Highlight articles 

Large sorted stone stripes have been discovered on the 4000 m high central Sanetti Plateau of the tropical Bale Mountains in Ethiopia. The stripes are a mystery as similar landforms have so far only been reported in the temperate zone and polar regions. Our investigations suggest that the stripes formed in the vicinity of a former ice cap on the plateau during a much colder climatic period. The distinct pattern is the result of a process related to cyclic freezing and thawing of the ground.

The 17 June 2017 Karrat landslide in Greenland caused a tsunami that killed four people. We apply a multidisciplinary workflow to reconstruct a timeline of events and find that three historic landslides occurred in 2009, 2016, and 2017. We also find evidence of much older periods of landslide activity. Three newly discovered active slopes might pose a future hazard. We speculate that the trigger for the recent events is melting permafrost due to a warming climate.

Organisms evolve in ever-changing environments under complex process interactions. We applied a new software modelling tool to assess how changes in river course impact the evolution of riverine species. Models illustrate the climatically and tectonically forced landscape changes that can drive riverine biodiversity, especially where topographic relief is low. This research demonstrates that river course changes can contribute to the high riverine biodiversity found in real-world lowland basins.

We propose a machine learning approach for the classification and analysis of large delta systems. The approach uses remotely sensed data, channel network extraction, and the analysis of 10 metrics to identify clusters of islands with similar characteristics. The 12 clusters are grouped in six main classes related to morphological processes acting on the system. The approach allows us to identify spatial patterns in large river deltas to inform modeling and the collection of field observations.

Large boulders found in two Himalayan valleys show signs of long fluvial transport (>10 km). Paleo-discharges required to mobilize these boulders exceed typical monsoon discharges. Exposure dating shows that a cluster of these boulders was emplaced ca. 5 kyr ago. This period is coeval with a weakening of the Indian monsoon and glacier retreat in the area. We, therefore, suggest that glacier lake outburst floods are likely mechanisms that can explain these exceptional transport processes.

Climate warming is causing significant ice surface lowering even in the uppermost parts of alpine glaciers. Using terrestrial lidar, we quantify rockfall in freshly exposed cirque walls. During 6-year monitoring (2011–2017), an extensive dataset was established and over 600 rockfall events identified. Drastically increased rockfall activity following ice retreat can clearly be observed as 60 % of the rockfall volume detached from less than 10 m above the glacier surface.

Rockfall size and frequency in two deglaciating cirques in the Central Alps, Austria, is analysed based on 6-year rockwall monitoring with terrestrial lidar (2011–2017). The erosion rates derived from this dataset are very high due to a frequent occurrence of large rockfalls in freshly deglaciated areas. The results obtained are important for rockfall hazard assessments, as, in rockwalls affected by glacier retreat, historical rockfall patterns are not good predictors of future events.

This review highlights potential contributions that Indigenous knowledge can make to geomorphic research. We evaluate several frameworks and models for including Indigenous knowledge in geomorphic research and discuss how they can be adapted for use with Indigenous communities across the world. We propose that weaving Indigenous knowledge with geomorphic science has the potential to create new solutions and understandings that neither body of knowledge could produce in isolation.

Drainage divides are believed to provide clues about divide migration and the instability of landscapes. Here, we present a novel approach to extract drainage divides from digital elevation models and to order them in a drainage divide network. We present our approach by studying natural and artificial landscapes generated with a landscape evolution model and disturbed to induce divide migration.

Drainage divides are believed to provide clues about divide migration and the instability of landscapes. Here, we present a novel approach to extract drainage divides from digital elevation models and to order them in a drainage divide network. We present our approach by studying natural and artificial landscapes generated with a landscape evolution model and disturbed to induce divide migration.

Avalanches and slush flows from Mt. Fuji are a major natural hazard as they may attain run-out distances of up to 4 km and destroy parts of the forest and infrastructure. We located and tracked them for the first time using seismic data. Numerical simulations were conducted to assess the precision of the seismic tracking. We also inferred dynamical properties characterizing these hazardous mass movements. This information is indispensable for assessing avalanche risk in the Mt. Fuji region.

Mountainous landscapes have long been recognized as potential drivers for genetic drift, speciation, and ecological resilience. We present a novel approach that can be used to assess and quantify drivers of biodiversity, speciation, and endemism over geological time. Using coupled climate–landscape models, we show that biodiversity under tectonic and climatic forcing relates to landscape dynamics and that landscape complexity drives species richness through orogenic history.

River deltas are valuable resources that support biodiversity and human habitation. Despite this we do not have a global census of deltas nor do we know the conditions that promote their formation. We surveyed 5399 river mouths greater than 50  m wide and found that 2174 (40  %) create a delta. The conditions that lead to delta formation are high sediment input and low wave and tide conditions. These results can be used to understand how deltas will adapt to environmental changes.

Assessing the impact of glaciation at the Earth's surface requires simultaneous quantification of the impact of climate variability on past glacier fluctuations and on bedrock erosion. Here we present a new approach for evaluating post-glacial bedrock surface erosion in mountainous environments by combining two different surface exposure dating methods. This approach can be used to estimate how bedrock erosion rates vary spatially and temporally since glacier retreat in an alpine environment.

We performed seven physical experiments to explore terrace formation and sediment export from a braided alluvial river system that is perturbed by changes in water discharge, sediment supply, or base level. Each perturbation differently affects (1) the geometry of terraces and channels, (2) the timing of terrace formation, and (3) the transient response of sediment discharge. Our findings provide guidelines for interpreting fill terraces and sediment export from fluvial systems.

We mapped eight monsoon-related (> 100 m²) and large (> 0.1 km²) landslides in the Nepal Himalayas since 1970. Adding inventories of Holocene landslides, giant landslides (> 1 km³), and landslides from the 2015 Gorkha earthquake, we constrain the size–frequency distribution of monsoon- and earthquake-induced landslides. Both contribute ~50 % to a long-term (> 10 kyr) total erosion of ~2 mm yr^-1, matching the long-term exhumation rate. Large landslides rarer than ¹⁰Be sampling time drive erosion.

Clast imbrication, which is a depositional fabric where clasts overlap each other similar to a run of toppled dominoes, is one of the most conspicuous sedimentary structures in coarse-grained fluvial deposits. However, the conditions leading to this fabric have been contested. Here, we calculate the hydrological conditions for various stream gradients. We find that clast imbrication most likely forms where channel gradients exceed a threshold and where upper flow regime conditions prevail.

Here we provide the first results on the evolution of the Ayeyarwady delta, the last unstudied megadelta of Asia. In addition to its intrinsic value as a founding study on the Holocene development of this region, we advance new ideas on the climate control of monsoonal deltas as well as describe for the first time a feedback mechanism between tectonics and tidal hydrodynamics that can explain the peculiarities of the Ayeyarwady delta.

This article is a contribution to a special issue on Two centuries of modelling across scales. It describes the historical observations, evolving hypotheses, and early calculations that led to the development of the field of glacial isostatic sdjustment (GIA) modelling, which seeks to understand feedbacks between ice-sheet change, sea-level change, and solid Earth deformation. Recent and future advances are discussed. Future progress will likely involve an interdisciplinary approach.

The role of mountain uplift and associated silicate weathering in the global climate over geological times is controversial. Previous soil column models suggest that weathering falls at a high denudation rate. We present the results of a 3-D model that couples erosion and weathering, a CO₂ consumer during mountain uplift. Our model suggests that the weathering of temporarily stocked colluvium may contribute significantly to the mountain weathering outflux at high denudation rates.

Sediments produced by glaciers are transported by rivers and wind toward the ocean. During their journey, these sediments are weathered, and we know that this has an impact on climate. One key factor is time, but the duration of this journey is largely unknown. We were able to measure the average time that sediment spends only in the glacial area. This time is 100–200 kyr, which is long and allows a lot of processes to act on sediments during their journey.

The layer known as the critical zone extends from the tree tops to the groundwater. This zone varies globally as a function of land use, climate, and geology. Energy and materials input from the land surface downward impact the subsurface landscape of water, gas, weathered material, and biota – at the same time that differences at depth also impact the superficial landscape. Scientists are designing observatories to understand the critical zone and how it will evolve in the future.

We use a seismometer network to detect and locate rockfalls, a key process shaping steep mountain landscapes. When tested against laser scan surveys, all seismically detected events could be located with an average deviation of 81 m. Seismic monitoring provides insight to the dynamics of individual rockfalls, which can be as small as 0.0053 m³. Thus, seismic methods provide unprecedented temporal, spatial and kinematic details about this important process.

Our work presents a novel method of measuring the capacity of deltaic landforms to trap and retain river-borne sediments, and we demonstrate that sediment retention is closely connected to sedimentary composition. Our results, supported by a unique high-resolution coring dataset in a major crevasse splay, show that finer sediments are a much larger component of the Mississippi Delta than is often acknowledged and that their abundance indicates exceptionally high rates of sediment retention.

Floodplains and fluvial terraces can provide information about current and past river systems, helping to reveal how channels respond to changes in both climate and tectonics. We present a new method of identifying these features objectively from digital elevation models by analysing their slope and elevation compared to the modern river. We test our method in eight field sites, and find that it provides rapid and reliable extraction of floodplains and terraces across a range of landscapes.

Spatial bedrock erosion data from stream channels are important for engineering issues and landscape evolution model assessment. However, acquiring such data is challenging and only few data sets exist. Detecting changes in repeated photographs of painted bedrock surfaces easily allows for semi-quantitative conclusions on the spatial distribution of sediment transport and its effects: abrasion on surfaces facing the streamflow and shielding of surfaces by abundant sediment.

Rapid dissolution of bedrock and regolith mobilised by landslides can be an important control on rates of overall chemical weathering in mountain ranges. In this study we analysed a number of landslides and rivers in Taiwan to better understand why this occurs. We find that sulfuric acid resulting from rapid oxidation of highly reactive sulfides in landslide deposits drives the intense weathering and can set catchment-scale solute budgets. This could be a CO₂ source in fast-eroding mountains.

Accurately predicting gravel transport rates in mountain rivers is difficult because of feedbacks with channel morphology. River bed surfaces evolve during floods, influencing transport rates. I propose that the threshold of gravel motion is a state variable for channel reach evolution. I develop a new model to predict how transport thresholds evolve as a function of transport rate, and then use laboratory flume experiments to calibrate and validate the model.

In regions formerly, or currently, covered by glaciers, landscapes have largely been shaped by glaciers. Glaciers erode bedrock through three main mechanisms: abrasion, quarrying, and subglacial meltwater erosion (SME). The latter, however, remains enigmatic. We present the first numerical modelling study of bedrock erosion by subglacial water and find that SME is negligible compared to abrasion and quarrying across the glacier, but its localization can explain the formation of bedrock channels.

A physical scale model of a gravel-bed braided river was used to measure vertical grain size sorting in the morphological active layer defined as the bed material between the maximum and minimum bed elevation. By normalizing active layer thickness and dividing into 10 sublayers we show that all grain sizes occur with almost equal frequency in all sublayers. Occurrence of patches and strings of coarser material relates to preservation of particular morphotextural features within the active layer.

We use ice-penetrating-radar data to identify a laterally continuous, gently sloping topographic block, comprising two surfaces separated by a distinct break in slope, preserved beneath the Institute and Möller ice streams, West Antarctica. We interpret these features as extensive erosion surfaces, showing that ancient (pre-glacial) surfaces can be preserved at low elevations beneath ice sheets. Different erosion regimes (e.g. fluvial and marine) may have formed these surfaces.

In this work we present DeltaRCM, a reduced-complexity model for river delta formation. It is a rule-based cellular morphodynamic model, in contrast to reductionist models based on detailed computational fluid dynamics. DeltaRCM is able to resolve channel dynamics and to produce stratigraphy. We also explain the meaning of complexity reduction, especially the essential processes to be included in modeling deltas.