A tsunamigenic delta collapse and its associated tsunami deposits in and around Lake Sils, Switzerland

AbstractLarge lacustrine mass movements and delta collapses are increasingly being considered as potential tsunamigenic sources and therefore hazardous for the population and infrastructure along lakeshores. Although historical reports document tsunami events in several lakes in Switzerland, and although the propagation of lake tsunamis has been studied by numerical wave modeling, only little is known about on- and offshore lacustrine tsunami deposits. In Lake Sils, Switzerland, a large prehistoric mass-movement deposit originating from the Isola Delta with a minimum estimated volume of 6.5 × 106 m3 and a basinal thickness of > 6 m in the seismic record has been identified by previous studies and radiocarbon dated to around 700 Common Era. Here, we combine (i) comprehensive sedimentological investigation of sediment cores recovered from the on- and offshore settings, (ii) mineralogical fingerprinting of the inflows from key catchments to characterize sediment provenance, and (iii) numerical tsunami modeling, to test the hypothesis of a tsunamigenic delta collapse in Lake Sils. We observe a clastic event deposit consisting of coarse-grained, fining-upward sand overlying an organic-rich peat deposit in the shallow water. This layer thins and fines landward on the coastal plain. Toward the deeper water (20–40 m), the deposit transforms into a thicker and more heterogeneous sediment package with multiple sequences of fining-upward sand and a well-pronounced clay cap at the top. Radiocarbon dating of the peat underlying the event deposit yields a maximum age of 225–419 calibrated Common Era. The tsunami models, which indicate wave heights reaching up to 5 m, simulate areas of inundation that coincide with the location of event deposits. Based on our results, we propose that the historically undocumented Isola Delta collapse generated a basin-wide tsunami that inundated the lakeshore, transporting large amounts of unconsolidated sediment along the lakeshore toward the coastal plain and into the deeper lake basin.

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A late Holocene Record of sediment dynamics obtained from Lake Altaussee (Salzkammergut, Austria).

10.5194/egusphere-egu21-1963 ◽

2021 ◽

Author(s):

Jasper Moernaut ◽

Sebastian Wagner ◽

Julia Rechenmacher ◽

Markus Fiebig ◽

Marcel Ortler ◽

...

Keyword(s):

Sediment Cores ◽

Mass Movement ◽

Sediment Dynamics ◽

Coastal Sediments ◽

Coarse Grained ◽

Lake Basin ◽

Stratigraphic Correlation ◽

X Ray ◽

The University ◽

Subbottom Profiling

Sedimentary records in inner-Alpine lakes typically show a rich history of changes in sediment dynamics and the occurrence of various geohazards. Lake Altaussee (712 m asl; 2.4 x 1.0 km; max. 72 m deep) is a dimictic, moderately-sized glacigenic lake located in the Northern Calcareous Alps. Currently, it has no major river inflow and most water input comes from several subaqueous springs, forming large and deep craters (max. 60 m diameter and 22 m deep) on the lake bottom. Since 2019, a wide suite of investigations (hydrogeology, microplastics, hydroacoustics, geomorphology, sedimentology) started under the framework of the Walter Munk Foundation for the Oceans (WMFO) and the University of Natural Resources and Life Sciences (BOKU) Vienna. In 2020, the University of Innsbruck (UIBK) became a project partner to undertake joint research on its sedimentary infill.We present preliminary results from lacustrine morphological mapping of high-resolution multibeam bathymetry (Kongsberg EM2040), seismic-stratigraphic analysis of subbottom profiling data (Innomar SES-2000 and Kongsberg GEOPULSE), and sedimentological/geochemical analysis on 22 short cores (60-170 cm long). Stratigraphic correlation between the 22 cores is based on visual detection of marker layers in Multi-Sensor Core Logging (MSCL), X-Ray CT and X-ray fluorescence (XRF) core scanning data.The sediment cores mainly exhibit slowly-accumulating organic-rich sediments, typical for lake systems that lack significant fluvial sediment input. One unit of finely-laminated clastic carbonate-rich sedimentation can be traced back to an episode in which a major creek &#8722;draining an area of active salt mining&#8722; was flowing into the western part of the lake. In medieval times, this creek was artificially diverted and depositional conditions in the lake returned to organic-rich sedimentation.&#160;The hydroacoustic data show a scattered pattern of large-scale blocks up to 50-70 m diameter in the eastern half of the lake basin. This suggests the occurrence of one or more large gravitational mass movements, which potentially originated at the steep rock slopes at the northern and eastern end of the lake. A megaturbidite (>1-2 m thick) can be traced over the entire basin floor in both subbottom profiling data and sediment cores, and directly overlies the blocks in the deep basin. Isopach mapping of this megaturbidite hints at sediment transport from both the eastern and western slopes, which we interpret to have occurred as the results of a mass-movement induced impulse wave that eroded coastal sediments at the opposite side of the lake and transported these to the deeper basin. On the shallower western plateau, the presence of an outstanding coarse-grained stratigraphic unit with an erosive base further supports this hypothesis, as it is stratigraphically coeval to the megaturbidite. Biogenic gas accumulation at the base of the megaturbidite prevents further penetration on the subbottom profiles, but some acoustic windows visualize up to 15 m of infill.Upcoming research involves the establishment of 14C-based age-depth models, the acquisition of single-channel airgun seismics to visualize the entire infill of the lake through the gas blanket, and long piston coring to investigate the sediment dynamics and geohazards recorded in the Holocene sedimentary infill.

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Lake Tsunamis: Causes, Consequences and Hazard investigated in a multidisciplinary project

10.5194/egusphere-egu2020-4711 ◽

2020 ◽

Author(s):

Katrina Kremer ◽

Flavio S. Anselmetti ◽

Paola Bacigaluppi ◽

Robert M. Boes ◽

Frederic M. Evers ◽

...

Keyword(s):

Sediment Cores ◽

Mass Movement ◽

Field Work ◽

Current Status ◽

Mass Movements ◽

Ocean Bottom ◽

Tsunami Deposits ◽

Tsunami Waves ◽

Lake Lucerne ◽

Run Up

Tsunamis can occur in lacustrine environments, similar to marine settings. In lake settings, these tsunamis are mainly generated by mass-movement processes displacing large volumes of water, and triggered by seismic or aseismic phenomena. In Swiss lakes, several historical tsunamis are reported. Some of the most prominent examples are: the 563 AD Lake Geneva tsunami presumably caused by a rockfall-induced delta failure, the 1601 AD Lake Lucerne tsunami caused by earthquake-triggered sublacustrine mass movements, and the 1687 AD Lake Lucerne tsunami that was caused by a delta failure.&#160;Nowadays, the shorelines of many Swiss lakes are densely populated and host important infrastructures. The occurrence of lake tsunamis in Switzerland is known, however, we still miss a workflow to assess the hazard related to tsunamis. Within the framework of a multidisciplinary project (Lake Tsunamis: Causes, Consequences and Hazard), funded by the Swiss National Science Foundation and the Federal Office for the Environment, we aim towards better understanding lake-tsunami processes using Swiss lakes as laboratories.&#160;The major objectives of this project are to investigate a) the diverse causes of lake tsunamis, b) the geotechnical and sedimentological properties of unstable slope sediment, c) the potentially unstable sediment volumes on charged slopes, d) the wave generation, propagation and shore run-up, e) the onshore and shallow offshore tsunami deposits and d) their related hazard.&#160;Since 2018, extensive field work using ocean bottom seismometers and cone penetration tests, as well as laboratory tests on sediment sample have been performed to assess the slope stability during seismic shaking on Lake Lucerne. Tsunami waves have been reproduced at laboratory scale to benchmark the numerical simulations of generation, propagation and run-up of tsunamis in lakes. To characterize and date historical and prehistorical tsunami deposits, on and off-shore sediment cores have been retrieved at Lake Lucerne, Geneva, Zurich and Sils. A first work-flow to assess the tsunami hazard related to earthquake-triggered sublacustrine mass movements is proposed. In this contribution, we will summarise the current status of this project.

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Effects of Macrofaunal Recolonization on Biogeochemical Processes and Microbiota—A Mesocosm Study

Water ◽

10.3390/w13111599 ◽

2021 ◽

Vol 13 (11) ◽

pp. 1599

Author(s):

Annika Fiskal ◽

Aixala Gaillard ◽

Sebastien Giroud ◽

Dejan Malcic ◽

Prachi Joshi ◽

...

Keyword(s):

Microbial Communities ◽

Bottom Water ◽

Surface Sediments ◽

Sediment Cores ◽

Lake Basin ◽

Sediment Properties ◽

Chironomid Larvae ◽

Sediment Reworking ◽

Mesocosm Experiments ◽

Tubificid Worms

Macroinvertebrates are widespread in lake sediments and alter sedimentary properties through their activity (bioturbation). Understanding the interactions between bioturbation and sediment properties is important given that lakes are important sinks and sources of carbon and nutrients. We studied the biogeochemical impact of macrofauna on surface sediments in 3-month-long mesocosm experiments conducted using sediment cores from a hypoxic, macrofauna-free lake basin. Experimental units consisted of hypoxic controls, oxic treatments, and oxic treatments that were experimentally colonized with chironomid larvae or tubificid worms. Overall, the presence of O2 in bottom water had the strongest geochemical effect and led to oxidation of sediments down to 2 cm depth. Relative to macrofauna-free oxic treatments, chironomid larvae increased sediment pore water concentrations of nitrate and sulfate and lowered porewater concentrations of reduced metals (Fe2+, Mn2+), presumably by burrow ventilation, whereas tubificid worms increased the redox potential, possibly through sediment reworking. Microbial communities were very similar across oxic treatments; however, the fractions of α-, β-, and γ-Proteobacteria and Sphingobacteriia increased, whereas those of Actinobacteria, Planctomycetes, and Omnitrophica decreased compared to hypoxic controls. Sediment microbial communities were, moreover, distinct from those of macrofaunal tubes or feces. We suggest that, under the conditions studied, bottom water oxygenation has a stronger biogeochemical impact on lacustrine surface sediments than macrofaunal bioturbation.

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Streamflow input to Lake Athabasca, Canada

Hydrology and Earth System Sciences ◽

10.5194/hess-17-1681-2013 ◽

2013 ◽

Vol 17 (5) ◽

pp. 1681-1691 ◽

Cited By ~ 16

Author(s):

K. Rasouli ◽

M. A. Hernández-Henr&iacute;quez ◽

S. J. Déry

Keyword(s):

Oil Sands ◽

Multiple Stressors ◽

Sediment Cores ◽

Lake Basin ◽

Ramsar Convention ◽

Athabasca River ◽

Oil Reserves ◽

Mk Test ◽

Streamflow Variability ◽

Shift Detection

Abstract. The Lake Athabasca drainage area in northern Canada encompasses ecologically rich and sensitive ecosystems, vast forests, glacier-clad mountains, and abundant oil reserves in the form of oil sands. The basin includes the Peace–Athabasca Delta, recognized internationally by UNESCO and the Ramsar Convention as a biologically rich inland delta and wetland that are now under increasing pressure from multiple stressors. In this study, streamflow variability and trends for rivers feeding Lake Athabasca are investigated over the last half century. Hydrological regimes and trends are established using a robust regime shift detection method and the Mann–Kendall (MK) test, respectively. Results show that the Athabasca River, which is the main contributor to the total lake inflow, experienced marked declines in recent decades impacting lake levels and its ecosystem. From 1960 to 2010 there was a significant reduction in lake inflow and a significant recession in the Lake Athabasca level. Our trend analysis corroborates a previous study using proxy data obtained from nearby sediment cores suggesting that the lake level may drop 2 to 3 m by 2100. The lake recession may threaten the flora and fauna of the Athabasca Lake basin and negatively impact the ecological cycle of an inland freshwater delta and wetland of global importance.

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Contrasting the ecological effects of decreasing ice cover versus accelerated glacial melt on the High Arctic's largest lake

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2020.1185 ◽

2020 ◽

Vol 287 (1929) ◽

pp. 20201185

Author(s):

Neal Michelutti ◽

Marianne S. V. Douglas ◽

Dermot Antoniades ◽

Igor Lehnherr ◽

Vincent L. St. Louis ◽

...

Keyword(s):

Sediment Cores ◽

Fold Increase ◽

Mass Gain ◽

Ecological Change ◽

Diatom Assemblages ◽

Lake Ice ◽

Glacial Meltwater ◽

Glacial Runoff ◽

Common Era ◽

Ecological Functioning

Lake Hazen, the High Arctic's largest lake, has received an approximately 10-fold increase in glacial meltwater since its catchment glaciers shifted from net mass gain to net mass loss in 2007 common era (CE), concurrent with recent warming. Increased glacial meltwater can alter the ecological functioning of recipient aquatic ecosystems via changes to nutrient budgets, turbidity and thermal regimes. Here, we examine a rare set of five high-resolution sediment cores collected in Lake Hazen between 1990 and 2017 CE to investigate the influence of increased glacial meltwater versus alterations to lake ice phenology on ecological change. Subfossil diatom assemblages in all cores show two major shifts over the past approximately 200 years including: (i) a proliferation of pioneering, benthic taxa at approximately 1900 CE from previously depauperate populations; and (ii) a rise in planktonic taxa beginning at approximately 1980 CE to present-day dominance. The topmost intervals from each sequentially collected core provide exact dates and demonstrate that diatom regime shifts occurred decades prior to accelerated glacial inputs. These data show that diatom assemblages in Lake Hazen are responding primarily to intrinsic lake factors linked to decreasing duration of lake ice and snow cover rather than to limnological impacts associated with increased glacial runoff.

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Alluvial fan dynamics in the El'gygytgyn Crater: implications for the 3.6 Ma old sediment archive

Climate of the Past Discussions ◽

10.5194/cpd-8-2187-2012 ◽

2012 ◽

Vol 8 (3) ◽

pp. 2187-2222 ◽

Cited By ~ 2

Author(s):

G. Schwamborn ◽

G. Fedorov ◽

N. Ostanin ◽

L. Schirrmeister ◽

A. Andreev ◽

...

Keyword(s):

Alluvial Fan ◽

Coarse Grained ◽

Lake Basin ◽

Mass Wasting ◽

Sandy Gravel ◽

Modern Soil ◽

Coarse Grained Material ◽

Near Shore ◽

Ice Content ◽

Flooding Events

Abstract. A sedimentological program has been conducted using frozen core samples from the 141.5 m long El'gygytgyn 5011-3 permafrost well. The drill site is located in sedimentary permafrost west of the lake that partly fills the El'gygytgyn Crater. The total core sequence is interpreted as strata building up a progradational alluvial fan delta. Four structurally and texturally distinct sedimentary units are identified. Unit 1 (141.5–117.0 m) is comprised of ice-cemented, matrix-supported sandy gravel and intercalated sandy layers. Sandy layers represent sediments which rained out as particles in the deeper part of the water column under highly energetic conditions. Unit 2 (117.0–24.25 m) is dominated by ice-cemented, matrix-supported sandy gravel with individual gravel layers. Most of the unit 2 diamicton is understood to result from alluvial wash and subsequent gravitational sliding of coarse-grained material on the basin slope. Unit 3 (24.25–8.5 m) has ice-cemented, matrix-supported sandy gravel that is interrupted by sand beds. These sandy beds are associated with flooding events and represent near-shore sandy shoals. Unit 4 (8.5–0.0 m) is ice-cemented, matrix-supported sandy gravel with varying ice content, mostly higher than below. It consists of slope material and creek fill deposits. The uppermost meter is the active layer into which modern soil organic matter has been incorporated. The nature of the progradational sediment transport taking place from the western and northern crater margins may be related to the complementary occurrence of frequent turbiditic layers in the central lake basin as is known from the lake sediment record. Slope processes such as gravitational sliding and sheet flooding that takes place especially during spring melt are thought to promote mass wasting into the basin. Tectonics are inferred to have initiated the fan accumulation in the first place and possibly the off-centre displacement of the crater lake.

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Geological Challenges of Archaeological Prospecting: The Northern Peloponnese as a Type Location of Populated Syn-Rift Settings

Remote Sensing ◽

10.3390/rs12152450 ◽

2020 ◽

Vol 12 (15) ◽

pp. 2450

Author(s):

Katharina Rusch ◽

Harald Stümpel ◽

Walter Gauß ◽

Silke Müth ◽

Alexander Sokolicek ◽

...

Keyword(s):

Case Studies ◽

Coastal Plain ◽

Urban Areas ◽

Coarse Grained ◽

Sea Level Changes ◽

Alluvial Deposits ◽

Archaeological Prospection ◽

Wave Refraction ◽

Wave Measurements ◽

Marine Terraces

The Northern Peloponnese is not only home of a series of ancient poleis that are being studied by archaeologists, but it is also located on the southern shoulder of the most active extensional crustal structure in the world; the Corinthian rift. This rift has shaped the Northern Peloponnese as we now see it today since the Pliocene. Normal faulting, the tectonic uplift of syn-rift sediments and sea level changes, has shaped a landscape of steps rising from the coast to the ridges in the hinterland that provides challenging conditions to a geophysical survey. Where we can find coarse grained slope and delta deposits of conglomerate on top of banks of marl on ridges and slopes, the lower marine terraces and the coastal plain as well as valleys show the protective caprock eroded and the marl covered by young alluvial deposits. These materials show only a small contrast in their magnetic properties, which reduces the importance of magnetic mapping for the archaeological prospection in this region. The human utilization of the coastal plain and the urban areas pose additional challenges. These challenges have been overcome through various approaches that are shown in exemplary case studies from Aigeira and Sikyon. Whereas a combination of magnetic mapping and ground-penetrating radar (GPR) works very well on the ridges and along the slopes where we find coarser sediments in addition to the magnetic mapping, it is not suitable in the coastal plain due to the attenuating properties of the alluvial sediment. Here, electrical resistivity tomography (ERT) proved to be very successful in mapping entire parts of a settlement in great detail. Seismic soundings were also sucessfully applied in determining the bedrock depth, the detection of walls and in the question of locating the harbor basin. In the presented six exemplary case studies, the following findings were made: (1) A fortification wall and building foundations at a depth of 0.4–1.2 m on a plateau northwest of the acropolis of Aigeira was found by 400 MHz GPR. (2) A honeycomb-shaped pattern of magnetic anomalies that suggested cavities could be identified as a weathering pattern of conglomerate rocks. (3) A rock basement 2.3 m deep and remains of an enclosing wall of the Aigeira theater area were found by shear wave refraction measurements. (4) Extensive ERT surveys detected several building remains in Sikyon like a potential building and grave monuments as well as several small houses. (5) A silted-up depression in the sediments of the coastal plane located through Love wave measurements, could be taken as evidence for either a silted harbor or a navigable riverbed.

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Tsunami hazard from lacustrine mass wasting in Lake Tekapo, New Zealand

Geological Society London Special Publications ◽

10.1144/sp477.21 ◽

2018 ◽

Vol 477 (1) ◽

pp. 413-426 ◽

Cited By ~ 5

Author(s):

Joshu J. Mountjoy ◽

Xiaoming Wang ◽

Susi Woelz ◽

Sean Fitzsimons ◽

Jamie D. Howarth ◽

...

Keyword(s):

High Resolution ◽

Sediment Cores ◽

Lake Basin ◽

Diverse Range ◽

Seismic Reflection Data ◽

Reflection Data ◽

Tectonically Active ◽

Tsunami Risk ◽

Western Shore ◽

The Impact

AbstractLacustrine-tsunami risk from landslides can be significant yet for most locations globally the hazard remains unquantified. Lake Tekapo, in the tectonically active mountain belt of New Zealand's South Island, has been chosen to develop surveying and modelling techniques to assess the hazard from landslide tsunamis. Lake Tekapo is ideal for this study due to the high sedimentation rates, steep surrounds and the proximity to active faulting that indicate a high landslide potential. The shoreline tourist settlement and hydropower infrastructure mean the impact of any tsunami could be significant. In 2016 a survey was carried out to collect high-resolution (1 m grid) EM2040 multibeam bathymetry, high-resolution seismic reflection data (Boomer and chirp) and 6 m long sediment cores. These data reveal a diverse range of sedimentary processes in response to high sediment input and numerous landslides with varied styles of emplacement. For example, a one-off landslide initiated 40 m above the shoreline with debris deposits that have runout onto the lake floor to 100 m water depth contrasts with the Cass River delta on the western shore that has failed multiple times during the lake-basin infilling history. Landslide-generated tsunami scenarios are used to determine the relative hazard at different regions of the lake to guide development of a probabilistic tsunami model.

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Environmental and rock magnetic investigations into provenance and processes of west Iberian margin sediments

10.5194/egusphere-egu2020-18890 ◽

2020 ◽

Author(s):

Matthew Nichols ◽

Chuang Xuan ◽

David A. Hodell ◽

Carl Richter ◽

Gary D. Acton ◽

...

Keyword(s):

Magnetic Material ◽

Grain Size ◽

Rock Magnetism ◽

Sediment Cores ◽

Hysteresis Loops ◽

Ice Cores ◽

Sediment Provenance ◽

The West ◽

Significant Difference ◽

Iberian Margin

Ocean sediment records from the West Iberian margin can be correlated to both Antarctic and Greenland ice cores as well as to European terrestrial pollen data. Previous studies have focussed on comparatively short sediment cores collected from relatively deep-water sites (i.e. >~2500mbsl). Here we present magnetic mineralogy and grain size from Integrated Ocean Drilling Programme Sites U1385 (2585mbsl) and U1391 (1085mbsl) to further understand magnetic sediment provenance and palaeocurrent evolution on the west Iberian margin dating back to ~416 ka. The gradient of IRM acquisition curves, shape of hysteresis loops, and marked decrease in magnetic susceptibility at ~580&#176;C indicate that magnetite is the dominant magnetic phase at Site U1391. At depth, increased contributions of a higher coercivity component are seen at intervals where the concentration of magnetic material is low. FORC diagrams indicate the presence of a narrow ridge elongated along the Bc axis consistent with a higher coercivity component observed in IRM acquisition data. Magnetic grain size proxy (kARM/k) records from Site U1391 also show a significant difference in pattern of variability at depth. After ~130 ka kARM/k closely follows relative sea level, however prior to ~130 ka there is higher frequency variability with apparent coarser magnetic grain size, suggesting the higher coercivity component could have resulted from diagenetic processes. This is particularly apparent during warm intervals where magnetic material concentration is low (MIS 7, 9 and 11). This behaviour differs from that observed at either Site U1385, or in the younger portion of the record at Site U1391. We infer that the intervals of diagenetically effected sediments at U1391 could have resulted from increased productivity, vertical migration of the Mediterranean outflow water and associated changes in bottom water ventilation. Further understanding of sediment composition, redox conditions, transport and provenance through the last few glacial cycles underpins much of the other palaeoclimatic investigation at these sites. Results from our analysis of rock magnetism will be used to guide the reconstruction of reliable relative palaeointensity records from the Iberian Margin sediments to assess past geomagnetic changes in the region.

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Late Holocene Varve Chronology and High-Resolution Records of Precipitation in the Central Tibetan Plateau

10.5194/egusphere-egu2020-4965 ◽

2020 ◽

Author(s):

Kejia Ji ◽

Erlei Zhu ◽

Guoqiang Chu ◽

Juzhi Hou

Keyword(s):

Tibetan Plateau ◽

Lake Sediment ◽

Sediment Cores ◽

Coarse Grained ◽

The Tibetan Plateau ◽

Past Climate ◽

Environment Changes ◽

The Past ◽

Varve Chronology ◽

Past 2000 Years

Precise age controls are fundamental prerequisites for reconstructing past climate and environment changes. Lakes on the Tibetan Plateau are one of the important archives for studying past climate and environment changes. However, radiocarbon ages for lake sediment core are subject to old radiocarbon reservoir effects, which caused severe problems in constructing age controls for lake sediment cores, especially on the Tibetan Plateau (TP). Here we present a varve chronology over the past 2000 years at Jiang Co on the central TP. The clastic-biogenic varves comprise of a coarse-grained layer and a fine-grained layer observed by petrographic microscope and Electron Probe Micro Analyzer. Varve chronology is supported by measurements of 210Pb and 137Cs, which is further used to determine the radiocarbon reservoir ages in the past ~2000 years. The percentage of coarse-grain layer thickness within single varves was considered as proxy for precipitation as the coarse grains were mainly transported by runoff, which is highly correlated with local meteorological observation. During the past 2000 years, the precipitation records show centennial-scale fluctuations that are consistent with regional records. The varve chronology at Jiang Co provides a valuable opportunity to examine variation in reservoir ages on the TP and a robust chronology for reconstructing paleoclimate.

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