Reconstructing the Roman topography and

Reconstructing the Roman topography and
environmental features of the Sarno River Plain (Italy)
before the AD 79 eruption of Somma-Vesuvius
Introduction & objectives
SEBASTIAN VOGEL1 & MICHAEL MÄRKER2
1Deutsches Archäologisches Institut, 2Heidelberg Academy
The Plinian eruption of Somma-Vesuvius volcanic complex AD 79,
which completely buried the Roman settlements of Pompeii and
Herculaneum belongs to the most well-known eruptions in
history. During this eruption almost the entire Sarno River plain
was covered by volcanic deposits (Sigurdsson et al., 1985)
showing a specific and therefore easily identifiable stratigraphy
(Fig. 1). Thus, these deposits can be considered as an ideal
chronostratigraphic marker.
The eruption AD 79 covered the Sarno River plain with volcanic
deposits of some meters. This not only caused a caesura in the
existence of an entire landscape, but also contributed to the
excellent preservation of the paleo-surface and the ancient
paleo-environmental conditions before the eruption of AD 79
(Foss et al., 2002). Consequently, almost 2,000 years later, this
paleo-surface is still accessible for stratigraphical investigations.
The objective of this research project is to reconstruct the paleotopography and paleo-environmental features of the Sarno River
plain before the eruption of Somma-Vesuvius in AD 79. The
objective is based on the hypothesis that the eruption caused a Fig. 1: Stratigraphical
coating of the ancient topography which left ancient cross-section south
physiographic elements still recognizable in the present-day of Pompeii.
topography. The utilized methodology combines stratigraphical
information from core drillings,present-day topographical
data,and classification and regression methods.
Methodology
To reconstruct the pre-AD 79 topography and paleo-environmental conditions more
than 1,800 drillings from construction works, as well as from past archaeological and
geological studies, were collected to gain a representative network of stratigraphical
information for the entire Sarno River plain (Fig. 1). By means of the drilling cores
the stratigraphy was determined, the volcanic deposits of AD 79 and the pre-AD 79
surface underneath were identified, and the pre-AD 79 stratum was characterized.
We reconstruct the pre-AD 79 topography with a sophisticated geostatistical
methodology based on a present-day high-resolution digital elevation model (DEM)
and a classification and regression tree approach.
Fig. 2 : Present-day digital
elevation model (DEM) and
fluvial network of the Sarno
River plain with the location of
more than 1,800 stratigraphical
core drillings. Letters indicate
sites of interest.
Results & discussion
Fig. 3 illustrates the modeled depth to the pre-AD 79 surface of the Sarno River
plain. It ranges from >0 to 15 m whereas the average depth is 5.7 m. The distinct
spatial distribution of volcanic deposits since AD 79 is most notably controlled by
two sets of processes: (i) the intial deposition during the eruption and (ii) the
subsequent redistribution by processes of erosion and transport. Originating from
the vent of Somma-Vesuvius, the pumice lapilli fallout was dispersed concentrically
towards the southeast resulting in thickest deposits on its southeastern flanks, near
the source of the eruption.
Fig. 3: Modeled depth to the pre-AD 79
surface of the Sarno River plain.
Outlook
of Sciences and Humanities
Greater thickness of the volcanic deposits along the coast on the other hand most likely
indicate re-deposited material that was mobilized by the Sarno River and its tributaries and
transported towards the Thyrrenian Sea. This corresponds with thinner deposits in the
central part of the Sarno River plain. Furthermore, an accu-mulation of volcanic deposits at
the foot of the Lattari and Sarno Mountains may result from slope deposits being mobilized
by mountain torrents or lahars after intense rainfall events.
Fig. 4: Present-day DEM and Sarno River (A); modeled pre-AD 79 DEM and deduced paleo-river network (B);
character of the pre-AD 79 stratum from the drilling documentations (C) and inferred reconstruction of preAD 79 environmental features (D).
Figs. 4A & B compare the present-day topography with the predicted pre-AD 79 topography.
Even though main physiographic elements appear on both DEMs, several differences can be
identified. Most evident is that the pre-AD 79 surface is approximately 5.7 m deeper than
the modern surface. Thus, the entire coastal area is lying below the recent sea level. In
comparison to the canalized present-day Sarno River, the modeled paleo-Sarno River follows
the natural depth contours of the pre-AD 79 DEM, resulting in more pronounced meander
type fluvial patterns.
By comparing the character of the pre-AD 79 stratum from the drilling data with the pre-AD
79 DEM we reconstructed some paleo-environmental features before AD 79 such as the
ancient coastline and the flood plain of the paleo-Sarno River (Fig. 4C, D). The littoral
deposits before AD 79 are distributed parallel to the present-day coastline at a horizontal
distance of 1,000 to 1,500 m. The fluvial/palustrine deposits cover the area where the paleoSarno River most likely had its ancient riverbed.
On closer examination of the coastal
area of the Sarno River plain a big
fan delta can be identified on both
the present-day DEM and the pre-AD
79 DEM (Fig. 4 & 5). This indicates
that this landform already existed in
Roman times. Converging contour
lines at the foot of the adjacent hill
slopes reveal escarpments that may
have derived from abrasion action of
the sea related to previous
coastlines. Southwest of Pompeii an
elevation discontinuity can be seen Fig. 5: Pre-AD 79 geomorphological map and paleoin the pre-AD 79 DEM which is based environmental reconstruction of the Tyrrhenian coast of the
on deeper littoral deposits in the Sarno River plain.
northern coastal area.
This discontinuity seems to be overprinted by recent deposition as it cannot be identified on
the present-day DEM. This implies that it was formed before AD 79 possibly associated with
the seismic activity preceding the AD 79 eruption, such as the big earthquakes of AD 62 and
AD 64.
In future studies this pre-AD 79 DEM will be used to identify potential locations of Pompeii’s marine or fluvial harbor, whose exact
location is still debated. Moreover, the combination of the pre-AD 79 DEM with archaeological findings enhances the paleoenvironmental reconstruction of the Sarno River plain. In the next project phase the pre-AD 79 DEM will be used to determine
the paleo-topographic setting of the known ‘villae rusticae’ of the Sarno River plain. In addition to paleo-pedological analyses, we
will use the pre-AD 79 topography to reconstruct soil and land use characteristics and to simulate the ancient cultural landscape
of the Sarno River plain.
Contact: Sebastian Vogel email: [email protected]
Michael Märker email: [email protected]
http://www.dainst.org/index_7902_it.html
References
Foss, J.E., Timpson, M.E., Ammons, J.T., Lee, S.Y., 2002. Paleosols of the Pompeii Area. In: Jashemski W.F. ed.. The Natural History of Pompeii. Cambridge University Press, 65-79.
Sigurdson, H., Carey, S., Cornell, W., Pescatore, T., 1985. The eruption of Vesuvius in A.D. 79. Natl. Geogr. Res. 1, 332-387.
Stefani, G., Di Maio, G., 2003. Considerazioni sulla linea di costa del 79 d.C. e sul porto dell’antica Pompei. Riv. Studi Pomp. XIV, 142-195.
Vogel, S. & Märker, M., 2009. Reconstructing the Roman topography and environmental features of the Sarno River Plain (Italy) before the AD 79 eruption of Somma-Vesuvius. Geomorphology, doi:
10.1016/j.geomorph.2009.09.031.

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