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Sudden glacier advances in the Cachapoal Valley, Southern Central Andes of Chile (34 degrees S)
(2021)
Throughout the Andes Mountains of South America, a general trend of glacier shrinkage has taken place in modern times. However, a few glaciers have undergone considerable temporally advances or even surged during the mid-19th to 20th century CE. These valley glaciers are mainly located in the Central Andes of Chile and Argentina. The research presented here focuses on the changes of the Cachapoal Glacier in the Southern Central Andes of Chile. Spectacular glacier advances occurred at least three times in historical times, which lead to river blockages and successive lake outburst floods. The glacier advances were reconstructed with a multi-method approach including geomorphological mapping, Be-10 cosmogenic exposure dating of moraines, multi-temporal comparison of historical and recent photographs and paintings as well as the interpretation of aerial photographs and satellite images and the analysis of early travel reports. The article highlights the diversity of environmental conditions for the formation of glaciers in terms of the topographical and climatic setting and the resulting distinct glacier behavior along the Andes Mountains. It is argued for the Cachapoal Glacier that the glacier advances are intrinsic to the glacier type and may not be necessarily climate-dependent. This is characteristic for avalanche-fed glaciers of which the glacier dynamic is strongly controlled by the topographic setting and sudden inputs of ice and rock avalanches as well as by the specific debris transfer system and hydrological drainage pattern. At the regional level, the fluctuations of the Cachapoal Glacier are compared with glaciers of neighboring mountain ranges in the Southern Central Andes and at the global scale with those of the Karakoram Mountains in High Asia with a similar dynamic glacier behavior.
Detecting whether and how river discharge responds to strong earthquake shaking can be time-consuming and prone to operator bias when checking hydrographs from hundreds of gauging stations. We use Bayesian piecewise regression models to show that up to a fifth of all gauging stations across Chile had their largest change in daily streamflow trend on the day of the M-w 8.8 Maule earthquake in 2010. These stations cluster distinctly in the near field though the number of detected streamflow changes varies with model complexity and length of time window considered. Credible seismic streamflow changes at several stations were the highest detectable in eight months, with an increased variance of discharge surpassing the variance of discharge following rainstorms. We conclude that Bayesian piecewise regression sheds new and unbiased insights on the duration, trend, and variance of streamflow response to strong earthquakes, and on how this response compares to that following rainstorms.
Along a subduction zone, great megathrust earthquakes recur either after long seismic gaps lasting several decades to centuries or over much shorter periods lasting hours to a few years when cascading successions of earthquakes rupture nearby segments of the fault. We analyze a decade of continuous Global Positioning System observations along the South American continent to estimate changes in deformation rates between the 2010 Maule (M8.8) and 2015 Illapel (M8.3) Chilean earthquakes. We find that surface velocities increased after the 2010 earthquake, in response to continental-scale viscoelastic mantle relaxation and to regional-scale increased degree of interplate locking. We propose that increased locking occurs transiently during a super-interseismic phase in segments adjacent to a megathrust rupture, responding to bending of both plates caused by coseismic slip and subsequent afterslip. Enhanced strain rates during a super-interseismic phase may therefore bring a megathrust segment closer to failure and possibly triggered the 2015 event.
The impressive number of stream gauges in Chile, combined with a suite of past and recent large earthquakes, makes Chile a unique natural laboratory to study several streams that recorded responses to multiple seismic events. We document changes in discharge in eight streams in Chile following two or more large earthquakes. In all cases, discharge increases. Changes in discharge occur for peak ground velocities greater than about 7-11cm/s. Above that threshold, the magnitude of both the increase in discharge and the total excess water do not increase with increasing peak ground velocities. While these observations are consistent with previous work in California, they conflict with lab experiments that show that the magnitude of permeability changes increases with increasing amplitude of ground motion. Instead, our study suggests that streamflow responses are binary. Plain Language Summary Earthquakes deform and shake the surface and the ground below. These changes may affect groundwater flows by increasing the permeability along newly formed cracks and/or clearing clogged pores. As a result, groundwater flow may substantially increase after earthquakes and remain elevated for several months. Here we document streamflow anomalies following multiple high magnitude earthquakes in multiple streams in one of the most earthquake prone regions worldwide, Chile. We take advantage of the dense monitoring network in Chile that recorded streamflow since the 1940s. We show that once a critical ground motion is exceeded, streamflow responses to earthquakes can be expected.
From north to south, denudation rates from cosmogenic nuclides are similar to 10 t km(-2) yr(-1) at the arid Pan de Aziicar site, similar to 20 t km(2) yr(-1) at the semi-arid site of Santa Gracia, -60 t km(-2) yr(-1) at the Mediterranean climate site of La Campana, and similar to 30 t km(-2) yr(-1) at the humid site of Nahuelbuta. A and B horizons increase in thickness and elemental depletion or enrichment increases from north (similar to 26 degrees S) to south (similar to 38 degrees S) in these horizons. Differences in the degree of chemical weathering, quantified by the chemical depletion fraction (CDF), are significant only between the arid and sparsely vegetated site and the other three sites. Differences in the CDF between the sites, and elemental depletion within the sites are sometimes smaller than the variations induced by the bedrock heterogeneity. Microbial abundances (bacteria and archaea) in saprolite substantially increase from the arid to the semi-arid sites. With this study, we provide a comprehensive dataset characterizing the Critical Zone geochemistry in the Chilean Coastal Cordillera. This dataset confirms climatic controls on weathering and denudation rates and provides prerequisites to quantify the role of biota in future studies.
This two-wave longitudinal study examined risky sexual scripts and sexual behavior regarding consensual sexual interactions, sexual self-esteem, initiation assertiveness, and religiosity as predictors of sexual aggression perpetration in a cross-cultural comparison of college students in Chile and Turkey. As predicted, risky sexual scripts were linked to higher odds of perpetration through more risky sexual behavior cross-sectionally in both the Chilean and the Turkish sample and indirectly predicted perpetration 12 months later. High sexual self-esteem increased the likelihood of perpetration via higher initiation assertiveness in the Turkish sample only. High religiosity reduced the odds of perpetration through less risky sexual scripts and less risky sexual behavior in both samples. In addition, high religiosity increased the probability of perpetration through lower sexual self-esteem in the Turkish sample. Implications of these findings and the role of cultural factors contributing to the differential functioning of religiosity and sexual self-esteem are discussed.
Sexual aggression is a major public health issue worldwide, but most knowledge is derived from studies conducted in North America and Western Europe. Little research has been conducted on the prevalence of sexual aggression in developing countries, including Chile. This article presents the first systematic review of the evidence on the prevalence of sexual aggression victimization and perpetration among women and men in Chile. Furthermore, it reports differences in prevalence rates in relation to victim and perpetrator characteristics and victim–perpetrator relationships. A total of N = 28 studies were identified by a three-stage literature search, including the screening of academic databases, publications of Chilean institutions, and reference lists. A great heterogeneity was found for prevalence rates of sexual victimization, ranging between 1.0% and 51.9% for women and 0.4% and 48.0% for men. Only four studies provided perpetration rates, which varied between 0.8% and 26.8% for men and 0.0% and 16.5% for women. No consistent evidence emerged for differences in victimization rates in relation to victims’ gender, age, and education. Perpetrators were more likely to be persons known to the victim. Conceptual and methodological differences between the studies are discussed as reasons for the great variability in prevalence rates, and recommendations are provided for a more harmonized and gender-inclusive approach for future research on sexual aggression in Chile.
We address the question of whether all large-magnitude earthquakes produce an erosion peak in the subaerial components of fluvial catchments. We evaluate the sediment flux response to the Maule earthquake in the Chilean Andes (Mw 8.8) using daily suspended sediment records from 31 river gauges. The catchments cover drainage areas of 350 to around 10,000 km(2), including a wide range of topographic slopes and vegetation cover of the Andean western flank. We compare the 3- to 8-year postseismic record of sediment flux to each of the following preseismic periods: (1) all preseismic data, (2) a 3-year period prior to the seismic event, and (3) the driest preseismic periods, as drought conditions prevailed in the postseismic period. Following the earthquake, no increases in suspended sediment flux were observed for moderate to high percentiles of the streamflow distribution (mean, median, and >= 75th percentile). However, more than half of the examined stations showed increased sediment flux during baseflow. By using a Random Forest approach, we evaluate the contributions of seismic intensities, peak ground accelerations, co-seismic landslides, hydroclimatic conditions, topography, lithology, and land cover to explain the observed changes in suspended sediment concentration and fluxes. We find that the best predictors are hillslope gradient, low-vegetation cover, and changes in streamflow discharge. This finding suggests a combined first-order control of topography, land cover, and hydrology on the catchment-wide erosion response. We infer a reduced sediment connectivity due to the postseismic drought, which increased the residence time of sediment detached and remobilized following the Maule earthquake.
Understanding how Earth-surface processes respond to past climatic perturbations is crucial for making informed predictions about future impacts of climate change on sediment "uxes. Sedimentary records provide the archives for inferring these processes, but their interpretation is compromised by our incomplete understanding of how sediment-routing systems respond to millennial-scale climate cycles. We analyzed seven sediment cores recovered from marine turbidite depositional sites along the Chile continental margin. The sites span a pronounced arid-to-humid gradient with variable relief and related sediment connectivity of terrestrial and marine environments. These sites allowed us to study event related depositional processes in different climatic and geomorphic settings from the Last Glacial Maximum to the present day. The three sites reveal a steep decline of turbidite deposition during deglaciation. High rates of sea-level rise postdate the decline in turbidite deposition. Comparison with paleoclimate proxies documents that the spatio-temporal sedimentary pattern rather mirrors the deglacial humidity decrease and concomitant warming with no resolvable lag times. Our results let us infer that declining deglacial humidity decreased "uvial sediment supply. This signal propagated rapidly through the highly connected systems into the marine sink in north-central Chile. In contrast, in south-central Chile, connectivity between the Andean erosional zone and the "uvial transfer zone probably decreased abruptly by sediment trapping in piedmont lakes related to deglaciation, resulting in a sudden decrease of sediment supply to the ocean. Additionally, reduced moisture supply may have contributed to the rapid decline of turbidite deposition. These different causes result in similar depositional patterns in the marine sinks. We conclude that turbiditic strata may constitute reliable recorders of climate change across a wide range of climatic zones and geomorphic conditions. However, the underlying causes for similar signal manifestations in the sinks may differ, ranging from maintained high system connectivity to abrupt connectivity loss. (C) 2017 Elsevier B.V. All rights reserved.