Drilling into Speleothems in the “Cave Kingdom of the World”

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 – Kẻ Bàng National Park, which is a UNESCO World Heritage site in the Quảng Bình Province and represents the largest limestone occurrence in Central Vietnam.

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.

EOS members and representatives of the Quang Binh Province in a room of Hang Bí Mật cave. From left to right: Mr. Mùi, Dr. Hướng, Dr. Dương, Prof. Phương, Dr. Sơn, Mr. Nghiêm, Mr. An and Mr. Thắng.

Our team relied on staff of Oxalis Adventure Tours for logistic support to facilitate the moderate-to-hard physical work during the Tú Làn Expedition.

Caves in Vietnam are unique environments protected by law. In order to collect speleothem samples for scientific research without damaging the appearance of caves, we took cores with a portable electric drilling system (e.g., Hilti TE -10A drill powered by 36 V Li-ion battery, a UKAM water supply system and a 35-mm o.d. drill-core bit; see picture below).

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.

On the first day of our expedition, after a light lunch, we hiked to Hang Tiên, known as Fairy Cave with two distinct sections. The impressive entrance to section Hang Tiên 1 lies beyond a field of boulders. Rimstone pools are stacked to impressive heights and add to the magical feel of the cave. After traversing Hang Tiên 1, we proceeded into section Hang Tiên 2 where we chose a flowstone to drill a core near the end of Hang Tiên 2.

A staff member of Oxalis Adventure Tours drills into a flowstone in Hang Tiên 2.

Thirty minutes of hard drilling by a staff member of Oxalis Adventure Tours yielded a 25-cm long speleothem core. After walking back through the cave, we exited at night and found our camp site near a river where we enjoyed a substantial dinner.

Our first speleothem core was recovered from Hang Tiên 2.

In the morning of the second day, we trekked over the hill to a road from where we were picked up by a car and driven to the Tân Hóa office. From there, a minibus drove us 2.5 km along peanut fields and water buffaloes to the Rào Nan River. After crossing the river, our group first traversed a cave called Hang Bí Mật (Secret Cave) and then proceeded through a field to reach the entrance of Hung Ton Cave.

Expedition team trekking across a field between Hang Bí Mật Cave and Hang Hung Ton Cave.

We swam across a river through Hung Ton Cave to reach the Tổ Mộ campsite where we took a break and enjoyed lunch until about 1:30 pm.

Swimming across a river through Hung Ton Cave.

From Tổ Mộ, we swam and then trekked through Kim Cave to the Tú Làn Campsite. At camp, we enjoyed a cup of coffee before swimming into Ken Cave. We managed to drill a shorter core of 25 mm diameter into a stalagmite in Ken Cave. While Dương and Hướng were drilling in Ken Cave, Prof. Phương explored and photographically documented the high scarp of sedimentary formations outside of the cave. Late in the afternoon, we swam to a small waterfall near the camp, while our porter team prepared a delicious dinner.

Hướng drills into a stalagmite in Hang Ken Cave.
After recovery of the central core, the topmost part of the stalagmite was broken.
The environmental impact of our scientific drilling was minimized by filling the drill hole with a mixture of Portland cement and cave sediment. The broken top was repaired, too.

It was starting to rain on the third day. Breakfast around 8:00 am was followed by paddling into the river passage of Tú Làn Wet Cave and climbing into Tú Làn Dry Cave. We decided to drill horizontally into a travertine terrace in Tú Làn Dry Cave. The relative softness of this speleothem enabled us to recover our longest core of ca. 30 cm.

A staff member of Oxalis Adventure Tours drills into a travertine terrace in Hang Tú Làn – dry passage.

After coring, we filled the drill hole with a mixture of Portland cement and cave sediment.

A mixture of Portland cement and cave sediment filled the drill hole after coring to reduce the visible environmental impact on cave structures.

After exiting from Tú Làn Cave, we trekked through a jungle and swam across rivers to visit two beautiful water falls. Several hours of heavy rain during the previous night had greatly enhanced the flow of water over the falls.  Near one of water falls, Prof. Phương pointed out geomorphologic evidence for ancient higher water levels that indicated changes in water level over time.

Ancient erosive terraces indicate changes in water level over time.

We trekked through a dry cave passage, then paddled along a river back to the Tú Làn campsite where we had a light lunch.

Paddling along a river to reach the Tu Lan campsite.

After lunch, we swam again to Kim Cave. Dương suggested to core a beautiful stalagmite higher up in the main cave passage. This stalagmite expressed a relatively high hardness and was thus difficult to drill, but we managed to recover a short core with a laminated structure.

Hướng drills into a stalagmite in Hang Kim Cave.
Drill site in Hang Ken Cave viewed from the main cave passage.
The rest of our team took a nap while Duong, Huong and staff members of the Oxalis Adventure Tours drilled in Hang Kim Cave.

As before, we minimized the environmental impact by filling drill holes with a mixture of Portland cement and cave sediment. While Dương, Hướng and some staff of Oxalis Adventure Tours were working, the rest of our team took a nap. Eventually the entire team had to swim hard upstream to get out of Kim Cave. During that day, we were always wet due to intermittent swimming.

Filling the drill hole with a mixture of Portland cement and cave sediment and cleaning up our work site in Hang Kim Cave.

Once out of Kim Cave, we went back to the Tổ Mộ campsite. Instead of staying at an outdoor camp site, Oxalis Adventure Tours arranged for our team to stay in a camp inside a large cave that is opposite to the outdoor camp across the river. The cave is located high above the river’s water level.

At the Tổ Mộ campsite, Prof. Phương (68) looks impressive like Tarzan.
Dương pointing to her tent at the Tổ Mộ campsite.

The entire team enjoyed the camp site in the cave. Everyone felt relaxed. It was the best camp site during the entire Tú Làn Expedition.

On the last day, we swam back into Hung Ton Cave and exited the cave through its dry passage. After trekking through a field and over a hill, we crossed the Rào Nan river and entered the last cave in our expedition, Hang Chuột. Although the entrance was not spectacular, the end of the cave was extremely beautiful. We decided to drill into an active stalagmite that was growing from the cave floor. Our successful drilling eventually reached the cave soil and yielded a nice core.

Drilling into an active stalagmite that grew from the floor of Hang Chuột Cave.
Core of a stalagmite recovered from Hang Chuột Cave.

While filling our last drill holes, we heard sounds from other visitors approaching. We were glad to have successfully recovered a stalactite core from Hang Chuột.

Filling the drill hole and cleaning up the coring site in Hang Chuột Cave.

Our expedition ended after all team members had safely trekked back to the Tân Hóa office. We enjoyed relaxing in outdoor showers and having Bún Bò (beef noodle) for lunch. After saying goodbye to the  helpful staff of Oxalis Adventure Tours, we drove back to Phong Nha and Dong Hoi city.

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.

Our experience during the Tú Làn Expedition qualifies us to wear the badge of a “professional” drilling team.

Geosciences are improving the lives of people in Vietnam