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At least 217 records · Page 12Linked to original sources

USGS2006

Audiomagnetotelluric data from Spring, Cave, and Coyote Spring Valleys, Nevada

Audiomagnetotelluric (AMT) data along four profiles in Spring, Cave, and Coyote Spring Valleys are presented here. The AMT method is used to estimate the electrical resistivity of the earth over depth ranges of a few meters to greater than one kilometer. This method is a valuable tool for revealing subsurface structure and stratigraphy within the Basin and Range of eastern Nevada, therefore helping to define the geohydrologic framework in this region. We collected AMT data using the Geometrics StrataGem EH4 system, a four-channel, natural and controlled- source tensor system recording in the range of 10 to 92,000 Hz. To augment the low signal in the natural field, an unpolarized transmitter comprised of two horizontal-magnetic dipoles was used from 1,000 to 70,000 Hz. Profiles were 1.4 - 12.6 km in length with station spacing of 100-400 m. Data were recorded with the electrical (E) field parallel to and perpendicular to the regional geologic strike direction. Station locations and sounding curves, showing apparent resistivity, phase data, and coherency data, are presented here.

Open-File Report↗

USGS2008

Audiomagnetotelluric data and preliminary two-dimensional models from Spring, Dry Lake, and Delamar Valleys, Nevada

This report presents audiomagnetotelluric (AMT) data along fourteen profiles in Spring, Delamar, and Dry Lake Valleys, and the corresponding preliminary two-dimensional (2-D) inverse models. The AMT method is a valuable tool for estimating the electrical resistivity of the Earth over depth ranges from a few meters to less than one kilometer, and it is important for revealing subsurface structure and stratigraphy within the Basin and Range province of eastern Nevada, which can be used to define the geohydrologic framework of the region. We collected AMT data by using the Geometrics StrataGem EH4 system. Profiles were 0.7 - 3.2 km in length with station spacing of 50-400 m. Data were recorded in a coordinate system parallel to and perpendicular to the regional geologic-strike direction with Z positive down. We show AMT station locations, sounding curves of apparent resistivity, phase, and coherency, and 2-D models of subsurface resistivity along the profiles. The 2-D inverse models are computed from the transverse electric (TE), transverse magnetic (TM), and TE+TM mode data by using a conjugate gradient, finite-difference method. Preliminary interpretation of the 2-D models defines the structural framework of the basins and the resistivity contrasts between alluvial basin-fill, volcanic units, and carbonate basement rocks.

Nevada↗

USGS1953

Pre-Cambrian geology of the Norway Lake area, Dickinson County, Michigan

The Norway Lake area straddles the south margin of the Sagola basin, an embayment of Ruronian sedimentary rocks into the west side of a complex of crystalline and sedimentary rocks of pre-Ruronian age. The north part of the Norway Lake area is underlain by the Randville dolomite, an unnamed succession of slates, Vulcan iron-formation, and interbedded slates and graywackes of the Sagola basin. The Sturgeon quartzite has not been definitely recognized in the Norway Lake area. The Handville dolomite is more than 800 feet thick and can be subdivided into upper and lower dolomite members separated by a slate member. The Vulcan iron-formation and the footwall slates are exposed only in the Deerhunt exploration. A thick section of red and gray slates with interbedded graywacke, of probable Upper Huronian age, underlies the northwest part of the mapped area. The south part of the Norway Lake area is underlain by granite gneiss, an arkose series, and schists, all of pre-Huronian age. The principal structural elements of the Norway Lake area are high angle faults, and such faults form most of the boundary between Huronian and pre-Huronian rocks in the area. The structure of the Huronian rocks. particularly in the vicinity of the Deerhunt exploration, cannot be determined with certainty on the basis of information now available. Magnetic anomalies were found to be associated with the slate member of the Randville dolomite, basalt interbedded with the arkose series, and a magnetite-bearing member in hornblende schist. It is possible that economic deposits of iron ore occur within the mapped area. However, exploration will be tedious and costly because of the structural complexity of the area and the paucity of exposures. Furthermore, the absence of strong magnetic anomalies, such as typically are present in areas known to be underlain by Vulcan iron-formation, suggests that the iron-formation is not present in abundance; in fact, it may be limited to the immediate vicinity of the Deerhunt exploration. Field mapping and petrographic examination do not provide data to determine whether the granite gneiss formed from a magma. Chemical analysis of one sample suggests that it was formed from rocks of the earth's crust rather than by fractional crystallization of a basaltic magma. The original feldspars of the granite gneiss were probably anorthoclase and analbite. During uplift and denudation these were changed to microcline microperthite and albite. These feldspars were contributed to the arkose series. During regional metamorphism of the granite gneiss and arkose replacement type microperthite and secondary perthite were formed, probably by redistribution of feldspars already present tither than by metasomatism.

Michigan↗

USGS2009

Audiomagnetotelluric investigation of Snake Valley, eastern Nevada and western Utah

Audiomagnetotelluric (AMT) data along four profiles in western Snake Valley and the corresponding two-dimensional (2-D) inverse models reveal subsurface structures that may be significant to ground-water investigations in the area. The AMT method is a valuable tool for estimating the electrical resistivity of the earth over depth ranges from a few meters to less than one kilometer. The method has the potential to identify faults and stratigraphy within basins of eastern Nevada, thereby helping define the hydrogeologic framework of the region. As support for an exploratory well-drilling and hydraulic-testing program, AMT data were collected using a Geometrics Stratagem EH4 system along four profiles that extend roughly east-west from the southern Snake Range into Snake Valley. The profiles range from 3 to 5 kilometers in length, and station spacing was 200 to 400 meters. Two-dimensional inverse models were computed using the data from the transverse-electric (TE), transverse-magnetic (TM), and combined (TE+TM) mode using a conjugate gradient, finite-difference method. Interpretation of the 2-D AMT models defines several faults, some of which may influence ground-water flow in the basins, as well as identify underlying Paleozoic carbonate and clastic rocks and the thickness of basin-fill sediments. These AMT data and models, coupled with the geologic mapping and other surface geophysical methods, form the basis for identifying potential well sites and defining the subsurface structures and stratigraphy within Snake Valley.

Nevada, Utah↗

USGS2011

Sensitivity of Pliocene ice sheets to orbital forcing

The stability of the Earth's major ice sheets is a critical uncertainty in predictions of future climate and sea level change. One method of investigating the behaviour of the Greenland and the Antarctic ice sheets in a warmer-than-modern climate is to look back at past warm periods of Earth history, for example the Pliocene. This paper presents climate and ice sheet modelling results for the mid-Pliocene warm period (mPWP; 3.3 to 3.0 million years ago), which has been identified as a key interval for understanding warmer-than-modern climates (Jansen et al., 2007). Using boundary conditions supplied by the United States Geological Survey PRISM Group (Pliocene Research, Interpretation and Synoptic Mapping), the Hadley Centre coupled ocean–atmosphere climate model (HadCM3) and the British Antarctic Survey Ice Sheet Model (BASISM), we show large reductions in the Greenland and East Antarctic Ice Sheets (GrIS and EAIS) compared to modern in standard mPWP experiments. We also present the first results illustrating the variability of the ice sheets due to realistic orbital forcing during the mid-Pliocene. While GrIS volumes are lower than modern under even the most extreme (cold) mid-Pliocene orbit (losing at least 35% of its ice mass), the EAIS can both grow and shrink, losing up to 20% or gaining up to 10% of its present-day volume. The changes in ice sheet volume incurred by altering orbital forcing alone means that global sea level can vary by more than 25 m during the mid-Pliocene. However, we have also shown that the response of the ice sheets to mPWP orbital hemispheric forcing can be in anti-phase, whereby the greatest reductions in EAIS volume are concurrent with the smallest reductions of the GrIS. If this anti-phase relationship is in operation throughout the mPWP, then the total eustatic sea level response would be dampened compared to the ice sheet fluctuations that are theoretically possible. This suggests that maximum eustatic sea level rise does not correspond to orbital maxima, but occurs at times where the anti-phasing of Northern and Southern Hemisphere ice sheet retreat is minimised.

Palaeogeography, Palaeoclimatology, Palaeoecology↗

USGS1987

Current loops fitted to geomagnetic model spherical harmonic coefficients.

One hundred-sixty circular current loops with radial axes were fitted by least squares to the 899 spherical harmonic coefficients of a 29 th degree model. In the first case, the parameters that were fitted for each loop were the normalized magnetic moment, the distance from the center of the Earth to the current element, the colatitude and E. longitude of the loop axis, and one-half of the central apex angle of the loop. For this case, two of the loops converged near the inner-core outer-core boundary. They accounted for most of the dipolar field. Twenty of the loops, all with much smaller magnetic moments than the two deep loops, converged in the distance range of 0.42 to 0.67 Earth's radius from the center of the Earth. The other 138 loops, after many iterations, were located at distances between 0.81 and 1.0 Earth's radius from the center of the Earth. The loops with radial distances between 0.21 and 0.67 Earth's radius from the center of the Earth are referred to as “core” loops and those at distances greater than 0.81 Earth's radius as “crustal” loops. The spherical harmonic coefficients from these 160 loops, when subtraced from the 899 coefficients of the original model, left a root-mean-square residual of only 0.2nT. A second case was tried which constrained the 138 “crustal” loops to be at 0.996 Earth's radius (25.5km depth). In this case, the root-mean-square residual of the spherical harmonic coefficients from the original model was 0.9nT.

Journal of Geomagnetism & Geoelectricity↗

USGS1990

Hydrology, aquatic macrophytes, and water quality of Black Earth Creek and its tributaries, Dane County, Wisconsin, 1985-86

An intensive data-collection program for the Black Earth Creek basin in southern Wisconsin was conducted from October 1984 through September 1986 to assess the hydrology, aquatic macrophytes, and water quality in Black Earth Creek by the U.S. Geological Survey, in cooperation with the Wisconsin Department of Natural Resources. Three sites on two cold-water trout streams Black Earth Creek at Cross Plains, Black Earth Creek near Cross Plains, and Garfoot Creek near Cross Plains were continuously monitored for streamflow and water-quality data. One site in a warm-water stream, Brewery Creek at Cross Plains, also was monitored. Aquatic macrophyte biomass was determined for three sites on Black Earth Creek. Streamflow at Black Earth Creek at Black Earth during the 1985 and 1986 water years (WY) were 44 and 60 percent greater than the long-term mean discharge of 33.3 ft3/s (cubic feet per second) for the period 1955-86. Water year 1986 had the highest annual mean discharge, 53.4 ft3/s, since records began in 1954 at the most downstream site Black Earth Creek at Black Earth. Although there have been considerable fluctuations in streamflow, it has tended to increase since WY 1965 as a result of above-average precipitation and consequent rising ground-water levels. Trout population densities may be related to annual mean streamflow. A regression analysis of adult trout populations and the 3-year moving annual mean discharge had a correlation coefficient of 0.75 with a standard error of 83 percent. Aquatic macrophyte biomass in Black Earth Creek was substantially less in 1986 than in 1985 as a result of substrate scouring from the flood of July 25, 1985. The frequency of occurrence of species during 1985 and 1986 was similar to that of 1981, and seasonal succession of species also was similar; Potamogeton crispus dominated early in the year and senesced in July. P. crispus and P. pectinatus, both indicative of eutrophic conditions, dominated upstream and downstream, respectively; neither species is native to the area. In 1985, the greatest biomass was found upstream from Cross Plains. This large biomass caused diurnal fluctuations in dissolved-oxygen concentration of 5 to 6 mg/L (milligrams per liter) as a result of photosynthesis and respiration. Many of the dissolved-oxygen minimums, recorded at night, were less than the State 6.0-mg/L water-quality standard for trout waters. Discharge from point sources may adversely affect Black Earth Creek's water quality. Warm water discharged to Black Earth Creek from a gravel pit operation upstream from Cross Plains increased water temperatures 2 to 4 degrees Celsius and decreased the dissolved oxygen about 1 mg/L at a site 1.8 miles downstream. Runoff from a settling pond from a landfill operation in the headwaters of the Black Earth Creek basin drains through a wetland that drains to Black Earth Creek and contained as much as 60 mg/L ammonia nitrogen, 980 mg/L biochemical oxygen demand, and 1,300 mg/L chemical oxygen demand, which may be detrimental to trout. Garfoot Creek had the highest suspended-sediment and phosphorus yields per unit area of the three upstream basins during low to moderate runoff. Detention ponds in the Brewery Creek basin appear to be less effective in controlling suspended-sediment and phosphorus loads during periods of high runoff than during moderate runoff. Brewery Creek had the highest concentrations of suspended sediment and total phosphorus during low and high flows. The water quality at the Black Earth Creek gaging station at Black Earth was affected by Garfoot Creek and unnamed tributaries. As a result, yields of suspended sediment, phosphorus, and nitrogen increased between Cross Plains and Black Earth. High streamflows during WY 1985 resulted in suspendedsediment yields at Black Earth Creek at Black Earth that were 29 percent greater than the 12-year (1955-65, 85-86) mean; yields ranged from 69.5 ton/mi2 (tons per square mile) in Black Earth Creek at Cross Plains to 116 ton/mi2 in the Brewery Creek basin. Phosphorus yields ranged from 312 lb/mi2 (pounds per square mile) in Black Earth Creek at Cross Plains to 628 lb/mi2 in the Brewery Creek basin. Total nitrogen yields ranged from 3,280 lb/mi2 in the Brewery Creek basin to 6,920 lb/mi2 in the Garfoot Creek basin. An increase in oxygen demand, caused by agricultural runoff, has resulted in reduced dissolved-oxygen content of the water in both Black Earth and Garfoot Creeks. The most substantial reduction occurred at Black Earth Creek at Cross Plains on July 25, 1985, as a result of the largest storm runoff event during the study. A rainfall of 5.54 inches caused streamflow discharges to increase from 9 to 122 ft3/s and dissolved-oxygen concentrations to decline to 3.0 mg/L; the dissolved-oxygen concentration was less than 6.0 mg/L for 30 hours.

Wisconsin↗

USGS2014

Symposium on land erosion: Introduction

One of the very obvious geologic phenomena that is continuously in operation throughout the Earth's land surface is erosion , the process of wearing away the soil or the surface mantle. The falling of rain drops on an unprotected slope, the flow of water across land or in a channel, the borings of a rodent, the expansion of a root, the pull of gravity, the gouging of a glacier, or the impinging of wind on an open surface are some of the forces continually at work in this erosion process. The tendency of these forces is to bring everything to a common level and the moment a point of land or a continent rises above its surroundings, gravity, rain, wind, and all the other forces set to work, bringing it back to the level of its nieghbor. The poetic expression “the everlasting hills” is an illusion, for these erosion forces have been operative since the dawn of geologic history and the evidence is conclusive that in this sequence of time numerous generations of hills and mountain ranges have been uplifted and then razed by erosion , the waste and rock debris of one range forming the source material for its successor. We could not have the great deposits of alluvium and the thick beds of conglomerate, sandstones, and shales that occur at present throughout the Earth without erosion to furnish the source material.

Eos, Transactions, American Geophysical Union↗

USGS2002

The global transport of dust: An intercontinental river of dust, microorganisms and toxic chemicals flows through the Earth's atmosphere

The coral reefs in the Caribbean have been deteriorating since the 1970s, and no one is quite sure why. Such environmental devastation is usually blamed on Homo sapiens , but that doesn’t seem to be what’s going on here. Recently, some scientists at the USGS think they’ve solved the puzzle: Bacteria and fungi have been hitching trans-Atlantic rides on dust from the Sahara desert and settling into the warm waters of the Caribbean. Microbiologist Dale Griffin and his colleagues make the case for this hypothesis and explore the dangers of dust and microbe transport across the globe.

American Scientist↗

USGS2011

Seismicity of the Earth 1900-2010 eastern margin of the Australia plate

The eastern margin of the Australia plate is one of the most seismically active areas of the world due to high rates of convergence between the Australia and Pacific plates. In the region of New Zealand, the 3,000 km long Australia-Pacific plate boundary extends from south of Macquarie Island to the southern Kermadec Island chain. It includes an oceanic transform (the Macquarie Ridge), two oppositely verging subduction zones (Puysegur and Hikurangi), and a transpressive continental transform, the Alpine Fault through South Island, New Zealand. Since 1900, there have been 15 M7.5+ earthquakes recorded near New Zealand. Nine of these, and the four largest, occurred along or near the Macquarie Ridge, including the 1989 M8.2 event on the ridge itself, and the 2004 M8.1 event 200 km to the west of the plate boundary, reflecting intraplate deformation. The largest recorded earthquake in New Zealand itself was the 1931 M7.8 Hawke's Bay earthquake, which killed 256 people. The last M7.5+ earthquake along the Alpine Fault was 170 years ago; studies of the faults' strain accumulation suggest that similar events are likely to occur again.

Open-File Report↗

USGS2019

The first 3D conductivity model of the contiguous US: Reflections on geologic structure and application to induction hazards

Estimation of ground level geoelectric fields has been identified by the National Space Weather Action Plan as a key component of assessment and mitigation of space weather impacts on critical infrastructure. Estimates of spatially and temporally variable electric fields are used to generate statistically based hazard maps and show promise toward monitoring and responding to geomagnetic disturbances in near real‐time. One approach to geoelectric field estimation is to employ three‐dimensional (3D) Earth conductivity models. These data‐constrained conductivity models are the results of regional magnetotelluric inversions based primarily on NSF’s Earthscope USArray impedances, which to date cover ~60% of the contiguous United States. Here, we present the first‐ever composite conductivity model of the contiguous United States and describe its compilation from 3D regional conductivity models, a global mantle conductivity model, offshore bathymetry, and sediment thickness data. We discuss structures within the conductivity model and how they relate to the complex geologic tapestry of the continent. Finally, we discuss the utility of this synthesis model for estimation and mitigation of geomagnetically induced currents.

Book chapter↗

USGS2018

Infrared heater system for warming tropical forest understory plants and soils

The response of tropical forests to global warming is one of the largest uncertainties in predicting the future carbon balance of Earth. To determine the likely effects of elevated temperatures on tropical forest understory plants and soils, as well as other ecosystems, an infrared (IR) heater system was developed to provide in situ warming for the Tropical Responses to Altered Climate Experiment (TRACE) in the Luquillo Experimental Forest in Puerto Rico. Three replicate heated 4-m- diameter plots were warmed to maintain a 4°C increase in understory vegetation compared to three unheated control plots, as sensed by IR thermometers. The equipment was larger than any used previously and was subjected to challenges different from those of many temperate ecosystem warming systems, including frequent power surges and outages, high humidity, heavy rains, hurricanes, saturated clayey soils, and steep slopes. The system was able to maintain the target 4.0°C increase in hourly average vegetation temperatures to within ± 0.1°C. The vegetation was heterogeneous and on a 21° slope, which decreased uniformity of the warming treatment on the plots; yet, the green leaves were fairly uniformly warmed, and there was little difference among 0–10 cm depth soil temperatures at the plot centers, edges, and midway between. Soil temperatures at the 40–50 cm depth increased about 3°C compared to the controls after a month of warming. As expected, the soil in the heated plots dried faster than that of the control plots, but the average soil moisture remained adequate for the plants. The TRACE heating system produced an adequately uniform warming precisely controlled down to at least 50-cm soil depth, thereby creating a treatment that allows for assessing mechanistic responses of tropical plants and soil to warming, with applicability to other ecosystems. No physical obstacles to scaling the approach to taller vegetation (i.e., trees) and larger plots were observed.

Puerto Rico↗

USGS2021

Geology of the Hawaiian Islands

Long known as the island chain farthest from any continental landmass, the Hawaiian Islands are the subaerial expression of volcanism above the relatively fixed Hawaiian hot spot as the Pacific plate drifts northwest above it. Each island is built by one or several overlapping shield volcanoes, some of the most voluminous on Earth. Plate translation creates the well-known age-progressive sequence of shield volcanoes from northwest to southeast. Total volume of magma produced along the Hawaiian chain has been irregular but generally increasing for the past 50 million years, a trend that has peaked in the last 3 million years. Hawaiian volcanoes grow through stages that have geologic expression and geochemical differences that reflect position relative to the underlying hot spot. Of these stages, the shield stage is the most productive when an estimated 80–95% of a volcano's ultimate volume is emplaced. The shield stage endures for about 1 million years. The burden of shield volcanoes depresses the ocean crust near the hot spot, creating the Hawaiian Moat. Greatest rate of subsidence today occurs at the Island of Hawai‘i, 2–3 mm per year along its coast. Flexural rebound occurs as volcanoes move away from the hot spot; the Island of O‘ahu shows the greatest uplift. Slow subsidence resumes downstream from the flexure, leading ultimately to submergence of each island in the chain. Large landslides, albeit infrequent, can occur at any stage of island evolution. Ground water is the principal source of potable and agricultural water on all islands; its distribution both reflects and influences island geology.

Hawaii↗

USGS2022

The role of monitoring and research in the Greater Yellowstone Ecosystem in framing our understanding of the effects of disease on amphibians

Emerging infectious disease threatens amphibian biodiversity worldwide, including in landscapes that are protected from many anthropogenic stressors. We summarized data from studies in the Greater Yellowstone Ecosystem (GYE), one of the largest and most complete temperate-zone ecosystems on Earth, to assess the current state of knowledge about ranaviruses and the novel amphibian chytrid fungus (Bd) in this landscape, and to provide insight into future threats and conservation strategies. Our comprehension of these amphibian diseases in the GYE is based on >20 years of monitoring, surveys, population studies, and opportunistic observations of mortality events. Research indicates that local species are affected differently, depending on temperature, community structure, and location in the GYE. Bd has not been linked to die-offs in the GYE but evidence for ongoing reductions in survival contributes to foundational data about the effects of this pathogen in North America. Localized mortality events attributed to, or consistent with, disease from ranaviruses, are widespread in the GYE, but there is less information on how ranaviruses affect amphibian vital rates. The significance of disease in the long-term persistence of amphibians in the GYE is linked to anticipated changes in climate, especially drought. Additionally, expected increases in visitor use, and its associated impacts, have the potential to exacerbate the effects of disease. Long-term information from this large, intact landscape helps to frame our understanding of the effects of disease on amphibians and provides data that can contribute to management decisions, mitigation strategies, and forecasting efforts.

Wyoming↗

USGS2019

Walk in the footsteps of the Apollo astronauts: A field guide to northern Arizona astronaut training sites

Every astronaut who walked on the Moon trained in Flagstaff, AZ. In the early 1960s, scientists at the newly formed United States Geological Survey (USGS) Branch of Astrogeology led this training, teaching geologic principals and field techniques to the astronaut crews. USGS scientists and engineers also developed and tested scientific instrument prototypes, and communication and transportation technologies that would aid in lunar exploration. Astronomers and cartographers based at the USGS and Lowell Observatory, using telescopes at Lowell Observatory and the U.S. Naval Observatory, also played a key role, preparing lunar navigation charts and landing site maps. This historical / educational field trip will take participants along a historical path to some of the key sites where the Apollo astronauts trained. Field trip participants will see: (1) Grover, the geologic rover simulator on which the Apollo astronauts trained, which is on display at the USGS Astrogeology Science Center; (2) Telescopes at Lowell Observatory used to map the lunar surface, as well as some of the original airbrushed maps; (3) the Bonito Lava Flow training area at Sunset Crater Volcano National Monument; (4) the Cinder Lake crater field, which was created in 1967 to simulate the lunar landscape for training astronauts and testing equipment; and (5) Meteor Crater, the best-preserved exposed impact crater on Earth. During this field trip, as we celebrate the 50th anniversary of one of the most remarkable events and most significant achievements in the history of humankind, we hope that the sites we visit will connect participants with the experiences of the astronauts, and the excitement and inspiration of the origins of human space exploration. We also hope to communicate the historical significance of these sites, facilitate continued visitation of the sites (e.g. through class field trips), and educate the broader scientific and science education communities about the role that Flagstaff scientists and engineers played in the Apollo expeditions to the Moon.

Arizona↗

USGS2021

Greater Yellowstone climate assessment: Past, present, and future climate change in the greater Yellowstone watersheds

The Greater Yellowstone Area (GYA) is one of the last remaining large and nearly intact temperate ecosystems on Earth. GYA was originally defined in the 1970s as the Greater Yellowstone Ecosystem, which encompassed the minimum range of the grizzly bear. The boundary now includes about 22 million acres (8.9 million ha) in northwestern Wyoming, south central Montana, and eastern Idaho (Figure ES-1). Two national parks, five national forests, three wildlife refuges, 20 counties, and state and private lands lie within the GYA boundary (Figure ES-1). The Tribal Nations of the Eastern Shoshone, Northern Arapaho, Apsa´alooke/Crow, Northern Cheyenne, Shoshone, and Bannock have reservations in and near the Greater Yellowstone Area, and 27 Tribes are formally recognized to have historical connections to the lands and resources of the region. Natural resources sensitive to climate change connect many of the major economic activities of the GYA, including tourism and recreation, agriculture, and energy development.

Idaho, Montana, Wyoming↗

USGS1996

A history of the Water Resources Division, U.S. Geological Survey; Volume VI, May 1, 1957 to June 30, 1966; the years of change

Luna B. Leopold became chief of the Water Resources Division in May 1957 and stepped down in January 1966 to resume his research'in geomorphology. Ernest L. Hendricks succeeded'Leopold as chief of the Division in May 1966. The dates May 1, 1957, and June 30,1966, bracket a period of profound change in the organization and programs and in the philosophy of operations of the Water Resource Division and indeed in the entire field of investigational hydrology both within and outside the Geological Survey. Leopold brought into his new position a conviction that water on and beneath the Earth's surface and the quality of both were interdependent parts of one water-resources system and that the organization and operation of WRD must change to reflect that oneness. He was also convinced that the research program of the Division was inadequate in scope, staff, and funding to meet the operational needs of the Division and the needs of the community of water-resources planners, developers, and administrators in the near and distant future. Leopold's vision of a Water Resources Division properly staffed to meet current and future technical challenges included the imposition of rigorous selection standards on new professional recruits and the development of specialized training in-house and at university undergraduate and graduate levels. The period of Leopold's administrative and technical leadership of the WRD was indeed the "Years of Change."

Report↗

USGS2025

Ageing of organic materials at the surface of Mars: A Raman study aboard Perseverance

The Perseverance rover is exploring Jezero crater on Mars, one of its goals being to collect samples to be returned to Earth to search for organic remains of ancient Martian life. However, the organic content of these rocks has likely suffered from the radiation environment on the surface of Mars to an extent yet to be quantified. For the first time, a 1000 sols long ageing experiment was conducted at the surface of Mars, i.e. under actual Martian conditions, relying on the 100 % organic Ertalyte target carried by Perseverance. White at landing, the Ertalyte target has turned brown with time, while its Raman signal changed, with a modification of the background (its maximum has shifted from 1500 to 2000 cm −1 ) and a reduction of the contribution of the Raman signal of Ertalyte (by a factor of 5 over the first 500 sols). Given the intrinsic resistance of the Ertalyte to UV exposure, which is not anticipated for most Martian organic materials, these results suggest that exposure at the surface of Mars will make the detection of Martian organic molecules challenging.

Geochemical Perspectives Letters↗