The Colgate Scene
Venice research, international style
by Charles E. McClennen
professor of geology
Albert Ammerman collecting coring samples.
Contributing scholars came from Italy, Great Britain and numerous institutions in the United States to participate in "Venice Before San Marco: Recent Studies on the Origins of the City," an international conference held on campus last October. Archaeological research in Venice during the last decade has become interdisciplinary and rapidly expanded with a focus on the formative and previously obscure fourth through ninth centuries AD.
Through professional presentations and informal conversations during the conference, the invited participants and attendees had opportunities to exchange ideas and learn of various evolving viewpoints. Scholars from fields as diverse as architecture, art history, archaeology, classics, dendrochronology, history, science of glass making, library science, literature, marine geology and paleo-botany were well represented.
Archaeological artifacts, some dating back to late Roman times and recently excavated from Venice, were on display courtesy of the Italian government. A series of 16 graphic display panels (3' x 4') of research results, as well as the actual field sampling equipment and maps, were installed in Everett Needham Case Library along with several Special Collections books related to early Venice. A full-color 50-page catalogue with an overview of the materials and abstracts of the presented research papers was produced for the event.
My own involvement with Venice, as a coastal-marine geologist, started in 1992 with an informal discussion of research tools and techniques. When asked if I could work with archaeologists searching for submerged and buried artifacts, structures and the surrounding sedimentary contexts in the lagoon of Venice, a moment's reflection over a glass of wine was sufficient. Productive use of my experience with sonar and coring equipment for this project would enrich my upcoming sabbatical of 1993. I was invited by Albert Ammerman, archaeologist and senior research associate in the department of classics, who had been working in Italy for more than two decades and was involved in the Venice research effort directed by Maurizia De Min of the Soprintendenza per i Beni Ambientali e Architettonici di Venezia (Government Office for the Preservation of the Environment and Architectural Heritage of Venice). A primary goal of this agency is the preservation of the renowned art and architecture of Venice. The agency is joined by numerous charitable organizations and individuals committed to funding fieldwork and research with the purposes of saving Venice and its treasures.
To familiarize myself with the area and thus prepare for effective fieldwork, I needed first to review the geologic literature of the Adriatic Sea, northern Italy, the lagoon and its sediments and, particularly, the issue of sea-level change. Previously developed models of coastal evolution and the historical growth of the city on salt marshes also helped me think more fully about Venice and why it rests only one to two meters above sea level.
Questions arose quickly, as past environmental research has surprising gaps. In particular, little is known of the dynamics that control the tidal channel system. We wanted to understand how the tidal waters cut through the extensive mudflats and salt marsh islands while directing the water circulation and much of the sediment erosion, transport and deposition. We needed to be aware of the dynamics of channel migration and shifting sediments in order to anticipate burial contexts.
Major changes in these dynamics during human history were caused by the diversion of rivers that once flowed directly into the lagoon, dumping unwanted deltaic sediments into the harbor navigation channels. Depriving the lagoon of this river water flow and sediment supply would have had a major environmental impact, leaving the tidal flow to dominate for the last six centuries. However, maritime trade was central to the economic prosperity of Venice for nearly ten centuries. Government policies and public works projects of the councils and Doges successfully supported this commerce and shipping activity right up to the time of the Napoleanic takeover. Studies of more modern urban interventions and pollution in the lagoon, as well as increasing incidence and magnitude of acqua alta (high water), all have relevance to our search for and analysis of archaeological contexts.
Graphic: "Radiocarbon Ages of Structures and Core Samples Documenting Lagoon Development and Sea Level Rise" [Enlarge]
In the larger scale of geologic time, it is important to understand how the
rapid melting of continental glaciers beginning 20,000 years ago brought
sea-level rise up to near-present levels about 6,000 years ago. This
transgression (flooding) of the flat-lying Veneto plain area, just north of the
Po River delta, initiated the lagoon formation where Venice now stands. |
Our initial field efforts targeted environments of deposition and potential structure locations within the lagoon, using coring and sonar equipment. We now have a fundamentally new and important understanding of the geologic evolution of the lagoon. This new framework has had a direct impact on proposals for constructing defensive floodgates designed to protect the city and lagoon islands from acqua alta flooding. Very briefly, we were able to better determine the rate of sea level rise over the last 60 centuries and several features of channel dynamics that had not previously been appreciated. These discoveries provided a realization that projections of the frequency and duration of acqua alta events should be substantially increased. That in turn caused an Italian cabinet-level review, in Rome, prior to the December 6, 2001 funding decision to go ahead with the Moses floodgate project at a cost of $2.6 billion.
The figure above summarizes the new sea level trend for Venice during the last third of the post-glacial period. It also shows that most of the lagoon sediments were deposited in the top five meters over the last 6,000 years. Tidal channels, on the other hand, have eroded their way down into the underlying and much older (approximately 20,000 years) river plain deposits. Channels as deep as 20 meters are presently noted in the three major inlets from the Adriatic Sea into the Venice lagoon.
The new view of the sedimentary structures and channel dynamics was made possible by bringing the latest technology in sub-bottom sonar profiling from the United States. This type of echo sounding system allows one to see the sedimentary layering recorded as the research vessel surveys along the selected route of travel. The "chirp" system incorporates correlation signal processing whereby transmitted signals are matched with returning echoes, thus producing the sharpest possible sonar records of sedimentary strata. We can identify layers as thin as 10 centimeters and down to depths as great as 20 to 30 meters in the silts and clays of lagoon sediments. These records allowed us to see for the first time how the channels had migrated over the centuries, shifting position due to erosion on some banks and deposition on others. Just as river channels meander, so do the tidal channels among the mud flats in the lagoon.
Carefully selected cores collected around the channel meander bends near San Francesco del Deserto enabled us to calculate the horizontal migration rates of seven to 22 meters per century (with an average of 12 m/100yrs). This is much faster than the vertical sedimentation rate of accumulation out on the mudflats (about six to 23 centimeters per century, with an average of 14 cm/100yrs). This just about keeps up with the combined long-term rates of local subsidence and sea level rise for the lagoon.
Charlie McClennen with research equipment in the exhibition.
These calculations are the results of the undergraduate research done by
senior geology concentrator Christy Visaggi '02. An independent study course
this past fall enabled her to experience all the excitement and frustrations of
conducting grain size analysis, reviewing sub-bottom sonar profiles and
interpreting Radiocarbon dates determined at the Radiocarbon Accelerator Unit
(Mass Spectrometer Laboratory) of Oxford University, England. Integrating these
multiple data types into a mature geological term paper was guided by talks
with conference participants, particularly Dr. Rupert Housley, formerly of the
Oxford AMS Laboratory and now of University of Glasgow, Scotland. Her
presentation at the end-of-term Geology Senior Seminar clearly demonstrated the
joy of meeting these numerous research challenges successfully.|
Venice opportunities for many other Colgate undergraduates have been possible through sampling trips conducted over the past eight years and participation in sample and data analysis at Colgate. Student members of the Colgate Venice Study Group, when directed by classics department members Rebecca and Albert Ammerman, have toured our ongoing fieldwork and other archaeological excavation sites in Venice and at Torcello. They also heard presentations of our research and discussed the evolving archaeological program as it has progressed.
Talks and poster session presentations at the Geological Society of America regional meetings by Colgate students and me, talks to Colgate alumni, research talks to colleagues at American and Italian universities, popular presentations to environmental and nature organizations have all made it possible for us to help others to see Venice in new and different ways. More formal publications of the research in the Journal of Coastal Research, Antiquity and Science have in combination generated a wide distribution of our findings on the archaeological and depositional environments within the Lagoon of Venice. The Science article of September 2000 that Albert Ammerman and I published also generated a flurry of coverage in the New York Times science section, BBC World News and other media outlets in Europe, where there is an ever-present concern with saving Venice.
All this field sampling, radiocarbon dating, travel and equipment funding was made possible by a series of grants provided by several organizations: the Gladys Krieble Delmas Foundation, the Samuel H. Kress Foundation, National Geographic Society, National Science Foundation and the Colgate Research Council. Joseph A. Mangin '50 made the essential gift to fund the production of the catalogue and exhibition panels for the conference. The quality of, and interest in, these conference products is such that plans are being completed for an early March 2002 hanging of the exhibition panels at the Smithsonian Institution, Washington, D.C.
Special thanks are also in order for Colgate technicians Ron Ray (electronics), who got the sonar systems to work properly with a connected GPS receiver, and Gary Ward (machinist), who helped me design and then machined the new coring components. Equally appreciated are: Stephanie McClintick (graphic designer), who developed the exhibition panels and many of the included research illustrations, Katheryne Gall, who edited and designed the conference catalogue (which is for sale at the Colgate bookstore for $15), Hannah McClennen, who assisted in numerous graphic designs, editing and preparation of many fine Italian meals, and Jane Pinchin, who allowed my research to continue while I served as her associate dean of faculty and who strongly encouraged and supported the whole Venice conference enterprise at Colgate. Note: the website http://groups.colgate.edu/Venice (prepared for the conference) remains available.
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