Introduction

The Peruvian volcanic arc results from the subduction of the oceanic Nazca plate beneath South-American continental lithosphere. This volcanic province, which belongs to the Central Volcanic Zone of the Andes, is formed upon the Western Cordillera of the Peruvian Andes, and it comprises at least 12 Late Pleistocene and Holocene volcanic centres and several monogenetic fields (Siebert et al. 2010). Among these volcanic centres, seven volcanoes have experienced eruptive activity since the arrival of the Spanish conquistadors in the sixteenth century. These edifices include the well-know El Misti, Ubinas, Sabancaya and Huaynaputina volcanoes, as well as other lesser-studied edifices such as Ticsani, Tutupaca and Yucamane (Fig. 1).

Fig. 1
figure 1

a Location of Tutupaca volcano in the Peruvian volcanic arc. b Regional map showing the location of the Tutupaca and Yucamane volcanoes

Full size image

On the basis of numerous studies over the last decades, the eruptive chronologies of a number of these volcanic centres are well constrained. The two last major explosive events in this part of the Andes were the large 2-ka BP plinian eruption of El Misti volcano (Volcanic Explosive Index-VEI of 5; Thouret et al. 2001; Harpel et al. 2011; Cobeñas et al. 2012) and the 1600 AD explosive eruption of Huaynaputina volcano which was the biggest historical explosive eruption in the Andes (VEI 6, Thouret et al. 1999; Adams et al. 2001). Other small to moderate explosive events occurred at El Misti in the 15th century (Thouret et al. 2001), as well as at the frequently active Ubinas edifice that experienced at least 25 eruptive episodes since the 16th century (Thouret et al. 2005; Siebert et al. 2010) including a moderate-size eruption in 1667 AD and the recent eruptions of AD 2006–2009 and 2013–2015 (Rivera et al. 2014). Last, rare historical accounts suggest that Sabancaya volcano was also active in the 18th century (AD 1750, 1784), and more recently, vulcanian explosive activity was described in AD 1988–1997 (Siebert et al. 2010; Gerbe and Thouret 2004). All this information shows that the Peruvian segment of the Andean Central Volcanic Zone experienced significant explosive activity through the last few centuries.

Tutupaca volcano (17° 01′ S, 70° 21′ W) is located at the southern end of the Peruvian arc (Fig. 1), 25–30 km to the north of Candarave village (Tacna Department, Southern Peru). Historical chronicles reported by Hantke and Parodi (1966) indicate that several volcanic eruptions affected this part of the Andes in AD 1780, 1787, 1802, 1862, and 1902. These authors suggested that the source of these eruptions was Tutupaca volcano. However, based on the youthful and uneroded morphology of the contiguous Yucamane volcano, several authors attributed these eruptions to the latter (Siebert et al. 2010; de Silva and Francis 1990). In this manuscript, we present results of a detailed study of recent Tutupaca eruptive products, which include field descriptions of the main volcanic units, petrologic characterisation of juvenile material, radiocarbon dating and correlation with historical records. With these results, we reconstruct the eruptive sequence associated with the last eruption of Tutupaca, which is an unidentified historical explosive event in the Andes.

Overall structure of Tutupaca volcano

The Tutupaca volcanic complex is constructed on top of a high volcanic plateau consisting of volcanic and volcano-sedimentary rocks, which include thick Mio-Pliocene ignimbritic deposits (Fidel and Zavala 2001; Mamani et al. 2010). This sequence is well exposed in the Callazas and Tacalaya valleys located at the eastern and western parts of the complex (Fig. 1). The Tutupaca volcanic complex rises from the basement at 4400–4600 m above sea level (m asl) and is composed of a big basal edifice and two small “twin” peaks (the Western and Eastern Tutupaca), which are located at the northern part of the volcanic complex and constructed on the remnants of the basal volcano (Figs. 1 and 2). Several fault systems have been identified in this part of the Andean cordillera, the main one being a series of normal faults with a sinistral component that has been mapped around the Suches lake and that displays a roughly N140 direction (Benavente et al. 2010). These faults affected the volcanic complex and seem to have influenced its structural development (Fig. 1).

Fig. 2
figure 2

Panoramic view of the north-east of Tutupaca volcano and its amphitheatre

Full size image

The Basal Tutupaca edifice is mostly composed of andesitic and dacitic lava flows. Based on the radial distribution and dips of these lavas, we infer that the former summit was located 2–3 km to the south of the current Tutupaca peaks. The summit zone is characterised by an uneven topography and strong hydrothermal alteration (Figs. 1 and 2). This edifice was strongly affected by Pleistocene glaciation, resulting in the highly eroded morphology and glacial modification of several radially oriented valleys. As a result, major moraine deposits (up to 100 m thick) were stacked mostly in the southern part of the complex, as well as in the Callazas and Tacalaya valleys. These moraines are probably formed during the Last Glacial Maximum (LGM), which has been broadly dated at 17–25 ka in the Western Cordillera of the Peruvian Andes (Smith et al. 2008; Bromley et al. 2009). In addition, a thick ignimbrite deposit of dacitic composition outcrops on the southern and western flanks of the edifice and represents a major explosive phase that probably occurred at the end of edifice evolution. This ignimbrite deposit is covered by the LGM moraines, suggesting an age older than 25 ka. The less massive Western Tutupaca peak (5815 m asl) is mostly composed of lava flows and domes of siliceous andesitic and dacitic compositions. This edifice was also eroded by the Late Pleistocene glaciers. A sequence of tephra fallout deposits outcropping in the distal south-western part of the volcano shows that this edifice experienced powerful plinian to subplinian eruptions during its history. Last, the younger Eastern Tutupaca peak (5790 m asl) is a dacitic dome complex characterised by a lack of glacial erosion, suggesting a Holocene age. It is composed of at least 7 coalescing lava domes (Manrique 2013), which are cut by a 1-km-wide horseshoe-shaped amphitheatre open to the NE (Fig. 1b). It is worth noting that the direction of opening of the amphitheatre is almost orthogonal to the N140 regional faults that cut the edifice. We identified at least two debris avalanche deposits associated with this edifice: an older deposit that is channelised in the valleys located to the E (Zuripujo) and SE of the volcano (e.g. Azufre Grande) and a younger deposit that outcrops immediately to the NE of the amphitheatre and that will be described in detail in this work.

The recent eruptive products

The north-eastern part of Eastern Tutupaca edifice (Figs. 2 and 3) exhibits a remarkably well-preserved volcanic sequence characterised by abundant surface structures. Here, we describe the main characteristics of these deposits in stratigraphic order. The detailed descriptions of these deposits and their surface structures, as well as their dynamic implications, are beyond the scope of this manuscript and are discussed in a companion paper (Valderrama et al. 2014).

Fig. 3
figure 3

Simplified geological map of the Recent Tutupaca deposits. Location of main stratigrafic sections is shown. Z-PDC Zuripujo pyroclastic density current deposit, HA-DAD hydrothermally altered debris avalanche deposit, P-PDC Paipatja pyroclastic density current deposit, DR-DAD dome-rich debris avalanche deposit. The area delimited by the black dashed line corresponds to the lateral and distal deposits related to the ash-cloud accompanying the P-PDC. Dots correspond to minimum thickness (in cm) of P-PDC

Full size image

The Zuripujo pyroclastic density current deposit (Z-PDC)

Exposed in the lower part of the Zuripujo valley, 8–10 km from the Eastern Tutupaca edifice, is a 2–5-m-thick unit composed of at least two or three block-and-ash flow deposits, which are interlayered with centimetre-thick ash-rich layers showing cross-bedding and lamination (Figs. 3, 4 and 5). The block-and-ash flow deposits are massive, matrix-supported, with 20–30 vol.% angular and subangular blocks in an unconsolidated, grey, medium ash matrix. The block sizes range from 5 to 10 cm, although 1-m diameter blocks are also locally observed. The deposit is mostly polylithologic, but the most common lithology is dark grey, unaltered, dense dacitic blocks with plagioclase, amphibole and biotite in a vitreous groundmass. These blocks, and the breadcrust bombs also locally observed, are interpreted as representing a collapsing dome. A large amount of slightly altered, dark grey, pyroxene-rich andesitic blocks are also present in the deposit and are interpreted as blocks entrained from underlying units of the older edifice. The most striking characteristic of this deposit, however, is the relatively large amount (5–10 vol.%) of centimetre-size, white-yellowish, highly altered, friable lava fragments that are also present as smaller clasts in the matrix of the deposit (Fig. 5). Three charcoal samples collected in this unit have been dated and yielded almost identical ages (190 ± 30, 220 ± 30 and 230 ± 30 aBP; Table 1). At the Zuripujo valley, the Z-PDC unit is overlain by an up to 1-m-thick (Figs. 4 and 5), locally reworked, grey-reddish ash-rich layer that includes some breadcrust bombs at the top and is interpreted as a lateral facies of the Paipatja pyroclastic density current deposit (P-PDC, see below). The contact between these two units is commonly flat, although in rare outcrops, we observed erosive features as well as a 10–30-cm-thick layer of reworked material.

Fig. 4
figure 4

Composite stratigraphic sections of the Tutupaca debris avalanche deposits and related pyroclastic flow deposits. Location of the stratigraphic sections is shown in Fig. 3

Full size image
Fig. 5
figure 5

Photos of the Zuripujo pyroclastic density current deposit (Z-PDC). a Outcrop of 4–5-m-thick outcrop of Z-PDC in the Zuripujo valley (site 11, samples TU-12-27 and TU-12-79, Fig. 3). b The upper 2 m of outcrop (a) showing the Z-PDC overlain by the Paipatja pyroclastic density current deposit (P-PDC). Note the presence of breadcrust bombs in the Z-PDC. c The Z-PDC at a small ravine located to the south of the main Zuripujo valley (site 12, sample TU-12-08, Fig. 3). d Detail of the matrix of the Z-PDC deposit showing a charcoal fragment. Note also the abundance of light-coloured hydrothermally altered fragments

Full size image
Table 1 14C age results obtained in this study
Full size table

The upper part of the Zuripujo valley exposes a 3–5-m-thick sequence of block-and-ash flow deposits that covers an older debris avalanche deposit. This block-and-ash unit, which can be traced up to the eastern foot of the Tutupaca domes, displays a rough surface morphology characterised by an enrichment in metric-size angular blocks and flow structures such as the fan observed at the Zuripujo valley bifurcation, 4–5 km from the Eastern Tutupaca summit. The spatial continuity between the proximal and distal deposits at Zuripujo valley, its stratigraphic position (both covered by the Paipatja PFD) and the petrography of the blocks indicate that they are parts of the same volcanic unit.

The Tutupaca debris avalanche deposits

This unit is exposed towards the northeast of the Tutupaca dome complex, in a zone between the amphitheatre and the Villaque and Taipicirca hills (Fig. 3), over an area of around 12–13 km2. In the proximal zone (i.e. the first 3 km from the Tutupaca amphitheatre), a heterogeneous breccia is exposed, composed of two successive units interpreted as debris avalanche deposits. At the foot of the amphitheatre, the lower unit forms a massive, Toreva block-like structure 1–1.5 km in diameter and 150–200 m high that is flanked by two 1.5-km-long levees diverging from the amphitheatre. Downhill, the deposit consists of several 200–700-m-long, 20–40-m-high megablocks, as well as smaller 100–200-m-long hummock-like hills (Figs. 3, 4 and 6). These features are composed of a heterogeneous, polymict breccia, which, following Glicken’s (1991) facies terminology, is a block facies consisting of highly cataclased, metric-size blocks with abundant jigsaw cracks in a fine-medium sand matrix. Lava blocks are mostly highly altered (hydrothermally altered), yellow-reddish andesites, although other petrographic types are observed and include oxidised, reddish-grey andesites, and scarce, unaltered, dark grey andesites and dacites. Given the high amount of altered fragments, we call this unit the Hydrothermally-Altered Debris Avalanche Deposit (HA-DAD, Fig. 6).

Fig. 6
figure 6

Photos of the debris avalanche deposit (DAD) corresponding to the proximal-medial zone (site 5, Fig. 3). a, b Lower hydrothermally altered unit (HA-DAD) and upper dome-rich unit (DR-DAD). We also note the deposits of the P-PDC. c Detail of the HA-DAD showing the large amount of altered blocks. d Surface structures (ridges) observed at HA-DAD

Full size image

In the medial zone (i.e. roughly 3 to 6 km from the amphitheatre), the debris avalanche deposit is characterised by a rough surface morphology consisting of longitudinal, elongated ridges that commonly diverge with distance from the amphitheatre (Figs. 3 and 6). These ridges are 5–10 m wide, 150–400 m long and 2–5 m high (for a detailed description of these structures, the reader is referred to the companion paper of Valderrama et al. (2014)). In this medial zone, the debris avalanche deposit is exposed along two corridors. The first one follows an NNE direction, reaching the Taipicirca valley and defining an 80-m-high run-up onto the Villaque hill, whereas the second corridor is between two old moraines and follows an NE direction to reach the Paipatja plain. In this latter part, the HA-DAD unit is overlain by an upper deposit, which is mainly composed of unaltered (fresh) dark grey dome rocks of dacitic composition (Dome-Rich Debris Avalanche Deposit, DR-DAD, Fig. 6). This upper unit shows scarce evidence of cataclasis (such as jigsaw cracks), but instead shows abundant prismatically jointed blocks, indicating an origin in a still-hot dome complex. In between these two DAD units, we observed the Paipatja pyroclastic flow deposit described below.

Last, in the distal zone (i.e. more than 6 km from the amphitheatre), on the Paipatja plain and up to the Callazas river, the debris avalanche deposits are mostly covered by the Paipatja pyroclastic flow deposits (see below). Several big (>1 m in diameter) blocks distributed on the plain, whose bases are surrounded by the Paipatja pyroclastic flow deposit, suggest, however, that there is an underlying debris avalanche deposit up to a distance of 7–8 km from the amphitheatre. We estimate a volume of 0.6–0.8 km3 on the basis of the mapped surface of the debris avalanche deposits and an average thickness of 25–40 m. This estimate probably represents a minimum volume, given that the Tutupaca debris avalanche deposit is covered by the Paipatja pyroclastic flow deposits.

The Paipatja pyroclastic density current deposit (P-PDC)

Distribution and stratigraphic relations

This unit spreads to the northeast of Tutupaca, reaching the Paipatja plain and the Callazas valley 8–10 km from the vent. A secondary branch of this unit reaches Suches lake 10–12 km from the vent (Fig. 3). In the proximal and medial zones (up to 6 km from the amphitheatre), this unit overlies the lower debris avalanche deposit unit (HA-DAD) and is covered by (and in some places interstratified with) the upper debris avalanche deposit unit (DR-DAD). In the distal zone (i.e. beyond 6 km from the amphitheatre), the P-PDC deposit also covers the main HA-DAD unit and appears to be mainly channelised in the numerous valleys draining the Paipatja plain, although an ash-rich, 10–20-cm-thick, over-bank deposit is also observed (Fig. 3). On the Paipatja plain, we observed two successive P-PDC units (Figs. 4 and 7). The widespread, lower unit covers the entire Paipatja plain and reaches the Callazas valley, whereas the upper unit is characterised by 1–1.5-m-thick bomb-rich lobes that overlie the lower unit (Figs. 4 and 7).

Fig. 7
figure 7

Paipatja pyroclastic density current deposit (P-PDC). a Lower and upper units of P-PDC at Paipatja plain (site 7, Fig. 3). b Detail of the upper P-PDC deposit showing the enrichment in decimeter-size cauliflower- and breadcrust-like bombs. c Detail of the P-PDC deposit at the Suches lake (site 1, Fig. 3). Note the crude stratification of the fine grained matrix and the presence of many charred twigs and Andean grass (TU-13-02, age indicated). d Detail of the P-PDC at the distal end at Callazas valley (site 9, Fig. 3). Note the presence of gas escape pipes (marked by arrows)

Full size image

The thickness of the P-PDC unit is highly variable, ranging from 0.5 to 2 m thick on the Paipatja plain and around Suches Lake, to 2–5 m in the channelised distal zone in the Callazas valley. In addition, given that the P-PDC unit overrides the lower debris avalanche unit in the medial zone, it is less thick on the ridges than between them. As a result, large thickness variations (from around 10 cm to 1 m) are also observed on a scale as small as ~10 m. We stress that due to a lack of erosion, no cross sections exist in the flat area of the Paipatja plain and thus thickness measurements are scarce.

Deposit description and dating

Over the whole Paipatja plain, the P-PDC deposit is massive, matrix-supported, with 20–40 vol.% of angular to subangular lava blocks and bombs in a dark grey, medium-to-coarse ash matrix. Block size ranges from ~3 to 20 cm, although occasional blocks 0.5–1 m in diameter are also observed. Bombs vary from 10 to 50 cm in size, and they are mostly observed at the deposit’s surface. The deposit exhibits slight normal grading overall. No clear differences in the amount of blocks and bombs are observed between the proximal and distal parts of the deposit. In contrast, a progressive decrease in block size is observed with distance.

Extensive exposures of P-PDC unit exist in the Callazas valley, which hosts the maximum deposit runout (sites 9 and 10 at 8–10 km from the amphitheatre, Figs. 3 and 4). There, the P-PDC unit rests on a volcano-sedimentary sequence that includes debris flow deposits and fine-grained lacustrine deposits. The P-PDC deposit is composed of two main layers. The lower layer is mostly ash-rich, whereas the upper layer is highly enriched in bombs at the top of the deposit, with many centimetre-size gas escape pipes. Debris flow deposits comprising reworked material cover the P-PDC unit. Charcoal is extremely scarce in the Paipatja plain deposits, probably because outcrops exposing the base of the deposit are rare. However, at site 10 (Figs. 2 and 3), we found plenty of carbonised grass that yielded an age (235 ± 35 aBP; Table 1), which is radiometrically indistinguishable from those obtained for the Zuripujo PDC deposits (190–230 aBP).

The northern branch of the P-PDC unit outcrops between the Villaque hill and Suches lake (Fig. 2). In this zone, the unit is topographically constrained, 1–2 m thick and appears as a grey, massive layer mostly composed of medium-to-coarse ash with scattered dense lapilli. Its base is composed of a 20–25-cm-thick layer exposing a crude planar stratification with some decimetric lenses of coarser and in places altered (oxidised) material. Overlying this basal layer, the bulk of the deposit does not have any laminations but shows a slight reverse grading. The fact that the P-PDC deposit is exposed in this zone suggests that at least the upper part of the PDC was able to surmount the Villaque hill. In this context, the deposits at Suches lake may have been formed by sedimentation from the uppermost, more dilute part of the PDC, following the scenario described by Druitt et al. (2002) at Soufrière Hills volcano. The lower part of the unit bears plenty of charred twigs as well as carbonized grass that yield a very similar age to those of the Paipatja plain (i.e. 220 ± 40 aBP; Table 1).

Granulometry and componentry

Grain size analysis was carried out on 14 selected samples from the P-PDC deposit. In the absence of natural, deep cross sections, we sampled the matrix of the deposit by digging (down to 150 cm) in flat areas from the proximal to distal parts of the deposit. Selected grain size histograms (Fig. 8) show that the deposit consists of fine ash to lapilli fragments (−4φ to +5φ), showing a large grain size distribution. Proximal (i.e. sites 11, 10) and central-distal (i.e. sites 12, 13) deposits have similar grain size distributions, which are clearly different from those of lateral deposits (i.e. sites 15C, 02D). In fact, the size distribution of the lateral facies, such as those in the Suches and Zuripujo valleys is almost unimodal, with a fines-enriched trend and good sorting (σφ ~ 1-2), whereas central deposits are characterised by a “flat” distribution and poor sorting (σφ > 2). The P-PDC deposits define a narrower grain size range and tend to be less well sorted than well-known blast deposits (Hoblitt et al. 1981; Druitt 1992; Belousov et al. 2007; Komorowski et al. 2013; Bernard et al. 2014), and fall instead (Fig. 8) into the “pyroclastic flow” field defined by Walker (1983).

Fig. 8
figure 8

a–d Selected grain size histograms for P-PDC samples. e Mdϕ vs σϕ diagram including the “Flow” field (Walker 1983) as well as the fields for different blast deposits (from Belousov et al. 2007). Mount St. Helens (MSH 1980), Bezymianny (BZ 1956) and Soufrière Hills (SHV 1997)

Full size image

Three main types of blocks are observed in the P-PDC deposit, the most abundant being angular to subangular, dense, porphyritic dacite blocks with many prismatically jointed fractures. A less abundant component corresponds to vesicular and highly porphyritic cauliflower- and breadcrust-type bombs, which are mostly observed on top of the deposit. A last, minor component corresponds to altered andesitic blocks interpreted as fragments entrained from the basement (cf. Roche et al. 2013). For the deposit matrix, we carried out a componentry analysis based on the methodology developed by Eychenne and Le Pennec (2012) in which at least 300 grains were chosen for fractions of −3φ to +1φ. We studied the same 14 samples as for the granulometric analyses, which are distributed from the proximal to distal zones. Three main classes of components were identified: fresh dome fragments, free crystals and altered lava fragments, the latter being interpreted as fragments from the old domes and the basal edifice. Fresh dome fragments range from 57 to 72 wt.%, free crystals (mostly present in the 0φ and +1φ classes) vary from 6 to 18 wt.% and altered fragments range from 20 to 48 wt.%.

Summary of petrologic characteristics

Based on 30 whole-rock major and trace element analyses, the Holocene eruptive products of Tutupaca volcano are classified as high-K calc-alkaline dacites (Fig. 9). All samples from the Eastern Tutupaca domes display a very restricted dacitic composition (64.4–66.1 wt.% SiO2, normalised to an anhydrous basis, Table 2, Fig. 9), as well as the lava blocks included in the debris avalanche deposits and in the Z-PDC deposits, which show similar chemical characteristics (64.5–65.9 wt.% SiO2). In contrast, the blocks and bombs of the P-PDC deposits have slightly higher silica contents (65.1–68.0 wt.% SiO2), especially the scarce pumiceous samples, which have silica-rich compositions (67–68 wt.% SiO2). For most major and trace elements, Eastern Tutupaca samples lie on the trend defined by the whole Tutupaca volcanic complex (Fig. 9). However, the Eastern Tutupaca rocks display a slight enrichment in some trace elements, namely the light rare earth elements (e.g. La) and a notable depletion in heavy rare earth elements (e.g. Yb), which leads to high La/Yb ratios for these Eastern Tutupaca samples (Fig. 9). A detailed petrological study is in progress, but our current hypothesis is that these characteristics are due to high-pressure crustal processes such as fractionation of amphibole and/or garnet and/or assimilation of deep crustal rocks (cf. Thouret et al. 2005; Mamani et al. 2010; Rivera et al. 2014).

Fig. 9
figure 9

Selected geochemical data for Tutupaca. a, b SiO2 vs K2O diagram and c SiO2 vs La/Yb

Full size image
Table 2 Selected whole-rock major (wt.%) and trace element (ppm) analyses of recent Tutupaca eruptive products
Full size table

Lava samples from the Eastern Tutupaca domes as well as those from the debris avalanche deposit are dark-grey, highly porphyritic (30–40 vol.%) dacites containing plagioclase (10–20 vol.%), amphibole (10 vol.%), biotite (5 vol.%) and Fe-Ti oxides (2–3 vol.%). We also found ortho- and clinopyroxene, sphene, quartz and apatite as accessory phases (≤1 vol.%). Two populations of plagioclase were observed, the main group corresponding to euhedral, fresh, zoned phenocrysts (up to 4 mm), and the subordinate group (<3–4 vol.%) consisting of subhedral crystals with frequent disequilibrium textures such as reaction rims and dusty concentric zones and cores. The second most abundant mineral is amphibole, which appears as fresh, euhedral crystals (<1 mm) or is partially to completely replaced by a microcrystalline assemblage composed of oxides (opacite). Biotite, which appears as euhedral to subhedral phenocrysts (up to 1–2 mm), represents the third main phase, frequently showing intergrowth textures with amphibole, plagioclase and Fe-Ti oxides. These phases, together with the other accessory minerals, are included in a vitreous to intersertal groundmass with a maximum of 5–10 vol.% vesicles. The dense blocks from the P-PDC deposit have a texture and a mineral assemblage similar to that of the lava dome blocks described above. In contrast, the bombs are more vesiculated (up to 40 vol.%) and display a high crystallinity (15–20 vol.% phenocryst) and the same mineral assemblage as the dense blocks. In conclusion, the geochemical and petrographical characteristics are useful tools to discriminate Eastern Tutupaca eruptive products from older products of Western and Basal Tutupaca edifices. We stress the strong homogeneity of the recent Tutupaca dacites and the fact that the young domes, the blocks from the DA deposit (namely those from the DR-DAD), and the juvenile samples from the P-PDC deposit share the same geochemical and petrographical characteristics.

Discussion

Historic chronicles and age of the Tutupaca sector collapse

Historical chronicles reported by Fidel and Zavala (2001) clearly point to an explosive eruption of Tutupaca volcano during the last few centuries. Zamacola y Jaúregui (1804) describes that “now 15 years (i.e. around 1789 AD) burst (a volcano) close to the village of Candarave, distant 60 leagues from this city (i.e. Arequipa; 1 Castellan league is about 4.2 kilometres), since that time, it has been smoking incessantly; but there will be two years (i.e. in 1802 AD), (the volcano) made a formidable explosion that its ashes and noise reached more than 100 leagues” (this text and the next one were translated by the authors from the original texts in Spanish). Valdivia (1847) is more explicit since he mentions that “on March, 20 1802 burst Tutupaca, leaving for five months ash in the air, (and) getting dark the atmosphere as far as Locumba, Tacna and Arica (cities located in the south-western coastal zone)”. These chronicles are corroborated by the oral tradition of the Candarave inhabitants, who consider Tutupaca as “the villain”, in comparison to the “the good” Yucamane. This perception seems clearly related to the past explosive eruptions of Tutupaca and their impacts on local communities (Zora Carvajal 1954). These chronicles clearly show that Tutupaca experienced a strong explosive episode that started around 1787 AD and whose paroxysm probably occurred in 1802 AD.

The historic information is corroborated by the five radiocarbon ages (Table 1) we obtained from charcoal samples from the Z-PDC deposit in the Zuripujo valley and the P-PDC deposit on the Paipatja plain and nearby Suches lake. Samples from the Z-PDC deposit yield two well-constrained ages (220 ± 30 and 230 ± 30 aBP, Table 1), and a third slightly younger one (190 ± 30 aBP), whereas the two samples from the P-PDC deposits give very close ages (220 ± 40 and 235 ± 35 aBP, Table 1). We calibrated these conventional 14C ages to calendar ages using the Calib 6.0 code (Stuiver and Reimer 1993; Stuiver et al. 2005) and the Southern Hemisphere calibration curve (SHCal04, McCormac et al. 2004), which is suitable for this region and is available back to 11 ka cal BP (Fig. 10). Results of this calibration procedure show that the five samples are statistically identical at a 95 % confidence level with a pooled mean of 218 ± 14 aBP. The calibrated calendar age for this average 14C age yields two age spans, the most important being 1731–1802 cal AD period (with a relative area of 85 %). We emphasise that the two historic eruptions (1787–89 and 1802 AD) reported by Zamácola y Jaúregui (1804) and Valdivia (1847) fall at the end of this period.

Fig. 10
figure 10

Density probability functions for the calibrated radiocarbon ages of the last Tutupaca explosive eruption

Full size image

Unfortunately, radiocarbon data are unable to discriminate between the pre-collapse flows (i.e. the Zuripujo event) and the syn-collapse pyroclastic event (i.e. Paipatja event). However, the stratigraphic evidence unambiguously shows that the Zuripujo event (Z-PDC) preceded the sector collapse and the associated explosive phase (DAD and P-PDC). Thus, we can state that the time between these two volcanic events was too short to be resolved using the radiocarbon method (i.e. some years to a few decades).

Magnitude of the explosive phase

With the aim of estimating the magnitude of the explosive phase accompanying the debris avalanche of Tutupaca, we estimated the volume of the Paipatja pyroclastic density current (P-PDC) deposit. Satellite image inspection, coupled with detailed fieldwork including almost 300 GPS points, led to the establishment of a detailed map and made it possible to constrain the whole area covered by the P-PDC deposits (Fig. 3). In addition, we also mapped the mostly reworked, distal and lateral deposits of the P-PDC, which are interpreted as the related derived ash-cloud surge deposit. As a result, the main unit of the P-PDC covers an area of ~35–40 km2, whereas the distal and lateral deposits have a larger distribution, covering an area of ~100–105 km2. Last, in absence of natural, deep cross sections, we estimated an average thickness by digging in flat areas representative of the different parts of the deposit (75 holes for the whole P-PDC unit). On the Paipatja plain we found an average thickness of ~0.5-1 m, whereas in the valleys descending to the Rio Callazas, we observed a thickness range of 2–5 m. Based on these estimates, we obtained a volume of ~5–6 × 107 m3 for the main P-PDC deposit. For deposits of the uppermost ash-cloud layer, we estimate an average thickness of 15 cm and obtain a volume of ~1.5 × 107 m3. Thus, the total bulk volume for the P-PDC is of the order of ~6.5–7.5 × 107 m3, corresponding to a VEI 3 eruption. We did not find proximal tephra fallout deposits associated with this eruption. Historical chronicles, however, suggest that distal fine ash fallout occurred in the coastal region at Locumba (77 km to the SW of Tutupaca), Tacna (110 km to the S) and Arica (165 km to the S). Because we have no constraints on the extent of these distal fine ash fallout deposits, the total eruption volume is underestimated. Considering such uncertainties, the bulk volume was probably greater than that calculated for the preserved deposits, implying that the eruption might well rank as a VEI 4. In summary, this eruption probably represents the youngest debris avalanche in the Andes and was accompanied by one of the larger explosive events in Peru during historical times.

Eruptive dynamics of the pyroclastic density currents

Explosive eruptive activity frequently accompanies sectorial collapse of volcanic edifices, especially in the case of violent decompression of a shallow magma body (see Belousov et al. 2007, for review and references therein). As a result, the explosive eruption produces so-called lateral or directed blast-generated pyroclastic density currents. Thus, blast deposits are intimately associated with debris avalanche deposits. This association formed during the recent eruptions of Bezymianny in 1956 (Belousov 1996), Mount St. Helens in 1980 (Hoblitt et al. 1981) and Soufrière Hills, Monserrat in 1997 (Voight et al. 2002). It is important to note that at Bezymianny and Mount St. Helens, the source of the explosion was a cryptodome that triggered the flank failure, whereas at Soufrière Hills, Monserrat, the source of the explosion was a growing lava dome. A similar scenario was described by Macías et al. (2010) at Tacaná volcano (southern México). In this case, however, the debris avalanche was associated with block-and-ash flows without a blast.

Explosive events also occur when the magma reservoir is too deep to produce a lateral blast. In these cases, decompression of the upper part of the magmatic system triggers a sustained plinian eruption and related pumice-rich pyroclastic flows. This occurred during the 1964 eruption of Shiveluch volcano (Belousov et al. 1999). In this case, a time delay exists between the sector collapse and the subsequent explosive activity. As a result, the contact between the debris avalanche deposits and the covering pyroclastic deposits is well-defined.

Lateral explosions producing similar blast-generated pyroclastic density currents are also associated with growing lava domes with no sector collapse. This occurred during the well-known eruption of Montagne Pelée, Martinique in 1902 (Bourdier et al. 1989), and recently during the 2010 Merapi eruption (Komorowski et al. 2013). This scenario also occurred during the explosive destruction of a lava dome at Chachimbiro volcanic complex, Ecuador (Bernard et al. 2014). In these cases, the growing lava dome exploded as a result of a high extrusion rate, which prevented efficient outgassing. It is also important to note that, in these examples, no associated debris avalanche deposits have been described.

In the case of the Tutupaca sector collapse, there is no plinian fallout deposit associated with the debris avalanche and the pyroclastic density current deposits. However, several pieces of evidence suggest that magmatic activity was intimately linked with the sector collapse. These include the intimate stratigraphic relations between the DA deposit and the P-PDC deposits, the fact that the P-PDC deposits cover a sector whose angle coincides with the that of the DA deposit (Fig. 11), the presence of prismatically jointed blocks in the DR-DAD, and the petrological similarity between the juvenile clasts in the DA, the P-PDC deposits and the recent Tutupaca domes. Figure 11 depicts the deposit of the lateral blasts that accompanied the Bezymianny, Mount St. Helens, and Soufrière Hills (Monserrat) sector collapses. At Tutupaca, the PDC deposits cover an area similar to that at Soufriere Hills, Montserrat, in agreement with the estimated bulk volumes (8 × 107 m3 for Tutupaca, and 3 × 107 m3 for Montserrat, Belousov et al. 2007). We also observe a similarity between Tutupaca and Mount St. Helens in terms of the blast propagation angle and the digitate shape of the devastation zone. This last feature, however, is probably related to the fact that the Mount St. Helens blast deposit was mapped in greater detail compared with the Bezymianny and Soufrière Hills blast deposits (note that the latter extend into the sea in distal areas). However, the sedimentological characteristics of the P-PDC deposit do not match those of the above-mentioned blast deposits as reported by Belousov et al. (2007). These authors report that blast deposits are characterised by three distinct units: (i) a basal layer with evidence of material entrainment from the substrate, (ii) a thicker, middle layer that is fines-depleted, normally graded and well sorted, and (iii) an upper, fines-rich layer with frequent planar and wavy laminations. This three-layer sequence may reflect emplacement of a dilute, turbulent and erosive current with a possible lower layer of higher particle concentration. The P-PDC deposits associated with the Tutupaca debris avalanche do not show the deposit sequence identified by Belousov et al. (2007). Instead, the field observation and the sedimentological characteristics suggest a fairly concentrated basal flow (Fig. 8) with an associated dilute cloud that was able to overpass topographic barriers (for instance the Villaque hill). Thus, we propose that the P-PDC deposits result from pyroclastic density currents formed during a lateral eruption by asymmetrical fountain collapse associated with the Tutupaca sector collapse. A last point to be stressed is that after the sector collapse and its associated pyroclastic density currents, no magmatic activity occurred at Tutupaca. This fact is in sharp contrast with what has been described at other volcanoes that experienced sector collapses (such as Bezymianny, Mount St. Helens or Soufriere Hills).

Fig. 11
figure 11

Distribution of the blast deposits (grey) associated with well-known debris avalanches (black). Dotted lines represent the amphitheatre. Modified from Belousov et al. (2007)

Full size image

Reconstruction of the eruptive events

The Eastern Tutupaca dome complex consists of at least 7 coalesced dacitic domes that grew during Holocene times on top of an old, hydrothermally altered basal edifice (Manrique 2013). This dome complex was active in the late 18th century and was affected, between 1787 and 1802 AD, by a major sector collapse that produced a debris avalanche and the associated pyroclastic density currents whose deposits are described in this manuscript. This event was preceded by the block-and-ash flows whose deposits outcrop in the Zuripujo valley to the SE of the Eastern Tutupaca summit (the Z-PDC deposits). These deposits have a limited lateral extent, and mostly outcrop in an almost orthogonal position with respect to the NE-opening amphitheatre, which may reflect a focused flow direction from the source area. In addition, the Z-PDC deposits are overlain by a partially reworked ash-rich layer that represents the lateral facies of the later Paipatja pyroclastic density current deposits (P-PDC, Fig. 5). On the basis of these constraints, we propose that the Z-PDC represents a volcanic event that preceded the Tutupaca sector collapse. This inference is also supported by the fact that charcoal fragments are abundant in the Z-PDC deposits but are extremely rare in the P-PDC deposits, which suggests that the Z-PDC charred and covered the rare vegetation (mainly grass and small bushes) of this high Andean plateau. An additional point to be taken into consideration concerns the fact that the Z-PDC deposit contains a large amount of altered (hydrothermal) components, which contrasts with the rather scarce juvenile material that has been observed in the P-PDC. Thus, the Z-PDC was probably associated with vent clearing explosions occurring in a pressurised lava dome and its subsequent collapse along a sliding plane that was deep enough in the dome to significantly affect the hydrothermal system. As a result, parts of the dome with large amounts of hydrothermally altered material collapsed, producing the pyroclastic flow deposits of the Zuripujo valley. This type of activity has been described at other andesitic and dacitic domes such as Galeras, Colombia (Calvache and Williams 1992) and Soufrière Hills, Monserrat (Sparks et al. 2002).

Dome growth activity proceeded on the Eastern Tutupaca edifice and culminated with the sector collapse that affected its NE flank, following a scenario that was described for the 1997 sector collapse of Soufrière Hills, Monserrat (Sparks et al. 2002) as well as at Tacaná volcano, México (Macías et al. 2010). In the case of Tutupaca, the sector collapse affected the dome complex and the hydrothermally altered lavas of the basal edifice. As a result, a relatively small (<1 km3) debris avalanche spread at the foot of the amphitheatre and reached the Paipatja plain 6–8 km away. The debris avalanche had two main units. The first unit is mainly composed of hydrothermally altered rocks (HA-DAD) from the basal edifice, although it also includes non-altered dome blocks. This lower unit (Unit 1 in Valderrama et al. 2014) is the more voluminous and shows morphological features such as megablocks and hummocks. The upper part of this unit indicates a different dynamical behaviour, expressed by the presence of surface ridges (Unit 2a of Valderrama et al. 2014). The second unit (DR-DAD) also displays frequent surface ridges (Unit 2b of Valderrama et al. 2014), covers the previous one and comprises unaltered dacitic blocks with frequent prismatically jointed blocks, which attest to thermal contraction. This suggests that the second debris avalanche pulse was associated with the collapse of an active dome complex located at the former Tutupaca summit.

In between these debris avalanche units, the voluminous (6.5–7.5 × 107 m3) Paipatja pyroclastic density current deposit (P-PDC) extends up to 10–12 km down the Callazas river (to the NE) and the Suches lake (to the N). This pyroclastic sequence overlies the HA-DAD and is interstratified with (or covered by) the DR-DAD, which shows that the debris avalanche and the pyroclastic flows were generated quasi-synchronously.

Comparison with other debris avalanche deposits in the Central Andes

Based on satellite image analysis, Francis and Wells (1988) published an inventory of the most prominent debris avalanche deposits in the Central Andes. Since then, many detailed field-based studies have been focused on these deposits, which rank among the most spectacular debris avalanches on earth. Examples include the debris avalanche deposits of Socompa (van Wyk de Vries et al. 2001; Kelfoun et al. 2008), Parinacota (Clavero et al. 2002), Tata Sabaya (de Silva et al. 1993), Ollagüe (Clavero et al. 2004) and Llullaillaco (Richards and Villeneuve 2001). Compared with these examples, the Tutupaca debris avalanche differs in its small areal coverage (12–13 km2) and volume (<1 km3); its area is one order of magnitude smaller that the huge surfaces covered by the Socompa (490 km2), Tata Sabaya (~300 km2), Parinacota (140 km2), Ollagüe (~100 km2) or Llullaillaco (165 km2) debris avalanche deposits. In spite of its modest size, the Tutupaca debris avalanche deposit is important for two main reasons. First, because at Tutupaca, the debris avalanche deposits are intimately associated with a sequence of pyroclastic density current deposits, pointing clearly to a magmatic origin for the sector collapse. Second, due to its young age and high degree of preservation, Tutupaca is a unique place for studying the origin and implications of the elongate ridges that characterise this deposit (cf. Valderrama et al. 2014).

Conclusions

The younger (Eastern) edifice of the Tutupaca volcanic complex is a Late Holocene dacitic dome complex that was affected by a sector collapse in historical times. The collapse triggered a small (<1 km3) debris avalanche and associated pyroclastic density currents whose deposits have a bulk volume of about 6.5–7.5 × 107 m3, which ranks this eruption as at least a VEI 3 event. Both deposits, of the avalanche and the pyroclastic density currents, were emplaced synchronously and spread onto the plain NE of Tutupaca volcano. The 14C age determinations obtained for the pyroclastic flow deposits yield a mean age of 218 ± 14 aBP, which corresponds to an eruption that occurred in the 18th century (1731–1802 cal AD). This age is in agreement with the historical chronicles that report major explosive activity at Tutupaca in the period between 1787 and 1802 AD.

The spatial and temporal relationships between deposits of the debris avalanche and the Paipatja pyroclastic density currents (P-PDC), coupled with the petrological similarity between the juvenile fragments in both deposits, indicate that juvenile magma was involved in the sector collapse. A pressurised dome complex triggered the first pyroclastic density currents (Z-PDC). Then, ascent of a dacitic magma batch, coupled with the fact that the Tutupaca dome complex was constructed on top of a highly altered and hydrothermally active volcanic system, triggered the destabilisation of the edifice, producing the debris avalanche and its related pyroclastic density currents represented by the P-PDC.

On the basis of our work on the most recent eruption at Tutupaca, a future eruption of this volcano may display similar eruptive dynamics characterised by viscous dome growth and related block-and-ash pyroclastic flows. This scenario is corroborated by the pre-historical activity of Tutupaca, which shows a frequent pattern of dome growth and collapse as well as at least one other, older debris avalanche event. During the past eruptions of Tutupaca, the eruptive products affected uninhabited areas of the high Andes in Peru, and tephra fallout had only a minor regional impact. However, if a large eruption occurred today, it could affect a much larger population of at least eight to ten thousand inhabitants living within a 25-km radius of the volcano, as well as the important mining (Toquepala, Cuajone) and geothermal (Calientes) infrastructures located in the proximity of Tutupaca.