New approaches to the Theran Eruption

Transcription

1 New approaches to the Theran Eruption Ray Rivers (Physics, IC) Collaboration with Carl Knappett (Art, Toronto) Tim Evans (Physics, IC) Maritime Networks Toronto 2013

2 Middle Bronze Age (MBA) Aegean Roughly selfcontained in space and time -c.2000 BC Distinct Minoan culture starts

3 Middle Bronze Age (MBA) Aegean Roughly selfcontained in space and time -c.2000 BC Distinct Minoan culture starts -c.1700 BC Knossos plays a dominant role Knossos

4 Middle Bronze Age (MBA) Aegean Roughly selfcontained in space and time -c.2000 BC Distinct Minoan culture starts Thera Knossos Thera: Gateway for Minoanisation of S. Aegean

5 Middle Bronze Age (MBA) Aegean Thera as gateway: Thera Knossos

6 Middle Bronze Age (MBA) Aegean Thera as gateway: Destroyed by volcanic eruption in 1575 ± 50 BC! (LMIA/LMIB border) Thera Knossos

7 Middle Bronze Age (MBA) Aegean Thera as gateway: Destroyed by volcanic eruption in 1575 ± 50 BC! (LMIA/LMIB border) Thera Huge ash (tephra) deposits Knossos Thera now uninhabitable, but Minoan maritime network continues to thrive!

8 Middle Bronze Age (MBA) Aegean Thera as gateway: Destroyed by volcanic eruption in 1575 ± 50 BC! (LMIA/LMIB border) Thera Huge ash (tephra) deposits Knossos Thera now uninhabitable, but Minoan maritime network continues to thrive! End of Minoan culture much later - Burning of the Palaces

9 Question: How do we understand this? Answer: Have a rich network which can survive local disaster! - A little like an extreme case of crop failure! Advantage: Have some knowledge of before and after, which we don t for drought. Network resilience: Straightforward test for network modelling! Imperial College London Page 9

10 Networking Thera: Vertices = Major Population or Resource Sites Edges = Exchange between sites - physical trade of goods or transmission of culture - soft power and hard power Interactions controlled by physical limitations of ancient sea travel -- Simple Links Imperial College London Page 10

11 Modelling Cycle Input settings: Geophysical MODEL ARCHAEOLOGICAL DATA Input parameters: Sociophysical Consistency check Predictions Imperial College London Page 11

12 MBA Nodes/Site settings: 39 key sites: Knossos (1) Thera (10) 12

13 Settings Model: Imperial College London Page 13

14 Settings Model: Parameters Imperial College London Page 14

15 Settings Model: Parameters Output Imperial College London Page 15

16 Outputs: Exchange : T ij Conflation/flattening of exchange into a single measure Population: P i Centrality: Page Rank Sites with strong exchange activity Betweenness : Measures how sites and links are on paths between other sites. Imperial College London Page 16 Several definitions in each case!

17 Agency: Networks come into existence and survive for many reasons. Optimisation: Assume networks are optimal in some sense Simple division: Most likely networks Most beneficial networks Page 17 Imperial College London

18 Most likely Networks: Epistemic approach Maximum Entropy modelling 1. Generalised gravity models: Alonso models Gravity models Transport models Retail models Iron Age Greek city states Tribute? - Rihll and Wilson 2. Intermediate opportunity models Migration/commuting models Include generalisations of PPA Page 18

19 Most likely Networks: Epistemic approach Maximum Entropy modelling 1. Generalised gravity models: Alonso models Gravity models Transport models Retail models Iron Age Greek city states Tribute? - Rihll and Wilson 2. Intermediate opportunity models Migration/commuting models Include generalisations of PPA Page 19

20 Very few knobs Don t expect too much - very broadbrush! E.g. Unadorned simple gravity model or PPA But still very useful Page 20

21 Example: Urban transport (e.g. Toronto) 1. Decide on basic network settings e.g. Tram stops (nodes/sites) Fare structure Total daily expenditure Total daily mileage 2. Construct all networks commensurate with this, Labelled by # of passengers on each route (exchange) and take a picture of each: 3. Give each equal weight and Look for the (statistically) most likely network: - the answer - no knobs! Page 21

22 Most beneficial Networks: Ontic approach 3. Cost benefit analysis: Some generalities but ultimately bespoke Considerable freedom in choosing costs and benefits More like a construction kit than a black box! Imperial College London Page 22

23 Most beneficial Networks: Ontic approach 3. Cost benefit analysis: Some generalities but ultimately bespoke Considerable freedom in choosing costs and benefits More like a construction kit than a black box! Need to worry that you are not getting out what you put in! Imperial College London Page 23

24 Question: What is special about the MBA Aegean? How universal are network exchange models? How would we know that our output is not equally acceptable as an iron age network or even a contemporary exchange network? Imperial College London Page 24

25 Settings Model: Parameters Imperial College London Page 25

26 Key point: MBA Marine technology matches distances: Regional groupings connect at sea distances of D 110km Sea distance from Knossos to Thera! Distance scale D 110km crucial: Imperial College London Page 26

27 Key point: MBA Marine technology: Sail replaces\supplements oar for large distances Single journeys of 100km possible and relatively easy For the first time in the BA, technology is good enough to enable a fully connected exchange network to form This is what singles out MBA from any other network analysis on the same set of sites Should only choose models whose dynamics are sensitive to geography! Imperial College London Page 27

28 Key point: MBA Marine technology: Sail replaces\supplements oar for large distances Single journeys of 100km possible For the first time in the BA, technology is good enough to enable a fully connected exchange network to form This is what singles out MBA from any other network analysis on the same set of sites Should only choose models whose dynamics are sensitive to geography! Effective distances: Sea journey (round headlands) + (frictional) land journey For the moment ignore wind assume it averages over travel season Will repair this later! Imperial College London Page 28

29 Minoan Civilisation: 3 phases Pre-eruption Vigorous maritime exchange network Eruption! Post-eruption resilience (Even more?) vigorous maritime exchange network (In)stability and Fire Destruction Internal collapse/external invasion/earthquake 29

30 Pre-eruption: Most likely model selection (D given) 1. Generalised gravity models: Simple Gravity Model (NULL) Singly constrained Gravity model Doubly constrained gravity model Retail models - Rihll and Wilson 2. Intermediate opportunity models PPA (NULL) Directed PPA Page 30

31 Pre-eruption: Most beneficial model selection (D given) Cost/benefit analysis: ariadne Benefits in establishing links Benefits from local resources Costs in supporting links, supporting population Imperfect rational choice : Optimisation Trade off costs against benefits to best advantage - minimising social potential 31

32 Model: Model aims for best Settles for the good Stochastic Optimisation! Imperial College London Page 32

33 is not Strong restrictions! familiar catastrophe fold in site exploitation (population) if exchange drops while lacking self-sufficiency Agrees with Broodbank et al. (2005) For the southern Aegean islands in the late Second and Third Palace periods,... there may often have been precariously little middle ground to hold between the two poles of (i) high profile connectivity, wealth and population, or (ii) an obscurity and relative poverty in terms of population and access to wealth that did not carry with it even the compensation of safety from external groups.

34 is more Strong restrictions! familiar catastrophe fold in site exploitation (population) if exchange drops while lacking self-sufficiency Goldilocks scenario: not too cold not too hot just right

35 is more Strong restrictions! familiar catastrophe fold in site exploitation (population) if exchange drops while lacking self-sufficiency Alternatively: harrys greece.com? Complete networks change models! (e.g. LBA?) distance less important short-distance Brownian motion replaced by non geographic motion - Toronto Transport Commision?

36 Tactics: 1. See which models describe the pre-eruption pattern of exchange? Weed out models that don t work! 2. Do surviving models help us understand the survival of the network? Weed out further models! Imperial College London Page 36

37 Pre-eruption: Model selection Model Sensitivity to D * Directed Weak links Minoan Standard Gravity model: D (NULL) Singly constrained gravity model: D Doubly constrained (transport) gravity model: D Retail (Rihll & Wilson) gravity model: D + attraction Hi-B, Hi- W Hi-B, Lo- W Hi-B, Lo- W ** Lo-B, Lo- W PPA (k=4) (NULL) *** Directed PPA (k=4) *** Ariadne : D + local resources + pop./network costs Ranking tables for vertices not a good guide links are more important here!

38 Pre-eruption: Model selection Model Sensitivity to D * Directed Weak links Minoan Standard Gravity model: D (NULL) Singly constrained gravity model: D Doubly constrained (transport) gravity model: D Retail (Rihll & Wilson) gravity model: D + attraction Hi-B, Hi- W Hi-B, Lo- W Hi-B, Lo- W ** Lo-B, Lo- W PPA (k=4) (NULL) *** Directed PPA (k=4) *** Ariadne : D + local resources + pop./network costs Ranking tables for vertices not a good guide links are more important here!

39 Example: sensitivity to D Gravity model: Doubly constrained Gravity model: D = 60km D = 100km

40 Immediate post-eruption: 2 Models Model Sensitivity to D Minoan Standard Gravity model: D (NULL) Ariadne : D + value of local resources + pop./network costs No Contest! Standard Gravity Model: No rearrangement just deletion! Pre-eruption: Post-eruption

41 Ariadne (V-Rank; L-Weight) Pre-eruption: Post-eruption Ariadne (V-Rank; L-Weight) Strong rearrangement through Phylakopi!

42 Ariadne (V-Rank; L-Weight) Pre-eruption: Post-eruption Keos! the evidence points to, if anything, an increase in Minoan trading activity in LM IB, particularly in our excavations at Ayia Irini, Keos (14) where we literally had thousands of LM IB vases imported from outside (Davis 1980) Ariadne (V-Rank; L-Weight) Strong rearrangement through Phylakopi!

43 Later post-eruption behaviour: Endogenous Instability Increasing costs of sustaining network a centralised economy which may be working under some adversity which might be increased population people coming in from Thera What I think you would expect to see is not a gradual decline, but an increasing intensity in the various subsystems of the culture system, including an increasing level of trade, until the system breaks down altogether. Renfrew (1980)

44 Later post-eruption behaviour: Endogenous Instability Increasing costs of sustaining network a centralised economy which may be working under some adversity which might be increased population people coming in from Thera What I think you would expect to see is not a gradual decline, but an increasing intensity in the various subsystems of the culture system, including an increasing level of trade, until the system breaks down altogether. Renfrew (1980)

45 Later post-eruption behaviour: Endogenous Instability Increasing costs of sustaining network a centralised economy which may be working under some adversity which might be increased population people coming in from Thera What I think you would expect to see is not a gradual decline, but an increasing intensity in the various subsystems of the culture system, including an increasing level of trade, until the system breaks down altogether. Renfrew (1980)

46 Endogenous Instability Increasing costs of sustaining network A few strong links form at the expense of weak links Network collapses as the few remaining strong links disappear Stability correlated to existence of weak links 46

47 Alternatives: Avoiding instability Waiting for the Myceneans (?)

48 Alternatives: Avoiding instability Waiting for the Myceneans (?)

49 Alternatives: Avoiding instability Waiting for the Myceneans (?)

50 Alternatives: Avoiding instability Waiting for the Myceneans (?) BUT instability generic!

51 Winds: Good proof of principle but still too simple in some regards: Meet Daedalus II! Aka Kanellos Kannelopoulos Human-powered flight from Heraklion to Thera (Santorini) in 1988 (almost Icarus II!) Thera is North of Crete: Summer winds are Northerly Winter winds are Southerly (and stormy) Occasional periods of Southern winds (or little wind) better weather for travelling North Daedalus II flew on one of the very few Spring days when weather was calm and there was a Southerly wind! 51

52 Winds: Good proof of principle but still too simple in some regards: Meet Daedalus II! Aka Kanellos Kannelopoulos Human-powered flight from Heraklion to Thera (Santorini) in 1988 (almost Icarus II!) Thera is North of Knossos: In general, summer winds are Northerly In general, winter winds are Southerly (and stormy) Occasional short periods of Southern winds (or little wind) in sailing period Daedalus II flew on one of the very few Spring days when weather was calm and there was a Southerly wind! 52

53 Winds: Idealised two stage process 1. Construct an effective distance d N between each pair of sites in the presence of Northerly winds - low friction going South - high friction going North - no change for East West (fuzzy) Construct an effective distance d S between each pair of sites in the presence of Southerly winds - low friction going North - high friction going South - no change for East West (fuzzy) 53

54 Winds: Idealised two stage process 2. The ease of travel function f(d/d) in the term showing benefits of exchange is replaced by f = (1- ε ) f(d N /D) + ε f(d S /D) where ε is the frequency of S. winds in the sailing period Too soon to see systematic behaviour - in progress! But N. Crete more active (East-West) More connection Crete - Rhodes (?) Less connection Cyclades to Dodecanese (?) 54

55 Preliminary conclusions:.mba provides a Goldilocks environment for network formation because marine technology in step with geography. Entropy models too rigid nothing special about MBA. ariadne takes marine technology into account; geographical sensitivity, weak links, directed links, emphasis on N. Crete and significant Thera 55

56 Preliminary conclusions (cont d): Eruption of Thera leads to plausible rearrangement not just link erasure. Network continues to thrive! Catastrophe fold shows existence of intrinsic instability collapse of Minoan dominance? Natural way to include variable winds more work needed! 56

57 References: C. Knappett, T. Evans, and R. Rivers, 'Modelling maritime interaction in the Aegean Bronze Age', Antiquity 82, T. Evans, C. Knappett, and R. Rivers, 'Using statistical physics to understand relational space: a case study from Mediterranean prehistory', in D. Lane, S. van der Leeuw, D. Pumain and G. West (eds.), Complexity Perspectives in Innovation and Social Change, Berlin: Springer Methodos Series 7. C. Knappett, T. Evans, and R. Rivers, 'Modelling maritime interaction in the Aegean Bronze Age II: The eruption of Thera and the burning of the palaces, Antiquity 85, R Rivers, C Knappett, T Evans 2013, Network Models and Archaeological Spaces, Computational Approaches to Archaeological Spaces, Editor(s): Bevan, Lake, Left Coast Press, ISBN: R Rivers, C Knappett, T Evans 2013, What makes a site important? Centrality, gateways and gravity, Network Analysis in Archaeology: New Approaches to Regional Interaction, Editor: Knappett, OUP, Pages:

58 Thank you!

59 Notes and Addenda For the southern Aegean islands in the late Second and Third Palace periods, an age of intensifying trans-mediterranean linkage and expanding political units, there may often have been precariously little middle ground to hold between the two poles of (i) high profile connectivity, wealth and population, or (ii) an obscurity and relative poverty in terms of population and access to wealth that did not carry with it even the compensation of safety from external groups. Broodbank et al. (2005)

60 Middle Bronze Age (MBA) Aegean Thera as gateway: Destroyed by volcanic eruption in 1575 ± 50 BC! (LMIA/LMIB border) Thera Knossos Equivalent to 10 subs worth of tomahawk cruise missiles with W80 nuclear warheads or 2 Trident submarines fully loaded

61 RW Gravity model

62 RW Gravity model

63 RW Gravity model

64 RW Gravity model

65 RW Gravity model

66 RW Gravity model

67 RW Gravity model

68 Ariadne (V,L - betweenness)

69 Ariadne (V,L - betweenness) Keos! the evidence points to, if anything, an increase in Minoan trading activity in LM IB, particularly in our excavations at Ayia Irini, Keos (14) where we literally had thousands of LM IB vases imported from outside (Davis 1980)

70 Endogenous Instability Increasing costs of sustaining network 70

71 Endogenous Instability Increasing costs of sustaining network 71

72 Endogenous Instability Increasing costs of sustaining network 72

73 Endogenous Instability Increasing costs of sustaining network 73

74 Endogenous Instability Increasing costs of sustaining network 74

75 Endogenous Instability Increasing costs of sustaining network 75

76 This might be the type of network that an archaeologist would like

77 Middle Bronze Age (MBA) Aegean -c.2000 BC Distinct Minoan culture starts Thera Thera: Important link between N. Crete and the S. Aegean Knossos

78 Middle Bronze Age (MBA) Aegean -c.2000 BC Distinct Minoan culture starts Thera: Destroyed by volcanic eruption in 1575 ± 50 BC Thera (LMIA/LMIB border) Knossos

79 Middle Bronze Age (MBA) Aegean -c.2000 BC Distinct Minoan culture starts Thera: Destroyed by volcanic eruption in 1575 ± 50 BC Thera Knossos (LMIA/LMIB border) Thera now uninhabitable, but Minoan maritime network continues to thrive!