Subglacial water modulates glacier velocity across a wide range of space and time scales by influencing friction at the glacier bed. Observations show ice acceleration due to supraglacial lake drainage and water draining through moulins, where both configurations involve water inputs to the bed. Here we consider the reverse: water extraction from the subglacial hydrologic system, which is a proposed intervention method intended to slow the flow of glaciers and reduce the associated sea-level rise. Removing subglacial water results in different dynamics than injecting water, and we hypothesize that understanding these processes will allow for improved characterization of the physics of subglacial hydrology. We set up these model experiments in the Subglacial Hydrology And Kinetic, Transient Interactions (SHAKTI) model coupled with the Ice-sheet and Sea-level System Model (ISSM). By analyzing the problem of an isolated borehole in a background pressure field to determine the region of extraction influence, we find an approximate analytical solution which shows that the water pressure returns to the background value approximately as a logarithm with distance. The benefit of the analytical solution is that the dependence of uncertain parameters is clear and may be used alongside data to constrain subglacial hydrology models. We find good agreement between this analytical result and numerical SHAKTI simulations. Using the coupled SHAKTI-ISSM model, we perform transient model experiments on Helheim Glacier, Greenland and Thwaites Glacier, Antarctica, to determine the effects of water extraction on glacier velocity. With continuous pumping, we simulate a velocity decrease on the order of 1 %, which depends on the site location. The response time to pumping initiation and the recovery time, following cessation, scale according to effective pressure, with typical times on the order of hours to days. These results demonstrate that water extraction is a method of probing the subglacial hydrologic system to better constrain the uncertain physics, and that further research is required to assess its effectiveness as an intervention method.
", "doi": "10.5194/tc-20-2659-2026", "issn": "1994-0424", "publisher": "European Geosciences Union", "publication": "The Cryosphere", "publication_date": "2026-05-08", "series_number": "5", "volume": "20", "issue": "5", "pages": "2659-2680" }, { "id": "authors:v9j9f-9z979", "collection": "authors", "collection_id": "v9j9f-9z979", "cite_using_url": "https://authors.library.caltech.edu/records/v9j9f-9z979", "type": "article", "title": "Rates of Sea-Level Rise Are Highly Sensitive to Ice Viscosity Parameters in Model Benchmarks", "author": [ { "family_name": "Martin", "given_name": "D. F.", "orcid": "0000-0003-4488-2538" }, { "family_name": "Kachuck", "given_name": "S. B.", "orcid": "0000-0002-8708-8425" }, { "family_name": "Trevers", "given_name": "M.", "orcid": "0000-0003-4199-3945" }, { "family_name": "Millstein", "given_name": "J. D.", "orcid": "0000-0002-8407-5485" }, { "family_name": "Cornford", "given_name": "S. L." }, { "family_name": "Minchew", "given_name": "B. M.", "orcid": "0000-0002-5991-3926", "clpid": "Minchew-B-M" } ], "abstract": "Glacier flow plays a major role in current and future rates of globally averaged sea-level rise. The viscosity of glacial ice, controlling the rate of flow, decreases as stress increases and is highly sensitive to the value of the stress exponent, n, in the constitutive equation for viscous flow. Glaciologists and climate modelers almost exclusively assume n = 3 when modeling ice flow and projecting sea-level rise through forward modeling. However, recent work suggests that n ≈ 4 better fits observations, prompting the question: How sensitive are projections of sea-level rise to the value of n? We use an established community ice flow model and standard benchmark experiments designed as an idealized representation of Pine Island Glacier, West Antarctica. While initializing an n = 3 model to match observations of an n = 4 ice sheet is possible, we find that incorrectly assuming n = 3 when in fact n = 4 dramatically underestimates rates of sea-level rise. The scale of this error grows nonlinearly with the magnitude of the climate forcing, acting to increase projection uncertainties. Additionally, we find that models often account for this stress-dependent rheology mismatch during model initialization in a way that masks this rheological effect in the short term while leaving model outputs vulnerable to larger biases in longer-term projections. Initializations to observations of Pine Island Glacier display similar rheology-mismatch fingerprints to our idealized example.
", "doi": "10.1029/2025av001946", "issn": "2576-604X", "publisher": "American Geophysical Union", "publication": "AGU Advances", "publication_date": "2026-04", "series_number": "2", "volume": "7", "issue": "2", "pages": "e2025AV001946" }, { "id": "authors:e9n78-c0970", "collection": "authors", "collection_id": "e9n78-c0970", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20230710-597219500.1", "type": "article", "title": "Inferring Tide\u2010Induced Ephemeral Grounding in an Ice\u2010Shelf\u2010Stream System: Rutford Ice Stream, West Antarctica", "author": [ { "family_name": "Zhong", "given_name": "Minyan", "orcid": "0000-0002-1382-7061", "clpid": "Zhong-Minyan" }, { "family_name": "Simons", "given_name": "Mark", "orcid": "0000-0003-1412-6395", "clpid": "Simons-M" }, { "family_name": "Minchew", "given_name": "Brent", "orcid": "0000-0002-5991-3926", "clpid": "Minchew-B-M" }, { "family_name": "Zhu", "given_name": "Lijun", "orcid": "0000-0002-7854-0424", "clpid": "Zhu-Lijun" } ], "abstract": "Antarctic ice shelves play a key role in regulating the rate of ice flow in tributary ice streams. Temporal variations in the associated ice-shelf buttressing stress are observed to impact ice flow in glaciers and ice streams. Ephemeral grounding induced by tides is an important mechanism for modulating the buttressing stress. Here, we develop an approach to inferring variations in 3-D surface displacements at an ice-shelf-stream system that explicitly accounts for ephemeral grounding. Using a temporally dense nine-month-long synthetic-aperture radar image acquisition campaign collected over Rutford Ice Stream, West Antarctica, by the 4-satellite COSMO-SkyMed constellation, we infer the ephemeral grounding zones and the spatiotemporal variation of the fortnightly ice-flow variability. We find ephemeral grounding zones along the western ice-shelf margin as well as a few prominent ephemeral grounding points in the central trunk and in the vicinity of the grounding zone. Our observations provide evidence for tide-modulated buttressing stress and the temporally asymmetric response of ice-shelf flow to tidal forcing. Long-term oceanic warming and ice-shelf thinning will cause the loss of ephemeral grounding and decrease in ice-shelf buttressing stress.", "doi": "10.1029/2022jf006789", "issn": "2169-9003", "publisher": "American Geophysical Union", "publication": "Journal of Geophysical Research. Earth Surface", "publication_date": "2023-02", "series_number": "2", "volume": "128", "issue": "2", "pages": "Art. No. e2022JF006789" }, { "id": "authors:e0g1w-6kp64", "collection": "authors", "collection_id": "e0g1w-6kp64", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20211015-222200700", "type": "article", "title": "Data-Driven Inference of the Mechanics of Slip Along Glacier Beds Using Physics-Informed Neural Networks: Case Study on Rutford Ice Stream, Antarctica", "author": [ { "family_name": "Riel", "given_name": "B.", "orcid": "0000-0003-1940-3910", "clpid": "Riel-Bryan-V" }, { "family_name": "Minchew", "given_name": "B.", "orcid": "0000-0002-5991-3926", "clpid": "Minchew-B-M" }, { "family_name": "Bischoff", "given_name": "T.", "orcid": "0000-0003-3930-2762", "clpid": "Bischoff-Tobias" } ], "abstract": "Reliable projections of sea-level rise depend on accurate representations of how fast-flowing glaciers slip along their beds. The mechanics of slip are often parameterized as a constitutive relation (or \"sliding law\") whose proper form remains uncertain. Here, we present a novel deep learning-based framework for learning the time evolution of drag at glacier beds from time-dependent ice velocity and elevation observations. We use a feedforward neural network, informed by the governing equations of ice flow, to infer spatially and temporally varying basal drag and associated uncertainties from data. We test the framework on 1D and 2D ice flow simulation outputs and demonstrate the recovery of the underlying basal mechanics under various levels of observational and modeling uncertainties. We apply this framework to time-dependent velocity data for Rutford Ice Stream, Antarctica, and present evidence that ocean-tide-driven changes in subglacial water pressure drive changes in ice flow over the tidal cycle.", "doi": "10.1029/2021MS002621", "issn": "1942-2466", "publisher": "American Geophysical Union", "publication": "Journal of Advances in Modeling Earth Systems", "publication_date": "2021-11", "series_number": "11", "volume": "13", "issue": "11", "pages": "Art. No. e2021MS002621" }, { "id": "authors:12czx-gpj38", "collection": "authors", "collection_id": "12czx-gpj38", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180912-135248522", "type": "article", "title": "Processes controlling the downstream evolution of ice rheology in glacier shear margins: case study on Rutford Ice Stream, West Antarctica", "author": [ { "family_name": "Minchew", "given_name": "Brent M.", "orcid": "0000-0002-5991-3926", "clpid": "Minchew-B-M" }, { "family_name": "Meyer", "given_name": "Colin R.", "clpid": "Meyer-C-R" }, { "family_name": "Robel", "given_name": "Alexander A.", "orcid": "0000-0003-4520-0105", "clpid": "Robel-A-A" }, { "family_name": "Gudmundsson", "given_name": "G. Hilmar", "orcid": "0000-0003-4236-5369", "clpid": "Gudmundsson-G-H" }, { "family_name": "Simons", "given_name": "Mark", "orcid": "0000-0003-1412-6395", "clpid": "Simons-M" } ], "abstract": "Ice rheology governs how glaciers flow and respond to environmental change. The rheology of glacier ice evolves in response to a variety of mechanisms, including damage, heating, melting and the development of crystalline fabric. The relative contributions of these rheological mechanisms are not well understood. Using remotely sensed data and physical models, we decouple the influence of each of the aforementioned mechanisms along the margins of Rutford Ice Stream, a laterally confined outlet glacier in West Antarctica. We show that fabric is an important control on ice rheology in the shear margins, with an inferred softening effect consistent with a single-maximum fabric. Fabric evolves to steady state near the onset of streaming flow, and ice progressively softens downstream almost exclusively due to shear heating. The rate of heating is sensitive to local shear strain rates, which respond to local changes in bed topography as ice is squeezed through the basal trough. The impact of shear heating on the downstream evolution of ice rheology in a laterally confined glacier suggests that the thermoviscous feedback \u2013 wherein faster ice flow leads to higher rates of shear heating, further softening the ice \u2013 is a fundamental control on glacier dynamics.", "doi": "10.1017/jog.2018.47", "issn": "0022-1430", "publisher": "International Glaciological Society", "publication": "Journal of Glaciology", "publication_date": "2018-08", "series_number": "246", "volume": "64", "issue": "246", "pages": "583-594" }, { "id": "authors:d01vb-pwk55", "collection": "authors", "collection_id": "d01vb-pwk55", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170705-164235369", "type": "article", "title": "Geodetic Imaging of Time-Dependent Three-Component Surface Deformation: Application to Tidal-Timescale Ice Flow of Rutford Ice Stream, West Antarctica", "author": [ { "family_name": "Milillo", "given_name": "Pietro", "orcid": "0000-0002-1171-3976", "clpid": "Milillo-P" }, { "family_name": "Minchew", "given_name": "Brent", "orcid": "0000-0002-5991-3926", "clpid": "Minchew-B-M" }, { "family_name": "Simons", "given_name": "Mark", "orcid": "0000-0003-1412-6395", "clpid": "Simons-M" }, { "family_name": "Agram", "given_name": "Piyush", "clpid": "Agram-P-S" }, { "family_name": "Riel", "given_name": "Bryan", "orcid": "0000-0003-1940-3910", "clpid": "Riel-B" } ], "abstract": "We present a method for inferring time-dependent three-component surface deformation fields given a set of geodetic images of displacements collected from multiple viewing geometries. Displacements are parameterized in time with a dictionary of displacement functions. The algorithm extends an earlier single-component (i.e., single line of sight) framework for time-series analysis to three spatial dimensions using combinations of multitemporal, multigeometry interferometic synthetic aperture radar (InSAR) and/or pixel offset (PO) maps. We demonstrate this method with a set of 101 pairs of azimuth and range PO maps generated for a portion of the Rutford Ice Stream, West Antarctica, derived from data collected by the COSMO-SkyMed satellite constellation. We compare our results with previously published InSAR mean velocity fields and selected GPS time series and show that our resulting three-component surface displacements resolve both secular motion and tidal variability.", "doi": "10.1109/TGRS.2017.2709783", "issn": "0196-2892", "publisher": "IEEE", "publication": "IEEE Transactions on Geoscience and Remote Sensing", "publication_date": "2017-10", "series_number": "10", "volume": "55", "issue": "10", "pages": "5515-5524" }, { "id": "authors:s1x4y-nbh74", "collection": "authors", "collection_id": "s1x4y-nbh74", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20171220-130521553", "type": "article", "title": "Tidal modulation of ice shelf buttressing stresses", "author": [ { "family_name": "Robel", "given_name": "Alexander A.", "orcid": "0000-0003-4520-0105", "clpid": "Robel-A-A" }, { "family_name": "Tsai", "given_name": "Victor C.", "orcid": "0000-0003-1809-6672", "clpid": "Tsai-V-C" }, { "family_name": "Minchew", "given_name": "Brent", "orcid": "0000-0002-5991-3926", "clpid": "Minchew-B-M" }, { "family_name": "Simons", "given_name": "Mark", "orcid": "0000-0003-1412-6395", "clpid": "Simons-M" } ], "abstract": "Ocean tides influence the flow of marine-terminating glaciers. Observations indicate that the large fortnightly variations in ice flow at Rutford Ice Stream in West Antarctica originate in the floating ice shelf. We show that nonlinear variations in ice shelf buttressing driven by tides can produce such fortnightly variations in ice flow. These nonlinearities in the tidal modulation of buttressing stresses can be caused by asymmetries in the contact stress from migration of the grounding line and bathymetric pinning points beneath the ice shelf. Using a simple viscoelastic model, we demonstrate that a combination of buttressing and hydrostatic stress variations can explain a diverse range of tidal variations in ice shelf flow, including the period, phase and amplitude of flow variations observed at Rutford and Bindschadler Ice Streams.", "doi": "10.1017/aog.2017.22", "issn": "0260-3055", "publisher": "Cambridge University Press", "publication": "Annals of Glaciology", "publication_date": "2017-04", "series_number": "74", "volume": "58", "issue": "74", "pages": "12-20" }, { "id": "authors:7xeyj-8j091", "collection": "authors", "collection_id": "7xeyj-8j091", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20161123-141844145", "type": "article", "title": "Tidally induced variations in vertical and horizontal motion on Rutford Ice Stream, West Antarctica, inferred from remotely sensed observations", "author": [ { "family_name": "Minchew", "given_name": "B. M.", "orcid": "0000-0002-5991-3926", "clpid": "Minchew-B-M" }, { "family_name": "Simons", "given_name": "M.", "orcid": "0000-0003-1412-6395", "clpid": "Simons-M" }, { "family_name": "Riel", "given_name": "B.", "orcid": "0000-0003-1940-3910", "clpid": "Riel-B" }, { "family_name": "Milillo", "given_name": "P.", "orcid": "0000-0002-1171-3976", "clpid": "Milillo-P" } ], "abstract": "To better understand the influence of stress changes over floating ice shelves on grounded ice streams, we develop a Bayesian method for inferring time-dependent 3-D surface velocity fields from synthetic aperture radar (SAR) and optical remote sensing data. Our specific goal is to observe ocean tide-induced variability in vertical ice shelf position and horizontal ice stream flow. Thus, we consider the special case where observed surface displacement at a given location can be defined by a 3-D secular velocity vector, a family of 3-D sinusoidal functions, and a correction to the digital elevation model used to process the SAR data. Using nearly 9 months of SAR data collected from multiple satellite viewing geometries with the COSMO-SkyMed 4-satellite constellation, we infer the spatiotemporal response of Rutford Ice Stream, West Antarctica, to ocean tidal forcing. Consistent with expected tidal uplift, inferred vertical motion over the ice shelf is dominated by semidiurnal and diurnal tidal constituents. Horizontal ice flow variability, on the other hand, occurs primarily at the fortnightly spring-neap tidal period (M_(sf)). We propose that periodic grounding of the ice shelf is the primary mechanism for translating vertical tidal motion into horizontal flow variability, causing ice flow to accelerate first and most strongly over the ice shelf. Flow variations then propagate through the grounded ice stream at a mean rate of \u223c29 km/d and decay quasi-linearly with distance over \u223c85 km upstream of the grounding zone.", "doi": "10.1002/2016JF003971", "issn": "2169-9003", "publisher": "American Geophysical Union", "publication": "Journal of Geophysical Research. Earth Surface", "publication_date": "2017-01", "series_number": "1", "volume": "122", "issue": "1", "pages": "167-190" }, { "id": "authors:whhd5-bb034", "collection": "authors", "collection_id": "whhd5-bb034", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150831-155844821", "type": "article", "title": "On the Synergistic Use of SAR Constellations' Data Exploitation for Earth Science and Natural Hazard Response", "author": [ { "family_name": "Milillo", "given_name": "Pietro", "orcid": "0000-0002-1171-3976", "clpid": "Milillo-P" }, { "family_name": "Riel", "given_name": "Bryan", "orcid": "0000-0003-1940-3910", "clpid": "Riel-B" }, { "family_name": "Minchew", "given_name": "Brent", "orcid": "0000-0002-5991-3926", "clpid": "Minchew-B-M" }, { "family_name": "Yun", "given_name": "Sang-Ho", "orcid": "0000-0001-6952-6156", "clpid": "Yun-Sang-Ho" }, { "family_name": "Simons", "given_name": "Mark", "orcid": "0000-0003-1412-6395", "clpid": "Simons-M" }, { "family_name": "Lundgren", "given_name": "Paul", "orcid": "0000-0002-6771-2876", "clpid": "Lundgren-P" } ], "abstract": "Several current and expected future SAR satellites missions (e.g., TanDEM-X (TDX)/PAZ, COSMO-SkyMed (CSK), and Sentinel-1A/B) are designed as constellations of SAR sensors. Relative to single satellite systems, such constellations can provide greater spatial coverage and temporal sampling, thereby enabling better control on interferometric decorrelation and lower latency data access. These improvements lead to more effective near real-time disaster monitoring, assessment and response, and a greater ability to constrain dynamically changing physical processes. Using observations from the CSK system, we highlight examples of the potential for such imaging capabilities to enable advances in Earth science and natural hazards response.", "doi": "10.1109/JSTARS.2015.2465166", "issn": "1939-1404", "publisher": "IEEE", "publication": "IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing", "publication_date": "2016-03", "series_number": "3", "volume": "9", "issue": "3", "pages": "1095-1100" }, { "id": "authors:4p9a4-sx717", "collection": "authors", "collection_id": "4p9a4-sx717", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150508-090857010", "type": "article", "title": "On the Use of Simulated Airborne Compact Polarimetric SAR for Characterizing Oil\u2013Water Mixing of the Deepwater Horizon Oil Spill", "author": [ { "family_name": "Collins", "given_name": "Michael J.", "clpid": "Collins-M-J" }, { "family_name": "Denbina", "given_name": "Michael", "clpid": "Denbina-M" }, { "family_name": "Minchew", "given_name": "Brent", "orcid": "0000-0002-5991-3926", "clpid": "Minchew-B-M" }, { "family_name": "Jones", "given_name": "Cathleen E.", "clpid": "Jones-C-E" }, { "family_name": "Holt", "given_name": "Benjamin", "clpid": "Holt-B" } ], "abstract": "Compact polarimetry (CP) synthetic aperture radar (SAR) is a form of coherent dual-pol SAR that has been shown to have great potential for maritime surveillance applications such as ship and ice detection. In this paper, we demonstrate the potential of CP data for oil spill characterization. As the availability of CP data is limited at this time, we simulate CP image data from UAVSAR L-Band quad-polarized images. We reconstruct quad-pol SAR data (termed pseudo-quad) from these simulated CP SAR data, and calculate an oil-water mixing index, termed Mdex. We show that the differences between the pseudo-quad and quad-pol Mdex maps are negligible. This contributes to the case that CP SAR has great potential for multiple applications in maritime surveillance.", "doi": "10.1109/JSTARS.2015.2401041", "issn": "1939-1404", "publisher": "IEEE", "publication": "IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing", "publication_date": "2015-03", "series_number": "3", "volume": "8", "issue": "3", "pages": "1062-1077" }, { "id": "authors:ev1ez-n2a56", "collection": "authors", "collection_id": "ev1ez-n2a56", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180709-161925653", "type": "article", "title": "Early melt season velocity fields of Langj\u00f6kull and Hofsj\u00f6kull, central Iceland", "author": [ { "family_name": "Minchew", "given_name": "Brent", "orcid": "0000-0002-5991-3926", "clpid": "Minchew-B-M" }, { "family_name": "Simons", "given_name": "Mark", "orcid": "0000-0003-1412-6395", "clpid": "Simons-M" }, { "family_name": "Hensley", "given_name": "Scott", "clpid": "Hensley-S" }, { "family_name": "Bj\u00f6rnsson", "given_name": "Helgi", "clpid": "Bj\u00f6rnsson-H" }, { "family_name": "P\u00e1lsson", "given_name": "Finnur", "clpid": "P\u00e1lsson-F" } ], "abstract": "We infer the horizontal velocity fields of the ice caps Langj\u00f6kull and Hofsj\u00f6kull, central Iceland, using repeat-pass interferometric synthetic aperture radar (InSAR). NASA's uninhabited aerial vehicle synthetic aperture radar (UAVSAR) acquired airborne InSAR data from multiple vantage points during the early melt season in June 2012. We develop a Bayesian approach for inferring three-dimensional velocity fields from multiple InSAR acquisitions. The horizontal components generally agree with available GPS measurements wherever ice motion is well constrained by InSAR observations. We provide evidence that changes in volumetric moisture content near the glacier surface induce phase offsets that obfuscate the vertical component of the surface velocity fields, an effect that could manifest itself on any glacier that experiences surface melt. Spatial patterns in the InSAR-derived horizontal speeds are broadly consistent with the results of a simple viscous flow model, and the directionality of the InSAR-derived horizontal flow field is nearly everywhere consistent with the ice surface gradient. Significant differences between the InSAR-derived horizontal speed and the speed predicted by the viscous flow model suggest that basal slip accounts for more than half the observed outlet glacier flow.", "doi": "10.3189/2015JoG14J023", "issn": "0022-1430", "publisher": "Cambridge University Press", "publication": "Journal of Glaciology", "publication_date": "2015", "series_number": "226", "volume": "61", "issue": "226", "pages": "253-266" }, { "id": "authors:v6k71-9xm15", "collection": "authors", "collection_id": "v6k71-9xm15", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130429-095854132", "type": "article", "title": "Fault-zone controls on the spatial distribution of slow-moving landslides", "author": [ { "family_name": "Scheingross", "given_name": "Joel S.", "orcid": "0000-0002-7220-8084", "clpid": "Scheingross-J-S" }, { "family_name": "Minchew", "given_name": "Brent M.", "orcid": "0000-0002-5991-3926", "clpid": "Minchew-B-M" }, { "family_name": "Mackey", "given_name": "Benjamin H.", "clpid": "Mackey-B-H" }, { "family_name": "Simons", "given_name": "Mark", "orcid": "0000-0003-1412-6395", "clpid": "Simons-M" }, { "family_name": "Lamb", "given_name": "Michael P.", "orcid": "0000-0002-5701-0504", "clpid": "Lamb-M-P" }, { "family_name": "Hensley", "given_name": "Scott", "clpid": "Hensley-S" } ], "abstract": "Slow-moving landslides (earthflows) can dominate hillslope sediment flux and landscape erosion in hilly terrain with mechanically weak, fine-grained rock. Controls on the occurrence of slow-moving landslides are poorly constrained and need to be understood for landscape evolution models, sediment budgets, and infrastructure and hazards planning. Here, we use airborne interferometric synthetic aperture radar (InSAR) and aerial photographs to document 150 previously unidentified active earthflows along the central, creeping portion of the San Andreas fault, California. The earthflows move seasonally in response to winter rainfall, occur on hillslopes at \u223c20%\u201340% gradients (less than typically associated with rapid, catastrophic landslides), and have similar morphological characteristics to earthflows in different climatic and tectonic settings. Although our data extend up to 10 km from the fault trace, \u223c75% of detected landslides occur within 2 km of the active fault. Topographic, precipitation, and rock type metrics alone are not enough to explain the observed spatial distribution of earthflows. Instead, we hypothesize that earthflows cluster near the creeping San Andreas fault because of a fault-induced zone of reduced bulk-rock strength that increases hillslope susceptibility to failure. In addition, similar lithology, topography, and climate exist north of the creeping section of the fault, yet earthflows there are rare. This may be due to large-magnitude earthquakes episodically triggering coseismic rapid landslides, which preferentially remove weak rock from the fault damage zone. Our analysis suggests that the necessary conditions for earthflow formation in central California include some combination of reduced rock strength, fine-grained sedimentary rock, threshold precipitation and relief, and possibly the absence of large-magnitude earthquakes. These conditions likely hold for earthflow development in other areas, and our work suggests that local variations in rock strength and seismicity, such as those associated with fault zones, need to be taken into account in order to accurately predict earthflow occurrence.", "doi": "10.1130/B30719.1", "issn": "0016-7606", "publisher": "Geological Society of America", "publication": "Geological Society of America Bulletin", "publication_date": "2013-03", "series_number": "3-4", "volume": "125", "issue": "3-4", "pages": "473-489" }, { "id": "authors:763ma-daw81", "collection": "authors", "collection_id": "763ma-daw81", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120925-142103679", "type": "article", "title": "Polarimetric Analysis of Backscatter From the Deepwater Horizon Oil Spill Using L-Band Synthetic Aperture Radar", "author": [ { "family_name": "Minchew", "given_name": "Brent", "orcid": "0000-0002-5991-3926", "clpid": "Minchew-B-M" }, { "family_name": "Jones", "given_name": "Cathleen E.", "clpid": "Jones-C-E" }, { "family_name": "Holt", "given_name": "Benjamin", "clpid": "Holt-B" } ], "abstract": "We analyze the fully-polarimetric Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR) data acquired on June 23, 2010, from two adjacent, overlapping flight tracks that imaged the main oil slick near the Deepwater Horizon (DWH) rig site in the Gulf of Mexico. Our results show that radar backscatter from both clean water and oil in the slick is predominantly from a single surface scatterer, consistent with the tilted Bragg scattering mechanism, across the range of incidence angles from 26\u00ba to 60\u00ba. We show that the change of backscatter over the main slick is due both to a damping of the ocean wave spectral components by the oil and an effective reduction of the dielectric constant resulting from a mixture of 65\u201390% oil with water in the surface layer. This shows that synthetic aperture radar can be used to measure the oil volumetric concentration in a thick slick. Using the H/A/\u03b1 parameters, we show that surface scattering is dominant for oil and water whenever the data are above the noise floor and that the entropy (H) and \u03b1 parameters for the DWH slick are comparable to those from the clean water. The anisotropy, A, parameter shows substantial variation across the oil slick and a significant range-dependent signal whenever the backscatter in all channels is above the instrument noise floor. For slick detection, we find the most reliable indicator to be the major eigenvalue of the coherency matrix, which is approximately equal to the total backscatter power for both oil in the slick and clean sea water.", "doi": "10.1109/TGRS.2012.2185804", "issn": "0196-2892", "publisher": "IEEE", "publication": "IEEE Transactions on Geoscience and Remote Sensing", "publication_date": "2012-10", "series_number": "10", "volume": "50", "issue": "10", "pages": "3812-3830" }, { "id": "authors:0tvqz-41k85", "collection": "authors", "collection_id": "0tvqz-41k85", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20121010-125905183", "type": "article", "title": "Determining the mixing of oil and sea water using polarimetric synthetic aperture radar", "author": [ { "family_name": "Minchew", "given_name": "Brent", "orcid": "0000-0002-5991-3926", "clpid": "Minchew-B-M" } ], "abstract": "Knowledge of the characteristics of spilled oil in the\nocean is important for cleanup operations, predictions of the impact on wildlife, and studies of the nature of the ocean surface and currents. Herein I discuss a method for\nevaluating the characteristics of oil in a marine environment using synthetic aperture radar (SAR) and present a new, simple classification, called the oil/water mixing index (Mdex), to quickly assess the results. I link the Mdex results to the Bonn Agreement for Oil Appearance Codes (BAOAC) for aerial observers and demonstrate the Mdex on Uninhabited Aerial Vehicle SAR (UAVSAR) data collected\nJune 23, 2010 over the former site of the Deepwater Horizon\n(DWH) drilling rig. The Mdex map shows a more\nheterogeneous oil swath than do radar backscatter images\nand features within the oil are consistent with features\npresent in previously published, near-coincident optical\nimagery. The Mdex results indicate that most of the oil near\nthe DWH was mixed with sea water to a minimum depth of\na few millimeters, though some areas containing relatively\nthin films are observed.", "doi": "10.1029/2012GL052304", "issn": "0094-8276", "publisher": "American Geophysical Union", "publication": "Geophysical Research Letters", "publication_date": "2012-08-23", "volume": "39", "pages": "Art No. L16607" }, { "id": "authors:bw135-4xw21", "collection": "authors", "collection_id": "bw135-4xw21", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120228-092625703", "type": "article", "title": "A physical model for seismic noise generation from sediment transport in rivers", "author": [ { "family_name": "Tsai", "given_name": "Victor C.", "orcid": "0000-0003-1809-6672", "clpid": "Tsai-V-C" }, { "family_name": "Minchew", "given_name": "Brent", "orcid": "0000-0002-5991-3926", "clpid": "Minchew-B-M" }, { "family_name": "Lamb", "given_name": "Michael P.", "orcid": "0000-0002-5701-0504", "clpid": "Lamb-M-P" }, { "family_name": "Ampuero", "given_name": "Jean-Paul", "orcid": "0000-0002-4827-7987", "clpid": "Ampuero-J-P" } ], "abstract": "Measuring sediment flux in rivers remains a significant problem in studies of landscape evolution. Recent studies suggest that observations of seismic noise near rivers can help provide such measurements, but the lack of models linking observed seismic quantities to sediment flux has prevented the method from being used. Here, we develop a forward model to describe the seismic noise induced by the transport of sediment in rivers. The model provides an expression for the power spectral density (PSD) of the Rayleigh waves generated by impulsive impacts from saltating particles which scales linearly with the number of particles of a given size and the square of the linear momentum. After incorporating expressions for the impact velocity and rate of impacts for fluvially transported sediment, we observe that the seismic noise PSD is strongly dependent on the sediment size, such that good constraints on grain size distribution are needed for reliable estimates of sediment flux based on seismic noise observations. The model predictions for the PSD are consistent with recent measurements and, based on these data, a first attempt at inverting seismic noise for the sediment flux is provided.", "doi": "10.1029/2011GL050255", "issn": "0094-8276", "publisher": "American Geophysical Union", "publication": "Geophysical Research Letters", "publication_date": "2012-01", "series_number": "L2", "volume": "39", "issue": "L2", "pages": "Art. No. L02404" } ]