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•Three vineyard practices were evaluated by spatial erosion models RUSLE and SIMWE.•Terraces prevent widespread gradual erosion, in contrast with vertical cultivation.•Intense ...rainstorms cause runoff concentration and erosion patterns in any practice.•Spatial design of slopes, roads and vines strongly affect patterns in any practice.•Sub-metric UAV-SfM data allows detailed erosion simulations in complex landscapes.
Soil erosion can cause a progressive degradation of hillslopes, especially in steep-slope agricultural landscapes. In this study, the formation of spatial erosion patterns was evaluated in three typical steep-slope vineyard cultivation practices in northern Italy: dry-stone wall terraces, earth bank terraces and vertical cultivation (Italian: rittochino). UAV surveys in three vineyards provided high-resolution data on topography and land use serving as input for two GIS-based erosion models: the Revised Universal Soil Loss Equation (RUSLE) and SIMulated Water Erosion model (SIMWE). Annual RUSLE simulations showed how the two terracing practices (i.e. dry-stone walls and earth banks) effectively safeguarded large areas from soil loss, whereas the non-terraced vertical cultivation produced widely distributed soil loss with increasing severity according to slope length and steepness. In intense single-event conditions simulated by SIMWE, all three practices showed the formation of critical preferential surface flow patterns, corresponding to several field-observed erosion patterns (piping of stone walls, landslides on earth banks, and rill erosion in the non-terraced vineyard), while also in this case showing the highest erosion rates for the non-terraced vertical cultivation. Simulated flow concentration was strongly determined by the spatial organisation of the hillslope, roads and vines, and several strategies were discussed for erosion mitigation (including drainage systems or enhanced soil cover). Furthermore, the results indicated that SIMWE is an optimal approach for the recognition of soil erosion processes occurring during intense rainfall conditions. This study provides an example of high-resolution erosion risk evaluation, which should play a crucial role in the design and management of steep-slope vineyards.
Few studies have focused on the post-eruption evolution of maar craters and associated lake level changes, although breaching of the crater rim poses mass-flow and flood hazards long after the ...initial eruption. Lake Pavin is a maar lake in the French Massif central formed by an eruption c. 6700 years ago. The maar is perched on the edge of a glacially-shaped valley and the rim overlooks the surrounding subdued landscape. The rim is breached to the north by an overflow channel, and to the south the maar has cut into the flank of the Montchal scoria cone and lava flows. Incision of the lake outlet led to the growth of an alluvial fan that pushed the Couze Pavin River towards the north side of the Gelat valley.
Two lake terraces within the crater are used to determine stages in the evolution of the lake. The highstand Stage 1 terrace +18 m above the current lake level indicates that the post-eruption lake surface and volume was 15% and 38% larger than the present-day lake, respectively, prior to the 5-7th Century CE. The poorly preserved Stage 2 bench, +4.35 m on the west side of the natural dam, indicates that incision paused between Stage 1 and achievement of present lake level (Stage 3) before the 18th Century. Four units of streamflow deposits (c. 0.087 km2 in area and 0.14–0.18 km3 in volume) that formed the fan at the mouth of the outlet in the Gelat valley have been 14C dated to between the 9th and 16th Century. From the fan sedimentology, we infer that the lake level dropped slowly between highstand Stages 1 and 2, when the outlet cut down through the rim saddle. The lake level drop accelerated between Stage 2 and Stage 3 before the 14th Century, inducing small debris flows. The latter may have resulted from heavy rainstorms, but there is no evidence for catastrophic events. Stepwise downcutting of the north rim saddle was also governed by contrasted properties of the deposits forming the dam. The current lake level has been stable since at least the early 18th Century, but the long-term stability of the dam is at risk.
•The lake level changes reflect a succession of three stages and erosion intervals.•The outlet formation included seepage, knick point retreat, and overflow.•Downcutting exploited lithological contrasts between deposits at the lake dam.•The lake level drop accelerated between Stages 2 and 3 prior to the 14th century.•No catastrophic event occurred, but long-term stability of the natural dam is at risk.
The Hikurangi subduction margin, New Zealand, has not produced large subduction earthquakes within the short written historic period (~180 years) and the potential of the plate interface to host ...large (M > 7) to great (M > 8) earthquakes and tsunamis is poorly constrained. The geological record of past subduction earthquakes offers a method for assessing the location, frequency and approximate magnitude of subduction earthquakes to underpin seismic and tsunami hazard assessments. We review evidence of Holocene coseismic coastal deformation and tsunamis at 22 locations along the margin. A consistent approach to radiocarbon age modelling is used and earthquake and tsunami evidence is ranked using a systematic assessment of the quality of age control and the certainty that the event in question is an earthquake. To identify possible subduction earthquakes, we use temporal correlation of earthquakes, combined with the type of earthquake evidence, likely primary fault source and the earthquake certainty ranking. We identify 10 past possible subduction earthquakes over the past 7000 years along the Hikurangi margin. The last subduction earthquake occurred at 520–470 years BP in the southern Hikurangi margin and the strongest evidence for a full margin rupture is at 870–815 years BP. There are no apparent persistent rupture patches, suggesting segmentation of the margin is not strong. In the southern margin, the type of geological deformation preserved generally matches that expected due to rupture of the interseismically locked portion of the subduction interface but the southern termination of past subduction ruptures remains unresolved. The pattern of geological deformation on the central margin suggests that the region of the interface that currently hosts slow slip events also undergoes rupture in large earthquakes, demonstrating different modes of slip behaviour occur on the central Hikurangi margin. Evidence for subduction earthquakes on the northern margin has not been identified because deformation signals from upper plate faults dominate the geological record. Large uncertainties remain in regard to evidence of past subduction earthquakes on the Hikurangi margin, with the greatest challenges presented by temporal correlation of earthquake evidence when working within the uncertainties of radiocarbon ages, and the presence of upper plate faults capable of producing deformation and tsunamis similar to that expected for subduction earthquakes. However, areas of priority research such as improving the paleotsunami record and integration of submarine turbidite records should produce significant advances in the future.
•We review - past coseismic coastal deformation on the Hikurangi subduction margin.•Along-margin temporal correlations are used to identify past subduction earthquakes.•Upper plate faults introduce uncertainty in earthquake source interpretation.•We identify ten possible subduction earthquakes in the past 7000 years.
GPS data reveal that the Brahmaputra Valley has broken from the Indian Plate and rotates clockwise relative to India about a point a few hundred kilometers west of the Shillong Plateau. The GPS ...velocity vectors define two distinct blocks separated by the Kopili fault upon which 2–3 mm/yr of dextral slip is observed: the Shillong block between longitudes 89 and 93°E rotating clockwise at 1.15°/Myr and the Assam block from 93.5°E to 97°E rotating at ≈1.13°/Myr. These two blocks are more than 120 km wide in a north‐south sense, but they extend locally a similar distance beneath the Himalaya and Tibet. A result of these rotations is that convergence across the Himalaya east of Sikkim decreases in velocity eastward from 18 to ≈12 mm/yr and convergence between the Shillong Plateau and Bangladesh across the Dauki fault increases from 3 mm/yr in the west to >8 mm/yr in the east. This fast convergence rate is inconsistent with inferred geological uplift rates on the plateau (if a 45°N dip is assumed for the Dauki fault) unless clockwise rotation of the Shillong block has increased substantially in the past 4–8 Myr. Such acceleration is consistent with the reported recent slowing in the convergence rate across the Bhutan Himalaya. The current slip potential near Bhutan, based on present‐day convergence rates and assuming no great earthquake since 1713 A.D., is now ~5.4 m, similar to the slip reported from alluvial terraces that offsets across the Main Himalayan Thrust and sufficient to sustain a Mw ≥ 8.0 earthquake in this area.
Key Points
New GPS velocity field in eastern HimalayaShillong Plateau is independent from IndiaStrain accumulated since the last earthquake is sufficient for a M > 8 earthquake
The upper–middle Yellow River flows through the Fenwei graben, a structure resulting from extensional tectonism that was formed and repeatedly extended during the Cenozoic. The drainage system within ...this graben was formerly isolated from the lower reaches of the Yellow River system by the Xiaoshan mountains, an actively growing ∼ NW–SE trending range. The modern course of the Yellow River takes it through this range along the Sanmen gorge, the formation of which was of great significance in that it initiated through-going drainage between the upper–middle and lower reaches of the system. The timing of this event, which was clearly a critical point in the evolution of the Yellow River, can be established by dating the terraces in the gorge. Intermittent deepening of this gorge by the Yellow River from a high-level planation surface capping the mountain range has resulted in the formation of five terraces. Magnetostratigraphic records from aeolian deposits accumulated on these surfaces provide a geochronological sequence for this geomorphic archive, in which the ages of the planation surface and of terraces T5, T4, T3, T2, and T1 have been determined as ∼3.63 Ma, ∼1.24 Ma, ∼0.86 Ma, ∼0.62 Ma, ∼129 ka, and ∼12 ka, respectively.
Under the constraint of this chronological framework, a model for landscape evolution is proposed here. Uplift of the inner Fenwei graben and of the surrounding mountain ranges led to dissection of the 3.63 Ma old planation surface in conjunction with the formation of the Sanmen gorge. Drainage of the lake previously occupying the basin would have promoted incision into the fluvio-lacustrine graben sediments; indeed, gorge formation through the Xiaoshan may have been initiated or intensified by lake overflow. The ages obtained for the planation surface and uppermost terrace suggest that the formation of the Sanmen gorge and the initiation of the through-going eastward drainage of the Yellow River occurred between 3.63 and 1.24 Ma. Before the start of gorge entrenchment, the products of erosion in the modern upper catchment of the Yellow River were unable to reach the sea. The dramatic increase in deposition rates in the Bohai Gulf (at the mouth of the modern Yellow River in the East China Sea), ∼1.0 Ma ago, thus resulted from the initiation of an integral (enlarged) Yellow River catchment drainage through the Sanmen gorge; it does not imply an increase in erosion rates at that time.
•We reconstructed a 3.6 Ma sequence based on the planation surface and terraces along the Sanmen gorge.•The landscape evolution from basin filling to excavation was outlined under the constraint of this chronology.•The present-day Sanmen gorge was formed by westward capturing the paleolake within the Fenwei graben.•Gorge formation may have been initiated by lake overflow during the period 3.63–1.24 Ma.•The dramatic increase in deposition rates in the Bohai Gulf resulted from the establishment of an integral Yellow River.
Millions of vulnerable smallholder farmers around the world cultivate crops on narrow hillside terraces and suffer from inadequate flat growing areas to support their families. A significant amount ...of surface area on terraces is actually vertical—specifically the underutilized terrace walls (risers). Some indigenous farmers in Nepal have been observed to cultivate wall-climbing and wall-descending crops, sown at the base or top edge of the walls, respectively, but these have not been evaluated for their economic benefits and adoption potential. Participatory on-farm trials were conducted on 280 terrace farms in two districts of Nepal (Kaski, Dhading) for two cropping seasons (2015–2016). Three wall-climbing crops (yam in sacks, chayote squash, pumpkin) and four wall-descending crops (ricebean, cowpea, horsegram, blackgram) were each grown by 20 farmers per crop per site and evaluated for potential net economic returns and perceptions of all 280 participating women farmers based on five adoption criteria. Here, we show, for the first time to the best of our knowledge, that terrace walls or risers can be intensified with suitable wall-climbing and wall-descending crops. All three wall-climbing crops were productive, with potential net economic returns ranging from US $27 per plant for chayote squash, $10/plant for pumpkin, and $2/plant for yam. Similarly, all four wall-descending crops were productive, with potential net economic returns ranging from US $9–$15 per 100 m of wall edge. All the wall crops received good-to-excellent ratings (typically > 8/10) by women farmers for simplicity, compatibility, affordability, potential economic returns, and willingness to continue. In terms of long-term adoption, yam, pumpkin, ricebean, and cowpea were ranked the highest, with > 90% farmers willing to continue each practice. We discuss the potential and constraints of transferring these terrace-intensifying strategies globally.
Located in the easternmost portion of the Central Apennines, the Mt. Morrone normal fault system is one of the highest seismic hazards in Italy. Previous geological and geomorphological observations ...revealed the presence of a ∼22 km‐long NW‐SE right‐lateral en echelon fault system made of two parallel faults affecting Quaternary deposits. Our analysis focused on the westernmost fault, which bounds the Sulmona Basin. Cumulative offsets were identified and quantified using high‐resolution Digital Elevation Models derived from LiDAR, Satellite Pleiades images, and drone acquisition at the three sites. Morphological markers displaced from a few to tens of meters were dated using 36Cl exposure dating. The results would be suggesting a fault slip rate of 0.2–0.4 mm/a. The deformed markers that dated at 36–44 ka consist of alluvial terraces emplaced by the main streams flowing down from Mt. Morrone to the Sulmona Basin, subsequently incised, and preserved when the fluvial base level dropped because of the former Sulmona lake fluctuations. The yielded ages for these markers fit well with the last major aggradational event associated with the 35–40 ka Heinrich event described and dated to other fluvial basins in the Apennines. Furthermore, the estimated rate agrees with the values obtained in previous studies over shorter and longer periods (105−6 years) and within similar uncertainties. This might then suggest that the period recovered by this study encompasses the entire seismic cycle.
Key Points
High‐resolution topography investigation allowed a morphotectonic mapping of the Mt. Morrone fault and a quantification of the fault offsets
Dating the morphotectonic displaced markers through cosmogenic nuclides technique yielded a slip rate of 0.2–0.4 mm/a over the last 40 ka
The slip rates retrieved over the last 40 ka are similar to rates both at longer and shorter times, suggesting a constant rate through time
Uplifted Pleistocene marine terrace sequences are used to quantify uplift rates along active margins by knowing terrace age and elevation, and sea level (SL) position at the time of terrace ...formation. When terraces are undated, ages are assigned by correlating terraces at progressively higher elevations with progressively older highstands. Uplift at convergent margins can be constant over time or occur coseismically during upper plate earthquakes. We explore the formation of terrace sequences under conditions of constant and earthquake‐driven uplift by using a forward numerical model. The modeling reveals that terraces are generally abandoned at SL highstands but they are carved during all stands, depending on the time spent within the sea erosional‐depth‐range. Therefore sea reoccupation of a same platform after formation is a common occurrence that decreases with increasing uplift rates, suggesting that most platforms in nature may be in fact polygenetic. Furthermore, the model run time influences the terrace sequences: terraces formed at the beginning of longer runs constitute an ‘inherited morphology’ affecting subsequent sequences. When coseismic uplift is applied, the formation and preservation of terraces for a given average uplift rate depend stochastically on the coseismic displacement ‐ recurrence interval combination in relation to the SL position at the time of the earthquake. These factors significantly contribute to a higher likelihood of non‐preserved terraces along a terrace sequence, which may affect age correlation and, consequently, the resulting uplift rates. Further research is needed to explore the effect of the full seismic cycle in shaping a terrace sequence.
Plain Language Summary
The topography of the upper plate in a subduction zone is subject to uplift over time. The action of the sea on the coast creates marine terraces, horizontal erosional platforms that, if uplifted, form a staircase morphology. Terrace staircase sequences are used to calculate the average uplift rate of the coast if the terrace age is known. In absence of datable material, the terrace age is inferred by assuming that terraces are preserved in chronological order of formation along the sequence. We use numerical models to explore the generation of subsequent marine terraces forming a staircase sequence on coastal margins subject to constant uplift over time or to instantaneous uplift caused by earthquakes occurring at a certain frequency (recurrence interval). We observe that: terraces are carved as long as they lie within the sea erosional depth; sea reoccupation of previously formed terraces occurs frequently, increasing with decreasing uplift rates; running the model for longer or shorter periods of time has changes morphology of the sequence; varying the earthquake recurrence interval results in different staircase morphologies even if the average uplift rate remains unchanged. The potential absence of terraces increases the chance of assigning, through cross correlation, wrong terrace ages, resulting in inexact uplift rates.
Key Points
Terraces form during all sea‐level stands, and sea reoccupation is common at uplift rates ≤0.5 mm/yr; most natural terraces may be polygenetic
Earthquake‐driven uplift may cause non‐preservation of individual terraces, depending on the recurrence interval ‐ coseismic uplift values
By keeping parameters constant and varying the model run time, terrace sequences with different morphology are created
A significant amount of the ongoing shortening between the Eurasian and Arabian plates is accommodated within the Zagros Fold‐Thrust Belt. However, the spatial and temporal distribution of active ...shortening within the belt, especially in its NW part, is not yet well constrained. We determined depositional ages of uplifted river terraces crossing the belt along the Greater Zab River using luminescence dating. Kinematic modeling of the fault‐related fold belt was then used to calculate long‐term slip rates during the Late Pleistocene to Holocene. Our results provide new insight into the rates of active faulting and folding in the area. The Zagros Mountain Front Fault accommodates about 1.46 ± 0.60 mm a−1 of slip, while a more external basement fault further to the SW accommodates less than 0.41 ± 0.16 mm a−1. Horizontal slip rates related to detachment folding of two anticlines within the Zagros Foothills are 0.40 ± 0.10 and 1.24 ± 0.36 mm a−1. Basement thrusting and thickening of the crust are restricted to the NE part of the Zagros belt. This is also reflected in the regional topography and in the distribution of uplifted terraces. In the southwestern part, the deformation is limited mainly to folding and thrusting of the sedimentary cover above a Triassic basal detachment. In the NE, deformation is associated with slip on basement thrusts. Our study sheds light on the distribution of shortening in the Zagros Mountains and helps to understand the regional tectonic system. Our results may be the foundation for a better seismic hazard assessment of the entire area.
Plain Language Summary
In active mountain belts, river terraces found above the present‐day river level can be indicative of differences in uplift rates due to the thickening, faulting, and folding processes in the Earth's crust. These processes, driven by the motion of tectonic plates, are responsible for the formation of mountain belts. Here, we took sediment samples from uplifted river terraces along the Greater Zab River that crosses the Zagros Mountains in the Kurdistan Region of Iraq. We determined their deposition age using luminescence dating. From their age and elevation, we calculated uplift rates. We built a geometrical model of the fault zones in the area and determined how fast the slip occurs on these faults based on the uplift rates. Our results indicate that there were less than two millimeter per year of slip on these faults on average during the last 60 thousand years. This motion is a result of the convergence between the Arabian and Eurasian plates. With studies like this we can measure how fast fault blocks move, even if they were not associated with large earthquakes in the recent past. This approach helps to better assess the potential earthquake hazard in the area under investigation.
Key Points
We estimated fault slip rates in the NW Zagros Mountains by luminescence dating of river terraces and structural modeling
There is c. 1.46 mm a−1 slip on the Mountain Front Fault and c. 1.64 mm a−1 slip from detachment folding in the NE part of the Foothill Zone
Crustal thickening and basement thrusting occur in the NE parts of the Foothill Zone and only cover deformation occur in the SW parts
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