GSM 2017 Nebraska Day 4
Sep 7, 2017Public
Photo: The area we explored is within the red rectangle, through which the Platte River flows.
Photo: In the morning, we explored near Kearney (the right ellipse) and in the afternoon southeast of North Platte (the left ellipse).
Photo: We stop at a quiet location while Jeremy & Paul give us an overview of the Platte River valley.
Photo: We learn much about loess, which is prominent on both side of the Platte River valley in this vicinity. We learn that the loess is the result of winds from the northwest blowing for millennia over the Sand Hills.
Photo: Loess is a clastic, predominantly silt-sized sediment that is formed by the accumulation of wind-blown dust. It covers about 10% of the Earth's surface.
Photo: So how do you pronounce "loess"? Lynne says to remember: "It's no fuss, it's loess."
Photo: At another location, Jeremy describes their most recent mapping and age determinations on alluvium and eolian sand. Here is a drill core from one location.
Photo: Map of the drill holes.
Photo: Photo of drill cores by Rita.
Photo: The shallowest part of this drill core (the soil at the surface) is on the left.
Photo: A second drill core from another location.
Photo: We next visit a borrow pit, where loess is being quarried to use as fill during road construction. In construction and civil engineering, a borrow pit, also known as a sand box, is an area where material (usually soil, gravel or sand) has been dug for use at another location. Borrow pits can be found close to many major construction projects. For example, soil might be excavated to fill an embankment for a highway, clay might be excavated for use in brick-making, gravel to be used for making concrete, etc.
Photo: Loess is an aeolian sediment formed by the accumulation of wind-blown silt, typically in the 20–50 micrometer size range, twenty percent or less clay and the balance equal parts sand and silt that are loosely cemented by calcium carbonate. It is usually homogeneous and highly porous and is traversed by vertical capillaries that permit the sediment to fracture and form vertical bluffs.
Photo: The loess is soft enough to be easily broken with a shovel, as Jeremy demonstrates.
Photo: (photo by Rita) Loess is homogeneous, porous, friable, pale yellow or buff, slightly coherent, typically non-stratified and often calcareous. Loess grains are angular with little polishing or rounding and composed of crystals of quartz, feldspar, mica and other minerals. Loess can be described as a rich, dust-like soil.
Photo: Loess deposits may become very thick; more than a hundred meters in areas of China and tens of meters in parts of the Midwestern United States. It generally occurs as a blanket deposit that covers areas of hundreds of square kilometers and tens of meters thick.
Photo: Loess often stands in either steep or vertical faces. Because the grains are angular, loess will often stand in banks for many years without slumping. This soil has a characteristic called vertical cleavage which makes it easily excavated to form cave dwellings, a popular method of making human habitations in some parts of China. Loess will erode very readily. Here a sunflower hopes it will not erode too readily.
Photo: These weeds suffered the fate of loess erosion.
Photo: Mud cracks in the loess
Photo: Maxwell, NE: Sounds like the start of a joke: A bus and an old tractor pull into a gas station in Nebraska...
Photo: Road to Bignell Hill, in the Loess Hills area of western Nebraska, where a road cut exposes the thickest known exposure (48 meters) of last-glacial loess in the world, overlain by 2 meters of Holocene loess.
Photo: This sign warns us there might be difficulties, but we consolidate into a few vehicles as possible and hope for the best.