Underwater archeological methodology
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Archaeological diving is a type of scientific diving used as a method of survey and excavation in underwater archaeology. The first known use of the method comes from 1446, when Leon Battista Alberti explored and attempted to lift the ships of Emperor Caligula in Lake Nemi, Italy. [1] Just a few decades later, in 1535, the same site saw the first use of a sophisticated breathing apparatus for archaeological purposes, when Guglielmo de Lorena and Frances de Marchi used an early diving bell to explore and retrieve material from the lake, although they decided to keep the blueprint of the exact mechanism secret. [1] The following three centuries saw the gradual extension of diving time through the use of bells and submersing barrels filled with air. In the 19th century, the standard copper helmet diving gear was developed, allowing divers to stay underwater for extended periods through a constant air supply pumped down from the surface through a hose. Nevertheless, the widespread utilisation of diving gear for archaeological purposes had to wait until the 20th century, when archaeologists began to appreciate the wealth of material that could be found under the water. This century also saw further advances in technology, most important being the invention of the aqualung by Émile Gagnan and Jacques-Yves Cousteau, the latter of whom would go on to use the technology for underwater excavation by 1948. [2] Modern archaeologists use two kinds of equipment to provide breathing gas underwater: self-contained underwater breathing apparatus (SCUBA), which allows for greater mobility but limits the time the diver can spend in the water, and Surface-supplied diving equipment (SSDE or SSBA), which is safer but more expensive, and can only be used in shallower waters.[ clarification needed ][ dubious ] [3]
Diving is a method that has uses for all stages of underwater excavation. Even with recent technological advances, diver searches remain of central importance for the location of sites. This can simply mean the diver swimming around and noting objects of interest of the seafloor, but it is usually supplemented through the use of a wide array of tools, such as hand-held metal detectors, lines to guide the search and make it more systematic. Alternatively, the diver may be towed by vessel on the surface or use an underwater vehicle, which preserves the diver's stamina and gives them greater speed, but can decrease accuracy. Once a site is located, divers continue to play an important role in surveying it. At this stage, diving is necessary to take the most basic of measurements and apply methods of surveying similar to those used on land, including trilateration, grid division and photography. These methods often require special training or equipment usually not necessary on land to be used for underwater archaeology. Most of the actual excavation is also done by diving, and again uses the same tools, but often requires different considerations. For example, trowels, brushes and other tools are used to move the soil, but the diver's movements might also disturb the sediment, which can lead to inadvertent damage of the site, but which can also be utilised to delicately expose artifacts. [4]
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Compared with methods of land survey and excavations, archaeological diving has distinct advantages and disadvantages. The equipment, such as air compressors, exposure suits, compressed air cylinders, masks and fins, together with the training required for proper scientific diving is considerably more expansive than the training and equipment usually used during land excavations, contributing to underwater archaeology generally requiring greater funding. [2] Time is also in more limited supply for divers, as it is determined by the available supply of air and the physical and physiological stress placed on them by spending prolonged periods of time underwater. Perhaps the greatest risk is posed by decompression sickness (DCS), caused by excessive concentrations of nitrogen from the breathing air dissolved in the diver's tissues, and which can be painful, debilitating and in some cases, fatal. Managing the decompression safely requires one of three methods: the use of dive tables or personal dive computers that stipulate the amount of time the diver can spend at a specified depth, staged decompression, (stops at shallower depths during the ascent) to allow the safe release of nitrogen from the body, or using a decompression chamber at the surface. Consequently, archaeologists may be limited to diving for only around 40 minutes each day, depending on the depth of the site. Further difficulties include heat loss due to the water temperature, nitrogen narcosis, a physiological effect of increased nitrogen levels on the central nervous system, and low or distorted visibility. Despite these difficulties, working in the water can have distinct advantages over land archaeology, resulting from both the environment and the nature of the finds themselves. Diving allows for vertical movement in the water, which lets the excavator view the site from different angles without having to disturb it. The removal and transportation of sediment is usually easier underwater, as it can be carried away by simple suction devices or even just the currents themselves. The moving of heavy objects is also easier in many cases, as they can be simply buoyed up to the surface using lift bags filled with air. The nature of the underwater material can also help the diver when they collect data. The majority of underwater sites, such as shipwrecks, are single-component meaning there is no contamination from earlier or later periods. Additionally, many objects might be better preserved underwater than on the land. [2]
In 1900, Greek sponge divers discovered numerous statues under the water near the island of Antikythera, deposited as a result of the sinking of a ship from the first century BCE. These statues were then raised under the direction of Director of Antiquities George Byzantinos. This initial excavation is a good example of the possibilities and early shortcomings of underwater archaeology and archaeological diving. The material recovered is of exceptional quality, but one diver died and two others were paralyzed by decompression sickness, while the seabed was not mapped and the excavation was not systematic. [5] Another, more detailed investigation of the site took place 1976, directed by Jacques-Yves Cousteau and supervised by the Greek archaeologist L. Kolonas. After the shipwreck was relocated, detailed photographs of it were taken. Due to the depth at which the wreck is located, divers could only work at the bottom for a maximum of six minutes at a time, and they used decompression techniques before surfacing. They used a kind of airlift called the seceuse to recover the objects, which included statuettes, jewellery and other cargo from the ship. [6]
The Uluburun shipwreck was discovered in 1982 by a sponge diver off the south-western coast of Turkey. It was excavated by the Institute of Nautical Archaeology over the following years. It has been dated to the late 14th century BCE, and the material retrieved, including large amounts of copper and tin, ceramics, precious metals, tools, weapons and other objects, reveal much about the long-distance trade and manufacturing practices of the time. Archaeological diving took centre stage in both the initial exploration and the subsequent excavation of the site, with 22,413 dives accounting for 6,613 hours spent at the seabed. This means that most dives took only around 20 minutes, which can in part be explained by great depth at which they were conducted, between 41 and 61 meters. [7] [8]
The famous Lighthouse of Alexandria in Egypt, considered one of the Seven Wonder of the Ancient World, was built during the Ptolemaic Period and was destroyed by a series of earthquakes in the medieval period. Early investigations of the site were conducted by the amateur underwater archaeologist Kamel Abul-Saadat in 1961 and then by a UNESCO mission led by Honor Frost. Following damage to the remains of the lighthouse by the construction of a concrete wall to defend a nearby medieval fortress, a Franco-Egyptian team under the leadership of Jean-Yves Empereur conducted salvage inspection and excavation of the site from 1994 to 1998. The mission included on average around 30 divers. They carefully mapped and recorded the site, and lifted multiple objects of note from the water. These included statues and pillars from earlier periods of pharaonic history, showing how these were relocated to the new capital by the Ptolemies. The site is an excellent example of how underwater archaeology can be used beyond shipwrecks. [9]
The Page–Ladson site is a sinkhole in the bed of the Aucilla River in Florida. Pre-Clovis and early Archaic artifacts have been recovered from stratified deposits at the bottom of the sinkhole 10 meters below the surface of the river. The pre-Clovis artifacts were associated with the bones of mastodons and other Pleistocene animals, with some bones showing apparent butchering marks. The site was discovered by amateur scuba divers in 1959. Systematic excavation of the site was carried out from 1983 until 1997, and again from 2012 until 2014. Equipment used to support excavations included surface air supplies for divers, underwater communications devices, waterproof housings for cameras, and a floating dredge to lift sediment to the surface for screening. [10] [11] [12]
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Underwater archaeology is archaeology practiced underwater. As with all other branches of archaeology, it evolved from its roots in pre-history and in the classical era to include sites from the historical and industrial eras.
Technical diving is scuba diving that exceeds the agency-specified limits of recreational diving for non-professional purposes. Technical diving may expose the diver to hazards beyond those normally associated with recreational diving, and to a greater risk of serious injury or death. The risk may be reduced by appropriate skills, knowledge and experience, and by using suitable equipment and procedures. The skills may be developed through appropriate specialised training and experience. The equipment involves breathing gases other than air or standard nitrox mixtures, and multiple gas sources.
Wreck diving is recreational diving where the wreckage of ships, aircraft and other artificial structures are explored. The term is used mainly by recreational and technical divers. Professional divers, when diving on a shipwreck, generally refer to the specific task, such as salvage work, accident investigation or archaeological survey. Although most wreck dive sites are at shipwrecks, there is an increasing trend to scuttle retired ships to create artificial reef sites. Diving to crashed aircraft can also be considered wreck diving. The recreation of wreck diving makes no distinction as to how the vessel ended up on the bottom.
Diving activities are the things people do while diving underwater. People may dive for various reasons, both personal and professional. While a newly qualified recreational diver may dive purely for the experience of diving, most divers have some additional reason for being underwater. Recreational diving is purely for enjoyment and has several specialisations and technical disciplines to provide more scope for varied activities for which specialist training can be offered, such as cave diving, wreck diving, ice diving and deep diving. Several underwater sports are available for exercise and competition.
Diving physics, or the physics of underwater diving is the basic aspects of physics which describe the effects of the underwater environment on the underwater diver and their equipment, and the effects of blending, compressing, and storing breathing gas mixtures, and supplying them for use at ambient pressure. These effects are mostly consequences of immersion in water, the hydrostatic pressure of depth and the effects of pressure and temperature on breathing gases. An understanding of the physics is useful when considering the physiological effects of diving, breathing gas planning and management, diver buoyancy control and trim, and the hazards and risks of diving.
Surface-supplied diving is a mode of underwater diving using equipment supplied with breathing gas through a diver's umbilical from the surface, either from the shore or from a diving support vessel, sometimes indirectly via a diving bell. This is different from scuba diving, where the diver's breathing equipment is completely self-contained and there is no essential link to the surface. The primary advantages of conventional surface supplied diving are lower risk of drowning and considerably larger breathing gas supply than scuba, allowing longer working periods and safer decompression. Disadvantages are the absolute limitation on diver mobility imposed by the length of the umbilical, encumbrance by the umbilical, and high logistical and equipment costs compared with scuba. The disadvantages restrict use of this mode of diving to applications where the diver operates within a small area, which is common in commercial diving work.
In-water recompression (IWR) or underwater oxygen treatment is the emergency treatment of decompression sickness (DCS) by returning the diver underwater to help the gas bubbles in the tissues, which are causing the symptoms, to resolve. It is a procedure that exposes the diver to significant risk which should be compared with the risk associated with the available options and balanced against the probable benefits. Some authorities recommend that it is only to be used when the time to travel to the nearest recompression chamber is too long to save the victim's life; others take a more pragmatic approach and accept that in some circumstances IWR is the best available option. The risks may not be justified for case of mild symptoms likely to resolve spontaneously, or for cases where the diver is likely to be unsafe in the water, but in-water recompression may be justified in cases where severe outcomes are likely if not recompressed, if conducted by a competent and suitably equipped team.
Scuba diving is a mode of underwater diving whereby divers use breathing equipment that is completely independent of a surface breathing gas supply, and therefore has a limited but variable endurance. The name scuba is an anacronym for "Self-Contained Underwater Breathing Apparatus" and was coined by Christian J. Lambertsen in a patent submitted in 1952. Scuba divers carry their own source of breathing gas, usually compressed air, affording them greater independence and movement than surface-supplied divers, and more time underwater than free divers. Although the use of compressed air is common, a gas blend with a higher oxygen content, known as enriched air or nitrox, has become popular due to the reduced nitrogen intake during long or repetitive dives. Also, breathing gas diluted with helium may be used to reduce the effects of nitrogen narcosis during deeper dives.
Diver rescue, following an accident, is the process of avoiding or limiting further exposure to diving hazards and bringing a diver to a place of safety. A safe place is often a place where the diver cannot drown, such as a boat or dry land, where first aid can be administered and from which professional medical treatment can be sought. In the context of surface supplied diving, the place of safety for a diver with a decompression obligation is often the diving bell.
Underwater diving, as a human activity, is the practice of descending below the water's surface to interact with the environment. It is also often referred to as diving, an ambiguous term with several possible meanings, depending on context. Immersion in water and exposure to high ambient pressure have physiological effects that limit the depths and duration possible in ambient pressure diving. Humans are not physiologically and anatomically well-adapted to the environmental conditions of diving, and various equipment has been developed to extend the depth and duration of human dives, and allow different types of work to be done.
Scientific diving is the use of underwater diving techniques by scientists to perform work underwater in the direct pursuit of scientific knowledge. The legal definition of scientific diving varies by jurisdiction. Scientific divers are normally qualified scientists first and divers second, who use diving equipment and techniques as their way to get to the location of their fieldwork. The direct observation and manipulation of marine habitats afforded to scuba-equipped scientists have transformed the marine sciences generally, and marine biology and marine chemistry in particular. Underwater archeology and geology are other examples of sciences pursued underwater. Some scientific diving is carried out by universities in support of undergraduate or postgraduate research programs, and government bodies such as the United States Environmental Protection Agency and the UK Environment Agency carry out scientific diving to recover samples of water, marine organisms and sea, lake or riverbed material to examine for signs of pollution.
Diving equipment is equipment used by underwater divers to make diving activities possible, easier, safer and/or more comfortable. This may be equipment primarily intended for this purpose, or equipment intended for other purposes which is found to be suitable for diving use.
Underwater breathing apparatus is equipment which allows the user to breathe underwater. The three major categories of ambient pressure underwater breathing apparatus are:
Scuba gas planning is the aspect of dive planning and of gas management which deals with the calculation or estimation of the amounts and mixtures of gases to be used for a planned dive. It may assume that the dive profile, including decompression, is known, but the process may be iterative, involving changes to the dive profile as a consequence of the gas requirement calculation, or changes to the gas mixtures chosen. Use of calculated reserves based on planned dive profile and estimated gas consumption rates rather than an arbitrary pressure is sometimes referred to as rock bottom gas management. The purpose of gas planning is to ensure that for all reasonably foreseeable contingencies, the divers of a team have sufficient breathing gas to safely return to a place where more breathing gas is available. In almost all cases this will be the surface.
Dive planning is the process of planning an underwater diving operation. The purpose of dive planning is to increase the probability that a dive will be completed safely and the goals achieved. Some form of planning is done for most underwater dives, but the complexity and detail considered may vary enormously.
There are several categories of decompression equipment used to help divers decompress, which is the process required to allow divers to return to the surface safely after spending time underwater at higher ambient pressures.
The following outline is provided as an overview of and topical guide to underwater diving:
The following index is provided as an overview of and topical guide to underwater diving:
Diving support equipment is the equipment used to facilitate a diving operation. It is either not taken into the water during the dive, such as the gas panel and compressor, or is not integral to the actual diving, being there to make the dive easier or safer, such as a surface decompression chamber. Some equipment, like a diving stage, is not easily categorised as diving or support equipment, and may be considered as either.
Diving procedures are standardised methods of doing things that are commonly useful while diving that are known to work effectively and acceptably safely. Due to the inherent risks of the environment and the necessity to operate the equipment correctly, both under normal conditions and during incidents where failure to respond appropriately and quickly can have fatal consequences, a set of standard procedures are used in preparation of the equipment, preparation to dive, during the dive if all goes according to plan, after the dive, and in the event of a reasonably foreseeable contingency. Standard procedures are not necessarily the only courses of action that produce a satisfactory outcome, but they are generally those procedures that experiment and experience show to work well and reliably in response to given circumstances. All formal diver training is based on the learning of standard skills and procedures, and in many cases the over-learning of the skills until the procedures can be performed without hesitation even when distracting circumstances exist. Where reasonably practicable, checklists may be used to ensure that preparatory and maintenance procedures are carried out in the correct sequence and that no steps are inadvertently omitted.
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