Underwater Archaeology

Underwater Archaeology

Maritime archaeology (also known as marine archaeology) is a discipline that studies human interaction with the sea, lakes and rivers through the study of vessels, shore side facilities, cargoes, human remains and submerged landscapes. One specialty is underwater archaeology, which studies the past through any submerged remains. Another specialty within maritime archaeology is nautical archaeology, which studies vessel construction and use.

Maritime archaeological sites usually result from shipwrecks or sometimes seismic catastrophes, and thus represent a moment in time rather than a slow deposition of material accumulated over a period of years. This fact has lead to shipwrecks being described as time capsules.

Archaeological material in the sea or in other underwater environments is typically subject to different factors than artifacts on land. However, as with land archaeology what survives to be investigated by modern archaeologists is a tiny fraction of the material originally deposited. The issue in maritime archaeology is that despite all the material that is lost, there are occasional rare examples of substantial survival, from which a great deal can be learned.

There are those in the archaeology community who see maritime archaeology as a segregated discipline with its own concerns (such as shipwrecks) and requiring the specialised skills of the underwater archaeologist. Others value an integrated approach, stressing that nautical activity has economic and social links to communities on land.

Integrating Land and Sea

Prior to the industrial era, travel by water was often easier than over land. As a result, marine channels, navigable rivers and sea crossings formed the trade routes of historic and ancient civilisations. For example, the Mediterranean sea was known to the Romans as the inner sea because the Roman empire spread around its coasts. The historic record as well as the remains of harbours, ships and cargoes, testify to the volume of trade that crossed it. Later, nations with a strong maritime culture such as the United Kingdom, Denmark and Spain were able to establish colonies on other continents. Wars were fought at sea over the control of important resources. The material cultural remains that are discovered by maritime archaeologists along former trade routes can be combined with historic documents and material cultural remains found on land to understand the economic, social and political environment of the past.

Preservation of material underwater

There are significant differences in the survival of archaeological material depending on whether a site is wet or dry, on the nature of the chemical environment, on the presence of biological organisms and on the dynamic forces present. Thus rocky coastlines, especially in shallow water, are typically inimical to the survival of artifacts, which can be dispersed, smashed or ground by the effect of currents and surf, possibly (but not always) leaving an artefact pattern but little if any wreck structure.

Saltwater is particularly inimical to iron artefacts including metal shipwrecks, and sea organisms will readily consume organic material such as wooden shipwrecks. On the other hand, out of all the thousands of potential archaeological sites destroyed or grossly eroded by such natural processes, occasionally sites survive with exceptional preservation of a related collection of artifacts. An example of such a collection is the Mary Rose.

Of the many examples where the sea bed provides an extremely hostile environment for submerged evidence of history, the RMS Titanic, though a relatively young wreck and in deep water so calcium-starved that concretion does not occur, has already incurred irreversible degradation of her steel and iron hull. As such degradation inevitably continues, data is forever lost, objects' context is destroyed and the bulk of the wreck will eventually become nothing more than a stain on the floor of the Atlantic Ocean. The USS Monitor, having been found in the 1970s, was subjected to a program of attempted in situ preservation, but deterioration of the vessel progressed at such a rate that the rescue of her turret was undertaken lest nothing be saved from the wreck.

Some wrecks, lost to natural obstacles to navigation, are at risk of being smashed by subsequent wrecks sunk by the same hazard, or are deliberately destroyed because they present a hazard to navigation. Even in deep water, commercial activities such as pipe-laying operations and deep sea trawling can place a wreck at risk. Large pipelines can crush sites and render some of their remnants inaccessible as pipe is dropped from the ocean surface to the substrate thousands of feet below. Trawl nets snag and tear superstructures and separate artifacts from their context.

The wrecks, and other archaeological sites that have been preserved, such as the Regalskeppet Vasa have generally survived because the dynamic nature of the sea bed can result in artifacts becoming rapidly buried in sediments. These sediments then provide an anaerobic environment which protects from further degradation. Wet environments, whether on land in the form of peat bogs and wells, or underwater are particularly important for the survival of organic material, such as wood, leather, fabric and horn. Cold and absence of light also aid survival of artifacts, because there is little energy available for either organic activity or chemical reactions. Salt water provides for greater organic activity than freshwater, so some of the best preservation in the absence of sediments has been found in the cold, dark waters of the Great Lakes in North America and in the Baltic Sea.

While the land surface is continuously reused by man, the sea bed was largely inaccessible until the advent of submarines and scuba equipment in the twentieth century. Salvagers have operated in much earlier times, but much of the material was beyond the reach of anyone. Thus the Mary Rose was subject to salvage from the sixteenth century and later, but a very large amount of material, buried in the sediments, remained to be found by maritime archaeologists of the twentieth century.

While preservation in situ is not assured, material that has survived underwater and is then recovered to land is typically in an unstable state and can only be preserved as a result of highly specialised conservation processes. The Holland 1 provides an example of a relatively recent (metal) wreck for which extensive conservation has been necessary, while the wooden structure of the Mary Rose, and the individual artifacts have been undergoing conservation since their recovery.

A challenge for the modern archaeologist is to consider whether in-situ preservation or recovery and conservation on land is the preferable option, or to face the fact that preservation in any form, other than as an archaeological record is infeasible. A site that has been discovered has typically been subjected to disturbance of the very factors that caused its survival in the first place, for example, when a covering of sediment has been removed by storms or the action of man. Active monitoring and deliberate protection may mitigate against further rapid destruction making in situ preservation an option, but long term survival can never be guaranteed. For very many sites, the costs are too great for either active measures to ensure in situ preservation or to provide for satisfactory conservation on recovery. Even the cost of proper and complete archaeological investigation may be too great to enable this to occur within a timescale that ensures that an archaeological record is made before data is inevitably lost.

Submerged sites

Pre-historic landscapes

Maritime archaeology studies prehistoric objects and sites that are, because of changes in climate and geology, now underwater.

Bodies of water, fresh and saline, have been important sources of food for people for as long as we have existed. It should be no surprise that ancient villages were located at the water's edge. Since the last ice age sea level has risen as much as 250 feet (approximately 75 meters).

Therefore, a great deal of the record of human activity throughout the Ice Age is now to be found under water.

The flooding of the area now known as the Black Sea (when a land bridge, where the Bosporus is now, collapsed under the pressure of rising water in the Mediterranean Sea) submerged a great deal of human activity that had been gathered round what had been an enormous, fresh-water lake.

Significant cave art sites off the coast of western Europe are now reachable only by diving, because the cave entrances are underwater, though the caves themselves are not flooded.

Historic sites

Throughout history, seismic events have at times caused submergence of human settlements. The remains of such catastrophes exist all over the world, and sites such as Alexandria and Port Royal now form important archaeological sites. As with shipwrecks, archaeological research can follow multiple themes, including evidence of the final catastrophe, the structures and landscape prior to the catastrophe and the culture and economy of which it formed a part. Unlike the wrecking of a ship, the destruction of a town by a seismic event can take place over many years and there may be evidence for several phases of damage, sometimes with rebuilding in between.

Coastal and foreshore

Not all maritime sites are underwater. There are many structures at the margin of land and water that provide evidence of the human societies of the past. Some are deliberately created for access - such as bridges and walkways. Other structures remain from exploitation of resources, such as dams and fish traps. Nautical remains include early harbours, and places where ships were built or repaired. At the end of their life, ships were often beached. Valuable or easily accessed timber has often been salvaged leaving just a few frames and bottom planking.

Archaeological sites can also be found on the foreshore today that would have been on dry land when they were constructed. An example of such a site is Seahenge, a Bronze Age timber circle.

Ships and Shipwrecks

The archaeology of shipwrecks can be divided in a three-tier hierarchy, of which the first tier considers the wrecking process itself: how does a ship break up, how does a ship sink to the bottom, and how do the remains of the ship, cargo and the surrounding environment evolve over time? The second tier studies the ship as a machine, both in itself and in a military or economic system. The third tier consists of the archaeology of maritime cultures, in which nautical technology, naval warfare, trade and shipboard societies are studied. Ships and boats are not necessarily wrecked: some are deliberately abandoned, scuttled or beached. Many such abandoned vessels have been extensively salvaged.

Bronze Age

The earliest boats discovered date from the Bronze Age and are constructed of hollowed out logs or sewn planks. Vessels have been discovered where they have been preserved in sediments underwater or in waterlogged land sites, such as the discovery of a canoe near St Botolphs. Examples of sewn-plank boats include those found at North Ferriby and the Dover Bronze Age Boat which is now displayed at Dover Museum[1]. These may be an evolution from boats made of sewn hides, but it is highly unlikely that hide boats could have survived.

Ships wrecked in the sea have probably not survived, although remains of cargo (particularly bronze material) have been discovered, such as those at the Salcombe B site. A close collection of artefacts on the sea bed may imply that artefacts were from a ship, even if there are no remains of the actual vessel.

Late Bronze Age ships, such as the Uluburun Shipwreck have been discovered in the Mediterranean, constructed of edge joined planks. This shipbuilding technology continued through the classical period.

Maritime archaeology by region

Mediterranean area

In the Mediterranean area, maritime archaeology mainly deals with the innumerable retrievals of ancient ages, especially regarding the Roman fleets. The earliest Mediterranean shipwrecks yet identified are two Phoenician ships of c. 750 BC that foundered off the Phoenician coast with cargoes of wine in amphoras, found in 1997 by the U.S. Navy deep submergence research submarine NR-1. The sites were subsequently investigated by Robert Ballard and Harvard University archaeology Professor Lawrence Stager in 1999. The many discoveries in the sea and in some lakes (notably in Nemi, Italy, where Caligula's ships were found) were really helpful in explaining some passages of the history of Romans, Phoenicians and Etruscans, and allowed to track respective presences in the related areas.

Italy is indeed one of the most important areas for these studies, with particular reference to Roman and Etruscan naval activities. Also because of the extremely high rate of expected wrecks (Romans calculated that at least 30% of cargo would have been lost by storms or pirate assaults), the traffic was proportionally (or perhaps more) increased, and many goods were found (ordinarily contained in amphoras or in the larger dolia) that let us understand what the commerce was about. Sometimes, as in the case of the two 'bronzi' found in Riace (Calabria), real artworks were brought to the surface. In other cases, like the very recent retrievals in Sarno river (near Pompeii), other details enlarge the knowledge of some interesting elements: this retrieval allows us to suppose in fact that on the Tyrrhenian shore too there were little towns with palafittes, like in ancient Venice. In the same area, the submerged town of Puteoli (Pozzuoli, close to Naples) contains the 'portus Julius' created by Marcus Vipsanius Agrippa in 37 BC, later sunk due to bradyseism.

The Antikythera mechanism, which appears to be an ancient clockwork astronomical computer, was discovered in a shipwreck off the Greek island of Antikythera.

But other areas too have no less interest, like the waters around Israel, where Herod the Great's port at Caesarea Maritima was found. Other finds are consistent with some passages of the Bible (like the so-called Jesus boat, which appears to be similar to those in use during the first century AD) from

Links

The Nautical Archaeology Society (NAS)

For more information about getting some training in Underwater Archaeology, Click here

Hampshire and Wight Trust for Maritime Archaeology

Lost Treasures of the Seven Seas - Ocean Research Group - Website on new shipwreck discoveries and expeditions around the world, underwater archaeology and treasures from the deep