OPPORTUNITIES FOR GEOGRAPHY IN THE U.S. OFFICE OF EDUCATION*     

Allen A. Schmieder  J. Fraser Hart 《The Professional geographer》1966,18(4):254-256

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Late‐Holocene buried forests on the Oregon Coast     

Roger Hart  Curt Peterson 《地球表面变化过程与地形》2007,32(2):210-229

Deposits of late‐Holocene beach sand buried conifer forests episodically emerge on beaches of the Oregon coast. Simultaneously, sand dunes buried late‐Holocene forests growing on marine terraces landward of the beaches. Dune ramps, up to 60 m in elevation, connected the beach and dune deposits. The average age of wood samples from stumps rooted on the shore platforms is 3·07 ± 1·45 ka. The average age of wood and charcoal samples embedded in forest soil on the marine terraces is 3·27 ± 1·46 ka. Between 1994 and 2006, winter storm waves exposed more than 4·5 km² of late‐Holocene forest soil on shore platforms at 19 localities. Rooted stumps without soil were uncovered at an additional 14 localities. Once exposed, wave action eroded the soil rapidly (one to two years). The intact forest soil and roots on the shore platforms must have been nearly continuously buried, protected and preserved prior to recent exposure. The late‐Holocene buried forest provides the basis for a conceptual model of coastal evolution. A three stage reversal of erosion and sand supply must have occurred: (1) wave erosion switched to seaward advancement of forests, (2) forest growth and soil development switched to burial beneath beach and dune sand and (3) burial and preservation switched to wave erosion, truncation of dune ramps and landward retreat of sea cliffs. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Simulation of artificial earthquakes     

G. Rodolfo Saragoni  Gary C. Hart 《地震工程与结构动力学》1973,2(3):249-267

A procedure is developed for the simulation of artificial earthquake accelerograms, The time variation of amplitude and frequency content is preserved in the simulation procedure. Sixteen artificial earthquake accelerograms are simulated and compared with a target accelerogram. The time variation of amplitude and frequency content for 26 historical earthquake accelerograms is characterized.  相似文献   

Particle track record of Apollo 15 green soil and rock     

R.L. Fleischer  H.R. Hart 《Earth and Planetary Science Letters》1973,18(2):357-364

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Spatio-temporal analysis of flowering using LiDAR topography     

Samantha Hart  Elena Mikhailova  Christopher Post  Patrick McMillan  Julia Sharp  William Bridges 《地理学报(英文版)》2017,27(1):62-78

Spatio-temporal patterns of flowering in forest ecosystems are hard to quantify and monitor. The objectives of this study were to investigate spatio-temporal patterns(e.g. soilssimple slope classesslope aspectand flow accumulation) of flowering around Lake IssaqueenaSouth Carolina(SCUSA) using plant-flowering database collected with GPS- enabled camera(stored in Picasa 3 web albums and project website) on a monthly basis in 2012 and Li DAR-based topography. Pacolet fine sandy loam had the most flowering plantsfollowed by Madison sandy loamboth dominant soil types around the lake. Most flowering plants were on moderately steep(17%–30%) and gently sloping(4%–8%) slopes. Most flowering plants were on west(247.5°–292.5°)southwest(202.5°–247.5°)and northwest(292.5°–337.5°) aspects. Most flowering plants were associated with minimum and maximum flows within the landscape. Chi-square tests indicated differences in the distributions of the proportions of flowering plants were significant by soil typeslopeaspectand flow accumulation for each month(February-November)for all months(overall)and across months. The Chi-square test on area-normalized data indicated significant differences for all months and individual differences by each month with some months not statistically significant. Cluster analysis on flowering counts for nine plant families with the most flowering counts indicated no unique separation by clusterbut implied that the majority of these families were flowering on strongly sloping(9%–16%) slopeson southwest(202.5°–247.5°) aspectsand low flow accumulation(0–200). Presented methodology can serve as a template for future efforts to quantify spatio-temporal patterns of flowering and other phenological events.  相似文献   

A comparison of the styles of deformation associated with two recent push moraines,South Van Keulenfjorden,Svalbard     

Jane K. Hart  Robert J. Watts 《地球表面变化过程与地形》1997,22(12):1089-1107

In this paper, two push moraine systems associated with two small subpolar glaciers, Finsterwalderbreen and Penckbreen, were investigated. This study showed that at these glaciers the push moraines were formed in association with surges, which produced a different style of moraine depending on the rheology of the deformed material and the glacial history. The moraines are similar in that they are formed by folded outwash sediments and contain little till. However, the forms of these moraines are very different. The Penckbreen moraine is composed of a lower shallow marine sand, silt and clay, and an upper fluvial sand and gravel. Deformation at this site led to the formation of large anticlines in the silts and clays, with disharmonic smaller folds and thrusts in the upper gravels, above a detachment surface between the fine-grained and overlying coarse-grained lithologies. This deformation decreases towards the foreland, with marine and fluvial sediments responding differently because of their different rheological properties. This moraine was formed during one surge event which occured during the early 19th century. In contrast, the Finsterwalderbreen moraine is composed of outwash sand and gravel, and was formed as the result of a series of surge events. These advances all reached a similar limit and occurred at regular intervals. © 1997 John Wiley & Sons, Ltd.  相似文献   

Diverse mid-Miocene silicic volcanism associated with the Yellowstone–Newberry thermal anomaly     

Matthew E. Brueseke  William K. Hart  Matthew T. Heizler 《Bulletin of Volcanology》2008,70(3):343-360

The Santa Rosa–Calico volcanic field (SC) of northern Nevada is a complex, multi-vent mid-Miocene eruptive complex that formed in response to regional lithospheric extension and flood basalt volcanism. Santa Rosa–Calico volcanism initiated at ∼16.7 Ma, concurrent with regional Steens–Columbia River flood basalt activity and is characterized by a complete compositional spectrum of basalt through high-silica rhyolite. To better understand the relationships between upwelling mafic magmatism, coeval extension, and magmatic system development on the Oregon Plateau we have conducted the first comprehensive study of Santa Rosa–Calico silicic volcanism. Detailed stratigraphic-based field sampling and mapping illustrate that silicic activity in this volcanic field was primarily focused along its eastern and western margins. At least five texturally distinct silicic units are found in the western Santa Rosa–Calico volcanic field, including abundant lava flows, near vent deposits, and shallow intrusive bodies. Similar physical features are found in the eastern portion of the volcanic field where four physically distinct units are present. The western and eastern Santa Rosa–Calico units are characterized by abundant macro- and microscopic disequilibrium textures, reflecting a complex petrogenetic history. Additionally, unlike other mid-Miocene Oregon Plateau volcanic fields (e.g. McDermitt), the Santa Rosa–Calico volcanic field is characterized by a paucity of caldera-forming volcanism. Only the Cold Springs tuff, which crops out across the central portion of the volcanic field, was caldera-derived. Major and trace element geochemical variations are present within and between eastern and western Santa Rosa–Calico silicic units and these chemical differences, coupled with the observed disequilibrium textures, illustrate the action of open-system petrogenetic processes and melt derivation from heterogeneous source materials. The processes and styles of Santa Rosa–Calico silicic magmatism are linked to three primary factors, local focusing of and thermal and material contributions from the regional flood basalt event, lithospheric extension within the northern portion of the Northern Nevada rift, and interaction of mid-Miocene silicic magmas with pre-Santa Rosa–Calico lithosphere. Similar processes and styles of mid-Miocene silicic volcanism likely occurred across the Oregon Plateau in regions characterized by both focused lithospheric extension and localized mafic magmatism. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. This paper constitutes part of a special issue dedicated to Bill Bonnichsen on the petrogenesis and volcanology of anorogenic rhyolites.  相似文献   

Long-term impact of the proglacial lake Jökulsárlón on the flow velocity and stability of Breiðamerkurjökull glacier,Iceland     

Nathaniel R. Baurley  Benjamin A. Robson  Jane K. Hart 《地球表面变化过程与地形》2020,45(11):2647-2663

Proglacial lakes are becoming ubiquitous at the termini of many glaciers worldwide due to continued climate warming and glacier retreat, and such lakes have important consequences for the dynamics and future stability of these glaciers. In light of this, we quantified decadal changes in glacier velocity since 1991 using satellite remote sensing for Breiðamerkurjökull, a large lake-terminating glacier in Iceland. We investigated its frontal retreat, lake area change and ice surface elevation change, combined with bed topography data, to understand its recent rapid retreat and future stability. We observed highly spatially variable velocity change from 1991 to 2015, with a substantial increase in peak velocity observed at the terminus of the lake-terminating eastern arm from ~1.00 ± 0.36 m day⁻¹ in 1991 to 3.50 ± 0.25 m day⁻¹ in 2015, with mean velocities remaining elevated from 2008 onwards. This is in stark comparison to the predominately land-terminating arms, which saw no discernible change in their velocity over the same period. We also observed a substantial increase in the area of the main proglacial lake (Jökulsárlón) since 1982 of ~20 km², equating to an annual growth rate of 0.55 km² year⁻¹. Over the same period, the eastern arm retreated by ~3.50 km, which is significantly greater than the other arms. Such discrepancies between the different arms are due to the growth and, importantly, depth increase of Jökulsárlón, as the eastern arm has retreated into its ~300 m-deep reverse-sloping subglacial trough. We suggest that this growth in lake area, forced initially by rising air temperatures, combined with the increase in lake depth, triggered an increase in flow acceleration, leading to further rapid retreat and the initiation of a positive feedback mechanism. These findings may have important implications for how increased melt and calving forced by climate change will affect the future stability of large soft-bedded, reverse-sloped, subaqueous-terminating glaciers elsewhere. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd  相似文献   

Supergiant temperatures and linear radii from near-infrared interferometry     

G. T. van Belle  M. J. Creech-Eakman  A. Hart † 《Monthly notices of the Royal Astronomical Society》2009,394(4):1925-1935

We present angular diameters for 42 Luminosity Class (LC) I stars and 32 LC II stars that have been interferometrically determined with the Palomar Testbed Interferometer. Derived values of radius and effective temperature are established for these objects, and an empirical calibration of these parameters for supergiants will be presented as a function of spectral type and colours. For the effective temperature versus  ( V − K )₀  colour, we find an empirical calibration with a median deviation of  Δ T = 70 K  in the range of  0.7 < ( V − K )₀ < 5.1  for LC I stars; for LC II, the median deviation is  Δ T = 120 K  from  0.4 < ( V − K )₀ < 4.3  . Effective temperature as a function of spectral type is also calibrated from these data, but shows significantly more scatter than the T _EFF versus  ( V − K )₀  relationship. No deviation of T _EFF versus spectral type is seen for these high-luminosity objects relative to LC II giants. Directly determined diameters range up to  400 R_⊙  , though are limited by poor distance determinations, which dominate the error estimates. These temperature and radii measures reflect a direct calibration of these parameters for supergiants from empirical means.  相似文献   

Exploration potential of Cu isotope fractionation in porphyry copper deposits   总被引：6，自引：0，他引：6  

Ryan Mathur  Spencer TitleyFernando Barra  Susan BrantleyMarc Wilson  Allison PhillipsFrancisco Munizaga  Victor MaksaevJeff Vervoort  Garret Hart 《Journal of Geochemical Exploration》2009

We examined the copper isotope ratio of primary high temperature Cu-sulfides, secondary low temperature Cu-sulfides (and Cu-oxides) as well as Fe-oxides in the leach cap, which represent the weathered remains of a spectrum of Cu mineralization, from nine porphyry copper deposits. Copper isotope ratios are reported as δ⁶⁵Cu‰ = ((⁶⁵Cu/⁶³Cu_sample/⁶⁵Cu/⁶³Cu_{NIST 976 standard}) − 1) ? 10³. Errors for all the analyses are ± 0.14‰ (determined by multiple analyses of the samples) and mass bias was corrected through standard-sample-standard bracketing. The overall isotopic variability measured in these samples range from − 16.96‰ to 9.98‰.  相似文献