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，快速气候变化期对堆积物和河流系统有重大影响。新的证据表明，降水脉冲--更高的降雨率或更强烈的风暴--与快速的气候变化有关。在许多情况下，降水脉冲会产生山坡侵蚀、高产沙量和增加洪水强度的脉冲。在美国西南部和中西部沙漠地区进行的研究表明，在全新世晚期的快速气候变化期间，大降水事件和大洪水尤其频繁。在大盆地，与晚更新世气候快速变化相关的降水增加的时期是从洪水湖水位的记录中推断出来的。初步数据表明，中西部和大平原的晚更新世和全新世的快速山坡侵蚀可能彼此同步，并与大盆地中发现的降水脉冲同步。这项博士论文研究项目将调查过去20,000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。重点将放在堆积停机坪上，这是沿河流和湖泊阶地发现的斜坡冲刷沉积。这些围裙在每个研究区域都有发现。它们通常记录了多个坡面侵蚀事件，它们对降水状况的变化很敏感，并且可以进行光学(OSL)测年。在每个区域的野外地点，将使用光学和放射性碳法测定堆积停机坪中的斜坡沉积记录的侵蚀事件的年代。这些记录将在不同地区之间进行比较。该项目的结果可能有助于解释以前在第四纪地貌系统研究中发现的山坡侵蚀速率、产沙量和洪水强度的阶段性变化。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。该项目将有助于限制目前在分散地区发现的降水和产沙量增加的实际地理范围，从而有助于实现这一目标。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.