TY - JOUR A1 - Illien, Luc A1 - Sens-Schönfelder, Christoph A1 - Andermann, Christoff A1 - Marc, Odin A1 - Cook, Kristen L. A1 - Adhikari, Lok Bijaya A1 - Hovius, Niels T1 - Seismic velocity recovery in the subsurface BT - transient damage and groundwater drainage following the 2015 Gorkha Earthquake, Nepal JF - Journal of geophysical research : Solid earth N2 - Shallow earthquakes frequently disturb the hydrological and mechanical state of the subsurface, with consequences for hazard and water management. Transient post-seismic hydrological behavior has been widely reported, suggesting that the recovery of material properties (relaxation) following ground shaking may impact groundwater fluctuations. However, the monitoring of seismic velocity variations associated with earthquake damage and hydrological variations are often done assuming that both effects are independent. In a field site prone to highly variable hydrological conditions, we disentangle the different forcing of the relative seismic velocity variations delta v retrieved from a small dense seismic array in Nepal in the aftermath of the 2015 M-w 7.8 Gorkha earthquake. We successfully model transient damage effects by introducing a universal relaxation function that contains a unique maximum relaxation timescale for the main shock and the aftershocks, independent of the ground shaking levels. Next, we remove the modeled velocity from the raw data and test whether the corresponding residuals agree with a background hydrological behavior we inferred from a previously calibrated groundwater model. The fitting of the delta v data with this model is improved when we introduce transient hydrological properties in the phase immediately following the main shock. This transient behavior, interpreted as an enhanced permeability in the shallow subsurface, lasts for similar to 6 months and is shorter than the damage relaxation (similar to 1 yr). Thus, we demonstrate the capability of seismic interferometry to deconvolve transient hydrological properties after earthquakes from non-linear mechanical recovery. KW - earthquake damage KW - earthquake hydrology KW - relaxation KW - Gorkha earthquake KW - seismic monitoring KW - ambient noise Y1 - 2022 U6 - https://doi.org/10.1029/2021JB023402 SN - 2169-9313 SN - 2169-9356 VL - 127 IS - 2 PB - American Geophysical Union CY - Washington ER - TY - JOUR A1 - Menges, Johanna A1 - Hovius, Niels A1 - Andermann, Christoff A1 - Dietze, Michael A1 - Swoboda, Charlie A1 - Cook, Kristen L. A1 - Adhikari, Basanta R. A1 - Vieth-Hillebrand, Andrea A1 - Bonnet, Stephane A1 - Reimann, Tony A1 - Koutsodendris, Andreas A1 - Sachse, Dirk T1 - Late holocene landscape collapse of a trans-himalayan dryland BT - human impact and aridification JF - Geophysical research letters N2 - Soil degradation is a severe and growing threat to ecosystem services globally. Soil loss is often nonlinear, involving a rapid deterioration from a stable eco-geomorphic state once a tipping point is reached. Soil loss thresholds have been studied at plot scale, but for landscapes, quantitative constraints on the necessary and sufficient conditions for tipping points are rare. Here, we document a landscape-wide eco-geomorphic tipping point at the edge of the Tibetan Plateau and quantify its drivers and erosional consequences. We show that in the upper Kali Gandaki valley, Nepal, soil formation prevailed under wetter conditions during much of the Holocene. Our data suggest that after a period of human pressure and declining vegetation cover, a 20% reduction of relative humidity and precipitation below 200 mm/year halted soil formation after 1.6 ka and promoted widespread gullying and rapid soil loss, with irreversible consequences for ecosystem services. KW - geomorphology KW - paleoclimate KW - human activity KW - Tibetan plateau KW - late Holocene Y1 - 2019 U6 - https://doi.org/10.1029/2019GL084192 SN - 0094-8276 SN - 1944-8007 VL - 46 IS - 23 SP - 13814 EP - 13824 PB - American Geophysical Union CY - Washington ER - TY - JOUR A1 - Cook, Kristen L. A1 - Andermann, Christoff A1 - Gimbert, Florent A1 - Adhikari, Basanta Raj A1 - Hovius, Niels T1 - Glacial lake outburst floods as drivers of fluvial erosion in the Himalaya JF - Science N2 - Himalayan rivers are frequently hit by catastrophic floods that are caused by the failure of glacial lake and landslide dams; however, the dynamics and long-term impacts of such floods remain poorly understood. We present a comprehensive set of observations that capture the July 2016 glacial lake outburst flood (GLOF) in the Bhotekoshi/Sunkoshi River of Nepal. Seismic records of the flood provide new insights into GLOF mechanics and their ability to mobilize large boulders that otherwise prevent channel erosion. Because of this boulder mobilization, GLOF impacts far exceed those of the annual summer monsoon, and GLOFs may dominate fluvial erosion and channel-hillslope coupling many tens of kilometers downstream of glaciated areas. Long-term valley evolution in these regions may therefore be driven by GLOF frequency and magnitude, rather than by precipitation. Y1 - 2018 U6 - https://doi.org/10.1126/science.aat4981 SN - 0036-8075 SN - 1095-9203 VL - 362 IS - 6410 SP - 53 EP - 57 PB - American Assoc. for the Advancement of Science CY - Washington ER -