ABSTRACT The Mitchell Plateau of south-central Indiana is one of the iconic karst landscapes of the United States. The sinkhole-dimpled forests, fields, and farms; the extensive cave systems; and the deep windows into the groundwater system have fostered curiosity, exploration, and publication since the mid-1800s. This paper is designed to complement a field excursion to the classic features of this landscape. Included are literature reviews focused on three karst basins of the Mitchell Plateau: Mill Creek–Mosquito Creek, Bluespring Caverns, and Lost River. Geomorphic, hydrologic, and geochemical data are synthesized in the modern context of our understanding of epigenetic karst. Revealed are three styles of karst basin: (1) small, shallow karst aquifers strongly controlled by meteoric recharge and epikarst percolation; (2) intermediate-size karst aquifers with significant base flow and surface-water–groundwater interaction; and (3) regional aquifer systems with outcrop belt recharge, downdip transport into confinement with long water-rock interaction times, and artesian flow or entrainment of mineralized waters through fractures into springs or surface waters. Quaternary glaciation has greatly influenced the vertical position of base level through river incision and sediment aggradation; conduit development is controlled by proximity to the major rivers and the stratigraphic position of conduits.

Abstract Relict glacial and periglacial environments are widespread, and the deposits that they are associated with mean it is inevitable that the design and construction of many projects will be influenced by their presence and nature. Tills and other glaciogenic deposits prove to be particularly challenging in this context for reasons that include: the spatial variability of the nature of the deposits; the wide range of particle sizes often included within a given soil, including large-sized particles; spatial variation in soil type and properties; variation in depth to rockhead and variable degrees of weathering and alteration; the presence of groundwater, that is misinterpreted as perched water, as well as sub-artesian and artesian conditions; the presence of solution features and fissures, partly or completely infilled with soft or loose material; and the presence of (often shallow) shear surfaces at residual strength. In this chapter, some of the more common problems and associated solutions associated with earthworks and man-made slopes, tunnels and underground structures, dams and reservoirs, foundations, and offshore engineering and installations are reviewed. It is important that great care is taken in addressing the influences of variability, complexity and uncertainty inherent in glacial/periglacial soil formations at all stages of the construction process, from feasibility to end-of-project activities, such as preparation of the as-built drawings.

ABSTRACT Steens Mountain, a fault-block in the northern Basin and Range Province, rises 1.7 km above flanking basins and drives hydrologic systems that include hot springs, fresh-water streams, and cold artesian wells in the Alvord Valley. It also feeds freshwater streams, desert wetlands, and shallow fresh-water and alkali lakes in the Harney Basin. Steens Mountain melt water from the winter snow pack partitions to surface-water and groundwater systems. How the composition of these fluids evolve along the various flow paths as a result of differences in the geology, interaction with geother-mal aquifers, surface storage time, degree of evaporation, and biology will be examined. Deep-seated flow paths feed Alvord Valley hot springs, which discharge to the east, in the rain shadow of Steens Mountain. The largest of these hot spring systems— Borax Lake—along with features at Mickey Hot Springs, offer ample opportunity to investigate how biosignatures form and become preserved in hydrothermally precipitated sinter deposits. Surface water moving off the westward-dipping slope of Steens Mountain passes through wetland environments to Malheur Lake in Harney Basin. This key point along the Pacific flyway provides wonderful wildlife viewing and the chance to ponder the impacts of biology on lake chemistry. Finally, we will visit the saline-alkaline Harney Lake, the terminal sump for the water moving through Malheur Lake and all of the nearly 40,000 km 2 Harney Basin. At this locale, the focus will be on the influence of evaporative processes on water composition.

The Chesapeake Bay impact structure is a late Eocene complex crater that was excavated ~35 Ma ago in a continental shelf environment at the Atlantic margin, in Virginia. It is the largest impact structure in the United States and the seventh largest on Earth. It has an average diameter of ~85 km and is centered near Cape Charles. The scientific well Eyreville B drilled within the framework of the International Continental Scientific Drilling Program (ICDP) penetrated the deep crater moat ~9 km from the center of the structure. Core holes drilled in impact structures are especially suited for investigations of the influence of lithological heterogeneities on petrophysical properties and the thermal field. In the Eyreville B core hole, two high-resolution temperature-logging campaigns and a petrophysical profile measured on core samples spaced at ~10 m intervals were recorded. The temperature values of the first campaign in December 2005 were heavily disturbed by outflow of artesian water and could only be used for an estimation of the depth where the fluid originated. For the second campaign in May 2006, a riser was constructed to enable measurements in standing (equilibrated) fluid of the well without opening the well head. This construction yielded a measurement of the undisturbed temperature profile as well as recognition of thermal relaxation after some outflow of artesian water, which heated the surrounding rock. The data allowed determination of (1) the origin of the artesian water, (2) equilibrium temperatures derived from the relaxation process, (3) microclimatic effects at the nearby test well STP2, (4) lateral heterogeneities in the core holes STP2 and Eyreville B, and (5) a profile of vertical heat-flow density in the Eyreville B core. From the calculated vertical component of the thermal gradient and the thermal conductivity measured on core samples, a mean heat-flow density of 65 ± 6 mW/m 2 in the 440–1100 m depth interval was determined. These data and results are now available for application in numerical models of the local and regional geologic, hydrologic, and geothermal regimes.

Abstract Over the past four decades, ongoing deformation of an 18-m-thick peat deposit within the flat-lying Mercer Slough has resulted in damaging deflections, and near-collapse in three cases, of pile-supported Interstate 90 bridges and a major water line on the east side of the slough. The peat is partially underlain by a dense sand unit, which includes a highly pressurized aquifer that produces artesian flow 1–2.5 m above the ground surface. Inclinometers on the east side of the slough show the peat flowing toward the structures and then apparently directed west along the interstate centerline. Large displacements recorded in several inclinometers near the center of the slough suggest a length of deforming peat that approaches 600 m, which is likely initiating retrogressively. Potential causal mechanisms include poor engineering characteristics of the peat, presence of high hydrostatic pressure transmitted within and beneath the peat, seasonal water-level variations of Lake Washington and induced hydraulic gradients within the peat, dredging of the Mercer Slough channel, puncturing of the underlying aquifer by numerous pile foundations, and fill placement along the eastern margin of the slough. The peat is flowing around the pile/shaft foundations; however, excessive lateral loads are still being applied to the foundations in a poorly understood and unpredictable manner. The most severe deflections have occurred in the outermost structures where the peat is primarily flowing transverse to the structures.

Cave, spring, and sinkhole development in the Ozarks of south-central Missouri is placed in a geologic framework through detailed geologic mapping. Geologic mapping shows that initial dissolution and inception of cave development is concentrated just beneath sandstone beds within Upper Cambrian and Lower Ordovician dolostone. Although rocks of the Ozarks have systematic and pervasive vertical joints, the development of karst conduits is controlled by bedding planes and stratigraphic variability. In the Salem Plateau of south-central Missouri, sinkholes occur in the lower part of the Ordovician Roubidoux Formation, where sinkholes are rimmed with and contain sandstone that has collapsed into voids in the underlying Ordovician Gasconade Dolomite. Cave diving by the Ozark Cave Diving Alliance into Alley Spring, a large (average flow 3.7 m 3 /s) spring along the Jacks Fork in the Ozark National Scenic Riverways, shows that although the spring discharges from the middle part of the Gasconade, the source of water is a cave passage just beneath the Gunter Sandstone Member of the Gasconade Dolomite. Artesian conditions cause the upward movement of groundwater from cavernous dolostone beneath the sandstone aquitards to the large springs. We hypothesize that sandstone, which is largely impermeable due to silica cementation, acts as a confining unit where hydraulic pressure, combined with mixing of water of differing chemistry, increases dissolution in the underlying dolostone beds.

Deep phreatic shafts and travertine-capped sinkholes characterize Sistema Zacatón, an isolated karst area in northeastern Mexico. At a depth of at least 329 m, El Zacatón is the deepest known underwater pit in the world. Hypogenic karst development related to volcanism is proposed to have formed El Zacatón and is thought to have diminished since the late Quaternary peak activity. The resulting geomorphic overprint of Zacatón displays features similar to hydrothermal groundwater systems throughout the world. Other karst areas in northeastern Mexico are known for deep pits and high-flow springs rising from great depths, but differ from Zacatón in the speleogenetic processes that developed the caves. Sótano de Las Golondrinas (378 m), 200 km to the southwest of Zacatón, is among the deepest air-filled shafts in the world. The Nacimiento del Río Mante, 100 km to the west, is a large artesian spring that extends a minimum of 270 m below the water table. Although these three world-class karst systems all formed in Cretaceous limestone and are located relatively close together, there are significant differences in lithology, tectonic setting, and geomorphic features. Geochemical, microbiological, and geomorphologic data for Zacatón indicate that cave formation processes are similar to those observed in other volcanically influenced systems.