Agent-based Modelling for Studying Shipwreck Site Formation Processes

By Rodrigo Vega-Sanchez, National School of Anthropology and History (Escuela Nacional de Antropologia e Historia - ENAH), Mexico, vegarodrig@gmail.com 

Shipwreck site formation processes (SSFP) have long interested maritime archaeologists as a means to understand how a sailing vessel transforms into a wreck site. Two of the most influential works in this area have been those of maritime archaeologists Keith Muckelroy in the 1970s and Martin Gibbs in the early 2000s. Muckelroy’s SSFP model focused mainly on the natural factors that modify a shipwreck (Muckelroy, 1978), while Gibbs’ proposal built on Muckelroy’s model concentrating on the cultural factors involved in the process, i.e., the decisions and actions that people make in different moments and how these may alter the contents and disposition of a wreck site (Gibbs, 2006).

We conceive SSFP as complex adaptive systems, where the non-linear interactions of both natural and cultural factors give rise to the observed distribution of elements in a shipwreck site. From this standpoint, agent-based modelling (ABM) may prove to be useful for studying the complex dynamics of SSFP.

As part of the Project Maritime Archaeology of the Mexican-American War 1846-1848 (PAMGI in Spanish)*, currently being carried out at the Institute for Anthropological Research, National Autonomous University in Mexico City, we developed an ABM for studying SSFP taking as a case study that of the USS Somers, a brig-of-war built in the United States in 1842 out of wood, propelled only by sail, and armed with 32-pdr carronades. The Somers sank in December 1846 while blocking the port of Veracruz in the Gulf of Mexico during the Mexican-American War; its shipwreck rests since then in a sandy seabed, 30 meters deep.

Our ABM of the Somers’ SSFP is based on the conceptual models of Muckelroy and Gibbs and integrates a wide variety of historical and contemporary data about the shipwreck. These include nautical characteristics taken from the original construction plans; details about its operation, wrecking event, and salvage operations obtained from historical documents; as well as modern environmental data including ocean currents and sediments; and also experimental data about the degradation of different types of woods and metals (Vega-Sánchez and Herrera, 2022).

Integrating all of these data, we constructed a simulation platform using a video game engine and a 3D model of the Somers created from the ship’s original blueprints (figure 1). Details of their development can be found in this online publication, and the ABM can be downloaded from the project’s repository.

Figure 1. A conceptual model and ABM simulation platform for studying SSFP. The conceptual model behind the ABM can be found in Vega-Sánchez & Herrera (2022), while the process of developing the ABM can be found in Vega-Sánchez (2022). 

In the ABM, we can alter the parameters of several natural and cultural variables involved in the SSFP to explore how this would modify the archaeological context. We used this platform to run a series of simulations where initial conditions were varied and the resulting simulated context compared to the real archaeological context, which was recorded during PAMGI’s 2018 field season.

Simulation scenarios allowed exploring specific research questions about different aspects of the Somers' SSFP, including equipment (dimensions of the hull metallic sheathing), wreck conditions (degrees of starboard listing), and post-depositional events (opportunistic salvage operations). Additionally, ABM provided a detailed sequence of degradation and deposition of all the elements within the shipwreck, mirroring a traditional stratigraphic analysis (figure 2). Thus, by integrating historical data with the conceptual model and ABM simulations, we were able to postulate a sustained interpretation of the Somers’ SSFP.

Figure 2. Simulation scenarios showing a degradation and deposition sequence of the Somers’ SSFP. The figure shows screen captures of the Somers SSFP simulation scenario that most resembled the actual shipwreck site during the 2018 archaeological recording by PAMGI. 

ABM and simulation contribute to archaeology by opening the possibility to raise a wide variety of hypotheses and carrying out controlled and repeatable experiments where it was previously not possible. This directly impacts our ability to analyze and interpret the archaeological context and answer questions about the past. In maritime archaeology, ABM could constitute a valuable methodological tool that, by integrating conceptual models, historical sources, and archaeological data, allows for generating sustained interpretations of shipwrecks and their site formation process.

*PAMGI was supported by the British Academy (Newton Advanced Fellowships Programme, AF160206); the National Autonomous University of Mexico (UNAM) through its PAPIIT program (IA400818) and its Laboratory of Oceanographic Vessels and the Coordination of Oceanographic Platforms (Campaña Guerra de Intervención 01 2018 aboard the Oceanographic Vessel Justo Sierra); and the National Science and Technology Council (CONACYT-Mexico, Frontier Science Program CF 2019 / 1327714).

References

Gibbs, M., 2006. Cultural Site Formation Processes in Maritime Archaeology: Disaster Response, Salvage and Muckelroy 30 Years on. International Journal of Nautical Archaeology 35, 4–19.

Muckelroy, K., 1978. Maritime archaeology. Cambridge University Press, London.

Vega-Sánchez, R. (2022). Developing an agent-based model for studying shipwreck site formation processes. Visualizing Objects, Places, and Spaces: A Digital Project Handbook. Retrieved from: https://handbook.pubpub.org/pub/case-somers-abm

Vega-Sánchez, R., Herrera, J.M., 2022. Agent-based modelling for the study of shipwreck site formation processes: a theoretical framework and conceptual model. F1000Research New Digital Archaeologies Collection.