About our EOS GROUP

The EOS Geoscience Research Group is being led by Assoc. Prof. Dr. Dương Nguyễn-Thùy and Dr. Hướng Nguyễn-Văn, both servering  as young faculty members at VIETNAM NATIONAL UNIVERSITY (VNU),  Hanoi. The name EOS refers to a Titaness – i.e. the Goddess of Dawn, who rose every morning. Seven additional active EOS members from VNU and VAST are Prof. Phương Tạ-Hòa, M.Sc. Nguyệt Nguyễn-Thị-Ánh, Dr. Hồng Nguyễn-Thị, M.Sc. Quốc Đỗ-Trọng, Dr. Thái Nguyễn-Đình, Dr. Dương Nguyễn-Thùy and M.Sc. Phong Trần Văn.

Our group collaborates with Dr. Arndt Schimmelmann (Indiana University, USA), his wife Minh Ngọc and his son Jan Schimmelmann (Bremen University) who visit frequently for interdisciplinary surveys and experiments in the field and laboratory at VNU, sometimes together with other international scientists. EOS receives invaluable support from local government officials and inhabitants of Hà Giang and Gia Lai provinces, as well as from VNU colleagues and students.


Subterranean methanotrophy is a potentially important but overlooked sink for the atmospheric greenhouse gas methane (CH4). The first research project of EOS group entitled “Microbial uptake of atmospheric methane from subterranean air in tropical karst” was successfully completed at the end of 2016. Our study documented a microbial CH4 sink in tropical subterranean karst cavities in Vietnam’s northern karst province where porosity, steep topography, and scarce soil and vegetation cover foster the exchange of subterranean air with the atmosphere. Our data are based on (i) surveys of CH4, carbon dioxide, and radon concentrations in the air of 11 caves, (ii) in situ mesocosm experiments in caves, as well as (iii) laboratory mesocosm measurements using sediment and rock from caves.

Above: Graphical abstract for a publication in Chemical Geology (Click image to enlarge).

The extent of CH4 depletion in cave air depends on the ventilation rate and the availability of moisture to provide a habitat for CH4-oxidizing bacteria. We conservatively estimate that 150,000 metric tons of atmospheric CH4 are microbially oxidized annually in the ~29,000 km2 of Vietnamese tropical karst, which would compensate for ~7 % of Vietnam’s agricultural CH4 emissions from rice farming and livestock.

The Department of Earth and Atmospheric Sciences, Indiana University composed a short video for the alumni about our methane research in Vietnam. Here is the link:


A chance discovery during field work for the first project about methane in the Đồng Văn district, Hà Giang province in 2015, yielded intriguingly high radon-222 concentrations in Rồng Cave near the Sảng Tủng commune.

Professors and students are relaxing in front of an ancient mud-built house that serves as a restaurant. The group first discovered high thoron (220 Rn) concentrations in this house behind plastic wall covering (Đồng Văn town, Hà Giang, March 2016).

Even higher levels of environmental radioactivity were measured in March 2016 when our group was relaxing in an ancient mud-built house in Đồng Văn town that serves as a restaurant. The latter geohazard for human health was discovered in the form of high thoron (radon-220) concentrations in room air near mud walls and the mud floor. Our discoveries led us to our second project entitled “radon isotopes in Northeastern Vietnam’s karst environment” (recently funded by Vietnam’s NAFOSTED science grant agency) and also encouraged us to propose a project entitled “radon health hazard in mud-built homes” which aims to organize radon/thoron workshops for scientists from developing Asian countries.

At the end of 2016, our international research team spent more than a week in the northernmost Hà Giang province in Vietnam to study the radon and thoron abundance in room air of traditional mud houses that have been built with compacted local soil. The floors of houses are typically bare soil. The interior walls have no surface covering and feature deep cracks from drying of wet building material. For radon-222 and thoron measurements, we were using a SARAD RTM2200 (from Indiana University) and a RAD7 instrument that we borrowed from other institute in Vietnam. All instruments gave comparable results.

Dương applies a dissolved chemical to an interior wall in a mud house in Bạch Đích commune, Yên Minh district, Hà Giang using a spayer (near the Vietnam – China border, December 2016).

EOS benefited from the availability of a traditional mud house where we were allowed to perform detailed experiments. Patches of walls and floor were treated with different methods (i.e. different kinds of surface coverings) to evaluate the effect on radon and thoron exhalation.

Open plastic boxes were fitted with foam insulating strips and were pressed against treated sections of mud walls to trap a constant volume of air that was in contact with a defined area of mud wall. The exhalation of radon and thoron was measured in closed-circuit mode with SARAD RTM2200 and RAD7 instruments at an air flow rate of 1 liter per minute. Proper surface treatment reduced thoron exhalation to below detection limits (Bạch Đích commune, Yên Minh district, Hà Giang province – near the Vietnam – China border, December 2016).

Radon-222 with a half-life of ca. 3.8 days never posed a problem in dwellings because mud houses are sufficiently ventilated through cracks and loosely fitted roofs to prevent accumulation of radon-222. In contrast, thoron proved to be an abundant health geohazard near dry mud surfaces. There was a strong gradient in thoron abundance in room air depending on the distance from walls and floors. The thoron dose rate in room air near walls where people sleep at night greatly exceeded all published safety thresholds.

Minh Ngọc Schimmelmann interviews a group of curious local students in an agriculturally used sinkhole next to Rồng Cave, Sảng Tủng commune to inquire about the general health of local inhabitants of mud houses (December 2016).

We were able to develop methodologies and test the results from specific methods of surface sealants to prevent thoron from entering room air. We met our goal to develop methods that are effective, affordable, non-toxic, environmentally sustainable, and socially acceptable. The required materials are readily available in developing countries.

Members of the EOS group with Mr. Minh’s family in a mountainous village at Bạch Đích commune, Yên Minh district, Hà Giang province – nearby the border between Vietnam and China. Mr. Minh (behind, left) is an officer at the Division of Culture and Information, People’s Committee of Yên Minh district, Hà Giang province. Minh’s family kindly permitted our EOS group to perform experiments in their mud house.

Vietnam’s Hà Giang province is located in the northernmost mountainous region. The time-consuming travel between Hà Giang and Hà Nội prevents our group from performing frequent measurements in inhabited mud houses. In October 2017, Mr. Minh’s family and friends from a village in Hà Giang province helped the EOS group transporting local mud to Hanoi, and then used traditional mud-house construction techniques to build a small mud house in a Hanoi suburb. The full-size  mud house is being used for assessment of various remediation strategies.

EOS members in front of newly built mud-built house in a Hanoi suburb in November 2017. The model mud house is being used exclusively for scientific experiments towards (1) developing recommendations for affordable and practical detection methods for radon and thoron in mud-built homes; (2) assessing the concentrations and distributions of thoron and radon in mud house air; (3) affordable, non-toxic and socially acceptable sealing of porous mud surfaces in homes to prevent escape of thoron and radon, and to improve public health.


In March 2016, our group of 7 (i.e. three professors and one graduate student from Vietnam National University Hanoi; three from Indiana, namely Arndt, Minh and Jan who is a graduate student at Bremen University, Germany) spent three days of hard work in and around Pleiku in the central highland of Vietnam.

Jan Schimmelmann from Bremen University and Quynh Nhi from Vietnam National University attach a pneumatically operated core catcher to a core liner prior to sediment coring. They are sitting in an inflatable boat on Bien Ho maar lake, Pleiku (January 2017).

There are three interconnected maar lakes (Biển Hồ – hồ T’Nưng) about 10 km north of Pleiku. The maximum water depth is about 25 m. Deeper water seems to be oxygen-depleted, since our echolot “fish finder” and GoPro underwater video coverage did not indicate any fish near the bottom. The sediment is an extremely organic-rich, black sapropel with no hydrogen sulfide and no indication of bioturbating benthos. A bacterial mat is stabilizing the sediment/water interface. A set of sediment traps has been moored to seasonally collect samples.

In January 2017, renewed coring yielded short sequences of Biển Hồ maar sediment. Our newly designed “autonomous sediment coring device with a pneumatically operated core catcher” worked well. An alternate design using an extended set of metal rods pushing a coring device into the soft sediment showed promise for deeper coring. We are optimistic that a combination of both coring methods will yield several meters of sediment from the maar lake when we will return. Cores are stored in Hanoi in the dark at room temperature. Sections of sediment are subject to resin impregnation for high-resolution imaging and analyses.

A poster at Maar2018 – 7th International Maar Conference, 21-25 May, Olot, Spain, 2018.

We returned to Biển Hồ maar lake in November 2017 with with new home-built platform and sediment coring devices. We were delighted to welcome Dr. Antti Ojala from the Geological Survey of Finland as a new member to our team. Antti’s expertise in lake coring and core-to-core correlation using paleomagnetic sediment properties proved invaluable. Two days of sediment coring in Biển Hồ in November 2017 yielded 17 wonderful piston and gravity cores from up to 21 m water depth with up to 3.5 meter penetration into sediment. Our mobile coring platform and the newly designed coring devices performed better than expected.

Team members carry our coring platform from an assembly point near the shore to Biển Hồ maar lake in November 2017.

In addition to coring in Biển Hồ maar lake, we also considered some shallower lakes and dry maars which can record bio-geochemical shifts relating to paleoenvironmental changes. We took short cores in Ia Bang lake and in the Plei Ốp swampy maar near Pleiku City.
The logistics worked out better than during previous coring expeditions, because our experienced team members know their duties and don’t require orders from the “boss”. We worked like a well-tuned professional coring team! See detail of our third coring expedition in Biển Hồ maar lake and core documentation and analyses in the laboratory at VNU in the session “I cored”.

As the fourth coring expedition in March 2018 , we were delighted to welcome Dr. Ingmar Unkel from Kiel University as a new member to our team. From Biển Hồ maar lake we retrieved 18 sediment cores with up to more than 5 meter penetration into sediment. Team members also did the very first freeze-coring ever in Biển Hồ.

As the fifth coring expedition in October – November 2018, we were delighted to welcome Dr. Agnieszka Drobniak, Dr. Peter Sauer and Ph.D. student Kelsey Doiron from Indiana University. Agnieszka led the water analysis team performing measurements along the water column in Bien Ho at three different locations. The most important aspect seems to be the depletion of dissolved elemental oxygen in Bien Ho water below 8 m depth. The coring team managed to piston-core 14 meters deep into Bien Ho sediment along repeat holes and offsets between the segments of the two piston core sequences. The recovered sediment may reach back 30,000 years. Our coring success is partially based on PVC casing that helped keeping the metal push rods straight and also let us re-enter the same hole repeatedly. The trick is to keep a good record of how deep we cored the last time, then going to the right depth, triggering the piston to lock, and then pushing the core liner further down. We also recovered sediment traps (Mar-Oct) and set new ones. Arndt was able to recover ‘grass with roots’ from about 4 to 5 m depth. The jury is still out whether ‘aquatic grass carpets’ ever existed. The lake level can go down by up to 5 m by the end of the dry season. A dive in March 2019 (i.e. at the end of the dry season) might offer a better answer. One complete set of cores was shipped to LacCore for analyses. Everybody is extremely happy.

We had planned for field work in February 2020 to retrieve even deeper sediment than during previous campaigns. Several participants from the USA and Japan had purchased airline tickets to fly to Vietnam but were forced to cancel their travel owing to the Covid-19. We had to delay our coring until March 2021. The EOS team remains active in the Central Highlands with a land-based survey in  Biển Hồ and travel to Buôn Ma Thuột city to core in another lake. In February-March 2020 , our coring team retrieved an 8.7 m long sediment core from Ea Tyn Lake, covering the last 1200 years. The unusually high sedimentation rate provides high temporal resolution for the last millennium. The new Ea Tyn Lake record, especially the summarizing XRF-based PC2 values are in good agreement with the tree-ring climate records of historically documented droughts.

Our latest coring expedition to Biển Hồ occurred in March-April 2021. We had improved our customized piston corer with larger-diameter metal rods and recovered parallel sediment cores with an overall length of up to 25 m, covering the last ca. 60,000 years. The fresh sediment cores were express-mailed to LacCore at the University of Minnesota in the USA for physical property logging, splitting, initial core description, photography, and high-resolution scanning for chemical composition. After the measurements at LacCore, the sediment cores were shipped to Indiana University’s cold storage. Cores were subsampled and analyzed at Indiana University for sedimentology, loss-on-ignition, carbon stable isotope ratios, and radiocarbon and paleomagnetic dating by Hướng Nguyễn-Văn when visiting Arndt Schimmelmann’s laboratory from May to October 2021 as a Fulbright Scholar.


Vietnam’s upper Devonian – Permian formations are composed mainly of thick limestones and relate to important World Heritage and Global Geopark landscapes such as Hạ Long Bay, Phong Nha – Kẻ Bàng National Park, and Đồng Văn Geopark Plateau. We aim to comprehensively update stratigraphic assignments and to evaluate sites with regard to potential value as ‘geological heritage’. The research has been recently funded by Vietnam’s NAFOSTED science grant agency.

Brachiopod fossil (Early Devonian) of Male formation in Đồng Văn, Hà Giang.


In August 2017, EOS members Prof. Phương and Drs. Dương and Hướng explored the Tú Làn cave system in the northern part of the Phong Nha – Ke Bang National Park, which is a UNESCO World Heritage site in the Quảng Binh Province and represents the largest limestone occurrence in Central Vietnam.

Portable electric drilling system for coring speleothems: Hilti TE -10A drill powered by 36 V Li-ion battery, UKAM water supply system, 35-mm outer diameter drill-core bit.

Our expedition was supported by the Department of Science and Technology of Quảng Bình Province and aimed to collect material for a book promoting tourism and popularizing the outstanding value of the regional karst cave system. We anticipate the book to be entitled “Quảng Bình – Cave Kingdom of the World”. We received permission to drill into speleothems in caves and extract rock cores for scientific study.

We are planning a second drilling expedition to Hang Va Cave and a third expedition to Hang Sơn Đoòng Cave for 2018, in addition to three outdoor geological surveys in the Phong Nha – Kẻ Bàng area in 2018. Dương plans the petrographic analysis of the recovered cores in our laboratory at VNU. Hướng will improve our drilling equipment in preparation for recovery of longer cores during future expeditions. We will strive to identify paleoclimate signals in our cores.


Outreach to local communities is an important part of applied science in remote regions. Here our group distributes winter clothing and school supplies to local students in Hà Giang province. The charitable logistics were arranged by Dương Nguyễn-Thùy and Minh Ngọc Schimmelmann.

Members of the EOS group donated stationery to students in a primary school in Sảng Tủng commune, Đồng Văn district, Hà Giang province, several days before Christmas Day in December 2016.


Dương meets Lauren Robel, provost and executive vice president of Indiana University. The visit of the IU delegation in Vietnam aimed at expanding partnerships and celebrating the launch of a new IU alumni chapter.


Several high-quality figures for our publications were drafted by using the program Generic Mapping Tools (GMT 5). We are willing to share our experience with VNU students as well as Vietnamese early career researchers. Examples have been prepared to run a *.bat file on Windows. First try to install GMT 5 on Windows, GSwiew and Ghostscript (both need to view output from Postscript files). Then download an example in the form of a *.zip file from the EOS website and decompress it (yielding full scripts and data files in a folder). First try to double-click or press enter on the *.bat file in your unzipped folder and view the output of the Postscript file. Later edit the *bat file in Notepad by adding the “#” character to the second row, then enjoy GMT.

Please browse through our website and get acquainted with our research. Don’t hesitate to contact us!

Many images posted on our website are courtesy of Minh Ngọc Schimmelmann, Jian LiuAgnieszka Drobniak, Indiana University and Đỗ Ngọc Điệp – a photographer in Pleiku.

Geosciences are improving the lives of people in Vietnam