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Highlights a 20-m high coastal terrace is likely affected by tsunami waves high resolution topogr... more Highlights a 20-m high coastal terrace is likely affected by tsunami waves high resolution topographic measurement using TLS and sUAV-based SfM-MVS possible erosional features (fluvial or tsunami) were examined clast imbriation and tsunami-driven rocks were identified abstract A coastal rocky terrace with an elevation of ca. 20 m a.s.l. is located around Cape Todogasaki at the middle section of the ria-type rocky coast in Sanriku, northeastern Japan. In spite of its 20-m height, the tsunami waves induced by the 2011 Tohoku Earthquake were high enough to spread over the terrace. To clarify the effects of tsunamis on the terrace surface micromorphology, we performed field measurements of structure-from-motion multi-view stereo (SfM-MVS) photogrammetry using a digital camera mounted on a small unmanned aerial vehicle (sUAV). Terrestrial laser scanning was also carried out on the site for data validation. Geographical coordinates of benchmarks for georeferencing the SfM data were measured in the field using a GNSS rover, capable of postprocessing carrier-phase correction with centimeter accuracies. A 10-cm resolution digital elevation model (DEM) was then generated in SfM software, and micromorphology of the terrace surface was analyzed using the DEM. Despite limited basin area draining into the terrace, erosional characteristics likely formed by streamflow were identified. Sedimentological characteristics of thin clasts accumulation likely derived from terrace edge in-situ bedrock were also examined in the field. Based on clast shape and degree of weathering, three layers of deposit were identified: large fresh and angular clasts recently emplaced laying on the top. The spatial pattern of their imbrication for the three layers evidenced a landward flow direction. Furthermore, some angular boulders (2-3 m diameter) showing different degrees of weathering on their faces suggest that they were recently dislodged and displaced landward. These observations indicate that the uplifted terrace surface underwent erosion by not only the 2011 tsunami but also repeated significant tsunamis in the past.

Geomorphologie Relief Processus Environnement, Sep 1, 2011

L'AMS (Anisotropie de la Susceptibilité Magnétique) est une méthode non destructive à faible coût... more L'AMS (Anisotropie de la Susceptibilité Magnétique) est une méthode non destructive à faible coût, qui offre une vision simplifiée de la fabrique des sédiments. L'AMS décrit l'orientation de l'ellipsoïde du champ électromagnétique induit (M) d'un échantillon lors de son exposition à un champ électromagnétique externe (H). La relation qui lie M et H est : M=k.H pour laquelle k est un scalaire qui varie en fonction de l'organisation cristalline de l'échantillon et de son orientation physique en 3D. Grâce à ces propriétés, il est possible de définir la fabrique du matériau étudié. L'étude de la fabrique se fait alors par la mesure des angles des trois tenseurs de caractérisation 3D des volumes par rapport à un plan horizontal. Ces trois tenseurs sont K max , K int et K min . Classiquement, la lecture de ces trois tenseurs se Abstract AMS (Anisotropy of Magnetic Susceptibility) is a geophysical method, which uses the electromagnetic properties of samples as a proxy of their fabric. Commonly used on hard rocks and cohesive sediments, the method has never been developed for unconsolidated sediments before. In this contribution, we present the usability of the AMS method on unconsolidated rocks and the new insights that AMS brings for the study of tsunami deposits, and for geomorphology. We have been working on the deposits of the coast of North Sumatra (Indonesia) because a devastating tsunami has struck these coasts and has redesigned the coastal environment and sediments distribution the 26 December 2004. Hence, this geographical setting has provided us with the necessary material for the study. We have carried out the analysis from 6 samples, which evidenced: (i) a first layer deposited by an uprush oriented to the SSW; (ii) a decanting phase; (iii) a layer deposited by a backwash oriented to the North; (iv) two other uprushes that deposited two units oriented to the SSW and the SSE. This research has proven that the AMS could be used on unconsolidated deposits, and that the orientation and an approximation of the energy during deposition could be inferred as well. It leads to new developments in marine and or fluvial geomorphology, even for unconsolidated sediments.

High energy coastal events transport large amounts of sediment and leave important signatures in ... more High energy coastal events transport large amounts of sediment and leave important signatures in the landscape. The configuration of the coastline and topography has a significant impact on sediment transport processes and the form of preserved features, and inundation patterns are affected by surface roughness and elevation. The aims of this research are to assess the flow patterns during deposition of a suite of coastal deposits, most likely related to historical tsunami, and assess the role of topography and landscape configuration on depositional patterns.

... Francisco José Pérez Torrado, Raphael Paris 1 , Maria Del Carmen Cabrera, Jean Luc Schneider,... more ... Francisco José Pérez Torrado, Raphael Paris 1 , Maria Del Carmen Cabrera, Jean Luc Schneider, Patrick Wassmer, Juan Carlos Carracedo, A. Rodriguez Santana, F. Santana. (2006). 1 : Laboratoire de Géographie physique et environnementale (GEOLAB). ...

... 7 : Laboratoire des sciences du climat et de l'environnement (LSCE). CNR... more ... 7 : Laboratoire des sciences du climat et de l'environnement (LSCE). CNRS : UMR1572 – INSU – CEA : DSM/LSCE – Université de Versailles-Saint Quentin en Yvelines – Institut Pierre Simon Laplace. Domaine, : Planète et Univers/Sciences de la Terre/Géomorphologie. ...

Geomorphology

In 2006, a series of block-and-ash flows swept the southwestern and southern flanks of Merapi Vol... more In 2006, a series of block-and-ash flows swept the southwestern and southern flanks of Merapi Volcano, Java, Indonesia. In the K. Gendol valley, near the village of Kaliadem, we conducted a GPR survey on the most distal lobe of the June 14th second block-and-ash flow deposit. For this 100 m-long transect, we used a commercial GPR RAMAC© mounted with 100 MHz antennas.We measured the topography with a synchronized GPS and a laser rangefinder. Back at the laboratory, we processed the dataset with the software REFLEX®. Data of the subsurface reveals a series of layers, separated by strong reflective horizons. These horizons are the manifestation of intercalations of fine materials in between more coarse layers. The architecture of these layers presents progradation, retrogradation and aggradation patterns that we relate to the block-and-ash flow deposition process. Based on these observations we proposed a relative chronology of the deposition and a simple conceptual model of the deposi...

Geografia Fisica e Dinamicca Quaternaria

ABSTRACT: WASSMER P., SCHWARTZ D., GOMEZ C., WARD S. & BARRÈRE P., Geomorphology and sedimentary ... more ABSTRACT: WASSMER P., SCHWARTZ D., GOMEZ C., WARD S. & BARRÈRE P., Geomorphology and sedimentary structures of Upper Pleistocene to Holocene alluvium within the Nyabarongo Valley (Rwanda). Palaeo-climate and palaeo-environmental implications. (IT ISSN 0391- 9838, 2013). At the confluence of the Nyabarongo River with the Mukungwa River, to the North of present Rwanda, there are thick alluvial sedimentary sequences, which can reach 30 m thickness, where they are capped by tufa deposits. From these deposits, two different sedimentary sequences have been identified, with (i) a first sedimentation stage characteristic of an obstructed valley controlled by contrasted seasonal flows during a dryer and cooler climate than at present, and (ii) on top of this unit a more recent sequence of alluvial terraces that were emplaced during a wetter and warmer context allowing the development and stabilisation of the rainforest. Palynological data and their comparison with a database at the East Afri...

The 11 March 2011 a Mw 9.0 earthquake triggered a tsunami off the Tohoku coast (Japan). To the no... more The 11 March 2011 a Mw 9.0 earthquake triggered a tsunami off the Tohoku coast (Japan). To the north of the infamous Sendai plain area, a series of small bays stretches from the North of Miyagi prefecture to mid-Iwate prefecture. At the border between both prefectures, the municipality of Rikuzentakata lies close to the river-mouth of the Kesen River. Both the built and the 'natural' environment of the municipality have been wiped off the map. In order to create more resilient communities, it is important to reduce the costs of reconstruction and restructuration by integrating lessons learned from the present tsunami. Therefore, this contribution provides a GIS evaluation of the different impacts in order to improve further planning. We have used remote-sensing based GIS -ESRI ArcGIS suite – using spatial data from July 2010 and March 2011. The GIS analysis has been completed using data collected in Japan during the period 2006 – 2010. The results show that the shoreline has...

Frontiers in Earth Science, 2015

NATO Science Series, 2006

ABSTRACT A chronological review illustrates the evolution of the geological interpretation of the... more ABSTRACT A chronological review illustrates the evolution of the geological interpretation of the Flims rockslide event and leads to new field evidences and dating results. Fundamental is the new dating of the rockslide event to the Boreal time of about 8,200 - 8,300 yBP (uncalibr.). During that time, the climate excluded any direct glacial influence on the rockslide mechanisms and on the surface morphology. All the supposedly "clear" evidences for glacial influences during or after the Flims event therefore must and can be explained by other processes. The main rockslide body has moved by a slab by slab mode with extreme deformation along the bedding planes, responsible for a high mobility. Nevertheless the sedimentary rock structure was well preserved. Despite the good stability conditions of the material the rockslide dam has broken. The extreme long runout distance of the most distal parts of the rockslide material can be attributed to secondary effects. The impact of the rockslide on the valley bottom, occupied presumably by a pre-existing lake, displaced the alluvial sediments and transported large parts of the Flims rockslide and of the nearby and older Tamins rockslide material far into the Hinterrhein valley. The displaced alluvium resedimented as "Bonaduz gravels", a characteristic graded but unstratified sediment.

Highlights a 20-m high coastal terrace is likely affected by tsunami waves high resolution topogr... more Highlights a 20-m high coastal terrace is likely affected by tsunami waves high resolution topographic measurement using TLS and sUAV-based SfM-MVS possible erosional features (fluvial or tsunami) were examined clast imbriation and tsunami-driven rocks were identified abstract A coastal rocky terrace with an elevation of ca. 20 m a.s.l. is located around Cape Todogasaki at the middle section of the ria-type rocky coast in Sanriku, northeastern Japan. In spite of its 20-m height, the tsunami waves induced by the 2011 Tohoku Earthquake were high enough to spread over the terrace. To clarify the effects of tsunamis on the terrace surface micromorphology, we performed field measurements of structure-from-motion multi-view stereo (SfM-MVS) photogrammetry using a digital camera mounted on a small unmanned aerial vehicle (sUAV). Terrestrial laser scanning was also carried out on the site for data validation. Geographical coordinates of benchmarks for georeferencing the SfM data were measured in the field using a GNSS rover, capable of postprocessing carrier-phase correction with centimeter accuracies. A 10-cm resolution digital elevation model (DEM) was then generated in SfM software, and micromorphology of the terrace surface was analyzed using the DEM. Despite limited basin area draining into the terrace, erosional characteristics likely formed by streamflow were identified. Sedimentological characteristics of thin clasts accumulation likely derived from terrace edge in-situ bedrock were also examined in the field. Based on clast shape and degree of weathering, three layers of deposit were identified: large fresh and angular clasts recently emplaced laying on the top. The spatial pattern of their imbrication for the three layers evidenced a landward flow direction. Furthermore, some angular boulders (2-3 m diameter) showing different degrees of weathering on their faces suggest that they were recently dislodged and displaced landward. These observations indicate that the uplifted terrace surface underwent erosion by not only the 2011 tsunami but also repeated significant tsunamis in the past.

Geomorphologie Relief Processus Environnement, Sep 1, 2011

L'AMS (Anisotropie de la Susceptibilité Magnétique) est une méthode non destructive à faible coût... more L'AMS (Anisotropie de la Susceptibilité Magnétique) est une méthode non destructive à faible coût, qui offre une vision simplifiée de la fabrique des sédiments. L'AMS décrit l'orientation de l'ellipsoïde du champ électromagnétique induit (M) d'un échantillon lors de son exposition à un champ électromagnétique externe (H). La relation qui lie M et H est : M=k.H pour laquelle k est un scalaire qui varie en fonction de l'organisation cristalline de l'échantillon et de son orientation physique en 3D. Grâce à ces propriétés, il est possible de définir la fabrique du matériau étudié. L'étude de la fabrique se fait alors par la mesure des angles des trois tenseurs de caractérisation 3D des volumes par rapport à un plan horizontal. Ces trois tenseurs sont K max , K int et K min . Classiquement, la lecture de ces trois tenseurs se Abstract AMS (Anisotropy of Magnetic Susceptibility) is a geophysical method, which uses the electromagnetic properties of samples as a proxy of their fabric. Commonly used on hard rocks and cohesive sediments, the method has never been developed for unconsolidated sediments before. In this contribution, we present the usability of the AMS method on unconsolidated rocks and the new insights that AMS brings for the study of tsunami deposits, and for geomorphology. We have been working on the deposits of the coast of North Sumatra (Indonesia) because a devastating tsunami has struck these coasts and has redesigned the coastal environment and sediments distribution the 26 December 2004. Hence, this geographical setting has provided us with the necessary material for the study. We have carried out the analysis from 6 samples, which evidenced: (i) a first layer deposited by an uprush oriented to the SSW; (ii) a decanting phase; (iii) a layer deposited by a backwash oriented to the North; (iv) two other uprushes that deposited two units oriented to the SSW and the SSE. This research has proven that the AMS could be used on unconsolidated deposits, and that the orientation and an approximation of the energy during deposition could be inferred as well. It leads to new developments in marine and or fluvial geomorphology, even for unconsolidated sediments.

High energy coastal events transport large amounts of sediment and leave important signatures in ... more High energy coastal events transport large amounts of sediment and leave important signatures in the landscape. The configuration of the coastline and topography has a significant impact on sediment transport processes and the form of preserved features, and inundation patterns are affected by surface roughness and elevation. The aims of this research are to assess the flow patterns during deposition of a suite of coastal deposits, most likely related to historical tsunami, and assess the role of topography and landscape configuration on depositional patterns.

... Francisco José Pérez Torrado, Raphael Paris 1 , Maria Del Carmen Cabrera, Jean Luc Schneider,... more ... Francisco José Pérez Torrado, Raphael Paris 1 , Maria Del Carmen Cabrera, Jean Luc Schneider, Patrick Wassmer, Juan Carlos Carracedo, A. Rodriguez Santana, F. Santana. (2006). 1 : Laboratoire de Géographie physique et environnementale (GEOLAB). ...

... 7 : Laboratoire des sciences du climat et de l'environnement (LSCE). CNR... more ... 7 : Laboratoire des sciences du climat et de l'environnement (LSCE). CNRS : UMR1572 – INSU – CEA : DSM/LSCE – Université de Versailles-Saint Quentin en Yvelines – Institut Pierre Simon Laplace. Domaine, : Planète et Univers/Sciences de la Terre/Géomorphologie. ...

Geomorphology

In 2006, a series of block-and-ash flows swept the southwestern and southern flanks of Merapi Vol... more In 2006, a series of block-and-ash flows swept the southwestern and southern flanks of Merapi Volcano, Java, Indonesia. In the K. Gendol valley, near the village of Kaliadem, we conducted a GPR survey on the most distal lobe of the June 14th second block-and-ash flow deposit. For this 100 m-long transect, we used a commercial GPR RAMAC© mounted with 100 MHz antennas.We measured the topography with a synchronized GPS and a laser rangefinder. Back at the laboratory, we processed the dataset with the software REFLEX®. Data of the subsurface reveals a series of layers, separated by strong reflective horizons. These horizons are the manifestation of intercalations of fine materials in between more coarse layers. The architecture of these layers presents progradation, retrogradation and aggradation patterns that we relate to the block-and-ash flow deposition process. Based on these observations we proposed a relative chronology of the deposition and a simple conceptual model of the deposi...

Geografia Fisica e Dinamicca Quaternaria

ABSTRACT: WASSMER P., SCHWARTZ D., GOMEZ C., WARD S. & BARRÈRE P., Geomorphology and sedimentary ... more ABSTRACT: WASSMER P., SCHWARTZ D., GOMEZ C., WARD S. & BARRÈRE P., Geomorphology and sedimentary structures of Upper Pleistocene to Holocene alluvium within the Nyabarongo Valley (Rwanda). Palaeo-climate and palaeo-environmental implications. (IT ISSN 0391- 9838, 2013). At the confluence of the Nyabarongo River with the Mukungwa River, to the North of present Rwanda, there are thick alluvial sedimentary sequences, which can reach 30 m thickness, where they are capped by tufa deposits. From these deposits, two different sedimentary sequences have been identified, with (i) a first sedimentation stage characteristic of an obstructed valley controlled by contrasted seasonal flows during a dryer and cooler climate than at present, and (ii) on top of this unit a more recent sequence of alluvial terraces that were emplaced during a wetter and warmer context allowing the development and stabilisation of the rainforest. Palynological data and their comparison with a database at the East Afri...

The 11 March 2011 a Mw 9.0 earthquake triggered a tsunami off the Tohoku coast (Japan). To the no... more The 11 March 2011 a Mw 9.0 earthquake triggered a tsunami off the Tohoku coast (Japan). To the north of the infamous Sendai plain area, a series of small bays stretches from the North of Miyagi prefecture to mid-Iwate prefecture. At the border between both prefectures, the municipality of Rikuzentakata lies close to the river-mouth of the Kesen River. Both the built and the 'natural' environment of the municipality have been wiped off the map. In order to create more resilient communities, it is important to reduce the costs of reconstruction and restructuration by integrating lessons learned from the present tsunami. Therefore, this contribution provides a GIS evaluation of the different impacts in order to improve further planning. We have used remote-sensing based GIS -ESRI ArcGIS suite – using spatial data from July 2010 and March 2011. The GIS analysis has been completed using data collected in Japan during the period 2006 – 2010. The results show that the shoreline has...

Frontiers in Earth Science, 2015

NATO Science Series, 2006

ABSTRACT A chronological review illustrates the evolution of the geological interpretation of the... more ABSTRACT A chronological review illustrates the evolution of the geological interpretation of the Flims rockslide event and leads to new field evidences and dating results. Fundamental is the new dating of the rockslide event to the Boreal time of about 8,200 - 8,300 yBP (uncalibr.). During that time, the climate excluded any direct glacial influence on the rockslide mechanisms and on the surface morphology. All the supposedly "clear" evidences for glacial influences during or after the Flims event therefore must and can be explained by other processes. The main rockslide body has moved by a slab by slab mode with extreme deformation along the bedding planes, responsible for a high mobility. Nevertheless the sedimentary rock structure was well preserved. Despite the good stability conditions of the material the rockslide dam has broken. The extreme long runout distance of the most distal parts of the rockslide material can be attributed to secondary effects. The impact of the rockslide on the valley bottom, occupied presumably by a pre-existing lake, displaced the alluvial sediments and transported large parts of the Flims rockslide and of the nearby and older Tamins rockslide material far into the Hinterrhein valley. The displaced alluvium resedimented as "Bonaduz gravels", a characteristic graded but unstratified sediment.