SSW from Volcán Chaitén (VC) (Data Repository Figure 1), and provides a detailed record

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1 GSA DATA REPOSITORY 0101 Moreno et al. Data Repository Appendi 1. Site setting and methods Site setting Lago Teo (LT) is located in the immediate vicinity of the Chaitén Township, ~8 km SSW from olcán Chaitén (C) (Data Repository Figure 1), and provides a detailed record of pyroclastic fallout deposits by virtue of its relatively high-sediment accumulating rates and constant depositional environment in an enclosed-basin lake isolated from, and perched well above the Río Chaitén floodplain. The lake is elliptical shape, has a maimum length of 18 meters, a surface area of ~ ha and a single concave depression with a maimum water depth of meters. Here we obtained two overlapping sediment cores from an anchored raft equipped with a 10-cm wide aluminum casing, using a -cm diameter Wright piston corer and a sediment-water interface piston corer with a 7.-cm diameter Pleiglas chamber. The stratigraphy of the cores was characterized by lithological descriptions, digital X-radiographs (Data Repository Figure ), and loss-on-ignition analysis following overnight drying at 10 C. We performed sequential burns at 0 C and 9 C for and 4 hours, respectively, to quantify the organic, carbonate, and siliciclastic content of the sediments (Bengtsson and Enell, 1986; Heiri et al., 001). The geomorphologic setting, distance and location of LT relative to C allows this lake to record most eplosive eruptions from C avoiding the deposition of fluvio-laharic detritus as well as thick and/or coarse-grained tephra carried predominantly eastward by the prevailing westerly winds. The small catchment area of LT and absence of inlet streams into the basin maimizes a local sedimentary record of predominantly or eclusively airfall

2 tephras, ruling out advection of reworked tephras into the site by fluvial or slope processes. A high-resolution palynological record developed from the LT core demonstrates continuous cover of aldivian/north Patagonian rainforests and absence of major lakelevel changes in the site which, along with the predominance of organic-rich lake mud, demonstrate depositional and environmental constancy in the basin. Chronology The chronology of the LT record is constrained by AMS radiocarbon dates (Data Repository Table 1) obtained from 1-cm thick sections along the core which, along with a core top age of -61 yr BP for the sediment-water interface, afford the basis for a Bayesian age model (Data Repository Figure ) using the Bacon (Blaauw and Christen, 011) package for R. This model takes into account the instantaneous deposition of all tephras by subtracting their cumulative thickness throughout the core. The tephra-free age model of LT suggests uninterrupted lacustrine sedimentation with relatively constant accumulation rate of lake sediments (median: 19.6 cm/kyr over the last ~10,000 years) (Data Repository Figure ). We note that the tephra from the 008 Chaitén eruption (LTT-1) occurs between depths 6-9 cm (Figure 1, Data Repository Table ) suggesting that this dense layer penetrated the uncompressed, partially suspended sediment-water interface on the lake floor. For this reason we decided not to carry out 10 Pb measurements on the upper portion of the water-sediment interface core. Our modeled age of 00 yr BP for LTT-1 must be taken with caution considering that this tephra occurs in the high-sediment accumulation, water-saturated uncompressed zone of the sediment core, and it constitutes an interpolation

3 between the core top age -61 yr BP and the age of AMS date UCIAMS-1607 (median probability calibrated age of 94 yr BP, Data Repository Table ). We interpret the modeled age of LTT-1 as an upper age limit for the effects of tephra penetration into previously deposited soft organic lake sediments, a factor that probably affects the interpolated and actual ages associated to all tephras in the LT record and, most likely, similar sites throughout our study area. Geochemistry All major element determinations were made on a JEOL Superprobe ± JXA-80 housed at ictoria University of Wellington, using the ZAF correction method. Analyses were performed using an accelerating voltage of 1 k under a static electron beam operating at 8 na. The electron beam was defocused between 10 and 0 µm. Oide values are recalculated to 100% on a volatile-free basis. Total Fe epressed as FeO t. We were unable to analyze some tephras ± LTT-11, LTT-1, LTT-16, LTT-19, LTT-1, LTT-4, either because of their fine grain-size (silicic) or the prevalence and density of crystal microlites within the glass matri (andesitic to basaltic).

4 References Bengtsson, L., and Enell, M., 1986, Chemical analysis, in Berglund, B.E., ed., Handbook of Palaeoecology and Palaeohydrology, John Wiley & Sons, p Blaauw, M., and Christen, J.A., 011, Fleible Paleoclimate Age-Depth Models Using an Autoregressive Gamma Process: Bayesian Analysis, v. 6, p Heiri, O., Lotter, A.F., and Lemcke, G., 001, Loss on ignition as a method for estimating organic and carbonate content in sediments: reproducibility and comparability of results: Journal of Paleolimnology, v., p

5 Data Repository Figure 1. Map of southern South America and the study area showing the location of Lago Teo, Chaiten township and nearly volcanic centres. Also indicated are selected andic cover-bed sections where proimal olcan Chaiten (C) and Michimahuida olcanic Comple (MC) tephra sequences have been described and sampled for comparative glass geochemistry (see Figure ). Data Repository Figure. X-radiographs of sediment cores obtained from Lago Teo. Core 001BT1 is shown in the left followed by cores 001AT1, 001AT and 001AT from left to right. Individual core tops oriented toward the top. Data Repository Figure. Probability distribution of individual calibrated radiocarbonage measurements from Lago Teo (blue pattern), also shown is the Bayesian age applied to the calendar age data. The intensity of the gray pattern represents the probability density of the age models bounded by dashed lines that represent the 9% confidence limits. Data Repository Figure 4. CaO and KO vs FeOt and KO vs SiO contents of glass shards from rhyolitic tephra layers preserved in the Lago Teo core. Analyses from the 008 Chaitén eruption are included for comparison (Alloway & illarosa, this study). Data Repository Figure. Tephrostratigraphy of the Lago Teo sediment core compared with equivalent-aged andic cover-bed sections in the same vicinity containing both olcán

6 Chaitén (C) and Michinmahuida olcanic Comple (MC)-sourced tephra beds. See Figure 1 for site locations and Figure for geochemical composition of MC and rhyolitic tephras. Data Repository Table 1. Tephra codes (LTT= Lago Teo Tephra), depth ranges and interpolated calibrated ages for each pyroclastic layer in the Lago Teo record. Yellow highlighted samples are rhyolitic tephras from C, green highlighted samples are from MC. We calculate time steps of 97 ± yr between pyroclastic layers from all sources over the past ~10,000 yr and 7 ± 186 yr between C events over the last millennium (mean ± 1σ), considering the correct calendar age for LTT-1 in both cases. Data Repository Table. Information on the radiocarbon dates from the Lago Teo record. All radiocarbon dates were converted to calendar ages before present using the southern hemisphere calibration dataset included in the CALIB 6.0 software. Data Repository Table. Summary of glass shard major element compositions of tephra beds preserved in Lago Teo. Mean ± 1 standard deviation, based on n analyses. All samples are normalized against glass standards ATHO-G & G Chaitén samples (unpublished data retrieved from 17 proimal & distal localities collected by G. illarosa,. Outes and B.. Alloway). Compositional Groups: 1 rhyolite (R), trachyte (T), dacite (D); basaltic trachyandesite (BTA), trachyandesite (TA), basaltic andesite (BA),

7 andesite (A) (see Figure ). Compositional fields after Le Maitre (1984). Analyst: B.. Alloway. Data Repository Table 4. Glass-shard electron microprobe data from the 008 Chaitén eruption compared with silicic tephra preserved in Lago Teo. 1 Samples retrieved from 17 proimal and distal localities.

8 7 4 W Caleta Gonzalo Fiordo Largo 0 10 Soil cover-bed sections containing proimal MC tephra beds Chile Talcán 14J1S4,T/T 14J1S,T1 Caleta Santa Bárbara n. Chaitén 96-m n. Michinmahuida 404-m Argentina Chaitén Lago Teo Pum-,T4/T Pum-4,T1/T/T Campo Grande, T1 4 S Golfo Corcovado Amarillo Chaitén n. Corcovado 90-m Puerto Cárdenas Lago Yelcho

9

10 0 0 Depth (cm) cal yr BP

11 CaO K O FeO FeO Chaiten tephra n = 0; 17 localities LTT-1, n = 70 4 LLT-, n = 10 LTT-4, n = 18 K O SiO SiO

12 CaO K O FeO FeO K O 4 LLT-, n = 18 LTT-6, n = Chaiten tephra n = 0; 17 localities 4 LLT-1, n = 48 LTT-17, n = 6 LTT-, n = 1 LTT-, n = 16 LTT-, n = Chaiten tephra n = 0; 17 localities SiO SiO

13 Pumalin- S 4º.0 W 7º R, -T1 (008) R, -T -T (mied, ant s nest) Pumalin-4 S 4º W 7º (m) Lago Teo S 4º W 7º 4.4 -T4 (GROUP ) -T (GROUP ) ± yr 0 ± yr 66 ± yr 1,00±0 yr 0 R, LTT-1 R, LTT- BTA-TA R, LTT-4 R, LTT- R, LTT-6 BTA-TA 1 R, -T6 unnamed tephra, na unnamed tephra, na BTA-T BA A na unnamed tephra, na 4,10± yr 4,890±40 yr R, LTT-1 na BA-A BA-A R, -T7 -T8, na R, 4-T7 4-T6, na 6,800± yr 7,09±0 yr 00 na R, LTT-17 T unnamed tephra, na T (GROUP ) na 8,6± yr 8,60±0 yr 8,91±40 yr 8,9±0 yr 00 * * T-D R, LTT- R, LTT- R, LTT- BA-A na - not analysed * - analysed but intensely microlitic R, 4-T4 KEY 1 4-T (GROUP ) Andic soil material Rhyolitic lapilli & ash Basaltic - Andesitic ash R, 4-T Andesitic lapilli 0 Basaltic scoriaceous lapilli & coarse ash Basaltic lava-flow deposit 1. Colluvium Pyroclastic flow & associated fall deposits 4-T1 (GROUP ).+

14 phra Depth range Thickness Interpolated age Interpolated age code (cm) (cm) Median (cal yr BP) ±σ (cal yr BP) LTT LTT LTT LTT LTT LTT LTT LTT LTT LTT LTT LTT LTT LTT LTT LTT LTT LTT LTT LTT LTT LTT LTT LTT LTT LTT ,46 1

15 Laboratory code Depth with tephras (cm) Depth without tephras (cm) 14 C yr BP ±1σ cal yr BP (-σ) cal yr BP (+σ) cal yr BP (median) UCIAMS ± UCIAMS ± CAMS ± CAMS ± UCIAMS ± CAMS ± CAMS ± 11 7 UCIAMS ± CAMS ± CAMS ± CAMS ± CAMS ± UCIAMS ± UCIAMS ± CAMS ± UCIAMS ± CAMS ± UCIAMS ± UCIAMS ± UCIAMS ± CAMS ± , UCIAMS ± UCIAMS ± ,17 10,016

16 Tephra SiO Al O TiO FeO MgO MnO CaO Na O K O Cl Total n Group LTT ± 0.1 LTT ± 0.7 LTT-.8 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± 0..1 ± ± ± ± ± ± LTT ± 0.8 LTT ± ± ± ± ± ± ± ± ± ± ± ± ± ± 0.17 nd ± ± LTT ± ± ± ± ± ± ± ± LTT-7.88 ± ± ± ± ± ± ± ± ± 0.71 LTT-8 Pop ± ± ± ± ± ± ± ± ± ± Pop. 7.6 ± ± ± ± ± ± ± ± ± ± LTT ± ± ± ± ± ± ± ± 0.07 nd 98.1 ± LTT ± ± ± ± ± ± ± ± 0.09 nd ± LTT ± ± ± ± ± ± 0.08 nd ± LTT ± ± ± ± ± ± ± ± 0.06 nd 98.6 ± LTT ± ± ± ± ± ± ± ± 0.1 nd 99.0 ± LTT ± ± ± ± ± ± 0.07 nd ± LTT ± ± ± ± ± 0.1. ± ± 0.0 nd ± LTT ± ± ± ± ± ± ± ± 0. nd 9. ± LTT-1 Contaminated (intensely microlitic) 8.77 ±.4 LTT ± ± ± ± ± ± ± ± ± ± ± ± ± ± 0..0 ± ± ± nd 1 1 LTT ± ± ± ± ± 0.1. ± ± LTT-4 Contaminated (intensely microlitic) 6.09 ±.94 LTT ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± nd 1 1 LTT-6 7. ± ± ± ± ± ± ± ± ± Chaitén ± 0.4 G ± ± ± ± ± ± ± ± 0.4. ± ± ± 0.04 nd 98.0 ± 1.6 nd 99.4 ± ATHO-G 7.61 ± ± ± ± ± ± ± ± ± ± 0. 19

17 Chaitén LTT-1 LTT- LTT-4 LTT- LTT-6 SiO 7.98 ± ± ± ± ± ± 0.71 Al O 14.0 ± ± ± ± ± ± 0.41 TiO FeO 1.7 ± ± ± ± ± ± 0.1 MgO 0.6 ± ± ± ± ± ± 0.0 MnO ± CaO 1.6 ± ± ± ± ± ± 0. Na O.86 ± ± ± ± ± ± 0.8 K O.14 ± ± ± ± ± ± 0.4 Total 98.0 ± ± ± ± ± ± 0.89 n LLT-1 LLT-17 LTT- LLT- LTT- SiO ± ± ± ± ± 0.9 Al O 14.0 ± ± ± ± ± 0.16 TiO FeO 1. ± ± ± ± ± 0.07 MgO MnO CaO 1.0 ± ± ± ± ± 0.0 Na O.9 ± ± ± ± ± 0.7 K O.1 ± ± ± ± ± 0.40 Total ± ± ± ± ± 0.89 n