We present the late Holocene eruption history of the poorly known Doña Juana volcanic complex, in SW Colombia, which last erupted in the twentieth century. This represents a case study for potentially active volcanism in the rural Northern Andes, where tropical climate conditions and a fragmented social memory blur the record of dormant volcanoes. We reconstructed the volcanic stratigraphy of the central-summit vent area by integrating new mapping at 1:5000 scale with radiocarbon ages, sedimentology analysis, and historical chronicles. Our results revealed cyclic transitions from lava-dome growth phases and collapse to explosive Vulcanian and possibly subplinian phases. Pyroclastic density currents were generated by dome collapse producing block-and-ash flows or by pyroclastic fountain/column collapse and were rapidly channelized into the deeply incised fluvial valleys around the volcano summit. The pyroclastic density currents were ~4–10 × 106 m3 in volume and deposited under granular flow– or fluid escape–dominated depositional regimes at high clast concentrations. In places, more dilute upper portions reached a wider areal distribution that affected the inhabited areas on high depositional terraces. The coefficient of friction (ΔH/L) is higher for block-and-ash flows and dense lava–bearing fountain/low-column-collapse pyroclastic density currents compared to pumice-bearing, column-collapse pyroclastic density currents. Associated mass-wasting processes included syneruptive and intereruptive debris flows, with the last one documented in 1936 CE.

In Colombia, monitoring networks are prioritized at volcanoes showing frequent unrest or at those with written eruption records, including the first chronicles of Pedro Cieza de León or Fray Pedro Simón during the Spanish colonization in the sixteenth century. Since the Nevado del Ruiz-Armero disaster in 1985 (Voight, 1990), volcanic surveillance and short-term volcanic hazard assessment have been improved locally (Servicio Geológico Colombiano, 2022; Cortés, 2011; Driedger et al., 2020). However, knowledge gaps remain at several of the potentially active volcanoes of the Northern Andes arc showing long dormancy periods (e.g., Samaniego et al., 1998; Hidalgo et al., 2008; Robin et al., 2008, 2010; Le Pennec et al., 2011). Eruptions at these volcanic centers remain extremely hazardous, due in part to the growth of surrounding populations, especially those where conflict and migration have fragmented intergenerational social memory (Siddiqi et al., 2019; Jenkins et al., 2020; Espinosa-Arango and Prieto, 2022), and oral accounts remain unclear or untrusted (Calder et al., 1999; Miyabuchi, 1999; Macorps et al., 2018; Monteil et al., 2020).

This work focused on developing a robust geologic framework and interpreting past eruption processes at the poorly known, calc-alkaline dacitic Doña Juana volcanic complex (Pardo et al., 2019). The completeness of the geologic record here is compromised by fast rates of weathering and erosion in the tropical climate and active tectonics across the North Andean block (Gregory-Wodzicki, 2000; Montgomery et al., 2001; Mora et al., 2008). In addition, there is a fragmented oral chronology of eruptions between 1897 and 1936 CE (Espinosa, 2012), with reports of damage and casualties at Las Mesas village and surrounding farms (Fig. 1). We therefore carried out new detailed geologic mapping and lithofacies analysis of the most recent Doña Juana volcanic complex erupted products, with emphasis on pyroclastic material, combined with new 14C radiometric ages, historical chronicles, literature review, and interviews with local elders. From these data, our goals were to (1) define and characterize the late Holocene eruption history and volcano behavior of the Doña Juana volcanic complex and (2) compile a new baseline of knowledge on a potentially active volcanic center of the Northern Andes experiencing explosive activity during the twentieth century.

The Doña Juana volcanic complex is located in the region of Nariño, SW Colombia (Figs. 1A and 1B), and it is part of the SW-NE active volcanic arc of the Northern Andes where the Nazca plate subducts beneath South America (Taboada et al., 2000; Cortés and Angelier, 2005). Similar to most active volcanoes in the Central Cordillera of Colombia (Monsalve-Bustamante, 2020), the oldest units (lava flows) known at the Doña Juana volcanic complex unconformably overlie a polymetamorphic Cretaceous basement (Cediel et al., 2003) and date to the Pleistocene.

The geologic setting presented here refers to Pardo et al. (2019). The volcanic complex consists of three spatially overlapping and successively active volcanoes: Santa Helena (ca. 1125–1097 ka), Ancestral Doña Juana (ca. 878–312 ka), and Old Doña Juana (ca. 231–77 ka). The summit of each edifice is truncated by a narrow extensional structure (vt) bordered by regional NE-SW faults, where volcanism was concentrated, together with two nested, tectonically controlled, collapse calderas (vc1 and vc2, respectively) and lateral volcanic collapses (Fig. 1C).

The Holocene stratigraphic record of Doña Juana volcanic complex relates to three summit vent areas: (1) Young Doña Juana (central summit), (2) Totoral (NE), and (3) Phyllo (E), which include lava domes emplaced within and along the borders of the youngest vc2 caldera (Fig. 1C). The corresponding eruptive products overlie a prominent regional marker bed, a Plinian pumice-fall deposit sourced from the adjacent Las Ánimas volcano (Fig. 1B). The fall deposit has a maximum age of 5904 ± 30 14C yr B.P. (6794–6661 calibrated yr B.P.) and a minimum age of 4422 ± 28–4250 ± 30 14C yr B.P. (5056–4813 cal. yr B.P.). The Totoral and Phyllo vents (Fig. 1B) were mainly effusive. Block-and-ash flows and reworked volcaniclastic deposits related to the collapse of earlier Totoral lava domes are the only recent Doña Juana volcanic complex products to the northeast of the study area (Ciénaga formation; Pardo et al., 2019). Young Doña Juana is the main active vent, which experienced explosive and effusive activity along with recurrent generation of pyroclastic density currents and lahars. Juvenile products are seriate porphyritic dacites of variable color and vesicularity, but with a homogeneous whole-rock composition (62.36 < SiO2 wt% < 66.61, anhydrous base) and mineral association of plagioclase + amphibole + quartz + biotite + oxidesFe-Ti ± pyroxene ± apatite.

We focused on the geology of the Young Doña Juana central summit vent zone because it is the best exposed feature, it is the only one showing pyroclastic (in addition to effusive) activity, and it has affected the inhabited territory to the west of the volcano in the twentieth century. We described new outcrops at 93 locations in the upper basin of the Juanambú River, with particular detail in the area of the Las Mesas village located on a depositional terrace beside the Humadal and Resina fluvial valleys (Figs. 1 and 2; labeled as DJ- in Supplemental Material Supplemental Material 11). We used a 5-m-resolution digital elevation model (DEM) obtained from 2007 GeoSAR images 1473, 1474, and 1574 of the Colombian National Image Bank (https://igac.gov.co/es/noticias/banco-nacional-de-imagenes-colombia-vista-desde-el-espacio) to construct a shaded relief map and a slope map, and the geologic information was recorded in ArcMap (v. 10.7; ©ESRI, 2019) at a scale of 1:5000 (Fig. 2; Supplemental Material 1).

We distinguished lithostratigraphic units (formations) according to distinctive lithologic features and stratigraphic positions, corroborated by radiocarbon ages (Supplemental Material 2). Formations were subdivided into members characterized by distinct lithology and lithofacies associations (Table 1). Members discriminate lava domes, pyroclastic products, and reworked volcaniclastic deposits (hereafter volcaniclastics). The pyroclastic members were subdivided into eruption units, each one representing the deposit of an individual and continuous eruption delimited by significant time breaks (Fisher and Schmincke, 1984). These eruption units are characterized by distinctive lithofacies associations and are separated by erosion surfaces, paleosols, and/or detrital deposits suggesting significant volcanic quiescence of variable duration (Lucchi, 2013). Hence, a particular pyroclastic member consists of one or multiple eruption units (in which case, they show overlapping radiocarbon ages) and represents the total of deposits produced over an “eruption episode” (modifying Jenkins et al., 2007).

Compared to older lithostratigraphic units of Doña Juana volcanic complex (Pardo et al., 2019), the late Holocene deposits do not generally form terraces at different elevations, hindering an obvious distinction between older (higher) and younger (lower) units in a geologic setting characterized by regional uplift. The different units are commonly juxtaposed laterally against each other at heights depending on the level of accumulation within the river valleys, and they have similar lithology. This makes it difficult to unequivocally distinguish the different lithostratigraphic units (and eruption units). Therefore, our new systematic 14C age data set in charred wood (Supplemental Material 2) was a major tool to develop the stratigraphic correlations. We combined 16 new radiocarbon ages and 74 previously published radiocarbon ages reported in Pardo et al. (2019). We used OxCal v4.4 (Bronk-Ramsey, 2009) for calibration by using the IntCal20 curve (Reimer et al., 2020), which is the updated calibration curve for Northern Hemisphere latitudes, and B.P. indicates the year before 1950 CE. Whole-rock compositions (6 new and 21 published) are also included in Supplemental Material 2. We attempted to correlate the geologic data from the latest eruption episode to the descriptions found in historical chronicles (Küch, 1892; Pereira-Gamba, 1919; Espinosa, 2012), local unpublished essays (Gómez-Bolaños, 2012), national newspapers (i.e., El Espectador, 1887; El Heraldo, 1899; El Derecho, 1936af; El Tiempo, 1936), and interviews with elders (Pulgarín et al., 2015; Arnulfo Bravo 2015, Maria Mercedes Muñoz 2015, Delfina Muñoz 2015, 2017, personal communications).

The main geometric parameters of deposits (outflow area, bulk volume, average thickness, equivalent runout, equivalent diameter, aspect ratio) related to pyroclastic density currents were calculated according to Giordano and Cas (2021) (see Supplemental Material 3). The interpretation of lithofacies associations for each unit (Table 1) followed classifications of Sulpizio et al. (2007, 2014) and Sulpizio and Dellino (2008).

Grain-size distributions were retrieved from field photographs and bulk samples. Coarse sizes (larger than −6ϕ) were obtained from image analysis within a 1 m by 1 m grid, using Image-J. Bulk samples were dry-sieved at 0.5ϕ fractions at the Geosciences Department laboratories of the University of Los Andes (Colombia), and particles smaller than 3ϕ were analyzed with a CILAS-1190 laser particle size analyzer at the Mechanical Engineering Department laboratories (22 °C and 50% relative humidity) of the same university. Grain-size data were processed with GRADISTAT (Blott and Pye, 2001). We report merged histograms, but for deposits having particles coarser than −6ϕ, we discriminated the cumulative curves obtained by each method. We excluded particles coarser than −6ϕ from the data set used to calculate the F1 (wt% finer than 4ϕ) and F2 (wt% finer than 0ϕ) parameters following Walker (1983), in order to facilitate comparison between samples (Supplemental Material 1).

Our new 1:5000 geologic mapping (Fig. 2; see specific sampling locations in Supplemental Material 1.1), volcanic stratigraphic analysis, and sedimentologic analysis (Fig. 3) allowed us to define four formations, namely (from eldest to youngest), Humadal, Las Mesas, Silencio, and Valle de Piedras. These are mainly exposed on fluvial terraces confined to the west and southwest quadrants of the volcano summit, within the upper Juanambú River catchment (Figs. 1 and 2). The areal distribution (Fig. 2), stratigraphy (Figs. 3 and 4), and lithofacies associations (Table 1) of newly defined lithostratigraphic units and their internal subdivisions are described below.

Humadal Formation

This is the oldest late Holocene lithostratigraphic unit newly defined here for the Young Doña Juana summit vent, comprising two pyroclastic members (lower and middle) and one volcaniclastic member (upper). Contacts between the lower and middle pyroclastic members are not clearly visible in the field, and they are distinguished by different areal distributions and lithofacies associations (Figs. 25). Juvenile components range 62.91 < SiO2 wt% < 65.71.

Lower Member (hul)

This member consists of distinctively valley-confined, massive, monolithologic, poorly sorted tuff breccias showing polymodal grain-size distributions, with red and dense dacitic blocks embedded in a lithic to lithic-crystalline medium lapilli to coarse ash matrix (Supplemental Material 1). Proximal exposures occur at the base of the western flank of the Young Doña Juana summit lava domes and form depositional terraces along the Hueco Seco stream, in the northwestern sector of the vc2 caldera (Fig. 2). They are ~75-m-thick deposits of massive blocks, lapilli, and ash (lithofacies mBLA; Table 1A) surmounting the remnants of older volcanic edifices. Grain-size distributions are mesokurtic and vary from positive skewed (i.e., positive skewness; location DJ-56; Blott and Pye, 2001) to symmetrical (DJ-55). Abutting the western flank of Montoso basement relief (Fig. 2; at DJ-52), the hul member is an ~15-m-thick succession of weakly reversely graded, very thick beds hosting meter-sized jigsaw-fit blocks (lithofacies mB[jw]LA[rl]; Table 1A; Figs. 5A5C). The best exposures of hul occur along the Humadal stream valley (Fig. 2), on the scarp of terraces. There, this unit is 8–10 m thick and exhibits a succession of weakly reversely graded, very thick beds marked by flat-lying trains of crudely imbricated blocks that are parallel to the base (lithofacies mBLA[rl], mALB[rl]; Table 1A; Fig. 5B). Grain-size distributions are platykurtic and range from very finely to positive skewed. Locally, the uppermost ~50–100-cm-thick bed at such terraces is massive and distinctively matrix rich, showing ash, lapilli, and a few blocks (lithofacies mALB; Table 1A). The abrupt distal limit of the deposit along the Humadal stream occurs ~7.5 km from the Young Doña Juana summit.

Up to 10-m-thick exposures of the hul member occur in the headwaters of the Florida and Carmelo stream valleys to the west-northwest of the summit vent (Fig. 2). Along the Carmelo stream valley, three to four 2–3-m-thick, poorly sorted, monolithologic beds are distinguished by local concentrations of blocks at the top of each bed (lithofacies mALB[rl]; Table 1A) or by intervals of ~50–70-cm-thick, low-angle, cross-stratified lapilli and ash (lithofacies sLA; Table 1A; Fig. 5D) between them. The thickest, coarse-grained beds show polymodal, symmetrical, and mesokurtic grain-size distributions (at DJ-81). Rare charred wood fragments are found in this sector, providing a new radiocarbon age of 4389 ± 22 14C yr B.P. (4986–4867 cal. yr B.P.). In general, the mesokurtic to platykurtic grain-size distributions of the matrix show −2.3 < D50(ϕ) < 0.03, coarse ash contents between 26 and 55 vol%, and fine ash contents between 4 and 16 vol%.

Middle Member (hum)

The hum member is composed of gray pyroclastic deposits exposed along the southwestern flank of Young Doña Juana (Fig. 4A). These deposits fill the vc2 caldera and form the base of a depositional terrace near the Sofía stream outflow into the Resina River, ~5.0 km from the current volcano summit (Fig. 2). Proximal deposits (DJ-70 in Supplemental Material 1.1; Fig. 5E) are poorly sorted, massive to weakly reversely graded tuff breccias hosting blocks, lapilli, and ash (lithofacies mBLA[rl]; Fig. 5E; Table 1A). The most complete exposures of hum (at DJ-10; DJ-36) are valley-confined, > 15-m-thick, poorly sorted, massive deposits of coarse ash, lapilli, and blocks (lithofacies mALB in Table 1A; Fig. 5F). Grain-size distributions are bimodal to polymodal, positive skewed to symmetrical, varying from mesokurtic at the base to platykurtic at the top (Supplemental Material 1.2). The matrix grain-size distributions show D50(ϕ) = −0.77, coarse ash contents between 33 and 46 vol%, and fine ash contents between 2 and 11 vol%. Angular clasts are embedded in a lithic-crystalline matrix ranging between fine lapilli and coarse ash, with common charred wood fragments. Some bread-crusted and cauliflower bombs are present. Besides the predominant dense components of porphyritic dacite, a few pale gray and brown pumiceous clasts occur. Also, oxidized schist and rounded hydrothermally altered lithics are found in the coarse lapilli to coarse ash fractions. In this study, we obtained an age of 4463 ± 22 14C yr B.P. (5284–4976 cal. yr B.P.) in charred tree trunks. In addition, the lithofacies associations of the hul member of Humadal formation are similar to the coeval 4400 ± 30 14C yr B.P. (5053–4863 cal. yr B.P.) Caicuanes formation (Fig. 3) reported by Pardo et al. (2019) outside the study area, sourced from the NE Totoral vent zone (Fig. 2).

Upper Member (huu)

The huu member overlies with sharp contact the hul member, or it forms low terraces juxtaposed with the hul member at lower elevations along the valleys of the Humadal, Carmelo, and Florida streams down to ~8–15 km from the source. The huu member consists of ~4–5-m-thick beds of massive to weakly reversely graded volcaniclastic deposits of very poorly sorted to poorly sorted, heterolithic (red >> gray dacites > accidental lithics) sandy-muddy gravels (lithofacies mGSM[rg]; Table 1B). Gravels show variable roundness and are locally imbricated within a hardened and porous silty-clay–rich matrix. Locally, the huu member includes massive muddy-gravelly sands (lithofacies mSMG; Table 1B) and muddy sands (lithofacies mSM; Table 1B) containing abundant large, oxidized but uncharred tree trunks within a clay-rich matrix. These clay-rich deposits are found on high-gradient surfaces in transitional contact above the hul member at the western foot of the Montoso basement relief.

Las Mesas Formation

This unit is recognized along the southwestern and western flanks of Young Doña Juana, partially overlapping with the Phyllo lava dome (Fig. 2), where a whitish to pinkish hydrothermally altered zone is visible and inhabitants report preexisting fumaroles. The Las Mesas formation fills the vc2 caldera and forms depositional terraces along the valleys, overlying or partially juxtaposed alongside the Humadal formation (Figs. 2 and 3). The Las Mesas formation is subdivided into a pyroclastic lower member (lml) and a volcaniclastic upper member (lmu; Fig. 4).

Lower Member (lml)

This is a pyroclastic succession that is subdivided into four eruption units (lml EU1–EU4) by distinctive lithofacies associations, erosive surfaces, sharp grain-size variations, and differences in color (Figs. 3 and 6). Juvenile clast composition is narrow (62.36 < SiO2 wt% < 66.61).

Eruption unit lml EU1. Unit lml-EU1 forms terrace remnants along the Sofía, Humadal, Carmelo, and Florida stream valleys and interfluves (Fig. 2). This unit is 15–20 m thick, and it consists of massive, poorly sorted ash and lapilli ± blocks (angular to subangular) embedded in a lithic-crystalline very coarse ash matrix (lithofacies mALB, mAL; Table 1A), locally showing gas pipes and containing abundant charred wood fragments. Dense to poorly vesicular medium gray > red > pale gray (porphyritic) dacites, and brown pumiceous clasts are predominant as juveniles, with fewer hydrothermally altered and oxidized lithics, as well as metasedimentary accidental lithics (Figs. 6A6D). At Las Mesas village, unit lml-EU1 overlaps with higher Pleistocene depositional terraces and is subdivided into two 15–50-cm-thick, well-sorted massive ash and lapilli beds (lithofacies mAL; Table 1A), locally embedding clast-supported lenses of fine lapilli (lithofacies lensL; Table 1A). The two beds are separated by a 5–7-cm-thick, discontinuous, fining-upward coarse to fine ash showing low-angle cross-lamination (lithofacies xlA; Table 1A). Grain-size distributions in massive lithofacies are mostly symmetrical and mesokurtic for 8.5 km downstream (Supplemental Materials 1.2 and 1.3). Rare positive skewed and platykurtic distributions occur where unit lml-EU1 overlaps with the higher Pleistocene terraces (DJ-07), and within the lowermost massive bed found at the most distal location on top of such terraces (DJ-91). New radiocarbon ages for lml-EU1 from different locations constrain its range between 3296 ± 23 yr B.P. (3565–3460 cal. yr B.P.) and 3070 ± 22 yr B.P. (3360–3217 cal. yr B.P.).

Eruption unit lml-EU2. Unit lml-EU2 is recognized only near the Las Mesas village, overlapping unit lml-EU1 with a flat or irregular sharp contact (Figs. 6C6D). Unit lml-EU2 is a distinctively reddish brown, pinching-and-swelling, massive lapilli tuff composed of medium to fine ash and lapilli (lithofacies mAL; Table 1A). Thickness varies laterally from 2 m to 0.01 m on an outcrop scale (Figs. 6C6D). Thickest exposures are poorly sorted deposits showing a few gray and red dense porphyritic medium to coarse lapilli within a lithic-crystalline coarse to very fine ash containing small (<3 cm) charcoal fragments. Very rare rounded pumice lapilli and subangular metamorphic lithics also occur. Grain-size distributions obtained from the lml-EU2 matrix are coarse skewed and vary from leptokurtic to mesokurtic, with coarse ash contents between 45 and 94 vol% and fine ash contents between 2 and 54 vol% (Supplemental Material 1.3). The uppermost parts of these deposits are poorly sorted, weakly laminated fine lapilli and ash tuffs (lithofacies wlLA; Table 1A) with positive skewed and leptokurtic grain-size distributions, locally containing clast-supported fine lapilli lenses (lithofacies lensL; Table 1A). At the top, these deposits are capped by a few centimeters of weakly laminated to cross-laminated, poorly sorted, very fine ash showing symmetrical and leptokurtic grain-size distributions (lithofacies wlA, wxlA; Table 1A). Laterally, these uppermost layers pass to well-sorted and massive, very coarse ash (lithofacies mA; Table 1A) exhibiting positive skewed and platykurtic grain-size distributions, locally containing ash aggregates (lithofacies maccrA; Table 1A). Small charcoal fragments found within the thickest massive lithofacies of lml-EU2 were dated in this study at 3062 ± 23 14C yr B.P. (3360–3210 cal. yr B.P.) and 3053 ± 22 14C yr B.P. (3352–3208 cal. yr B.P.).

Eruption unit lml-EU3. Unit lml-EU3 overlaps with lml-EU2 or lml-EU1 with an erosive or sharp contact (Figs. 6B6D), and it ranges in thickness from 0.5 to 5 m. It is gray in color and very similar to lml-EU1 (lithofacies mALB, mAL; Table 1A), but it generally shows higher fines content, a slightly more heterolithic nature, and pale brown pumice, yellowish-brown hydrothermally altered medium lapilli, and soil rip-up clasts. At its thickest, the unit contains a few small gas pipes, and the upper parts of the deposits are weakly pinkish oxidized. Poorly sorted grain-size distributions are polymodal to bimodal, mesokurtic to platykurtic, and mostly symmetrical, except at the most proximal (DJ-68) and most distal (DJ-91) locations, where these are positive skewed (Supplemental Materials 1.2 and 1.3). The lithofacies mALB of lml-EU3 is commonly found on the topographic surface along interfluves between the Humadal stream and the Resina River, and (locally) between the Carmelo and Florida streams, directly overlying the paleosol on the Ánimas pumice fallout, or above the older hul or hum members. On top of higher Pleistocene terraces at Las Mesas village, the basal portion of lml-EU3 (~20–80 cm thick) shows low-angle cross-stratification (lithofacies xsAL, xsLA; Table 1A), laterally changing to laminated and massive ash (lithofacies lA, mA; Table 1A). Laterally, lml-EU3 changes into a finer-grained massive ash and lapilli bed with abundant accidental lithics (lithofacies mAL; Table 1A; Fig. 6B).

Over distance and on top of the high Pleistocene terraces, exposures comprise a bedded succession of two 2–3-m-thick beds of massive ash and lapilli (lithofacies mAL; Table 1A), separated by a thin (5 cm), weakly cross-stratified ash and lapilli bed (lithofacies wxsLA; Table 1A). Unit lml-EU3 is the most widespread unit of the lml member, exposed down to 10 km from the volcano summit. In general, matrix grain-size distributions of lml-EU1 and lml-EU3 massive lithofacies show −2.4 < D50(ϕ) < 0.11 and higher coarse ash contents (23–68 vol%) than fine ash content (0–16 vol%). Radiocarbon dating from charcoal fragments within lml-EU3, reported by Pardo et al. (2019), gave ages of 3052 ± 22 yr B.P. (3351–3207 cal. yr B.P.) and 3018 ± 23 yr B.P. (3265–3148 cal. yr B.P.), largely overlapping with those of the other eruption units.

Eruption unit lml-EU4. The uppermost unit lml-EU4 is local and discontinuous, consisting of clast-supported horizons of dense, gray to brown, vesicular, dacitic, angular medium to fine lapilli (lithofacies mL; Table 1A). At only one location (DJ–25), these deposits mantle unit lml-EU3. Other isolated and discontinuous horizons of clast-supported angular lapilli are commonly found at the base of the thick soil profile developed on top of the Ánimas fallout marker along the road connecting Las Mesas village to La Cruz town. Although the stratigraphic position and lithology match Las Mesas formation, such middle-distance deposits could not be assigned to a specific eruption unit.

Based on the radiocarbon dates revisited here (Supplemental Material 2), the Las Mesas formation is coeval with the 2860 ± 30 14C yr B.P. (3072–2877 cal. yr B.P.) La Cabaña formation reported by Pardo et al. (2019) as the only one related to the Young Doña Juana summit vent area to the northwest of Doña Juana volcanic complex (outside our study area; Fig. 3). The pyroclastic deposits of La Cabaña formation correspond to a massive and poorly sorted, monolithologic red tuff-breccia (lithofacies mALB[rl]; Table 1A).

Upper Member (lmu)

This volcaniclastic member is locally exposed along the Humadal stream, overlying or juxtaposed at lower elevations against the lml member. The lmu member comprises 4–8-m-thick successions of massive to weakly reversely graded beds of very poorly sorted to poorly sorted, heterolithic (gray >> red dacites > accidental lithics) sandy-muddy gravels and gravelly muddy sands (lithofacies mGSM[rg], mSGM; Table 1B). Gravels show variable roundness and are locally imbricated within a hardened and porous silty-clayish matrix.

On the terrace where the Las Mesas village is located, the lmu member is finer grained than the channel-filling lithofacies, and it is represented by a 30–50-cm-thick, pale yellow-brown, lensoid, muddy-gravelly sand bed (lithofacies mSMG; Table 1B) capped by a 30–70-cm-thick, dark brown paleosol.

Silencio Formation

This unit encloses the deposits of the late nineteenth century eruption episode, draping the previous units. It extends from the base of the Young Doña Juana lava dome field apron and along the Hueco Seco stream to the southwest, forming a smooth volcaniclastic lobate landform hosting young vegetation (Figs. 24 and 7A). Some outcrops also occur along the Carmelo and Florida streams, overlying the Las Mesas formation. Intermediate to distal outcrops occur along the Humadal stream valley close to its outflow into the Resina River, and on top of high Pleistocene terraces close to the Las Mesas village.

The Silencio formation consists of a pyroclastic lower member (sil) and a volcaniclastic upper member (siu).

Lower Member (sil)

This is a pyroclastic succession that is subdivided into four eruption units (sil EU1–EU4) by means of distinctive lithofacies and locally interbedded reworked deposits (Fig. 3). The composition of juvenile clasts is the most narrow (64.73 < SiO2 wt% < 65.84) of the studied deposits.

Eruption unit sil-EU1. Proximal outcrops of unit sil-EU1 are within the vc2 caldera (DJ-74) and consist of massive, poorly sorted deposits of lapilli and blocks within a lithic-crystalline to vitric-crystalline, very coarse ash matrix (lithofacies mALB; Table 1A). Unit sil-EU1 abuts the Las Mesas formation and is best exposed between 4.3 and 8.9 km from the volcano summit, forming discontinuous depositional terraces along the Humadal stream. The thickest outcrops of sil-EU1 (12–20 m; Figs. 7B and 7C) show coarse-tail graded deposits hosting dense blocks and bread-crust bombs at the base and pumiceous bombs at top (lithofacies mBLA[g-ct], mALB[g-ct]; Table 1A). The uppermost portions also contain sparse accidental metamorphic and multicolored hydrothermally altered accessory lithic lapilli. In general, grain-size distributions are polymodal and symmetrical at the base to positive skewed at the top (Supplemental Materials 1.2 and 1.3). Large charred wood fragments are abundant at the base and provided a new radiocarbon age of 146 ± 21 14C yr B.P. (1780–1906 CE). Lateral variations were identified at Sofía stream valley, where unit sil-EU1 thins and overlies fluvial and colluvial deposits found on top of the Las Mesas formation. There, a 1-m-thick bedded unit occurs; its base is a dark gray, massive, lithic-crystalline, very coarse ash showing degassing pipes and transitioning upward into a 12-cm-thick, massive, pale gray, crystalline-lithic medium ash bed (lithofacies mAL; Table 1A) capped by 1–2 cm of massive very fine ash (lithofacies mA; Table 1A). Grain-size distributions are poorly sorted and mesokurtic, changing from positive skewed at the lowermost bed to coarse skewed at the uppermost bed (Supplemental Materials 1.2 and 1.3). Charred branches embedded in unit sil-EU1 in this sector gave new radiocarbon ages of 125 ± 2114C yr B.P. (1802–1937 CE) and 115 ± 21 14C yr B.P. (1805–1928 CE).

Eruption unit sil-EU2. Unit sil-EU2 is a pumice-rich, massive, reddish-gray tuff-breccia that overlaps sil-EU1 with a sharp erosive contact, best exposed as a distinctive lobe near the base of the Young Doña Juana volcaniclastic apron. Proximal outcrops (DJ-68; 1.7 km from the summit) are reversely graded and contain abundant bread-crust pumiceous bombs forming distinct levees (lithofacies mALB[rp]; Table 1A; Fig. 7D). Grain-size distributions are polymodal, poorly sorted, and symmetrical and platykurtic at the base to positive skewed and mesokurtic at the top (Supplemental Materials 1.2 and 1.3). In general, the matrix of massive tuff-breccias in units sil-EU1 and sil-EU2 shows higher contents of coarse ash (33–87 vol%) versus fine ash (2–25 vol%). Lateral lithofacies variations of sil-EU2 were identified at overbank environments along the Sofía stream. There, the unit is composed of a 95-cm-thick ash and fine lapilli deposit, where its lowermost and uppermost 10 cm intervals are well-sorted, reddish-gray, weakly cross-stratified and pumice-bearing deposits (lithofacies wxsAL; Table 1A). The intermediate, thicker portion is massive and poorly sorted, with abundant pumice and hydrothermally altered fine lapilli (lithofacies mAL; Table 1A), locally containing gas pipes. In addition, there are bread-crust to cauliflower pumice bombs on the present landscape, down to ~6 km west and southwest from the source, with maximum diameters of 56 cm. A new radiocarbon age was obtained in charred branches within unit sil-EU2 at 201 ± 21 14C yr B.P. (1653–1927 CE).

At ~6 km downstream from the summit, units sil-EU1 and sil-EU2 are separated by a layer of massive to reversely graded, heterolithic sandy-muddy gravels (lithofacies mG, SM[rg], mSGM; Table 1B) of the siu member. Charred trees within the latter were dated by Pardo et al. (2019) to 127 ± 25 14C yr B.P. (1800–1941 CE), likely relevant to reworked material of sil-EU1.

Eruption units sil-EU3 and sil-EU4. These are distinctively clast-supported tephras and are only recognized at location DJ-77 (Supplemental Material 1.1), 5.6 km southwest from the volcano summit, capping a 27-cm-thick deposit of tuffaceous (pumice-bearing), muddy-gravelly sands (lithofacies mSMG, mSM; Table 1B) above unit sil-EU2. Unit sil-EU3 is an ~9 cm-thick, discontinuous, poorly sorted (symmetrical, leptokurtic), normally graded, and clast-supported (subangular) pumice lapilli and coarse ash gray horizon (lithofacies mL, mA; Table 1A), whereas unit sil-EU4 is a 2–4-cm-thick, moderately to well-sorted (positive skewed, mesokurtic), pumiceous, very coarse ash bed (lithofacies mA; Table 1A). Units sil-EU3 and sil-EU4 are capped with transitional contacts by ~30–40-cm-thick, brown, tuffaceous, muddy-gravelly sands belonging to the siu member (lithofacies mSMG; Table 1B).

Distal deposits of the sil member were identified on the high Pleistocene terrace hosting the Las Mesas village, 10 km from the volcano summit. There, the sil member is locally represented by whitish, discontinuous patches (<6 cm thick) of massive ash or aligned angular pumice fine lapilli within the uppermost soil profile (lithofacies mA; Table 1A), which cannot be attributed to a particular eruption unit.

Upper Member (siu)

This volcaniclastic member interfingers with the pyroclastic member, and it is also recognized at the junctions of Hueco Seco stream, Humadal stream (Fig. 7B), and Sofía stream with the Resina River (~3–8 m thick). There, massive to weakly reversely graded heterolithic gravels and sandy-muddy gravels of variable roundness form low depositional terraces (lithofacies mG, mGSM[rg], mSGM; Table 1B) beside the sil member. In addition, and locally on top of the coarse-tail graded, sil-EU1 depositional terrace at the outflow of Humadal stream into Resina River, there is a thinly laminated deposit of well-sorted silt and clay, alternating in color from pale gray to pinkish brown (lithofacies altSC; Table 1B).

Valle de Piedras Formation

This unit includes the predominantly lava products of the effusive activity reported during 1897–1936 CE (Table 2). It includes a lower lava member (vpl) and upper volcaniclastic member (vpu).

Lower Member (vpl)

The lower member comprises the endogenous dacitic (65.06 < SiO2 wt% < 65.58) lava domes and spines forming the Young Doña Juana volcano summit, together with their surrounding blocky talus aprons (Figs. 2, 3, and 8A). At least five different eruption units (vpl EU1–EU5) were recognized by means of crosscutting relationships and deformation structures. The oldest unit, vpl-EU1, corresponds to the eastern-northeastern lava dome remnants crosscutting the eastern Phyllo and northeastern Totoral lava domes (Fig. 2). It is composed of fractured porphyritic dacites with irregular foliation and blocky surfaces, forming a semi-cupola exposed at the eastern side of the lava dome field. Its surrounding monolithologic talus apron drapes the base of the elder Phyllo and Totoral lava domes, as well as the Las Mesas formation within the vc2 caldera. At a similar stratigraphic position, but not in direct contact, unit vpl-EU2 is another lava dome remnant and surrounding apron, which is partially exposed in the northwestern portion of the Young Doña Juana lava dome field (Fig. 2). This lava dome has several spines, which are partly plastered by a deposit of hydrothermally altered lithic and angular fine blocks and coarse lapilli (Fig. 8B; lithofacies mL in Table 1A). Both the vpl-EU1 and vpl-EU2 lava domes are cut by the highest cuspate lava dome of vpl-EU3, which is almost entirely covered by a talus of lava blocks, and it deforms the earlier and lithic-covered lava spines (Fig. 8C). Most of the vpl-EU3 talus is exposed to the north-northwest of the Young Doña Juana lava dome field, and meter-sized dacitic blocks fill the valley between the vpl-EU1 and vpl-EU3 domes. A younger extrusion is represented by the lava spines of vpl-EU4 crosscutting the previous units along the rim of the summit lava dome field (Figs. 8C). The corresponding apron is exposed to the west, draping the vpl-EU1 and vpl-EU2 talus (Fig. 2), and overlapping the Silencio formation. Finally, an inflated, cracked protrusion (Fig. 8D), named by the locals as the “papa” (i.e., Spanish term for “potato”), represents the latest lava dome, vpl-EU5. This inflated dome deforms the preexisting top of vpl-EU2.

Upper Member (vpu)

The upper member is a volcaniclastic deposit comprising sparse, meter-sized angular megablocks (Figs. 7A and 8E), together with monolithologic, massive or reversely graded breccias forming levees (lithofacies mB[rl]; Table 1A). The vpu member is interlayered within the talus blocky apron of the vpl-EU4 dome (Fig. 7A), and it forms a distinctive hummocky topography (grass-covered) extending 4.5 km from the volcano summit. Further down the outflow of this apron into the Resina River, the vpu member changes into hard, massive, heterolithic gravels or local superpositions of reversely graded, sandy-muddy gravels (lithofacies mG, mGSM[rg]). These deposits form 6-m-high depositional terraces at the intersection of the Sofía stream and Resina River, which are difficult to distinguish from the earlier siu member (Fig. 8E). Overall, no pumice clasts were found within the Valle de Piedras formation.

Eruption Styles and Chronology

The new stratigraphic reconstruction allowed us to identify different eruption episodes related to the Young Doña Juana central vent area in the late Holocene (Figs. 9 and 10A), with at least three main explosive eruption episodes ca. 5 cal. k.y. B.P. (Humadal), ca. 3 cal. k.y. B.P. (Las Mesas), and 1897–1936 CE (Silencio–Valle de Piedras). These occurred simultaneously or alternating with the activity described by Pardo et al. (2019) for the adjacent vent areas, (1) Phyllo and (2) Totoral (Figs. 2 and 3).

The late Holocene Young Doña Juana produced alternating effusive and explosive eruptions (Fig. 9), typical of many dome-forming volcanoes (e.g., Samaniego et al., 1998; Platz et al., 2007, 2012; Lerner et al., 2019; Massaro et al., 2019). Modern dacitic analogues showing eruption transitions without development of Plinian phases include Cayambe (Samaniego et al., 1998), Imbabura (Andrade et al., 2019), Soufrière Hills (Druitt et al., 2002; Formenti et al., 2003; Burgisser et al., 2010; Gottsmann et al., 2011), Mount Unzen (Nakada and Fujii, 1993), and Mount Merapi (Cronin et al., 2013). These contrast with similar dacitic lava dome systems that also produce Plinian eruptions, like Mount Peleé (Fisher and Heiken, 1982) or Volcán de Colima (Sulpizio et al., 2010; Capra et al., 2016; Pensa et al., 2018).

5 cal. k.y. B.P. Humadal Eruption Episode

This episode is represented by successive block-and-ash flows produced by lava dome collapses, a pyroclastic density current generated by lava dome explosion (Boudon et al., 2015) and pyroclastic fountain collapse, and subsequent lahars. The valley-confined, massive to weakly reversely graded, poorly sorted, and monolithologic lithofacies associations of the hul member (lithofacies mBLA, mB[jw)]LA[rl], mBLA[rl], mALB[rl]; Table 1A) support deposition from block-and-ash flows (Supplemental Material 1; Figs. 10B and 10C). The matrix grain-size distributions indicate that the bulk of the material was transported within the high-density ground-hugging basal part of the current (e.g., Schwarzkopf et al., 2005). The superposition of weakly reversely graded beds indicates that grain-grain interaction in a granular flow depositional regime favored kinetic sieving (Savage and Lun, 1988) and kinematic squeezing (Le Roux, 2003), which segregated the largest blocks to the top of the flows. Their homogeneous reddish color indicates syneruptive oxidation of the collapsed lava domes due to temperature, which means that they were likely extruded at a higher temperature compared to the successive ones. The vertical repetitive occurrences of reversely graded lithofacies and horizons of flat-lying blocks parallel to the base indicate either the stepwise aggradation of different pulses developed within the same block-and-ash flow or the recurrence of multiple, discrete dome collapses in a short time generating successive block-and-ash flows (e.g., Sulpizio et al., 2007, 2014; Sulpizio and Dellino, 2008; Lucchi et al., 2022). Deposition from successive pulses is best recorded in the Carmelo catchment area, where the low-angle cross-laminated deposits (lithofacies sLA) suggest traction and deposition from a turbulent regime in the dilute region at the top of each high-concentration block-and-ash flow pulse (Macorps et al., 2018).

The sedimentologic data from the hum member (lithofacies mBLA[rl] and mALB) suggest rapid deposition from the underflow of concentrated pyroclastic density currents dominated by granular flow depositional regimes (Figs. 10B10C). No fall deposits were recognized, suggesting the pyroclastic density currents were generated from the collapse of low pyroclastic fountains associated with ballistic ejection of bread-crusted bombs. The presence of bombs, pumice, and accidental lithic clasts indicates explosive disruption of a lava plug/dome and the fragmentation of metamorphic country rock (e.g., Benage et al., 2014; Macías et al., 2020). The estimated minimum total bulk volume for the combined pyroclastic hul and hum members of the Humadal formation is 9.7 × 106 m3.

The massive to weakly reversely graded, heterolithic, coarse-grained deposits of the huu member (lithofacies mGSM[rg]; Table 1B) are interpreted as debris-flow deposits reworking the hul pyroclastic member along the main river valleys. Mud-rich lithofacies mSMG and mSM are interpreted as mudflow deposits (Fig. 9A).

Ca. 3 ka Las Mesas Eruption Episode

This episode was characterized by lava dome collapses, plug removal upon Vulcanian explosions, low columns that partially or totally collapsed producing pyroclastic density currents, and lahars. The componentry of both the lml-EU1 and lml-EU3 eruption units indicates explosive disruption of a lava plug or a fresh lava dome (Fig. 9B), expelling mostly dense to poorly vesicular juvenile materials. The presence of metamorphic lithics indicates that the fragmentation depth reached the country rock or that the violence of the eruption favored conduit erosion. Matrix-poor massive lithofacies associations mALB, mAL, and lensL (Table 1A) of lml-EU1 and lml-EU3 suggest rapid deposition from the underflow of highly concentrated pyroclastic density currents, with a granular flow dominated flow-boundary zone (Figs. 10B10C). Matrix-rich lithofacies were deposited in a fluid-escape depositional regime zone (Figs. 10B10C) at high clast concentration, during which gas retention within the granular mixture was a function of the porosity of the moving mixture. The occurrence of gas pipes in places supports the presence of high quantities of gas in the eruptive mixture at the time of deposition. The distinctive reddish-brown lml-EU2 deposits (lithofacies mAL; Table 1A) indicate rapid deposition and fines entrapment, where the common occurrence of charred woods and local tanned pink colors likely indicate high temperatures of emplacement. The rip-up soil intraclasts reflect the erosional capability of these currents, particularly for the uppermost lml-EU3. The channelized flows of lml-EU1 and lml-EU3 were able to overtop high elevations, with slightly increasing fines content and improved sorting toward the front, where two depositional flow pulses were recorded. There, and in overbank environments, the lowermost cross-stratified portions (lithofacies xlA, xsAL, xsLA, wxsLA; Table 1A) suggest grain-by-grain deposition from the basal turbulent zone in a flow boundary dominated by traction at the pyroclastic density current front. Upward transitions in lml-EU2 at overbank environments to weakly stratified or laminated deposits (lithofacies wsLA, wlA, wxlA; Table 1A), and embedded clast-supported lapilli lenses (lensL) suggest enhanced turbulence upon current dilution. The massive and thinly laminated ash (lithofacies lA, mA, maccrA; Table 1A) found at top of each unit reflects current waning and subsequent settling from elutriated (decoupled?) ash clouds. In addition, the poorly preserved clast-supported (angular) lapilli beds (lithofacies mL; Table 1A) represent remnants of fall deposits, thus supporting the hypothesis of low-column-collapse–derived pyroclastic density currents. The total estimated (minimum) volume for the pyroclastic density current deposits of the lml member is 24.0 × 106 m3.

The massive and monolithologic tuff-breccias (lithofacies mALB) of the coeval La Cabaña formation reported by Pardo et al. (2019) outside the study area, but which also originated at the central Young Doña Juana vent, reflect the accumulation of block-and-ash flow pulses to the north. Whether these flows occurred as opening phases or were synchronous with Las Mesas formation deposition remains unclear due to the absence of stratigraphic relations in the field between the two units.

The coarse-grained volcaniclastic deposits of the lmu member (lithofacies mGSM[rg]; Table 1B) are interpreted as debris-flow deposits, while matrix-rich mSMG lithofacies correspond to sand-rich mudflow deposits, both reworking the pyroclastic deposits of the lml member (Fig. 9C). The capping paleosol, together with correlative discontinuous 2–3-m-thick colluvial and fluvial deposits, and a proximal angular unconformity (Fig. 8A), marks a significant period of quiescence between the Las Mesas formation and the overlying Silencio formation.

1897–1936 CE Silencio–Valle de Piedras Episode

This episode records lava dome/plug disruptions developing violent, partially to totally collapsing Vulcanian to subplinian columns that generated pyroclastic density currents and lahars; this predominantly explosive activity transitioned into successive lava dome and spine extrusions that gravitationally collapsed, generating a rock avalanche and subsequent lahar. Pumice-bearing, massive tuff-breccias (lithofacies mALB) described for the sil-EU1 and sil-EU2 units of the Silencio formation indicate deposition from the underflow of high-concentration pyroclastic density currents (Figs. 10B10C). Proximal reversely graded levees (lithofacies mALB[rp]) and coarse-tail graded lithofacies (mBLA[g-ct], mALB[g-ct]) suggest strong density segregation within the currents. Lateral variations at overbank environments were found at the edge of the southwesternmost apron reaching Sofía stream (DJ-10; Supplemental Material 1.1). There, the occurrence of lithofacies mAL (Table 1A) in unit sil-EU1 indicates rapid deposition from valley-confined pyroclastic density currents dominated by a fluid escape flow-boundary zone, followed by current waning. The occurrence of lithofacies wxsAL at the base and at the top of unit sil-EU2 indicates deposition from a traction-dominated flow-boundary zone at the front and at the end of the main concentrated pyroclastic density current body. The total minimum volume of the pyroclastic density current deposits for the whole sil member, calculated using the available data, is 8.7 × 106 m3.

The occurrence of clast-supported lithofacies mL and mA in units sil-EU3 and sil-EU4 records at least two fallout depositional phases from an associated eruptive column (Fig. 9D). It is clear that the Silencio activity indicates higher explosivity involving a deeper level of the conduit than the Humadal and Las Mesas eruption episodes. However, we do not have enough elements to confirm a progressive transition into open-conduit conditions.

The heterolithic lithofacies mSMG and mSM of the siu member indicate lahars reworking previous pyroclastic deposits. Local occurrence of lithofacies altSC (Table 1B) suggests formation of ephemeral ponds in distal overbank areas.

The vpl member of Valle de Piedras formation suggests at least five subsequent phases of growth of the summit lava domes and spines (vpl EU1–EU5; Fig. 9E). The total minimum volume of the lava domes currently exposed at the Young Doña Juana summit area is estimated as 6.8 × 108 m3, subdivided as follows: ~4.3 × 108 m3 for vpl-EU1, ~5.7 × 104 m3 for vpl-EU2, ~1.3 × 105 m3 for vpl-EU3, ~2.4 × 108 m3 for vpl-EU4, and ~9.5 × 106 m3 for the youngest (endogenous) vpl-EU5.

The monolithologic hummocky breccias and sparse blocks described for the vpu member suggest the accumulation of a rock avalanche where kinetic sieving was important in forming reversely graded deposits. This event likely resulted from the gravitational collapse of one or more lava domes/spines among the most recent ones in the summit lava dome field (Fig. 9E). Similar partial collapses of lava domes have been reported at Soufrière Hills by Watts (2002) and Stinton et al. (2014). The abrupt change to heterolithic gravels at the break in slope, 1.4 km from the lava spines representing the likely source area, reflects the transformation of the rock avalanche into a debris flow.

In the case of the Silencio–Valle de Piedras eruption episode, we can integrate our geologic data with the available historical chronicles (Table 2). Brief written communications within national and regional journal repositories describe ballistic ejection during minor Vulcanian explosions and lava dome growth in 1897–1898, followed by two major paroxysms with ash dispersal beyond ~150 km and a subsequent lahar in 1899 (Table 2). Historical chronicles also indicate that some seismic events occurred over the following decades, but they could not be confirmed by other sources as accompanying volcanic eruptions (Espinosa, 2012) because their dates coincide with major regional tectonic activity noted by the Colombian Geological Survey (http://sish.sgc.gov.co/visor/). These events include the MW 8.8 earthquake in 1906 (Pacific coast epicenter: lat 0.99°N, long 79.35°W), the MW 6.2 earthquake in 1923 (southern Nariño epicenter: lat 0.87°N, long 77.78°W, with ash emission reported from Doña Juana volcanic complex 3 h later), and the ML 6.0 earthquake in 1926 (southern Nariño epicenter: lat 0.87°N, long 77.78°W). The final collapse event at Doña Juana volcanic complex was documented in 1936, but we do not know if it occurred during or after the growth of the domes/spines, or if there was an active hydrothermal system. For sure, the studied deposits do not show any evidence for associated explosive activity.

Flow Mobility

The mobility ratio (ΔH/L), based on the height difference (ΔH) and horizontal distance (L) between the source area and the distal limit of the deposit, captures the ability of gravity-driven mass flows to move downslope (e.g., Iverson, 1997). The ratio ΔH/L defines the coefficient of friction for the mass flow (Hayashi and Self, 1992) and reflects the Mohr-Coulomb angle of internal granular friction (Freundt, 1999). The mobility ratio of block-and-ash flows from Young Doña Juana has values of 0.21–0.22 (Supplemental Material 3), similar to parameters calculated for those derived by lava dome collapse in the Soufriere Hills volcano on Montserrat (Calder et al., 1999). For pyroclastic density currents related to column collapse, ΔH depends on whether the source area is assumed to correspond to the volcano summit or to the height where column collapse occurred (Hayashi and Self, 1992). For Young Doña Juana, a column collapse height of 500 m above the volcano summit produces ΔH/L values from 0.18 (along Humadal stream) to 0.24 (along Carmelo stream) for pyroclastic density currents dominated by dense juvenile material (Las Mesas formation), and between 0.20 (along Humadal stream) and 0.24 (along Hueco Seco stream) for pumice-bearing currents (Silencio formation). Moreover, along Humadal stream, where all studied units occur and can be compared to one another, ΔH/L is lower for fountain/column-collapse pyroclastic density currents, consistent with slightly longer runout distances (ΔH/L = 0.18–0.20) and slightly lower internal granular friction than for block-and-ash flows (ΔH/L = 0.21).

The Young Doña Juana central vent within the Doña Juana volcanic complex is an excellent example of a dome-dominated, tropical arc volcano. By merging the late Holocene geologic record, radiocarbon ages, and eyewitness chronicles from the late nineteenth and early twentieth centuries, we interpreted the recent-past eruption behavior to include: (1) summit lava dome growth associated with occasional (minor) explosions; (2) gravitational lava dome collapses, generating rock avalanches or larger block-and-ash flows reaching ≥7 km from the vent; and (3) deep dome collapses and plug disruptions leading to Vulcanian to subplinian eruptions forming pyroclastic density currents from pyroclastic fountains/column collapses reaching ≥10 km from the vent, with rare pyroclastic fallout reaching ≥150 km (see Table 2). Historical chronicles (Table 2) suggest that cyclic transitions from lava dome growth phases to explosive phases likely occur over 1–2 yr.

Most of the studied pyroclastic density currents veered toward the west and were channeled through a low saddle on the western rim of the vc2 caldera (Figs. 2 and 7A) and then cascaded into the Humadal stream valley and reached the inhabited depositional terrace of the Las Mesas village (Figs. 24). In addition to this main flow trajectory, most pyroclastic density currents overflowed through other saddles of the vc2 caldera rim toward the west into the upper valleys of the Florida and Carmelo streams (Fig. 2). Deposition of the studied pyroclastic density currents mostly occurred under granular flow or fluid escape depositional regimes at high clast concentrations (Figs. 10B10C), had volumes similar to those calculated for Vulcanian eruptions in other volcanoes elsewhere (e.g., Cole et al., 2014; Capra et al., 2016; Albino et al., 2020), and are classified as Vulcanian ignimbrites following Giordano and Cas (2021) (see Supplemental Material 3; Fig. 10D). The absence of traction-dominated pyroclastic density current deposits in the upper slopes of Young Doña Juana suggests limited generation of diluted and turbulent pyroclastic density currents from overpressurized jets at the source. Traction structures occur only sporadically and mostly in overbank regions, related to more diluted conditions and accompanying turbulent ash clouds possibly induced by the interaction with irregular topography. All of these processes were associated with inter- and posteruptive lahars.

1Supplemental Material. Supplemental Material 1: Link to the interactive map (1.1), histograms (1.2), and statistics (1.3) of grain-size distributions of each pyroclastic unit. Supplemental Material 2: Radiocarbon dating (n = 90) and whole-rock geochemical data (n = 27) of juvenile clasts. Supplemental Material 3: Details on volume calculation and calculation of main geometric parameters following Giordano and Cas (2021). Please visit https://doi.org/10.1130/GSAB.S.21365685 to access the supplemental material and contact editing@geosociety.org with any questions.
Science Editor: Brad Singer
Associate Editor: Michael Ort

This study was funded by a University of Los Andes FAPA inner grant allocated to N. Pardo, and by the Visiting Researcher fellowship allocated to N. Pardo at Università degli Studi di Bari Aldo Moro (DR no. 3208 of 2018). S. Cronin was supported by the Transitioning Taranaki to Volcanic Future project of the New Zealand Ministry for Business, Innovation and Employment (UOAX1913). The research was included within agreement no. 35–2018 between the Universidad de Los Andes and the Geological Survey of Colombia. We deeply thank Ricardo Villota, Manuel Chávez, Las Mesas village inhabitants, and the staff of Doña Juana–Cascabel National Natural Park for their lessons and support during fieldwork. The Historical Ecology and Social Memory Research collective (EHMS of the Universidad de Los Andes) and C. Laverde (Geological Survey of Colombia) helped to interpret the historical documentation. Markus Egli directed the work to obtain the radiocarbon ages at the Radiocarbon Laboratory of the University of Zürich (Switzerland). The technical staff of the Geosciences and Mechanical Engineering laboratories of the Universidad de Los Andes, M.A. Arias, E.S. Villamil, L. Acosta, and D.F. Martinez helped with granulometry analyses. Diego Palechor (Geological Survey of Colombia) helped with the setup of the geographic information system geodatabase. Shari van Treeck (Institute of Geosciences and Meteorology, Universität Bonn, Germany) carried out part of the volume calculations. We greatly thank P. Samaniego, an anonymous reviewer, and the associate editor for their constructive suggestions, which helped to optimize the latest version of this manuscript. Part of the publication costs were covered with the funds of the call “PUBLICA, EXPÓN O FORTALECE TU PRODUCTO DE TRANSFERENCIA” approved by the Vicerrectoría de Investigación y Creación of the Universidad de Los Andes, Bogotá, D.C., Colombia.

Gold Open Access: This paper is published under the terms of the CC-BY license.