Fukashi Maeno, Kenji Niihori, Takayuki Kaneko, Toshitsugu Fujii, Setsuya Nakada,

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1 Bull. Earthq. Res. Inst. Univ. Tokyo Vol. 2.,**3 pp.,1+,23 :,**0,**2.1, +,, *. +, -. Reconstruction of Burial Process of Roman Villa on the Northern Flank of Mt. Vesuvius, Italy: insights from laharic deposits of the.1, eruption newly discovered in,**0,**2 +, Fukashi Maeno, Kenji Niihori, Takayuki Kaneko, Toshitsugu Fujii, Setsuya Nakada, Keiko Suzuki-Kamata, Atsushi Yasuda Earthquake Research Institute, University of Tokyo, and Masanori Aoyagi -. Institute, Faculty of Science, Kobe University, The National Museum of Western Art, Crisis& Environmental Management Policy Abstract Burial process of Roman Villa on the northern flank of Mt. Vesuvius, Italy, was reconstructed based on sedimentation processes of laharic deposits newly discovered during,**0-,**2 for the extended excavation site in NE to E parts of the Roman Villa. The laharic deposits are distributed on the lower level of the excavation site. The deposits are divided into four subunits, G+ -MfL +, G+ - DfL +, G+ -MfL,, G+ -DfL,, based on their sedimentary facies (Mf and Df facies). Mf is characterized by massive and matrix-supported facies, indicating en masse deposition from a laminar flow process, and Df is characterized by stratified and clast supported facies, indicating grain-by-grain aggradation from suspension or traction process. These di# erent types of facies are partially transitional and attributed to variations of sediment/water ratio and internal stress condition inside flows, and may be resulted from an evolutional process, like a flow transformation, of a single debris flow. These laharic deposits directly overlie pyroclastic fallout deposits (G+-Af) in the initial phase of the AD.1, eruption, but are eroded and covered by epiclastic deposits (G+-Mf +,,, -,. and G+ -Df) derived from later- and larger-scale laharic events related to the same eruption. The later laharic deposits include more amounts of basement lava of Mt. Somma, compared with the newly discovered deposits. Characteristics and interpretation of the deposits suggest that lahars just after the.1, eruption came from the north to bury the lower level of buildings and have experienced various types of sedimentation processes. An erosion of the edifice of Mt. Somma may have mainly acted in the later laharic events. Key words: Somma-Vesuvio, Pollena eruption, laharic deposits, debris flows, burial process * fmaeno@eri.u-tokyo.ac.jp ++- **-,

2 + 13,**3.1, /+, / *0 +3-* Lirer, et al.,,**+; Mastrolorenzo et al., +33- ; Rolandi et al., +332 ; Rosi et al., +33-1*,**, Fig. + : Figs.,, -,**,,**/ 3 m Vano Niihori et al.,**1,**/ +. C Vano +. ; Fig.,.1, 13 Kaneko et,**0 al.,,**/ +. 0 Fig.,,**2 Rosi and, +/** m,**3 Santacroce, +32- ; Mastrolorenzo et al.,,**,; Santac- Vano 0 ++ roce and Sbrana,,**-; Rolandi et al.,,**.; Sulpizio et Area +, Figs., - al.,,**/,.1, / Vano 1 +* Fig. -a, Fig. +. Location of Somma-Vesuvius volcano and excavation site in Somma-Vesuviana. 272

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4 Fig. -. Photographs of (a) the eastern side (Vano 1) of newly excavated in September,**0, (b) Apsis (Vano 1 and +* ), taken in September,**1, (c) Dolias in Area +,, taken in September,**2. b Area +, cm+* cm dolia Fig. - c,**0 Niihori et al.,,**1 +,,* Vano +. - m 0 1 km 1 +* - +* kgs Perrotta et al.,,**0 a;,**0 b; Niihori et al.,,**1.1, Sulpizio et al.,,**/,**0 Mastrolorenzo,**0 et al.,,**,; Rolandi et al.,,**. Vano 0 ++ Area +, Niihori et al.,**1 Niihori et al.,,**1,.1,.1, Rosi and Santacroce, +32- ; Mastrolorenzo et al.,,**,; Rolandi Sulpizio et al.,,**1 et al.,,**.; Sulpizio et al.,,**/ 1 cm-* cm Kaneko et al., Sulpizio et al.,,**/,**/; Niihori et al.,,**1.1, 274

5 +0-+ Perrotta et al.,,**0 a;,**0 b, Niihori et al.,,**1 - Group + G+ Group, G, Group - GA, - GB, - GC - / Kaneko et al.,,**/; Niihori et al.,,**1 G+.1, G, G-AC Niihori et al.,**1 G, 0 /+, /-0 G-C +0-+ Niihori et al.,**1 G+ G+ -Af 0 G-Mf + +. G-Df + +, Fig..,**0 Fig. / a-d subunit Af air fall deposits Mf Df laharic deposits Smith +320 Vallance,*** Fig... Model column of deposits related to the.1, eruption of Vesuvius volcano in areas excavated in Mf,**0,**2. Mf means massive, matrix-supported mas- sive, matrix-supported facies Df a southern area. debris flow facies. Df means stratified, clast-supported debris flow facies. G+ -Mf+ directly covers G+ -Af in stratified, clast-supported facies subunit Niihori et al.,**1 Vano +. Table + G+ -Af 2,**0 G+ -Mf+.1, G-Af G+ -MfL, G+ -DfL, G+ -MfL+ G+ -DfL+ Fig.. Figs.. / 0 1 Fig. 0 G+ -MfL, G+ -DfL, G+ -Af+ Area +, G+ -MfL+ G+ - + cm DfL+ G+ -Af, G-Af + - Niihori et al.,**1 G+ -Af G, G- AC, cm. G-Af Group + G-Af + / G-Af + G+ -Af.1, - cm. 275

6 Table +. Characteristics and interpretation of flow deposits G-Af + 0 G-Af + 1 G-Af + 2 G+ -Af+ 2 Vano 2 -* cm Fig. 1 Area +, / +* cm Figs. / c, / d, 2, cm Fig. 3 G+ -MfL, G+ -Af+ / G+ - ma- Af0 G+ -Af12 trix-supported Niihori et al.,,**1 G-Mf + + G+ -MfL,. Fig.., Table + + m G+ -MfL, dolia Area +, G+ -Af Fig. / c G+ -DfL, plane bedding Fig. 0 Fig.., Table + - cm G+ -MfL, Area +, Figs. / c, 2 2 cm clast-supported struc-.1, +/ ture cm AD 13 Area +, 0.-0/ y.b.p. cm + cm 276

7 Fig. /. Stratigraphy of the walls of area excavated in,**0,**2. (a) Southern side. (b) Eastern side. (c) Northern side. (d) Western side. 277

8 Fig. 0. Distribution of newly discovered laharic deposits. A broken line shows an erosion contact between G+ - Mf+ and the lower deposits, G+ -DfL+ and G+ -MfL +. Upper right figure shows a cross section of deposits along the line of X-X. On the basis of this mapping, an inferred flow direction of the laharic deposit, G+ -Mf +, is shown. A photo of the erosion contact is also shown. G+ -MfL, G+ -MfL, G+ -MfL+ + cm, + cm Fig.., Table + + m + cm + cm Figs. / c, 2 Vano 0 1 G-Mf + + G+ -MfL, Fig. 0 Area MfL, +, G+ -Af Fig. 3 plane bedding lucite 278

9 Fig. 1. (a) A photograph of a western half of Southern wall in Vano 2. The succession shows thin fallout deposits overlaid by thick laharic deposits with massive poor-sorted facies. (b) Magnification of fallout layers (G+-Af), consisting of the lowest part of Southern wall. The deposits directly lie on bricks on the floor of Vano 2 at this part. (c) A sketch of a western half of Southern wall. Coarse lava blocks concentrate in the lower part of G+ -Mf +. Left-half of G+ -Mf+ directly covers the floor. +* cm G+ -MfL, 1 cm +* cm / cm +* cm G- + G-DfL + + MfL, DfL+ a DfLc plane bedding 279

10 Fig. 2. (a) A photograph and (b) a sketch of fallout and laharic deposits in the western side of Area +,. The location is indicated in Fig.,. G+ -Mf+ includes more boulder-sized lava fragments than lower layers. G+ -MfL+ and L, includes much plants or woods, indicating low temperature of the flow. 280

11 Fig. 3. (a) A sketch of laharic deposits in the western side of Vano +*. The location is indicated in Fig.,. (b) A photograph of the same outcrop. (c) Magnification of fallout layers (G+-Af), consisting of the lowest part of the succession. (d) Magnification of a part of G+ -DfL +, showing very well-sorted and clast-supported facies like a fallout deposit. 281

12 Fig. +*. (a) A sketch of laharic deposits in the northern side of Vano +*. The location is indicated in Fig.,. (b) A photograph of the same outcrop. G+ -DfL+ is basically characterized by stratified, well-sorted, and clast-supported facies (subunits a and c), but sometimes has massive poor-sorted and matrix supported facies (subunit b) like G+ -Mf +. clast-supported structure Fig.., Table Mf DfL+ DfL+ Area +, + /* cm Fig. 2 Vano +* DfL+ b Figs. 2, +*, m Figs. / +* DfL+ DfL+ a b MfL+ MfL, DfL+ a c Fig. / c Vano +* DfL+ b 282

13 Fig. ++. (a) A photograph and (b) a sketch of fallout and laharic deposits in the northern side of Area +,. The location is indicated in Fig.,. G+ -Mf+ includes many fragments of stucco, indicating the destruction of building before or during this lahar event. Fig. 3 G+ -DfL+ +* cm Fig. 3d - cm G+ -MfL+ DfL 283

14 + ac Mf G+ -Mf+ Vano 0 Vano +* G+ -Mf+ Fig. 3d Vano +* Fig. 0 G+ -Af G-Af + 2 DfL+ b G+ -MfL+ DfL+ G-Mf + + G+ G-Mf + + Fig.., Table +, m Vano 1 Vano +, G+ -DfL+ Figs. / c, 2, ++ G+ -Mf,. Figs. / c, 0 lucite Fig.., Table + + m,, m G+ - +/. m, Mf+ +* cm, +* cm, Figs. / 1 +* cm G+ -Mf+ +* cm Area +,, /* cm G+ -Mf+ m Figs. / c, ++ G+ -Mf, Area +, G+ -MfL+ Vano 0 Fig. +/. m Fig. / d / c G+ -Mf. Vano 0 1 G+ -Af Fig. / d G-Mf + + G-Mf +, G- + Mf+ G+ -Mf, G-Mf + + G-Mf +, G-Mf + + cm + cm G+ -DfL+ L, G+ -Mf+ G-Df + clast-supported structure Table + cross-bedding Area +, Vano +* + m Vano +* G+ -Mf. Fig. /.1, G+ -So 284

15 .1, G+ -Mf+..1, +* cm G+ -DfL Mf + L, cross-bedding Df Mf Df Mf Df G+ -Df cross-bedding G-Mf +. ;,**. debris flow streamflood flow Niihori et al.,**1 Table + G Mf + -DfL+ L, matrix strength -, Group, - G, G+ +* cm m G, -Af+, grain G-Af, -. G-Df, + m Fig. / a, b dispersive pressure; vesiculated tuff G, 0 /+, /-0 Mf Perrotta et al.,,**0 b; Niihori et al.,,**1 debris flow Vano - -m Df G-Mf + + Mf G- G, stream flow, m G-A, -B, - C Fig. / a, b DfL debris flow,**0 - G, G- C +0-+ debris flow stream flow Nii- hori et al.,,**1 G-A G-B +32, hyperconcentrated flow Smith, ; Smith and Lowe, Lirer et al.,**+ AD 13 e.g. Smith, +320; Smith and Lowe, +33+ ; Vallance,,***;,**. 285

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17 Area +, dolia.1, AD 13 G+ -Af Vano +. 2 Lirer et al.,,**+ + debris.1, flow head, hyperconcentrated flow.1, body - stream Area +, flow tail Sohn et al , + stream flow,, hyperconcentrated flow, - debris flow Sulpizio et al.,,**/ cm+* cm Sohn et al., +333 ; G+ -Af+ / Fig. +, b Vallance,,***,.1, Mf, Df G+ -Af0 Fig. +, c.1, Mf Df., G+ -Af1 Af2 Niihori et al.,**1,**3.1, Area +, G+ -MfL, DfL+ Fig. +, a,**3 Fig. +, d Vano 0 1 Fig. 0 Area +, Fig. 0 lucite Fig. +,. Burial process of the Roman villa in Somma-Vesuviana. (a) Pre-.1, eruption. Buildings were reconstructed based on sedimentological and archaeological data obtained in,**,,**2. (b) Initial subplinian phase of the.1, eruption. Scoria and ash were multiply dispersed from the eruptive columns. A few to +* cm fallout deposits (G+- Af+ to /) remained. (c) Column collapsing occurred and produced scoria flows in the later phase of subplinian eruption. After that, many phreatomagmatic explosions occurred and pyroclastic flows were produced in the climactic phase. G+ -Af0 to 2 were produced by these explosive eruptions. (d) Just after the.1, eruption, lahars buried a northern part of the villa and G+ -MfLs and G+ -DfLs were deposited. (e) In major laharic events after the.1, eruption, many flows occurred. The flows transported large boulders and buried channels produced by stream flows. Some parts of building may have been destroyed by these energetic debris flows. G+ -Mfs and Df were deposited during this stage. (f) After the laharic events, vegetation recovered. (g) AD /+,//-0 eruption occurred, and the fallout and lahar deposits (G,) buried the villa again. (h) After experiences of the +0-+ eruption and other eruptive events which produced G -, vegetation recovered again, and today many people live around the archeological site in Somma-Vesuviana. 287

18 Fig. +, e G+ -Mf+. Df G+ -Mf+ G+ -Mf,.1, Fig. +, f.1, /+, / G, G- Fig. +, g.1, *0 Fig. +, h /. G+ -MfL+ G+ -DfL+ G+ -MfL, G+ - DfL, Mf Df G-Mf , G-Af *23,*. Kaneko, T., Nakada, S., Yoshimoto, M., Fujii, T., Yasuda, A., Yoneda, M. and Aoyagi, M.,,**/, Determination of burial ae of the Augustus s villa (Italy). Geochem. J., -3, /1- /12. Lirer, L., Vinci, A., Alberico, I., Gifuni, T., Bellucci, F., Petrosino, P. and Tinterri, R.,,**+, Occurrence of intereruption debris flow and hyperconcentrated flood-flow deposits on Vesuvio volcano, Italy. Sedimentary Geology, +-3, +/ Mastrolorenzo, G., Munno, R. and Rolandi, G., +33-, Vesuvius +3*0 : a case study of a paroxysmal erupton and its relation to eruption cycles. J. Volcanol. Geotherm. Res., /2,,+1,-1. Mastrolorenzo, G., Palladino, D.M., Vecchio, G. and Taddeucci, J.,,**,, The.1, AD Pollena eruption of Somma- Vesuvius (Italy) and its environmental impact at the end of the Roman Empire. J. Volcanol. Geotherm. Res., ++-, +3-0.,**3,, 0/ 13. Niihori, K., Nagai, M., Kaneko, T., Fujii, T., Nakada, S., Yoshimoto, M., Yasuda, A. and Aoyagi, M.,,**1, Detailed stratigraphical and geological characteristics of volcanic and epiclastic deposits burying a Roman Villa on the northern flank of Mt. Vesuvius (Italy). Bull. Earthq. Res. Inst. Univ. Tokyo, 2,, Perrotta, A., Scarpati, C. and Luongo, G.,,**0a, Volcaniclastic resedimentation on the northern slope of Vesuvius as a direct response to eruptive activity. Landslides, -,,3/ -*+. Perrotta, A., Scarpati, C., Luongo, G. and Aoyagi, M.,,**0b, Burial of Emperor Augustus villa at Somma Vesuviana (Italy) by post-13 AD Vesuvius eruptions and reworked (lahars and stream flow) deposits. J. Volcanol. Geotherm. Res., +/2,../.00. Rolandi, G., Petrosino, P. And Geehin, J. Mc, +332, The interplinian activity at Somma-Vesuvius in the last -/** years. J. Volcanol. Geotherm. Res., 2,, +3 /,. Rolandi, G., Munno, R. and Postiglione, I.,,**., The AD.1, eruption of the Somma volcano. J. Volcanol. Geotherm. Res., +,3,, Rosi, M. and Santacroce, R., +32-, The A.D..1, Pollena erupton : volcanological and petrological data for this poorly-known Plinian type event at Vesuvius. J. Volcanol. Geotherm. Res., +1,,.3,1+. Rosi, M., Principe, C. and Vecci, R., +33-, The +0-+ Vesuvius eruption. A reconstruction based on historical and stratigraphical data. J. Volcanol. Geotherm. Res., /2, +/+ +2,. Santacroce, R. and Sbrana, A.,,**-, Geological map of Vesuvius. Universita degli studi di PISA. Smith, G.A., +320, Coarse-grained nonmarine volcaniclastic sediment: terminology and depositional process. Geol. Soc. Am. Bull., 31, ++*. Smith, G.A. and Lowe, D.R., +33+, Lahars : volcano-hydrologic events and deposition in the debris flow-hyperconcentrated flow continuum. In : Fisher, R.V. and Smith, G.A., Eds. Sedimentation in volcanic settings. Tulsa, Okka., Soc. Sed. Geol. (SEPM), Spec. Publ.,./, /31*. Sohn, Y.K., Rhee, C.W. and Kim, B.C., +333, Debris flow and hyperconcentrated flood-flow deposits in an alluvial 288

19 fan, Northwestern Part of the Cretaceous Yongdong tology, /., 0*10-/. Basin, Central Korea. J. Geol., +*1, ,. +32, - Sulpizio, R., Mele, D., Dellino, P. and LaVolpe, L.,,**/, A,/ complex, Subplinian-type eruption from low-viscosity, B-, -,1-.2. phonolitic to tephri-phonolitic magma: the AD.1, (Pol-,**. pp.-,. lena) eruption of Somma-Vesuvius, Italy. Bull. Volcanol., Vallance, J.W.,,***, Lahars. In : Siggurdsson, H. et al. Eds. 01, Encyclopedia of Volcanoes. Academic Press, San Diego, Sulpizio, R., Mele, D., Dellino, P. and LaVolpe, L.,,**1, Depos- pp. 0* its and physical properties of pyroclastic density cur- (Received December +.,,**3) rents during complex Subplinian eruptions : the AD.1, (Accepted February +3,,*+*) (Pollena) eruption of Somma-Vesuvius, Italy. Sedimen- 289