As well as enabling professionals to carefully excavate shipwreck sites and recover historic artefacts for the edification of generations to come, Unesco schemes to safeguard Thailand’s submarine cultural heritage will also benefit tourist activities such as scuba-diving, points out Bobby Orillaneda, an academic working for the Underwater Archaeology Section at the National Museum of the Philippines.
Orillaneda and a handful of other researchers participated in the first ever foundation course on underwater cultural heritage organized in Rayong province recently by Unesco’s Asia-Pacific Regional Field Training Centre.
“Recreational divers can unintentionally damage or destroy vital evidence, so it’s important for us archaeologists to get to these sites first. After we sift through the findings we can educate divers on how to conduct themselves in these spots and this, I believe, can make the experience a lot more enjoyable for them,” noted Orillaneda, who’s been here on three previous occasions for similar practical training sessions.
“I’ve been participating in these schemes for 10 years now and this particular Unesco-led course has helped me to brush up on basic methodology procedures and on the latest technology used during excavations.”
Orillaneda first flew in for a training session in Chanthaburi six years ago, later visiting Chon Buri to help excavate a shipwreck site. He says he knows of at least five such sites in the Kingdom’s territorial waters which date back to the 15th century.
What does Thailand have going for it in terms of underwater archaeology?
You Thais are very lucky in the sense that you have the financial and manpower resources to do research on your own. The Philippines has yet to reach that level; we just don’t have the funds to do it. I don’t believe that Southeast Asia has any other established maritime archaeology center except for the one in Thailand.
To what use will you put the knowledge you have gained from training sessions here?
Honestly, all we can do at the moment is give feedback to our superiors and hope for the best. If the National Museum [of the Philippines] has the money to fund research, I’m sure that we can put the data we’ve accumulated to good use. I strongly believe in the importance of working together with other Southeast Asian countries in research and in sharing information. These types of academic collaborations also improve networking, which eventually benefits us in updating our knowledge. I’d also like to evaluate more critically the Unesco Convention and [determine] if it is applicable to the Philippines.
What can be done to prevent our underwater cultural heritage from being destroyed by unscrupulous people out to make a fast buck?
It’s important to establish a more solid legal framework. If you see someone looting or treasure-hunting you can immediately use this legal framework as your back-up. Despite the existence of penalties for such offences, however, people will often go ahead and break [the laws]. This is why I feel that an awareness programme should be put in place to educate the general public on the importance of preserving the cultural heritage found in our seas.
With the exception of the well-traveled and well-educated in our society, the average person has no interest in going to museums and doesn’t give a hoot about culturally significant artifacts. Cultural appreciation can only come about when we’re able to reach people from all walks of life. In my country we organize information-dissemination activities to make the public aware of our work, but since we have to target settlements on over 7,000 islands and we suffer from a serious lack of manpower we aren’t able to reach everyone.
Most of our shipwrecks are found by fishermen and because they need to earn a living these people would prefer to financially benefit from such finds rather than report them to our museum. Giving them monetary rewards would be a step in the right direction.
Tell our readers about a few of the more memorable experiences you’ve had while working as an underwater archaeologist.
One that immediately comes to mind was the sunken city of Alexandria, in Egypt. It was such a fantastic experience to visit this ancient city which lies completely underwater only a few meters from the shore.
Sattahip [where the foundation course was held] was the first place I went for recreational diving. That was very memorable in the sense that I ended up rescuing someone that day!
An anchor from a shipwreck thought to be Blackbeard’s flagship, the Queen Anne’s Revenge, was so unstable that divers in North Carolina retrieved it Wednesday rather than waiting until next year.
Divers raised the 4.5-foot, 160-pound grapnel, or anchor, from the wreck in the Atlantic Ocean near Beaufort on Wednesday and will display it Thursday at the North Carolina Maritime Museum in Beaufort. The anchor originally had four prongs, but now has 1 1/2.
Two divers put straps on the anchor, then small lift bags that they filled with air, said Mark Wilde-Ramsing, the director of the Queen Anne’s Revenge shipwreck project. When the grapnel reached the surface, a crane brought it on the boat.
“It went great,” he said. “It went as smooth as it could be.”
The grapnel probably was an anchor for a smaller boat that would have been used to transport items between ships or from land to ship, Wilde-Ramsing said.
Archaeologists and conservators with the state Department of Cultural Resources say the grapnel was at risk of washing away after nearly 300 years in the sea and might not weather possible storms until next year, when a full-scale expedition is planned.
The rest of the shipwreck looks very stable, Wilde-Ramsing said.
Queen Anne’s Revenge was a French slave ship that measured about 100 feet long with three masts and a crew of 150 to 200. Blackbeard captured the ship, then known as La Concorde, in 1717 and renamed it before it ran aground off Atlantic Beach a year later. The shipwreck, discovered in late 1996, is within sight of Fort Macon State Park.
About 18 feet underwater off Key Largo lies a mystery ship, one of hundreds in just these waters.
It’s cargo, name and destination are unknown. All that remains of the wreck are planks of timber, iron rods and some pieces of coal.
State underwater archaeologist Roger Smith and his team will spend about two weeks mapping the site that has become a bountiful coral reef. In time they will also try to piece together what ship this was, its voyage and whether it should be nominated for the National Register of Historic Places.
The work is part of an ongoing effort to take an inventory of Florida’s shipwrecks and artifacts, which number around 300 just off Key Largo alone.
Named the “Marker 39″ wreck for its location just two miles off the coast of Key Largo, the remains hold many clues that could help unlock its secrets. A buoy has marked the spot since 1863, which could help date the shipwreck because it could be when the ship ran aground that people realized the area was dangerous.
Iron fasteners held the wood together and from what is left, it looks like it was about 150 feet long. So far, archaeologists are hypothesizing it was a barge because of its long, flat deck. Smith predicts it dates back to the 19th century, when there was a bustling business of carrying cargo, including coal, lumber and manufactured goods, up and down Florida’s coast. It may have been a steam ship because of the iron rods and steam pipes that were found on it.
“The Keys is a trap for ships, always has been, always will be,” he said. “There is all of this maritime history in the Keys. All these shipwrecks represent episodes in that history.”
The wreck was found by two volunteers in the 1990s diving along the channel between the shore and the large coral reef that runs parallel to the Keys.
Experts say there are about 400 ship groundings a year, some due to captain inexperience, some to weather and changes in water depth.
Smith says that when he dives a wreck, he is always looking for manmade objects to tell the story. This wreck doesn’t have many left. He believes salvors of the 19th century may have beaten him to them. They were otherwise known as wreckers. Some were fishermen and they would wait for a ship to be distress, and then come out and get the goods for a share in the profit.
“The law was, if you were the first salvor to negotiate with the captain, you got to be the salvor,” he said.
There is a Florida Master Site File where all the state’s historic sites are given a number for inventory. This wreck will get one too. The group has created a photo mosaic of the site. They will also map out the wreck and shoot video for people who will never dive it.
They will then take the pieces of coal they have brought ashore to the Florida Geological Survey and also search in the archival records of admiralty courts to see if they can find out what ship this is.
“Sometimes you never do find the name of a ship,” Smith said.
The ship itself is not very well-preserved. It’s exposed to the elements and not totally buried.
“Part of all this is detective work and making conclusions based on hard evidence,” he said. “You have to let the shipwreck tell its own story. Sometimes it’s tempting to hypothesize what a site might be.”
There are several references to ships going down in the area, said Brenda Altmeier, program support specialist at NOAA’s Florida Keys National Marine Sanctuary.
She says she “can’t help but think of the people aboard … just the fear and panic,” she said.
This project is a partnership between the Division of Historical Resources and the sanctuary.
“It’s merging two sciences. it’s biology merging with archaeology,” she said.
Senior archaeologist Franklin Price said so far they know it wasn’t a sailing ship. It had no ballast or evidence of rigging to hold up a mast or sails.
Smith said there are many filters archaeologists have to get past when analyzing a wreck, including time, the sea and animals.
But the wreck has also become a breeding ground for new life. It is a bustling reef with hard and soft coral and home to many different kinds of fish including a great barracuda, a scorpion fish and even a spotted eagle ray.
Part of the effort is also to make sure more people get a chance to snorkel and dive in wrecks off the Keys, said archaeologist Daniel McClarnon.
Smith has also devised a seminar targeted towards people that certify scuba divers to educate them about respecting Florida shipwrecks called The Heritage Awareness Diving Seminar, which is taught around the state at different points during the year.
“We find, as archaeologists, that there isn’t any future, it’s just the past repeating itself,” he said.
In the world of archeology there are no digs more difficult than those lying beneath watery depths. With land sites archaeologists are sometimes faced with extremely difficult challenges such as such as the environment in Ozette Washington where they found themselves digging through sticky mud and trying to preserve spongy artifacts. Or the Inca site of Machu Picchu where the air is so thin that it’s difficult to breathe, and the sun so intense that it burns the skin almost immediately. No matter how difficult the dry land dig, however, some basic human needs exist in this environment that are simply not there underwater. The most obvious is air and gravity, but there are literally a myriad of other logistical challenges that become apparent when a team goes to plan an underwater dig.
Digging underwater has in fact, proven so difficult that most archaeologists find more reasons to avoid these sites than to dig them. When an underwater site is taken on the team will sometimes resort to extremely complex and costly ends to make it a dry site. They may, for instance, attempt to divert or drain the water from a shallow site, effectively making it a dry land dig, avoiding the challenges involved with a submerged site. Techniques like these are not cheap, and require massive amounts of time and planning so the fact that they are done in the first place tells us that if at all possible any archaeological project is best dug on on dry land. This gives us a hint as to how complex and challenging an underwater dig must be.
Why is it so difficult? Shouldn’t a team just be able to put on some scuba gear and head on down to the site? After all, the bottom of the ocean is silty and soft; shouldn’t that make it even easier to dig? In this study, I will talk about some of the less obvious problems involved in underwater archeology; the ones that people might not think of right away like physiological and mobility issues. I will start by talking about shallow water digging which is usually the simplest, then more on the more complex problems with digging deeper sites in the 100 to 500 feet deep range. I’ll then move on to the most complex challenges with underwater digs that lye in very deep water like the Titanic or the Yorktown. These sites are tens of thousands of feet deep and if it’s not amazing enough that they’ve been found in the first place, the obstacles involved in actually digging them are mind boggling. Finally, I’ll conclude by talking a little about some of the political and moral issues involved in underwater archeology and explain why it is important that these sites are responsibly dug.
In almost all cases, projects that involve digging in shallow water (15-50 feet) are the simplest. They render only slight physiological complexities and divers are usually able to stay down much longer than on deeper dives. This is, however, not to say that they aren’t without their challenges. How for instance, does an archeologist remove the silt covering the artifacts without causing the water around him to become so clouded with sediment that he can’t even see? One might think that you could just brush the silt aside and the water would carry it away but it doesn’t. Once the visibility has been ruined it can take several hours for it to settle again. Underwater archaeologists have had to invent techniques and tools that literally suck up silt, leaving behind the covered artifacts. These giant underwater vacuum cleaners are usually powered by the thrust generated by the boat’s propeller, and the silt is forced by the engine away from the site, while the artifacts are filtered out by a screen on the front of the vacuum hose. (Martin)
Of course if the site is at the bottom of a river or in an area of the ocean where there is a current, the silt is simply washed away by the moving water, but how does the team keep themselves and the artifacts from being washed away as well? I can say from my own experience that fighting against a strong current gets to be exhausting and frustrating after only a few minuets. It is important also to remember that in a current the simple action of the water moving over the sediment will kick it up and ruin the visibility without any help from the divers. When we take this into account, it is no surprise that the sites with the least visibility tend to be the ones with the most current. Archaeologists have gone so far as to build structures around a shallow site that divert the current. This technique does not actually emerge the site, but rather acts as a shield against the current much as a car’s windshield diverts the strong wind from the driver’s face. This allows for a calm area over the site where the visibility will be improved and the archaeologists won’t have to tether themselves to a solid object or swim against the current. (Martin)
Finally there is the concern of air consumption. If the water is extremely cold, a diver must plan for his dive taking in to account that his bottom time will be shorter because his body has to work harder to keep warm, thus needs more oxygen. However, even under ideal conditions, using divers with the most developed breath control, a team can’t really expect a diver to get more than about an hour out of a single 80 cubic foot tank. More tanks can be added to increase bottom time, but it is important to remember that the more tanks a diver must carry, the more difficult it is for him to move around and the more quickly he will grow tired. It is exhausting enough to work in an underwater environment where every movement is met with the resistance of water; the effect is only compounded when more gear is strapped on. It has to be expected then that a diver can only work four or five hours as day and not the eight or ten he would be able to in a dry land environment, thus the project either has to employ many more people, or it will take much longer than a conventional dig.
When it comes to SCUBA (Self Contained Underwater Breathing Apparatus) some unique problems begin to pop up when the diver gets to depths of much more than thirty feet and they become the primary concern at depths in excess of one hundred feet. Since very few shipwrecks lie in shallow water and the cost of diving on an extremely deep wreck is often too great, most underwater archeology in done in water in water ranging in depth from 100 to 500 feet. As any experienced scuba diver will attest to, these are the depths where the danger in scuba becomes most apparent, but they are also the depths where you will find the most interesting things, especially if you are into wrecks. So why is it more dangerous to dive on sites at these depths than those in the fifteen to thirty foot range? One might think that it would be because of the risk of equipment failure or the diver running out of air, but in reality, these are of very little concern. The real danger at these depths come from the way a diver’s body reacts to the pressure from the water above him.
The most notorious of these physiological complications is the bends or DCI (decompression illness). Most people have heard of this, but many who don’t dive don’t understand exactly what it is. Whenever a diver goes underwater, he is under the pressure of the water above him. This is why your ears hurt when you dive to the bottom of a swimming pool. At around thirty feet, the pressure is twice what it is at sea level and it grows greater as the diver descends. As the depth increases and the pressure increases each breath the diver takes consists of air that is denser because of the outside pressure. This means that at thirty feet, the diver is breathing twice as much air as he is breathing at sea level. As we know, our bodies absorb the gasses from the air we breathe into our bloodstream and since normal air is almost all nitrogen, our blood is absorbing more nitrogen than anything else. (McCallum)
Take for instance a diver at sixty feet. With each breath he is absorbing roughly three times the nitrogen of a person on the beach. This doesn’t become a problem however until there is a change in pressure. After all, everyone has a good deal of dissolved nitrogen in their blood at any given point, but we need not worry about it because we know the pressure around us is not likely to change much. With the diver, however, this is not the case. If he has been working at a site lying in 200 feet of water four twenty minuets, he’s been absorbing outrageous amounts of nitrogen into his bloodstream and if he were to suddenly decide to come to the surface, the dissolved nitrogen, like any gas in its liquid form under pressure, would turn back into its gaseous state as the pressure diminished.
As we know, having gas bubbles in our bloodstream is extremely dangerous, and in some cases it can even lead to death, so those planning underwater excavations at these depths must take great care and planning to avoid this dangerous problem. Many divers use, for instance, dive computers which will calculate how much time a diver spent at a given depth with his rate of air consumption to determine the nitrogen levels in his blood and tell him when he must come up and at what depths he must make timed decompression stops to outgas nitrogen. These computers allow divers maximum flexibility in their work because they can dive right up to their physiological limits, yielding the best bottom time. (TDI)
If the site is under water ranging in depth from sixty to one hundred feet, the team may chose to use a special gas mixture called NITROX to yield even more bottom time than can be achieved with normal air. Historically, this gas has been used by the navy and research teams, but in recent years, it has fallen into the mainstream of casual scuba. NITROX doesn’t actually introduce any unfamiliar gasses into the compressed air, but rather increases the oxygen level, replacing some of the nitrogen. This means that if a diver is breathing a 40/60 (40% oxygen and 60% nitrogen) blend, he is dissolving roughly twenty five percent less nitrogen into his bloodstream, allowing him to stay on the site longer. (C.N.P Program)
Why then don’t underwater archaeologists simply breathe pure oxygen and eliminate the nitrogen completely from the equation? The answer is that under pressure, oxygen levels in a divers blood can become too high causing the diver to convulse. As I mentioned above, the deeper a diver goes, the more actual gas he breaths, and at even a very shallow depth pure oxygen will cause blood-oxygen levels to become so great that they are toxic to the diver. NITROX, then is a very customizable gas and a team will choose the best mix for the depth of the site. If, for instance, the site is in eighty feet of water, the team might use a NITROX blend of 40% which would become toxic if the diver was to descend to eighty five, but yields the best bottom times at eighty because of the reduced nitrogen levels. The trouble with NITROX is that it is only beneficial for relatively shallow dives because you quickly reach a point of diminishing return as you go deeper. If a team needs to reach a depth below two hundred feet, even the air we are breathing now has oxygen levels that are too high and would become toxic. (C.N.P Program) How then do teams carry on projects at say three hundred feet?
The answer: use a gas called TRIMIX by partially replacing both the nitrogen and oxygen with helium. This type of diving is highly theoretical and is usually reserved only for the Navy, research teams and highly trained technical divers. However, if the financial and technical resources are available, archeological teams may sometimes use it to conduct their excavations. Since these dives usually involve very long decompression stops on the way back up, and since the gas mixtures consumed at the bottom are often so thin in oxygen that they wouldn’t even support life at sea level, it is not uncommon for as many as eight individual tanks to be used by each diver on a single dive. (TDI) This is extremely expensive and the diver’s bottom time is usually limited to only a few minuets, so the work must be conducted quickly and sometimes with haste, since a high element of danger hangs over each diver’s head. The team usually needs to have a recompression, or hyperbaric chamber on location to deal with any instances of DCI, as well as many diving teams since a single diver may only be able to make one or two.
Again, diving with TRIMIX is extremely expensive. Depending on the blend a single tank of TRIMIX can cost as much as $80, and each diver needs a separate regulator for each blend of gas he breathes. (TDI) Hyperbaric chambers often have to be leased from the government or hospitals and the staff that runs them costs in the realm of two hundred dollars per hour. Each diver is highly trained and faces a strong element of danger, so they don’t come cheap, and the team usually needs a full fledged research vessel just to carry all the gear. These dives are also extremely dangerous. DCI is not an uncommon occurrence, and since the depths they are dealing with are so great, any slight error in planning leads to disastrous consequences. It is not surprising then that only the most glamorous projects at these depths are taken on.
Even TRIMIX reaches a point of diminishing return at about six hundred feet (although at least one person has made it past one thousand breathing it). Thus, for very deep wrecks like the Yorktown, another solution must be found. Without a tremendous budget, raw determination and the latest sonar technology, Pieces of history like the Yorktown and the Titanic can’t even be found, let alone dug. Bob Ballard, above all others, has pioneered this technology, and exemplified the strong will it takes to discover wrecks at these astronomical depths. On his deepest discovery, the Yorktown, he combined a vast array of technological innovations and sheer luck to discover and make the three mile trip down to the ship’s decks. (National Geographic)
So where does an archaeologists begin to take on a project of this magnitude? Well, as it would logically follow, the first challenge is actually finding the wreck. On his search for the Yorktown, Ballard used mostly eyewitness accounts and charts from World War II to outline a one hundred square mile section of midway which he searched by using a massive research vessel to pull a navy sonar module in a criss-cross pattern. As he covered the ocean floor, he took note of anything unusual that came up on the sonar screen and charted them as possible sites of the ship. Once he had the possibilities narrowed down, he attempted to send an unmanned Navy probe into the depths to try and get a first hand look at what he thought was sure to be the Yorktown. He didn’t get his chance this time, however, since four hundred feet from the ocean floor, the probe imploded and needed serious repair. Navy technicians spent days repairing the crippled probe and it was only after the second dive that Ballard was able to confirm that what he had found was indeed the Yorktown. (National Geographic)
Needless to say, not every archeologist has access to a research vessel and cutting edge Navy sonar and submarine technology, so clearly this type of research is left to those like Ballard with the highest budgets. But the cost of a project like this only begins with finding the site. Once the wreck is found, deep diving research subs and costly camera equipment must be obtained to properly map and chart the site. If the decision is made to bring artifacts to the surface it can take years and costly chemicals to properly preserve them. For these reasons, most sites at these depths will never be explored. Tragically, there are simply not enough institutions willing to foot the bill for such expensive research.
Since we can’t have a shipwreck to explore without a wrecked ship, and since the action of a ship wrecking tends to kill people, archaeologists, have to be sensitive to the idea that in most cases these sites should be treated as graveyards. Some archaeologists like Ballard take great care not to disturb the wrecks he finds. He refuses to bring any artifacts at all to the surface and focuses instead on mapping and charting the sites. This “take only pictures, leave only bubbles” mentality shows great respect for those who have perished and their families. The archeologist is still able to discover and learn key facts about the history of the ship or the way it went down but the wreck is left intact.
All too often, however, another team will come in after the serious archaeologists have left and pillage the site. The most notorious of these cases is the Titanic where Ballard, as usual, went to great effort not to disturb the anything, only to have a French team come in later and recover artifacts so they could sell them for a profit. This kind of treasure hunting really is a tragedy, not only because it shows no respect for the people who have died, but because it causes governments to be cautious about letting anyone conduct research in their waters. Countries have had so many artifacts stolen from them in this way that they often assume any archeologist is a treasure hunter and refuse to give research permits to anyone at all.
If our base of knowledge is to continue to grow with respect to maritime history and ship construction, it is absolutely essential that archaeologists are allowed to continue exploring both the very shallow and the very deep wrecks alike. For this to happen, universities and research institutions must be willing to finance these projects, and there must be some world wide provisions put in place to eliminate the trend of treasure hunting so that countries will be able to trust this delicate research to those most qualified. Bob Ballard stands out as a shining example of a good scientist with his priorities firmly in place. He has respect for both the memories of those who died in the wreck as well as the countries who’s waters hold these fascinating sites. Anyone planning an underwater dig would do well to follow his lead.
Martin, Dean (1995).
Archaeology underwater: The NAS guide to principles and practices
McCallum, Paul (1970).
The Scuba Diving Handbook
Pearson, Cliff (1998).
Cliff’s NITROX Project (computer program)
Publishing Staff (1999).
National Geographic Explorer: The search for the Yorktown
Film Archive: National Geographic
Publishing Staff (1999). TDI Website.
Government move to boost tourism backfires as looters descend on antiquities
For centuries they have lain forgotten and untouched in the murky depths of the Mediterranean. But the sunken glories of Greece are now threatened by modern treasure hunters, who are targeting their riches since the lifting of a ban on coastal scuba-diving.
At risk, say archaeologists, is an unseen part of the country’s cultural patrimony, comprising thousands of shipwrecks dating from Classical, Hellenic, Roman, Byzantine and early modern times and their priceless cargoes of coins, ingots, weapons and gold.
“Greek waters are some of the richest in antiquities in the world,” said the marine archaeologist Katerina Dellaporta. “Thanks to very stringent controls over underwater exploration shipwrecks have been extremely well preserved.”
Until recently divers were allowed access to just 620 miles of the country’s 12,000 mile coastline, but in an attempt to boost tourism, the conservative government opened the country’s entire coastal waters to underwater exploration in 2003.
Since then, looting has proliferated, say archaeologists.
Treasure hunters, encouraged by scuba-diving websites from America to Australia, are homing in on the “archaeological sea parks” armed with hi-tech scanners, cameras and nets.
One US-based diving company offers on its website an exhaustive list of “underwater treasures” which have been discovered by scuba divers, including sculptures, jewellery, warrior helmets, Phoenician beads, vases, and a variety of personal items reflecting life in the region in ancient times, from oil lamps to medical supplies.
“Man has been sailing the Greek seas for more than 9,000 years,” it says. “This means that ships have been sinking for over 9,000 years – ideal for treasure hunters.”
It offers a fleet of 400 yachts, some with crews, and “customised” diving packages for everyone from beginners to experienced divers as the “best way to discover Greece”.
Marine archaeologists, who have appealed to Greece’s highest administrative court to reverse the relaxation of the law, also point to the surge in blogging by divers boasting of their finds.
Last summer, one police raid intercepted two trucks crammed with ancient artefacts discovered in a wreck off the island of Kalymnos.
But with growing numbers of would-be looters posing as tourists on yachts, Greece appears ill-equipped to tackle the problem.
Unlike Italy, which has units of specially trained divers and helicopters to chase underwater thieves, Greece has an art squad that is under-funded and, with just 20 members, woefully understaffed.
The sheer scale of the problem is also an issue: an estimated 6,000 wrecks are believed to dot the Greek seas, with most of them in the Mediterranean, where entire submerged cities are thought to exist.
“The future of archaeology is in the water – on land most riches have been discovered – but in the sea there are thousands of sunken ships with cargoes that have yet to be found,” said Harry Tzalas, a marine archaeologist who has discovered numerous treasures off the coast of Alexandria in Egypt.
“Each time an artefact is removed from the sea its value in terms of information and context is automatically lost, a tragedy for archaeologists.”
|— Underwater archaeologists are taking to Loch Tay to try to uncover more about a submerged prehistoric woodland.
The stumps of about 50 trees were discovered in 2005 – some of them are thought to be about 6,000 years old.
The experts are now aiming to find their root system and establish the depth to which the trees are buried.
Meanwhile, a campaign has been launched to help restore the reconstructed crannog, an ancient loch dwelling, which attracts thousands of visitors.
The Scottish Trust for Underwater Archaeology will spend the next two weeks inspecting the drowned forest.
They will be focusing on two trees – one dating from 4,270 BC to 4,040 BC and the other dating from 2,350 BC to 2,120 BC.
As well as looking for the tree roots, they will be taking samples of the sediment and organic materials to establish if there were any landslips taking place between the Mesolithic and the Bronze Ages.
Barrie Andrian, who is an underwater archaeologist, told the BBC Scotland news website they could also uncover other secrets.
She said: “Last year, when we took a sample of organic material – because that’s one of the beauties of underwater archaeology, all the things are preserved very well underwater generally – we found a sample that had evidence of charcoal, bone and cereal grains.
The experts are unsure whether it washed in from another crannog, from the shore, or by another means.
She added: “Potentially we could be finding evidence of human impact on the environment from several thousand years ago.
“But in general terms, in underwater archaeology we’re looking for remains of people travelling up and down the loch, things they’ve dropped, how they’ve used the loch and settlement alongside or in the water, because crannogs were built out in the water.
Archaeologists are aiming to find the trees’ root system
“So if we’re going to find out more information about crannogs and the people who built them and lived in them we need to excavate underwater.”
Ms Andrian is also the director of the Scottish Crannog Centre, near Aberfeldy, which is visited by an estimated 25,000 people every year.
The centre is urgently in need of money to refurbish the reconstructed Iron Age home on the loch.
Ms Andrian said: “When we started building in 1994, and it was a total experiment, we were using authentic materials, so no pile drivers, no water proofing, no weather proofing, no creosote, no nothing, just the way it would’ve been done in the past.
“We used the same species as the ancient people did – that’s mainly alder, we would’ve liked to use more oak because there was oak in the original houses as well, but obviously oak is very expensive.
“What we’ve discovered since then is that alder doesn’t last very long in the water – that’s because the most exposed parts of the timbers are where the loch level rises and falls between winter and summer and it’s causing erosion in that area.”
Staff will now look into ways of naturally protecting the structure and Polish specialists have even visited to give their advice.