Terrestrial laser scanners (TLS) are well known for providing an efficient means to monitor coastal cliff erosion. Cliffs along micro-tidal coasts, however, have often escaped quantification because the narrow or absent coastal platforms do not offer stable and embracing vantage points. To circumvent this issue, mobile laser scanning surveys from a boat can be used. We present a case study from Provence-Alpes-Côte-d'Azur (Mediterranean coast-southern France) to quantify cliff erosion in such micro-tidal environments. Three surveys were subcontracted over a period of 17 months to monitor a 3.5-km-long cliff of Carry-le-Rouet (15 km west of Marseille). Data quality was checked independently using man-made planar walls positioned above the cliff face, to retrieve survey precision and change detection thresholds. A boat-borne mobile LiDAR system was capable of describing planar features with a precision of 3–4 cm (epoch 1 and 2) and improved to 2.6 cm (epoch 3) with point densities around 100 points/m 2 . Absolute positioning accuracy varied between 0.1 cm and 0.3 cm. Because the coastline is very sinuous, we describe a method to unfold the point clouds using a continuous analytical surface made of vertical planes joined by arcs of cylinders and perform the analysis in 2.5D. Change was detected using a unique, conservative, threshold of 14 cm (99% quantile estimated on the plane change) on grids of 10 × 10 cm pixels. Integrated over the entire cliff face, the average annual cliff recession rate at Carry-le-Rouet is 1.1 cm/year. In 17 months, erosion was three times more effective in sandstone and marl layers than in calcarenites and conglomerates. Erosion varies vertically with erosion three times more effectively in the lower 25 m of the cliffs than above. Despite imperfections, boat-borne laser scanning systems are capable of delivering meaningful erosion data even in this low erosion context.

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In this study, a new measurement method to quantify 129I at low level by ICP-MS/MS (Agilent 8900) was developed. This new method is based on a new measurement medium and mass-shift mode. The developed measurement medium is composed of 0.1% NH4OH, 10 g L-1 ascorbic acid and 3% Tween® 20 which considerably decrease the memory effect and increase the sensitivity. Different reactional gas were compared on on-mass and mass-shift modes and finally, O2 was selected on mass-shift mode. The mass-shift mode with O2 allows having the most quantitative iodine oxidation rate while eliminating isobaric and polyatomic interferences. Isobaric interference due to 129Xe+ is eliminated following a charge transfer in the reaction/collision cell and polyatomic interferences are eliminated with the second quadrupole. This new measurement method improves the limit of detection of 129I to 11 mBq L-1, without chemical treatment.

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Mass wasting events are frequent processes that occur on the steep slopes of passive margin escarpments located in humid tropical regions. Not much is known about their role in the morphodynamics and morphogenesis of these escarpments. This study measured long-term denudation processes using cosmogenic 10Be produced in situ and characterized the sedimentary deposits to understand the role that debris flows have played in the dynamics and evolution of the oceanic slope of a sector of Serra do Mar, Brazil, the steepest passive-margin escarpment in South America. The findings indicate that the catchments were subjected to episodic debris flows, albeit with an uneven temporal distribution, and that these infrequent mass wasting episodes account for most of the escarpment erosion in Serra do Mar. In conclusion, debris flows are among the main geomorphological processes responsible for most of the erosion in this passive margin escarpment, and they played a significant role in its retreat.

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