Doctoral Dissertation Research: Holocene Megadroughts of the Central Great Plains

像20世纪30年代和50年代那样的历史性干旱，对大平原产生了严重的社会、经济和环境影响。然而，它们被全新世更严重、更广泛的史前巨灾所超越。在这些大规模的干旱条件下，植被覆盖减少，土壤屈服于侵蚀性的风，导致覆盖大平原大部分地区的沙尘沉积广泛流动。在堪萨斯大学地理系威廉·约翰逊教授的指导下，博士生艾伦·哈尔芬将确定大平原中部史前特大干旱的时期，从而更好地确定过去干旱的模式。史前干旱的年代将通过使用光激发发光技术(OSL)测定堪萨斯州西南部阿肯色河流域对干旱敏感的沙丘的年代来确定。这种测年方法可以确定单个沙粒最后一次暴露在阳光下的时间，将提供可靠的沙丘活动年龄和伴随的干旱条件。还将对沙丘区域进行分析，以评估其矿物学成熟度，这是景观年龄的相对指标。矿物学成熟度提供了有关沙丘沉积来源、运移历史和沙丘区风化史的信息。最后，沙丘活动期将与大平原其他地方的类似研究进行比较，以确定史前干旱的空间和时间模式。鉴于气候模型已经预测了本世纪大平原气温上升和降水减少，这项研究将进一步增强我们对过去干旱模式的了解，并将为更好地校准现有气候模型提供重要的古气候数据。这项研究促进了学术机构和政府机构之间的多元化合作，提高了本科生的教育水平。

Historic droughts, like those of the 1930s and 1950s, had severe social, economic, and environmental ramifications for the Great Plains. They were, however, transcended by the more severe and geographically extensive prehistoric megadroughts of the Holocene. Under these massive drought conditions, vegetation cover was diminished, and soils succumbed to erosive winds, causing the widespread mobilization of dust and sand deposits, which mantle much of the Great Plains. Doctoral student Alan Halfen under the guidance of Professor William Johnson in the Department of Geography at the University of Kansas will determine periods of prehistoric megadroughts in the central Great Plains, thereby better defining patterns of past droughts. The chronology of prehistoric droughts will be determined by dating drought-sensitive sand dunes in the Arkansas River valley, southwestern Kansas, using optically stimulated luminescence (OSL). This dating method, which determines when individual sand grains were last exposed to the sun, will provide reliable ages of dune activity and attendant drought conditions. The dune field will also be analyzed to assess its mineralogical maturity, a relative indicator of landscape age. Mineralogical maturity provides information regarding dune sediment provenance, transport history, and weathering history of a dune field. Lastly, periods of dune activity will be compared to similar studies elsewhere in the Great Plains to identify spatial and temporal patterns of prehistoric drought. Given that climate models have predicted increased temperatures and decreased precipitation in the Great Plains this century, this study will further enhance our knowledge of patterns of past drought and will provide vital paleoclimatic data to better calibrate existing climatic models. This study promotes diverse collaboration between academic institutions and government agencies, and enhances the education of undergraduate students.