SOEST Faculty & Researcher Works
Permanent URI for this collectionhttps://hdl.handle.net/10125/36248
Browse
Recent Submissions
Item type: Item , Item type: Item , Widths of imbricate thrust blocks and the strength of the front of accretionary wedges and fold-and-thrust belts(2021-12-03) Garrett ItoBesides the large-scale wedge shape itself, the most prominent structural feature of accretionary wedges and foldand- thrust belts is the common pattern of imbricate thrust faults. This study illuminates the fundamental mechanical processes and material properties controlling the width of the crustal blocks bounded by major thrusts using analytical solutions of stress as well as two-dimensional finite-difference models. The numerical models predict that the initial width w0 of a thrust block is set when that block first forms at the very front of the wedge. The width is found to subsequently decreases approximately in proportion to the mean horizontal strain needed for an ideally triangular-shaped Coulomb wedge with a critical taper. Block width is proportional to the thickness H of the incoming, accreting sediment. A key quantity that influences the normalized initial block width w0/H is the distance L forward of the frontal thrust needed for the net horizontal force from shear on the base of the incoming sediment to balance the net force on the frontal thrust. It is within this distance where stress in the incoming sediment is substantially elevated and thus where the new frontal thrust forms. Results show that L/H and, correspondingly, w0/H increase with increasing sediment friction angle ϕ, cohesive strength C0 and porefluid pressure ratio λ, and decrease with increasing basal friction angle ϕb and basal dip β. Normalized width is sensitive to ϕ and relatively insensitive to ϕb and λ. Results for submarine and subaerial wedges follow the same scaling law. The scaling law relates the observables, w0/H and β, to the material properties, ϕ, ϕb, λ, and therefore provides a theoretical relation that can be used independent of, or together with critical Coulomb wedge theory (CWT) to constrain these properties.Item type: Item , Oceanic fault zones reconstructed(2021-03-18) Garrett ItoAt undersea structures called oceanic spreading centres, two tectonic plates split apart, and molten rock from volcanic activity solidifies to produce the crust of the sea floor. These spreading centres are separated into individual segments that are tens to hundreds of kilometres long. At the ends of the segments, shearing (side-by-side sliding) of the two plates occurs along plate boundaries known as oceanic transform faults. Since their discovery in the mid-1960s 1, these faults have been considered as sites where plate material is neither created nor destroyed. But on page 402, Grevemeyer et al. 2 report that this description is too simplistic. They show that, in a several-kilometre-wide region called the transform deformation zone, the crust generated at one spreading segment undergoes episodes of thinning and then regrowth as it drifts towards and past the adjacent segment.Item type: Item , Honing in on the climate signal in seafloor topography(2022) Garrett ItoThe corrugated surface of the seafloor expresses the most areally extensive landform on Earth, known as “abyssal hills”, inherited from when the oceanic crust was created at a midocean ridge spreading center (1, 2) (Fig. 1). The main process is the shifting and rotation of adjacent blocks of crust relative to one another along fault zones predominantly during periods of low magmatic activity, interspersed between times of robust magmatism and the emplacement new crust (1, 3). In the presence of the steady far-field tug of plate tectonic forces, this interplay between faulting and magmatism depends on processes influencing the time dependence of magma generation, storage, and delivery to the surface (4, 5). In PNAS, Huybers et al. (6) argue that one such process originates with the fall and rise of sea level during glacial–interglacial climate cycles.Item type: Item , East Pacific Rise 9N: Compiled station, shot, and travel time data for EPR88, EPR93, and EPR97(2022-01-05) Dunn, RobertA combined data set is provided that gives the station and source position information and travel time data for three combined active-source ocean bottom seismograph data sets located along the East Pacific Rise near latitude 9˚N.Item type: Item , The Brugd Undergraduate Student Data Solution: A Data Management Collaboration Between Global Environmental Science and Hamilton Library at the University of Hawaiʻi at Mānoa(2021-08-13) Ramfelt, Oscar; Guidry, Michael W.; Young, Jonathan S.This paper describes the outcome of the Brugd project, a customized data management solution for undergraduate student learning analytics in the University of Hawaiʻi at Mānoa Global Environmental Science program, with guidance from librarians at Hamilton Library. Our collective effort was to develop a sustainable means of combining past, present, and future institutional and programmatic-collected sources of undergraduate student data, specifically for the Global Environmental Science Program, into a common database for analysis and visualization. The resulting database also needed to be anonymized to both address student privacy concerns and so that resulting analyses could be easily shared and communicated amongst researchers, faculty, and other program stakeholders. This project may serve as a model for in-house learning analytics tools and future data management collaborations between the library and departments both at UHM and other institutions.Item type: Item , Extensive Magmatic Heating of the Lithosphere Beneath the Hawaiian Islands Inferred From Salt Lake Crater Mantle Xenoliths(2020-11-13) Guest, Imani; Ito, Garrett; Garcia, Michael O.; Hellbrand, EricAn ongoing challenge in studies of the oceanic upper mantle is how intraplate hotspots impact the thermal structure of the lithosphere. To address this issue at the Hawaiian hotspot, we analyze mineral compositions for a petrographically diverse suite of garnet pyroxenite xenoliths from the Salt Lake Crater (SLC) rejuvenation stage, volcanic tuff ring in Honolulu. Garnet-clinopyroxene geobarometry and two-pyroxene geothermometry indicate equilibrium pressures of 13–18 kbar and temperatures of 1000°C–1100°C. These pressures place the xenoliths at mid-lithospheric depths of 45–55 km, with temperatures 200°C–300°C hotter than expected for normal 90-Myr-old oceanic lithosphere. Garnet and clinopyroxene occur as discrete primary grains, as well as exsolution blebs and lamellae, with lateral dimensions up to several hundred microns. Compositions within garnet and pyroxene grains are remarkably uniform and display no systematic variation with distance to grain boundaries. Together, these observations indicate that the calculated pressures and temperatures reflect the thermal state of the lithosphere under which the xenoliths last equilibrated. We attribute the elevated lithospheric temperatures under Honolulu primarily to the heating by magma as it penetrated the lithosphere during rejuvenation magmatism and the voluminous shield magmatic stage. We anticipate such magmatic heating to be common among all Hawaiian volcanoes, supporting conclusions of a recent study of earthquakes beneath Hawai‘i Island. This local lithospheric thermal anomaly may also contribute to the enigmatically weak flexural response of the lithosphere due to volcano loading along the Hawaiian hotspot chain.Item type: Item , Science Commuication Portfolio: A guide to creating communication materials that complement your science(2015-04-06) Wood-Charlson, Elisha M; Varga, MelissaAre you working on a research manuscript, grant, annual report, or project summary that requires technical language? Do you feel that your finding, if communicated properly, could be useful to people beyond your professional network? This communication-training document for scientists is designed to help you do just that – on your own time and for a variety of verbal and written communication styles. We also provide an example portfolio on the topic of sea level rise for reference.Item type: Item , An unexpected disruption of the atmospheric quasi-biennial oscillation(Science, 2016-09-23) Osprey, Scott M.; Butchart, Neal; Knight, Jeff R.; Scaife, Adam A.; Hamilton, Kevin; Anstey, James A.; Schenzinger, Verena; Zhang, ChunxiOne of the most repeatable phenomena seen in the atmosphere, the quasi-biennial oscillation (QBO) between prevailing eastward and westward wind jets in the equatorial stratosphere (approximately 16 to 50 kilometers altitude), was unexpectedly disrupted in February 2016. An unprecedented westward jet formed within the eastward phase in the lower stratosphere and cannot be accounted for by the standard QBO paradigm based on vertical momentum transport. Instead, the primary cause was waves transporting momentum from the Northern Hemisphere. Seasonal forecasts did not predict the disruption, but analogous QBO disruptions are seen very occasionally in some climate simulations. A return to more typical QBO behavior within the next year is forecast, although the possibility of more frequent occurrences of similar disruptions is projected for a warming climate.Item type: Item , Nonlinear climate sensitivity and its implications for future greenhouse warming(Science Advances, 2016-11-09) Friedrich, Tobias; Timmermann, Axel; Tigchelaar, Michelle; Timm, Oliver Elison; Ganopolski, AndreyGlobal mean surface temperatures are rising in response to anthropogenic greenhouse gas emissions. The magnitude of this warming at equilibrium for a given radiative forcing—referred to as specific equilibrium climate sensitivity (S)—is still subject to uncertainties. We estimate global mean temperature variations and S using a 784,000-year-long field reconstruction of sea surface temperatures and a transient paleoclimate model simulation. Our results reveal that S is strongly dependent on the climate background state, with significantly larger values attained during warm phases. Using the Representative Concentration Pathway 8.5 for future greenhouse radiative forcing, we find that the range of paleo-based estimates of Earth’s future warming by 2100 CE overlaps with the upper range of climate simulations conducted as part of the Coupled Model Intercomparison Project Phase 5 (CMIP5). Furthermore, we find that within the 21st century, global mean temperatures will very likely exceed maximum levels reconstructed for the last 784,000 years. On the basis of temperature data from eight glacial cycles, our results provide an independent validation of the magnitude of current CMIP5 warming projections.Item type: Item , Magmatic and tectonic extension at the Chile Ridge: Evidence for mantle controls on ridge segmentation(American Geophysical Union, 2016-05) Howell, Samuel M.; Ito, Garrett; Behn, Mark D.; Martinez, Fernando; Olive, Jean-Arthur; Escartin, JavierWe use data from an extensive multibeam bathymetry survey of the Chile Ridge to study tectonomagmatic processes at the ridge axis. Specifically, we investigate how abyssal hills evolve from axial faults, how variations in magmatic extension influence morphology and faulting along the spreading axis, and how these variations correlate with ridge segmentation. The bathymetry data are used to estimate the fraction of plate separation accommodated by normal faulting, and the remaining fraction of extension, M, is attributed primarily to magmatic accretion. Results show that M ranges from 0.85 to 0.96, systematically increasing from first-order and second-order ridge segment offsets toward segment centers as the depth of ridge axis shoals relative to the flanking highs of the axial valley. Fault spacing, however, does not correlate with ridge geometry, morphology, or M along the Chile Ridge, which suggests the observed increase in tectonic strain toward segment ends is achieved through increased slip on approximately equally spaced faults. Variations in M along the segments follow variations in petrologic indicators of mantle melt fraction, both showing a preferred length scale of 50620 km that persists even along much longer ridge segments. In comparison, mean M and axial relief fail to show significant correlations with distance offsetting the segments. These two findings suggest a form of magmatic segmentation that is partially decoupled from the geometry of the plate boundary. We hypothesize this magmatic segmentation arises from cells of buoyantly upwelling mantle that influence tectonic segmentation from the mantle, up.Item type: Item , Double layering of a thermochemical plume in the upper mantle beneath Hawaii(Elsevier, 2013-06) Ballmer, Maxim D.; Ito, Garrett; Wolfe, Cecily J.; Solomon, Sean C.According to classical plume theory, purely thermal upwellings rise through the mantle, pond in a thin layer beneath the lithosphere, and generate hotspot volcanism. Neglected by this theory, however, are the dynamical effects of compositional heterogeneity carried by mantle plumes even though this heterogeneity has been commonly identified in sources of hotspot magmas. Numerical models predict that a hot, compositionally heterogeneous mantle plume containing a denser eclogite component tends to pool at ∼300–410 km depth before rising to feed a shallower sublithospheric layer. This double-layered structure of a thermochemical plume is more consistent with seismic tomographic images at Hawaii than the classical plume model. The thermochemical structure as well as time dependence of plume material rising from the deeper into the shallower layer can further account for long-term fluctuations in volcanic activity and asymmetry in bathymetry, seismic structure, and magma chemistry across the hotspot track, as are observed.Item type: Item , Petrology and Geochemistry of Volcanic Rocks from the South Kauaʻi Swell Volcano, Hawaiʻi: Implications for the Lithology and Composition of the Hawaiian Mantle Plume(Oxford University Press, 2015-06) Garcia, Michael O.; Weis, Dominique; Swinnard, Lisa; Ito, Garrett; Pietruszka, Aaron J.The South Kauaʻi Swell (SKS) volcano was sampled during four JASON dives and three dredge hauls recovering rocks that range from fresh pillow lavas to altered volcanic breccias. Two geochemical groups were identified: shield-stage tholeiites (5·4–3·9 Ma) and rejuvenation-stage alkalic lavas (1·9–0·1 Ma). The young SKS ages and the coeval rejuvenated volcanism along a 400km segment of the Hawaiian Islands (Maui to Niʻihau) are inconsistent with the timing and duration predictions by the flexure and secondary plume melting models for renewed volcanism. The SKS tholeiites are geochemically heterogeneous but similar to lavas from nearby Kauaʻi, Niʻihau and Waiʻanae volcanoes, indicating that their source regions within the Hawaiian mantle plume sampled a well-mixed zone. Most SKS tholeiitic lavas exhibit radiogenic Pb isotope ratios (208Pb*/206Pb*) that are characteristic of Loa compositions (>0·9475), consistent with the volcano’s location on the west side of the Hawaiian Islands. These results document the existence of the Loa component within the Hawaiian mantle plume prior to 5 Ma. Loa trend volcanoes are thought to have a major pyroxenite component in their source. Calculations of the pyroxenitic component in the parental melts for SKS tholeiites using high-precision olivine analyses and modeling of trace element ratios indicate a large pyroxenite proportion (≥50%), which was predicted by recent numerical models. Rejuvenation-stage lavas were also found to have a significant pyroxenite component based on olivine analyses (40–60%). The abundance of pyroxenite in the source for SKS lavas may be the cause of this volcano’s extended period of magmatism (>5 Myr). The broad distribution of the Loa component in the northern Hawaiian Island lavas coincides with the start of a dramatic magma flux increase (300%) along the Hawaiian Chain, which may reflect a major structural change in the source of the Hawaiian mantle plume.Item type: Item , The origin of the asymmetry in the Iceland hotspot along the Mid-Atlantic Ridge from continental breakup to present-day(Elsevier, 2014-03) Howell, Samuel M.; Ito, Garrett; Breivik, Asbjørn J.; Rai, Abhishek; Mjelde, Rolf; Hanan, Barry; Sayit, Kaan; Vogt, PeterThe Iceland hotspot has profoundly influenced the creation of oceanic crust throughout the North Atlantic basin. Enigmatically, the geographic extent of the hotspot influence along the Mid-Atlantic Ridge has been asymmetric for most of the spreading history. This asymmetry is evident in crustal thickness along the present-day ridge system and anomalously shallow seafloor of ages ∼49–25 Ma created at the Reykjanes Ridge (RR), SSW of the hotspot center, compared to deeper seafloor created by the now-extinct Aegir Ridge (AR) the same distance NE of the hotspot center. The cause of this asymmetry is explored with 3-D numerical models that simulate a mantle plume interacting with the ridge system using realistic ridge geometries and spreading rates that evolve from continental breakup to present-day. The models predict plume-influence to be symmetric at continental breakup, then to rapidly contract along the ridges, resulting in widely influenced margins next to uninfluenced oceanic crust. After this initial stage, varying degrees of asymmetry along the mature ridge segments are predicted. Models in which the lithosphere is created by the stiffening of the mantle due to the extraction of water near the base of the melting zone predict a moderate amount of asymmetry; the plume expands NE along the AR ∼70–80% as far as it expands SSW along the RR. Without dehydration stiffening, the lithosphere corresponds to the near-surface, cool, thermal boundary layer; in these cases, the plume is predicted to be even more asymmetric, expanding only 40–50% as far along the AR as it does along the RR. Estimates of asymmetry and seismically measured crustal thicknesses are best explained by model predictions of an Iceland plume volume flux of ∼100–200 m^3/s, and a lithosphere controlled by a rheology in which dehydration stiffens the mantle, but to a lesser degree than simulated here. The asymmetry of influence along the present-day ridge system is predicted to be a transient configuration in which plume influence along the Reykjanes Ridge is steady, but is still widening along the Kolbeinsey Ridge, as it has been since this ridge formed at ∼25 Ma.Item type: Item , Patterns in Galápagos Magmatism Arising from the Upper Mantle Dynamics of Plume-Ridge Interaction(John Wiley & Sons, Inc., 2014-08) Ito, Garrett; Bianco, ToddThe origin of various patterns seen in Galápagos magmatism is investigated using numerical simulations of mantle plume-ridge interaction with the realistic geometry and evolution of the Galapágos Spreading Center (GSC). Models predict magma generation and composition from a mantle composed of fusible veins of material enriched in incompatible elements, and a more refractory depleted matrix. Model 1 simulates a low-viscosity plume, owing to a temperature-dependent mantle rheology; Model 2 includes the added dependence on water content, which leads to high viscosities in the dehydrated, shallow upper mantle. Model 1 produces the most favorable results. It shows how a modest crustal thickness anomaly observed along the Western GSC can arise from a plume with large excess temperatures (greater than 100°C). Model 1 also predicts geographic patterns in magma isotopic compositions broadly resembling those observed along the GSC as well as around the Galapágos Archipelago. These patterns are predicted to arise out of the differences in melting depths between the enriched veins and depleted matrix, coupled with spatial variations in the rate of mantle upwelling and decompression melting. The results provide an alternative to traditional explanations involving the plume mixing with or entraining the ambient mantle. The models are still missing some essential factors, as indicated by the predicted increases, rather than the observed decrease in incompatible element concentration away from the hotspot along the GSC. Possible factors include a regional-scale zoning in incompatible element and water content within the plume, or melt migration that delivers a larger flux of incompatible-element-rich melts to the GSC.Item type: Item , New Insights from Seafloor Mapping of a Hawaiian Marine Monument(Earth & Space Science News, 2015-05) Kelley, Christopher; Smith, John R.; Miller, Joyce; Tree, Jonathan; Boston, Brian; Garcia, Michael; Ito, Garrett; Taylor, Jeremey; Lichowski, Frances; Wagner, Daniel; Leonard, Jason; Dechnik, Belinda; Leurs, DanielOn 15 June 2006, when U.S. President George W. Bush signed the proclamation creating the Papahānaumokuākea Marine National Monument (PMNM), he probably wasn’t thinking about underwater morphology. To fully understand the coral reefs and marine ecosystems that the monument was created to protect, however, scientists need to have a detailed picture of the seafloor features, home to corals and other species, as well as the geologic history of the area.
Thanks to a recent, multi-institution expedition, such a seafloor features that will not only inform conservation efforts but also enable geologists and geophysicists to revise their understanding of Hawaii’s complex geologic past.
Specifically, data should help scientists answer fundamental questions about the area’s regional geology. For instance, which seamounts were truly formed because of Hawaiian hotspot volcanism, and which seamounts were not?Item type: Item , Seismic anisotropy and shear wave splitting associated with mantle plume-plate interaction(American Geophysical Union, 2014-06) Ito, Garrett; Dunn, Robert; Li, Aibing; Wolfe, Cecily J.; Gallego, Alejandro; Fu, YuanyuanGeodynamic simulations of the development of lattice preferred orientation in the flowing mantle are used to characterize the seismic anisotropy and shear wave splitting (SWS) patterns expected for the interaction of mantle plumes and lithospheric plates. Models predict that in the deeper part of the plume layer ponding beneath the plate, olivine a axes tend to align perpendicular to the radially directed plume flow, forming a circular pattern reflecting circumferential stretching. In the shallower part of the plume layer, plate shear is more important and the a axes tend toward the direction of plate motion. Predicted SWS over intraplate plumes reflects the asymmetric influence of plate shear with fast S wave polarization directions forming a pattern of nested U shapes that open in the direction opposing both plate motion and the parabolic shape often used to describe the flow lines of the plume. Predictions explain SWS observations around the Eifel hot spot with an eastward, not westward, moving Eurasian plate, consistent with global studies that require relatively slow net (westward) rotation of all of the plates. SWS at the Hawaiian hot spot can be explained by the effects of plume-plate interaction, combined with fossil anisotropy in the Pacific lithosphere. In ridge-centered plume models, the fast polarization directions angle diagonally toward the ridge axis when the plume is simulated as having low viscosity beneath the thermal lithosphere. Such a model better explains SWS observations in northeast Iceland than a model that incorporates a high-viscosity layer due to dehydration of the shallow-most upper mantle.Item type: Item , Investigating seismic anisotropy beneath the Reykjanes Ridge using models of mantle flow, crystallographic evolution, and surface wave propagation(American Geophysical Union, 2013-08) Gallego, A.; Ito, Garrett; Dunn, R.A.Surface wave studies of the Reykjanes Ridge (RR) and the Iceland hotspot have imaged an unusual and enigmatic pattern of two zones of negative radial anisotropy on each side of the RR. We test previously posed and new hypotheses for the origin of this anisotropy, by considering lattice preferred orientation (LPO) of olivine A-type fabric in simple models with 1-D, layered structures, as well as in 2-D and 3-D geodynamic models with mantle flow and LPO evolution. Synthetic phase velocities of Love and Rayleigh waves traveling parallel to the ridge axis are produced and then inverted to mimic the previous seismic studies. Results of 1-D models show that strong negative radial anisotropy can be produced when olivine a axes are preferentially aligned not only vertically but also subhorizontally in the plane of wave propagation. Geodynamic models show that negative anisotropy on the sides of the RR can occur when plate spreading impels a corner flow, and in turn a subvertical alignment of olivine a axes, on the sides of the ridge axis. Mantle dehydration must be invoked to form a viscous upper layer that minimizes the disturbance of the corner flow by the Iceland mantle plume. While the results are promising, important discrepancies still exist between the observed seismic structure and the predictions of this model, as well as models of a variety of types of mantle flow associated with plume-ridge interaction. Thus, other factors that influence seismic anisotropy, but not considered in this study, such as power-law rheology, water, melt, or time-dependent mantle flow, are probably important beneath the Reykjanes Ridge.Item type: Item , A low-relief shield volcano origin for the South Kauaʻi Swell(American Geophysical Union, July 2013) Ito, Garrett; Garcia, Michael O.; Smith, John R.; Taylor, Brian; Flinders, Ashton; Jicha, Brian; Yamasaki, Seiko; Weis, Dominique; Swinnard, Lisa; Blay, ChuckThe South Kauaʻi Swell (SKS) is a 110 km x 80 km ovoid bathymetric feature that stands >2 km high and abuts the southern flank of the island of Kauaʻi. The origin of the SKS was investigated using multibeam bathymetry and acoustic backscatter, gravity data, radiometric ages, and geochemistry of rock samples. Most of the SKS rock samples are tholeiitic in composition with ages of 3.9–5.4 Ma indicating they were derived from shield volcanism. The ages and compositions of the SKS rocks partially overlap with those of the nearby Niʻihau, Kauaʻi and West Kaʻena volcano complexes. The SKS was originally described as a landslide; however, this interpretation is problematic given the ovoid shape of SKS, its relatively smooth, flat-to-convex surface, and the lack of an obvious source region that could accommodate what would be one of Earth’s most voluminous (6 x 10^3 km^3) landslides. The morphology, size, and the surrounding gravity anomaly are more consistent with the SKS being a low-relief shield volcano, which was partially covered with a small volume of landside debris from south Kauaʻi and later with some secondary volcanic seamounts. A shield origin would imply that Hawaiian and possibly other hotspot shield volcanoes can take on a wider variety of forms than is commonly thought, ranging from tall island-building shields, to smaller edifices such as Kaʻena Ridge and Mahukona, to even lower-relief volcanoes represented by the SKS and possibly the South West Oʻahu Volcanic Field.Item type: Item , Intrusive dike complexes, cumulate cores, and the extrusive growth of Hawaiian volcanoes(American Geophysical Union, 2013-07) Flinders, Ashton F.; Ito, Garrett; Garcia, Michael O.; Sinton, John M.; Kauahikaua, Jim; Taylor, BrianThe Hawaiian Islands are the most geologically studied hot-spot islands in the world yet surprisingly, the only large-scale compilation of marine and land gravity data is more than 45 years old. Early surveys served as reconnaissance studies only, and detailed analyses of the crustal-density structure have been limited. Here we present a new chain-wide gravity compilation that incorporates historical island surveys, recently published work on the islands of Hawai‘i, Kaua‘i, and Ni‘ihau, and >122,000 km of newly compiled marine gravity data. Positive residual gravity anomalies reflect dense intrusive bodies, allowing us to locate current and former volcanic centers, major rift zones, and a previously suggested volcano on Ka‘ena Ridge. By inverting the residual gravity data, we generate a 3-D view of the dense, intrusive complexes and olivine-rich cumulate cores within individual volcanoes and rift zones. We find that the Hāna and Ka‘ena ridges are underlain by particularly high-density intrusive material (>2.85 g/cm3) not observed beneath other Hawaiian rift zones. Contrary to previous estimates, volcanoes along the chain are shown to be composed of a small proportion of intrusive material (<30% by volume), implying that the islands are predominately built extrusively.