River water and suspended sediment samples were collected between 2015 and 2018 from the Narayani, Saptakoshi and Sunkoshi rivers in Nepal. Samples formed part of the Perturbations of Earth Surface Processes by Large Earthquakes PRESSurE Project (https://www.gfz-potsdam.de/en/section/geomorphology/projects/pressure/). This project aims to better understand the role of earthquakes on earth surface processes. Hydrological stations were installed on the rivers draining the epicentral area following the April 2015 Gorkha earthquake (Mw 7.9). The stations were operated for four consecutive monsoon seasons. All stations were equipped with river stage height measurements and manned daily for sampling. A small batch of river water samples were also collected from the Narayani River. These samples were collected upstream of Narayanghat using a raft between 2015 and 2017. These samples were collected at varying depths in the river. Dissolved river water ion concentrations (N=672) and sediment-adsorbed cation concentrations (N=74) were determined. Radiogenic strontium isotopes (87Sr/86Sr) of both phases were measured for a small number of paired samples (N=9). Dissolved river water anion concentrations were measured at the GFZ German Research Centre for Geosciences, Potsdam, Germany. Dissolved river water cation concentrations were measured at GFZ German Research Centre for Geosciences, Potsdam, Germany and the Department of Earth Sciences, University of Cambridge, Cambridge, UK. Sediment-adsorbed cation concentrations and radiogenic strontium isotope ratios were measured at the Department of Earth Sciences, University of Cambridge, Cambridge, UK.

This data set forms part of the Perturbations of Earth Surface Processes by Large Earthquakes PRESSurE Project (https://www.gfz-potsdam.de/en/section/geomorphology/projects/pressure/). Strong earthquakes cause transient perturbations to the near Earth’s surface system. These include widespread land-sliding, subsequent mass movement, and the loading of rivers with sediments. In addition, brittle-rock deformation occurs during the event, forming cracks that affect rock strength and hydrological conductivity. Often overlooked in the immediate aftermath of an earthquake, these perturbations can represent a major part of the overall disaster with impacts that can persist for years before restoring to background conditions. This relaxation phase is therefore part of seismically induced earthquake changes and needs to be monitored to understand the full impact on the Earth system. The fundamental questions motivating the PRESSurE project are ‘How do earthquakes impact erosion during and following seismic activity?’ and ‘What is the role of earthquakes on Himalayan landscape evolution?’. In early June, shortly after the April 2015 Gorkha earthquake, we installed twelve hydrological stations covering all rivers draining the epicentral area. Each station was equipped for daily river water and suspended sediment sampling. Samples are filtered and packed in Nepal, before being shipped to the sediment lab at GFZ for further analysis (SedLab: https://labinfrastructure.geo-x.net/laboratories/91). The sampling network is complemented by an array of seismometers, repeated satellite image observations, and on-side stage high recording. This array is optimized for the monitoring of Earth surface processes (land-sliding, mass wasting and debris flows) and for the monitoring of properties of the shallow subsurface by coda analysis. The monitoring network is the first and most complete observatory to monitor the perturbation of Earth surface process by a major earthquake.