Drilling into Speleothems in World’s Cave Kingdom

On August 2017, our team includes EOS members: Prof. Phuong, Duong and Huong, exploring Tu Lan cave system at the north of Phong Nha – Ke Bang national park – UNESCO World Heritage site in Quang Binh province – the largest limestone massive in Central Vietnam.

Supported by Department of Science and Technology of Quang Binh province the goal of our expedition is to collect materials for writing a tourism promotion book which aim to reveal to people premier values of karst cave system in the area. Our possible book title has been proposed as “Quang Binh – the Cave Kingdom of the World”. We were also permitted to drill into speleothems in caves.

EOS members and Quang Binh province’s officers standing in a room of Hang Bi Mat. From left to right: Mr. Mui, Huong, Duong, Prof. Phuong, Dr. Son, Mr. Nghiem, Mr. An and Mr. Thang.

The Tu Lan Expedition is moderate-to-hard for visitors so our team must have relied on accommodation of Oxalis Adventure Tours staffs.

Caves are unique environments protected by laws of Vietnam. To collect speleothem sample for scientific purposes without heritage impact, we used portable drilling system to take cores including an electric drill (Hilti TE -10A) powered by 36 V Li-ion battery, water supply system (UKAM) and drill-core bit (outer diameter 35 mm).

A portable drilling system including an electric drill (Hilti TE -10A) powered by 36 V Li-ion battery, water supply system (UKAM) and drill-core bit (outer diameter 35 mm)

On the first day of the expedition, after having a light lunch, we hiked to Hang Tien, known as Fairy Cave. Hang Tien has two sections. Hang Tien 1 lies beyond a field of boulders and the entrance is so impressive. Rimstone pools are stacked high and add to the magical feeling of this cave (Oxalis). Journey through Hang Tien 1 to its exit and then we went through Hang Tien 2. We chose a flowstone to drill a core near the end of Hang Tien 2.

An Oxalis’s porter helps us in drilling into a flowstone in Hang Tien 2

After 30 minutes of hard drilling with helps of Oxalis’s porters we successfully collected a speleothem core of 25 cm in length. When it was dark we were back through Hang Tien 1 to the camp site near a river. The first day ended with a big dinner at the camp site.

The first speleothem core was recovered from Hang Tien 2

In the morning of the second day, we trekked over the hill to the road where we were be picked up and transferred to Tan Hoa office. From the office a minibus drives us across peanut and buffalo fields (2.5 km) to the Rao Nan River. After crossing the river, our group went through a cave called Secret Cave. The journey within Secret Cave then proceeds forward with a trek through a field to Hung Ton Cave entrance.

Expedition team trekking across a field between Hang Bi Mat Cave and Hang Hung Ton Cave

Then we swam a river through Hung Ton cave to To Mo campsite. We took a break and enjoy lunch at To Mo until about 1:30 pm.

Swimming a river through Hung Ton Cave

From To Mo, we swam and then trekked through Kim cave to Tu Lan Campsite. At camp, we enjoyed a cup of coffee before swimming into Ken Cave. We managed to drill a shorter core (25 mm diameter) into a stalagmite in Ken Cave. While Duong and Huong were drilling in Ken Cave, Prof. Phuong took a look and pictures on a very high scarp of sedimentary formations outside of the cave. Late in the afternoon, we were swimming afterwards at the small waterfall by the camp, while our porter team prepares a delicious dinner.

Huong is drilling into a stalagmite in Hang Ken Cave
After core recovered, topmost part of stalagmite broken…
A mixture of Portland cement and cave deposit is filled to drilled hole to reduce environment impact on cave structures before and after coring.

The third day: It started to rain. Breakfast started this adventurous day around 8:00 am. We paddled into the river passage of Tu Lan Wet Cave and them climb to Tu Lan Dry Cave. We decided to drill horizontally into a travertine terrace in Tu Lan Dry Cave. The speleothem is softer than previous drilled ones so we can easily recover a longest core at this site ( c.a 30 cm) with the support of our guide team.

A team of Oxalis’s porters help us drilling into a travertin terrace in Hang Tu Lan – dry passage

We filled drilled hole using a mixture of a small quantity of Portland  cement and cave deposits. We also used milky stream of suspended carbonate particles produced by the flushing process  to decorate drilled site and carefully cleaning the workplace after coring.

A mixture of Portland cement and cave deposit is filled to drilled hole to reduce environment impact on cave structures before and after coring. Milky stream of suspended carbonate particles produced by the flushing process was used to decorate drilled site

We exited from Tu Lan cave and trekked through a jungle, swam rivers to visit two beautiful water falls. Several hours of heavy raining last night makes the fall flow violently.  Near one of water falls, Prof. Phuong introduced to our team a relic of ancient water level that is  evidence of ground level changing  over time.

A relic of ancient water level showing  evidence of ground level changing  over time

We trekked through a dry cave passage, then paddled through a river to back to Tu Lan campsite and had a light lunch at the camp.

Paddling through a river to back to Tu Lan campsite

After lunch, we swam again to Kim Cave. Duong suggested a nice stalagmite at higher level of the main cave passage. It was quite hard to drill because the stalagmite is supper hard. But we managed to recover a short core with perfect laminae.

Huong is drilling into a stalagmite in Hang Kim Cave
Drilling site in Hang Ken Cave viewed from the main cave passage
The rest of our team took a nap while Duong, Huong and some Oxalis’s porters drilling in Hang Kim Cave

We also filled drilled hole using a mixture of a small quantity of Portland  cement and cave deposits. While Duong, Huong and some Oxalis’s porters drilling, the rest of our team took a nap. All team had to swim hard upstream to get out of Kim Cave. Our bodies were always wet because of swimming that day.

Filling a mixture of Portland cement and cave deposit into drilled hole and cleaning cored site in Hang Kim Cave.

Out of Kim Cave, we went back to To Mo campsite. Instead of staying at outdoor camp, Oxalis arranged for our team staying at a camp in a large cave opposite to outdoor camp across a river. This is a fossil cave high above stream water level.

Prof. Phuong looks like Tazan at his age (68), To Mo campsite
Duong pointing to her tent in To Mo campsite

All team enjoyed the camp in the cave. Everyone felt relaxed. It is the best camp in Tu Lan expedition.

In the last day, we swam back into Hung Ton cave, then we got out of the cave through its dry passage.  Trekking through a field, then over a hill, and crossing Rao Nan river, we accessed the last cave in our expedition: Hang Chuot. It seems  fossil cave at its entrance but supper beautiful at the end. We decided to drill into active stalagmite growing from the cave floor. Drilling was quite smooth and was stopped when it reached the cave soil. We recovered a nice core from its top to bottom.

Drilling into an active stalagmite growing from the cave floor of Hang Chuot Cave
A perfect core recovered from Hang Chuot Cave (recovered from top to bottom of the stalagmite).

Filling the last drilled holes had to be fastened due to sounds from other coming visitors. We were really happy with recovered core in Hang Chuot.

Oxalis guider helping us in filling drilled hole and cleaning coring site in Hang Chuot cave.

Our expedition ended when all team safety trekked back to Tan Hoa office. We were really relax in outdoor showering. We had a Bun Bo for lunch, said goodbye to Oxalis porters, then drove back to Phong Nha and finally back to Dong Hoi city.

We planned to the second drilling expedition in Hang Va Cave and the third in Hang  Son Doong Cave next year. We also planned three outdoor geological surveys in Phong Nha – Ke Bang area in 2017-2018. Duong is thinking about how to petrographically analyse the recovered cores in our VNU labs. Huong will improve drilling equipment to recover longer cores for our next expeditions. We will also try to find paleoclimate signals in those cores.

After Tu Lan Expedition, we are actually “professional” drilling team. We even “earned” some money from Dr. Duong A – our VNU colleague for helping her in drilling into speleothems in Hang Boi cave in Trang An, Ninh Binh.

Geosciences are improving the lives of people in Vietnam