https://eos.org/science-updates/sensing-icelands-most-active-volcano-with-a-buried-hair Close * Sign Up for Newsletter Search for: [ ] Search * About * Special Reports * Topics + Climate + Earth Science + Oceans + Space & Planets + Health & Ecosystems + Culture & Policy + Education & Careers + Opinions * Projects + ENGAGE + Third Pod from the Sun + Eos en Espanol + Eos Jian Ti Zhong Wen Ban + Print Archive * Newsletter * Submit to Eos * AGU.org * AGU Publications + AGU Journals + Editors' Highlights + Editors' Vox * Career Center * AGU Blogs * Join AGU * Give to AGU * Twitter * Facebook * LinkedIn * RSS * Tumblr * Instagram * YouTube Close * About * Special Reports * Topics + Climate + Earth Science + Oceans + Space & Planets + Health & Ecosystems + Culture & Policy + Education & Careers + Opinions * Projects + ENGAGE + Third Pod from the Sun + Eos en Espanol + Eos Jian Ti Zhong Wen Ban + Print Archive * Newsletter * Submit to Eos Skip to content Menu [svg]Eos Eos Science News by AGU Sign Up for Newsletter Menu Open Search Search for: [ ] Search Posted inScience Updates Sensing Iceland's Most Active Volcano with a "Buried Hair" Distributed acoustic sensing offered researchers a means to measure ground deformation from atop ice-clad Grimsvotn volcano with unprecedented spatial and temporal resolutions. by Sara Klaasen, Solvi Thrastarson, Andreas Fichtner, Yesim Cubuk-Sabuncu and Kristin Jonsdottir 4 January 20224 January 2022 Share this: Print [svg]A snowcat plows its way through snow with a rocky ridge in the background. A snowcat plows its way through snow near the caldera rim of Grimsvotn volcano in Iceland in spring 2021 during the deployment of a fiber-optic cable for distributed acoustic sensing (DAS). Credit: Yesim Cubuk-Sabuncu Icelandic legend tells of an outlaw named Grimur who hid in the highlands of the island after avenging the murder of his father. A widow assisted him, directing him to some remote lakes where he could sustain himself by fishing. However, there was already a giant living near the lakes. Grimur fought and killed the giant, so upsetting the giant's daughter that she laid a curse on the landscape. From then on, fires would burn in the lakes and the surrounding woods would vanish. To this day, Grimur's lakes, Grimsvotn in Icelandic, continue to spit fire, even as they are buried under hundreds of meters of the ice of Europe's largest glacier, Vatnajokull. In fact, since the settlement of Iceland, Grimsvotn has been the island's most active volcano--and it may be due for another major eruption. In spring 2021, researchers from ETH Zurich and the Icelandic Meteorological Office (IMO) set out for Grimsvotn to take a closer look at its activity, using an emerging geophysical technology called distributed acoustic sensing (DAS; Figure 1). DAS can yield unprecedentedly high resolution data in hazardous and difficult-to-access environments. In addition to measuring previously unobserved seismic activity at the volcano, the experiment also indicated the presence of continuous seismic tremor and a variety of other signals at Grimsvotn not observed before in such detail. [svg]Map showing where a fiber-optic cable was deployed atop Grimsvotn volcanoFig. 1. This map of Grimsvotn shows the layout of the fiber-optic cable (black line with numbers indicating distance in kilometers) deployed in the DAS-BummBumm experiment in spring 2021. Locations of the research huts (GFUM) near one end of the cable and a GPS station at the other end are also shown, as are the years and approximate locations of previous fissure eruptions (orange and red). The site of Grimsvotn (red triangle) amid the Vatnajokull ice sheet in Iceland is indicated in the inset. Topographic information in this figure is based on ArcticDEM. The Hazards of Grimur's Lakes Grimsvotn is a complex volcanic system that is governed by both geothermal heat from below and the ice of the overlying glacier. Grimsvotn is a complex volcanic system that is governed by both geothermal heat from below and the ice of the overlying glacier. The heat melts the underside of the glacier, creating runoff and forming a subglacial lake within the caldera of the volcano. This lake occasionally drains during major outburst floods called jokulhlaups, which inundate the coastal plains south of the ice cap. Past jokulhlaups from Grimsvotn have destroyed bridges and cut off transit between western and eastern Iceland. Recently, Grimsvotn again showed such increased activity. Around 20 November, GPS measurements recorded the ice shelf above Grimsvotn starting to subside slowly, marking the beginning of a jokulhlaup as water flowed out of the subglacial lake. The jokulhlaup peaked on 5 December in the Gigjukvisl glacier river, and more than 0.8 cubic kilometer of water in total drained from below the volcano. [svg]The Sun sets behind a snow-covered volcanic caldera.Sunset over the caldera of Grimsvotn, as seen from the research huts near the caldera rim. Credit: Solvi Thrastarson In addition to the flood hazard, ash clouds pose threats to humans and livestock when direct interaction between magma and meltwater causes Grimsvotn to erupt explosively. Recent eruptions occurred in 1998, 2004, and 2011, each of which sent plumes of ash and debris into the atmosphere (the 1998 and 2004 events were also associated jokulhlaups). These plumes can spread heavy layers of ash over the local landscape, cause intense lightning, and reduce air quality and visibility, conditions that can impair aircraft and roads. If winds are unfavorable during an eruption, ash clouds can also cause major shutdowns and economic damage in the air traffic industry, as happened during the 2010 eruption of Eyjafjallajokull, located about 140 kilometers southwest of Grimsvotn. Rapid and substantial pressure decreases, such as that seen beginning in late November, have previously caused Grimsvotn to erupt (in 2004, 1932, and 1922). The IMO, which is responsible for providing warnings about impending eruptions, was thus on full alert and raised the aviation alert level from yellow to orange as seismicity started to pick up at Grimsfjall, peaking with a magnitude 3.6 earthquake on 6 December. However, the seismicity quickly subsided that same day, and on 8 December, IMO lowered the code back to yellow. Instrumenting the Ice Over roughly 80 kilometers of ice, we hauled all the equipment we needed for our 5-day expedition until we reached three huts near the highest point of the caldera rim. Conducting a large-scale field experiment in the middle of 7,900-square-kilometer Vatnajokull was challenging. After months of planning, the effort began with our team of nine traveling by trucks from Reykjavik to the glacier's edge. From there, we continued aboard snowmobiles, superjeeps (trucks specially equipped with large tires for traversing ice), and a snowcat, following a carefully selected route to Grimsvotn to avoid the largest crevasses. Over roughly 80 kilometers of ice, we hauled all the equipment we needed for our 5-day expedition, including three large cable drums, each roughly 50 kilograms and holding 4-kilometer-long segments of fiber-optic cable, until we reached three huts near the highest point of the caldera rim at Grimsfjall. Built in 1957, 1987, and 1994 to conduct scientific research, the huts--geothermally heated by the volcano and collectively housing a small kitchen, bunks, and even a steam sauna--served as our base of operations. [svg]Aerial photo of a snowcat, a truck, and several people standing amid a vast snowfield atop a volcanoA superjeep and a snowcat used by researchers atop Grimsvotn are seen in this drone-captured photo, with the volcanic caldera in the background. Credit: Hildur Jonsdottir The fiber-optic cable was the core component of our experiment. DAS makes use of a standard fiber-optic cable together with an instrument called an interrogation unit (IU), which sends laser pulses through the fiber and receives them back. Inhomogeneities in the fiber cause backscattering of the light, which is measured by the IU. Small shifts in the return timing of the backscattered signals can be related to localized deformations of the fiber caused by seismicity or other sources of vibration. The different segments of fiber-optic cable had to be spliced together, which was a surgical task given that each fiber is about as thin as a human hair. Thus, long lengths of fiber can be used to create a dense seismic network, collecting measurements in the millihertz to kilohertz range every few meters with lower labor and financial costs compared with those from conventional seismic arrays covering areas of similar sizes. The high spatiotemporal sampling is especially beneficial in remote and harsh environments, such as Grimsvotn, where the installation of conventional arrays either would require substantially more personnel and time or is altogether infeasible. (In populated areas exposed to volcanic hazards, unused "dark" fibers in existing fiber-optic communications networks coupled with edge computing--data analysis that happens in real time at an instrument--may have great potential for noninvasive volcano monitoring and other applications of DAS.) [svg]Researchers work in the back of a truck.Andreas Fichtner (left) and Sara Klaasen splice fiber-optic cables together in the back of a superjeep during the deployment at Grimsvotn, a task that required safety gear and surgical precision. Credit: Solvi Thrastarson To build our detection network at Grimsvotn, we set up the IU in one of the huts, where electricity and Internet are available, and from there, we laid out our 12 kilometers of fiber-optic cable in a hook-shaped pattern along much of the caldera rim and atop the subglacial lake (Figure 1). Using the snowcat equipped with a custom-made plow, we trenched the cable 50 centimeters deep into the snow, thereby protecting it from atmospheric influences. Because the cable was delivered on three separate drums, the different segments had to be spliced together, which was a surgical task given that each fiber is about as thin as a human hair. This surgery was complicated by the fact that it had to be performed during the trenching, and thus in the back of a cold, cramped superjeep rather than in the relative comfort of the huts. Badminton and a Bad Connection Deploying the entire length of cable took 2 days, a process that ran smoothly overall despite the difficult conditions of working atop an active, glacier-capped volcano. During the deployment, we were always in direct contact with the volcano monitoring room at the IMO. At the first signs of volcanic unrest, we would have evacuated immediately. [svg]A researcher pounds on a metal frame in the snow with a sledgehammer in front of a snowcat.Sara Klaasen conducts a hammer test to create a seismic signal that the DAS cable can record. To increase the strength of their hammer blows, the researchers pounded on the metal plate on the plow used to deploy the cable. Credit: Solvi Thrastarson On the third day, we conducted hammer tests to locate the DAS channels and to provide first glimpses of seismic wave propagation in the ice. This entailed pounding a sledgehammer on the ice in different places so the fiber-optic cable would record the signals at those locations. In the data, we could then see exactly where along the cable the signals were recorded, allowing us to link the data with their geographic location. From these initial tests, the experimental setup--our "buried hair," as we jokingly called it--appeared to work as expected. This success gave us reason to celebrate, and the team was excited to have a good time amid the challenging days of fieldwork. Among our supplies, we had packed a badminton set--not at all standard equipment because the glacier is notoriously windy--hoping for an opportunity to spice up the expedition in the event of low-wind conditions inside the caldera, which is partly shielded by Grimsfjall mountain. We were extremely lucky to experience such a day. We set up a net amid the snow and enjoyed a sunny break for badminton--albeit wearing snowsuits instead of shorts and T-shirts--surrounded by the hills of the caldera rim. With the help of a large speaker we had brought up the glacier, the celebration turned into a small party, and because both the speaker and the party were referred to as "bummbumm" in Icelandic, our experiment was subsequently named DAS-BummBumm. [svg]Two people play badminton on a vast snow-covered expanse. Researchers take a break for a short badminton game amid their work. Badminton in knee-deep snow is its own sport, although the snow makes for a soft landing when someone falls. Credit: Solvi Thrastarson After our celebrations, however, we learned the experiment would not be without hiccups. Our original plan included collecting 2 months of continuous measurements, but upon arrival back in Reykjavik, we found that the connection to our instruments was lost. A week later, after waiting for a storm to pass, we returned to Grimsvotn and diagnosed that this lack of communication occurred because of a broken drive in the instrument. The issue prevented it from recording, and we could not repair it atop the glacier--unfortunately, the DAS system was more "brokebroke" than "bummbumm." Once we arranged for a replacement instrument, we went to Grimsvotn a third time and corrected the problem, and in the end we still managed to collect 1 month of measurements. Experimental Expectations Experiments on volcanoes are a relatively new application of distributed acoustic sensing (DAS), so the science is still exploratory. Our goal is eventually to develop DAS as a real-time volcano monitoring tool. Experiments on volcanoes are a relatively new application of DAS, with only a few examples to date, such as an experiment on Mount Meager in 2019, so the science is still exploratory. Our goal is to develop DAS as a real-time volcano monitoring tool. To achieve this, we need to conduct several DAS experiments in different volcanic settings to develop algorithms that can identify, locate, and characterize volcanic signals on the fly. We are still analyzing the data from this first-ever DAS deployment at Grimsvotn. So far, they reveal an unexpected level of seismic activity. Prior to the DAS-BummBumm experiment, there had been one seismic station at Grimsvotn to record seismic signals, whereas we effectively recorded ground motions every 8 meters along the fiber-optic cable. With a single station only, it is hard to distinguish smaller signals from background noise, but in our DAS data, we can see the propagation of even the smallest signals. We recorded previously unknown tremor inside the caldera, for example, as well as frequently occurring small, local events that were detected all along the fiber-optic cable. These events may have been caused by a wide range of phenomena, such as volcanic and geothermal activity, icequakes, snow avalanches, and resonance of the subglacial lake and the overlying ice sheet (Figure 2). Because the cable loops closely past fumarole fields, their activity is likely recorded as well. [svg]Sample data plot showing ground deformation measured along a fiber-optic cableFig. 2. This sample data plot shows ground deformation along the fiber-optic cable deployed at Grimsvotn over about 50 seconds. A large event arrived near the middle of the cable at about 18:44:50 on this day as it propagated through the glacier. The signal observed around kilometers 10-12 of the fiber, which sat on top of the subglacial lake, oscillated with longer periods than the large event and may have been caused by bending of the ice sheet on top of the lake. In our initial analyses, we are locating the detected events, carefully accounting for the rough topography and the presence of the ice and the lake, which affect seismic signals differently from the bedrock below. This work will be followed by a process of iteratively inverting the data to help determine the internal structure of Grimsvotn, including its magma chamber and conduits. We hope that our results and experiences from this experiment--and from future experiments planned for a range of volcanological settings in Santorini, Tenerife, and Indonesia--will shed light on hidden processes at hazardous active volcanoes and bring us closer to enhanced volcano monitoring using versatile fiber-optic cables. Acknowledgments We thank everyone involved with this experiment: Bergur H. Bergsson, Vilhjalmur Kjartansson, Vala Hjorleifsdottir, Bergur Einarsson, Laufey Gudmundsdottir, Gudlaugur Jakob Thorsteinsson, Hlynur Skagfjord, Johannes Rognvaldsson, Hildur Jonsdottir, Snaebjorn Sveinsson, Nadine Widmer, Patrick Paitz, and Andre Blanchard. We also thank Silixa for its incredible technical support. This work was supported by the project Real-Time Earthquake Risk Reduction for a Resilient Europe (RISE), funded by the European Union's Horizon 2020 research and innovation program under grant agreement 821115. It was also partly supported by the Icelandic Centre for Research's (RANNIS) Icelandic Research Fund through the IS-TREMOR project (217738-051). Author Information Sara Klaasen (sara.klaasen@erdw.ethz.ch), Solvi Thrastarson, and Andreas Fichtner, Swiss Federal Institute of Technology (ETH) Zurich, Zurich, Switzerland; and Yesim Cubuk-Sabuncu and Kristin Jonsdottir, Icelandic Meteorological Office, Reykjavik Citation: Klaasen, S., S. Thrastarson, A. Fichtner, Y. Cubuk-Sabuncu, and K. Jonsdottir (2022), Sensing Iceland's most active volcano with a "buried hair," Eos, 103, https://doi.org/10.1029/2022EO220007. Published on 4 January 2022. Text (c) 2022. The authors. CC BY-NC-ND 3.0 Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited. Related * Mars Polar Intrigue Spurs Multidisciplinary Collaboration * [svg]A view of Mars's south polar ice cap, taken by Mars Express. * Adapting to Receding Glaciers in the Tropical Andes * [svg]A glacier- and snow-covered high mountain peak with glacial lakes * Long Live the Laurentian Great Lakes * [svg]A springtime satellite view of the five Great Lakes shows the snowline roughly following the U.S.-Canadian border. 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