Surface melt forces summertime ice-flow accelerations on glaciers and ice sheets. Here, we show that large meltwater-forced accelerations also occur in winter in Greenland. We document supraglacial lakes (SGLs) draining in cascades at unusually high elevation, causing an expansive flow acceleration over a ~5200 km2 region during winter. The 3-component interferometric surface velocity field and decomposition modeling reveals the underlying flood propagation with unprecedented detail as it traveled over 160 km from the drainage site to the margin, providing novel constraints on subglacial water pathways, drainage morphology, and links with basal sliding. The triggering SGLs continuously grew over 40 years and suddenly released decades of stored meltwater into regions of the bed never previously forced, demonstrating surface melt can impact dynamics well beyond its production. We show these events are common and thus their cumulative impact on dynamics should be further evaluated.

A document by Sean James Trim. Click on the document to view its contents.

High-quality digital rock images are essential for subsequent high-precision numerical simulations. But limited by the imaging capability of computed tomography (CT), high resolution digital rock images with wide imaging field of view (FOV) cannot be acquired simultaneously. To cope with this constraint, we propose a novel Multi Attention Super-Resolution Neural Network (MASR) that enhances the resolution of images with wide FOV. Considering that textures and edges are more crucial in digital rocks, MASR introduces the component attention mechanism of Component Divide-and-Conquer Super-Resolution (CDCSR) model. By redesigning the hourglass network with spatial and channel attention mechanisms, proposing a spatial attention-based mask module, and optimizing the component attention mask calculation process, MASR delivers higher information utilization with fewer parameters and faster training than CDCSR. And we optimize the depth of MASR to trade off speed and super-resolution quality. Furthermore, we retrained several state-of-the-art models. Through quantitative evaluations and qualitative visualizations, it is verified that MASR can recover sharper edges while removing noise, and obtain digital rock images with superior quality and reliability. The pixelwise relative errors of MASR reconstructions are reduced by 15% to 26% over bicubic interpolation method. Our codes are publicly available at https://github.com/MHDXing/MASR-for-Digital-Rock-Images.

During hurricane season, the U.S. Geological Survey (USGS) forecasts the probability of coastal change prior to named storm landfall. Forecasts both quantify potential storm effects on the sandy coastlines and test our understanding of the drivers of coastal change. The forecasts can also be used to aid emergency response and management decisions in real-time. This study analyzed the skill of three USGS forecasts of coastal change, defined as the probability of collision, overwash, and inundation (PCOI) along the approximately 250 km of Louisiana coast from Hurricanes Laura, Delta, and Zeta in 2020. To test forecast skill, forecasts were compared with coastal changes identified in post-storm emergency response aerial imagery. Forecasts accurately identified areas where overwash and inundation were likely (true positive forecast ratios >0.75). Forecasts also produced an overly conservative estimation of overwash and inundation (false positive forecast ratios 0.56). High false positive forecast ratios for overwash and inundation may be the result of an overestimate in forecast extreme water levels.

Pulsing seepages of native hydrogen (H2) have been observed at the surface on several emitting structures. It is still unclear whether this H2 pulsed flux is controlled by deep migration processes, atmosphere/near-surface interactions or by bacterial fermentation. Here, we investigate mechanisms that may trigger pulsating fluid migration at depth and the resulting periodicity. We set up a numerical model to simulate the migration of a deep constant fluid flow. To verify the model’s formulation to solve complex fluid flows, we first simulate the morphology and amplitude of 2D thermal anomalies induced by buoyancy-driven water flow within a fault zone. Then, we simulate the H2 gas flow along a 1-km draining fault, crosscut by a lower permeable rock layer to investigate the conditions for which a pulsing system is generated from a deep control. For a constant incoming flow of H2 at depth, persistent bursts at the surface only appear in the model if: (I) a permeability with an effective-stress dependency is used, (II) a strong contrast of permeability exists between the different zones, (III) a sufficiently high value of the initial effective stress state at the base of the low permeable layer exists, and (IV) the incoming and continuous fluid flow of H2 at depth remains low enough so that the overpressure does not “open” instantly the low permeability layer. The typical periodicity expected for this type of valve-fault control of H2 pulses at the surface is at a time scale of the order of 100 to 300 days.

The Christiana-Santorini-Kolumbo volcanic field in the southern Aegean Sea is one of the most hazardous volcanic regions in the world. Forming the northeastern part of this volcanic field, the Kolumbo Volcanic Chain (KVC) comprises more than 20 submarine volcanic cones. However, due to their inaccessibility, little is known about the spatio-temporal evolution and tectonic control of these submarine volcanoes and their link to the volcanic plumbing system of Santorini. In this study, we use multichannel reflection seismic imaging to study the internal architecture of the KVC and its link to Santorini. We show that the KVC evolved during two episodes, which initiated at ~1 Ma with the formation of mainly effusive volcanic edifices along a NE-SW trending zone. The cones of the second episode were formed mainly by submarine explosive eruptions between 0.7 and 0.3 Ma and partly developed on top of volcanic edifices from the first episode. We identify two prominent normal faults that underlie and continue the two main trends of the KVC, indicating a direct link between tectonics and volcanism. In addition, we reveal several buried volcanic centers and a distinct volcanic ridge connecting the KVC with Santorini, suggesting a connection between the two volcanic centers in the past. This connection was interrupted by a major tectonic event and, as a result, the two volcanic systems now have separate, largely independent plumbing systems despite their proximity.

The petrophysical properties of rocks are a strong and an effective indicator of the extent of the susceptibility of the rocks themselves to building and construction operations above and above them. As these tests are conclusive evidence that such rocks will not have a landslide or semi-collapse, and from here we focus in this scientific proposal paper on them practically in a manner of step-by-step, to make it easier for the specialist to understand the well. These properties are an assistant to the geologist and civil engineer in the field of work, as they work to provide actual numbers of the rocks, or in other words, the process of converting rocks into mere numbers that speak for themselves effectively and feasibly, such properties are sufficient.

There are now more interferograms being generated from global satellite radar datasets than can be assessed by hand. The reliable, automatic detection of true displacement from these data is therefore critical, both for monitoring deformation related to geohazards and understanding solid earth processes. We discuss improvements to an unsupervised, event agnostic method for automatically detecting deformation in unwrapped interferograms. We use an anomaly detection framework that recognises any deformation as “anomalies” by learning the ‘typical’ spatio-temporal pattern of atmospheric and other noise in sequences of interferograms. Here, we present developments to our prototype model, ALADDIn (Autoencoder-LSTM based Anomaly Detector of Deformation in InSAR) using (1) a self-attention training technique to exploit redundancy in interferogram networks to capture the temporal structure of signals and (2) the addition of synthetic data for training. We evaluate the impact of these developments using two geophysical scenarios: (1) the detection of the same M_w 5.7 earthquake used to test our original model (20.03.2019, south-west Turkey), (2) the persistent uplift of Domoyu volcano (17.05.2017 to 14.12.2018, Argentina). We make a quantitative evaluation of the performance of our method using synthetic test data and find that for peak displacements exceeding a few cm and of length-scale greater than a few hundred metres, overall detection accuracy is 80 to 90%.

Tidal salt marshes are widespread along the World’s coasts, and are ecologically and economically important as they provide several valuable ecosystem services. In particular, their significant primary production, coupled with sustained vertical accretion rates, enables marshes to sequester and store large amounts of organic carbon and makes them one of the most carbon-rich ecosystems on Earth. Organic carbon accumulation results from the balance between inputs, i.e. organic matter produced by local plants or imported, and outputs through decomposition and erosion. Additionally, organic matter deposition actively contributes to marsh vertical accretion, thus critically affecting the resilience of marsh ecosystems to rising relative sea levels. A better understanding of organic-matter dynamics in salt marshes is key to address salt-marsh conservation issues and to elucidate marsh importance within the global carbon cycle. Toward this goal, we empirically derived rates of organic matter decomposition by burying 712 commercially available tea bags at different marshes in the microtidal Venice Lagoon (Italy), and by analyzing them following the Tea Bag Index protocol. We find values of the decomposition rate (k) and stabilization factor (S) equal to 0.012±0.003 day-1 and 0.15±0.063, respectively. Water temperature critically affects organic matter decomposition, enhancing decomposition rates by 8% per °C on average. We argue that, at least in the short term, the amount of undecomposed organic matter that actively contributes to carbon sequestration and marsh vertical accretion strongly depends on the initial organic matter quality, which is a function of marsh and vegetation characteristics.

An intense earthquake swarm is occurring in the crust of the northeastern Noto Peninsula, Japan. Fluid movement related to volcanic activity is often involved in earthquake swarms in the crust, but the last volcanic activity in this area occurred in the middle Miocene (15.6 Ma), and no volcanic activity has occurred since then. In this study, we investigated the cause of this earthquake swarm using spatiotemporal variation of earthquake hypocenters and seismic reflectors. Hypocenter relocation revealed that earthquakes moved from deep to shallow areas via many planes, similar to earthquake swarms in volcanic regions. The strongest M5.4 earthquake initiated near the migration front of the hypocenters. Moreover, it ruptured the seismic gap between the two different clusters. The initiation of this earthquake swarm occurred at a locally deep depth (z = ~17 km), and we found a distinctive S-wave reflector, suggesting a fluid source in the immediate vicinity. The local hypocenter distribution revealed a characteristic ring-like structure similar to the ring dike that forms just above the magma reservoir and is associated with caldera collapse and/or magma intrusion. These observations suggest that the current seismic activity was impacted by fluids related to ancient or present hidden magmatic activity, although no volcanic activity was reported. Significant crustal deformation was observed during this earthquake swarm, which may also be related to fluid movement and contribute to earthquake occurrences. A seismic gap zone in the center of the swarm region may represent an area with aseismic deformation.

While Hg in sediments is increasingly used as a proxy for deep-time volcanic activity, the behaviour of Hg in OM-rich sediments as they undergo thermal maturation is not well understood. In this study, we evaluate the effects of thermal maturation on sedimentary Hg contents and, thereby, the impact of thermal maturity on the use of the Hg/TOC proxy for large igneous province (LIP) volcanism. We investigate three cores (marine organic matter) with different levels of thermal maturity in lowermost Toarcian sediments (Posidonienschiefer) from the Lower Saxony Basin in Germany. We present Hg content, bulk organic geochemistry, and total sulfur in three cores with different levels of thermal maturity. The comparison of Hg data between the three cores indicates that Hg content in the mature/overmature sediments have increased > 2-fold compared to Hg in the immature deposits. Although difficult to confirm with the present data, we speculate that redistribution within the sedimentary sequence caused by the mobility and volatility of the element under relatively high temperatures may have contributed to Hg enrichment in distinct stratigraphic levels of the mature cores. Regardless of the exact mechanism, elevated Hg content together with organic-carbon loss by thermal maturation exaggerate the value of Hg/TOC in mature sediments, suggesting that thermal effects have to be considered when using TOC-normalised Hg as a proxy for far-field volcanic activity.

Variations in fault maturity have intermittently been invoked to explain variations in some seismological observations for large earthquakes. However, the lack of a unified geological definition of fault maturity makes quantitative assessment of its importance difficult. We evaluate the degree of empirical correlation between field measurements indicative of fault zone maturity and remotely measured seismological source parameters of 34 large shallow strike-slip events. Metrics based on fault segmentation, such as number of primary rupture segments and surface rupture azimuth, correlate best with seismic source attributes and the correlations with cumulative fault slip are somewhat weaker. Average rupture velocity shows the strongest correlation with metrics of maturity, followed by relative aftershock productivity. Mature faults have relatively lower aftershock productivity and higher rupture velocity. A more complex relation is found with moment-scaled radiated energy. There appears to be distinct behavior of very immature events with no prior mapped fault and < 1 km cumulative slip, which radiate modest seismic energy, while moderately mature faults have events with higher moment-scaled radiated energy and very mature faults with increasing cumulative slip tend to have events with reducing moment-scaled radiated energy. We also explore qualitative and composite assessments of maturity and arrive at similar trends. This empirical approach establishes that there are relationships between remote seismological observations and fault system maturity that can help to understand variations in seismic hazard among different fault environments and to assess the relative maturity of blind fault systems for which direct observations of maturity are very limited.

The presence of the Etendeka flood basalts in northwestern Namibia is taken as evidence for the activity of the Tristan da Cunha mantle plume during the breakup process between Africa and South America. We investigate seismic anisotropy beneath NW Namibia by splitting analysis of core-refracted teleseismic shear waves (XKS phases) to probe mantle flow and lithospheric deformation related to the tectonic history of the region. The waveform data were obtained from 34 onshore stations and 12 Ocean Bottom Seismometers. The results presented here are from joint splitting analysis of multiple XKS phases. The majority of the fast polarization directions (FPDs) exhibit an NE-SW orientation consistent with a model of large-scale mantle flow due to the NE motion of the African plate. No evidence for a direct effect of the mantle plume is observed. In the northern part, we observe NNW-SSE-oriented FPDs that is likely caused by shallow lithospheric structures.

The Ethiopia-Yemen flood basalts are spatially zoned with progressively lower TiO2 lavas from near the Afar depression toward the margins. The timing and rate of emplacement of low TiO2 (LT) lavas are poorly known compared with the ultra-high TiO2 (HT2) lavas. We measured two high-precision 40Ar/39Ar ages of 29.63 ± 0.14 and 30.02 ± 0.22 Ma (2σ) from basalts of the 2-km-thick LT lava sequence at the Afar plume head margin. Using our eruption age model constructed from our and previous 40Ar/39Ar ages with the paleomagnetic directions, we estimate that the LT lava eruption continued over Chrons C12r-C12n-C11r. The eruption of the plume head margin started earlier than the plume head axis emplacement in C12n. Also, the eruption rate was low at the margin, high at the axis. We estimate that the LT lavas are induced by the edge-driven convection, the result of a plume-lithosphere interaction, not a plume head.

A major challenge in the inversion of subsurface parameters is the ill-posedness issue caused by the inherent subsurface complexities and the generally spatially sparse data. Appropriate simplifications of inversion models are thus necessary to make the inversion process tractable and meanwhile preserve the predictive ability of the inversion results. In the present study, we investigate the effect of model complexity on the inversion of fracture aperture distribution as well as the prediction of long-term thermal performance in a field-scale single-fracture EGS model. Principal component analysis (PCA) was used to map the original cell-based aperture field to a low-dimensional latent space. The complexity of the inversion model was quantitatively represented by the percentage of total variance in the original aperture fields preserved by the latent space. Tracer, pressure and flow rate data were used to invert for fracture aperture through an ensemble-based inversion method, and the inferred aperture field was then used to predict thermal performance. We found that an over-simplified aperture model could not reproduce the inversion data and the predicted thermal response was biased. A complex aperture model could reproduce the data but the thermal prediction showed significant uncertainty. A model with moderate complexity, although not resolving many fine features in the “true” aperture field, successfully matched the data and predicted the long-term thermal behavior. The results provide important insights into the selection of model complexity for effective subsurface reservoir inversion and prediction.

The way Alpine rivers mobilize, convey and store coarse material during high-magnitude events is poorly understood, notably because it is difficult to obtain measurements of bedload transport at the watershed scale. Seismic sensor data, evaluated with appropriate seismic physical models, can provide that missing link by yielding absolute time-series of bedload transport. Low cost and ease of installation allows for networks of sensors to be deployed, providing continuous, watershed-scale insights into bedload transport dynamics. Here, we deploy a network of 24 seismic sensors to capture the motion of coarse material in a 13.4 km2 Alpine watershed during a high-magnitude bedload transport event. First, we benchmark the seismic inversion routine with an independent time-series obtained with a calibrated acoustic system. Then, we apply the procedure to the other seismic sensors across the watershed. Spatially-distributed time-series of bedload transport reveal a relative inefficiency of Alpine watersheds in evacuating coarse material, even during a relatively infrequent high-magnitude bedload transport event. Significant inputs measured for some tributaries were rapidly attenuated as the main river crossed less hydraulically-efficient reaches, and only a comparatively negligible proportion of the total amount of material mobilized in the watershed was exported at the outlet. Cross-correlation analysis of the time-series suggests that a faster moving water wave (re-)mobilizes local material and bedload is expected to move slower, and over shorter distances. Multiple periods of competent flows are likely to be necessary to evacuate the coarse material produced throughout the watershed during individual source-mobilizing bedload transport events.

Extraction of sulfide liquid from partially molten mantle is vital to elucidate the cycling of metal and sulfur elements between different geochemical circles but has not been investigated systematically. Using the reaction couple method of laboratory experiments and theoretical calculations, this study documents systematical variations in lithologies and compositions of silicate minerals and melts, which are approximately consistent with the results of thermodynamically-constrained model. During melt-peridotite reaction, dissolution of olivine and precipitation of new orthopyroxene produce an orthopyroxene-rich layer between melt source and peridotite. With increasing reaction degree, more melt is infiltrated into and reacts with upper peridotite, which potentially enhances the concomitant upward transport of dense sulfide droplets. Theoretical analyses suggest an energetical focused melt flow with a high velocity (~ 170.9 μm/h) around sulfide droplet through pore throat. In this energic melt flow, we, for the first time, observed the mechanical coalescence of sulfide droplets, and produced drag force was likely driving upward entrainment of fine μm-scale sulfide. For coarse sulfide droplets whose sizes are larger than the pore throat in partially molten peridotite, their entrainment through narrow constrictions in crystal framework seems to be physically possible only when high-degree melt-peridotite reaction drives high porosity of peridotite and some channelized melt flows with extremely high velocity. Hence, melt-rock reaction could drive and enhance upward entrainment of μm- to mm-scale sulfide in the partially molten mantle, potentially contributing to the fertilization of the sub-continental lithospheric mantle and the endowment of metal-bearing sulfide for the formation of magmatic sulfide deposits.

Benthic carbonates in perennially ice-covered Lake Fryxell (Mc-Murdo Dry Valleys, Antarctica) precipitated from pore waters in microbial mats as calcite rhombs, acicular botryoids and interfering bundles. Carbonates span the pronounced Lake Fryxell oxycline; variations in carbonate-associated manganese and iron concentrations are consistent with local oxycline conditions and seasonal fluctuations in pore water oxygenation. Precipitation is most abundant in shallow oxic waters, but extended through the oxycline during a discrete episode lasting multiple years, as evidenced by patterns of cathodoluminescence consistent with predicted seasonal changes in redox modulating dissolved manganese and iron concentrations. Carbonates did not precipitate in isotopic equilibrium with the water column, and are enriched in 18 O relative to predicted equilibrium values. Carbonate layer 18 O values vary by >20‰ at the mm-scale, suggesting precipitation was driven by mixing of isotopically heterogeneous fluids in the mat pore waters. Correlation of carbonate geochemistry and mat morphology with historical observations indicates that precipitation postdates recent lake level rise. Further investigation of the physical and geochemical carbonate proxies from Lake Fryxell and other ice-covered lakes in the Dry Valleys promises to provide a valuable framework for interpreting Antarctic carbonates as records of modern and ancient climate, Antarctic biogeochemical and hydrological systems, and the drivers of carbonate precipitation at polar climate extremes.

Bagana is a remote, highly active volcano, located on Bougainville Island in southeastern Papua New Guinea. The volcano has exhibited sustained and prodigious sulfur dioxide gas emissions in recent decades, accompanied by frequent episodes of lava extrusion. The remote location of Bagana and its persistent activity have made it a valuable case study for satellite observations of active volcanism. This remoteness has also left many features of Bagana relatively unexplored. Here, we present the first measurements of volcanic gas composition, achieved by unoccupied aerial system (UAS) flights through the volcano’s summit plume, and a payload comprising a miniaturised MultiGAS. We combine our measurements of molar CO2/SO2 ratio in the plume with coincident remote sensing measurements (ground- and satellite-based) of SO2 emission rate, to compute the first estimate of CO2 flux at Bagana. We report low SO2 and CO2 fluxes at Bagana from our fieldwork in September 2019, ~320 ± 76 td-1 and ~320 ± 84 td-1 respectively, which we attribute to the volcano’s low level of activity at the time of our visit. We use satellite observations to demonstrate that Bagana’s activity and emissions behaviour are highly variable and advance the argument that such variability is likely an inherent feature of many volcanoes worldwide and as yet is inadequately captured by our extant volcanic gas inventories, which are often biased to sporadic measurements. We argue that there is great value in the use of UAS combined with MultiGAS-type instruments for remote monitoring of gas emissions from other inaccessible volcanoes.

Slow, aseismic slip plays a crucial role in the initiation, propagation and arrest of large earthquakes along active faults. In addition, aseismic slip controls the budget of elastic strain in the crust, hence the amount of energy available for upcoming earthquakes. The conditions for slow slip include specific material properties of the fault zone, pore fluid pressure and geometrical complexities of the fault plane. Fine scale descriptions of aseismic slip at the surface and at depth are key to determine the factors controlling the occurrence of slow, aseismic versus rapid, seismic fault slip. We focus on the spatial and temporal distribution of aseismic slip along the North Anatolian Fault, the plate boundary accommodating the 2 cm/yr of relative motion between Anatolia and Eurasia. Along the eastern termination of the rupture trace of the 1944 M7.3 Bolu-Gerede earthquake lies a segment that slips aseismically since at least the 1950’s. We use Sentinel 1 time series of displacement and GNSS data to provide a spatio-temporal description of the kinematics of fault slip. We show that aseismic slip observed at the surface is coincident with a shallow locking depth and that slow slip events with a return period of 2.5 years are restricted to a specific section of the fault. In the light of historical measurements, we discuss potential rheological implications of our results and propose a simple alternative model to explain the local occurrence of shallow aseismic slip at this location.

Mass recycling from subduction to magmatic extrusion shapes our habitable environment and Earth’s interior. Subducted igneous crust may form pyroxenites before participating magmatism, but the deep journey of associated carbonates remains unclear. Here we report new Mg-isotope data for ~89 to 81 Ma basaltic rocks in Langshan area, central Asia (δ26Mg = -0.391 to -0.513 ‰) with a synthesis for post-110 Ma basalts across eastern Asian continent. The merged low-δ26Mg basaltic province normally interpreted as derivations from carbonated sources paradoxically displays geochemical signatures (low Ca/Al and high K2O contents) resembling partial melts of uncarbonated sources. Negative correlations of δ26Mg vs TiO2 and FCKANTMS, the proxy of pyroxenitic melts, and adiabatic melting modeling suggest presence of Mg-isotopically light source pyroxenites transformed from decarbonated altered oceanic crust. This may explain ubiquitous pyroxenitic contributions in many low-δ26Mg basaltic suites and has significant implication for deep carbon cycling.

The Main Ethiopian Rift (MER) is accompanied by extensive volcanism and the formation of geothermal systems, both having an imminent impact on lives of millions of local inhabitants. Although previous studies from the region found evidence that asthenospheric upwelling and associated decompression melting provide melt to magmatic mush systems that feed the tectono-volcanic segments in the rift valley, no geophysical model imaged these regional and local scale transcrustal structures within a single comprehensive 3-D model. To fill this gap, we combined regional and local magnetotelluric data sets to obtain the first multi-scale 3-D electrical conductivity model of the central MER. The model clearly images a magma ponding zone with up to 7 vol.% melt at the base of the crust in the western part of the rift, its connection to Aluto volcano via a tectonically controlled transcrustal magmatic mush system and how the melt, stored at shallow crustal depths, supplies heat for Aluto’s geothermal system. Our model provides evidence that different volcano-tectonic lineaments in the rift valley share a common melt source, which has been debated in the past. The presented multi-scale model provides new constraints as well as geologic insights into the melt distribution below the rift and will facilitate future geothermal developments and volcanic hazard assessments in the MER.

Dynamic stress evolution during earthquake rupture contains information of fault frictional behavior that governs dynamic rupture propagation. Most of earthquake stress drop and evolution studies are based on kinematic slip inversions. Several dynamic inversion methods in the literature require dynamic rupture modeling that makes them cumbersome with limited applicability. In this study, we develop a fault-stress model of earthquake sources in the framework of the representation theorem. We then propose a dynamic stress inversion method based on the fault-stress model to directly invert for dynamic stress evolution process on the fault plane by fitting seismic data. In this inversion method, we calculate numerical Green’s function once only, using an explicit finite element method EQdyna with a unit change of shear or normal stress on each subfault patch. A linear least-squares procedure is used to invert for stress evolution history on the fault. To stabilize the inversion process, we apply several constraints including zero normal slip (no separation or penetration of the fault), non-negative shear slip, and moment constraint. The method performs well and reliably on a synthetic model, a checkerboard model and the 2016 Mw 5.0 Cushing (Oklahoma) earthquake. The proposed fault-stress model of earthquake sources with inversion techniques such as one presented in this study provides a new paradigm for earthquake source studies using seismic data, with a potential of deciphering more physics from seismic recordings of earthquakes.

During the last ice age, the western United States was covered by large lakes, sustained partly by higher levels of precipitation. Increased rainfall was driven by the atmospheric circulation associated with the presence of large North American ice sheets, yet Pleistocene lakes generally reached their highstands not at glacial maximum but during deglaciation. Prior modeling studies, however, showed nearly monotonic drying since the last glacial maximum. Here I show that iTraCE, a new transient climate simulation of the last deglaciation, reproduces a robust peak in winter rainfall over the Great Basin near 16 ka. The simulated peak is driven by a transient strengthening and southward shift of the midlatitude jet. While meltwater forcing is an important driver of changes to the North Pacific Jet, changing orbital conditions and rising atmospheric CO2 also shift the jet south and contribute to wetter conditions over the western US during deglaciation.