Geophysical evidence of gas seepage and mass movement in the Laacher See volcanic lake, western Germany

The Laacher See caldera lake, formed by a series of phreatomagmatic and Plinian eruptions around 12,900 years BP, has been receiving increased attention lately with several studies investigating the present-day volcanic and geodynamic activity in the eastern Eifel, a densely populated area in western Germany. Volcanic activity beneath Laacher See is most notably evidenced by several gas seeps in the lake and its surrounding shore, emitting CO2 of magmatic origin. During a 2019 survey, several geophysical techniques were used to investigate the CO2 seeps at the lake floor. Here, we present results from multibeam echosounder and sub-bottom profiler data showing the presence of gas in both the water column (i.e. gas flares) and the lake sedimentary infill. Enhanced seismic reflections and acoustic blanking illustrate different levels at which free gas is accumulated in the lake sediments. Additionally, several stratigraphic horizons containing mass-transport deposits (MTDs) are observed in the laminated lake infill. The origin of these MTDs remains unclear, yet possible causes of slope failure in Laacher See might include seismic shaking, anthropogenic lake level fluctuation, and an increased fluid/pore pressure in the sediment due to free gas. Our results give a first indication of free gas in the lake infill, with further research needed to investigate the possible link between gas presence and mass movement in the lake. The monitoring of gas seeps at Laacher See and a further understanding of its gas-laden sedimentary infill can ultimately contribute to a better volcanic hazard assessment in the area.

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Recurrent rock avalanches progressively dismantle mountain ridges in the Longmen Shan, China, most recently in the 2008 Wenchuan earthquake

10.5194/egusphere-egu21-1663 ◽

2021 ◽

Author(s):

Janusz Wasowski ◽

Maurice McSaveney ◽

Luca Pisanu ◽

Vincenzo Del Gaudio ◽

Yan Li ◽

...

Keyword(s):

Wenchuan Earthquake ◽

Ambient Noise ◽

Slope Failure ◽

Mass Movement ◽

Rock Avalanche ◽

Ground Vibration ◽

Source Area ◽

Slope Failures ◽

Rock Avalanches ◽

Beichuan County

Large earthquake-triggered landslides, in particular rock avalanches, can have catastrophic consequences. However, the recognition of slopes prone to such failures remains difficult, because slope-specific seismic response depends on many factors including local topography, landforms, structure and internal geology. We address these issues by exploring the case of a rock avalanche of >3 million m3 triggered by the 2008 Mw7.9 Wenchuan earthquake in the Longmen Shan range, China. The failure, denominated Yangjia gully rock avalanche, occurred in Beichuan County (Sichuan Province), one of the areas that suffered the highest shaking intensity and death toll caused by co-seismic landsliding. Even though the Wenchuan earthquake produced tens of large (volume >1 million m3) rock avalanches, few studies so far have examined the pre-2008 history of the failed slope or reported on the stratigraphic record of mass-movement deposits exposed along local river courses. The presented case of the Yangjia gully rock avalanche shows the importance of such attempts as they provide information on the recurrence of large slope failures and their associated hazards. Our effort stems from recognition, on 2005 satellite imagery, of topography and morphology indicative of a large, apparently pre-historic slope failure and the associated breached landslide dam, both features closely resembling the forms generated in the catastrophic 2008 earthquake. The follow-up reconstruction recognizes an earlier landslide deposit exhumed from beneath the 2008 Yangjia gully rock avalanche by fluvial erosion since May 2008. We infer a seismic trigger also for the pre-2008 rock avalanche based on the following circumstantial evidence: i) the same source area (valley-facing, terminal portion of a flat-topped, elongated mountain ridge) located within one and a half kilometer of the seismically active Beichuan fault; ii) significant directional amplification of ground vibration, sub-parallel to the failed slope direction, detected via ambient noise measurements on the ridge adjacent to the source area of the 2008 rock avalanche and iii) common depositional and textural features of the two landslide deposits. Then, we show how, through consideration of the broader geomorphic and seismo-tectonic contexts, one can gain insight into the spatial and temporal recurrence of catastrophic slope failures&#160; in Beichuan County and elsewhere in the Longmen Shan. This insight, combined with local-scale geologic and geomorphologic knowledge, may guide selection of suspect slopes for reconnaissance, wide-area ambient noise investigation aimed at discriminating their relative susceptibility to co-seismic catastrophic failures. We indicate the feasibility of such investigations through the example of this study, which uses 3-component velocimeters designed to register low amplitude ground vibration.

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High-Resolution Studies of Mass Transport Deposits: Outcrop Perspective for Understanding Modern Submarine Slope Failure and Associated Natural Hazards

Engineering Geology for Society and Territory – Volume 4 ◽

10.1007/978-3-319-08660-6_40 ◽

2014 ◽

pp. 209-213

Author(s):

K. Ogata ◽

G. A. Pini ◽

A. Festa ◽

Ž. Pogačnik ◽

G. Tunis ◽

...

Keyword(s):

High Resolution ◽

Mass Transport ◽

Natural Hazards ◽

Slope Failure ◽

Submarine Slope ◽

Mass Transport Deposits

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Shear margin moraine, mass transport deposits and soft beds revealed by high-resolution P-Cable three-dimensional seismic data in the Hoop area, Barents Sea

Geological Society London Special Publications ◽

10.1144/sp477.29 ◽

2018 ◽

Vol 477 (1) ◽

pp. 537-548 ◽

Cited By ~ 4

Author(s):

Benjamin Bellwald ◽

Sverre Planke

Keyword(s):

High Resolution ◽

Mass Transport ◽

Seismic Data ◽

Slope Failure ◽

Barents Sea ◽

3D Seismic ◽

Seismic Reflection Data ◽

Shallow Subsurface ◽

Mass Transport Deposits ◽

Amplitude Reflection

AbstractHigh-resolution seismic data are powerful tools that can help the offshore industries to better understand the nature of the shallow subsurface and plan the development of vulnerable infrastructure. Submarine mass movements and shallow gas are among the most significant geohazards in petroleum prospecting areas. A variety of high-resolution geophysical datasets collected in the Barents Sea have significantly improved our knowledge of the shallow subsurface in recent decades. Here we use a c. 200 km2 high-resolution P-Cable 3D seismic cube from the Hoop area, SW Barents Sea, to study a 20–65 m thick glacial package between the seabed and the Upper Regional Unconformity (URU) horizons. Intra-glacial reflections, not visible in conventional seismic reflection data, are well imaged. These reflections have been mapped in detail to better understand the glacial deposits and to assess their impact on seabed installations. A shear margin moraine, mass transport deposits and thin soft beds are examples of distinct units only resolvable in the P-Cable 3D seismic data. The top of the shear margin moraine is characterized by a positive amplitude reflection incised by glacial ploughmarks. Sedimentary slide wedges and shear bands are characteristic sedimentary features of the moraine. A soft reflection locally draping the URU is interpreted as a coarser grained turbidite bed related to slope failure along the moraine. The bed is possibly filled with gas. Alternatively, this negative amplitude reflection represents a thin, soft bed above the URU. This study shows that P-Cable 3D data can be used successfully to identify and map the external and internal structures of ice stream shear margin moraines and that this knowledge is useful for site-survey investigations.

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Monitoring of recent mass movement activity in anthropogenic slopes of the Krušné Hory Mountains (Czech Republic)

Natural Hazards and Earth System Science ◽

10.5194/nhess-11-1463-2011 ◽

2011 ◽

Vol 11 (5) ◽

pp. 1463-1473 ◽

Cited By ~ 4

Author(s):

J. Burda ◽

L. Žižka ◽

J. Dohnal

Keyword(s):

Czech Republic ◽

Slope Failure ◽

Water Saturation ◽

Mass Movement ◽

Interdisciplinary Approach ◽

Open Pit ◽

Mass Movements ◽

Slope Failures ◽

The Czech Republic ◽

Krušné Hory Mountains

Abstract. Recent mass movements currently comprise one of the main morphogenetic processes in the extensive anthropogenic relief of the foreground of the Krušné Hory Mountains in the Czech Republic. These mass movements result in several types of deep-seated slope failures, depending on the type of movement and the water saturation of the landslide material. This paper presents the results of a detailed geomorphic survey and orthophotograph analysis combined with geodetic monitoring data in an area affected by open-pit coal mining. An interdisciplinary approach has enabled an in-depth review of both the dynamics and development of recent slope failures. The article describes deep-seated landslide complex in this part of the foothills of the Krušné Hory Mountains. At the study site, mass movements occur in thick colluvial mantle and weathered Tertiary claystones. The main factors influencing their development include rainfall culminations, groundwater flowing from the valley of Šramnický Brook and former slope failures. All of the slope failures that have occurred here have originated at former slope failure sites.

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Gas Seepage along the Edge of the Aquitaine Shelf (France): Origin and Local Fluxes

Geofluids ◽

10.1155/2017/4240818 ◽

2017 ◽

Vol 2017 ◽

pp. 1-13 ◽

Cited By ~ 7

Author(s):

Livio Ruffine ◽

Jean-Pierre Donval ◽

Claire Croguennec ◽

Laurent Bignon ◽

Dominique Birot ◽

...

Keyword(s):

Microbial Reduction ◽

Local Estimate ◽

Microbial Origin ◽

Continental Shelves ◽

Gas Fluxes ◽

Gas Seepage ◽

The Mean ◽

First Time ◽

Gas Seeps

During the scientific expedition GAZCOGNE2 at the Bay of Biscay nine gas seeps were sampled for the first time and their flux was measured using an in situ pressure-preservation sampler (PEGAZ, ©IFREMER). Overall, three sites were investigated to determine the nature and the origin of the gases bubbling at the seafloor and forming acoustic plumes into the water column, as this was the question raised from the first geologic study of the area. This has guided our study and accordingly corresponds to the main purpose of the present article. Thus, the molecular and isotopic (δD and δ13C) analyses revealed that the gas seeps were primarily composed of methane. Both methane and ethane are of microbial origin, and the former has been generated by microbial reduction of carbon dioxide. Heavier hydrocarbons accounted for less than 0.06% mol of the total amount. Despite the microbial origin of methane, the samples exhibit subtle differences with respect to the δ13CCH4 values, which varied between −72.7 and −66.1‰. It has been suggested that such a discrepancy was predominantly governed by the occurrence of anaerobic methane oxidation. The PEGAZ sampler also enabled us to estimate the local gas fluxes from the sampled streams. The resulting values are extremely heterogeneous between seeps, ranging from 35 to 368 mLn·min−1. Assuming a steady discharge, the mean calculated methane emission for the nine seeps is of 38 kmol·yr−1. Considering the extent of the seep area, this very local estimate suggests that the Aquitaine Shelf is a very appropriate place to study methane discharge and its fate on continental shelves.

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Unravelling earth flow dynamics with 3-D time series derived from UAV-SfM models

Earth Surface Dynamics ◽

10.5194/esurf-5-791-2017 ◽

2017 ◽

Vol 5 (4) ◽

pp. 791-806 ◽

Cited By ~ 12

Author(s):

François Clapuyt ◽

Veerle Vanacker ◽

Fritz Schlunegger ◽

Kristof Van Oost

Keyword(s):

High Resolution ◽

Slope Failure ◽

Drainage Basin ◽

Time Lag ◽

Mass Movement ◽

Three Dimensional ◽

Sediment Budget ◽

Swiss Alps ◽

Surface Displacements ◽

Sediment Redistribution

Abstract. Accurately assessing geo-hazards and quantifying landslide risks in mountainous environments are gaining importance in the context of the ongoing global warming. For an in-depth understanding of slope failure mechanisms, accurate monitoring of the mass movement topography at high spatial and temporal resolutions remains essential. The choice of the acquisition framework for high-resolution topographic reconstructions will mainly result from the trade-off between the spatial resolution needed and the extent of the study area. Recent advances in the development of unmanned aerial vehicle (UAV)-based image acquisition combined with the structure-from-motion (SfM) algorithm for three-dimensional (3-D) reconstruction make the UAV-SfM framework a competitive alternative to other high-resolution topographic techniques. In this study, we aim at gaining in-depth knowledge of the Schimbrig earthflow located in the foothills of the Central Swiss Alps by monitoring ground surface displacements at very high spatial and temporal resolution using the efficiency of the UAV-SfM framework. We produced distinct topographic datasets for three acquisition dates between 2013 and 2015 in order to conduct a comprehensive 3-D analysis of the landslide. Therefore, we computed (1) the sediment budget of the hillslope, and (2) the horizontal and (3) the three-dimensional surface displacements. The multitemporal UAV-SfM based topographic reconstructions allowed us to quantify rates of sediment redistribution and surface movements. Our data show that the Schimbrig earthflow is very active, with mean annual horizontal displacement ranging between 6 and 9 m. Combination and careful interpretation of high-resolution topographic analyses reveal the internal mechanisms of the earthflow and its complex rotational structure. In addition to variation in horizontal surface movements through time, we interestingly showed that the configuration of nested rotational units changes through time. Although there are major changes in the internal structure of the earthflow in the 2013–2015 period, the sediment budget of the drainage basin is nearly in equilibrium. As a consequence, our data show that the time lag between sediment mobilization by landslides and enhanced sediment fluxes in the river network can be considerable.

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Multi Tiered Approach to Slope Movement Management: Case Study

Volume 2: Pipeline Integrity Management ◽

10.1115/ipc2012-90628 ◽

2012 ◽

Author(s):

Millan Sen ◽

John Richmond ◽

Aaron Dinovitzer ◽

Abdelfettah Fredj

Keyword(s):

Stress Analysis ◽

Slope Failure ◽

Action Plan ◽

Large Diameter ◽

Mass Movement ◽

Strain Analysis ◽

Slope Movement ◽

Soil Movement ◽

Slope Movements ◽

Inspection Data

A major slope in southern Manitoba is currently experiencing deep seated movements of approximately 60mm per year. This 20m high × 70m long slope contains a pipeline right of way with five large diameter crude oil lines that were constructed from 1950–1998. It is estimated that the slope has moved over 3 meters since the pipeline installations. Management of the effects of this slope movement on the pipelines has involved cross-functional strategies that include geotechnical, integrity, and stress evaluations. The slope is assessed annually by a geotechnical engineer, and the most likely cause for the slope movements has been determined. Slope monitoring equipment has been installed at key locations and is monitored at frequent intervals. A toe berm has been installed to prevent lower slope failure at the creek bed that is located at the slope toe. A finite element stress analysis, which considers the interaction between the soil movement and pipeline, has been generated. This stress analysis evaluated the pipeline stresses due to the slope movements to date, and also due to a possible sudden mass movement. The results are backed up by a bending strain analysis based on inertial in-line inspection data was conducted for several of the lines. This paper presents an overview of the engineering assessment considering structural, material, geotechnical and operational concerns involved in developing an integrity management action plan.

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