The volcanic eruption of Thera and its effect on the Mycenaean and Minoan civilizations

Journal qf’Archaeologica1

Science 1985, 12,9-24

The Volcanic Eruption of Thera and its Effect on the Mycenaean and Minoan Civilizations I. G. Nixona (Received

5 June

1980,

accepted

16 July

1984)

Since Professor Sp. Marinatos linked the eruption of Thera with the destruction of Cretan sites, difficulties have been met in reconciling the dates of the two incidents which, based on pottery, were c. 1520 BC and 1450 BC, respectively, giving a “time gap” of 70 years. None of the mechanisms proposed for the Cretan site destructionstsunamis, ash fallout, earthquakes, civil disturbances or invasion can be reconciled with the magnitude of the simultaneous site destructions. Therefore, an alternative theory is proposed that the Cretan holocaust was caused by “nukes ardentes” emanating from Thera. It is postulated that these were releasedthrough a “split” in the cone wall, of limited area, generating a high velocity jet of tephra fluidized in a red hot gas stream. Such ajet is immensely destructive and lethal, causing death by pulmonary oedema. The shape (like a blowtorch) and course of the ash fallout, as measured by deep seacores, shows that these n&es ardentes passed over the eastern part of Crete, causing severe destruction and depopulation. The geological record confirms that tephra deposits from such PelCan eruptions have travelled for 160km, or more, and that normally the ma% eruption is preceded by a preliminary one of lesserintensity, with a time gap ranging from 51 to 203 years. Settlements on or at the base of the volcano would have been abandoned at the time of the preliminary eruption/earthquakes (c. 1520BC). A time gap of 70 yearswould be reasonable, fitting with the Cretan catastrophe around 1450 BC. In the meantime, reoccupation had commenced, but was terminated by the final eruption. Apparently, Knossos on the periphery of the blast was severely damaged by fire (possibly again in LMII) and rebuilt, being finally destroyed in late LM IIIB. During this time span some “blurring” of pottery dating may be attributed to recovery and use of pottery “heirlooms”. The nuee ardente theory explains the simultaneous destruction of sites by fire and blast, the Cretan depopulation, aswell asthe time gap. In general 14Cresultsconfirm the dates proposed. So far tephra deposits have not been identified on Crete itself, but grains of it have been found at Pyrgos. It is suggestedthat cores from lake bottoms should be examined for the area, and that Cretan soil samples should be checked for tephra particles by employing the flotation technique, used in mining, for separating them. THERA, CRETAN DESTRUCTION, TSUNAMIS, EARTHQUAKE, NUEE ARDENTE, ASH FALLOUT, ASH FLUIDIZATION, AGGLOMERATION, IGNIMBRITE, DEPOPULATION, BLAST EFFECTS, PYRGOS, CRETAN RESETTLEMENT, CHANIA, THERAN CHRONOLOGY, ERUPTION STAGES, KNOSSOS DESTRUCTION, i“C DATING, TEPHRA CORES, FLOTATION.

Keywords:

Introduction It is now generally agreed that the Plinian eruption of the volcanic island of Thera, in the 2nd millenium BC, must have had the most profound consequences. Marinatos (1939) provides an example of studies on the effects of the eruption on the island of Crete. “ler. Stock Switzerland.

Ost

“Matterhorngruss”

Steinmattstrasse,

3920

Zermatt,

Valais,

9 0305-4403/85/010009

+ 16 $03.00/O

@ 1985 Academic

Press Inc. (London)

Limited

10

1. G. NIXON

Pomerance (1970) takes the wider view that the resulting destruction could have even reached Egypt and the Greek mainland.Renfrew (1979) has made a valuable up-to-date summary. Although there is almost complete unanimity that this explosive eruption or eruptions, led to the destruction of many of the Cretan cities at that time, there is considerable deviation in the views expressed regarding its cause. Opinions vary from destruction by earthquakes, by tsunamis (incorrectly called tidal waves), by shock waves from the explosion, or by wind-borne volcanic dust (Page, 1970). More than one of these causes could have contributed to the widespread havoc. Tsunamis must have been generated by a massive eruption, followed by the collapse of the cone into a caldera, as discussed by Pomerance (1970). Bullard (1976) points out that the tsunami from Krakatoa reached heights of up to 120 ft in protected baysif the eruption of Thera was much larger than Krakatoa (which appears to be the case), then the tsunamis generated would have been larger. Further, their size is governed by the depth of the water, which between Thera and Crete is much greater than that surrounding Java (F. M. Bullard, pers. comm. 1979). Those from Thera are not likely to have penetrated far inland in mountainous Crete due to the dissipation of the kinetic energy of the waves on the shore. Hence destruction would probably have been mainly restricted to coastal settlements such as Amnisos on the northern coast of Crete (Page, 1970). Inland, cities such as Knossos or Phaistos on elevated sites are not likely to have been reached by tsunamis, so that damage there must be attributed to other causes. Moreover, tsunamis travel in straight lines so that sites on the east or south coast of Crete would be protected by Cape Sideto, and only subjected to the force of reflected secondary tsunamis. Considering Crete in isolation, the most striking feature is that virtually all of the sites for which evidence is available from excavations, were destroyed by fire-a feature stressed by Page (1970). Moreover, it seems too much of a coincidence that fires started by earthquakes would destroy all the Cretan cities listed by Page (1970: 8) and it has been suggested that these cities may have been sacked and burnt by invaders, or destroyed as a result of internal disorders following the initial destruction caused by the Theran eruption (Lute, 1969). However, it would be unlikely that an invader would fire all the settlements, nor would mobs of local rioters, when it was to their advantage to retain them intact (Page: 1970). This thesis is supported by both the archaeological record and tradition which show that there was a large influx of Myenaeans, and later Dorians, who came from the mainland to settle. Indeed, the palace at Zakro, also destroyed by fire, was apparently buried under the ash fall from the Theran eruption, and in this case neither invasion nor local uprisings can have been responsible. If the devastated coastal settlements in Crete, were overwhelmed by tsunamis, how could the water soaked ruins have been fired at that time? As stated by Page (1970: 41) if the tsunamis came after the fire, for example at Gournia, “. . . there would not have been any little heaps of charcoal or plaster left in situ for the excavators to find”. None of the explanations put forward give an entirely satisfactory interpretation of the recorded facts, fitting all cases (Sparks, 1978). It appears that there is room for an alternative basic explanation for the destruction of these Cretan sites. Reassessment of the evidence has led to the hypothesis that the devastation in the eastern half of Crete could have been caused by nukes ardentes emanating from a Theran eruption. A nuee ardente is a special form of PelCan eruption, in which the ash (or “tephra”) is fluidized in the escaping volcanic gases and ejected at high velocity from the volcano (Bullard, 1962). The phenomenon of fluidization is well known, the particles being dispersed in a stream of gas in a uniform manner so that the mixture behaves, and flows, as a fluid. Fluidized catalysts are used, for example, in catalytic crackers in the

THERA’S Table

ERUPTION

1. Distances

travelled

AND

CRETAN

11

DESTRUCTION

by nudes ardentes Distance

Geological record Eruption of Mount Pelee Eruption of Krakatoa Southwestern U.S.A. (Utah) Crater Lake (western U.S.A.) Mount St Helens Deep sea cores ex Thera Vema core V.10.50 Vema core V.10.58 Vema core V. 10.52 Distance to Cretan sites Thera to Mallia Thcra to Knossos Thera to Zakro

travelled

lo+ 70+ 160+

56+ 40+

(km)

Over

sea or land

Land then sea Sea then land Land only Land only Land only

157 116 268

Sea only Sea only Sea only

122 128 164

Sea then land Sea then land Sea then land

petroleum refining industry. A fluidized nuee ardente has more kinetic energy due to its solids content, and geological records show that they can travel very long distances before their energy is dissipated (Table 1). Gaseous expansion as the nuke ardente is formed has a cooling effect, so that the resulting porous tephra is reduced below its softening point, so particles do not stick together. If the temperature is too high, or the pressure is low, the particles can agglomerate together, fluidization ceases, and the ash is deposited as ignimbrite (or welded tuft). The unusual pattern of the ash fallout from the Theran eruption, which had an elliptical shape with a relatively long axis like a “blowtorch” flame, differed from the more normal fan-like pattern, and indicated that the nuees ardentes had been ejected at high velocity through an orifice of relatively small area. If the theory that the Cretan destruction was caused by nuees ardentes coming from Thera is to be accepted, it is necessary to establish five points: (1) explanation of the time gap between the abandonment of Akrotiri (c. 1520 BC) in Thera, and the destruction of the Cretan sites (c. 1450 BC); (2) n&es ardentes at Thera; demonstration that they did occur; (3) ash fallout pattern and extent of travel-to show that this covered the eastern part of Crete ; (4) distance of travel-to establish that a ride ardente should be capable of covering the distances between Thera and the Cretan sites; (5) archaeological record-to establish that this can be correlated with the effects of a nuee ardente passing over these sites. The Time Gap

The recent Proceedings of the Second International Scientific Congress (Popham, 1979; Magnusson, 1979) reached the opinion that Thera could not have been responsible for the Minoan collapse because of the c. 50 year time gap, indicated by pottery dating, between the destruction of Akrotiri and the Minoan collapse, i.e. the eruption at Thera could not have been spread over 50 years. However, comparison of cases of known PelCan eruptions (cf. Table 2) specifically those including nutes ardentes, shows that “normally” such major eruptions are preceded by a much milder one, associated with earthquakes, to give a 51-203 year time gap between the two eruptions, averaging 115 years.

12

1. G. NIXON

Such a milder eruption, accompanied by the usual earthquakes, would have led to the evacuationofThera, and the settlement ofAkrotiri. Thus the time gap can be accounted for as a normal phenomenon and there is no need to attempt to explain it as having occurred as an interruption of the final explosive eruption. Nukes Ardentes at Thera

A description of PeEan eruptions has been given by Bullard, and more details of nukes ardentes by Macdonald (Bullard, 1962). These eruptions are caused by the vent of the volcano becoming plugged by a stopper of solidified lava. The internal pressure within the magma chamber builds up until it approaches that of the rock strata, deep in the earth, from which the molten magma originates, and ultimately the cone wall fails suddenly at its weakest point. The resulting PelCan explosion releases an enormous amount of energy, almost momentarily, comparable with that of a hydrogen born& the recent relatively small eruption at Mt St. Helens had an energy release equivalent to 50 x lo6 tons of TNT, or about 2500 of the Hiroshima type atomic bombs (The Columbian, 1980). The energy release at Thera would have been many times greater. The lava magma is saturated with gas, largely water vapour, at very high pressure, together with noxious gases such as hydrogen sulphide and fluorine compounds. Consequently its explosisve decompression, on ejection at the point of failure, forms a foam, which breaks up into tiny particles of high porosity, solidifying as they cool, termed tephra, which are fragmented and fluidized in the escaping gas stream. This explosion empties the magma chamber in a short time, the vent can then plug again and the cycle be repeated several times. Usually the explosive discharges follow one another at short intervals, extending over several days, but longer intervals can elapse between the cycles (Bullard, 1962). These PelCan explosive eruptions can be classified as vertical, horizontal-high velocity and horizontal-lower velocity. (1) Vertical (e.g. Krakatoa, 1882): the stopper of solidified lava is eroded by molten magma and blown out explosively. The tephra is ejected vertically and carried as a cloud by the wind, spreading laterally as it goes. The tephra fallout has a typical fan shaped pattern, the amount decreasing as the distance from the axis of the fan increases, with some segregation in particle size as the distance from the source increases (Ninkovitch & Heezen, 1965). (2) Horizontal-high velocity (e.g. Thera c. 1450 BC, Mount St. Helens, 1980): the wall of the cone splits under the mounting pressure, and the tephra/gas is ejected horizontally as a high velocity fluidized jet, termed a nute ardente, capable of travelling long distances. This ash fallout pattern is typical, having the shape of a blow torch flame, and little classification (or “fractionation”) takes place as it is fluidized in the jet (Figure 1). (3) Horizontal-lower velocity (e.g. Mount PelCe, 1902) : a milder form of nuke ardente consists in a “boiling over” of the magma, running down the slope of the cone in fluidized form. This can occur through a notch, or split (Bullard, 1962) in the rim of the cone, as at Mount Pelke, and can result in deposits of ignimbrite. Until recently the best documented examples were those of Mount PelCe and Krakatoa, and it was on this basis that the Theran nuke ardente theory was postulated. The recent eruption of Mount St Helens (1980) has provided additional f&t hand information incorporated here (Tables 1, 2). At Mount St Helens failure of the cone wall was observed and measured. A blister was formed in the wall, measuring 0.97 km vertically and 3.22km in a circumferential direction, which expanded at the rate of 1’50m a day for a period of 10 days in radial direction. At the point of failure-the observer was killed at his post-the blister on the north wall was blasted away

THERA’S

ERUPTION

AND

CRETAN

13

DESTRUCTION

400

.,I

b---l s

350

xx54

55

AFRICA

3o”

I 25O

I 200

150

E6gure 1. Distribution Pleistocene sediments 1965 : figure 162).

Date

Krakatoa (East Indies) Mount Pelee (Martinique) La Soufritre (St Vincent) Mount St Helens (Washington, U.S.A.) Proposed dates for Thera eruption (2nd millenium BC)

300

pattern of the upper tephra layer (n = 1.509) in postin the eastern Mediterranean. (after Ninkovitch & Heezen,

Table 2. Time gap between

Location

I 3o”

and main Plinian

of eruption

Preliminary AD 1680 (a) AD 1792 (b) AD 1851 AD 1812 AD 1857

1520 BC

preliminary

Main AD AD AD AD AD

1883 1902 1902 1902 1980

1450 BC

eruptions

Duration (days)

Gap Wars)

98

203

114 120

110 51 90

123

70

instantaneously forming a nuee ardente, which rolled down the north flank for about 3 h, and was closely followed by a Pelean vertical ejection. as the roof fell in. This blew ash vertically over 18-29 km towards the stratosphere, and excellent photographs of these stages were automatically recorded. (The Columbian, 1980; The Sunday Times, 1980). This confirmed that the Theran eruption resulted in a number of nukes ardentes, as can be deduced from the blowtorch shape of the ash fallout, of high velocity capable of travelling long distances. Bullard (1976: 99) has confirmed that there is direct evidence from Thera that nuee ardente emissions occurred during the eruption: “. . . the well developed columnarjointing . . . on some ofthe ash. . indicates that some ofthe material

14

1. G. NIXON

was ejected as pumice flows in nuee ardente eruptions”, and adds that the columnar jointing indicated that the material was “hot” and part of a single cooling unit, resulting in columnar jointing which is characteristic of such deposits. Samples of the deep sea cores taken by Ninkovitch & Heezen (1965) prove that the relevant portion was derived from Thera as the refractive index of the tephra was in agreement with that deposited on Thera itself and the pattern of deep sea cores blanketing the area including the eastern part of Crete (Figure 1). No actual tephra deposits have been located in Crete, but Cadogan (1978) has reported traces of sherds in samples ofdebris taken from a house at Pyrgos burnt down or destroyed in Late Minoan IB. These sherds, presumably from tephra, had a refractive index of n = 1.509, identical with a reference sample from Akrotiri (Cadogan et al., 1972). Ash Fallout Pattern and Extent of Travel

Reports of deposits on land, or vessels at sea, and more recently cores taken from the ocean bed have established the ash fallout pattern and the extent of travel. The pattern is determined by the type of Pelean eruption involved, all three can take place successively, so that a fan shaped pattern can be superimposed on an existing blow-torch one, or vice versa. Failures of the cone walls tend to follow the fault lines. For example, at Mount PalCe vertical and lateral blasts occurred almost simultaneously, and it was the latter which obliterated St Pierre (Bullard, 1962). At Krakatoa several nukes ardentes, probably from a split along the northwest fault lines, distorted the fan-shaped fallout pattern in that direction, as shown in Figure 2(a), where the latter is drawn symmetrically about the line starting at the point of origin and following the direction of the blast. A notional area covered by nukes ardentes on the slopes of Mount Rajah Bassa, which followed the direction of the fault lines (5o”N) from Krakatoa (Ninkovitch & Heezen, 1965) is shown in Figure 2(b), this ash fallout is indicated in the northern area of the distorted fan shaped pattern showing the windborne ash derived from the nukes ardentes (carried upwards from them by convection currents) superimposed on the normal fan shaped pattern of the fallout from the main vertical blasts (Figure 2). A similar phenomenon is noted for the Theran eruption, where the axis of the fallout pattern, and that of the fault lines concerned, are on a bearing from Thera of 40”s and an average of 41” (range 25-58) respectively (Figure 1). The direction and the distance travelled from Thera, of these postulated nukes ardentes would have blanketed the eastern part of Crete. This specific information (Figure 1) for the ash fallout from Thera, is reinforced by the geological record of eruptions (see below) which record nute ardente ash flows of up to 160 km. Another important feature of nukes ardentes is terminal fallout. This can be appreciated by observing the fallout of spray from a garden hose equipped with a high velocity jet. The jet travels as particles of water fluidized by entrained air. As the energy is dissipated by friction and gravitational pull, the jet reaches a terminal velocity, at which the bulk of the spray falls-out over a relatively restricted area, a similar result would be shown by a military flame thrower. The same considerations would apply to a truly fluidized nuee ardente and can be detected in sections from deep sea cores, derived from the eruption of Thera in the 2nd millenium BC, as measured by Ninkovitch & Heezen (1965) and supplemented by Watkins (1978). These measurements were taken during the voyages of the Vema and Trident, respectively. The Vema core No. V-1&50 showed a 212 cm thickness of tephra at a distance of 157 km from Thera, while No. V-l& 58 had a thickness of 78 cm at 116 km, all the other cores, taken at greater or lesser distances from the source, had much smaller tephra thicknesses (1.54 cm) (Ninkovitch & Heezen, 1965). Two tephra layers attributable to Thera were detected, layers below

THERA’S

I

(b)

ERUPTION

AND

CRETAN

DESTRUCTION

I SUMATRA

JA”+EA ,

/

.

Thousand ‘.: - lslonds ,’

Figure 2. (a) Limits of the volcanic ash and the noise of the explosion in the 1883 eruption of Krakatoa. a, indicates ash fallout from nuees ardentes (after Bullard 1962: figure 8). (b) Krakatoa and adjacent coasts showing probable area (shaded) covered by the northeastern n&es ardentes (eruptions of 27 August 1883) (after Page 1970: figure 11).

having been derived from a much earlier eruption. The Trident cores confirmed in general the earlier Vema cores, but indicated that fallout on Crete itself had been less than originally thought. Calculations, including an estimate for tephra dispersal due to bioturbation, but with no allowance for compactation of freshly fallen tephra, gave isopachs showing a fallout of about 5 cm on the eastern tip of Crete and 1.5cm at Knossos (Figure 4). The Trident cores included three which indicated terminal fallout (Nos. 26, 25 and 9) with

16

I. G.

NIXON

36O

c- -O;flv‘\ \ io’, oo, ‘-;:;, (------’ _: I /

- -. 150cj~o I Contour interval 11 24O

.

I 25’=

‘, .-_-.

// 200

I L-x ,‘

/

J

km ’

500m I 26O

I 27O

I 280

I 290

I(

1 300

I

310

Figure 3. Isopach maps of Minoan tephra cores in eastern Mediterranean, including cores from R/V Trident cruises 171/172 (17 September to 3 October 1975). Measured thickness (cm) shown in boxes and core number in italics. Curve .B-B shows region of maximum terminal fallout (core VI O-S&) and A-A and C-C the limits indicated for terminal fallout (hatched band). A Verma core 10; n , Trident core 171; l Trident core 172 (after Watkins et al., 1978; figure la).

thicknesses of 12, 26 and 25cm, respectively, making a total of five cores, indicating terminal fallout, including the VCWI~cores. Their actual measured thicknesses, together with all other cores, is shown in Figure 4. As would be expected for terminal ash fallout from a nuke ardente the thickness tapers off on either side of the central line of the band (prescribed by the Vera cores) drawn at a radius of 160 km with Thera as the locus. Because the tephra is fluidized in the superheated gas stream, only limited fractionation or classification of the ash particles takes place during travel. Data for Vema core 50, after travelling 157 km still showed grain size distribution for the fine ash: 1>20% of 0.25 mm, and 4550% of 0.125 mm (Ninkovitch & Heezen, 1965). The median grain size for cores 58, 50 and 52 with paths of travel from Thera ranging from 145 to 280km showed little variation with distance travelled, the two extremes (58 and 52) having virtually the same median grain size. Hot air convection currents can carry tephra particles high into the atmosphere, where they will be transported by the prevailing wind to give a secondary wind-borne ash fallout pattern superimposed on that of the nuee ardente, and extending beyond its periphery. This can be seen by the fallout pattern from the eruption of Krakatoa (Figure 2) although in this case the secondary wind-borne pattern is derived from the vertical Pelean blasts. Distance Travelled and the Geological Record

In addition to the actual record of the ash fallout from Thera shown by the deep sea cores, there is also the geological record of distances actually travelled by nuees

THERA’S

ERUPTION

AND

CRETAN

DESTRUCTION

17

ardentes (Table 1). Generally a nuee ardente could travel the distances of for instance 110-160 km and could thus account for the devastation in eastern Crete. Not many actual nuee ardente eruptions have been described in detail, because of their catastrophic nature. As well as the best authenticated cases (Mount St Helens, Mount PelCe and Krakatoa) others have been described from La Soufriere, St Vincent (Bullard, 1962) and a typical n&e ardente from Mount Pelee has been observed and photographed by scientists 2 months after the main eruption. The narrow front of the “blowtorch” and the rising clouds of ash, from the nuke ardente proper, were carried upwards by convection currents into the upper atmosphere. The latter are generated by the heat radiated from the surface of the jet which heats the sea and air above it which becomes saturated with water vapour. The nuee ardente was probably “cushioned” by the expanding mixture of air-steam generated, on the principle of the Hovercraft, thus prolonging the distance travelled compared with that over land. Important factors contributing to the distance travelled are: the pressure in the magma chamber, size and shape of the orifice through which the lava is ejected, the rate at which the fracture spreads and the size of the resevoir. All these contribute to the magnitude of the energy released and its duration. For example, the recent eruption of Mount St Helens (1980) showed a path of travel of about 40 km for the lateral. blast, and that of Mount Pelee about 10 km over land. Those from Krakatoa extended mainly over the sea (Figure 2B), in the direction of Mount Raja Bassa in Sumatra. A prehistoric ash flow in southwestern Utah stretched for more than 160 km (F. M. Bullard, pers. comm.), and another from Crater Lake in the western U.S.A., where a caldera was formed, ran for 56 km carbonizing tree trunks embedded in the ash at 48 km. Thirgeological record (Table 1) clearly demonstrates that it would have been entirely possible for n&es ardentes from Thera to have devastated eastern Crete. By accepting the nute ardente theory, and “terminal fallout”, it is no longer necessary to attribute the abnormally thick tephra sections from Thera, in the Vema cores (Nos. 50 and 58) to slumping, or secondary transportation [accumulation due to turbidity currents (Lute, 1969)]. This is ruled out anyway by the report by Ninkovitch & Heezen (1965) that Vema core 50, taken on an abyssal plain on the sea bed about 12 km west of the northern point of Carpathos, comprised six alternating layers of coarse and fine ash with sharp contacts between each. The coarse ash here constituting the lower layer (Lute, 1969) exactly as found in the ash deposits on Thera. On the principle of “first in, last out” the transportation of the ash would have resulted in the ash layers being reversed, and the sharp contacts blurred. Also, for Vera core 58 Ninkovitch & Heezen (1965: 422) state that, “concentration of tephra by turbidity currents can therefore be excluded”. Terminal fallout gives a logical explanation. The Archaeological Record The effects of a nute ardente must be linked with the archaeological record to determine their likely effects on the Cretan sites. Before doing this it should be emphasized that the effects of a Pelean (or Plinian) explosion are stupendous because of the enormous kinetic energy release, which varies considerably for individual eruption. The energy release from the Theran eruption has been calculated as being around 4.45 x 1O26 pJ, i.e. 10 times more powerful than that of Krakatoa (Pomerance, 1970). Unfortunately, the total energy release cannot be used directly to calculate the length of travel of a related nute ardente, as vertical blasts and earthquakes occur as well during the same eruption, and may account for a major part of the energy release. Even if only a small part of the energy is available for the propulsion of a nute ardente it would be ample to account for the distances travelled

18

I. G.

NIXON

given by the geological record for nukes ardentes, and for the site destruction accompanied by massive conflagration and depopulation. The traditional depopulation of eastern Crete can be illustrated from the result of recent incidents involving nutes ardentes. Graphic accounts have been given of the eruptions of Krakatoa and Mount PelCe, as well as the recent explosion of Mount St Helens, although the number of casualties in the latter was relatively low as the area was not populated. In the case of Crete the area over which the Theran nukes ardentes would have passed contained a large number of populated sites, so that destruction and depopulation would have been severe. The heavy casualties on the mainland of Sumatra, such as those reported by the Beyerinck family (Furneaux, 1965) in the Mt Rajah Bassa region, illustrate the lethal effects of a nube ardente. In the case of vertical blasts, which were the main energy outlets at Krakatoa, the heat and energy is dissipated harmlessly in the upper atmosphere. The more deadly nature ofthe horizontal blast at Krakatoa was experienced by the Beyerinck family (Furneaux, 1965) in its path, 60 km northwest of the volcano, and is in sharp contrast to the experience of the vessel Charles Bal which was untouched as it cruised only 16 km east of it [Figure 2(b)]. Natural features, such as hills or ridges, and windowless structures facing away from the blast offered some chance of survival. One of the survivors at St Pierre was a prisoner in a windowless underground dungeon (Bullard, 1962: 109) while 132 persons survived the La Soufribe blast of 1902 in the island of St Vincent by taking refuge in a partly underground rum cellar whose small window and door were closed and faced away from the blast. Most of the victims of a nuke ardente die from searing and clogging of the wall of the lungs, caused by the hot gases inhaled and extensive external burns-the effects of a nuke ardente can be as lethal as an atom bomb, but without the radiation effects. A nute ardente passing over the eastern part of Crete would account for the extensive depopulation recorded in Greek legend (Lute, 1969). This (Page, 1970) does not call for any complex explanations of heavy ash deposits, or poisonous ones making the land unproductive for decades. Heilprin reported that the ash deposit over the levelled city of St Pierre was hardly over 1 ft indepth over the greater part of it, but the population was annihilated (Bullard, 1962: 113). Much of this ash was deposited from the eruptions preceding the ride ardente. Destruction byjre

The superheated ash suspension, at an initial temperature of about 12OO”C, dropping to around 650” to 1050” on arrival at St Pierre would ignite anything inflammable in its path, like a flash forest fire. It explains the problem of coastal towns which had apparently been destroyed by tsunamis, but still showed final obliteration by fire, an anomaly pointed out by Page (1970) who estimated the time a tsunami would take to reach the north coast of Crete as about 20 min. A nuke ardente, travelling at a speed noted for the Mt Pelee case of about 300 km per hour would take about the same time. The flood from the tsunami, and the blast of superheated ash would knock down buildings, and the receding flood would remove some of the debris, leaving the remainder saturated with water, but heated by the blast. However, the explosion of Thera would create a subsequent vacuum at its origin, this vacuum would then be filled by a prolonged inrush of air from the periphery, leading to a reverse flow over the path of the earlier nute ardente. As already mentioned such a phenomenon has been reported (Bullard, 1962). In the case of Knossos recent work demonstrated that it was destroyed by fire and rebuilt (Hallager, 1977) in the LM IIIA period. The smoke stains reported by both Pendlebury (1967) and Hallager can now be attributed to the same south wind and to the nuke ardente from Thera. The former reported that a strong south wind carried the flames of the burning beams northwards, almost horizontally, the flames marking

THERA’S

ERUPTJON

AND

CRETAN

DESTRUCTION

19

the walls with soot. This might have occurred in the summer (Nixon, 1967: 85), but alternatively could be attributed to another season if the reverse air flow (“backlash”) to the source of the blast at Thera was responsible. This backlash of the nute ardente from Thera would consist partly of the superheated gases laden with fine ash, and partly of air, passing over ground already heated by its passage, and speeding the return of the flood waters to the sea, and drying out and igniting the remaining inflammable debris, giving a final and complete destruction by fire. The resulting heaps of charcoal, ash and burnt plaster would then remain on site undisturbed by the receding flood waters. Blast effects

The blast effect from a nute ardente is enhanced by its fluidized ash content, which for a given velocity greatly increases its kinetic energy, and destructive power, above that of, for example, a hurricane. Even the comparatively mild blast at St Pierre was sufficient to carry a statue weighing more than 3 tons over a distance of 15.2 m, 152 mm cannon were sheared from their mountings, and 0.9 m thick walls of stone and concrete were torn to pieces like cardboard (Bullard, 1962). The displacement of walls and foundations, which is characteristic of reports of excavations on Thera and at Cretan sites destroyed in the catastrophe of the 2nd millenium BC, is thus readily explicable. At Mount St Helens trees were levelled, and bark abraded off. Of course, all the destruction which took place in Crete, and elsewhere, at this period does not have to be attributed solely to the effect of nukes ardentes. The other physical consequences of the volcanic disturbances associated with them will also have played their part. For example, the far spreading effect of tsunamis postulated by Pomerance (1970), and the effect ofazfi fallout on the fertility of the soil and the ability to raise crops on the land affected (Page, 1970) still apply, as well as the effect of earthquakes. All these will have compounded the consequences of the nuke ardente, particularly in the earlier and later stages of the disaster. For example, the n&e ardentes could be fully capable of toppling walls of hewn porous stone “in one piece as the result of sudden enormous pressure” reported by Platon for the Zakros excavations, and by others for different sites. While, in the cases of Zakros, this pressure effect could have been caused by tsunamis it can be more probably attributed to the blast from a nute ardente, as the site at Zakros is protected from the direct effect of one by the northeast cape and only the secondary effect of a tsunami can travel round corners. Thus it can be postulated that earthquakes may have affected sites in Crete before the maindisaster ofthe nute ardente occurred and could account for damage, and repairs, to buildings before the final destruction. The very extensive depopulation caused by the nute ardente over the area affected by it fully accounts for the depopulation reported by Greek legend (Lute, 1960), and for the fact that it was the eastern part of the island which was worse affected by the disaster. Records of the nuke ardente occurring in historical times show that casualties become negligible outside the immediate area covered by it, while people sheltered by taking refuge in cellars in the lee of a hillside, or in a shielded building, may survive the blast (Bullard, 1962). There is some slight evidence that such a case, of the shielding of a site from the full force of a n&e ardente, may have been recorded for Pyrgos IV destroyed by fire in late LM IB. Cadogan mentions that the main buildings of this site were located on a hill top. The fire damage reported show the signs which would be expected for those from the impact of a nuke ardente, including, “ . . . solidified mud bricks of the superstructure” but, “ . . . it did not touch the houses of the village (built on the upper west, and the east and north slopes of the hill) except on the upper north slope immediately under the brow of the hill” (Cadogan, 1978: 790. The Lasthi mountains, located between Pyrgos and Thera in the path of the nuke ardente, would have deflected the blast somewhat upwards, the fluidized

20

I. G. NIXON

ash behaving as a fluid, so that only the hill top and the upper north slope were affected, conforming to the reported pattern of destruction by fire. Traces of Thera type ash were identified in the destruction levels of the main buildings, and in the village houses not then destroyed by fire. It is evident that Knossos was on the western fringe of the nuke ardente from Thera, so that land to the west of it was relatively untouched and its population mainly survived. Later these would have been reinforced by refugees from the eastern part of the island who were fortunate enough to escape the holocaust, and then by migrants from the west of Crete, flocking in to take up unoccupied land and dwellings once the terror generated by the phenomenon had subsided. The amount of ash fallout in the eastern part of Crete could have been from about two to five times that indicated from the nearest isopachs of the deep sea cores, and would have been enough to make the land a problem for cultivation for several decades (Page, 1970). Resettlement of the eastern part of Crete would have been slow, and may well have taken several generations before normality was reached. Meantime, life would have gone on more normally in the western part of Crete, where the effects of the nute ardente were not directly felt, except for the political problem of the temporary shift in central control of the island produced by unrest and the influx of survivors from the holocaust and the borders of devastated regions. There is indication that there was destruction also at Chania at the time of the major disaster. This may have been due to the effects of nutes ardentes from Thera, although the evidence indicates that the site was beyond the fallout periphery, or alternatively to the actions of refugees from the fringes of the blast fleeing westward. Chronology of the Theran Eruption and its Consequences The chronology of Crete, Thera and associated areas, based on 14C dating, is uncertain for the period in question, mainly due to the inadequate number of samples available to yield a reliable statistical average, and to the doubtful correlation of the archaeological levels with the samples in some cases (Betancourt & Weinstein, 1976). Thus the archaeological evidence from Thera of the ‘time intervals’ between the stages of the main eruption is particularly useful. Although these intervals are no longer essential to explain the “time gap”, if the nuee ardente theory advanced here is accepted, they are very useful in clarifying the Theran chronology. Doumas (1974) suggests that there was a “time interval” between the start of the main Theran eruption and its completion and he advances evidence that in this “interval” efforts were being made for the systematic resettlement of Akrotiri, rather than the casual influx of squatters. This theory is now strengthened by the evidence that nukes ardentes occurred at Thera, as it explains. why very little weathering or indications of soil deposits can be detected between the pertinent ash layers. The abrasive action of the high velocity tephra jets will have sandblasted them away before the new ash deposits accumulated. This hypothesis applies particularly to Doumas’ postulated time interval (Doumas, 1974) and that of Fouque (Lute, 1969) who reported indications of water erosion of the surface of one layer. Bullard points out that, “the area now covered by the caldera of Thera was a large volcanic complex made up of many overlapping cones. It is quite likely that the collapse may have been in stages, representing or reflecting the various magma chambers of the coalescing cones” (F. W. Bullard, pers. comm. 1979). Ninkovitch & Heezen (1965) noted three separate eruptions in their deep sea cores, but there is no information regarding the intervals between them. Money (1973) noted the presence of a brownish layer between the rubble of buildings uncovered in the Akotiri site and the layer of fine pellety pumice covering it, analysis of this 2-4cm deposit shows the presence of humus. He postulated initial destruction by severe

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21

earthquakes leading to the abandonment of the site by the inhabitants. This was followed by a period of “probably several decades” before the initial eruption. In the interval it is suggested that partial occupation of the site took place (Doumas, 1974). A television film from Mount St Helens showed the carcass of a deer lightly sprinkled with tephra, like hoar frost. Inhalation of only a small amount had proved fatal. The tephra jet was highly abrasive and destructive. The bark of the trees facing its source was “sandblasted off’, while trees nearer to it were levelled completely, or their upper part sheared off if sheltered from the blast by a ridge. A similar abrasive effect applied at Thera, confirmed by evidence at Akotiri that, in the case of the last layer of very coarse pumice sealed in by the very fine ash fall which followed, “its top layer is always levelled” (Doumas, 1974: 112, fig. 1). This is in marked contrast to the earlier pumice layers which followed the contours of the debris. The same phenomenon would apply to Fouque and Reck’s evidence (Lute, 1969) of the marked erosion of the pumice surface at the Phira quarry by the water runoff. The blast of fine ash would have removed much, if not all, of the evidence of weathering for a substantial lapse of time between the falls of pumice and that of the layers of ash from the following nukes ardentes, only the distinctive deep water course remaining as a record of the runoff. A further feature to be taken into consideration, regarding humus layers registering a time gap between deposits, is that vegetation does not grow for a long period on ash or pumice deposits which are thick particularly where they contain poisonous fluorine and sulphur compounds-for which the Thera eruptions are notorious-which inhibit plant growth (Ninkovitch & Heezen, 1965). The town at Thera (Akrotiri) was buried not later than the LM IA period, say, around 150&1520 BC (Marinates, 1971). The site was abandoned following a severe earthquake before the ruins were buried by a fall of pumice from the initial eruption by which time some settlers had returned to clear part of the ruins and had started to recover and put on one side valuable pots they recovered. The latest excavations record the discovery of demolition tools; indicating that reconstruction was under way when it was interrupted by the first explosive eruption. This buried the ruins under a thick pumice layer, followed later by a massive deposit of white ash, the two layers being separated by a thin “coloured ribbon” of deposit indicating three stages of activity in total. This evidence, now strengthened by the data on the abrasive action of the nute ardente and its implications, now indicate that this “time interval” could have amounted to several decades, which fits with the archaeological records. It is not, of course, sufficient to explain solely the time gap between the major Theran eruption and the Cretan catastrophe which is now accounted for by the nute ardente theory. From Table 2 the geological record of historically recorded eruptions ranges from 203 to 51 years, with the average for Mount Pelte and La Soufriere amounting to 70 years. It would be reasonable to assume this figure for the time gap between the initial and final eruptions at Thera. From the archaeological record the major Cretan disasters are dated as LM Ib, c. 1450 BC (Hood, 1978) except for Knossos itself for which a date of 138&1400 BC is generally assigned. If the initial disturbance led to the abandonment of settlements in Thera, and the final cataclysm to the destruction in Crete, the time gap based on dating from pots is in line with what might be expected from the whole sequence of events involved in the eruptions (Table 3). Recently important surveys of 14C dates have become available, and are given in Table 3 (Hood, 1978; Michael & Weinstein, 1978) covering this area and the period of the Thera eruptions. In these surveys aspects which assist in correlating the i4C dates are brought out. The MASCA dates are for the period in which the organic material grew, and have to be corrected for the time which elapsed between then and the destruction of the site. To this has to be added the correction for the loss of

I. G.

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NIXON

Table 3. Recent

No. of tests

Site and reference Ayia Irini, Keos (Betancourt & Weinstein, 1976) Pyrgos, Crete (short-lived) (Hood, Akrotiri, Thera (Michael Weinstein,

14C dates for sites afleeted “‘C

5730

by the Thera

eruption

dates (average)

f life

MASCA

(corrected)

Suggested date of destruction Final

at

5

1340 BC

1550 BC

Thera:

2

1467 BC

1685 BC

8

1472 BC

1692 BC

Final disaster at Thera: c. 1450 BC First Thera eruption: c. 1520 BC

1978) 1978)

disaster

c. 1450 BC

outside tree rings when beams were squared for construction, and those burnt off when the beams were involved in a conflagration. This correction may be as much as 200-300 years, or considerably more if a beam from an old structure was re-used (Michael & Weinstein, 1978). Even charcoal from cooking fires may need correction to the extent that it was derived from long-lived trees or timber salvaged from old structures. To these normal corrections, all of which give later dates, there may have to be made a further correction if it is proved that the MASCA curve gives dates which are too old. Also for samples from Thera indicated dates may have to be rejected if it appears that the samples have been contaminated by ingested “fossil” carbon dioxide from the volcano. From Table 3 it appears that the MASCA dates when so corrected, would correlate reasonably well with suggested destruction dates. These agree with the dates for the destruction attributable to the first eruption at Thera by Marinatos (1939) and others, and that for general destruction in Crete in the LM IB period (c. 1450 BC) attested by Page (1970). Pyrgos is an exception, being somewhat earlier than expected. This tentative discussion indicates that the suggested dates for the destruction of Thera can be reconciled with those for surrounding sites, notably in Crete, but no definite opinion can be given until more data are available : more samples, completion of the European calibration curve, and more accurate methods of 14C determination. In special cases, such as Akrotiri, the possible influence of fossil COz from a nearby volcano also has to be taken into account. Also the hypothesis that the general site disasters c. 1450 BC may have been mainly caused by a catastrophic nuee ardente originating in Thera needs closer examination by obtaining further information for the pattern of ash-fallout, particularly terminal fallout, and by checking the data from excavations. For example, just as the fallout can be measured by cores taken from the ocean bed, it should be possible to find similar records in the lake beds in the area. There are few such lake sites available, but cores from lake Kournas in Crete, that near Cape Gata in Cyprus and Osmanga Lagoon near Pylos would show whether any substantial fallout of tephra from the 2nd millenium BC eruption at Thera extended to these areas. This would help to establish if the final explosion was mainly a vertical one or a horizontal ride ardente, and also provide data for the actual fallout on land areas. Successful cores would link the tephra deposits with those of the pollen series, giving a cross reference between their time scales and an indication of the period between successive ash fallouts. Cores should also be taken from stagnant areas such as marshes, and soil samples could be taken from areas in which tephra might have been trapped, although the tephra may have subsequently weathered. These samples could then be concentrated by using the flotation technique employed in the mining industry to separate ore from gangue.

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conclusions

It appears that a good case can be made for the proposed nuke ardente theory. Based on the available evidence the major destruction of sites in Crete, and elsewhere, can be attributed mainly to a nuke ardente from the final explosion at Thera, and inter ah the theory can explain several features of the remaining evidence. (1) The fact that most of the sites were destroyed by fire c. 1450 BC. (2) The peculiar pattern of tephra fallout, and in particular the evidence for “terminal” ash fallout from these nuke ardentes indicated by the cores taken from the ocean bed. (3) The extensive depopulation of the eastern part of Crete at this period, vouched for by site excavations in the area, dating from subsequent periods and recorded in Greek legends (Lute, 1969). The lethal effects of nuke ardente ash explains this aspect without the need to establish a heavy ash fallout. (4) The evidence that Thera itself was evacuated (c. 150&l 520 BC) and then abandoned at the time of the final explosive eruptions is consistent with the theory. The nukes ardentes from them caused simultaneously the widespread destruction in Crete (c. 1450 BC). The historical record for such eruptions (Table 2) shows that the major catastrophe may have been preceded by a mild eruption together with earthquakes of sufficient intensity to have caused the abandonment of Thera c. 1520 BC. This is supported by other evidence from Thera that appreciable intervals did exist (Lute, 1969; Page, 1970; Doumas, 1974) between the successive tephra deposits. This theory thus provides additional evidence for their views, and for those of other authorities, namely Reck and Gourgalas (Page, 1970), that such an interval occurred. .,p Acknowledgements

I would like to thank Professor Fred M. Bullard, Professor Emeritus of Geology, University of Texas, for helpful data and suggestions relating to the role played by volcanic action; and Professor Paul Astriim of Gothenburg for reading the original manuscript and encouraging the development of the theory. References

Betancourt, P. P. & Weinstein, G. A. (1976). C-14 and the beginning of the late Bronze Age in the Aegean. American Journal of Archaeology 80, 329-348. Bullard, F. M. (1962). Volcanoes. Austin: University of Texas Press. Bullard, F. M. (1976). Volcanoes qffh Earth. Austin: University of Texas Press. Cadogan, G., Harrison, R. K. & Stoney, G. E. (1972). Volcanic glass sherds in the late Minoan I Crete. Antiquity XLVZ, 184, 31&313. Cadogan, G. (1978). Pyrgos, Crete 1970-7. British School at Athens, Archaeological Reporfs 19778 24,7&81. Doumas, C. (1974). The Minoan eruption of the Santorim volcano. Antiquity XLVZZZ, 190, 112, fig. 1. Furneaux, R. (1965). Krakatoa. London: Seeker& Warburg. Hallager, E. (1977). The Mycemzen palace at Knossos. Stockholm: Medelhavsmuseet, Memoir 1 45, 46-47, 87. 94. Hood, S. (1978). Discrepancies in C-14 dating. Archaeometry 20, 197-198. Lute, J. V. (1969). The End qf Atlantis. London: Thames & Hudson. Magnusson, M. (1979). Santorini. The Listener 7,771-772. Marinatos, S. (1939). The volcanic destruction of Minoan Crete. Antiquity XIII, 42%439. Money, J. (1973). The destruction of Akrotiri. Antiquity 47, 5&53. Ninkovitch, D. & Heezen, B. C. (1965). The Santorinin Tephra. London: Proceedings of the 17th Symposium of the Colston Research Society. Nixon, I. G. (1967). The Rise qf the Dorians. Cambridge: Chancery Press.

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Page, D. L. (1970). The Santorini volcano and the destruction of Minoan Crete. London: The Society for the promotion of Hellinic studies, Supplementary Paper No. 12. Pendlebury, J. D. C. (1967). The Archaeology of Crete. London: Methuen. Pomerance, L. (1970). In (P. Astrom, Ed.) Studies in Mediterranean Archaeology, XXVI, 10. Goteborg. Popham, M. (1979). Thera and the Aegean world. LHI Antiquity, 207, 57-59. Renfrew, C. (1979). The eruption of Thera and Minoan Crete. In (P. D. Sheets & D. K. Grayson Eds) Volcanic Activity and Human Ecology. London: Academic Press. Sparks, R. S. J., Sigurdsson, H. & Watkins, N. D. (1978). The Thera eruption & late Minoan IB destruction on Crete. Nature, London, 271, 91. The Columbian (Newspaper) (1980). Mount St Helens Diary, 28 May Vancouver. The Sunday Times (Newspaper) (1980). 25 May. pp. 17-00. Watkins, N. D., Sparks, R. S. J., Sigurdson, H., Huang, T. C., Federman, A., Carey, S. & Ninkovitch, D. (1978). Volume and extent of Minoan tephra from Santorinin volcano,. Nature, London 271, 122-126. Weinstein, G. A. & Michael, H. N. (1978). Radiocarbon dates from Akrotiri. Archaeometry 20, 203-209.