Subaqueous mass movements in the context of observations of contemporary slope failure

The consequences of subaqueous landslides have been at the forefront of societal conscience more than ever in the last few years, with devastating and fatal events in the Indonesian Archipelago making global news. The new research presented in this volume demonstrates the breadth of ongoing investigation into subaqueous landslides, and shows that while events like the recent ones can be devastating, they are smaller in scale than those Earth has experienced in the past. Understanding the spectrum of subaqueous landslide processes, and therefore the potential societal impact, requires research across all spatial and temporal scales. This volume delivers a compilation of state-of-the-art papers covering regional landslide databases, advanced techniques for in situ measurements, numerical modelling of processes and hazard

Holocene earthquake-triggered mass-wasting events recorded in the sediments of Lake Puyehue (South-Central Chile)

Despite South-Central Chile’s high seismicity and the occurrence of earth’s largest instrumentally recorded earthquake (AD 1960; Mw: 9.5), paleoseismic data is still scarce for this region. In this study, very high-resolution reflection seismic profiles (3.5 kHz) in Lake Puyehue (41°S) were utilized to trace giant seismic events back into time. The seismic profiles show repeated occurrences of multiple mass-wasting deposits (slumps, debris flows, homogenites) occurring at a same seismic-stratigraphic horizon, indicating that they are coeval and caused by a single mass-wasting event of basin-wide importance. An age-depth model, based on 9 AMS radiocarbon datings and varve-counting on an 11 m-long sediment core, has been used to develop a “seismic chronostratigraphy”. It allows dating of the mass-wasting events by interpolation between dated seismic horizons to the distal parts of the mass-wasting deposits. The mass-wasting events are assumed to be earthquake-triggered because:The recentmost mass-wasting events correlate with the devastating historical earthquakes of AD 1575 and AD 1960.Synchronicity of multiple slope failures (mass-wasting events) requires a strong regional trigger, such as an earthquake. Consequently, local slope oversteepening at delta fronts or local fluid expulsion could not initiate such widespread events.South-Central Chile has been historically subjected to several strong (M > 8) subduction earthquakes and subduction processes have been constantly active since Mesozoic times.Multiple slope failures occur at water depths > 70 m, which rules out shallow instability triggers, such as storm wave action and lake-level fluctuations.This study reveals nine paleoseismic events during the Holocene with a mean recurrence rate of about 1000 yr, but with an overall relatively aperiodic occurrence (ranging between 400-2000 yrs.). The most prominent event took place around 1660 cal. yr. BP, evidenced by at least 29 simultaneous mass-movements and a homogenite deposit. Quantitative comparison of mass-wasting events related to the historical earthquakes of AD 1960 and AD 1575 showed significant differences (respectively 17 and 4 observed mass-wasting deposits) although these earthquakes are assumed to have had a comparable strength. This can be attributed to a lowered sedimentation rate on the potentially unstable slopes in the period 3000 cal. yr. BP – 500 cal. yr. BP, which would have made lacustrine earthquake recording less likely in AD 1575. The absence of mass-wasting deposits associated with other historical earthquakes (e.g.: AD 1737 (Ms: 7.5) and AD 1837 (Ms: 8)) indicates that only mega-earthquakes (Mw >8.5) within a range of about 300 km are recorded in the sedimentary sequence of Lake Puyehue.Reflection seismic profiles also show vertical fluidisation structures with large-scale sediment injections, which disturb the upper sedimentary sequences. The top of these fluidisation structures and diverse deformation levels could be spatially linked to seismically induced mass-wasting deposits and consequently indicate an additional method for lacustrine paleo-earthquake tracing.Several reconaissance seismic surveys on other glacigenic lakes in the Chilean Lake District also show promising paleoseismic records, which will offer the opportunity to correlate lacustrine records to reveal South-Central Chile’s paleoseismic history in detail and the earthquake registration capacities of its glacigenic lakes

The Hazar pull-apart along the East Anatolian Fault: Structure and active deformation

Understanding the irregularity of seismic cycles: A case study in Turke

The Hazar pull-apart along the East Anatolian Fault: Structure and active deformation

Understanding the irregularity of seismic cycles: A case study in Turke

A 25,000 years climate record from the East African equator: Half-precessional climate forcing and the history of temperature and hydrological change

Particularly in tropical and subtropical regions, high-resolution climate records have demonstrated major variability in the hydrological cycle at orbital, millennial and sub-millennial time scales in the last 25,000 years. Geographical patterns of past climate change (from the equator to both poles, and among continents and ocean basins at similar latitude) at these various time scales hold the key to understanding the climate-dynamical processes governing them, and to resolution of longstanding questions about the relative importance of tropical and high-latitude climate dynamics in translating external climate-forcing mechanisms into regional climate variability. Currently, dynamical analysis of past tropical climate variability is being hampered by the fragmentary or poorly dated nature of available records from key continental regions, debate to what extent marine records are representative for climate history on the continents, and uncertainty about whether traditional isotopic tracers applied to tropical continental records mainly reflect temperature or hydrological change. What has been missing is a continuous, high-resolution climate record from the tropics that adequately separates the evolution of temperature and hydrological change, and covers the period from the Last Glacial Maximum until the present with sufficient age control to establish supra-regional phase relationships in past climate anomalies at millennial and century time scales.In this context, the EuroCLIMATE project CHALLACEA here presents a reconstruction of climate history on the East African equator, based on multiple proxy-indicator analyses in the sediment record of a permanently stratified crater lake (Lake Challa, a 4.2 km2, 92 m deep crater lake on the lower East slope of Mt. Kilimanjaro, Tanzania) with stable physical limnology and sedimentation dynamics over the past 25,000 years. This has resulted in a unique combination of high temporal resolution, excellent radiometric (210Pb, 14C) age control, and confidence that the recording parameters of the climatic proxies (i.e. the relationship between climate change and its proxy signals extracted from the sediment record) have remained constant through time. The equatorial (3° S) location of our study site in East Africa, where seasonal migration of the Intertropical Convergence Zone spans the widest latitude range, provides unique information on how varying rainfall contributions from the Indian Ocean monsoons have shaped the region’s climate history. The detailed reconstruction of the temperature and moisture-balance history of equatorial East Africa from before the Last Glacial Maximum to the present uniquely weaves together tropical climate variability at orbital, millennial and century time scales. The temporal pattern of reconstructed climate changes bears the clear signature of half-precessional insolation forcing of tropical monsoon dynamics on the East African equator, modified by high southern latitude influence on the timing of post-glacial temperature rise, and by high northern latitude influence on tropical hydrological variability at millennial and century time scales

Radionuclide profiles and recent earthquakes history of Lake Hazar Pull-apart basin (East Anatolian Fault, Turkey)

In Turkey, the continuous Pull-apart sediment records constitute powerful chronometers for tracking environmental perturbations such as earthquakes. In South-east Turkey, the East Anatolian Fault (EAF) is a major strike-slip fault along which large earthquakes (Ms > 7) occurred in the 19e century. According to chronicles, the seismicity of this area has been minimal for most of the last century; the latest surface rupturing earthquakes may be the Ms = 7.1 in AD 1874 and the Ms = 6.7 in AD 1875. The EAF consists of two large surface rupturing segments interrupted by a pull-apart basin at Lake Hazar (the Sincik/Lake Hazar and the Lake Hazar/Palu segments). In this geological context, the present project seeks to assess: 1) the recent sedimentation rates of Lake Hazar main Pull-apart system located on the EAF; 2) the occurrence of recent past earthquakes along the EAF. For these purposes, we use a diverse array of complementary techniques involving sediment coring, and radionuclide profiles of sediment cores. Here, we present the first results obtained within the framework of a EU-project focusing on the “seismic cycles” in Turkey (“Understanding the irregularity of seismic cycles: A case study in Turkey”). We present 210Pb and 137 Cs age models obtained from a series of short sediment cores. The radionuclide profiles are utilized for both, annual sediment rates estimates, and for tracking the historic earthquakes. The correlation between several cores and the comparison between radionuclide profiles and preliminary sedimentological data shows that sedimentary structures induced by the last AD 1874 and 1875 earthquakes can be detected by ultra-high resolution X-ray radiographies. However, our results show the presence of an additional hypothetic event in the early 20e century. These first results will be further utilized for tracking past earthquakes in longer Lake Hazar sediment time series

La depresión submarina de Guaracayal, estado Sucre, Venezuela: Una barrera para la propagación de la ruptura cosísmica a lo largo de la falla de el pilar

La depresión de Guaracayal, en el golfo de Cariaco, estado Sucre, Venezuela, fue inicialmente reconocida a partir de un levantamiento batimétrico realizado en la década de los ochenta. Un levantamiento de sísmica somera de alta resolución adquirido en el golfo de Cariaco a bordo del B/O Guaiquerí II en enero 2006 reveló que esta depresión resulta ser una cuenca en tracción activa (“active pull-apart basin”) sobre la traza activa submarina de la falla dextral de El Pilar, por su geometría y lo fresco y prominente de los escarpes de fallas que la limitan. Esta cuenca, con una profundidad de aguas de ~15m mayor que el fondo plano ubicado a unos -80m, mide aproximadamente 8km de longitud en dirección este-oeste y unos 2km transversalmente. La cuenca se forma en un relevo dextro, es decir transtensivo, de la traza submarina de la falla de El Pilar, que secciona en dos porciones lo propuesto anteriormente como un único segmento de falla con extensión entre Cumaná y Casanay-Guarapiche. Esta separación entre ambas trazas de 2km parece ser suficiente barrera para la propagación lateral de la ruptura sísmica, tal como lo evidencia la sismicidad contemporánea e histórica. El tramo de falla Cumaná-Casanay, de unos 80km de longitud, ha requerido en dos ocasiones de la conjunción de dos sismos contiguos en dirección oeste-este (1797-1684 y 1929-1997) para romperse en su totalidad. No obstante, no se excluye la posibilidad de un evento que rompa toda la extensión del segmento, a pesar de este comportamiento sísmico reiterado

The 600 yr eruptive history of Villarrica Volcano (Chile) revealed by annually laminated lake sediments

Lake sediments contain valuable information about past volcanic and seismic events that have affected the lake catchment, and they provide unique records of the recurrence interval and magnitude of such events. This study uses a multilake and multiproxy analytical approach to obtain reliable and high-resolution records of past natural catastrophes from similar to 600-yr-old annually laminated (varved) lake sediment sequences extracted from two lakes, Villarrica and Calafquen, in the volcanically and seismically active Chilean Lake District. Using a combination of micro-X-ray fluorescence (mu XRF) scanning, microfacies analysis, grain-size analysis, color analysis, and magnetic-susceptibility measurements, we detect and characterize four different types of event deposits (lacustrine turbidites, tephra-fall layers, runoff cryptotephras, and lahar deposits) and produce a revised eruption record for Villarrica Volcano, which is unprecedented in its continuity and temporal resolution. Glass geochemistry and mineralogy also reveal deposits of eruptions from the more remote Carran-Los Venados volcanic complex, Quetrupillan Volcano, and the Huanquihue Group in the studied lake sediments. Time-series analysis shows 112 eruptions with a volcanic explosivity index (VEI) >= 2 from Villarrica Volcano in the last similar to 600 yr, of which at least 22 also produced lahars. This significantly expands our knowledge of the eruptive frequency of the volcano in this time window, compared to the previously known eruptive history from historical records. The last VEI >= 2 eruption of Villarrica Volcano occurred in 1991. Based on the last similar to 500 yr, for which we have a complete record from both lakes, we estimate the probability of the occurrence of future eruptions from Villarrica Volcano and statistically demonstrate that the probability of a 22 yr repose period (anno 2013) without VEI >= 2 eruptions is <= 1.7%. This new perspective on the recurrence interval of eruptions and historical lahar activity will help improve volcanic hazard assessments for this rapidly expanding tourist region, and it highlights how lake records can be used to significantly improve historical eruption records in areas that were previously uninhabited

A consistent global approach for morphometric characterisation of subaqueous landslides

Landslides are common in aquatic settings worldwide, from lakes and coastal environments to the deep sea. Fast-moving, large-volume landslides can potentially trigger destructive tsunamis. Landslides damage and disrupt global communication links and other critical marine infrastructure. Landslide deposits act as foci for localized, but important, deep-seafloor biological communities. Under burial, landslide deposits play an important role in a successful petroleum system. While the broad importance of understanding subaqueous landslide processes is evident, a number of important scientific questions have yet to receive the needed attention. Collecting quantitative data is a critical step to addressing questions surrounding subaqueous landslides. Quantitative metrics of subaqueous landslides are routinely recorded, but which ones, and how they are defined, depends on the end-user focus. Differences in focus can inhibit communication of knowledge between communities, and complicate comparative analysis. This study outlines an approach specifically for consistent measurement of subaqueous landslide morphometrics to be used in the design of a broader, global open-source, peer-curated database. Examples from different settings illustrate how the approach can be applied, as well as the difficulties encountered when analysing different landslides and data types. Standardizing data collection for subaqueous landslides should result in more accurate geohazard predictions and resource estimation