Doctoral Dissertation Research: Precipitation Pulses and Geomorphic Response During Periods of Late Quaternary Climate Change, Western United States

地貌学家长期以来一直认为，气候快速变化的时期对崩积和河流系统有重大影响。 新的证据表明，降水脉冲-更高的降水率或更强烈的风暴-与快速的气候变化有关。 在许多情况下，降水脉冲将产生山坡侵蚀脉冲，高产沙量，并增加洪水量级。 在美国西南部和中西部沙漠地区进行的研究表明，在全新世晚期气候快速变化期间，产生大洪水的大降水事件特别频繁。 在大盆地，与更新世晚期气候快速变化相关的降水增加事件是从洪积湖水位记录中推断出来的。 初步数据表明，晚更新世和全新世的情节迅速山坡侵蚀在中西部和大平原可能已同步彼此和降水脉冲确定在大盆地。 本博士论文研究项目将调查过去2万年来中西部、大平原、大盆地和西南地区降水脉冲和山坡响应的空间范围。 重点将放在崩积裙上，崩积裙是沿着河流和湖泊阶地发现的斜坡冲刷沉积物。 在每个研究区域都发现了这些围裙。 它们通常记录多个事件的斜坡侵蚀，他们是敏感的降水制度的变化，他们是服从光学（光释光）定年。 在每个区域的实地，将使用光学和放射性碳方法对崩积物裙滩中的坡面冲刷沉积物记录的侵蚀事件进行测年。 然后将这些记录在地区之间进行比较。该项目的结果可能有助于解释先前关于第四纪地貌系统的工作中认识到的山坡侵蚀速率、产沙量和洪水量级的阶段性变化。 为了预测对未来气候变化的响应，了解过去降水脉冲的空间尺度和机制尤为重要。 该项目将有助于实现这一目标，帮助限制目前在分散的地方确定的降水和沉积物产量增加脉冲的实际地理范围。 作为博士论文研究改进奖，该奖项还将提供支持，使有前途的学生建立一个强大的独立的研究生涯。

Geomorphologists have long believed that periods of rapid climate change have significant impacts on colluvial and fluvial systems. New evidence suggests that precipitation pulses -- episodes of higher precipitation rates or more intense storms -- are associated with rapid climatic changes. In many settings, precipitation pulses would produce pulses of hillslope erosion, high sediment yield, and increased flood magnitude. Studies conducted in the desert Southwest and Midwestern U.S. suggest that large precipitation events, producing large floods, were especially frequent during rapid climate changes of the late Holocene. In the Great Basin, episodes of increased precipitation associated with rapid late Pleistocene climatic change are inferred from records of pluvial lake levels. Preliminary data suggest that late Pleistocene and Holocene episodes of rapid hillslope erosion in the Midwest and Great Plains may have been synchronous with each other and with precipitation pulses identified in the Great Basin. This doctoral dissertation research project will investigate the spatial extent of precipitation pulses and hillslope response across the Midwest, Great Plains, Great Basin, and Southwest over the past 20,000 years. The focus will be on colluvial aprons, which are slope wash deposits found along fluvial and lacustrine terraces. These aprons are found in each of the study regions. They typically record multiple episodes of slope erosion, they are sensitive to changes in precipitation regime, and they are amenable to optical (OSL) dating. At field sites in each region, episodes of erosion recorded by slopewash deposits in colluvial aprons will be dated using both optical and radiocarbon methods. These records will then be compared between regions.The results of this project may help explain episodic changes in hillslope erosion rates, sediment yield, and flood magnitudes, recognized in previous work on Quaternary geomorphic systems. For predicting response to future climate changes, it is particularly important to understand the spatial scale and mechanisms of past precipitation pulses. This project will contribute toward that goal by helping to constrain the actual geographic extent of pulses of increased precipitation and sediment yield presently identified in scattered localities. As a Doctoral Dissertation Research Improvement award, this award also will provide support to enable a promising student to establish a strong independent research career.