen1, (1)Department of Geology, The College of Wooster, 944 College Mall, Wooster, OH 44691, (2)Environmental and Ocean Sciences, University of San Diego, 5998 Alcala Park, San Diego, CA 92110

Black Mountain Open Space Park in San Diego, CA is part of the Santiago Peak Volcanic Formation, a heterogeneous meta-volcanic unit that is locally ultra-enriched in arsenic (As). Small scale, artisanal-type As mining occurred during the early 1920s. Mines were abandoned with little documentation and no obvious remediation efforts. Initial field study by portable XRF yielded As concentrations up to 480,000 ppm in abandoned mines and rock outcrops throughout the park. This study is a first step towards understanding As fractionation in soils surrounding the mines. Twelve samples from the surface 5 cm of soil were collected in a ~48 m2 grid between two of the abandoned mines to determine how As concentration varies spatially, the degree of As mobilization during rain events, and how plants sequester As and affect soil As. Soils were pressed into pellets for analysis via WDXRF, and LOI was used to distinguish between organic and mineral-rich soils. To simulate transport by precipitation, 1:5 DI water leaches were performed on soils for 1 h, 24 h, and 7 day periods. Vegetation (miner’s lettuce, lemonade berry, and fern) was collected from the grid and will be analyzed by SEM-EDS for the extent of As throughout plant roots and bodies. While the crustal average for As is 1.5 ppm, soil concentration of As varies from hundreds of ppm to tens of thousands of ppm between the two mines. Consistent with hypotheses, the two greatest As concentrations occurred in rocky soils, possibly due to the presence of waste rock in the naturally occurring San Miguel-Exchequer rocky silt loam. Vegetation in the area appears healthy, but is not growing consistently across the grid, so SEM data will be compared with soil organic matter content and As concentration. San Diego’s semi-arid climate causes low precipitation and increased rates of soil erosion, making aeolian dispersion a likely mode of As transport. Consequently, there’s a potential health risk for those traveling off trail to visit the mines, hiking along the trails, and living in the canyon outlet. This is the first soil-plant arsenic study in a broader project aimed at understanding potential impact to public health. Additionally, this project has implications for the geologic occurrence of extreme As concentrations in igneous rocks from island arc settings.

filtration

Filtration step of 24h deionized water leach on <1.0 mm Black Mountain soil.

After the prescribed leach time, samples are centrifuged and filtered using a syringe fitted with a nylon filter to separate leachate (amber to red liquid above) from soil.

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