Darryll T. Pederson

Boiling sand springs, Dismal River, Nebraska: Agents for formation of vertical cylindrical structures and geomorphic change

Boiling (motion, not temperature) sand springs fed by ground water moving upward along distinct conduits occur along the Dismal River in the Nebraska Sand Hills. The cylindrical conduits are developed in alluvium and are as large as 10 m in diameter and 44 m deep. Sides of the spring conduits are firm. Boiling sand is overlain in several places by a clear layer of water in the spring. Time-varying wave patterns and boils can be observed along the interface between these layers. Sediment within the conduits is generally well sorted, although some debris is present. Because of their large size, firm sides, and persistence in time, the conduits have the potential for preservation as vertical cylindrical structures comparable to those reported in sedimentary rocks of several ages. The discovery of preserved structures is evidence of paleo-ground-water discharge, and therefore the structures are a useful mapping tool for determining position in landscape evolution.

Jurassic earthquake sequence recorded by multiple generations of sand blows, Zion National Park, Utah

Earthquakes along convergent plate boundaries commonly occur in sequences that are complete within 1 yr, and may include 8–10 events strong enough to generate sand blows. Dune crossbeds within the Jurassic Navajo Sandstone of Utah (western United States) enclose intact and truncated sand blows, and the intrusive structures that fed them. We mapped the distribution of more than 800 soft-sediment dikes and pipes at two small sites. All water-escape structures intersect a single paleo-surface, and are limited to the upper portion of the underlying set of cross-strata and the lower portion of the overlying set. A small portion of one set of crossbeds that represents ∼1 yr of dune migration encloses eight generations of eruptive events. We interpret these superimposed depositional and deformational structures as the record of a single shock-aftershock earthquake sequence. The completeness and temporal detail of this paleoseismic record are unique, and were made possible when sand blows repeatedly erupted onto lee slopes of migrating dunes. Similar records should be sought in modern dunefields with shallow water tables.

Estimating hydraulic conductivity from drainage patterns—A case study in the Oregon Cascades

This study introduces a new method for estimating hydraulic conductivity based on the concept of effective groundwater drainage length and DuPuit-Forchheimer assumptions. The effective groundwater drainage length is related to the surface drainage dissection patterns (as expressed in drainage density) forming over long periods of time. Application of the new method to the Oregon Cascades yielded hydraulic conductivity values similar to those documented in the literature. This method represents an effective and efficient way of estimating hydraulic conductivity for regions where the interplay among surface drainage, groundwater, and topography has established a steady-state dynamic equilibrium. It also provides a theoretically sound approach for extrapolating limited local measurements to a large region and revealing the spatial variation of hydraulic conductivity.

An Economical Sampling Pump for Ground-Water Investigations

An economical ground-water sampling system was constructed using readily available parts. The design is durable and easy to use in the field. Problems with cross contamination between wells are minimized; however, this sampling system is limited to shallow depths and is not appropriate when change in sample pressure would significantly affect the water chemistry.