changing landscapes, natural causes of
changing landscapes, natural causes of
- John Bintliff
The classical world witnessed many forms of landscape change in its physical geography, mostly due to longer-term geological and climatological processes, whilst only a minority were due purely to human action. The physical environment of Greek and Roman societies saw alterations through earthquakes, volcanic eruptions, sea-level fluctuations, erosion, and alluviation.
Already in Greek antiquity, Plato (Critias iii) observed how the Aegean physical landscape was being worn down over time as erosion from the uplands filled the lowland plains. Indeed, the Mediterranean region is amongst the most highly erodible in the world.1 However, scientific research in the field known as geoarchaeology has revealed a more complex picture than a continuous degradation of the ancient countryside.2
To uncover a more realistic picture of Mediterranean landscape change, the element of timescales proves to be central, and here the framework developed by the French historian Fernand Braudel3 provides the appropriate methodology. Braudel envisaged the Mediterranean past as created through the interaction of dynamic forces operating in parallel but on different “wavelengths” of time: the Short Term (observable within a human lifetime or less), the Medium Term (centuries or more, not clearly cognisant to contemporaries), and the Long Term (up to as much as thousands or millions of years, not at all in the awareness of past human agents).4 Even the longest operating processes, just as much as the medium-term and short-term ones, will be active nonetheless in an era such as classical antiquity in the Mediterranean region.
The Long Term
For the Long Term, the most obvious motor for change is the tectonic effect on the landscape. The Mediterranean sits at the active interface between the clashing African and Eurasian tectonic plates, while parts of Italy and the Aegean are further broken into subplatelets, promoting even further geological instability. Earthquake and volcanic zones mark the most mobile areas of this neotectonic activity. The eruption of Thera-Santorini around 1628 bce,5 of Vesuvius in 79 ce, the swallowing up of the town of Helike in 373 bce,6 and the uplift of parts of western Crete in the 5th century ce7 are only the best-known instances of dramatic events which are the product of these long-term forces. Still, it is unclear whether any of these or similar disruptions caused wider change than the loss of life in the immediate impact zone of those disasters. Even recent claims that the explosion of Santorini set in chain the collapse of Minoan civilisation remain problematic.8
A second long-term effect whose operation can still be traced in the classical world is that of the glacial-interglacial cycle. Global ice ages running for around 100,000 years each have been punctuated for over 1 million years by short, around 10,000-year interglacial warm eras. Since 12,000 years ago, we have fortunately been living in such a warm era, but we would by now have been entering the early stages of a new glacial period had the greenhouse effect (the result of human interference with the climate) not delayed its inception.
The Medium Term
The glacial cycles are driven by regular changes in the tilt of the Earth, but within these major cold and warm phases we know of systematic subcycles (running from several millennia to several centuries) of rather warmer and rather colder global climates. These latter, operating at our medium-term timescale, can also be linked to the Earth’s rotation, but other factors behind such lesser variations are created by sunspot cycles, volcanic activity, and variability in oceanic currents.9 We also now know that these medium-term causative elements can have contrasting effects in the southern as compared to the northern Mediterranean (around a hinge at 40° north).10 As concerns classical antiquity, it is probable that the Final Bronze Age and Early Iron Age were cold and dry in the more southerly parts of the Mediterranean, but cold and wet in the north.11 In Classical Greek and early Roman times, the climate was generally what we consider typically Mediterranean, warm and dry with mild winters, and thus more favourable to human communities, but in late antiquity (the 4th to 7th centuries ce) there may have been more severe climate effects, with again very dry and cold climate in the southern parts of the region.12 It is not too difficult to relate these positive and negative phases to history, if only at the level of suggesting that climate change may have assisted cultural florescence and decline: here one might highlight climatic stress during the Final Bronze Age and Early Iron Age era ca. 1200–800 bce, and the period of late antiquity from the 6th century ce onwards into the earliest medieval centuries.
In terms of landscape change, the glacial-interglacial cycle also caused massive alterations in sea level and the elevation of land masses. How does this affect the Greco-Roman eras? When the current interglacial reached its warmest peak around 6,000 years ago, sea level would in theory have been at its maximum owing to peak glacier melt worldwide, and would be expected to decline since, with the gradual return to the next glacial phase. However, two effects have counteracted this normal process. First, global warming over the past two centuries has caused increased sea-level rise, but more relevant to the ancient world are the remarkable effects of isostatic rebound.13 When northern Europe lay under thick sheets of ice, the weight depressed the land immediately beneath. Through the current interglacial, or Holocene, period, the continual retreat of these massive glaciers has caused the glaciated lands to rebound upward from their depression into the Earth’s crust, causing a corresponding depression in adjacent lands such as those of southern Europe. Ancient harbours of the classical world are generally submerged, as a result, by one or more metres below their original elevation relative to sea level.
The medium-term climate fluctuations may also have had effects on erosion and alluviation throughout the Mediterranean. Contrary to Plato’s opinion, geoarchaeology has made it abundantly clear that the hills and fields of the Mediterranean have not been continually washed away throughout the period of human occupancy. It was the pioneer Claudio Vita-Finzi14 who, in 1969, first documented throughout the Mediterranean the frequency and scale of erosion since the end of the last ice age. He argued that severe erosion was rare and confined to certain periods (notably late antiquity), and was caused by climatic fluctuations, whereas for most of the last 12,000 years stable landscapes and soil growth have dominated. Although subsequent geomorphological studies returned to the traditional view that human abuse of the landscape was the culprit, nonetheless both schools of thought were in agreement that widescale erosion phases were rare compared to those of landscape quiescence, a “punctuated equilibrium” model in the sense of Stephen Jay Gould.15
Meanwhile, fundamental research into Mediterranean erosion16 produced a more sophisticated picture: most soil loss was due to rare and unusual weather, “extreme climatic events,” which then had greater or lesser impact depending on how much of the landscape had been cleared by human activity. These “events” were typically commoner during longer periods of climatic divergence from the Mediterranean norm, but they could also occur randomly as a byproduct of the Mediterranean climate. Thus, even in Classical Greek and Hellenistic times, when a moderate Mediterranean climate dominated, there could be widespread crop failures, as recorded in contemporary historical sources and inscriptions.17
One of the most complex environments in the classical landscape is that of cities situated on major river estuaries. Unsurprisingly, they show considerable instability over the medium term of centuries. First, the rivers can change course or bring variable amounts of sediment into the city environment and the port areas, as well as erupting into floods at unpredictable intervals. At the same time, the marine environment will never be stable. Onshore and longshore currents deposit and redeposit sediments of different grades, while large deltas tend to sink over time.18 Sea levels have been in a delicate dialectic with the land since 6,000 years ago, when a fast sea-level rise gave way to stable sea level or a light rise (see earlier). The scale of sea-level change was therefore relatively small in most coastal regions of the Mediterranean during the Greco-Roman era, so that even minor alterations in the effects of currents and the weight of river sediment borne into the estuary were able to give rise to the advance of the delta or its retreat—leaving a port increasingly cut off from the sea, or alternatively eroded by it.19 These processes have been especially well documented for several large river systems draining from the Anatolian plateau west into the Aegean Sea, and effecting radical changes to the physical surroundings of towns ranging from Bronze Age Troy20 to Greco-Roman Ephesos and Miletos.21 There has been a tendency to ascribe the progressive silting up of such former harbour cities and their current remoteness from the sea to purely human-created erosion in the hinterland during Classical times. However, an equal role should be allowed for coastline instability resulting from the change from a fast sea-level rise until 4,000 bce (when most Mediterranean coastal plains became submerged by the sea), to that of minimal rise subsequently, when natural as well as human-driven river sediments were generally more dominant and deltas advanced at variable rates into the sea.
The Short Term
Finally, let us turn to the Short Term. We have tied earthquakes and eruptions to the punctuated effects of long-term geological forces, but there can be rare cases of abrupt disruption to physical geography consequent on short-lived forces. One example currently being investigated is that of tsunamis (erroneously called “tidal waves”): although commonly caused by violent tectonic or volcanic fractures of the Earth’s surface, they can also occur unpredictably as a result of submarine slumping of oceanic sediments and through freak combinations of storms and tides (“meteotsunamis”). A series has recently been documented on the island of Levkas.22
We know from historical meteorological data that the Mediterranean region on average suffers, in its traditional climate regime, one drought year in ten. Particularly if the landscape is aridified, the kind of short, extreme rainstorm that can occur in such years outside of winter and spring has been seen to create localised flooding and mass movement of surface deposits. Archaeological excavations have often recorded such events.23 Apart from the destruction of human habitats, such events can locally destroy fields of crops and the rich surface soil with its accumulated nutrients. Severe frosts can likewise appear uncharacteristically in regions where major crops sensitive to cold are significant, killing off, for example, potential olive harvests over whole districts. Storing cereals, root crops, and tree crops were a critical adaptation to these threats, while the alternate-year fruiting of olive trees was also a vital element in allowing economic sustainability.
- Bintliff, John L., ed. The Annales School and Archaeology. Leicester: Leicester University Press, 1991.
- Bintliff, John L. “Time, Process and Catastrophism in the Study of Mediterranean Alluvial History: A Review.” World Archaeology 33 (2002): 417–435.
- Bintliff, John L. The Complete Archaeology of Greece, from Hunter-Gatherers to the Twentieth Century AD. Oxford and New York: Wiley-Blackwell, 2012.
- Braudel, Fernand. The Mediterranean and the Mediterranean World in the Age of Philip II. London: Fontana/Collins, 1972.
- Brueckner, Helmuth. “Coastal Changes in Western Turkey: Rapid Delta Progradation in Historical Times.” Bulletin de L’Institute Oceanographique special issue 18 (1997): 63–74.
- Buentgen, Ulf, W. Tegel, et al. “2500 Years of European Climate Variability and Human Susceptibility.” Science 331 (2011): 578–582.
- Casana, Jesse. “Mediterranean Valleys Revisited: Linking Soil Erosion, Land Use and Climate Variability in the Northern Levant.” Geomorphology 101 (2008): 429–442.
- Lambeck, Kurt. “Sea-level Change and Shore-line Evolution in Aegean Greece since Upper Palaeolithic Time.” Antiquity 70 (1996): 588–611.
- Macklin, Mark G., and J. Lewin. “Quaternary Fluvial Systems in the Mediterranean Basin.” In Mediterranean Quaternary River Environments. Edited by Mark G. Macklin et al., 1–25. Rotterdam: Balkema, 1995.
- Mainwaring, A. Bruce., R. Giegengack et al., eds. Climate Crises in Human History. Philadelphia: American Philosophical Society, 2010.
- Stanley, Dean J., and A. G. Warne. “Holocene Sea-level Change and Early Human Utilization of Deltas.” GSA Today 7.12 (1997): 1–7.
- Thornes, John B. “The Palaeo-ecology of Erosion.” In Landscape and Culture: Geographical and Archaeological Perspectives. Edited by J. Malcolm Wagstaff, 37–55. Oxford: Blackwell, 1989.
1. Mark G. Macklin and J. Lewin, “Quaternary Fluvial Systems in the Mediterranean Basin,” in Mediterranean Quaternary River Environments, eds. Mark G. Macklin et al. (Rotterdam: Balkema, 1995), 1–25.
2. John L. Bintliff, The Complete Archaeology of Greece, from Hunter-Gatherers to the Twentieth Century AD (Oxford and New York: Wiley-Blackwell, 2012), chap. 1.
3. Fernand Braudel, The Mediterranean and the Mediterranean World in the Age of Philip II (London: Fontana/Collins, 1972).
4. John L. Bintliff, ed., The Annales School and Archaeology (Leicester: Leicester University Press, 1991).
5. Sturt Manning, F. Höflmayer et al., “Dating the Thera (Santorini) Eruption: Archaeological and Scientific Evidence Supporting a High Chronology,” Antiquity 88 (2014): 1164–1179.
6. Steven Soter, P. Blackwelder et al., “Environmental Analysis of Cores from the Helike Delta, Gulf of Corinth, Greece,” Journal of Coastal Research 17 (2001): 95–106.
7. Dieter Kelletat, “The 1550 BP Tectonic Event in the Eastern Mediterranean as a Basis for Assessing the Intensity of Shore Processes,” Zeitschrift fur Geomorphologie N.F. suppl. 81 (1991): 181–194.
8. Jan Driessen, “Crisis Cults on Minoan Crete,” Aegaeum 22 (2001): 361–369; and Carl Knappett, R. Rivers et al., “The Theran Eruption and Minoan Palatial Collapse: New Interpretations Gained from Modelling the Maritime Network,” Antiquity 85 (2011): 1008–1023.
9. Mainwaring, A. Bruce., R. Giegengack et al., eds., Climate Crises in Human History (Philadelphia: American Philosophical Society, 2010).
10. Michel Magny, J. L. de Beaulieu et al., “Holocene Climate Changes in the Central Mediterranean as Recorded by Lake-level Fluctuations at Lake Accesa (Tuscany, Italy),” Quaternary Science Reviews 26 (2007): 1736–1758.
11. Information from an article in preparation by C. Heymann, I. Unkel, J. Bintliff et al., “The impact of climate on the Late Bronze-Early Iron Age transition in Mainland Greece.”
12. Ulf Buentgen, W. Tegel et al., “2500 Years of European Climate Variability and Human Susceptibility,” Science 331 (2011): 578–582.
13. Kurt Lambeck, “Sea-level Change and Shore-line Evolution in Aegean Greece since Upper Palaeolithic Time,” Antiquity 70 (1996): 588–611.
14. Claudio Vita-Finzi, The Mediterranean Valleys: Geological Changes in Historical Times (Cambridge, U.K.: Cambridge University Press, 1969).
15. Stephen J. Gould, Wonderful Life (London: Hutchinson, 1989).
16. John B. Thornes, “The Palaeo-ecology of Erosion,” in Landscape and Culture: Geographical and Archaeological Perspectives, ed. J. Malcolm Wagstaff (Oxford: Blackwell, 1989), 37–55.
17. Robin Osborne, Classical Landscape with Figures: The Ancient Greek City and its Countryside (London: George Philip, 1987).
18. Dean J. Stanley and A. G. Warne, “Nile Delta: Recent Geological Evolution and Human Impact,” Science 260 (1993): 628–634.
19. Dean J. Stanley and A. G. Warne, “Holocene Sea-level Change and Early Human Utilization of Deltas,” GSA Today 7.12 (1997): 1–7; and John L. Bintliff, “Time, Process and Catastrophism in the Study of Mediterranean Alluvial History; A Review,” World Archaeology 33 (2002): 417–435.
20. Ilhan Kayan, “Die Troianische Landschaft,” in Troia: Traum und Wirklichkeit, ed. Joachim Latacz (Stuttgart: Theiss, 2001), 309–314.
21. Helmuth Brueckner, “Coastal Changes in Western Turkey: Rapid Delta Progradation in Historical Times,” Bulletin de L’Institute Oceanographique special issue 18 (1997): 63–74.
22. Andreas Vött, Helmuth Brückner et al., “Traces of Holocene Tsunamis across the Sound of Lefkada, NW Greece,” Global and Planetary Change 66 (2009): 112–128.
23. Uwe Rust, “Die Reaktion der fluvialen Morphodynamik auf anthropogene Entwaldung östliches Chalkis (Insel Euboea, Griechenland),” Zeitschrift für Geomorphologie suppl. 30 (1978): 183–203.