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The National Geographic and Rolex Perpetual Planet Everest Expedition is a multidisciplinary project dedicated to understanding climate change and its impacts, improving climate predictions, and providing a framework for future research in mountain environments. This issue of One Earth offers a first look at the science emerging from the expedition.

Summary In April and May 2019, as part of National Geographic and Rolex's Perpetual Planet Everest Expedition, an interdisciplinary scientific effort conducted a suite of research on the mountain and recognized many changing dynamics, including emergent risks resulting from natural and anthropogenic changes to the biological system. In this Primer, the diverse research teams highlight risks to ecosystem and human health, geologic hazards, and changing climbing conditions that could affect the local community, climbers, and trekkers in the future. We bring together perspectives from across the atmospheric, biological, geological, and health sciences to highlight the need to better understand emergent risks on Mt. Everest and in the Khumbu region. Understanding these risks is critical for the ∼10,000 people living in the Khumbu region, the thousands of visiting trekkers, and the hundreds of climbers who attempt to summit each year.

Convergent orogens are typically linear with laterally continuous, orogen-parallel folds and thrusts. Over the years, geoscience research has revealed evidence for important orthogonal/cross struct...

Glacier-based mountain water systems are the water towers of the world, and billions are dependent on the vital services they provide. In an effort to better understand the effects of climate change on the glaciers of the Hindu Kush-Himalaya, National Geographic and Tribhuvan University conducted a multidisciplinary expedition to Mount Everest. These are the voices from that journey.

The continental collision process has made a large contribution to continental growth and reconfiguration of cratons throughout Earth history. Many of the mountain belts present today are the product of continental collision such as the Appalachians, the Alps, the Cordillera, the Himalaya, the Zagros, and the Papuan Fold and Thrust Belt. Though collisional mountain belts are generally elongate and laterally continuous, close inspection reveals disruptions and variations in thrust geometry and kinematics along the strike of the range. These lateral variations typically coincide with cross structures and have been documented in thrust fault systems with a variety of geometries and kinematic interpretations. In the Himalaya, cross faults provide segment boundaries that, in some cases separate zones of differing thrust geometry and may even localize microseismicity or limit areas of active seismicity on adjacent thrust systems. By compiling data on structural segmentation along the length of the Himalayan range, we find lateral variations at all levels within the Himalaya. Along the Gish fault of the eastern Indian Himalaya, there is evidence in the foreland for changes in thrust-belt geometry across the fault. The Gish, the Ganga, and the Yamuna faults all mark boundaries of salients and recesses at the mountain front. The Benkar fault in the Greater Himalayan sequence of eastern Nepal exhibits a brittle-ductile style of deformation with fabric that crosscuts the older thrust-sense foliation. Microseismicity data from several regions in Nepal shows linear, northeast-striking clusters of epicenters sub-parallel to cross faults. The map pattern of aftershock data from the 2015 Nepal earthquakes has an abrupt northeast-trending termination on its eastern side suggesting the presence of a structure of that orientation that limited slip. The orientations of the recognized cross faults and seismic patterns also align with the extensional zones to the north on the Tibetan Plateau and the Indian basement structures to the south. Results from multiple studies are consistent with a link between cross faults and either of these structural trends to the north or south and suggest that cross faults may play a role in segmenting deformation style and seismic activity along the length of the Himalaya.

In 2019, the National Geographic and Rolex Perpetual Planet Everest expedition successfully retrieved the greatest diversity of scientific data ever from the mountain. The confluence of geologic, hydrologic, chemical and microbial hazards emergent as climate change increases glacier melt is significant. We review the findings of increased opportunity for landslides, water pollution, human waste contamination and earthquake events. Further monitoring and policy are needed to ensure the safety of residents, future climbers, and trekkers in the Mt. Everest watershed.

The Mount Everest region is characterized by its alpine glacial environment. In an effort to understand environmental change in the area, our team cored Taboche Lake, situated at 4,712 m along the western margin of the lateral moraine of the Ngozumpa Glacier. This research catalogues past earthquakes using geological records of the lake core that are important for the assessment of future earthquake hazards in the region. To achieve the aims of the study, core grain size characteristics and internal sedimentary structures from CT scan tomography, were coupled with radiocarbon dating of organic matter preserved in the core to reconstruct the environmental history of Loboche Lake. The 58 cm-long core consists of laminated silty sands and sandy silts with particle diameters less than 2 mm, covering ∼ 2,000 years of sedimentation history. Syn-sedimentary deformational structure, folding of sediments, rhythmically alternating dark- and light-coloured laminations, and turbidites are discussed in terms of their origins as past climatic and tectonic indicators.

We present preliminary observations from the Solukhumbu region of Nepal, coupled with structures described in the literature, to suggest the importance of structural and metamorphic discontinuities within the Himalayan metamorphic core (Greater Himalayan Sequence) and reactivation of at least one of these thrust discontinuities with a normal (down-to-the-north) sense of displacement. Based on preliminary geochronologic data, development of these discontinuities may have evolved over time. In the Dudh Kosi Valley near Ghat, gneissic rocks and pegmatites exhibit tectonized fabrics and yield argon cooling ages of ~4 Ma for K-feldspar and ~9 Ma for biotite. Just north of Khumjung there is a prominent topographic break from which sheared gneissic rocks indicate a top-to-the-north, or normal, sense of shear. Near Pangboche, a repeated section of kyanitebearing rocks interleaved with sillimanite-muscovite schist suggests structural imbrication and/or interleaved retrograde metamorphism. Below the peaks of Nuptse and Lhotse, the Khumbu thrust (Searle 1999) appears to form the floor of a thick succession of leucogranite sills. We suggest that these discontinuities were formed over time, possibly from early MCT and STDS deformation at ~21 Ma to as recent as ~4 Ma, and need to be considered in kinematic models that combine channel flow with critical taper and tectonic denudation. Moreover, orogenic collapse in the Himalayan core may be migrating southward through time as the orogenic wedge continues to uplift in response to underthrusting of India and southward propagation of the Main Frontal Thrust system.

Summary The Everest region is characterized by its alpine glacial environment. In an effort to understand environmental change and tectonic activity, our team cored Taboche Lake, situated at 4,712 m along the western margin of the Ngozumpa Glacier. This research catalogs past earthquakes using geological records of the lake core that are important for the assessment of future earthquake hazards in the region and provides information for tectonic risk of glacial lake floods. Core grain size characteristics and internal sedimentary structures from computed tomographic scan were coupled with radiocarbon dating of organic matter preserved in the core to reconstruct the environmental history of the area. The 58-cm-long core consists of laminated silty sands and sandy silts with particle diameters, Graphical abstract, Highlights • Sedimentology and dating are essential to identify environmental changes in lake cores • Post-1807 AD ± 112 years flood turbidite record indicates warming trend in the Himalaya • Earthquake-triggered turbidite and slump event in the core relate to historic tremors • Earthquake records in glacial lake core highlight tectonic risk, which can cause GLFs, Glacial Landscapes ; Glacial Processes ; Sedimentology ; Tectonics

International audience; Rapid assessments of landslides (including other mass movements of rock, snow and ice) as well as human impacts were conducted by many organizations immediately following the 25 April 2015 M7.8 Gorkha earthquake and its aftershock sequence. In particular, a NASA-led satellite mapping campaign identified over 4,300 coseismic and post-seismic landslides throughout Nepal, largely concentrated in the “down-dropped northern tectonic block” well north of Kathmandu in the Greater Himalaya (Kargel et al., 2016). The Solukhumbu District lies at the eastern margin of this zone, near the epicenter of the 12 May 2015 M7.3 aftershock. Given the enormous cultural and economic value of the Khumbu region to Nepal, we conducted two post-monsoon ground assessments of geomorphic and structural damage in the fall of 2015, and a third ground assessment of rebuilding efforts in May, 2016. While landslides and other mass movements were not as extensive as those to the west, numerous landslides and slumps were identified, mostly on steep, convex-up, east-facing slopes where the dip of metamorphic foliation (Namche orthogneiss and related rocks) is towards the Dudh Kosi River channel. Also, building damage was more extensive where villages were located on terraces of unconsolidated sand and gravel perched above the Dudh Kosi River (Nakchun Village). The area upstream from Phakding experienced several co-seismic mass movements on steep slopes that had clearly failed before (previous temblors?), as evidenced by old vegetated slump blocks and steep, unstable hummocky terrain. Particularly hard-hit was the Sherpa village of Thame northwest of Namche Bazaar, constructed on unconsolidated, water-saturated glacial outwash between two lateral moraines at the mouth of the Thame Khola Valley. Aside from Thame, one is struck by the randomness of structural damage in many Sherpa villages, reflecting micro-ground conditions beneath buildings and the style and/or age of construction (dry-stacked fieldstone versus the use of mud or cement mortar, the presence of wire mesh or gabion bands/spacers within stone walls, etc.). Fresh valley-flank slumps and landslides were markedly less obvious further north (towards Everest) where wide glacial valleys exist, although evidence of large rock falls and other mass movements in the past is clearly present.