Physical and chemical characteristics of active sulfur flows observed at Lastarria volcano (northern Chile) in January 2019

Lastarria volcano (25°10′ S, 68°31′ W; 5,697 m above sea level), located in the Central Andes Volcanic Zone (northern Chile), is characterized by four distinct fumarolic fields with outlet temperatures ranging between 80°C and 408°C as measured between May 2006–March 2008 and April–June 2009. Fumarolic gasses contain significant concentrations of high temperature gas compounds (i.e., SO2, HCl, HF, H2, and CO), and isotopic ratios (3He/4He, δ13C–CO2, δ18O–H2O, and δD–H2O) diagnostic of magmatic gas sources. Gas equilibria systematics, in both the H2O-H2-CO2-CO-CH4 and alkane–alkene C3 system, suggest that Lastarria fumarolic gasses emanate from a superheated vapor that is later cooled and condensed at relatively shallow depths. This two-stage process inhibits the formation of a continuous aquifer (e.g., horizontal liquid layer) at relatively shallow depth. Recent developments in the magmatic gas system may have enhanced the transfer and release of heat causing shallow aquifer vaporization. The consequent pressure increase and aquifer vaporization likely triggered the inflation events beginning in 2003 at the Lastarria volcano.

One of the major problems in the volcanic surveillance is how data from several techniques can be correlated and used to discriminate between possible precursors of volcanic eruptions and changes related to non-eruptive processes. Gas chemical surveys and measurements of SO2 emission rates performed in the past (2006–2019) at Lastarria volcano in Northern Chile have revealed a persistent increment of magmatic sourced gas emissions since late November 2012, following a 13 years period of intense ground uplift. In this work, we provide new insights into the gas-chemical evolution of Lastarria’s fumarolic discharges obtained from direct sampling (2006–2019) and SO2 emission rates using UV camera and DOAS instruments (2018–2019) and link these to pre-existing information on ground deformation (1998–2016) in order to determine the origin of observed degassing and ground deformation processes. We revise the four mechanisms originally proposed as alternatives by Lopez et al. (Geosphere, 2018, 14 (3), 983–1007) to explain the changes observed in the fluid geochemistry and ground deformation between 2009 and 2012, in order to explain major changes in gas-geochemistry over an extended period between 1998 and 2019. We hypothesize that a continuous sequence of processes explains the evolution in the fluid geochemistry of fumarolic discharges. Two mechanisms are responsible of the changes in the gas composition during the studied period, corresponding to a 1) deep magma chamber (7–15 km depth) pressurized by volatile exsolution (1998–2020), which is responsible of the large-scale deformation; followed by 2) a crystallization-induced degassing (2001–2020) and pressurization of the hydrothermal system (2003-early November 2012), where the former process induced the changes in the gas composition from hydrothermal-dominated to magmatic-dominated, whereas the last produced the small-scale deformation at Lastarria volcano. The changes in the gas composition since late November 2012, which were strongly dominated by magmatic volatiles, produced two consecutive processes: 1) acidification (late November 2012–2020) and 2) depletion (2019–2020) of the hydrothermal system. In this work we have shown that a long-term surveillance of the chemistry of fluid discharges provides valuable insights into underlying magmatic/volcanic processes, and consequently, for forecasting future eruptions.

Lastarria volcano (Chile) is located at the North-West margin of the `Lazufre' ground inflation signal (37x45 km²), constantly uplifting at a rate of ~2.5 cm/year since 1996 (Pritchard and Simons 2002; Froger et al. 2007). The Lastarria volcano has the double interest to be superimposed on a second, smaller-scale inflation signal and to be the only degassing area of the Lazufre signal. In this project, we compared daily SO2 burdens recorded by AURA's OMI mission for 2005-2010 with Ground Surface Displacements (GSD) calculated from the Advanced Synthetic Aperture Radar (ASAR) images for 2003-2010. We found a constant maximum displacement rate of 2.44 cm/year for the period 2003-2007 and 0.80- 0.95 cm/year for the period 2007-2010. Total SO2 emitted is 67.0 kT for the period 2005-2010, but detection of weak SO2 degassing signals in the Andes remains challenging owing to increased noise in the South Atlantic radiation Anomaly region.

Lastarria volcano, a major emitter of boron and chalcophiles in northern Chile and the Central Volcanic Zone

Intraoceanic arcs of the world are dominated by submarine volcanoes, many of which host active hydrothermal systems. A considerable number of the morphological features common to subaerial volcanoes are also present on the submarine edifices, including summit craters. Surprisingly, some of the craters, such as at Daikoku and Nikko volcanoes of the Mariana Arc, and Macauley Cone of the Kermadec Arc, are host to lakes of molten sulfur, both ancient and modern. These lakes, up to ~200 m in diameter, act as condensers of gases that derive from the underlying magmas. Volcanic vents beneath these lakes provide a steady outflow of hot gases that continuously generate molten sulfur. At Daikoku, an extraordinary lake of liquid sulfur is in constant convective and gas escape-driven motion. Smaller pools of molten sulfur occur on Nikko, and there is evidence of older, larger lakes on both this volcano and Macauley, based on the accumulation of large quantities of sulfur in the subsurface. The elemental S at these sites is produced largely by the reaction 2H2S + SO2 = 3S + 2H2O and the disproportionation of magmatic SO2. Anomalous concentrations of Au and Cu in the lakes are most likely transported by vapor.

Although several authors have suggested that sulphur plays an important role in the volcanism on the jovian moon Io1–8, some deny the participation of elemental sulphur there, at least in the form of cooled flows9. Studies of volcanism on Io have focused attention on the role of sulphur in terrestrial volcanism. On Earth, fumarolic sulphur is very common in almost all active volcanoes, but sulphur flows are rare, having been reported only on Siretoko–Iosan volcano in Japan10, on Sierra Negra and Azufre volcanoes in the Galapagos Islands11,12 and on Mauna Loa in Hawaii13,14. Of these, the Siretoko–Iosan example is the only natural molten sulphur flow to have been observed in the process of formation; the others being rather poorly exposed. I describe here a singularly well-exposed example of sulphur lava flows, on Lastarria volcano in Chile, where the liquid sulphur appears to have been formed by melting of fumarolic sulphur deposits caused by a rise in the thermal gradient owing to the renewed activity of the magmatic source.

This chapter is a tribute to Bokuichiro Takano and Minoru Kusakabe for their important contributions to our knowledge of sulfur chemistry and dynamics in hyper-acid crater lakes and geothermal lakes. Hyper-acid crater lakes are perched at the summit of active volcanoes and represent the uppermost manifestation of a shallow active magma-hydrothermal system. They act as traps for strongly acidic condensates formed as sulfur-rich magmatic gases rising from depth expand and cool in the main hydrothermal upflow zone. The remarkable sulfate content of hyper-acid crater lakes is sourced to disproportionation-hydrolysis of magmatic SO2 in the upper part of the hydrothermal conduit. This reaction generates a strong, temperature-dependent sulfur isotopic fractionation, which typically produces high $$\updelta^{ 3 4} {\text{S}}_{{{\text{SO}}_{ 4} }}$$ values. In contrast, sulfate in geothermal lakes displays much lighter sulfur isotopic compositions linked to oxidation of H2S-rich hydrothermal discharges. Polythionates are ubiquitous in hyper-acid crater lakes and are usually attributed to aqueous interaction between SO2 and H2S in the lake. Fluctuations in lake polythionate concentrations have been used to infer changes in the SO2/H2S ratio of magmatic hydrothermal inputs. However, polythionates may also originate from hydrolysis of elemental sulfur. Elemental sulfur in hyper-acid crater lakes occurs primarily as a molten body at the hydrothermal vent-crater floor interface. The origin of this material is not entirely clear; several deposition reactions are compatible with the observed range of sulfur isotopic compositions. Sulfide and sulfosalt minerals commonly occur as impurities in molten sulfur from hyper-acid crater lakes. Molten sulfur is also found in some geothermal lakes. There are still plenty of research opportunities for decoding the complex cycling of sulfur between aqueous and gaseous species and elemental sulfur in hyper-acid crater lakes. In particular, efforts are needed to track intermediate sulfur species. The role that subaqueous molten sulfur plays in modulating heat and mass transfers to the overlying lake and in trapping metals transported by magmatic gases deserves further investigations.

Lazufre volcanic center, located in the central Andes, is recently undergoing an episode of uplift, conforming one of the most extensive deforming volcanic systems worldwide, but its magmatic system and its connection with the observed uplift are still poorly studied. Here we image the electrical resistivity structure using the magnetotelluric method in the surroundings of the Lastarria volcano, one of the most important features in the Lazufre area, to understand the nature of the magmatic plumbing, the associated fumarolic activity, and the large‐scale surface deformation. Results from 3‐D modeling show a conductive zone at 6 km depth south of the Lastarria volcano interpreted as the magmatic heat source which is connected to a shallower conductor beneath the volcano, showing the pathways of volcanic gasses and heated fluid. A large‐scale conductive area coinciding with the area of uplift points at a magma intrusion at midcrustal depth.

Thermal and gas dynamic investigations at Lastarria volcano, Northern Chile. The influence of precipitation and atmospheric pressure on the fumarole temperature and the gas velocity

With animal species disappearing at unprecedented rates, we need an efficient monitoring method providing reliable estimates of population density and abundance, critical for the assessment of population status and trend.We deployed 160 camera traps (CTs) systematically over 743 locations covering 17,127 km2of evergreen lowland rainforest of Salonga National Park, block South, Democratic Republic of the Congo. We evaluated the applicability of CT distance sampling (CTDS) to species different in size and behaviour. To improve precision of estimates, we evaluated two methods estimating species' availability (‘A’) for detection by CTs.We recorded 16,700 video clips, revealing 43 different animal taxa. We estimated densities of 14 species differing in physical, behavioural and ecological traits, and extracted species‐specific availability from available video footage using two methods (a)‘ACa’(Cappelle et al. [2019]Am.J.Primatol., 81, e22962) and (b)‘ARo’(Rowcliffe et al. [2014]MethodsEcol.Evol. 5, 1170). With sample sizes being large enough, we found minor differences betweenACaandARoin estimated densities. In contrast, low detectability and reactivity to the camera were main sources of bias. CTDS proved efficient for estimating density of homogenously rather than patchily distributed species.Synthesis and applications.Our application of camera trap distance sampling (CTDS) to a diverse vertebrate community demonstrates the enormous potential of this methodology for surveys of terrestrial wildlife, allowing rapid assessments of species' status and trends that can translate into effective conservation strategies. By providing the first estimates of understudied species such as the Congo peafowl, the giant ground pangolin and the cusimanses, CTDS may be used as a tool to revise these species' conservation status in the IUCN Red List of Threatened Species. Based on the constraints we encountered, we identify improvements to the current application, enhancing the general applicability of this method.

Flat vein formation in a transitional crustal setting by self-induced fluid pressure equilibrium — an example from the Géant Dormant gold mine, Canada

ABSTRACT. 1. Patterns of daily and seasonal activity for seven species of tenebrionid beetles, genus Eleodes , were investigated in the shortgrass prairie of northeastern Colorado. The relationship between time of activity, body temperatures, and rates of water loss of the beetles was examined in the field and in laboratory experiments. 2. Common species were active from April until the end of October; however, asynchronous peaks of abundance occurred. 3. Beetles were diurnally active with peaks of daily activity occurring 2–4 h after sunrise and before sunset. Less than a 2 h shift in mean time of activity occurred between seasons. 4. Within species, body temperatures measured in the field closely corresponded to temperatures selected in an experimental thermal gradient; hence, species seemed to prefer particular body temperatures and were most active during times when those temperatures could be achieved. Body temperatures measured in the field approximated ambient temperatures measured in the vicinity of the beetle. 5. Significant differences among several species were found for times of daily activity and corresponding body temperatures. 6. Ability to resist water loss by evaporation was not correlated with daily or seasonal activity patterns.

The timing and pattern of mammalian behavioral activities are regulated by an evolutionary optimized interplay of the genetically based biological (circadian) clock located in the brain’s suprachiasmatic nuclei and direct responses to environmental factors that superimpose and thus mask the clock-mediated effects, the most important of which is the photically induced phase-setting (synchronization) of the circadian rhythmicity to the 24-hour solar day. In wild and captive animals living under the natural conditions prevailing in their habitat, to date, only a few attempts have been made to analyze the role of these two regulatory mechanisms in the species’ adaptation to the time structure prevailing in their habitat. We studied the impact of housing conditions and season on the daily timing and pattern of activity in Mexican spider monkeys (Ateles geoffroyi). To this end, we carried out long-term activity recordings with Actiwatch® AW4 accelerometer/data-logger devices in 11 adult Ateles living under identical natural lighting and climatic conditions in either a large wire netting cage or a 0.25 ha forest enclosure in the primatological field station of Veracruz State University near Catemaco, Mexico. In a gravid female in the forest enclosure, we obtained first-hand information on the effect of late pregnancy and parturition on the monkey’s activity rhythm. The Ateles behaved strictly diurnal and undertook about 90% of daily total activity during this activity time. Due to a higher second activity peak in late afternoon, the bimodal activity pattern was more pronounced in monkeys living in the forest enclosure. Although the spider monkeys kept there had an earlier activity onset and morning activity peak than their conspecifics in the cage, no consistent differences were found in the parameters characterizing the phase-setting of the circadian system to the environmental 24-h periodicity, either by comparison or correlation with the external time markers of sunrise (SR) and sunset (SS). The most obvious effect of late pregnancy, parturition and lactation was a distinct reduction of the activity level during the week of parturition and the next. Seasonal variations in the form of significant differences between the long-day summer half year and the short-day winter half year were established in the phase-angle differences of the morning activity peak to SR, in the evening activity peak and activity offset to SS, as well as in the activity time and the peak-to-peak interval, but not in the phase position of activity onset to SR or in the height of the morning and evening activity peak. These findings in combination with a high variability of the phase angle differences indicate that in A. geoffroyi, a relatively weak circadian component and strong masking direct effects of environmental factors are involved in the regulation of the daily activity rhythm.

Native sulfur occurrences, which are very common in the Andes of northern Chile (18–28° S lat), are usually found directly related to summits, craters, and/or along flanks in almost all Upper Cenozoic volcanic edifices, mainly as sulfur mantos, breccias, veins, and amygdaloidal fillings. Other less common occurrences in these environments are sulfur flows, such as in the Lastarria volcano (Naranjo 1985).

Unraveling the origin of the Andean IOCG clan: A Re-Os isotope approach