Reply to comments by E. Galili et al. on “Holocene tsunami's from Mount Etna and the fate of Israeli Neolithic communities”


1. Introduction

[1] In the early Holocene a devastating tsunami flooded the coasts of the Eastern Mediterranean Sea [Pareschi et al., 2006b, 2006c, 2007, 2008]. This tsunami was triggered by a landslide from the eastern flanks of the Mt. Etna volcano (Sicily, Italy). There is unquestionable evidence of the inland-offshore tsunami-triggering landslide event: (1) the Valle del Bove, a scar tens of square kilometres wide on the volcano eastern slopes, (2) inland landslide deposits (the Milo and Chiancone units, the latter protruding from the previous coastline), and (3) offshore landslide deposits [Pareschi et al., 2006a]. However, it is difficult to assess the age of a landslide from its debris, because they are reworked material. The inland Chiancone landslide deposit is covered by debris and hyperconcentrated flow deposits emplaced after the main volcano collapse; a sample from one of these layers dates back to 7.59 ± .13 cal. kyr B.P. A reworked soil material at the base of the Milo Unit is dated to 8.15–8.38 cal. kyr B.P., whereas the youngest upper lithofacies of this unit are dated to 5.3 cal. kyr B.P. [Calvari and Groppelli, 1996; Calvari et al., 1998]. Overall, the ages of the sporadic deeper inland landslide deposits on Mt. Etna seem compatible with the abandonment of Atlit-Yam, occurred around 8.3 cal. kyr. B.P [Galili et al., 2005], as supported by the drastic decrease of later-dated findings. Indeed, the few younger (plant) finds of the Israeli Neolithic village [Galili et al., 2008] could be due to “bioturbation”, and in any case their age matches 8.3 cal. kyr. B.P. within a 2σ14C dating error.

2. Archaeological and Geological Considerations

[2] In their comment, Galili et al. [2008] advance some doubts about the impact of Mt. Etna tsunami on the Neolithic village of Atlit-Yam, today sited at −10 m b.s.l. Their doubts are based on archaeological interpretations. Our answers are below listed:

[3] 1. At the Levantine shelves, simulations [Pareschi et al., 2006c, 2008] suggest that the amplitude of Mt. Etna tsunami waves was in places smaller than that of many tsunami waves linked to seismically-triggered offshore slumps along the Israeli coasts, the tsunami deposit evidences of which are almost everywhere lacking [Zviely et al., 2006; Salamon et al., 2007]. In other words at Atlit-Yam it is reasonable to find field evidences of the early Holocene Mt.Etna tsunami, because of the clay embedding matrix, but not a “perfectly preserved continuum” tsunami deposit on account of the site's high exposure to atmospheric-marine agents, including a shelf exposure.

[4] The main points contrasting the use of water well n.11 as a garbage pit are discussed by Pareschi et al. [2007]. In addition here we remark that there is no chronological order in the findings from the well: some younger findings were located deeper than older ones, with depths differing by a few meters [Galili et al., 2002, 2005]. For finding dates in the well, Galili et al. [2002] report: (1) waterlogged wood, at well depth (i.e. depth of archaeological layer under the sea bottom) 2.9–3.1 m, uncalibrated date: 7300 ± 120 B.P.; (2) waterlogged tree branch, at well depth 1.9–2.3 m, uncalibrated date: 7460 ± 55 B.P.; (3) waterlogged tree branch, at well depth 2.3–2.9 m, uncalibrated date: 7605 ± 55 B.P.; and (4) waterlogged tree branch, at well depth 3.5–4 m, uncalibrated date: 7465 ± 50 B.P.

[5] Some stones-pebbles scattered in the fine matrix suggest a bimodal distribution, characteristic of tsunami deposits; indeed tsunami currents are able to transport and pick up large objects. Galili et al. [2008, 2005, 1993] attribute the matrix infilling of the well to possible recurrent flooding by the neighbouring Nahal Oren Stream. However, these hypothesized floods do not explain the shallow marine fauna (foraminifera and molluscs) in the well. Moreover, it is not clear how a village could survive repeated devastating floods from the neighbouring Nahal Oren Stream, which would have had to have been strong enough to reach the well and overturn its 1.5 m high walls. In addition, the well is sited on the opposite slopes of the inter-kurkar trough to the stream, and a few meters above the stream-level.

[6] 2. Galili et al. question about the possibility of some standing stones of Atlit-Yam to survive a tsunami. We argue the 1.5 m high standing stones in Structure n.56 and the upper stone structure of Water well n.11 were able to survive a flowing around-inside tsunami, impacting them some hundred meters from the coastline, because these features were also able to survive: (1) in the surf zone of a rising sea and (2) in the Galili et al. hypothesized scenario, to devastating floods from the neighbouring Nahal Oren Stream. Tsunami scours may have been cancelled by aeolian or rain agents or erased by the rising sea.

[7] 3. Some additional considerations supporting a rapid abandonment of the Neolithic village are listed in the following. Galili et al. observe that no injuries, supporting a tsunami impact, affect human bones. However human findings are scattered all around the village, some of them in strange arrangements/locations as in the water well, around the fishes of Locus 10A, sometimes with a living floor detectable below, or semi-embedded in the clay as the semi-skull of Homo VI [Hershkovitz and Galili, 1990, Figure 6]. The right half of this skull, buried in the clay, was found intact, whereas the other half is missing, suggesting that only the part of the find embedded in the fine clayed tsunami deposit was preserved. A “polished” surface on the same hemi-skull can be ascribed to impacting/scraping of the cranial find by a flux of particles [Hershkovitz and Galili, 1990] transported by Mt. Etna tsunami, we add.

[8] Local combustion, locally potentially affecting some human bones near plant matter, embedded in the tsunami deposit also explains the thousands of thermally fractured clayed pebbles dispersed throughout the pre-pottery village and into the well.

[9] Galili et al. [2008] provide no satisfactory explanation for the unique assemblage of wheat seeds and guttered fishes ready for consumption or trade of Locus 10A [Zohar et al., 2001]. Prehistoric finds in other sites refer only to small seed accumulations in arid conditions. Because fishes encapsulate the cereal lens, it contradicts the hypothesis by Galili et al. [2008] of accumulation of these findings “over a long period of time”. A “casual” accumulation was also rejected by Zohar et al. [2001]. We interpret the assemblage as a vortex of tsunami debris which developed in the tsunami flow; the debris was at first “captured” by a local topographic “roughness” (a fire hearth) and soon after deposited on a topographic slope. In their paper, Galili et al. report date of the seeds (8,340 ± 80 cal. yr B.P.), but not of the fishes; in any case the reservoir effects on 14C dating of marine animals (and of men/terrestrial animals who use them as food) are known. A trampling floor does not occur above the fishes-cereal concentration; but, on the contrary, the position of a contiguous hearth suggests a village trampling floor below that seed-fishes assemblage.

[10] In the village, a few meters SE of structure n.10, a 2–5 m2 platform made of clay bricks covers a dense layer of unidentified, ancient plant fiber [Galili et al., 1993]. Again, this assemblage (buried in a clay matrix) suggests a sudden impact and tsunami devastation.

[11] 4. Schlichting and Peterson [2006] observe that coastal tsunami deposits have a broadly regional correlation. Dark clay deposits with marine fauna, today 5 ÷ 7 m below sea level, occur as a narrow strip in the eastern part of the Zevulun Plain, near the present course of the Qishon River, few kilometres apart from its estuary at Haifa [Zviely et al., 2006]. Moreover they overlay early Holocene grey clays dated to ∼10,000 cal. yr B.P. It is possible that such deposits are tsunamigenetic ones, because it is well known that tsunamis funnel for kilometres into rivers and fiords, as simulated and in-field detected in Norway by Bondevik et al. [2005], for the almost coeval to Mt. Etna-collapse Storegga slide.

[12] 5. Pareschi et al. [2006c] suggest that Mt. Etna tsunami occurred after the deposition of Sapropel S1a. In the literature, such a period, corresponding to S1 Sapropel interruption in the Eastern Mediterranean Basin [Mercone et al., 2000], was characterized by a colder environment, with saltier Eastern Mediterranean upper waters and possibly less rains and less freshwater supply from the Atlantic [Myers et al., 1998; Myers and Rohling, 2000; De Rijk et al., 1999]. In any case, cold-dry environmental conditions contrast the following two hypotheses by Galili et al.: (1) the reconstruction of an ultimately too fast sea level rise, about 2 cm/yr [Galili and Nir, 1993; Nir, 1997], based on the infill of the water wells of Atlit-Yam and Crusader (Israeli coast), just emplaced during cold-dry weather conditions. On the contrary, in our scenario, the infill of those wells consist almost all of tsunami deposits. (2) Multiple floods from the Nahal Oren Stream, possible source-trigger of the fine matrix infill of water well n.11 [Galili and Nir, 1993; Galili et al., 2002, 2008]. Such floods seem improbable given that they would have occurred during a drier-colder period, corresponding to the S1 Sapropel interruption.

[13] Core MD90-9502 from the Levantine Basin (Eastern Mediterranean), located about 100 km offshore from the Lebanon coasts, shows re-deposition of Sapropel material inside the S1 Sapropel unit, compatible with Mt. Etna tsunami date. Such re-deposition, outlined but not discussed by Mercone et al. [2000], can be explained by bottom sediment reworking/transport by tsunami waves.

3. Conclusions

[14] As a conclusion, we outline the role of numerical simulations. I.e. landslide deposits detected offshore from Mt. Etna support a volume of debris at least ∼20 km3 sized [Pareschi et al., 2006a, 2006c]. Simulations of such a landslide, entering the Ionian Sea with average velocities 50–15 m/s, support tsunami waves able to liquefy soft sediments on the Ionian marine slopes (on account of tsunami overpressure), and trigger sediment flows if marine sediment cohesion is of a few kPa [Pareschi et al., 2006c, 2008]. In the Levantine Basin, the deepening South-to North bathymetry of the Eastern Mediterranean bents a fraction of tsunami front toward the Carmel coast of Israel. The ∼120° (to the North) angle of impact allows Mt. Etna tsunami to funnel into the trough between two ridges, bordering the Neolithic village of Atlit-Yam in early Holocene. At that time the western ridge was semi-submerged some hundreds of meters to the north of the settlement. Further simulations in a paleo-environment of just those waves coming from Mt. Etna are shown to be able to reach Atlit-Yam and its structures from the north-west, some hundreds of meters inland [Pareschi et al., 2007].

[15] In future work we will show how Mt. Etna tsunami interacted with Sapropel S1 and the evidences of such interaction.