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Excursion A

Ingmar Unkel, Max Dunkel & Scott Fick

Version from: Sun Jun 13 12:59:26 2021

Olympia, Coastal Hazards and Lagoon Development

Figures

  • Figure 1. Excursion A overview map. Tops are marked in red, and the suggested route starts in Ancient Olympia, thereafter moving towards Patras. (Map: S. Fick 2016)

  • Figure 2. Ancient Olympia, situated at the banks of the Kladeos River. (Source: Wikimedia Commons)

  • Figure 3. An aerial view of the Alpehos and Kladeos Rivers as sediment transport pathways to Ancient Olympia, marked here by the Temple of Zeus. (Source: Google Earth 2016, modified)

  • Figure 4. The ruins of the Temple of Zeus at Olympia, where the way the columns have fallen are consistent with destruction by a major tectonic event, likely in the 6th Century CE. (Photo: I. Unkel 2010)

  • Figure 5. Kladeos (above) and Alpheios (below) rivers. These rivers are the likely transportation pathway for a large proportion of sediment that buried Ancient Olympia over the last 1500 years. (Photos: I. Unkel 2016)

  • Figure 6. The coastline of Elis and the geological surface features, including Kotychi Lagoon and Prokopos Lagoon. Nearly the entire coastline from Cape Araxos to Cape Kyllini is a National Park or other significant natural area. Kotychi is the largest existing lagoon in the Peloponnese.

  • Figure 7 Kotychi Lagoon, its tributaries and the dominant surface features immediately surrounding it. (map based on Haenssler et al. 2014 and Avramidis et al. 2008)

  • Figure 8. Prokopos Lagoon, as seen from an overlook point at the northern end of the Lagoon. The long, narrow inlet can be seen to the right. (Photo: I. Unkel 2015)

Tables

  • Table 1. Tsunamis are not uncommon in Greece. Here, tsunami intensity (K0) of tsunamis in Greece and the respective wave heights, return periods and number of historically recorded events are shown (i.e. within the last 3500 years). Note that return periods correspond to a statistical average based on available data. (after Papathoma et al., 2003)

  • Table 2. A summary of these stages, the driving mechanisms, and the proxies used to interpret the coastal development at Kotychi Lagoon .

GPS-Coordinates

Stop Nr. Name of the Stop Latitude Longitude
A-1 Ancient Olympia 37,638742 21,629164
A-2 Alpheios-Kladeos River Junction 37,633083 21,626150
A-3 Kotychi Lagoon 38,005964 21,284947
A-4 Prokopos Lagoon 38,151817 21,385347
A-5 Mycenean Fortress (Teichos Dymaion)* 38,156336 21,403028

*optional stops, of cultural or natural interest

Map

 

A. Introduction

We begin in the northwestern Peloponnese to explore coastal processes that range from single high-impact events (such as tsunamis) to long-term processes (like lagoon development). We will start at the iconic site of Ancient Olympia (A.1) and the nearby river of Alfeios (A.2) to take a closer look at the burial of the ancient site with 4-6 meters of sediment over the last 1500 years. At these sites, we will consider which kinds of environmental forces could account for the accelerated sediment accumulation. From there, the excursion leads to the coastal lagoons in the coastal plains of Elis shifting topics to lagoon development. Kotychi Lagoon (A.3) is located in the Kotychi-Strophylia National Park and has international ecological importance. Kotychi provides an in-depth look at the development of a Mediterranean lagoonnal environment and will also be our first inspection of using climate records to reconstruct past climate (various other climate records are considered further in Excursions C, D and E). Finally, we stop at Prokopos Lagoon (A.4), at the north end of the Kotychi-Strophylia National Park, which has considerably different characteristics.

A.1 Ancient Olympia

GPS-Coordinates

Stop Nr. Name of the Stop Latitude Longitude
A-1 Ancient Olympia 37,638742 21,629164

Ancient Olympia is likely the most well-known site visited throughout this excursion. It is an important archaeological site, with ruins most notably from the Temple of Zeus, and is the namesake and inspiration of the international Olympic Games. Olympia was one of the four Panhellenic sanctuaries (the others at Isthmia, Nemea and Delphi), which were important centers to bring together the different peoples of Ancient Greece for spirituality, athletics, economics and politics, especially during the Panhellenic Games (Weiberg et al., 2016). The Panhellenic games occurred at Olympia every four years, and rotated through the other sites in between.

Beyond this, and most importantly for this excursion, Ancient Olympia offers an interesting site to begin considerations of environmental history in the Northern Peloponnese. We will review the destruction of the ancient site with the subsequent burial and take the site to briefly consider earthquake and tsunami hazards.

 

A.1.1 Ancient Olympia: Sediment Burial

Geomorphologically, the site of Olympia sits on what is sometimes known as the Olympia terrace, related downstream to the Alpheios River and upstream to the Kladeos River valley (Vött et al., 2011b). One of the most outstanding characteristics is the sediment burial of the site: since the 6th Century CE, Ancient Olympia was buried by 4-6 m of sediment (Vött et al., 2011b). This is a substantial amount of sediment to accumulate in the last 1500 years, such that it requires an explanation beyond typical sedimentation rates. In fact, Voett (2011) goes so far as to call it “one of the most interesting geoarchaeological mysteries in the Mediterranean world” (263). Several hypotheses have been proposed to explain the enhanced sedimentation of the site. First off, some explanations argue for the anthropogenic increase in soil erosion in the area during this time, especially related to unmanaged land use (e.g. after Slavic invasion in early medieval times), also seen in increased sedimentation at the mouth of the Kladeos River (e.g. Fouache and Pavlopoulos, 2010). A second hypothesis cites climatic forcing with several periods of a particularly wet climate and increased flooding of the Kladeos and Alpheos Rivers, causing rapid sedimentation in their floodplains (Fountoulis and Mavroulis, 2008).

A third and the most catastrophic hypothesis proposes that one or multiple tsunami events are responsible for disastrous, high-energy floods destroying and burying the site of Ancient Olympia (Vött et al., 2011b). This hypothesis cites the presence of marine species found in high-energy flood sediments at the site, and evidence of the earthquakes and destructive tsunamis in the coastal areas of Elis, such as the site of Ancient Pheia in the Bay of Aghios Andreas (Vött et al., 2011b, 2011a). Additionally, supporters of this hypothesis argue that the Kladeos River basin is much too large for the size of the stream, and the river bed has been eroded 8-10 meters deep since the 6th Century, which could be consistent with extreme tsunami events (Vött et al., 2011b). We will consider the plausibility of these hypotheses in the following sections at the Kladeos and at the Alpheos Rivers (A.3).

A.1.2 Tectonic Events in Elis

As we will expand further in Excursion B, Western Greece and the Peloponnese belong to one of the most seismically active regions of the Mediterranean (Weiberg et al., 2016). The African plate subducts below the Eurasian plate here, in addition to the convergence of smaller plates including the Aegean Sea Plate, which results in a plethora of very active faults (Fountoulis and Mariolakos, 2008; Röbke, 2016). The fault system is rather complex, meaning that earthquakes can stem from any number of faults. Examples of the long term landscape impacts are discussed further in Excursion B, while we will here focus on the potential impacts of tectonic events, that is, earthquakes and associated tsunamis.

One of the most recent strong earthquake events occurred on 8 June 2008 with a magnitude of 6.3 (Kontopoulos and Koutsios, 2010). In the landscape, the impact of this particular earthquake remains visible in a 6 km long vertical displacement of up to 25 cm (Kontopoulos and Koutsios, 2010, and sources therein). This recent example gives an idea of the significant influence that individual events can have on the landscape in this region over time.

 

Figure 2. Ancient Olympia, situated at the banks of the Kladeos River. (Source: Wikimedia Commons)

 

Figure 3. An aerial view of the Alpehos and Kladeos Rivers as sediment transport pathways to Ancient Olympia, marked here by the Temple of Zeus. (Google Earth 2016, modified)

Earthquake events along the Kyparissiakos Gulf (east of Ancient Olympia) have not been infrequent throughout the Holocene (Reicherter, 2011). For example, the site of Ancient Olympia has experienced a number of significant earthquakes ever since the construction of buildings at the site (Reicherter, 2011). The most illustrative historical earthquake is documented from the 6th Century CE, which is credited for the destruction of the Temple of Zeus (see Figure 4), in addition to various other forces across the site of Ancient Olympia including landslides, flooding, and human destruction (Reicherter, 2011). Following or concurrent with destruction, the site was flooded, buried with sediment, and forgotten until 1829 CE (Reicherter, 2011).

A.1.3 Tsunami Hazards

In addition to the effects of the earthquake itself, earthquakes of such magnitudes can create tsunamis that can have equally or more catastrophic impacts on the landscape (Zapletan, 2013). Historically, around 160 tsunamis are estimated to have affected Greece and the surrounding areas in the last 3500 years (Papathoma et al., 2003; Zapletan, 2013). Among the strongest known earthquakes in the Mediterranean was one that occurred in Crete in 365 CE, with an estimated magnitude above 8.0, and tsunami heights (intensity class VI, see Table 1) estimated to reach up to 25 m (Papadopoulos et al., 2007). Table 1 gives an impression of the historical record of tsunami intensities and how frequently they have occurred in Greece.

In this light, recent work has attempted to model tsunami hazard under different scenarios in western Greece, including the Kyparissiakos Gulf (see Röbke, 2016). While a moderate tsunami would likely only inundate the coastal plain of the Gulf of Kyparissakos, Roebke (2016) shows how the Alfeios River valley functions as a pathway for tsunami flooding, especially during extreme tsunami events.

 

Figure 4. The ruins of the Temple of Zeus at Olympia, where the way the columns have fallen are consistent with destruction by a major tectonic event, likely in the 6th Century CE. (Photo: I. Unkel 2010)

 

Table 1. Tsunamis are not uncommon in Greece. Here, tsunami intensity (K0) of tsunamis in Greece and the respective wave heights, return periods and number of historically recorded events are shown (i.e. within the last 3500 years). Note that return periods correspond to a statistical average based on available data. (after Papathoma et al., 2003)

Tsunami intensity (K0) Wave height documented in and near Greece Return period in Greece (years) Number of events in Greece (historically recorded)
III + 1 m 4 55
IV + 5 m 26 25
V + 11 m 170 10
VI + 20 m 1100 2

The Gulf of Kyparissakos is particularly prone to tsunamis. Roebke et al. (2012) say “[the] Gulf of Kyparissa is located in the most tsunamigenic area of the entire Mediterranean, namely the west coast of Greece. According to (Schielein et al. (2007]: 164ff.) and (Soloviev et al. (2000]: 14)) there are 47 and 44 tsunami reports for this coastal area since 373 BC, respectively.” Hence, we should certainly consider the possibility of a particularly large tsunami reaching as far inland as the site of Ancient Olympia, but maintain a cautious perspective: “[i]mpressive as though may be, we must guard against privileging catastrophic events to explain major historical changes(Fouache and Pavlopoulos, 2010 citing Helly 1987).

A.2 Alfeios and Kladeos Rivers – A Tsunami Pathway?

GPS-Coordinates

Stop Nr. Name of the Stop Latitude Longitude
A-2 Alpheios-Kladeos River Junction 37,633083 21,626150

About 0.5 km to the south of the Temple of Zeus, lie the junction of Alfeios River and Kladeos River. Whether via tsunami or flood, the Alfeos River and Kladeos Rivers are the likely pathways via which the sediments that buried Ancient Olympia were transported. Here, one can observe the breadth of the floodplains in comparison to the relatively small streams seen today. For example, (Vött et al., 2011b) observe a distance of 200 m between the terraces on either side of the river, while the river itself reaches a current maximum width of 5-8 m and a maximum depth of 2-3 m (263). This suggests that some kind of powerful flood waters (either tsunami or fluvial) have occurred carving such wide valley.

Revisiting Figure 3 helps visualize how a tsunami could reach Ancient Olympia. Although the model considered today does not quite reach Olympia, it follows that a tsunami larger than that modeled for present day (i.e. the tsunami reported in the 6th Century, see section A.2.3) could have reached the site. Furthermore, (Vött, 2011) argues that the coastline was likely 8 km closer to Ancient Olympia than it is today, which could allow for further penetration of the tsunami flooding landwards to Ancient Olympia. A remaining question is even if tsunami flood waters reach the site, whether the depth of inundation and force behind the flooding would be enough to significantly impact the site. Still, the force of a potential tsunami arriving so far inland and how high the flood waters could have been could use further research. For example, a shallow inundation level at Olympia could bring marine sediment, but might not be such a significant contributing factor to the destruction of the site.

Overall, one should not rule out the possibility of such a large tsunami reaching and having destructive impacts on Ancient Olympia. Likewise, all of the possible scenarios responsible for burying Ancient Olympia under so much sediment should be considered. Increased erosion in surrounding areas, transportation via Kladeos and Alfeios Rivers and deposition at Olympia (e.g. Fouache and Pavlopoulos, 2010) as well as increased sedimentation from wet climate cycles (e.g. Fountoulis and Mavroulis, 2008) could also be responsible for such high sedimentation at Olympia. An additional possibility is the combination of these processes, which may have synergetic effects.

 

A.3 Kotychi Lagoon

GPS-Coordinates

Stop Nr. Name of the Stop Latitude Longitude
A-3 Kotychi Lagoon 38,005964 21,284947

On the coast between the towns of Lechaina and Varda, shortly off of the main coastal road between Amaliada and Patras, lies the Kotychi Lagoon. The lagoon is part of the Kotychi-Strophalia Wetlands National Park, which stretches about 30 km along the coastline of the Western Peloponnese. It is part of the European Union’s NATURA 2000 network of protected areas. Kotychi is the largest existing lagoon on the Peloponnese and is part of a critical habitat for many birds, wildlife and plants (e.g. the most extensive forest of stone pine, Pinus pinea, in Greece) (Kamberos, 2006). From an ecological integrity perspective, Kotychi has been evaluated in a moderate quality class, and there are suggestions for how to further improve the management (especially in the watershed) (Tziortzis et al., 2014).

Kotychi Lagoon has received considerable attention in research over the past few decades. In addition to reports on conservation management and ecological evaluations (e.g. Kamberos, 2006; Kardakari, 2006; Tziortzis et al., 2014), the lagoon development has been aim of sedimentological and geochemical investigations (Avramidis et al., 2008; Haenssler et al., 2014; Kontopoulos and Koutsios, 2010). Broader landscape development of the region of coastal Elis with relation to archaeological sites area is available (Kraft et al., 2005) in addition to tectonic activity studies with remote sensing techniques (Fountoulis et al., 2011). Meanwhile, more recent changes in Kotychi lagoon (i.e. within the last century) have been analyzed with GIS (Kalivas et al., 2003). A short description of the current lagoon (A.4.1) is followed by a summary of the lagoon’s development.

 

Figure 6. The coastline of Elis and the geological surface features, including Kotychi Lagoon and Prokopos Lagoon. Nearly the entire coastline from Cape Araxos to Cape Kyllini is a National Park or other significant natural area. Kotychi is the largest existing lagoon in the Peloponnese. (map based on E.Haenssler 2014 and Fountoulis et al. 2011)

A.3.1 Kotychi Lagoon Description

The lagoon spans over 3.5 km of coastline and is just over 1.5 km across at the widest point. It roughly has an orthogonal shape and sits in the north part of the Elis graben (Kontopoulos and Koutsios, 2010). A thorough and concise description of the lagoon comes from (Avramidis et al., 2008):

The lagoon is located along a wave dominated and microtidal coast. On the west side it is separated from the open sea by a low relief barrier island, and has limited communication with the open sea, with a stable, short and narrow inlet. On the landward lagoonal margins to the east, small scale deltas are prograded into the lagoon. Intertidal and supratidal mud flats are developed among deltas, covered with plants, e.g. Salicornía […]. Depths in lagoon decrease gradually with distance from the landward side of the barrier island to the inner lagoonal margins. (Avramidis et al., 2008), p.263)

Other important features of the lagoon include the average depth of 0.5 m, average surface temperatures from 10 °C to 27 °C in winter and summer respectively and a tidal range around 10-15 cm (Avramidis et al., 2008). At the inlet, the maximum depth is 2.5 m, where the tidal current reaches speeds of 10-30 cm/s, whereby the current speed in the lagoon itself is much slower at 0.5-1.0 cm/s (Avramidis et al., 2008; Bouzos and Kontopoulos, 1998). The surface sediment contains some clay and mud, but the vast majority (75%) of surface sediment of the lagoon is sandy mud (Bouzos and Kontopoulos, 1998; Kontopoulos and Koutsios, 2010). The lagoon sediments are largely supplied by the small rivers that feed into the lagoon: Vergas, Klimatsidi, Kapeleteikos, Pepa, Gouvos, Sykios and Trykokia; the largest discharges come from the Vergas and Trykokias, with 278 m3/sec and 108 m3/sec respectively (Avramidis et al., 2008). Sedimentation rate from 150 cal BP until today has been estimated at around 5.2 mm/yr (Kontopoulos and Koutsios, 2010).

As with many landscapes visited throughout this excursion guide, human activities have shaped the Kotychi Lagoon and the surrounding landscape. For example, the water level was significantly lowered from 1945 and 2000 (Kontopoulos and Koutsios, 2010). Human activities are attributed for this change, including intensified agriculture with irrigation and deforestation, which drastically influenced the environment of the Kotychi Lagoon region (Avramidis et al., 2008). Illustrative features of these impacts are artificial irrigation trenches that run parallel to the lagoon (Avramidis et al., 2008). Detailed explorations of human impacts can be found in Kalivas et al. (2003) as well as Kontopoulos & Koutsios (2010). Hence, human forces must not be forgotten when considering the most recent changes in the landscape.

 

Figure 7. Kotychi Lagoon, its tributaries and the dominant surface features immediately surrounding it. (map based on Haenssler et al. 2014 and Avramidis et al. 2008)

A.3.2 Lagoon Development – Holocene

In order to illustrate the development of the lagoon a number of studies have been performed. These studies include: recent grain-size spatiotemporal trend analysis of sediment surface samples (Avramidis et al., 2008); long-term grain-size, organic matter, carbonate and fossil analysis of two sediment cores (Kontopoulos and Koutsios, 2010); and, most recently, geochemical (X-ray fluorescence, XRF) analysis in addition to sedimentological changes over one of the previous and two additional sediment cores (Haenssler et al., 2014). In general, there are many correlations of the development of the Kotychi lagoon and the development of many lagoons across the Mediterranean associated with post-glacial sea level rise around 6500-5500 cal BP (Haenssler et al., 2014). Therefore, Kotychi Lagoon serves as a representative example of lagoon development for the larger Mediterranean region.

To begin, the lagoon is situated in the former prograded delta of the Palaeo-Pheneos River starting around 7000 cal BP. Since this point in time, Kontopoulos and Koutsios (2010) identify three distinct phases of coastal development:

  1. 7000 to 3810 cal BP was a period of static coastline where lagoon sedimentation kept pace with sea level rise;
  2. 3810 to 1400 cal BP, an increased level of sedimentation with predominantly fluvial sediments that show transition from marginal to fully terrestrial sediments, likely due to progradation of the Pheneos River delta
  3. 1400 cal BP to present, migration of the coastline landward and the re-establishment of lagoon sedimentation patterns, likely related to the change of the Peneus river course.

However, (Haenssler et al., 2014) were able to take a sediment core up to 10 m in depth, such that they were able to see the sedimentation before the existence of the lagoon and add a fourth stage of landscape development. Moreover, the XRF scanning techniques (see excursion D for more details) and location of the previous core in a river channel that causes an erosion gap (Kontopoulos and Koutsios, 2010) yielded different dates and interpretations in the more recent publication (Haenssler et al., 2014). They propose four stages of coastal development:

  1. 8500 to 8000 cal BP the area was dominated by marine conditions;
  2. 8000 to 6300 cal BP, a progradation of the coastline into the sea created the conditions for the lagoon to develop with a transition from marine sediments to increasing proportions of terrestrial sediment;
  3. 6300 to 5200 cal BP is the first marked period of lagoon conditions dominated by silt and terrestrial sediments;
  4. 5200 cal BP to present is a period of geomorphological instability that oscillates between marine and terrestrial sediment dominance.

An example of the instability in the last period is influenced first by post-glacial sea level rise (see Excursion B) followed by increasing influence of local and regional processes such as human-exacerbated erosion (Haenssler et al., 2014).

 

Table 2 provides a summary of these stages, the driving mechanisms, and the proxies used to interpret the coastal development at Kotychi Lagoon according to Haenssler et al. (2014).

Stage Proxy evidence Palaeoenvironmental Interpretation Driving machanism
4 Oscillating proxy profils Phase of geomorphological instability indicated by a rapid succession of marine, lagoonal and marginal environments Influence of post glacial sea level rise is influenced by local and regional processes (climate, sediment supply, topography, bathymetry, wave regime…)
3 Marine proxies: low, Silty sediments, brownish, mottled Second, pronounced period of lagoon/barrier formation, shallow lagoon in the back barrier environment, temporal termination of waterlogging Mid-Holocene cessation of sea level rise
2 Lower part: clayey sediments rich in OC and terrestrial proxies, high CN, greyish sediments partly laminated. Upper part: coarse, homogeneous layers enriched in carbonate and marine proxies increase First episode of barrier/lagoon formation and subsequent barrier breaching -> reestablishment of marine conditions First, short-lived episode of a deceleration of sea level rise
1 Coarse greyish sediments; Marine/carbonate proxies: high; OC: low Marine phase Controlled by post glacial sea level rise

A.4 Prokopos Lagoon

GPS-Coordinates

Stop Nr. Name of the Stop Latitude Longitude
A-4 Prokopos Lagoon 38,151817 21,385347
A-5 Mycenean Fortress (Teichos Dymaion)* 38,156336 21,403028

Prokopos Lagoon has not been as intensively researched as Kotychi, but is just as important for habitat. Prokopos Lagoon is situated further north adjecent to Cape Araxos and is smaller, at about 150 ha in total area (Tziortzis et al., 2014). It is located behind a wide dune ridge and is connected to the Ionian Sea via a narrow channel of 2300 m length (Tziortzis et al., 2014). The Prokopos Lagoon experiences frequent and significant changes in conditions such as water level and salinity, providing dynamic habitat conditions throughout the year (Ioannidis and Mebert, 2011). Like Kotychi Lagoon, Prokopos Lagoon serves as darming site for local fishermen (Christia et al., 2014), but impacts are lower than in Kotychi (Tziortzis et al., 2014). Even though brackish, Prokopos receives more significant contributions of freshwater tha Kotychi, resulting in lower salinity values overall (Tziortzis et al., 2014). The overall ecological quality of Prokopos lagoon is in the “good quality” class (Tziortzis et al., 2014).

 

style="width:5.0%" /> More information on the Kotychi-Strophylia National Park: External Link

 


References

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