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Climatic controls on aeolian activity in the Mojave and Colorado Deserts, California.

机译：加利福尼亚州莫哈韦沙漠和科罗拉多沙漠中风沙活动的气候控制。

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摘要

This research assesses the response of aeolian sand to climatic conditions during the period 1973-1994. Sand dune (aeolian sand) mobility is in part controlled by sediment supply, wind energy, and surface conditions (i.e. vegetation cover and character, surface crusting, soil development etc.). In the Mojave and Colorado Deserts of California a dune mobility index based on climatic variables (wind energy, precipitation and potential evapotranspiration) predicts that dunes should be mostly active. In point of fact, the dunes are mostly inactive. A combination of complex topography, which leads to mesoclimatic variations, and the seasonality of precipitation gives rise to a pattern of aeolian activity that reflects local influences as much as, or more than regional climatic influences.; In order to test the utility of the mobility index, an independent measure of dune mobility is developed. The field index of sand mobility (FISM) uses field observations to objectively measure the mobility of a sand dune landscape. Observations of vegetation type and cover, surface stabilizing features, and aeolian landforms and features are assigned relative numerical values. Dunes with low index values have high degrees of mobility. Higher values of FISM are found in more relict dune areas.; The FISM performs well in evaluating the actual mobility state of a location. Active dune fields like Kelso and Algodones have FISM less than 100. The less active flanks of these dunes have higher FISM values. Many dunes in the eastern Mojave Desert are episodically active and have FISM values between 100-300. Dormant dunes have FISM values over 300, as illustrated by the dune field in Antelope Valley.; Principal component analysis of the mobility index distinguishes four distinct regions of mobility: the moderately active to dormant central Mojave Desert; the very active Colorado Desert; the Lancaster and Palm Springs areas which are dormant, but prone to reactivation; and the southeastern Mojave Desert where sand transport pathways exist. The field index of sand mobility provides an independent measure of dune activity. Regression analysis shows that the field index of sand mobility does a good job of estimating the Lancaster mobility index (57.4% of variance explained). The combination of both methods provides a powerful tool in evaluating the mobility state of desert dunes.; Reactivation of stabilized dunes in the Mojave and Colorado Deserts may occur if the climate during the next century becomes warmer and drier as suggested by global climate models. Eight consecutive years of below normal precipitation and particularly the severe drought of 1989-1990 led to an overall reduction in natural vegetation cover by October 1990, when approximately 20,000 ha had been been wind eroded. Unfortunately it is not possible to disentangle the effects of 8-years of drought (1984-1990)) from 2-years of severe drought (1989-1990) from one year of very severe drought (1990) and determine which was/were responsible for the increase in wind erosion during 1990.; Considerable paleoclimatic research has been conducted in the Mojave Desert, but there is not a satisfactory contemporary data base for comparison. A better understanding of the physical processes linking contemporary climate and the contemporary aeolian system will allow process-based interpretations of paleoclimatic indicators, such as relict dune features. This dissertation bridges that gap by increasing understanding of the dynamics of the contemporary aeolian system.
机译：这项研究评估了1973-1994年期间风沙对气候条件的响应。沙丘（风沙）的流动性部分受沉积物供应，风能和地表条件（即植被覆盖和特征，地表结皮，土壤发育等）的控制。在加利福尼亚的莫哈韦沙漠和科罗拉多沙漠中，基于气候变量（风能，降水和潜在的蒸散量）的沙丘流动性指数预测，沙丘应该主要是活跃的。实际上，沙丘大多不活跃。复杂的地形会导致中温气候变化，而降水的季节性会导致风沙活动模式的发生，这种活动反映的是当地的影响，甚至多于区域的气候影响。为了测试迁移率指数的效用，开发了沙丘迁移率的独立度量。沙土迁移率的现场指数（FISM）使用野外观察来客观地测量沙丘景观的迁移率。为植被类型和覆盖率，表面稳定特征以及风沙地貌和特征的观测分配了相对数值。折射率值较低的沙丘具有较高的活动度。在更多的沙丘地区发现FISM的价值更高。 FISM在评估位置的实际移动状态方面表现良好。活跃的沙丘场（例如Kelso和Algodones）的FISM小于100。这些沙丘的较不活跃的侧翼具有较高的FISM值。莫哈韦沙漠东部的许多沙丘都活跃着，FISM值在100-300之间。休眠沙丘的FISM值超过300，如羚羊谷地的沙丘场所示。流动性指数的主成分分析区分了四个不同的流动性区域：中度活跃到休眠的莫哈韦沙漠中部；非常活跃的科罗拉多沙漠；处于休眠状态但易于恢复活动的兰开斯特和棕榈泉地区；还有东南部的莫哈韦沙漠（Mojave Desert），那里存在着输沙途径。沙流动性的现场指数提供了沙丘活动的独立度量。回归分析表明，砂流动性的现场指数在估算兰开斯特流动性指数方面做得很好（解释了57.4％的方差）。两种方法的结合为评估沙漠沙丘的流动状态提供了有力的工具。如果全球气候模型表明，如果下一世纪的气候变得更温暖和更干燥，则可能会在莫哈韦沙漠和科罗拉多沙漠恢复稳定的沙丘。连续八年低于正常降水，特别是1989-1990年的严重干旱导致到1990年10月自然植被的总覆盖率下降，当时大约20,000公顷被风蚀。不幸的是，不可能将8年干旱（1984-1990）与2年严重干旱（1989-1990）与非常严重干旱（1990）的影响区分开来，并确定是哪个原因1990年风蚀增加。在莫哈韦沙漠进行了大量的古气候研究，但没有令人满意的当代数据库可用于比较。对联系当代气候和当代风沙系统的物理过程的更好理解将允许对古气候指标（例如沙丘特征）进行基于过程的解释。本文通过对现代风尘系统动力学的认识的弥合，弥合了这一差距。

著录项

  • 作者

    Bach, Andrew James.;

  • 作者单位

    Arizona State University.;

  • 授予单位 Arizona State University.;
  • 学科 Physical Geography.; Geology.
  • 学位 Ph.D.
  • 年度 1995
  • 页码 310 p.
  • 总页数 310
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 自然地理学;地质学;
  • 关键词

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