Geoarchaeological Evidence for a Chola Era Flood.pdf

Geoarchaeology: An International Journal© 2011 Wiley Periodicals, Inc.Published online in Wiley Online Library (wileyonlinelibrary.com). DOI:10.1002/gea.20376

Geoarchaeological Evidence of a Chola-Period Tsunami from an Ancient Port at Kaveripattinam on the Southeastern Coast of India

C.P. Rajendran,1,* Kusala Rajendran,1 S. Srinivasalu,2

Vanessa Andrade,1 P. Aravazhi,3 and Jaishri Sanwal1

1Centre for Earth Sciences, Indian Institute of Science, Bangalore, India 560 0122Department of Geology, Anna University, Chennai, India 600 0253Archaeological Survey of India, Karnataka Circle, Hassan, India 573 121

Literature of the ancient Chola Dynasty (A.D. 9th–11th centuries) of South India and recentarchaeological excavations allude to a sea flood that crippled the ancient port at Kaveripattinam,a trading hub for Southeast Asia, and probably affected the entire South Indian coast, analo-gous to the 2004 Indian Ocean tsunami impact. We present sedimentary evidence from anarchaeological site to validate the textual references to this early medieval event. A sandylayer showing bed forms representing high-energy conditions, possibly generated by a seabornewave was identified at the Kaveripattinam coast of Tamil Nadu, South India. Its sedimentarycharacteristics include hummocky cross-stratification, convolute lamination with heavy min-erals, rip-up clasts, an erosional contact with the underlying mud bed, and a landward thinninggeometry. Admixed with 1000-year-old Chola period artifacts, it provided an optically stimu-lated luminescence age of 1091 ! 66 yr and a thermoluminescence age of 993 ! 73 yr for theembedded pottery sherds. The dates of these proxies converge around 1000 yr B.P., correla-tive of an ancient tsunami reported from elsewhere along the Indian Ocean coasts. © 2011Wiley Periodicals, Inc.

INTRODUCTION

The Mw 9.3 earthquake in 2004 that ruptured the plate interface along the 1200-km-long Sumatra–Andaman subduction zone generated a transoceanic tsunami,which severely impacted the Indian Ocean countries and killed a quarter of a mil-lion people. Its impact on the southern coasts of India and Sri Lanka was particu-larly surprising (Figure 1). An area not previously affected by any historically knowntsunamis, an important question is whether 2004-type events have reached thesecoasts in the past. Since the search for past events has to be extended beyond recentdocumented history, archaeological and geological data on past coastal surges arethe major source of information. The eastern Tamil Nadu coast of India does not have

*Corresponding author; E-mail: [email protected].

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a documented history of tsunami inundation—the only previous record is that ofthe 1881 tsunami, which recorded an !0.25-m wave at Chennai, previously knownas Madras (Ortiz & Bilham, 2003; Figure 1).

In regions located close to the sources of tsunamigenic earthquakes, previousevents leave coseismic evidence such as land subsidence or uplift together with syn-chronous deposits of tsunami sands. Such observations, when combined with care-fully archived historical data, have helped identify tsunami sources and model futureruptures (Minoura et al., 2001). Work carried out elsewhere demonstrates that theevent layers suggestive of tsunami deposition can be identified from coastal strati-graphic records in the vicinity of the earthquake source as well as from distant shores

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GEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL2

Figure 1. Map of coastal Tamil Nadu, India. Vertical bars: black " storm surge heights (Dube et al.,1997); gray " 2004 wave heights (Chadha et al., 2005). Horizontal lines: black solid " 2004 tsunami run-up distances; dashed lines " extent of 2004 deposits (Chadha et al., 2005; Srinivasalu et al., 2007); dottedlines " river courses. Inset: Indian Ocean region; AP " Andhra Pradesh coast; TN " Tamil Nadu coast;Ch " Chennai; A&N " Andaman and Nicobar Islands.

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GEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL

GEOARCHAEOLOGICAL EVIDENCE OF A MAJOR TSUNAMI, COASTAL INDIA

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(Atwater, 1987; Atwater & Moore, 1992; Bondevik, Svendsen, & Mangerrud, 1997;Dawson & Shi, 2000; Goff, Goff, & Nichol, 2001; Nanayama et al., 2003; Cisternas et al.,2005). By combining distant field evidence with near source data, one can establishthe extent of the effects and thus speculate on the size and possible rupture sourcesof past earthquakes.

The 2004 transoceanic tsunami severely impacted the Tamil Nadu coast, the wavestravelling as far as inland as 1 km. The inundation also resulted in copious deposi-tion of tsunami sands along the coastal strip of Tamil Nadu. The tsunami scouringeffects exposed part of a 7th-century temple complex at Mamallapuram, Tamil Nadu(Figure 1). Previous excavations at this location have led to the identification of anearlier sea surge about 1000 years ago that destroyed the temple (Rajendran et al.,2006). Encouraged by the success of using archaeological sites as potential recordersof past sea surges, we extended our search to other sites along the Tamil Nadu coast.We focused on Kaveripattinam, as it was an important port city on the southeasterncoast of India in the first millennium (e.g., Keay, 2000), which was affected by the 2004tsunami. This paper presents the results of our field investigations supported by his-torical and literary evidence arguing for a large sea surge around 1000 years ago thatdestroyed the ancient town of Kaveripattinam.

BACKGROUND

Available Information on Past Tsunami Events in the Bay of Bengal

Two historically known sources of tsunamis in the Bay of Bengal are theAndaman–Sumatra subduction zone and off the Arakan coast of Myanmar (see insetin Figure 1). The former is known to have generated a few large earthquakes duringrecent and historic times. Among the earlier earthquakes, only those in 1881(Mw 7.9) and 1941 (Mw 7.7) are significant (Bilham et al., 2005; Rajendran et al., 2007).The 1881 earthquake caused a tsunami surge that reports say did not exceed 0.75 cmat Car Nicobar (Rogers, 1883; Table I). The 1941 earthquake may not have produceda notable tsunami, an inference we arrived at based on interviews with senior resi-dents of Port Blair, south Andamans, who experienced the earthquake but no tsunami.The newspapers also did not mention a tsunami in their reports on the earthquake(Rajendran et al., 2007). Another large earthquake is reported from the middle ornorth Andamans, which occurred on January 28, 1679, which also appears to havebeen non-tsunamigenic (Iyengar, Sharma, & Siddiqui, 1999).

An earthquake also occurred off the Arakan coast of Myanmar (Burma) on April 2,1762 (Oldham, 1883; Chhibber, 1934; see inset in Figure 1 for location). During thisearthquake the Arakan coastal tract was elevated by 3 to 6 m, and the rupture resultedin a tsunami that affected the coast of Bengal, including the cities of Kolkata (formerlyCalcutta) and Chittagong (Table I). The 1883 eruption of Krakatau also generated atsunami that registered nominally on tide gauges in Tamil Nadu (Ortiz & Bilham, 2003;Pelinovsky et al., 2005). The available historical records, therefore, show that theDecember 26, 2004, event had no known historical precedent in the region in terms ofits magnitude, rupture length, or tsunamigenic potential. Geological studies from the

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Sumatran and the western Thailand coasts, however, suggest paleotsunamis in theIndian Ocean during A.D. 780–990 and A.D. 1290–1450 (Jankaew et al., 2008; Moneckeet al., 2008; Table II).

Ancient Sea Flood Events from Tamil Nadu, South India

Early south Indian literary writings and archaeological sources suggest the occur-rence of an ancient sea flood in Tamil Nadu, along the southeastern coast of India(Table I). Kaveripattinam (Pumpuhar), the celebrated port city of the Chola kings (ofthe first millennium) on the Tamil Nadu coast, was the hub of maritime trade at thebeginning of the Christian era and continued to be active until the 11th century A.D.

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Table I. Ancient sea disturbances on the Bay of Bengal coasts from historical sources (see Figure 1 forlocations).

Year Type of Source/(A.D.) Evidence Area Comments Reference

750–1000 Historical; Kaveripattinam, Descriptions of sea Hikosaka, 1989; archaeological southeastern coast, India flooding in Tamil Rajan, 1994

classics; archeological evidence of breaks inhabitations; regional impact; possibly tsunami

1112 Historical Baptala, 450 km north of Temple inscriptions from Nilakanta Sastri, Chennai, southeastern Baptala; probably local 2000coast of India

1124 Historical Tiruvatur from the Tamil Local temple inscriptions; Appadorai, 1936;Nadu coast of India probably local. " Currey and

Hugo, 1984

1480 Historical Rameshwaram, south- Temple archives/inscriptions Maclean, 1893eastern coast of India report as a sea disturbance;

the area is known for majorcyclones

1762 Reports Coasts of Kolkata, India; Regional impact; possible Oldham, 1883; Chittagong, Bangladesh; tsunami Chhibber, 1934and Myanmar

1881 Instrumental Car Nicobar Island Earthquake magnitude: Rogers, 1883;records; Mw 7.9; tsunami wave Ortiz andgovernment heights 75 cm and 25 cm, Bilham, 2003reports respectively, along Car

Nicobar and the eastern coast of India

1883 Instrumental Minor surges reported Tsunami generated due to Ortiz and Bilham,records from Kolkata Krakatau volcanic eruption 2003; Pelinovsky

et al., 2005

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(Keay, 2000). Mamallapuram, located about 200 km to its north, was also a port andfamous for its stone temples of the 8th century A.D. Literary works and archaeo-logical evidence suggest sea incursions at both the aforementioned locations(Rajendran et al., 2006). According to Manimekhalai, an early Tamil literary work(see Danielou, 1989, for a prose translation), part of Kaveripattinam “was swallowed”by the “angry” sea (Cantos XXVIII:1:80 and XXIX 11:3:25). According to Hikosaka(1989), this literary work was written between A.D. 890 and 950, an inference basedon his linguistic assessment of the age of this epic. Available epigraphical writingsindicate that due to inundations from the sea, land was submerged and silted up.Around A.D. 1148–1203, such lands in the Sirkazhi Taluk of the Tanjore District (ofwhich Kaveripattinam was a part), were reclaimed by “paying 500 kasu per ma”(Appadorai, 1936; “kasu” generally denotes copper or gold coins and “ma” is approx-imately 144 ft2). When Marco Polo visited this coast in A.D. 1292 (Yule, 1993), hechose “Cail” (the modern village of Kayal), a port !180 km south of Kaveripattinam,to anchor his ship. Kaveripattinam is said to have been “destroyed by an inunda-tion,” a probable reason for his choice of the Cail port (close to modern Tuticorin) todock his ship (Figure 1).

References to coastal inundations are also obtained from temple inscriptions. In his book on the history of the Chola kings, Nilakanta Sastri (2000) mentions that“some of the salt pans at Baptala were lost in AD 1112 owing to encroachment by thesea,” a piece of information obtained from temple inscriptions. Baptala is located!450 km north of Chennai, along the Andhra Pradesh coast (Figure 1; Table I); the2004 tsunami inundation limit along this coast was 0.2–1.0 km (Sheth et al., 2006). A series of disasters including a “severe sea inundation” at Tiruvathur during A.D. 1124(Nilakanta Sastri, 2000) can be deciphered from the temple inscriptions (Appadorai,1936: 748; Currey & Hugo, 1984: 72–78). It can be argued that these references to thedisasters are about the major regional sea flooding during the Chola period, and the disparity in ages could possibly be due to inconsistencies in converting the localcalendric year to the Christian era. Alternatively, they may be related to independ-ent local events of sea inundation, not related to tsunamis.

Another reference to a sea surge is obtained from the Glossary of MadrasPresidency (Maclean, 1893), in which it is reported that the people from Tamil Naduused a narrow natural bridge that existed across the sea connecting Sri Lanka andRameswaram (Figure 1) on the Tamil Nadu coast, which was used for foot traffic up

Table II. Paleotsunamis of the Bay of Bengal inferred from coastal geology.

Year (A.D.) Type of Evidence Area/Study Site References

780–990 Sand layer within peaty soil Meulaboh, northern Sumatra Monecke et al., 20081290–1400 Sand layer within peaty soil Meulaboh, northern Sumatra Monecke et al., 20081300–1450 Sand layer within peaty sand Phra Thong, western Thailand Janakew et al., 20081020–1160 Sand layer preserved between Mamallapuram in Tamil Nadu, Rajendran et al., 2006

the two levels of settlements southeastern coast of India

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to A.D. 1480 (Maclean, 1893). In the same year, a very strong sea surge destroyed thisland bridge. The exact nature of this sea disturbance is not known (Table I).

PREVIOUS ARCHAEOLOGICAL EXCAVATIONS ON THE TAMIL NADU COAST

The Chola Port of Kaveripattinam

The archaeological excavations conducted in Kaveripattinam (also historicallyknown as Pumpuhar) during 1963 to 1973 suggested a silting event that disrupted earlysettlements and transformed the delta (Rajan, 1994). A report on the excavationrefers to this event as “a cataclysmal event of the inward transgression of the sea inthe early historic times which left its scar on the delta tract and its permanent ver-bal record in the literary references to the event in several sources of information,epics, religious and social documentation of the period [sic]. This transgression hadbrought a very heavy clay deposit on the stretch up to which the sea ingressed”(Rajan, 1994: 19). Some of the pottery that they found from the silted horizon belongedto 5th–6th centuries A.D., and the large time gap in the settlement history was attrib-uted to “the psychological and physical effect of the cataclysmal event of a tempo-rary sea incursion” (Rajan, 1994). These interpretations also agree with the sea floodalluded to in the ancient Tamil literary works mentioned earlier. However, this reportpresented no sedimentary evidence to relate the silty layer to a marine source of thestratigraphic unit in question, although they reported a temporal gap in the settlementhistory, which they attributed to the impact of a severe sea incursion. Further, theirmethodology was primarily based on the visual inspection of the styles of pottery,and in the absence of any thermoluminescence or radiocarbon ages, the idea of a puta-tive ancient sea inundation remained ambiguous.

Excavations at the Ancient Port of Mamallapuram

Another site of historical importance is the town of Mamallapuram, 200 km northof Kaveripattinam (Figure 1). From the descriptions of the early navigators,Mamallapuram is known as a town of seven pagodas (pagodas are the turrets ofHindu temples), submerged under water, with only the top parts visible until a fewcenturies ago (Chambers, 1788; Raman, 1998). William Chambers, an early Britishexplorer, attributed part of the submergence to “the overflowing sea” caused by anearthquake (1788: 154), and the event is described as “an earthquake that may havecaused the sea to overflow its boundaries.” It is possible that the reference to atsunami in the writings of William Chambers may have been sourced from the localoral history on an ancient tsunami. The actual cause of submergence of temples hasbeen attributed to processes related to coastal erosion—an observation based onmarine archaeological work in the shallow waters along the Mamallapuram coast(Sundaresh Gaur et al., 2006).

The scouring action by the 2004 tsunami exposed the buried cultural settlements onthe Mamallapuram coast, 6 km south of the town, which were subsequently excavated

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by the Archaeological Survey of India (ASI). These excavations exposed two stages ofdestruction, corresponding to a lower-level brick temple (4th–6th centuries A.D.) andan upper-level granite temple of the 8th–9th centuries A.D. (Rajendran et al., 2006). The charcoal dates are from the sand sheets associated with these levels suggest 5th–6th(1465 ! 75 cal. yr B.P.) and 9th–10th centuries A.D. (860 ! 70 cal. yr B.P.; Table II).From the lithology and the stratigraphic context of these deposits, it was argued thata major sea surge, possibly a tsunami, had caused the destruction of the stone temple(Rajendran et al., 2006).

NEAR-SHORE SEDIMENTARY SECTIONS AT KAVERIPATTINAM

The 2004 Tsunami Deposits: A Template for Paleotsunamis

The 2004 tsunami deposited extensive sand sheets on the Tamil Nadu coast extend-ing up to 2 km inland. These landward thinning deposits are distinguished on thebasis of heavy mineral laminations, very fine laminations, rip-up clasts, mud drapes,an erosional base, and a sharp contact with the underlying beach sand or soil(Bahlburg & Weiss, 2007; Srinivasalu et al., 2007). In some cases, the tsunami sanddeposits on the Tamil Nadu coast exhibit a set of lithotypes, indicating types of trans-portation mechanisms (Table III). Among these we have observed sedimentary struc-tures indicative of an upper flow regime (both normal graded and cross-bedding)and a post-inundation flooding regime (Figure 2). The sedimentary characteristicsof the 2004 tsunami deposits at various locations on this coast provide useful tem-plates for comparative study of specific sedimentary characteristics.

Geological studies conducted by us are centered on the Kaveripattinam coast,which, according to ancient textual references, was impacted by previous sea flood-ing (Table I). On this coast, the 2004 tsunami had a run-up elevation of 4 to 5 m andinundation up to 800 to 1000 m (Figure 1), which left behind sediments of varyingthickness (30 to 50 cm). Most of these deposits can be demarcated on the basis of

Table III. Aspects of 2004 tsunami sand deposits from the southeastern coast of India (Switzer et al., 2009).

Nature of Deposits Possible Interpretation

Parallel laminated facies with Strong, unidirectional, turbulent high-velocity flow; upper flow high proportion of heavy minerals regime (Fielding, 2006).

Massive or graded facies Most dominant facies associated with the 2004 tsunami deposits.Rapid deposition when flow decelerates between the run-up andbackwash, leading to single layer homogeneous and structurelesstsunami deposits (Morton et al., 2007). Fining upward sand faciesare also observed.

Run-out facies Deposition during the final stages of tsunami inundation, mostlyassociated with the return flow; composed of two sandy units. Thebedding includes low-angle cross-bedding and graded beds withsharp erosional contact with the underlying preexisting surface.

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the sharp erosive contacts they make with the preexisting land surface and from thepresence of heavy mineral laminae. Apart from its historic significance and docu-mented evidence for destruction of previous settlements along the Kaveripattinamcoast, the reach of 2004 tsunami is what makes this site a suitable candidate for thestudy of past sea surges.

Geomorphological Setting of the Study Area

Kaveripattinam adjoins the mouth of the Cauvery (Kaveri) River and its adjoiningdelta plain (Figure 3a). The coastal landscape 1000–2000 years ago was probablymarked by a wider network of intervening channels (as evidenced by the distributionof marine archaeological findings in the present-day intertidal zone (SundareshJayakumar & Sanil Kumar, 2006). The discovery of a 1000-year-old wharf on a pale-ochannel about a kilometer inland suggests that an extended and active network ofbackwaters existed during the Chola period (Rajan, 1994). The river-dominated deltaicprocesses are not active currently at Kaveripattinam, as the main channel has shiftednorthwestward (Figure 3a). The current landscape may have resulted from a delta plainthat prograded to the present wave-dominated delta front (Babu, 1991).

At present, the Kaveripattinam coast is straight and low, fringed by a sandy beachwith sparse vegetation. Beach dunes, representative of strand lines, running paral-lel to the present coastline and linear beach ridges, along with the intermittent shore-parallel swales, dominate its morphology (Figure 3a). The beach ridges are linked tothe mid-Holocene sea level rise (Meijerink, 1971). Human settlements started in theregion 2000 years ago (Rajan, 1994), and at least three generations of settlements canbe deciphered, as evidenced by different levels and vintages of pottery (Table IV).

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Figure 2. View of 2004 tsunami deposit from Tamil Nadu Coast (Nagapattinam; see Figure 1 for location).

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The low-lying areas may have been occupied by channels or lakes at times in thepast, and they are now filled up and mostly used for paddy cultivation. This is prob-ably a consequence of the decrease in channel flows due to the construction of damsupstream, an intermittent human activity that dates back from ancient times to thepresent day (Meijerink, 1971).

A previously existing morphology consisting of backwater swamps and natural leveesis reflected in the shallow stratigraphy defined by alternating silty sand and organic-rich mud (Figure 3a). Clean fine sand, with either parallel or cross-laminations, dom-inated by heavy minerals occurs below the fluvial deposits, possibly representing the

Figure 3. (a) Geomorphic map of the Cauvery delta around Kaveripattinam (modified after Meijerink,1971). Rectangle indicates study area near Vanagiri. (b) Google images of the study area with locationsof trenches excavated near Vanagiri, Kaveripattinam. (c) East–west profile along the trench locations atVanagiri, Kaveripattinam; BOB " Bay of Bengal.

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beach facies (Meijerink, 1971). In the seaward direction we also find thick blackishmud at the bottom of some of the trenches, probably representative of the formertidal channels. The stratification, however, has virtually disappeared in the top part of the sections (30–50 cm), which have been reworked anthropogeni-cally by long-continued cultivation and leveling. Therefore, the relative thickness andthe transitions between various sedimentary units in the top part of the sections arenot clearly defined (Meijerink, 1971).

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Table IV. Summary of the facies characteristics from Kaveripattinam trenches (see Figures 3, 4, 5, and6 for locations and sections).

Sedimentary Archaeological Facies Characteristics Artifacts Comments

Unit 5 (TS) Top soil Occasional pottery sherds Topsoil highly disturbed byagricultural activities.

Unit 4 (FS) Silty sand/sandy silt Occasional pottery sherds Present in all the trenches;natural levee deposits,formed by channel migration and river floods.

Unit 3 (GF) Graded facies; fining Transported pottery sherds Present in all the trenches; upward sequence occurring at the lower level reddish in color and highly

oxidized, without any laminations; possibly indicativeof a temporally stagnantwater that develops whenwave reaches run-up limit.

Unit 2 (L1) Sandy layer with con- Occasional pottery sherds Present in most of the voluted laminations with trenches; the sequence in erosional contact with trench T11 is much thicker,the underlying unit 4 with additional bed forms

like hummocky and swaleycross beddings, indicativeof high-velocity currents.

Unit 1A (BM) Brownish and black mud No archaeological artifacts Brownish mud, possibly in the layer formed as bed in locally

developed water ponds andthe black mud as the substratum in tidal channels.Seen in the trenches T21,T11, T15, and T14.

Unit 1 (LS) Planar bedded fine- Generally barren of Occurs as the lowermost grained sand with archaeological artifacts unit in most of the trenchesoccasional low-angle except in T15. Planar concross-bedding with centration of heavy minabundant heavy minerals eral, indicative of a beach

foreshore deposit (e.g., Clifton et al., 1973).

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Sedimentary Facies at the Kaveripattinam Site

We excavated 21 trenches in the village of Vanagiri in Kaveripattinam. The trenchesof varying dimensions (1–2.5 m deep and 3–10 m long) are located along a 1.4-kmstretch on the local highs and lows (Figures 3b, 3c). Six major facies (litho-units) havebeen identified in the sections, as shown in Table IV. The local shallow stratigraphyis dominated essentially by six litho-units (Figure 4). The bottom-most lithologicalunit (Unit 1; LS) consists of parallel laminated layers of fine to very fine sand. In most of the trenches this unit is overlain by a yellowish to grayish layer of silty sand(10–50 cm). We consider this layer, containing pottery sherds and brickbats and char-acterized by occasional cross-beddings and convoluted laminae, as the event layer(Unit 2; L1). An additional layer of brownish mud (Unit 1A; BM) occurs in sometrenches as a subjacent bed, as exemplified in T11. Located in a swale between twobeach ridges, we consider that this trench area was conveniently located for thedeposition and preservation of material remobilized by an onrush of water. Layer L1shows convolute lamination and occurs directly above the brownish mud, which ismissing in the elevated parts. One ubiquitous bed (Unit 3; GF) observed in most of thetrenches is a fining upward sequence of reddish-brown clayey sand with brickbats andoccasional pottery sherds. This layer is devoid of any laminations. A layer of fine sand(Unit 4; FS) devoid of structures and generally barren of pottery or brickbats over-lies unit 3. This is overlain by topsoil of variable thickness (Unit 5; TS).

Among all the sedimentary sections, the trench T11 revealed greater developmentof the graded facies, GF (Figure 5a, 5b). Here, L1 occurs directly above a layer ofbrownish mud (thickness: 2 to 5 cm), making a sharp contact. This layer is best devel-oped here as a fining upward sequence with larger clay content, suggesting depositionunder still water conditions. The lower part mostly consists of fine sand with heavy min-erals. With convolute laminations as well as hummocky cross-stratifications alongwith occasional mud drapes, mud clasts, brickbats, and pottery sherds, this layerstands out in the trench (Figure 6a, 6b). The L1 layer does not repeat vertically in anyof the trenches in the region except in the trench T15 (Figure 3b, 4), where a sandylayer showing an erosional contact with underlying laminated sand facies along withconvoluted heavy mineral laminae occurs at the upper level of the section.

All the event layers in trenches were devoid of any microfossils. Unlike depositsin the temperate latitudes, the absence of foraminifers and diatoms in the paleot-sunami sand sheets in the tropical latitudes is explained as being due to their poorpreservation potential, including dissolution of shells. This dissolution process isprobably aided by agricultural activities, which also use insecticides and fertilizersand may lead to acidification (e.g., Mackensen et al., 1995).

RESULTS

Stratigraphic Constraints of the Event Layer

The appearance of L1 unit in T11 is unique in that this is the only section thatshows what appears to be a hummocky cross-bedded layer. Multiple sets of hum-mocky cross-bedding are known to be consistent with long period flows of high

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Figure 4. Logs of selected trenches along east–west lines showing the shallow stratigraphy at Vanagiri,Kaveripattinam. LS: laminated sand; BM: brown mud; L1: layer 1; GF: graded facies; FS: fine sand; TS: top-soil. Ages in A.D. derived from TL and OSL dates are also shown (see Table V for more details).

oscillatory velocity, and such wave-generated features are linked to storms ortsunamis (Eyles & Clark, 1986; Klein & Marsaglia, 1987; Cheel, 1991; Dumas & Arnott,2006). Clasts observed in such deposits are possibly ripped off from the basal mud

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and are suggestive of an inflow with scouring effects and basal traction associatedwith tsunamis (Nanayama et al., 2003; Goff, McFadgen, & Goff, 2004).

A number of features in the section, including the large-scale cross-stratificationswith low dip angles (10–15 degrees) and the small-scale climbing cross sets and theundulatory bedding style, can be attributed to the action of oscillatory flows (Rossetti,1997). The section also showed a lateral transition from more open foreset bedding toclosely bounded bedding in the direction of flow (Figure 6a, 6b), which possibly sug-gests subtle changes in flow velocity within short distances. The erosional boundingsurfaces also indicate highly unsteady flow, leading to internal scour and drape surfaces.These are not associated with purely tidal-influenced settings and are attributed to

Figure 5. (a) Photograph of the central pit (trench T11) showing vertical sequence of sedimentary units;side panel shows the generalized stratigraphic log. (b) Sketch showing the stratigraphy exposed on thewest wall (made from the photograph shown in Figure 6a); filled circles indicate the sampling spots forTL and OSL dates; side panel shows the mean grain size of various layers.

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storm-generated flows (Rossetti, 1997). The hummocky cross-stratifications con-sidered to represent high-energy and high-density sediment flows are also associatedwith tsunamis (Bartsch-Winkler & Schmoll, 1984; Klein & Marsaglia, 1987). The con-volutions seen in the layer (L1) can also be produced by the surface drag of eddy-ing currents of waning strength flowing over loosely consolidated sand and silty claylaminae. This mechanism is more applicable in the region west of T11, where thetsunami run-up energy is expected to decrease (see Figure 4).

The continuity of the L1 in a few other trenches can be traced but these are lessspectacular compared to what was observed in T11 (Figure 4). For example, in T14and T15 it is about 10 cm thick and shows convoluted heavy mineral laminae, mudclasts, bricks, and pottery sherds, but not cross-bedding or other structures causedby oscillatory motions, as would be expected to form in the swale. The sand-over-sand

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Figure 6. (a) View of the north segment (west wall) of T11. The mud drapes (inset a) suggest occasionalstill-water conditions during the depositional phase, as reported for other tsunami deposits (Fujiwara, 2008).Note the sharp contact that the sand layer makes with the underlying clay (inset b). (b) View of the eastsegment (north wall) showing hummocky and swaley cross stratification (inset c) as well as sharp con-tacts between flows.

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stratigraphy, where tsunami sand occurs directly over the preexisting beach sand orestuarine silt (which is the case even in many of the 2004 tsunami deposits) offersmany interpretational challenges in defining the contact zone of the event horizon.Therefore, among all the trenches in Vanagiri (Kaveripattinam), our interpretationof an earlier tsunami in the area is based conclusively on the observations from T11,because of the intervening mud layer.

Discrimination Between Storms vs. Tsunami Scenarios

We considered a storm-related origin for these deposits. For example, Dube et al. (1997) note that peak storm surges on the east coast of India are highly local-ized, affecting only narrow stretches, and the average run-up elevation of histori-cally known surges is 2 to 2.5 m. Historically, Kaveripattinam has not been subjectedto large cyclonic impacts, unlike Nagapattinam, located to the south and withincyclonic tracks (IMD, 2008:Figure 1a). Further, the local stratigraphy should be agood indicator of storm deposits, and the frequency of such events is expected to behigher than tsunamis. The sedimentary unit observed in T11 is temporally and spa-tially unique with an unusual inland reach, !900 m inland from the present coastline,comparable to the 2004 tsunami inundation. The 2004 run-up elevation in the studyarea was 5 m, leading to inundation of !1000 m and the consequent sand depositionup to 800 m inland (Chadha et al., 2005).

No storms in documented history are known to have affected such inland loca-tions, nor are there any indications of this in the stratigraphy. Further, sea level inthe region has not showed much variation over a long period, as evident from thearchaeological studies. Another question is whether this layer (L1) had a fluvial ori-gin. The streams in the Cauvery basin are either northwest or east flowing, and theevent layer (L1) in the T11 section shows a westward thinning geometry and flowdirection. Besides this, the event layer is also characterized by high heavy mineralcontent. For these reasons, we rule out a fluvial origin for the L1 layer in T11.

The long run-up distance is generally considered to be a positive criterion to dis-tinguish the tsunami deposits from storm-derived deposits since a very large wave-length is associated with tsunami waves (Fujiwara, 2008). This is true forKaveripattinam, as observed also during the 2004 tsunami. Another distinguishing fea-ture at Kaveripattinam is the wedge-shaped and landward thinning nature of thesand deposit. It is also remarkable that the event layer in the study area is overlainby a sequence of coarsening upward layers with no laminations. It is possible tointerpret this as a deposit during still-water conditions when the run-up processslackened and reached its limit far inland.

An additional trench, which is referred to as the Chola trench (T14; see Figure 3bfor location) exposed a layer of yellowish sand making a sharp contact with pale-obeach facies (Figure 7a). The cultural disturbance is inferred from the buried urnin an upright position. The urn was broken during the trenching, although a large por-tion of the urn was exposed in the northern wall of the trench (Figure 7b). The char-acteristics of this trench are further discussed in the next section.

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Chronological Constraints of the Event Layer

Chronological constraints on the event layer were developed on the basis of lumi-nescence dating of embedded pottery sherds and the deposits themselves. Potteryobserved in various trenches is mostly fragmentary and comminuted, making a propervisual evaluation difficult, except for an embedded urn—a burial artifact (red ware;early Chola) found in the one of the trenches (Figure 7a, 7b). Overall, the potterysherds obtained from the region revealed black and red ware (early historic period),“rouletted” ware (indicating of Indo-Roman trade), red-polished variety (early medievalperiod), green glazed ware, and thin black wares (typical indicator of Chinese andSouth Asian trade links). Such an assemblage of pottery indicates continuity of thesettlement in Kaveripattinam from the 3rd century B.C. to 12th century A.D. (Rajan,1994). The pot sherds from the trenches in the study area are mostly represented byred ware and occasionally older black wares that may have been reworked anddeposited along with red ware.

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Figure 7. (a) Section (trench T14; for location, see Figure 3) on the northern wall showing the earlyChola urn burial (thermoluminescence date: 1846 ! 45 yr). (b) Another view of the section showing thecomplete width of the urn, revealing the nature of sediment within the pot. Side panel shows the stratig-raphy of the trench. (c) A generalized log of the trench; legend is the same as in Figure 4.

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The age of the event layer in trench T11 was determined using optically stimulatedluminescence dating as 1091 ! 66 years (A.D. 850–980), which we consider as the con-temporary age of the deposition. The rolled pottery sherds from the top of Unit 4 pro-vided TL ages or 993 ! 73 years (A.D. 940–1090) (Figure 4c; Table V). The TL dates ofthe pottery from trenches T15 and T11 vary between 1017 ! 165, 993 ! 73, and 676 !60 yr B.P (A.D. 820–1150, 940–1090, and 1270–1390, respectively), which correspondto the ages of various coastal settlements. The older dates of pot sherds from trenchesT11 and T15 are comparable and correlative of the Chola-period tsunami. But theyounger date of 676 ! 60 yr within the upper L1 layer of the trench T15 (Figure 3) isexceptional, with no correlation in other trenches of the area. Whether or not anothertsunami inundation occurred in late medieval times requires further validation.

Further corroboration on the tsunami inundation during the Chola period comesfrom trench 14 (Chola trench in Figure 3). In this trench, a broken urn was found inan upright position at a depth of 2 m from the surface. It was dated to 1846 ! 45 yearsand 1807 ! 394 years before present (Figure 7a, 7b), that broadly corresponds to thesettlement of the early Cholas in Kaveripattinam (300–200 B.C.; Keay, 2000). The bur-ial practice of interring a body in an urn in a sitting posture was practiced during theearly Chola period in South India. The urn, with a diameter of !80 cm, was found

Table V. TL/OSL* dates of samples from Kaveripattinam.

Location Sample ID Lab Code Age (years) Age (years A.D.) Sample Type

11°07.420'N, T11/TL-1 WIHG 1182 ! 160 660–990 Pottery sherd (TL)79°50.954'E11°07.420'N, T11/OSL-1 LI 1091 ! 66 850–980 Sand (OSL)79°50.954'E11°07.497'N, T15/TL-1 WIHG 1017 ! 165 820–1150 Pottery sherd (TL) 79°51.007'E (location further north

of T11)11°07.420'N, T11/TL-2 WIHG 993 ! 73 940–1090 Pottery sherd (TL)79°50.954'E11°07.497'N, T15/TL-2 WIHG 676 ! 60 1270–1390 Pottery sherd (TL)79°51.007'E11°07.443'N, T9/Ch/1 WIHG 1846 ! 45 100–200 Pottery sherd (TL)79°50.073'E11°07.443'N, T9/Ch/1D RIN 1807 ! 394 195–550 Pottery sherd (TL)79°50.973'E

* Thermoluminescence (TL) procedures used in the analyses are after Aitken (1985). TL and optically stimulatedluminescence (OSL) were measured with RisoTL/OSL (model TL DA-15) reader. The dose rate was determinedon the basis of assaying Th, U, and K by XRF analyses of the bulk samples. Standard laboratory procedureswere followed to extract quartz from the 90–125-mm size fraction. The extracted quartz grains were etched for80 minutes in hydrofluoric acid (40%) to remove the 10-mm layer (the HF treatment also removes any feldsparcontamination). The water content was determined for all the samples by heating at 100°C. TL/OSL ages backcalculated from A.D. 2006. The single aliquot regeneration protocol was used for equivalent dose (ED) deter-mination (Murray & Wintle, 2003).LI: Department for Geochronology and Isotope Hydrology, Leibniz Institute for Applied Geosciences, Germany.WIHG: TL/OSL Laboratory, Wadia Institute of Himalayan Geology, India.RIN: Duplicate sample T/14/Ch/1D analyzed at Research Institute of National Sciences, Okayama University ofSciences, Japan.

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embedded at the base of a 2.5-m-deep trench (T14 in Figure 3) that bottomed onbeach facies. A layer of yellowish sand of varying thickness (maximum 10 cm) occursabove the beach facies (Figure 7a, 7b). This layer abruptly terminates against the eastside of the pot, and the sediment inside the urn exhibits cross-bedded sandy facieswith heavy mineral laminae overlain by thin sequences of brownish mud (Figure 7c).The base of the yellowish sand exhibits a wavy pattern and is erosional in nature.These characteristics suggest that the yellowish sand is possibly allochthonous withinthe originally present beach sand. Within the pot, the yellow sand occurs in traceswithin brownish sand, and the depositional facies is dominated by cross-bedding withheavy mineral laminae dipping against each other. These depositional characteris-tics indicate that it is a product of the micro-depositional environment within the potas the transported material probably entered into a swirling motion. The burial ofthe urn predates the inferred tsunami as the event layer terminates outside the pot.

All our dates from Kaveripattinam trenches come from either OSL or TL datingmethods (Table V). It should also be noted that the accuracy and precision of lumi-nescence dating can be compromised on a number of accounts. The most impor-tant problem that can lead to an overestimate in age by 10 to 200 percent is due tothe fact that the sediment may not have been exposed to adequate sunlight (Forman,2000). Apart from the problem of anomalous fading (mostly for feldspar grains), theerror in luminescence dating can be due to the variations in possible pore pressurecontent since burial. There is also a problem related to limited exposure to sunlight,which is especially relevant in the case of rapidly deposited sediment, as in the caseof tsunamis. Thus, water-laid sediments may have a higher residual level, which wasmostly compensated for by improved laboratory procedures (Forman, 2000). In thecase of dating of event layer in Kaveripattinam trench (T11), we have obtained bothOSL results (1091 ! 66 yr) for the sediment and a TL date (993 ! 73 yr) from theembedded pottery. These multiple dates more or less converge and help us to reducethe uncertainty in the dating of the event horizon at Kaveripattinam.

CONCLUSIONS

An enigmatic anecdote on a devastating sea flood in Tamil classical literature hasremained in the collective memory of the coastal communities of the southeasterncoast of India for a very long time. The mythological references in the ancient liter-ary classics implicate this event as a turning point in the fortunes of the port city ofKaveripattinam on the southeastern coast of India, which flourished in the first mil-lennium. Authentic historical information does not, however, exist to validate thenature of this disaster, nor are such sources clear about the exact date of its occur-rence. In this study the tsunami event layer at Kaveripattinam has been identified onthe basis of sedimentary characteristics whose age has been constrained by OSL(1091 ! 66 yr) and TL methods (993 ! 73 yr). The OSL date of the inferred tsunami sandand the TL date of embedded pottery sherds along with the archaeological context ofthe event layer support our contention on the Chola-period tsunami on the Indiancoast. Our studies suggest that this implicated event is a high-intensity tsunami thatinundated deep into the then existing coast.

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This ancient tsunami may have also impacted other parts of the southeasterncoast of India, as revealed in an earlier excavation in Mamallapuram, an ancient portof lesser importance located to the north of Kaveripattinam. A period marked bycultural and commercial advancement during the time of the historically prominentChola kings of South India, this disaster may have led to the collapse of a thrivingport, never to regain its past glory. The combined regional database pointing to atransoceanic tsunami of the same period, reported from other shores of the IndianOcean, including those of northern Sumatra, located close to the epicenter of the 2004earthquake, suggests that the impact of the Chola-period event was regional, com-parable to the transoceanic nature of the 2004 tsunami. Therefore, this event that musthave occurred between the 9th and10th centuries qualifies as an early predecessorof the 2004 tsunami, comparable in terms of its rupture size and magnitude. Furthergeoarchaeological explorations of the ancient ports in India might provide chrono-logical constraints for such lesser-known events in the past, thus contributing to thedisaster assessment of infrequent but high-impact coastal hazards.

The Indian National Centre for Ocean Information Services (INCOIS), Ministry of Earth Sciences, fundedthis work. The Ministry of Earth Sciences, Government of India, is thanked for the infrastructural fund-ing for the Centre for Earth Sciences in the Indian Institute of Sciences, Bangalore. Terry Machado, SenthilKumar Babu, D. Raju, Saravanan, and Uma offered assistance during various phases of field investigationsand laboratory work. Local residents have been a source of inspiration and support. Reviews by BrianAtwater and Adam Switzer on earlier versions of this manuscript are gratefully acknowledged. We wouldlike to thank the journal editor Jamie Woodward, the first reviewer (anonymous), and the second reviewer(Alastair Dawson) for their constructive comments. VA and CPR thank the Council of Scientific andIndustrial Research and the Department of Science and Technology under the Government of India forthe Shyama Prasad Mukherjee and the Ramanujan Fellowships, respectively. We acknowledge the serv-ices of the Department for Geochronology and Isotope Hydrology, Leibniz Institute for AppliedGeosciences, Germany; Wadia Institute of Himalayan Geology, Dehra Dun, India; and the Research Instituteof National Sciences, Okayama University of Sciences, Japan, for thermoluminescence and optically stim-ulated luminescence dating of the samples.

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Received 28 July 2011Accepted for publication 30 July 2011Scientific editing by Jamie Woodward

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