Geology topics

Rachel Sortor

Publications and source records attributed to Rachel Sortor.

2 recordsLinked to original sources

USGS2026

FluOil—A tool for estimating the transport and deposition of oil-particle aggregates in rivers

The FluOil tool was developed to help with planning and early response for oil spills in rivers where subsurface oil-sediment interactions result in the formation of oil-particle aggregates (OPA). The turbulence and variable velocity associated with water flowing within a natural stream channel creates the conditions needed for an oil slick to break up into small droplets and mix in the water column, collide with sediment or organic detritus, and form OPA. This process is similar to what occurs due to wave action along a shoreline. The FluOil tool estimates how fast OPA travel downstream in rivers as well as when and where they may deposit. The FluOil tool relies on pre-existing channel hydraulic data along with user-specified OPA characteristics of size, settling velocity and critical shear stress to compute OPA transport. It is important to know where OPA are transported and accumulated for understanding potential impacts on drinking water intakes, burial of sensitive habitat beds, potential toxicity to benthic organisms, and prolonged sheening from resuspension and breakup. OPA tend to accumulate with fine-grained (silt and clay) sediment deposits (“mud” or “muck”) in backwater areas, oxbows, side channels, pools, and other slow-moving reaches of rivers during low flows. Deposited OPA can be resuspended during high flows, driving continued environmental impact concerns that may extend beyond typical oil spill response timelines.

Fact Sheet↗

USGS2021

Early Pleistocene climate-induced erosion of the Alaska Range formed the Nenana Gravel

The Pliocene-Pleistocene transition resulted in extensive global cooling and glaciation, but isolating this climate signal within erosion and exhumation responses in tectonically active regimes can be difficult. The Nenana Gravel is a foreland basin deposit in the northern foothills of the Alaska Range (USA) that has long been linked to unroofing of the Alaska Range starting ca. 6 Ma. Using 26 Al/ 10 Be cosmogenic nuclide burial dating, we determined the timing of deposition of the Nenana Gravel and an overlying remnant of the first glacial advance into the northern foothills. Our results indicate that initial deposition of the Nenana Gravel occurred at the onset of the Pleistocene ca. 2.34 Ma and continued until at least ca. 1.7 Ma. The timing of initial deposition is correlative with expansion of the Cordilleran ice sheet, suggesting that the deposit formed due to increased glacial erosion in the Alaska Range. Abandonment of Nenana Gravel deposition occurred prior to the first glaciation extending into the northern foothills. This glaciation was hypothesized to have occurred ca. 1.5 Ma, but we found that it occurred ca. 0.39 Ma. A Pleistocene age for the Nenana Gravel and marine oxygen isotope stage 10 age for the oldest glaciation of the foothills necessitate reanalysis of incision and tectonic rates in the northern foothills of the Alaska Range, in addition to a shift in perspective on how these deposits fit into the climatic and tectonic history of the region.

Alaska↗