J. Michael Daniels

Floodplain aggradation and pedogenesis in a semiarid environment

Alluvial valley fills in the upper Republican River basin, southwestern Nebraska, provide evidence for processes of aggradation and pedogenesis on semiarid cut-and-fill floodplains. Sheetflow deposition on unchanneled valley floors represents an important mechanism of valley aggradation. Sheetflow deposits contain parallel to sub-parallel laminae and discontinuous lobate sedimentary structures. Rates of sediment deposition on cut-and-fill floodplains strongly determine the degree to which pedogenic features develop within aggrading alluvium. Three pedofacies common to semiarid alluvial deposits correspond with increasing aggradation rates: (1) cumulic soils; (2) multiple buried soils; and (3) no pedogenic features. Radiocarbon age determinations from alluvial fills indicate that floodplain aggradation greater than approximately 0.5 cm year−1 limits soil formation: this represents a threshold rate of pedogenic assimilation. Floodplain soils formed under aggradation rates lower than this exhibit a strong positive relationship between aggradation rate and total CaCO3 percent, and a negative relationship between aggradation rate and organic carbon percent. Recognizing the associations between pedogenic/sedimentologic features and floodplain aggradation rates can help interpret past rates of sediment transport, storage and deposition.

Paleolithic Landscapes and Seascapes of the West Coast of Portugal

The antiquity of coastal adaptations has gained renewed attention in the last several years as archaeologists have recognized that coasts have long been important foci of human settlement (Bailey 2004; Bailey and Milner 2003; Erlandson and Fitzpatrick 2006; Fa 2008; Price 1995; Sauer 1962; Westley and Dix 2006).

Influence of Rock Glaciers on Stream Hydrology in the La Sal Mountains, Utah

Abstract While valley glaciers have received considerable attention for their contributions to summer runoff during the past decade, the contributions of rock glaciers to summer runoff patterns have largely been ignored, especially in the western United States. This article examines summer runoff from two basins in the La Sal Mountains, Utah: the non—rock glaciated Wet Fork and rock glaciated Gold Basin. Runoff events were analyzed for volume of stormflow, stormflow duration, and peak flow duration. Four events were recorded in Wet Fork (n = 4), five events were recorded in Gold Basin (n = 5), and six events at a flume immediately adjacent to the Gold Basin rock glacier (n = 6). Wet Fork hydrographs are dominated by baseflow throughout the summer and a small proportion (0.13%–0.31%) of precipitation leaves the basin as stormflow during storms. Gold Basin hydrographs are characterized by early season snowmelt with flood peaks associated with summer storms. Runoff from the gaged rock glacier represents 15%–30% of total basin runoff and is inversely related to precipitation and directly related to rainfall intensity. Removal of rock glacier hydrographs from total basin hydrographs indicates that there is increased surface runoff from alpine drainage basins that contain rock glaciers, suggesting rock glaciers act as impervious surfaces. This short-term study in Utah suggests that alpine drainage basins with rock glaciers could have greater surface runoff and higher flood peaks than drainage basins that lack rock glaciers. While the long-term effects of rock glaciers on summer water resources is still unknown, this investigation demonstrates rock glaciers may profoundly influence hydrographs in alpine drainage basins.