Wooster undergraduate researchers will share findings at international conference

August 2nd, 2019

Wooster, OH – Team Geochemistry finished a highly productive summer research season with two conference abstracts that we submitted to the 2019 Fall Meeting of the American Geophysical Union. AGU will be an excellent opportunity for the team to hone their presentation skills, network with potential employers and graduate school advisors, and explore the wide range of disciplines in the geosciences. Read about our work in the abstracts:

Ok and Bræðravirki offer us opportunities to explore past climates and interactions between volcanoes and glaciers, helping us predict what might be in store for Iceland and other ice-covered volcanoes across the world. (Photo Credit: Hannah Grachen)

A Geochemical Study of Bræðravirki Ridge (Western Volcanic Zone, Iceland) Reveals Regional Glaciovolcanic Variations and Complex Tindar Construction 

By Hannah Grachen, Simon Crawford-Muscat, Billy Irving, Meagen Pollock, Benjamin R. Edwards, Shelley A. Judge, Layali Banna, Kendra Devereux, Marisa Schaefer

Summary: As global ice recedes in response to climate change, volcanoes that erupted under the ice are becoming more exposed. We studied one such subglacial volcano in Iceland called Bræðravirki Ridge, and found that Bræðravirki is chemically different from other nearby subglacial volcanoes. We also found that there were several packages of volcanic ash and lava that were erupted at different times. These findings show that subglacial eruptions are complicated, and we might be able to use these types of observations to understand more about the history of volcanoes and glacial ice in an area.

Although tuyas in the Western Volcanic Zone (WVZ) of Iceland have been studied in detail, little work has been done on the numerous smaller tindars there. This study compares Bræðravirki Ridge, a 3-km long tindar on the southeastern flank of Ok shield volcano in the WVZ, to regional tuyas and creates a model for ridge formation based on combined mapping and geochemical analyses. Bræðravirki is dominated by palagonitized lapilli tuff with scattered intrusions, rare exposures of intact pillow lavas, and multiple tuff/lapilli tuff units. Whole rock samples were measured for major and trace elements by XRF and ICP-MS. Mineral compositions were measured by SEM-EDS. Major elements show that Bræðravirki is relatively enriched in SiO2 and depleted in CaO, FeO*, and MgO compared to regional data. Within the ridge, vitric tuff/lapilli tuff units are more evolved (MgO 6.29-6.66 wt.%) than other units (MgO 6.94-7.72 wt.%). Preliminary Rhyolite-MELTS (v. 1.0.1) models are consistent with the two compositional groups being genetically related by 3 kb fractional crystallization of a common parent magma. The MELTS models generate plagioclase (An61 to An70) and two pyroxene (low- and high-Ca) compositions that are observed in the SEM-EDS mineral data. Incompatible trace elements show limited variation between the two compositional groups (Nb/Y 0.37-0.41), suggesting stable melting conditions. We propose a two-stage eruptive model that begins with an explosive phase, followed by a second explosive-effusive phase that forms intrusions and pillows. The second phase is hypothesized to be initiated by a recharge event, emplacing the higher-MgO units. This study demonstrates that small tindars can be constructed through multiple eruptive events that shift in eruptive style and that glaciovolcanic edifices in the same region can have significant compositional differences, possibly providing insights into the understanding of their timing, magmatic history, and paleo-ice conditions.

Microscope photo of one of the granitic rock samples that was classified using the new and old naming systems.

New Igneous Classification System Produces Consistent Rock Names and Illuminates Modal Data

By Hannah Grachen, Anna Cooke, Charley Hankla, Ethan Killian, Cody Park, Layali Banna, Kendra Devereux, Meagen Pollock

Summary: Rock names are useful for understanding what a rock is made of, how it formed, and how it might be useful. For rocks that form from molten magma, the current naming system doesn’t communicate all of the relevant information. Earlier this year, scientists proposed a controversial new naming system to make rock names more meaningful. We tested the new naming system and found that it worked well at the microscopic scale but was more confusing when using the naked eye. We found that the new rock names contained more useful information than the old rock names, and we think that the new system could become the future of rock classification.

In the February 2019 issue of GSA Today, Glazner et al. proposed a new classification system for igneous rocks, citing shortcomings within the standard International Union of Geological Sciences (IUGS) classification system, in use since 1974; chiefly its inability to convey modal data and its arbitrary division of interrelated rocks into disparate types. Their proposed system recognizes rock classifications on ternary diagrams to be “fuzzy” rather than distinct, therefore better representing the continuous nature of rock sequences and lending their system the term “fuzzy classification scheme”. They suggest a system of limited root names combined with modal percentage numbers and significant accessory minerals to provide more informative and straightforward rock names. To test this claim, we have named a suite of six thin sections and hand samples of granitic rocks from Songo Pluton, North Jay Quarry, Mount Waldo, and Deer Isle, using both the IUGS and “fuzzy” classification schemes. We also obtained modes on thin sections through quantitative image analysis using Adobe Illustrator and ImageJ, this being an important step in our process due to the difficulty of differentiating alkali feldspar and plagioclase in our samples. We determined that while the comments on Glazner et al.’s paper are critical, in the tests we performed, some of those criticisms, such as the non-replicability of the proposed system due to interpretive bias, are insubstantial. In thin section, the fuzzy system naming led to more consistent naming results than in hand sample observations, while the opposite was true in hand sample. One of the things we would suggest after conducting our tests is to include boundaries to distinguish the names in a better way. Overall, the proposed system’s ease of data communication is an improvement on the IUGS system that warrants more attention and modification.

Team Geochemistry’s Grand Finale

July 31st, 2019

Wooster, OH – Team Geochemistry wrapped up their grand adventure last week. The summer research experience left us with fond memories of trips to Dickinson College and Iceland, knowledge of lots of new analytical techniques, and many new friendships, not to mention the important findings from a critical field site that we’ll be presenting at the December meeting of AGU. Here are some parting thoughts on our bittersweet ending from guest blogger Kendra Devereux (’21):

After returning from Iceland, team geochemistry has been hard at work prepping their samples. In just two short weeks, all 23 whole rock samples from the field have been cleaned, powdered, sieved and turned into fused glass beads and pressed pellets.

Hannah, Layali, and Kendra spent the first week back from Iceland sieving their powdered samples.

Layali happily sieving!

Hannah happily sieving!

Hannah finished her time for the summer last week and is busy moving to Florida with her family, leaving Layali and Kendra on their own for their last week of work. Layali and Kendra spent this past week making 23 fused glass beads and 23 pressed pellets

Pressed pellets and glass beads are all ready to be analyzed with the XRF next week!

As a celebration of all their hard work, Dr. Pollock, Layali, and Kendra enjoyed “Taste of Wooster” downtown on Thursday night.

A delicious chocolate marshmallow whoopie pie from The Blue Rooster.

After 8 weeks together, team geochemistry have said goodbye until the 2019-2020 school year begins!

Wooster geologists working at site of first glacier memorial in Iceland

July 23rd, 2019

Iceland – Big news this week as researchers dedicate the first-ever monument to Okjökull glacier, memorializing the first Icelandic glacier to lose its glacier status to climate change. Ice loss in Iceland is dramatic; researchers expect all of Iceland’s glaciers to go extinct in the next ~200 years, with drastic changes to Icelandic culture and economy. As the ice retreats and reveals the underlying land, scientists can investigate ancient volcanoes that erupted thousands of years ago under the glacier. Wooster geologists were with a team from Dickinson College on the scene of Ok volcano this summer, exploring a glaciovolcanic ridge that is now exposed on the southeast flank of Ok volcano.

View of Ok shield volcano from the south. Bræðravirki is the glaciovolcanic ridge on the southeast flank of Ok volcano. (Photo Credit: Hannah Grachen)

Another view of Bræðravirki ridge from the east. The summit of Ok volcano is off of the photo to the right. (Photo Credit: Hannah Grachen)

Most of Bræðravirki ridge is made of yellow ash that was erupted explosively and has been consolidated into a rock called tuff. The patterns in the rock tell us about how it formed. (Photo Credit: Hannah Grachen)

The tuff has a distinct yellow color that forms when the volcanic ash reacts with hot water. We also see glassy black rocks in the ash that we think are volcanic bombs, which form when lava is ejected violently during an explosive eruption. (Photo Credit: Hannah Grachen)

The ridge also has irregularly shaped bodies of massive rock. These are light gray and extremely hard, with a unique pattern of cracks that forms as the molten rock cools and solidifies. We think these are fingers of magma that get injected into the growing ash pile. (Photo Credit: Hannah Grachen)

Ok volcano and Bræðravirki ridge give us the opportunity to explore past climates and interactions between volcanoes and glaciers, helping us predict what might be in store for Iceland and other ice-covered volcanoes across the world. (Photo Credit: Hannah Grachen)

Look for us at the December 2019 meeting of the American Geophysical Union in San Francisco, CA (USA), where we will be presenting our findings from Bræðravirki ridge.

Summer undergraduate researchers travel to Iceland to explore volcanoes

July 19th, 2019

Iceland – In our last post, Team Geochemistry was getting ready to head to Iceland for some field work on volcanoes. Our goals were to map and sample volcanoes that erupted under glaciers, which have since retreated, exposing the pillow lavas and ash that formed when lava met ice. We met up with a research team from the Dickinson College Earth Sciences Department, and also brought Dr. Shelley Judge, Wooster’s structural geologist. Together, we collected over 30 samples, took 1000s of photos, flew the drone for 8 hours, and made 100s of structural measurements. Overall, it was a successful and productive field season, with some laughs along the way! Layali Banna, member of Team Geochemistry (and basalt goddess), describes their field experience.

[Guest blogger Layali Banna] Last week, team geochemistry went to Iceland. We met up with some old friends there, but we met some new ones as well. In total there were ten of us and we were ready to take Iceland by storm.

All of us walking along Undirhlíðar (from left to right: Phoebe, Dr. Edwards, Marisa, Dr. Judge, Dr. Pollock, Kendra, Layali and Ethan; Hannah Is behind the camera taking the photo.)

After a long day of flying we decided to mostly take it easy, just doing a short walk around a nearby quarry to learn more about what we will be looking for out in the field.

Dr. Pollock posing for her glamour shot.

The second day was much different though – we spent almost all day out on Hannah’s site collecting samples for her project at Bræðravirki ridge. Divided into two teams, one group walked the ridge collecting samples, while the other group used a drone to map the ridge. This was a prime time up at the ridge since there was no snow cover, unlike past years where the gullies were hidden by snow, allowing us a great look at it without anything in the way.

Kendra smiling with Prestahnúkur in the background, which is a rhyolite volcano.

A gulley on Bræðravirki that was buried in snow during past years was now accessible for sampling.

Our third day in Iceland after that long day in Bræðravirki we spent the morning inside working on our field books and collecting some data, making observations on our samples.

 

Everyone working together to look through all the samples we had collected the day prior.

The latter half of the day we surveyed Undirhlíðar and ended up goofing around a bit at a certain spot called the bowl.

Kendra and Marisa trying to figure out how they are going to climb up the side of the bowl.

After our half day we returned to Undirhlíðar. This time we were split up into three groups all doing different things in separate areas. One group mapped with drones, another analyzed and mapped deformation bands, taking samples and pictures of the bands, and the last group went and took samples for Marisa’s project.

A beautiful, thick, glassy dike found on Undirhlíðar.

Time for a snack break! Marisa is eating a nutritious energy boosting cookie.

Finally, on our last day in Iceland everyone was given a free day to do what they want, exploring some of the natural wonders the island has to offer as well as touring the capital of Iceland, ReykjavÍk.

Hannah finally getting her photo taken instead of her always being the one taking them at Krýsuvík thermal zone.

The group stopped for some famous Icelandic street dogs in ReykjavÍk, Kendra is ready to dig in.

All too soon it was time for us to pack our bags and say goodbye to our friends and Iceland. It was time to head back to Wooster and work on the samples we collected in the lab.

 

The week leading up to international field work

July 6th, 2019

Wooster, OH – In the week leading up to field work, Team Geochemistry was frantically trying to “put out fires” and clean up loose-ends.

The “fires” started first thing Monday morning, when a leak in the geochemistry lab caused the ceiling to collapse. Fortunately, the students and cleaning staff were quick thinking and all ended well.

Next, we tried to wrap up our petrology classification project, which involved lots of microscope work. Classifying minerals in the microscope was more challenging than we expected, and we still have more work to do when we return from the field.

Finally, we had to gather our field gear, double-checking that we had everything we needed. Undoubtedly, there will be something that we forgot.

Even with the frantic pace of the week, we still made some time for an ice cream (or two!). It was the Fourth of July holiday, after all.

Team Geochemistry in currently en route to Iceland for some field work. We’ll be reunited with Marisa, our teammate from Dickinson College, along with Dr. Ben Edwards and three other Dickinson students. Dr. Shelley Judge, from Wooster, is also joining us for this field excursion. Look for updates from the field late next week!

Hands-on experience troubleshooting geochemical instruments

June 21st, 2019

Wooster, OH – Team geochemistry returned to Wooster this week with a serious focus on sample prep and data quality. Anyone with geochemical research experience understands the importance of preparing samples carefully and thoroughly, and having an analytical instrument that is well-calibrated for your samples. Some of our recent analyses have yielded surprising results, and now we’re double checking our sample prep process and instrument calibration to make sure the data are reliable.

Kendra and Layali are loading samples into the XRF. They are gaining a lot of hands-on experience operating the instrument.

The XRF measures the chemical composition of samples by exciting them with an X-ray beam. The X-ray beam causes the atoms in the sample to emit their own X-rays, which travel through a series of filters and crystals and are measured by a detector. The signal from the detector is converted to a concentration using a calibration curve that was made by measuring standards with known concentrations.

We are running the XRF at full capacity with drift-correct samples, unknowns, and standards, so that we can test the quality of the calibration and resulting data.

But we didn’t just work in the lab all week. We’re also preparing to for our upcoming trip to Iceland. We needed to pick up a few things, like rain gear. Only the essentials, of course.

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.

How thick was the ice?

November 8th, 2016

AMHERST, MA – Our Keck project studying the construction of a glaciovolcanic ridge in southwest Iceland is in full swing and our students are hard at work on their research. You may remember that we traveled to Iceland this summer to conduct field work, then returned to Wooster, where we prepared our samples for analysis. All of the time and energy devoted to sample preparation is finally paying off. This weekend, Chloe Wallace (’17, Wooster) and I met Cara Lembo (’17, Amherst) at UMass Amherst to analyze their samples by Fourier Transform Infrared Spectroscopy (FTIR) and Electron Microprobe.

Chloe and Cara are trying to determine the emplacement pressure of the samples. The emplacement pressure should reveal information about water depth (or ice thickness) at the time of the eruption. To estimate emplacement pressure, they are using the volatile contents of the quenched glass rims of pillow lavas. Volatiles are lost during an eruption as a function of pressure; the smaller the pressure, the more degassing. So, by measuring the volatiles that are trapped in the glass, we can figure out how much pressure the glass experienced when it was formed.

Prior to the visit, Chloe and Cara selected the freshest glass chips, then polished them into ~100-200 micron-thick wafers. They analyzed them for H2O using the FTIR, making sure to avoid any vesicles, crystals, and fractures. They collected nearly 300 data points on 16 samples, so they have a thorough and extensive dataset to work with.

Chloe (left) is looking for an ideal measurement location on her glass chip. Cara (right) is operating the data collection and reduction software.

Chloe (left) is looking for an ideal measurement location on her glass chip. Cara (right) is operating the data collection and reduction software.

In order to calculate water depth (or ice thickness) from H2O concentration, we use a solubility model. The model requires additional inputs, including the glass composition, which we measured by electron microprobe.

After the glass chips were analyzed by FTIR, they were mounted on a glass slide for probe analysis.

After the glass chips were analyzed by FTIR, they were mounted on a glass slide for probe analysis.

The electron microprobe allows us to measure the composition of a very small (micron-scale) spot on the glass chip.

Chloe is examining her glass chips on the microprobe.

Chloe is examining her glass chips on the microprobe.

Cara uses the map to find her way around the slide. They analyzed several points on each chip, and will use those data to determine the glass composition.

Cara uses the map to find her way around the slide. They analyzed several points on each chip, and will use those data to determine the glass composition.

It was a short and intense visit, but we accomplished all of our goals. We especially would like to recognize Dr. Sheila Seaman for generously giving her time and energy. She made it all possible.

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.

Keck Iceland takes over the Wooster Lab

July 18th, 2016

Wooster, OH – Keck Iceland 2016 by the numbers:

  • Scientists in Keck Iceland: 10
  • Time in the field: 14 days
  • Pillows described in detail: >40
  • Samples collected: 71
  • Structural measurements made: 94
  • Photos taken: >2000
  • GPS data recorded: ridiculous

With a few extra charges for baggage fees, and a lot of help from the airport luggage carts, we successfully returned to Wooster to begin processing our samples and photos.

For the samples that we want to analyze for geochemistry, our first step is to powder them. Rachel Heineman ('17, Oberlin College) is cutting her samples on the rock saw.

For the samples that we want to analyze for geochemistry, our first step is to powder them. Rachel Heineman (’17, Oberlin College) is cutting her samples on the rock saw.

 

 

Cara Lembo ('17, Amherst College) is hammering her rocks into smaller pieces, preparing them for the shatterbox.

Cara Lembo (’17, Amherst College) is hammering her rocks into smaller pieces, preparing them for the shatterbox.

Every student has a project box in which they're keeping all of their materials. Rachel's is organized with thin section billets on the left, powders in the middle, and pieces to archive on the right.

Every student has a project box in which they’re keeping all of their materials. Rachel’s is organized with thin section billets on the left, powders in the middle, and pieces to archive on the right.

Some of the boxes look like this one, though. (Cara)

Some of the boxes look like this one, though. (Cara)

For samples that we want to analyze for trace elements, we prepare pressed powder pellets. Carl-Lars is showing Cara how to use the manual press to compress the powder in the die into a solid pellet.

For samples that we want to analyze for trace elements, we prepare pressed powder pellets. Carl-Lars is showing Cara how to use the manual press to compress the powder in the die into a solid pellet.

The result of all of our hard work is a desiccator full of samples ready for the XRF.

The result of all of our hard work is a desiccator full of samples ready for the XRF.

Another part of our work involves analyzing the compositions of volcanic glasses. Chloe Wallace ('17, Wooster) is picking out the freshest glass so that she can polish it for analysis by FTIR (Fourier Transform Infrared Spectroscopy) and Electron Microprobe. The FTIR will allow us to measure H2O contents while the microprobe will give us chemical compositions over small spatial scales.

Another part of our work involves analyzing the compositions of volcanic glasses. Chloe Wallace (’17, Wooster) is picking out the freshest glass so that she can polish it for analysis by FTIR (Fourier Transform Infrared Spectroscopy) and Electron Microprobe. The FTIR will allow us to measure H2O contents while the microprobe will give us chemical compositions over small spatial scales.

Lab work entails more than physical preparation of samples. Michelle Orden ('17, Dickinson College) and Anna Thompson ('17, Carleton College) are analyzing high-resolution photos of pillow lavas to understand the physical volcanology.

Lab work entails more than physical preparation of samples. Michelle Orden (’17, Dickinson College) and Anna Thompson (’17, Carleton College) are analyzing high-resolution photos of pillow lavas to understand the physical volcanology.

Michelle is identifying fracture patterns in her images.

Michelle is identifying fracture patterns in her images.

Anna and Ben Edwards (Dickinson College) are identifying vesicle patterns in pillow lavas.

Anna and Ben Edwards (Dickinson College) are identifying vesicle patterns in pillow lavas.

It's not all work, of course. We occasionally take breaks to play wiffle ball and frisbee on the quad.

It’s not all work, of course. We occasionally take breaks to play wiffle ball and frisbee on the quad.

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