Abstract Rare jökulhlaup events, also known as subglacial lake outburst flood events, have been observed at the Law Dome ice margin and provide an insight into the physical characteristics of subglacial meltwater and drainage. The subglacial topography based on data from the BEDMAP2 and ICECAP projects, together with subsurface transects of the ice margin obtained using ground-penetrating radar, reveal several lakes and lake-like depressions and the drainage pathways of two jökulhlaup events. Oxygen isotope typing of the meltwater during the most recent (2014) jökulhlaup event, combined with ice margin stratigraphy, enable the identification of ice tunnel melt pathways that exploit the 30–90° dipping basal ice layering. The presence of subglacial meltwater beneath Law Dome during the Holocene to Glacial periods is confirmed by the dendritic drainage pattern in the subglacial morphology and extensive layers of basal regelation ice and subglacial carbonate precipitate deposits found within the Løken Moraines sediments. These subglacial carbonates, including ooid layers, formed from the mixing of glacial meltwater and seawater at 72 ka BP. The combined evidence indicates that the ocean discharge of subglacial meltwater may be variable and/or is periodically blocked by basal freezing events near the ice sheet terminus.

Geologic structure often controls the location of recharge points, flow paths, velocities, and discharge locations in karst regions such as Morell Cave and its springshed, Bluff City, Tennessee. This study explores groundwater recharge points, velocities, and discharge locations within the Morrell springshed and its associated cave. Two dye tracing experiments were conducted in the spring and fall of 2012 to identify recharge sources, delineate the springshed, and to interpret structural controls for groundwater flow. The experiments confirmed that allogenic recharge from the northern slopes of Holston Mountain enters the karst system through swallets and flows to the northwest following dominant joint trends that transect local folds. When the groundwater reaches Morell Cave, the flow is redirected northeast and parallels a shallow thrust fault, along which Morell Cave has developed, before resurging at Morell Spring. Using a joint-path flow model, groundwater velocities ranged from 0.04–0.007 m/s, which is consistent with typical groundwater velocities in karst systems.

Abstract Upper North Chickamauga Creek in Hamilton and Sequatchie Counties, Tennessee, is severely impacted by acid mine drainage (AMD) emanating from more than 15 abandoned coal mines in headwater tributaries. AMD is formed when pyrite and other sulfide minerals are exposed to air and water during coal mining. It is characterized by low pH (<2.8) and elevated concentrations of acidity, iron, aluminum, sulfate, and other pollutants. These attributes tend to be toxic to most aquatic life and result in reduced aesthetics and potential uses of the water. The North Chickamauga Creek Watershed Restoration Project is a multi-organizational effort to restore the upper 18 miles of the North Chickamauga Creek watershed to a level that will support a warm-water fishery. Several passive treatment systems (PTS) have been installed at abandoned mining sites in the North Chickamauga Creek watershed where AMD is generated and is flowing into surface waters. PTS is the engineered use of natural and enhanced geological, biological, chemical, and physical processes to prevent pollutant generation or to remove pollutants from aqueous discharges. PTS include technologies such as constructed wetlands, anoxic limestone drains, mine seals and flooding, successive alkalinity-producing systems, limestone trenches, and other components. During this field trip to the upper reaches of the North Chickamauga Creek watershed, we will visit several of the operational systems and observe untreated AMD. Participants will gain an understanding of how AMD is generated, its impacts and characteristics, and how it can be prevented or treated. This field trip requires extensive hiking over moderate slopes and sometimes vegetated terrain.

It has long been hypothesized that flux of fresh meltwater from glacial Lake Minong in North America's Superior Basin to the North Atlantic Ocean triggered rapid climatic shifts during the early Holocene. The spatial context of recent support for this idea demands a reevaluation of the exit point of meltwater from the Superior Basin. We used ground penetrating radar (GPR), foundation borings from six highway bridges, a GIS model of surface topography, geologic maps, U.S. Department of Agriculture–Natural Resources Conservation Service soils maps, and well logs to investigate the possible linkage of Lake Minong with Lake Chippewa in the Lake Michigan Basin across eastern Upper Michigan. GPR suggests that a connecting channel lies buried beneath the present interlake divide at Danaher. A single optical age hints that the channel aggraded to 225 m as elevated receipt of Lake Agassiz meltwater in the Superior Basin began to wane <10.6 ka. The large supply of sediment required to accommodate aggradation was immediately available at the channel's edge in the littoral shelves of abandoned Lake Algonquin and in distal parts of post-Algonquin fans. As discharge decreased further, the aggraded channel floor was quickly breached and interbasin flow to Lake Chippewa was restored. Basal radiocarbon ages on wood from small lakes along the discharge path and a GIS model of Minong's shoreline are consistent with another transgression of Minong after ca. 9.5 ka. At the peak of the latter transgression, the southeastern rim of the Superior Basin (Nadoway Drift Barrier) failed, ending Lake Minong. Upon Minong's final drop, aggradational sediments were deposited at Danaher, infilling the prior breach.

Abstract Gullies are common features throughout the southwestern United States including Army training facilities such as the Pinon Canyon Maneuver Site. These gullies have depths up to several meters, which can restrict the mobility of troops and vehicles during training exercises. They also have the potential to grow in size, which can degrade training lands. At the upstream end, gullies usually begin with an abrupt headwall, and in the downstream direction, gullies also tend to terminate abruptly. In this paper, we hypothesize that the small extent of convective storms and significant transmission losses in channels promote the downstream disappearance of gullies. The role of these factors is tested by applying a geomorphic model in which storms occur within circular portions of the simulation domain and channel flow is lost to seepage up to a specified infiltration or seepage capacity in each grid cell. The net effect of these processes is to reduce the sediment transport capacity in the downstream direction relative to the case with an infinite storm size and no channel losses. The reduced sediment capacity alters the relationship between slope and drainage area for topographies at equilibrium. In addition, limited storm sizes can also produce disconnected areas of incision within generally depositional portions of the landscape.

Studies of groundwater flow within the Mosier syncline, part of the Yakima Fold Belt, have shown complex flow system boundaries that result from the interaction of Columbia River Basalt Group flows with the paleoenvironment. A developing Mosier syncline provided low areas that hosted drainages and accumulated sediment and controlled the distribution of Saddle Mountains and Wanapum Basalt lava flows of the Columbia River Basalt Group. Those flows interacted with water and water-saturated sediment within the developing syncline to form permeable zones at the flow contacts. Aquifers have been identified in the Pomona Member of the Saddle Mountains Basalt, and in the Priest Rapids and Frenchman Springs Members of the Wanapum Basalt. Units stratigraphically equivalent to the Ellensburg Formation locally form low-permeability sedimentary interbeds within the Columbia River Basalt Group section. Boundary conditions of present groundwater flow systems within Columbia River Basalt Group terrains reflect the stratigraphy and permeability distribution resulting from the depositional environment, and the influences of postdeposition landscape development. Low-permeability boundaries tend to be controlled by stratigraphy and structure. Recharge and discharge boundaries tend to result from postdepositional landscape development such as changes in topography and drainage systems. Analysis of hydrologic information provides insights into the influences of stresses and boundaries on Columbia River Basalt Group groundwater systems. Hydraulic head data have shown that the main stresses to the flow system near Mosier are pumping, interaquifer flow through uncased wells, and climate fluctuations. Long-term groundwater declines are the result of overpumping in the Pomona aquifer and depressurization of other aquifers connected to the Pomona aquifer through uncased wells. The groundwater system discharges to Mosier Creek, and the elevation of the discharge point appears to control the lower limit of observed heads throughout the aquifer system.

We have developed a conceptual model for the Tesuque aquifer system in the southeastern Española Basin near Santa Fe, New Mexico, based on measurements of chemical, isotopic, and thermal properties of groundwater from 120 wells. This study concentrates on a single groundwater-flow unit (GFU) of the Tesuque aquifer associated with the Santa Fe River drainage, where groundwater flows east to west across north-trending rift structures. We examine links between groundwater flow, temperature, water chemistry, and major fault structures. Hydrologic and hydrochemical processes are assessed through spatial mapping of temperature and chemical composition (Ca:Na ratios, F, As, B, Li, δ 2 H, and δ 18 O), Piper and bivariate plots, Spearman rank-order correlations, and flow-line modeling of mineral saturation (PHREEQC software). Results help delineate recharge and discharge areas and demonstrate spatial correspondence of major rift structures with changes in chemical and thermal data. Thermal wells with anomalous discharge temperatures and regional thermal gradients exceeding 40 °C/km align with structural boundaries of the Cañada Ancha graben and Caja del Rio horst. Mg-Li geothermometry characterizes temperatures associated with deep circulating groundwater. Important features of the conceptual model are (1) a forced convection system in the Tesuque aquifer associated with the Caja del Rio horst drives upward flow and discharge of warm, Na-rich groundwater in the western half of the Cañada Ancha graben; and (2) major horst-graben structures concentrate upward flow of deep, NaSO 4 thermal waters from underlying bedrock. Both features likely contribute to chemical anomalies and thermal disturbances in the shallow Tesuque aquifer.

In 2002, Yucca Mountain, Nevada, was selected as the proposed site for the U.S. high-level nuclear waste repository. Yucca Mountain lies within a large topographically closed basin, in which surface water is internally drained. Groundwater, however, can and does flow into and out of this basin at depth through a regional carbonate-rock aquifer (commonly referred to as the lower carbonate-rock aquifer). Most groundwater recharge (water infiltrating downward through the unsaturated zone into the water table) originates in the highlands north of Yucca Mountain and flows generally southward. Some groundwater discharges within the basin, as in Oasis Valley and the southern Amargosa Desert, but the ultimate discharge is in Death Valley, where water is returned to the atmosphere by evapotranspiration. Groundwater flows through a heterogeneous medium produced by a complex geologic history including both compressional and extensional tectonics. For hydrologic purposes, the rocks and alluvium are divided into 25 hydrogeologic units. Regionally, the most important unit for regional groundwater flow is composed of Paleozoic carbonate rocks, which are locally separated into two aquifers by an intervening shale. Rocks of the southwestern Nevada volcanic field form thick deposits in the northern part of the basin, and these rocks host both aquifers and confining units. The potentiometric surface of the site-scale flow system contains areas of large hydraulic gradient (as great as 0.13) and small hydraulic gradient (as small as 0.0001). Both extremes are found within the Yucca Mountain site area, where they are well constrained by numerous boreholes. At Yucca Mountain, a single borehole penetrates to the regional carbonate-rock aquifer, and, at this locality, the hydraulic head at depth is 20 m greater than in the overlying volcanic rocks. This head difference is likely widespread, as indicated by thermal highs at the groundwater table in the vicinity of block-bounding faults, where upward leakage of water from the regional carbonate-rock aquifer is postulated. Since the early 1980s, numerous two- and three-dimensional flow models have been developed to depict regional groundwater flow. A 2004 transient flow model of the Death Valley region has 16 layers and a 1500 m/side horizontal grid; it is composed of 194 rows and 160 columns. The model was first calibrated to a steady-state condition and then to transient conditions. The model matches observed flow patterns well, and it generally agrees with measured water levels except in areas of large hydraulic gradient. The regional model provides the boundary conditions for a detailed site-scale flow model. The finite-element heat and mass transfer code, FEHM v2.24, was used to simulate flow through the saturated zone at Yucca Mountain. Cells in the site-scale model are 250 m/side in the horizontal grid; it is composed of 181 rows and 121 columns. The model may use as many as 67 layers, but the framework model allows a stair-stepped ground surface, so the number of layers is variable. Layer thickness ranges from 600 m at the bottom of the model to 10 m south of Yucca Mountain. The site-scale flow model was constructed and calibrated, matching observed hydrologic data well. The site-scale flow model provides a means for assessing the hypothetical flow path for any radioactive materials originating from the proposed repository.

Surface, unsaturated-zone, and saturated-zone hydrologic conditions at Yucca Mountain responded to past climate variations and are at least partly preserved by sediment, fossil, and mineral records. Characterizing past hydrologic conditions in surface and subsurface environments helps to constrain hydrologic responses expected under future climate conditions and improve predictions of repository performance. Furthermore, these records provide a better understanding of hydrologic processes that operate at time scales not readily measured by other means. Pleistocene climates in southern Nevada were predominantly wetter and colder than the current interglacial period. Cyclic episodes of aggradation and incision in Fortymile Wash, which drains the eastern slope of Yucca Mountain, are closely linked to Pleistocene climate cycles. Formation of pedogenic cement is favored under wetter Pleistocene climates, consistent with increased soil moisture and vegetation, higher chemical solubility, and greater evapotranspiration relative to Holocene soil conditions. The distribution and geochemistry of secondary minerals in subsurface fractures and cavities reflect unsaturated-zone hydrologic conditions and the response of the hydrogeologic system to changes in temperature and percolation flux over the last 12.8 m.y. Physical and fluid-inclusion evidence indicates that secondary calcite and opal formed in air-filled cavities from fluids percolating downward through connected fracture pathways in the unsaturated zone. Oxygen, strontium, and carbon isotope data from calcite are consistent with a descending meteoric water source but also indicate that water compositions and temperatures evolved through time. Geochronological data indicate that secondary mineral growth rates are less than 1–5 mm/m.y., and have remained approximately uniform over the last 10 m.y. or longer. These data are interpreted as evidence for hydrological stability despite large differences in surface moisture caused by climate shifts between the Miocene and Pleistocene and between Pleistocene glacial-interglacial cycles. Secondary mineral distribution and δ 18 O profiles indicate that evaporation in the shallower welded tuffs reduces infiltration fluxes. Several near-surface and subsurface processes likely are responsible for diverting or dampening infiltration and percolation, resulting in buffering of percolation fluxes to the deeper unsaturated zone. Cooler and wetter Pleistocene climates resulted in increased recharge in upland areas and higher water tables at Yucca Mountain and throughout the region. Discharge deposits in the Amargosa Desert were active during glacial periods, but only in areas where the modern water table is within 7–30 m of the surface. Published groundwater models simulate water-table rises beneath Yucca Mountain of as much as 150 m during glacial climates. However, most evidence from Fortymile Canyon up gradient from Yucca Mountain limits water-table rises to 30 m or less, which is consistent with evidence from discharge sites in the Amargosa Desert. The isotopic compositions of uranium in tuffs spanning the water table in two Yucca Mountain boreholes indicate that Pleistocene water-table rises likely were restricted to 25–50 m above modern positions and are in approximate agreement with water-table rises estimated from zeolitic-to-vitric transitions in the Yucca Mountain tuffs (less than 60 m in the last 11.6 m.y.).

Thermal spring deposits are features of considerable interest to Mars scientists because of their potential as astrobiological oases and as records of the paleohydrology of the planet. Terrestrial counterparts can assist in recognizing such features on Mars and in developing technologies for their study and sampling. In this paper, we describe one such analog, the Dalhousie Springs complex in central Australia. The Dalhousie Springs complex is one of largest groundwater discharge landforms known on Earth. It is a carbonate-limited precipitation system due to the non-supersaturated ascending water. Spring carbonates are deposited as discrete mounds and outflow channels resting unconformably on older units. Although subject to postformation geomorphic modification, the spring deposits persist in the landscape and are recognizable long after the parental spring has shut down. We identify 14 specific microfacies belonging to seven facies, which form three environmental associations related to specific depositional environments. Diagenesis has occurred in several stages, as evidenced by distinctive textures on the deposits. Spring deposits on Mars would potentially be recognized by similar textures (although compositions may be quite different) and similar geomorphic relationships. However, in satellite images, spring deposits may be difficult to differentiate from deposits resulting from other processes that produce similar geomorphic features, including mud volcanoes, pingos, and rootless cones. Mineralogical data may assist, but ultimately ground truth will be required.

Previous palynological studies of the Caspian–Black Sea–Mediterranean corridor primarily focused on pollen and spores for paleoecological and chronostratigraphic studies. Until recently, there has been less emphasis on the nonpollen palynomorphs, such as dinoflagellate cysts, algal and fungal spores, and animal remains. New studies of nonpollen palynomorphs in land-locked seas, estuaries, and lakes reported here indicate that they are important markers of salinity, nutrient loading, and human activity, including ballast discharge, farming, and soil erosion. We describe the nonoxidative laboratory processing methods necessary to extract nonpollen palynomorphs from marine- and brackish-water sediment samples. We list 48 nonpollen palynomorphs taxa from 37 surface sediments (including the past millennium) for cores along the salinity gradient from <16‰ off the Danube Delta to >39‰ in the Aegean, Mediterranean, and Red Seas, for two Crimean saline lakes, the Caspian and Aral Seas, and for lakes in Iran and Kazakhstan. The main nonpollen palynomorphs taxa are illustrated and listed systematically to provide a baseline for future collaborative studies among Black Sea corridor palynologists. We outline the biological affinities of some nonpollen palynomorphs and discuss the initial results of the study in terms of what nonpollen palynomorphs may reveal about the history of the salinity in the Black Sea corridor and the impact of humans on soil erosion, plankton production, and harmful algal blooms.

Multiyear measurements of geologic processes with slow rates of change can provide valuable data sets for student learning in the classroom and opportunities for undergraduate independent research. Here, we describe three projects for which data have been collected for 34, 20, and 10 yr, respectively: the erosion of a small meandering stream, the weathering of limestone cubes, and local stream hydrology/chemistry, including discharge, dissolved and suspended load, and major ion chemistry. These data have been used at all levels of the curriculum in various ways, from visualizing basic geologic principles in introductory courses to sophisticated statistical analysis and interpretation in upper-level courses, always in a context of student research leading to discovery about Earth systems. Depending on the project and the schedule for data collection, students have played a major role in the data collection, synthesis, and interpretation while also learning valuable analytical and statistical skills. Because the data sets are the product of many classes of students, there is a strong sense of ownership of the data and thus significant quality control, making the data sets useful as baseline studies for future projects. Where the study requires frequent and time-sensitive sampling, it is more difficult for students to collect data or make measurements. They may, however, have a hand in analyzing the samples collected in order to learn analytical and interpretive techniques. In some cases, these projects have expanded to include new long-term data sets that augment the original studies.

Major-ion chemistry, strontium isotope ratios ( 87 Sr/ 86 Sr), stable isotope ratios (δ 18 O, δ 2 H), and tritium were analyzed for water samples from the southern Bear Lake Valley, Utah and Idaho, to characterize the types and distribution of groundwater sources and their relation to Bear Lake’s pre-diversion chemistry. Four ground-water types were identified: (1) Ca-Mg-HCO 3 water with 87 Sr/ 86 Sr values of ~0.71050 and modern tritium concentrations was found in the mountainous carbonate terrain of the Bear River Range. Magnesium (Mg) and bicarbonate (HCO 3 ) concentrations at Swan Creek Spring are discharge dependent and result from differential carbonate bedrock dissolution within the Bear River Range. (2) Cl-rich groundwater with elevated barium and strontium concentrations and 87 Sr/ 86 Sr values between 0.71021 and 0.71322 was found in the southwestern part of the valley. This groundwater discharges at several small, fault-controlled springs along the margin of the lake and contains solutes derived from the Wasatch Formation. (3) SO 4 -rich groundwater with 87 Sr/ 86 Sr values of ~0.70865, and lacking detectable tritium, discharges from two springs in the northeast quadrant of the study area and along the East Bear Lake fault. (4) Ca-Mg-HCO 3 -SO 4 -Cl water with 87 Sr/ 86 Sr values of ~0.71060 and sub-modern tritium concentrations discharges from several small springs emanating from the Wasatch Formation on the Bear Lake Plateau. The δ 18 O and δ 2 H values from springs and streams discharging in the Bear River Range fall along the Global Meteoric Water Line (GMWL), but are more negative at the southern end of the valley and at lower elevations. The δ 18 O and δ 2 H values from springs discharging on the Bear Lake Plateau plot on an evaporation line slightly below the GMWL. Stable isotope data suggest that precipitation falling in Bear Lake Valley is affected by orographic effects as storms pass over the Bear River Range, and by evaporation prior to recharging the Bear Lake Plateau aquifers. Approximately 99% of the solutes constituting Bear Lake’s pre-diversion chemistry were derived from stream discharge and shallow groundwater sources located within the Bear River Range. Lake-marginal springs exposed during the recent low lake levels and springs and streams draining the Bear Lake Plateau did not contribute significantly to the pre-diversion chemistry of Bear Lake.

This paper deals with channel evolution over the past 200 yr in 12 selected streams in northern and central Italy and aims at reconstructing the evolutionary trends (e.g., trends of channel width and bed elevation) and understanding the causes of channel adjustments. The selected streams have been studied using various sources and methods (historical maps, aerial photographs, topographic surveys, and geomorphological surveys). The selected rivers have undergone almost the same processes in terms of temporal trends; however, the magnitude of adjustments varies according to several factors, such as original channel morphology. Initially, river channels underwent a long phase of narrowing (up to 80%) and incision (up to 8–10 m), which started at the end of the nineteenth century and was intense from the 1950s to the 1980s. Then, over the last 15–20 yr, channel widening and sedimentation, or bed-level stabilization, have become the dominant processes in most of the rivers. Different human interventions have been identified as the causes of channel adjustments in Italian rivers (sediment mining, channelization, dams, reforestation, and torrent control works). Such interventions have caused a dramatic alteration of the sediment regime, whereas effects on channel-forming discharges have seldom been observed. Some notable implications for river management and restoration are (1) the state of rivers before major human disturbances and channel adjustments can rarely be taken as a reference, as at present rivers are far from their pristine condition; and (2) sediment management is and will be a key issue in such fluvial systems.

Effective watershed-scale environmental management and restoration require a sound understanding of the dynamics of fluvial systems at the watershed-scale and the impact of humans on these dynamics. In Illinois, concern has arisen about the need to implement bank stabilization along meandering rivers, where bank erosion associated with lateral migration is often viewed as a sign of channel instability. Also, many rivers in the state are low-energy fluvial systems that exhibit limited responses to direct human modification such as channel straightening. From an ecological perspective, the lack of response is problematic owing to its potential long-term alteration of aquatic habitat. This study examines the spatial relationship between the planform dynamics of meandering rivers and stream power in the Kishwaukee River watershed in northern Illinois. The spatial extent of planform change at the scale of drainage network is quantified and related to spatial variations in the magnitude of stream power throughout the watershed. Historical channel change was determined using GIS-based analysis of aerial photography of several reaches scattered throughout the watershed. The results show that the amount of lateral migration per reach is greatest where stream power is highest, but that planform response to channelization is limited regardless of the magnitude of stream power. The findings from this historical analysis of channel change are useful for understanding both the fluvial dynamics of unmodified meandering rivers and the influence of human modification on these dynamics— knowledge that can help guide environmental decision making about the need to implement channel stabilization or restoration measures.

Geomorphic changes in reconfigured reaches of three Colorado rivers in response to floods in 2005 provide a benchmark for “restoration” assessment. Sediment-entrainment potential is expressed as the ratio of the shear stress from the 2 yr, 5 yr, 10 yr, and 2005 floods to the critical shear stress for sediment. Some observed response was explained by the excess of flood shear stress relative to the resisting force of the sediment. Bed-load entrainment in the Uncompahgre River and the North Fork Gunnison River, during 4 and 6 yr floods respectively, resulted in streambed scour, streambed deposition, lateral-bar accretion, and channel migration at various locations. Some constructed boulder and log structures failed because of high rates of bank erosion or bed-material deposition. The Lake Fork showed little or no net change after the 2005 flood; however, this channel had not conveyed floods greater than the 2.5 yr flood since reconfiguration. Channel slope and the 2 yr flood, a surrogate for bankfull discharge, from all three reconfigured reaches plotted above the Leopold and Wolman channel-pattern threshold in the “braided channel” region, indicating that braiding, rather than a single-thread meandering channel, and midchannel bar formation may be the natural tendency of these gravel-bed reaches. When plotted against a total stream-power and median-sediment-size threshold for the 2 yr flood, however, the Lake Fork plotted in the “single-thread channel” region, the North Fork Gunnison plotted in the “multiple-thread” region, and the Uncompahgre River plotted on the threshold. All three rivers plotted in the multiple-thread region for floods of 5 yr recurrence or greater.

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.