Recent ucla_epss_rw items

Role of tectonic rock damage in erosional processes: A global analysis.

Wed, 3 Jun 2026 00:00:00 +0000

The role of active faults in driving rock uplift is well known, but their influence on rock damage and erosional efficiency remains unclear globally. Using 1744 beryllium-10 (¹⁰Be)-derived erosion rates, we show that erosional efficiency is elevated on average within ~15 kilometers of a fault trace and decreases with distance, up to ~100 kilometers. Reverse faults and those longer than 140 kilometers show the strongest effects. This length scale of decay suggests that tectonic damage extends beyond fault-core pulverization on primary faults, possibly including fracturing or grain-to-grain contact weakening due to seismic shaking and distributed deformation on complex fault networks. Machine learning identified fault proximity as a dominant control on erosional efficiency, exceeding precipitation and lithology, particularly when a measure of seismic shaking is included. These findings indicate that active tectonics are associated with erosion not only through uplift...

Polycyclic Metamorphism, Exhumation, and Recycling of Subduction Complex Rocks, Cedros Island, Baja California

Mon, 1 Jun 2026 00:00:00 +0000

Abstract High‐pressure rocks from subduction complexes are key records of the physical and chemical processes that operate on the subduction interface, but interpretation of these records requires accurate structural understanding of where they formed in the subduction zone and the mechanisms by which they were exhumed. We present new geologic mapping, outcrop‐scale observations, and geochronology from subduction‐zone assemblages at Punta Prieta Ridge on Cedros Island, Baja California (Mexico), to investigate the history of subduction, exhumation, and structural assembly of these rocks. The rocks of Punta Prieta Ridge are exposed in the footwalls of high‐ and low‐angle normal faults that carry Cretaceous forearc basin strata and attenuated mantle sections of the Cedros Island Ophiolite in their hangingwalls. The footwall rocks are subduction‐zone assemblages organized into distinct nappes that decrease in metamorphic grade and degree of strain structurally downward. Garnet‐amphibolite...

Magnetohydrodynamic control of differential rotation and dynamo transitions: rise of the local magnetic Rossby number

Wed, 22 Apr 2026 00:00:00 +0000

ABSTRACT We investigate how the strength of the Lorentz force alters stellar convection zone dynamics in a suite of buoyancy-dominated, 3D, spherical shell convective dynamo models. This is done by varying only the fluid’s electrical conductivity via the non-dimensional magnetic Prandtl number, $Pm$. Because the strength of the dynamo magnetic field and the Lorentz force scale with $Pm$, it is found that the fluid motions and mode of dynamo generation differ across the $0.25 \le Pm \le 10$ range investigated here. For example, we show that strong magnetohydrodynamic effects cause a fundamental change in the surface zonal flows: differential rotation switches from solar-like with prograde equatorial zonal flow for larger electrical conductivities (i.e. stronger dynamo magnetic field) to an anti-solar differential rotation with retrograde equatorial zonal flow at lower electrical conductivities (i.e. weaker magnetic field). This study shows that the value of electrical conductivity...

Tabletop Atmospheric Rivers

Wed, 22 Apr 2026 00:00:00 +0000

Tabletop Atmospheric Rivers

Transition from wall modes to multimodality in liquid gallium magnetoconvection

Wed, 22 Apr 2026 00:00:00 +0000

Coupled laboratory-numerical experiments of Rayleigh-Bénard convection in liquid gallium subject to a vertical magnetic field are presented. The experiments are carried out in two cylindrical containers with diameter-to-height aspect ratio Γ=1.0 and 2.0 at varying thermal forcing (Rayleigh numbers 105≲Ra≲108) and magnetic field strength (Chandrasekhar numbers 0≲Ch≲3×105). Laboratory measurements and numerical simulations confirm that magnetoconvection in our finite cylindrical tanks onsets via nondrifting wall-attached modes, in good agreement with asymptotic predictions for a semi-infinite domain. With increasing supercriticality, the experimental and numerical thermal measurements and the numerical velocity data reveal transitions between wall mode states with different azimuthal mode numbers and between wall-dominated convection to wall and interior multimodality. These transitions are also reflected in the heat transfer data, which combined with previous studies connect onset...

Eddy-driven Zonal Jet Flows in the Laboratory

Wed, 22 Apr 2026 00:00:00 +0000

Zonal jets are a ubiquitous feature of the circulation of planetary atmospheres, oceans and interiors. Many of the dynamical mechanisms that lead to the formation and evolution of such jets can be reproduced and studied in laboratory experiments, which have proved to be important sources of insight for understanding the nature of planetary jets. Here we introduce some of the key concepts underlying the production and maintenance of patterns of zonal jets in rotating and/or stratified flows. We then review a broad range of laboratory experiments that have helped to test and verify many of the dynamical mechanisms proposed to interpret geophysical jets involving the interaction of eddies and zonal flows. Laboratory experiments continue to have an important role to play in elucidating a quantitative understanding of zonal jets and their interactions with other aspects of planetary circulation systems.

Observed Changes in Mars Soil Thermophysical Properties Due to Rover Wheel Interactions: MER Mini-TES Observations and Applications to Upcoming Lunar Rover Exploration

Wed, 8 Apr 2026 00:00:00 +0000

Abstract: The Mars Exploration Rovers (MER) Spirit and Opportunity each carried a thermal infrared (IR) instrument called the Miniature Thermal Emission Spectrometer (Mini-TES) used to determine rock and soil composition and thermophysical properties. In this work, we investigate how rover operations affect soil thermophysical properties by analyzing Spirit Mini-TES observations of both disturbed and undisturbed soils in Gusev crater. Observations of one location disturbed by rover wheels and two nearby undisturbed locations were acquired multiple times per sol over sols 172–174 and were compared with a thermal model to derive quantitative thermal inertia. We found that the disturbed soils have higher average thermal inertia and lower albedos than nearby undisturbed soils. These results are consistent with an increase in apparent particle size caused by the fine particulate, high-albedo airfall dust layer that coats all undisturbed surfaces in Gusev crater...

Melting of MgSiO3 determined by machine learning potentials

Fri, 30 Jan 2026 00:00:00 +0000

Melting in the deep rocky portions of planets is important for understanding the thermal evolution of these bodies and the possible generation of magnetic fields in their underlying metallic cores. But the melting temperature of silicates is poorly constrained at the pressures expected in super-Earth exoplanets, the most abundant type of planets in the galaxy. Here, we propose an iterative learning scheme that combines enhanced sampling, feature selection, and deep learning, and develop a unified machine learning potential of ab initio quality valid over a wide pressure-temperature range to determine the melting temperature of MgSiO3. The melting temperature of the high-pressure, post-perovskite phase, important for super-Earths, increases more rapidly with increasing pressure than that of the lower pressure perovskite phase, stable at the base of Earth's mantle. The volume of the liquid closely approaches that of the solid phases at the highest pressure of our study. Our computed...

Quantifying the impacts of rainfall and evaporation on Lake Bonneville

Tue, 6 Jan 2026 00:00:00 +0000

Improved understanding of hydroclimatic drivers in water-stressed regions enables more accurate forecasting of future climate change impacts. Lake Bonneville was the largest Pleistocene lake in western North America, with a maximum surface area of ~52,000 km², before shrinking markedly to become the modern Great Salt Lake. After more than a century of study, the balance between enhanced precipitation and reduced evaporation as drivers of lake growth continues to be debated. Multiple studies identify precipitation as the main factor associated with the highest lake levels, but most proxies provide an estimate of net evaporation and cannot independently resolve precipitation from evaporation. Therefore, factors associated with lake size, growth, and retreat remain uncertain. This study uses the thermodynamically based carbonate clumped isotope geothermometer to estimate temperature, evaporation, and precipitation at Lake Bonneville from 23 to 16 thousand years ago (ka)....

Evaluating the Shinumo-Sespe drainage connection: Arguments against the “old” (70–17 Ma) Grand Canyon models for Colorado Plateau drainage evolution