Reconstructing the geochronological evolution of large landslides by means of the trenching technique in the Yesa Reservoir (Spanish Pyrenees)

摘要: Abstract Detailed geomorphological mapping has revealed that the slopes upstream of Yesa Dam are affected by several flysch landslides. The largest landslides correspond to La Refaya rotational slide (11 million m3), situated just spillway and El Vertedero translational (6 million located 1.5 km dam. A portion landslide (3 million m3) was reactivated in 2006 due overloading caused an earth heap. higher dam will be built on downstream side existing gravity concrete raise maximum water level reservoir 23 m. retrodeformation analysis deposits exposed two trenches excavated upper part these together with obtained absolute ages (C14 OSL) have provided information kinematics evolution slope movements. main findings derived from 45 m long trench dug closed depression developed at foot head scarp include: (1) is older than 12 ka undergone a cumulative rotation 17°, yielding mean rate about 1.4°/millennium. (2) Most (14°) occurred before 5.8 ka according stratigraphy been dominated progressive displacement; no evidence catastrophic reactivation found. across bench non reveals that: 38 ka. trenched least one subsequent 20 ka remained inactive for time as suggested highly degraded bedrock scarp, 18° compared 60° dip underlying failure plane. Based this study, corrective measures estimated cost 11.5 million euros designed slope. investigation illustrates usefulness cost-effectiveness trenching technique allied geochronological methods obtain precise limits, age, mechanism, (progressive vs. episodic displacement, movement rate) chronological