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Diving Into History With Thailand’s Sira Ploymukda

Certifiable Venezuelan dive geek Carlos Lander explores the discoveries of Thailand’s underwater archeology research team headed by resident expert Sira Ploymukda, who’s been involved in at least ten shipwreck excavations. Their findings are shedding light on Thailand’s role in early transoceanic commerce.

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by Carlos Lander

Lead image courtesy of Siwat Worachananant and Sira Ploymukda

Thailand is famous for its stony beaches, picturesque scenery, and outstanding dive sites, including reefs, deep drop-offs, wrecks, walls, and caverns. Most of the must-see sites are in the Andaman Sea along the west coast.

Thailand has a splendidly nuanced cultural heritage, one that has recently been explored in unprecedented depth by a new generation of marine archaeologists.

Despite what you may assume, marine archaeology is not about shipwrecks—it’s about human development. Luckily, Thailand is home to a resident expert: Sira Ploymukda, head of the country’s underwater archaeological research team.

Photo courtesy of Siwat Worachananant and Sira Ploymukda

Ploymukda (pronounced ploy-mook-da) is an expert archaeologist, who studies traditional artifacts, ports, and harbors. During his studies, he unearthed substantial evidence indicating that Thailand was a transoceanic corridor and a trans-peninsula route; his research also explores ship construction technology and its role in Thailand’s archaeological history. These subjects constitute his doctoral dissertation, the defense of which has, unfortunately, been delayed by the pandemic. 

Ploymukda has also contributed to the excavations of at least ten shipwreck sites in Thailand. He was trained in the diving arts by explorer and instructor Bruce Konefe who also leads shipwreck discovery teams in the country. As the head of the field department of Thailand’s Underwater Archaeology Division for over ten years, Ploymukda has taken the time to explore and study new archaeological sites. Over time, his efforts have paid off.

Ploymukda and his team are exploring newly-discovered wrecks in an effort to determine the ranges of each particular ship based on their design, the cargo content and type, and the average payload weight in order to calculate the economic value of the cargo that was moved across cultures by these particular ships. While the Thai government is engaging with neighboring countries to publicize the importance of this academic exploration, divers are taking the lead in these research efforts. Their first major task: finding the wrecks in the first place.

Discovering New Shipwrecks 

Ploymukda describes two basic methods for finding shipwrecks: active and passive. Many countries utilize satellite images to search, but sonar is more effective for exploring a specific area. Once the team has a lead on a new wreck based on sonar images, a diver or a remote underwater vehicle (ROV) is sent to verify what’s down below. This is active searching.

The second method, passive searching, happens when a village fisherman catches his net or line on the ocean floor, losing it or tearing it apart. This indicates that there is something on the sea floor that’s not supposed to be there—an object big enough to get a net stuck. At this point, an archaeologist becomes a detective. 

While an archaeologist’s role is to explore, exploration is costly. So, one way to reduce expenditures is asking fishermen to report these kinds of incidents. Archaeologists or explorers gather as much information as possible from fishermen for the purpose of determining if a potential site is worth exploring (economically speaking).

In the end, there’s only one way to be sure of what’s “down there,” and that’s diving.

Photo courtesy of Sira Ploymukda and the Ministry of Art’s

Once researchers decide to investigate a site, they closely guard their leads; looting is a big problem in Thailand. Since most site robberies take place in shallow waters, dive teams tend to excavate and survey sites at around 40-70 m/131-230 ft, making them more difficult for robbers to access. Ploymukda dives with a rebreather and often uses trimix (an oxygen, helium nitrogen mix to reduce narcosis) as diluent.

The site location remains confidential until all data and artifacts are collected, but for organizational purposes, it’s customary to name each wreck after the nearest port. GPS coordinates aren’t published until after excavation is complete. 

The present study includes the wrecks below:

Table courtesy of Sira Ploymukda

Boots, err Fins On the Ground 

Underwater archaeology is a scientific diving effort with forensic diving elements, meaning that divers must adhere to written protocols and prepare appropriately-sized teams. In general, a complete team is composed of one land team—including an officer who is responsible for all planning and contingencies—and two diving groups, one to perform the dive and the other to serve as a backup team. The backup team needs to be ready to enter the water in less than one minute in case of any emergencies. 

Depending on the depth, a bottom time of 30 minutes plus decompression is customary. But, the officer is responsible for adjusting the plan based on a variety of factors, including weather conditions, currents, or depths. 

Ploymukda explained that, in the past, the location of a shipwreck was manually recorded using a compass, a nautical map, and depth gauge, and wrecks were only sketched—a far cry from today’s sophisticated GPS, photogrammetry, and modeling technologies. Along with recording the specific location, divers also survey the sites, collect samples, and take measurements, videos, and photographs. 

In the event that the team salvages any artifacts, they take immediate action to prevent those artifacts’ decay.  Tanks of saline on the boat mimic the artifact’s familiar underwater conditions until the object is sent to a lab facility for further conservation work. Fortunately, in Ploymukda’s case, he has his own lab. 

The first step in the lab is removing the salt from an artifact by putting it in distilled water. Depending on the artifact, other processes are undertaken; for example wooden findings are saturated with a wax-like material, vacuum-sealed, and freeze-dried. Then, artifacts are sent to a separate lab for dating, which is paramount to the next step: building a narrative.

Building the Story

Archaeology’s purpose is to construct a narrative: a story that fits into historical context. But, it’s not that simple underwater. Data collected from the site during a dive is integral to discovering that context, but those data aren’t the only useful tool. 

Context, to an archaeologist, includes the place where an artifact was found, the soil, the site type, the layer of soil the artifact came from, what else was found in that layer, and numerous other minutiae. A shipwreck, unless it was found in a harbor, is much more difficult to put into a context than a site on land; luckily, Ploymukda’s research expertise fills in some crucial gaps.

The design of each individual ship serves as an indicator of their travel range, their cargo content and type, and the average payload capacity. These data, along with historical manuscripts or logs, are particularly important tools for cultural context identification. 

The ancient peoples of the Southeast Asia region were seafarers, and they knew how to use various types of sailing vessels for long-distance voyages. But, Ploymukda and his team are trying to understand the intercultural exchange that occurred as a result of these sailing routes in the Andaman Sea and the Gulf of Thailand. 


Their investigations uncovered two types of shipwrecks with distinct construction and rigging, which are integral details when determining a ship’s commercial route. Shipwrecks found were classified using ship typology, building technique, and rigging styles to pinpoint the sailing routes; once a ship was classified, the distance she could travel, the number of people she could carry and the amount of cargo she could hold could be estimated.

The shell base shipbuilding technique originated in Egypt, and was widely adopted throughout the Indian and the Pacific Oceans, as confirmed by various wreck recoveries. Frame base, however, is a technique from the east, popularly used in Chinese junk ships. Between 2008 to 2018, 46 shipwrecks were excavated in the Andaman Sea and the Gulf of Thailand, and researchers encountered both the shell base and frame base in their explorations. 

In addition, researchers observed different rigging techniques. Rigging refers to the system of ropes, cables, and chains that support a sailing ship. According to archaeological evidence, rigging implements have been in use in the Pacific Ocean for the past 3,000. Two rigging techniques were discovered: Lateen and Junk rigs. Lateen rigs were found in sewn boats in South East Asia. Junk rigs have been found in China; this is evidence of cultural interchange between China and Thailand.

A shell base boat. Photo courtesy of Sira Ploymukda and the Ministry of Art’s

A frame base boat. Photo courtesy of Sira Ploymukda and the Ministry of Art’s

As you can imagine, all this work takes time. Not only must researchers discover a shipwreck, salvage artifacts, and conserve them, but they also must study the wreck, associate it with a timeframe history, build a narrative theory, and test that theory. And, after all of that, many of the artifacts are sent to museums for display and further preservation.

In this line of work, you don’t just do research using books; to paraphrase Indiana Jones, “If you wanna be a good archaeologist, you gotta get out of the library.” In Ploymukda’s case, he has fulfilled that admonition entirely.

Ploymukda’s work is still ongoing. If you want to learn more about this project, you can visit the Fine Arts Department of Thailand online, where you can access the virtual museum  and contribute to the project.

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Photo courtesy of Siwat Worachananant and Sira Ploymukda

Additional resources:

SEAARCH: Southeast Asian Archeology, Underwater Archaeology Division (Thailand)

Ancient Maritime Cross-Cultural Exchanges 

X-Ray: Ancient Wrecks Ming Pottery Wreck: Exploratory Expedition in the Gulf of Thailand

Other stories by Carlos Lander:

InDepth: They Helped Foment a Dive Computing Revolution: RIP Cochran Undersea Technology (1986-2020)

InDepth: ¡Oh Deco! ¡h Doppler!, O’dive: Evaluando la primera herramienta personal de seguridad para una “deco” conocida


Carlos LanderI’m a father, a husband, and a diver. I’m a self-taught amateur archaeologist, programmer, and statistician. I think that the amateur has a different mind set than the professional and that this mindset can provide an advantage in the field. I studied economics at university. My website is Dive Immersion.  You can sign up for my newsletter here.

Cave

EXPLORING AND DOCUMENTING SA CONCA ‘E LOCOLI CAVE

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Text by Andrea Marassich. Photos courtesy of Phreatic. Header image: An inflatable (aka The love boat) is used to facilitate transportation of diving gear through the lakes.

Locoli cave is an amazing and challenging spring in the wilderness of Montalbo, Sardinia. It took me three years to set up the project, but it was all worth it. After all, David Rhea taught me that, “Slow is smooth, smooth is fast.”

I’m Andrea Marassich. I began exploring underwater caves in 2003, and I have taken part in cave exploration missions all around the world. In 2010, I fell in love with the powerful, majestic cave systems of Northern Sardinia, Italy. As a result, in 2014, I founded a nonprofit association, Phreatic, which collaborates with scientists and researchers in geology, paleontology, and earth sciences to study and document these unique environments. 

In 2019, I presented at Icnussa, the international speleology meeting in Sardinia, and spoke about Phreatic projects. During the event, a local caving club offered to carry diving gear to the first sump of a cave I had never heard of: Sa Conca ‘e Locoli. I dove with fellow GUE instructor Stefano Gualtieri, and  it was love at first sight. During the dive, I realized that I wanted to get back for more survey and exploration.

The Environment

“Locoli” is a temporary spring (active after rainfall and during certain seasons) located into Montalbo limestone massif, and is included in the UNESCO MaB (Man and the Biosphere) reserve of Tepilora, Rio Posada e Montalbo. 

Unesco Mab Tepilora Park: Karst, wetlands and coastline.

This Sardinian version of the Dolomites Alps, with its white rocks, looks out onto 25 km/16 miles of coastline. The silver ridge of Montalbo features evocative itineraries: historic trails for coal merchants and shepherds, archaeological sites, holm oak forests, and Mediterranean scrub (populated with mouflon, the golden eagle, and the red-billed chough). The peak presents doline valleys, chasms, underground rivers, as well as caves prehistorically inhabited by the Nuragic civilization. Archaeologists uncovered iron weapons in Bona Fraule, Gane ‘e Gortoe is rich in limestone concretions, Sa Conca ‘e Locoli  is eroded by the fierceness of the water, and Sa Prejone ‘e ‘Orcu is a cave-sanctuary.

Sa Conca’e Locoli

Locoli spring, which can submerge the whole valley during winter flooding, forms the entrance to the massive cave system hidden beneath Montalbo. The entrance cavern leads to a series of crystal-clear, freshwater lakes, and though the access is not technically complex, it requires the use of ropes through multiple changes of elevation, while the decorations and speleothems inside alternate with the smooth rocks levigated by water passage. 

Rope work and SRT is required to reach sump1. Hauling gear and physical effort is a serious part of the game.

After the lakes, the cave splits in two. The south passage leads to a shallow sump looping back downstream and connecting to a minor spring in the valley. The north passage goes through a series of changes in elevation, which require the use of ropes, and leads to a wide passage that provides access to the surface of Sump 1. 

This is the entrance gate to a series of huge flooded passages of breathtaking dimensions with obvious signs of a huge aquifer. The first sump is not particularly long or deep at 250 m/820 ft long with a maximum depth of 23 m/76 ft, but it leads to a very important second split. Here the subterranean river flows downstream toward the village of Siniscola and the Fruncu ‘e Oche spring, while on the upstream side it heads toward four other challenging sumps and dry areas. 

In the island of Sardinia, Sump 3 is the deepest, reaching 90 m/295 ft. 

The last exploration dive carried out in 2009 by Rick Stanton led to a collapse in Sump 5; consequently, the present survey only covers the first two sumps.  

The Project

In 2020, I organized the first scouting mission of the deeper sumps, together with Jan Medenwaldt. COVID-19 travel limitations presented difficulties in gathering a bigger team. 

In 2021, finally, we managed to organize a three-week campaign encompassing both survey and photogrammetry. The exploration of the system is particularly complex for a variety of reasons. First, the underwater portion is accessible after a relatively long dry passage, one in which cavers and cave divers must carry all their heavy gear. Subsequently, the series of sumps is difficult from a technical point of view, as the diving profiles involve serious exposures in Sump 3 and 5. 

After the dives were completed, the long clean up requires a couple days, but the smile don’t lie. Operations went smooth.

In order to complete the working goals connected with survey, mapping, photo/video, and research tasks, divers needed to extend their diving time and elected to stay inside the cave and set up a bivouac; entering the cave with dry tubes and bivouac gear without knowing where to establish the camp was risky. We found a new dry section between Sump 3 and 4, which proved to be ideal to bivouac and minimize the decompression risks connected with the profile. 

The main challenge is dealing with the geology of the cave, one that presents multiple elevation changes to move from one sump to the next. Sump 3 is the most demanding of the five underwater galleries, as the cave drops initially to 45 m/148 ft deep, then rises to 15 m/49 ft, drops to 90 m/295 ft, ascends again to 45 m/148 ft, and drops again to 65 m/213 ft before the final ascent. 

We deeply believe exploration without documentation is not getting the job done. Survey and documenting with media is a key component of our activities and we prioritize it over simply “reaching a distance”.

The exploration efforts are now divided in two areas: the newly discovered dry section between Sump 3 and Sump 4, featuring massive rooms and high chimneys that potentially connect with a fossil gallery above, and Sump 5, whose exploration stopped at a depth of 50 m/164 ft and needs  further investigation.

We are already working on new project sessions for summer 2022. 

Considering the importance of the karst system of Montalbo and its water reservoirs, the UNESCO MaB reserve decided to support our project, specifically in relation to our documentation and conservation efforts. We also received the sponsorship of the Italian Speleological Society and are now searching for more partners. 

The main objectives will be:

  • Completing the survey of the upstream section up to Sump 5. To perform this task, we will use the SUEX DRIVe and mapping devices combined with MNemo.
  • Creating a documentary featuring the most beautiful passages of the cave with the help of an expert photogrammeter and videographer.
  • Improving public awareness about caves and karst in partnership with the International Year of Karst and Cave initiative provided by the International Union of Speleology.


Citizen Science

Phreatic believes in the power of Citizen Science. All our projects and missions rely upon the crucial involvement of skilled, specially trained individuals. The Sa Conca ‘e Locoli cave project involves a number of local and foreign volunteers with various sets of competences. Many thanks to Speleo Club Nuorese for the support in the dry portions of the cave, and to all the Phreatic volunteers who joined us in 2021 including Jan Medenwaldt, Peter Brandt, Sven Bertelmann, Keith Kreitner, Laura Marroni, Elke Riedl, and Irene Homberger. 

Entrance of one of the multiple downstream passages; While one team was diving the upstream sumps and bivouacked in the further section, operations continued with oc team working in a different area.

Collaborations and Partnerships

Phreatic can count on a long-term partnership with SUEX, a world leader in high-performance underwater vehicles designed for long-range technical and professional diving.

The Locoli project operates under the supervision of the geologist Dr. Francesco Murgia, author of multiple scientific publications on the areas of Montalbo and Supramonte.

For more information see: Phreatic: Citizen Science and Groundwater Research. Email contact: info@phreatic.org

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