Derivation of an analytical model for the slope of a strath terrace created following an upstream propagating wave of incision reveals that for detachment‐limited river incision the exponent on ...channel slope, n, governs terrace tread slope. Terrace elevations can increase upstream (n > 1), downstream (n < 1), or can be horizontal (n = 1). Numerical modeling confirms these results for temporally evolving knickpoint geometries and for incision due to sudden base level fall and an increase in rock uplift rate. Except in the case of bedrock river incision with a slope threshold only exceeded during knickpoint propagation, a terrace created from transient headward incision contains no information about the paleo‐channel gradient. Gradients in rock uplift rate along channels potentially complicate the interpretation of terraces by altering the primary tilt on strath terraces. In particular, monotonic gradients in rock uplift can produce terrace treads that are apparently folded. Because gradients in rock uplift rate are common, where terraces are not longitudinally traceable, care is warranted in terrace correlation. In simple tectonic settings where terraces are longitudinally traceable, the slope of a strath terrace created from headward incision may provide a means of estimating the dependency of river incision rate on channel slope. Terraces in four locations argued to have formed from headward incision are parallel or close to parallel with the active channel, implying a slope exponent on river incision rate that is much greater than one or a threshold slope for incision that is only exceeded during knickpoint propagation.
Key Points
Time‐transgressive terraces constrain incision rate dependence on channel slope
Time‐transgressive terraces do not record the rock uplift field in a simple way
A process of incision with a slope threshold best explains terrace gradients
Like faults, landslides can slip slowly for decades or accelerate catastrophically. However, whereas experimentally derived friction laws provide mechanistically based explanations for similarly ...diverse behavior on faults, little monitoring exists over the temporal and spatial scales required to more clearly illuminate the mechanics of landslide friction. Here we show that displacement of an active slow landslide is accommodated primarily through mm‐scale stick‐slip events that recur on timescales of minutes to hours on asperities that are small (<100 m) relative to the landslide. The frequency of slip events tracks both landslide velocity and pore fluid pressure. The stick‐slip nature demonstrates by itself that slow slip is governed, at least in part, by velocity‐weakening frictional asperities. This observation, in combination with the sensitivity of slow slip to pore fluid pressure and the small relative scale of asperities, suggests similarities between slow slip in landslides and episodic slow slip along faults.
Plain Language Summary
Some landslides creep steadily for years or decades. In others, the creep appears similar, then abruptly transitions to catastrophic failure. Distinguishing these two scenarios is crucial for landslide hazard mitigation. Given the obvious similarities between landslides and faults, some have proposed using models of fault friction to understand and predict landslide failure. In this paper, we show that motion of a slow landslide that has been active for decades occurs through mm‐scale stick‐slip events (analogous to very small earthquakes) that occur more frequently when pore water pressure is higher. These results suggest that slow slip in landslides and episodic slow slip events observed on some faults may be similar, and that a fault mechanics treatment of landslide failure is appropriate.
Key Points
Displacement of an active slow landslide occurs via mm‐scale stick‐slip events that recur on timescales of minutes to hours
The stick‐slip nature demonstrates by itself that slow landslide displacement is governed, at least in part, by velocity‐weakening friction
The small scale of asperities and the sensitivity of stick‐slip to pore pressure suggests similarities to episodic slow fault slip
Persistent motion of slow‐moving landslides has been linked to entrapment of water in slide masses by weak, low‐permeability shear zones at their basal and lateral margins. This so‐called “bathtub ...effect” should have remotely sensible effects on soil moisture and vegetation health. Here we assess this effect at a seasonally active earthflow in northern California with analysis of soil properties and nine years (2009–2018) of multispectral satellite imagery. The shear zone has low hydraulic conductivity, and the earthflow shows elevated water content relative to its surroundings. Spectral indices suggest that the earthflow is perennially wetter, and its vegetation thrives for longer into the dry season as a result. The magnitude of the bathtub effect is correlated with cumulative multiyear rainfall, and its surface expression disappears during the driest year of the 2012–2015 drought. These findings demonstrate a new method for identifying and monitoring mechanical and hydrological interactions that enable persistent landslide motion.
Plain Language Summary
The ability of some landslides to move slowly and persistently for many years without accelerating catastrophically may be linked to entrapment of rain water in slide masses by slow‐draining boundaries at their sides and bottoms. The existence of this so‐called “bathtub effect” can be tested for directly with soil analysis but should also have visible effects on soil moisture and vegetation health that can be measured remotely using satellite imagery. We examined a seasonally active landslide in northern California with slow‐draining boundaries and elevated water content relative to its surroundings. Nine years (2009–2018) of satellite imagery suggest that the earthflow is perennially wetter and its vegetation thrives for longer into the dry season as a result. The magnitude of this effect is correlated with cumulative multiyear rainfall. These findings demonstrate a new method for identifying and monitoring the hydrology and movement of persistent landslides.
Key Points
Persistent movement of earthflows is linked to entrapment of water within weak, low‐permeability shear zones
Excess water stored in earthflows has remotely sensible effects on soil moisture and vegetation health that scale with multiyear rainfall
Predicting rainfall‐induced landslide motion is challenging because shallow groundwater flow is extremely sensitive to the preexisting moisture content in the ground. Here, we use groundwater ...hydrology theory and numerical modeling combined with five years of field monitoring to illustrate how unsaturated groundwater flow processes modulate the seasonal pore water pressure rise and therefore the onset of motion for slow‐moving landslides. The onset of landslide motion at Oak Ridge earthflow in California’s Diablo Range occurs after an abrupt water table rise to near the landslide surface 52–129 days after seasonal rainfall commences. Model results and theory suggest that this abrupt rise occurs from the advection of a nearly saturated wetting front, which marks the leading edge of the integrated downward flux of seasonal rainfall, to the water table. Prior to this abrupt rise, we observe little measured pore water pressure response within the landslide due to rainfall. However, once the wetting front reaches the water table, we observe nearly instantaneous pore water pressure transmission within the landslide body that is accompanied by landslide acceleration. We cast the timescale to reach a critical pore water pressure threshold using a simple mass balance model that considers variable moisture storage with depth and explains the onset of seasonal landslide motion with a rainfall intensity‐duration threshold. Our model shows that the seasonal response time of slow‐moving landslides is controlled by the dry season vadose zone depth rather than the total landslide thickness.
Plain Language Summary
Landslides are often triggered by rainfall events that increase water pressure within rock and soil. A key impediment to predicting landslide motion is that movement of water in the ground is extremely sensitive to preexisting moisture content. Hence, rainfall history exerts a strong control on water movement into the ground. For large landslides, it is commonly assumed that the ground is saturated to the surface, which simplifies the modeling of pressure changes. Here we show, however, that the dynamics of infiltration through the unsaturated ground at the start of the wet season fundamentally control both the style and timing of landslide response to rainfall, which we verify through field monitoring of a large, slow‐moving landslide in the California Coast Range. At the start of the wet season, we observe no pressure response at depth for weeks to months. However, eventually, a sudden pore pressure rise in the landslide body marks the shift to a regime where pressure transmission and landslide acceleration from rainfall is nearly instantaneous. This bimodal behavior, which we can predict by comparing the seasonal rainfall rate to the unsaturated groundwater velocity, is an expected consequence of infiltration into initially unsaturated ground with the material properties observed.
Key Points
Vadose zone properties, especially thickness, modulate the style and timing of landslide pore pressure response to seasonal rainfall
Field monitoring of a large, slow‐moving landslide confirms acceleration in response to rainfall depends strongly on saturation state and hence rainfall history
The onset of landslide motion can be cast as a rainfall intensity‐duration threshold using knowledge of landslide material and hydraulic properties
Arid regions are often characterized by exceptionally high rates of fluvial sediment transport, but the processes responsible for this apparent connection between climate and sediment transport ...remain unclear. We examined decades of continuous flow records and suspended sediment concentrations from 71 rivers across the United States by comparing the suspended sediment rating curve behavior, quantified using power law coefficients and exponents, to an aridity index. Results indicate that higher aridity correlates with both greater overall suspended sediment concentration and lower sensitivity of concentration to changes in discharge, demonstrating that rivers in arid locations on average have greater suspended sediment transport efficiency across most discharges, and achieve high transport rates at a relatively lower discharge than rivers in temperate climates. Furthermore, based on additional analyses of the Normalized Difference Vegetation Index, specific suspended sediment yield, and a hydrograph flashiness index, we attribute the relationships between sediment transport and climate primarily to differences in vegetation density, precipitation, and runoff, variables that all influence both sediment supply and riverbed grain sorting. Finally, we note that the observed contrasts in sediment transport behavior likely represent climate‐driven differences in the magnitude and frequency of sediment supply rather than annual suspended sediment load, which does not depend significantly on climate. This study highlights a critical connection between multiple interrelated climatic factors and sediment transport, an important finding for future hazard mitigation in a changing climate with rapidly shifting vegetation patterns and hydrology.
Plain Language Summary
There is a wide variation in the appearance and behavior of rivers throughout the world, which often relates to how rivers move sediment. For example, the degree of erosion and sediment deposition following large floods does not depend solely on the size of the flood but also on the amount of sediment it contains. To this point, some evidence suggests that rivers in dry climates carry larger volumes of sediment at a given flow than rivers in temperate climates, but this connection has not been sufficiently explored on a large scale. We addressed this scientific gap by examining how sediment concentrations in rivers respond to changes in flow. Our results from dozens of rivers across the United States indicate that streams in more arid climates often carry higher concentrations of sediment at a given flow rate than their temperate counterparts, especially during smaller flood events. This behavior may relate to differences in vegetation density and rainfall patterns, as both of these climate‐dependent factors influence the quantity of sediment entering streams and the organization of sediment on the streambed. These findings reveal an important link between climate and sediment transport, which is important to consider as we prepare for future climate change.
Key Points
Flow records and suspended sediment data from 71 rivers in the US reveal a significant relationship between aridity and sediment transport
In arid climates, suspended sediment concentration is on average higher and less sensitive to changes in discharge than in humid climates
Climate‐dependent factors like vegetation density and runoff variability likely explain observed differences in sediment transport behavior
Seismic signals near rivers are partially composed of the elastic waves generated by bedload particles impacting the river bed. In this study, we explore the relationship between this seismic signal ...and river bedload transport by analyzing high-frequency broadband seismic data from multiple stations along the Chijiawan River in northern Taiwan following the removal of a 13 m check dam. This dam removal provides a natural experiment in which rapid and predictable changes in the river's profile occur, which in turn enables independent constraints on spatial and temporal variation in bedload sediment transport. We compare floods of similar magnitudes with and without bedload transport, and find that the amplitude of seismic shaking produced at a given river stage changes over the course of a single storm when bedload transport is active. Hysteresis in the relationship between bedload transport and river stage is a well-documented phenomenon with multiple known causes. Consequently, previous studies have suggested that hysteresis observed in the seismic amplitude-stage response is the signature of bedload transport. Field evidence and stream profile evolution in this study corroborate that interpretation. We develop a metric (Ψ) for the normalized magnitude of seismic hysteresis during individual floods. This metric appears to scale qualitatively with total bedload transport at each seismic station, indicating a dominance of transport on the rising limbs of both storms. We speculate that hysteresis at this site arises from time-dependent evolution of the bed, for example due to grain packing, mobile armoring, or the temporal lag between stage and bedform growth. Ψ reveals along-stream variations in hysteresis for each storm, with a peak in hysteresis further downstream for the second event. The pattern is consistent with a migrating sediment pulse that is a predicted consequence of the dam removal. Our results indicate that hysteresis in the relationship between seismic wave amplitude and river stage may track sediment transport.
•We compare two floods of similar magnitudes following a dam removal.•Sediment transport is constrained by field observations and bed elevation changes.•We develop a metric Ψ for hysteresis between seismic amplitude and flow depth.•Ψ appears to scale with total bedload transport at each seismic station.•Ψ tracks the downstream migration of a sediment pulse released from behind the dam.
Background
Enzyme replacement therapy (ERT) for infantile-onset Pompe disease has been commercially available for almost 10 years. We report the experience of its use in a cohort treated at three ...specialist lysosomal treatment centres in the UK.
Methods
A retrospective case-note review was performed, with additional data being gathered from two national audits on all such patients treated with ERT. The impact on the outcome of various characteristics, measured just prior to the initiation of ERT (baseline), was evaluated using logistic regression.
Results
Thirty-three patients were identified; 13/29 (45 %) were cross-reactive immunological material (CRIM) negative, and nine were immunomodulated. At baseline assessment, 79 % were in heart failure, 66 % had failure to thrive and 70 % had radiological signs of focal pulmonary collapse. The overall survival rate was 60 %, ventilation-free survival was 40 % and 30 % of patients were ambulatory. Median follow-up of survivors was 4 years, 1.5 months (range 6 months to 13.5 years). As with previous studies, the CRIM status impacted on all outcome measures. However, in this cohort, baseline failure to thrive was related to death and lack of ambulation, and left ventricular dilatation was a risk factor for non-ventilator-free survival.
Conclusion
The outcome of treated patients remains heterogeneous despite attempts at immunomodulation. Failure to thrive at baseline and left ventricular dilation appear to be associated with poorer outcomes.
The rate and timing of hydrologically forced landslides is a complex function of precipitation patterns, material properties, topography, and groundwater hydrology. In the simplest form, however, ...slopes fail when subsurface pore pressure grows large enough to exceed the Mohr‐Coulomb failure criterion. The capacity for pore pressure rise in a landslide is determined in part by the thickness of the unsaturated zone above the water table, which itself is set by weathering patterns that should have predictable patterns across different lithologies. To investigate how this structure affects landslide behavior, we exploit a multi‐year record of precipitation, pore pressure, and velocity from Oak Ridge earthflow, a slow‐moving landslide set in Franciscan mélange, northern California, USA. In conjunction with electrical resistivity tomography and hydraulic conductivity measurements, these data show that Oak Ridge has a thin weathered profile that is comparable in thickness to other mélange landslides in California. We propose that due to the inherently thin vadose zone, mélange landscapes experience an unusually high water table that frequently brings them close to movement; however, the capacity to increase stress is limited by the small amount of dynamic storage available. Instead, excess pore pressure is shed via springs and saturation overland flow once the water table reaches the surface. Linkages between weathering patterns, hydrology, and deformation can explain behavior patterns exhibited by Franciscan mélange earthflows across a large precipitation gradient.
Plain Language Summary
Rainfall often triggers landslides by increasing water pressure below Earth's surface. The resulting landslides vary in speed from slow, persistent landslides that may move a few millimeters a day to rapid, catastrophic landslides that may race hundreds of meters downhill in a few minutes. Developing criteria to predict landslide speed is critical for mitigating the effects of natural hazards. We documented water pressure and landslide velocity over 4 years at a large, slow‐moving landslide in California's Diablo Range to investigate how the subsurface weathered rocks—in a profile extending vertically from the ground surface down to fresh, unweathered bedrock—control landslide movement. We found that our site had a thin weathered profile which limited how much water could be stored in the subsurface and consequently how much water pressure could build up. This in turn may influence the speed of the landslide (∼1 cm/day at the fastest) as excess water was shed via springs at the landslide surface. This water storage limitation may explain why researchers have observed remarkably similar landslide movement patterns in rainier regions of northern California. We discuss how subsurface weathering patterns, dictated largely by rock type, may indirectly influence landslide velocity.
Key Points
Field monitoring of a large earthflow suggests that a thin unsaturated zone caps pore pressure rise
We explore how lithologically controlled weathering patterns influence earthflow hydrology and deformation
Due to subsurface water storage limitations, earthflows across California behave similarly despite large differences in annual rainfall
Alpha-mannosidosis is a rare lysosomal storage disease. Hematopoietic SCT (HSCT) is usually recommended as a therapeutic option though reports are anecdotal to date. This retrospective multi ...institutional analysis describes 17 patients that were diagnosed at a median of 2.5 (1.1-23) years and underwent HSCT at a median of 3.6 (1.3-23.1) years. In all, 15 patients are alive (88%) after a median follow-up of 5.5 (2.1-12.6) years. Two patients died within the first 5 months after HSCT. Of the survivors, two developed severe acute GvHD (>=grade II) and six developed chronic GvHD. Three patients required re-transplantation because of graft failure. All 15 showed stable engraftment. The extent of the patients' developmental delay before HSCT varied over a wide range. After HSCT, patients made developmental progress, although normal development was not achieved. Hearing ability improved in some, but not in all patients. We conclude that HSCT is a feasible therapeutic option that may promote mental development in alpha-mannosidosis.
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